CHARACTERIZATION OF THIOSALTS - Laurentian...

PROTECTED BUSINESS INFORMATION

CHARACTERIZATION OF THIOSALTS GENERATION DURING MILLING OF

SULPHIDE ORES

OCTOBER 1999

MINING AND MINERAL SCIENCES LABORATORIES T. Negeri, A.D. Paktunc, M. Boisclair and D.M. Kingston Work Performed for: THIOSALTS CONSORTIUM

Job No. 601838 CONFIDENTIAL MINING AND MINERAL SCIENCES LABORATORIES REPORT MMSL 99-055 (CR)

THIOSALTS CONSORTIUM PROTECTED BUSINESS INFORMATION Project No. 601838

i

EXECUTIVE SUMMARY

Experimental studies were undertaken on a pyritic Cu-Zn ore from the Louvicourt mill and

pyrrhotite-rich Cu-Ni ore from the Strathcona mill with the overall purpose to identify the

processes, conditions and mineralogical characteristics that may influence the production of

thiosalts during milling of sulphide ores.

Experimental studies involved batch, semi-batch and continuous milling and flotation tests to

(1) study the influence of pH, temperature and residence time, (2) assess grinding media

effect, (3) simulate the Louvicourt and Strathcona mill conditions, and (4) study the effects of

mineralogy on thiosalts generation.

The effects of pulp temperature, residence time and pH on thiosalts generation appear to be

linear. The pyrrhotitic ore appears to be more sensitive to pulp temperature, whereas the

pyritic ore is more sensitive to changes in pH. Pulp residence time significantly affected the

thiosalts generation during processing of the pyrrhotitic ore, but not the pyritic ore.

The amount of thiosalts generated during grinding strongly depends on the type of grinding

media used; the stainless steel produces more thiosalts than mild steel grinding media. The

pyritic ore is oxidized faster than the pyrrhotitic ore during grinding regardless of the

grinding media type. The use of more active media or semi-autogenous grinding would

generate less thiosalts than inert media or autogenous grinding.

Flotation of the pyrrhotitic ore produced more thiosalts than the pyritic ore at pH values

typical for flotation. Continuous testing results on the pyritic ore indicated that an estimated

23% of the overall thiosalts determined originated from the feed while grinding, aeration,

copper circuit flotation and Zn circuit flotation contributed 17%, 5%, 50% and 5%

respectively. Semi-batch testing results on the pyritic ore indicated that grinding contributed

approximately one-third of the total thiosalts generated. Copper rougher/scavenger/cleaner

circuit produced 23% of the total thiosalts present, Cu cleaning stage being responsible for

approximately half of this amount. Zinc rougher/flotation/cleaner produced 26% of the total

thiosalts. Semi-batch testing results of the pyrrhotitic ore indicated that the collector


ii

conditioning contributed the highest amount of thiosalts generated in the circuit, followed by

the regrinding of flotation products in the pyrrhotite rejection circuit. The amount of thiosalts

in pulp solution increases with an increase in the collector xanthate and the amount of SO2

used during conditioning. The rate of thiosalts generation is the highest during the first few

minutes of conditioning including aeration.

Thiosalts generation is influenced by sulphide mineralogy. Thiosalts generation generally

increases with sulphide mineral content of the ore. Thiosalts generation rate appears to be

linearly dependent on the abundance of sulphide minerals in the ore.

A good portion of the thiosalts in mill circuit comes with the ore in dry form. Scrub washing

under inert atmosphere results in total removal of thiosalts contained in the feed ore.


iii

CONTENTS

EXECUTIVE SUMMARY iINTRODUCTION 1BACKGROUND INFORMATION 3THE INFLUENCE OF pH, TEMPERATURE AND RESIDENCE TIME ON THIOSALTS GENERATION

9

Test Methodology 10 Feed Sample Compositions 11 Mineralogical composition of the Strathcona Ore 12 Mineralogical composition of the Louvicourt Ore 13 Experiments on Thiosalts Generation 14 Mineralogical Composition of the Strathcona Samples 16 Mineralogical Composition of the Louvicourt Samples 19INFLUENCE OF GRINDING MEDIA ON THIOSALTS GENERATION 26 Test Methodology 26 Results and Discussion 26STUDY OF THIOSALTS FORMATION UNDER SIMULATED SULPHIDE ORE PROCESSING PLANT CONDITIONS

29

Continuous Testing of Thiosalts Generation by the Louvicourt Ore 29 Semi-batch Testing of Thiosalts Generation by Louvicourt Ore 31 Test Methodology 31 Results and Discussion (Louvicourt) 33 Semi-batch Testing of Thiosalts Generation by Strathcona Cu-Ni Ore 35 Results and Discussion (Strathcona) 35EFFECTS OF MINERALOGY ON THIOSALTS GENERATION DURING MILLING AND FLOTATION

37

Louvicourt Ore 37 Sample Preparation and Testing Methodology 37 Mineralogy 38 Test Results and Discussion 40 Strathcona Ore 42 Sample Preparation, Sample Mineralogy and Testing Methodology 42 Test Results and Discussion 47EFFECTS OF REAGENTS ON THIOSALTS GENERATION 50 Effects of Xanthate on Thiosalts Generation by the Pyrrhotitic Cu-Ni Ore 50 Effects of Sulphur on Thiosalts Generation by the Pyritic Cu-Zn Ore 51 Test Methodology 52 Test Results and Discussion 53CONCLUSIONS 53RECOMMENDATIONS 55ACKNOWLEDGEMENTS 55REFERENCES 56APPENDIX A: FIGURES (See Figure Listing - page vi) A1-A45APPENDIX B: PULP SAMPLES COLLECTED AT THE MILLS AND MEASUREMENTS B1-B2APPENDIX C: THIOSALTS (INDIVIDUAL SPECIES AND TOTAL THIOSALTS) ANALYSIS OF THE PULP SAMPLES

C1-C2


iv

TABLES

Table 1 Galvanic series of sulphide minerals 6Table 2 Bulk chemical analysis of the Strathcona (ST) and

Louvicourt (LV) ore samples 11

Table 3 Minerals identified, their relative abundances and particle sizes in the Strathcona ore

12

Table 4 Minerals identified, their relative abundances and particle sizes in the Louvicourt ore

14

Table 5 Test design parameters and results 15Table 6 Bulk chemical analysis of the experimental samples 15Table 7 Bulk chemical analyses of the Louvicourt samples resulted

from batch experiments 16

Table 8 Minerals identified, their relative abundances and particle sizes in the Strathcona samples

17

Table 9 Mineral quantities (wt%) of the feed and experimental samples 19Table 10 Minerals identified, their relative abundances and particle sizes in

the Louvicourt samples 20

Table 11 Mineral quantities (wt%) of the feed and experimental samples 22Table 12 Contributions by factors and their interactions to thiosalts generation

when factor settings change from low to high levels investigated 22

Table 13 ANOVA for selected factorial model (Pyritic Cu ore) 24Table 14 ANOVA for selected factorial model (Cu-Ni pyrrhotitic ore) 24Table 15 Experimental conditions and results of grinding media effect study 26Table 16 Effects of pulp pH (lime addition) on thiosalts generation

during grinding with stainless steel 27

Table 17 Flotation conditions for the Louvicourt ore 30Table 18 Thiosalts generation in the experimental grinding and flotation circuit 30Table 19 Bulk chemistry and mineralogical quantification of the flotation

products 34

Table 20 Flotation test results (separate Cu and Zn concentrates) 34Table 21 Flotation test results (combined Cu and Zn concentrates) 34Table 22 Bulk chemistry and mineralogical composition of the flotation

products 36

Table 23 Flotation Test Results (Strathcona ore) 36Table 24 Louvicourt experimental samples 38Table 25 Bulk chemical analysis of the samples prepared by gravity

separation 38

Table 26 Minerals identified, relative abundances and particle sizes in the Louvicourt experimental samples

39

Table 27 Mineral quantities (wt %) of the Louvicourt experimental samples 40Table 28 Louvicourt experimental sample size distributions 41Table 29 Test results 41Table 30 Strathcona experimental samples 43


v

TABLES (Cont'd)

Table 31 Bulk chemical analysis of the samples prepared from magnetic and non-magnetic fractions

43

Table 32 Minerals identified in the Strathcona samples 44Table 33 Grain sizes (µm) of the minerals identified in the Strathcona samples 45Table 34 Mineral quantities (wt%) of the samples resulting

from magnetic separation 47

Table 35 Grinding and simulated flotation conditions 47Table 36 Strathcona experimental sample grain size distribution 47Table 37 Thiosalts concentrations (g/t) generated during experiments 48Table 38 Effects of SO2 conditioning on thiosalts generation 53


vi

FIGURES Figure 1 Metal sulphide oxidation to sulphate generalized path A-1Figure 2 Experimental set-up for the thiosalts generation studies A-2Figure 3 Representative backscattered electron (BSE) photomicrograph

of SAR-Ore A-3

Figure 4 BSE photomicrograph of SAR-Ore A-3Figure 5 BSE photomicrograph of SAR-Ore A-4Figure 6 Representative BSE photomicrograph of various sulphides and

gangue minerals in LVR-Ore A-4

Figure 7 BSE photomicrograph of a composite particle made of pyrite, chalcopyrite and quartz

A-5

Figure 8 Backscattered electron (BSE) photomicrograph of an unknown sulfosalt in sphalerite, magnesian siderite and quartz

A-5

Figure 9 BSE photomicrograph of a rhombohedral magnesian siderite grain A-6Figure 10 BSE photomicrograph of liberated pyrrhotite displaying variable

sizes A-6

Figure 11 BSE photomicrograph of liberated pyrite and chalcopyrite grains LVR5-LLL

A-7

Figure 12 BSE photomicrograph of carbonate grains in LVR5-LLL A-7Figure 13 BSE photomicrograph showing chalcopyrite attached to an anhedral

pyrite grain in LVR7-MMM A-8

Figure 14 Model adequacy for the pyritic ore A-9Figure 15 Model adequacy for the pyrrhotitic ore A-9Figure 16 Effect of pulp temperature on thiosalts generation A-10Figure 17 Effect on pH on thiosalts generation during flotation under constant

temperature and residence time A-11

Figure 18 Effect of pH and temperature on thiosalts generation for residence time of 22 minutes

A-12

Figure 19 Effect of residence time on thiosalts generation A-13Figure 20 Overall effects of pH, temperature and residence time on total

thiosalts generation (pyritic ore) A-14

Figure 21 Overall effects of pH, temperature and residence time on total thiosalts generation (pyrrhotitic ore)

A-14

Figure 22 Effect of grinding media composition on total thiosalt generation by the pyritic ore at natural pH

A-15

Figure 23 Effect of grinding media composition on total thiosalt generation by the pyrrhotitic ore at natural pH

A-16

Figure 24 Comparison of grinding media effects on pyritic and pyrrhotitic ores based on total thiosalts generation at natural pH

A-16

Figure 25 Change in grinding mill discharge pH as a function of time addition rate

A-17

Figure 26 Effect of lime controlled grinding pH on thiosalts generation A-18Figure 27 Experimental continuous grinding, classification and flotation A-19Figure 28 Distribution of the total thiosalts among the major process and the

ore A-20

Figure 29 The PC controlled automatic flotation cell A-21


vii

FIGURES (Cont’d)

Figure 30 Semi-batch test flowsheet used to investigate thiosalts generation in various circuits (Louvicourt)

A-22

Figure 31 Distribution of thiosalts generated among sub processes A-23Figure 32 Semi-batch test flowsheet used to investigate thiosalts generation in

various circuits (Strathcona) A-24

Figure 33 Proportions of total thiosalts generated in various process circuits A-25Figure 34 Sample preparation, grinding and flotation simulation of Louvicourt

pyritic Cu-Zn ore A-26

Figure 35 Sample preparation, grinding and flotation simulation of Strathcona pyrrhotitic Cu-Ni ore

A-27

Figure 36 BSE photomicrograph of pyrite grains attached to an encapsulated in gangue

A-28

Figure 37 BSE photomicrograph of a pyrite grain attached to an encapsulated in gangue. Note the sharp grain boundaries on exposed surfaces of pyrite grains

A-28

Figure 38 Effect of mineralogical composition of Louvicourt ore on total thiosalt generation rate

A-29

Figure 39 Dissolved oxygen concentration and pulp oxidation-reduction potential data for LVT4

A-30

Figure 40 Change in pulp oxidation-reduction potential with residence time A-31Figure 41 Louvicourt test. Change in pH with resident time A-32Figure 42 Pulp conductivity A-33Figure 43 Representative BSE photomicrograph of various sulphides from

SAMM-HEAD A-34

Figure 44 Representative BSE photomicrograph of various sulphides in SAMM6

A-34

Figure 45 Representative BSE photomicrograph of various gangue minerals in SAMM5

A-35

Figure 46 BSE photomicrograph of pyrrhotite surrounded by fine particles of pyrrhotite

A-35

Figure 47 Representative BSE photomicrograph of pyrrhotite SAMM5 A-36Figure 48 Effect of mineralogical composition of Strathcona ore on total thiosalt

generation rate A-37

Figure 49 Change in rate of total thiosalt generation (Strathcona core) A-38Figure 50 Thiosalts generation rate as a function of residence time interval and

sulphide mineral content of samples A-39

Figure 51 Comparison of correlations between initial thiosalts generation rate and mineral quantities (first 15 minutes of processing)

A-40

Figure 52 Comparison of correlations between initial thiosalts generation rate and mineral quantities (last 20 minutes of processing)

A-41

Figure 53 Thiosalts generation rate as a function of bulk sulphur assays (%) A-42Figure 54 Change in pulp oxidation-reduction potential A-43Figure 55 Change in pulp pH A-44Figure 56 Effect of xanthate addition rate on thiosalts generation A-45


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INTRODUCTION

Thiosalts, which are defined as metastable sulphur oxyanions containing S-S bonds, are

produced in varying quantities during processing of sulphide ores. Primary mechanism for

the formation of thiosalts is the oxidation of sulphide minerals. Thiosalts are intermediate

products formed during the conversion of sulphides to sulphates; therefore, they are

considered as metastable and the reactions producing thiosalts can be reversible.

Earlier studies (e.g. Wasserlauf and Dutrizac 1982, Rolia and Tan 1985, Thiosalts Workshop

notes, Montreal, June 1996) indicated that the milling processes such as grinding,

conditioning, flotation and dewatering contribute to thiosalts generation. More specifically,

the following factors promoted the generation of thiosalts in mill circuits: (1) high sulphide

content of ore, (2) finer grain size, (3) alkaline grinding solution, (4) higher dissolved oxygen

in grinding solution, (5) longer retention time, (6) higher temperature, (7) lower pulp density,

(8) increased agitation rate during flotation, and (9) SO2 additions. In addition, it was found

that airflow had a marginal effect on the production of thiosalts. A study conducted by

Noranda Mining and Exploration in a Brunswick concentrator, however, was unable to

identify a specific unit process or reagent that generated more thiosalts than others (Thiosalts

Workshop notes, Montreal, June 1996).

The presence of thiosalts in effluents causes the potential acidification of water courses.

Thus, current treatment or control practices are designed to destroy thiosalts prior to their

release to the environment. The treatment/control options include natural degradation in

ponds, liming and water recycling, subaqueous tailings disposal in impoundments and sea

disposal. Annual treatment costs range from 4 million dollars for the natural degradation

option to 72 million dollars for options involving technologies (Wasserlauf et al. 1985).

Thus, liabilities to mining companies arising due to thiosalts generation are paramount.

The magnitude of thiosalts production vary with the location and type of operation; however,

environmental and economic implications of thiosalts disposal are such that identification of

processes that contribute to thiosalts production is of profound importance to mining

companies. Development of predictive and control measures can not be properly achieved


2

without establishing sound relationships between the mill processes and thiosalts generation.

If the effects of unit operations on mineral surface chemistry and on thiosalts generation are

better understood, then appropriate control or prevention measures can be designed with the

objective to minimize the formation of thiosalts, to prevent the persistence of thiosalts in

process streams or to bring the oxidation reactions to a completion before they are released to

the environment. Control or prevention measures may include the use of alternate reagents,

alternate reagent addition points, alternate process units, such as columns instead of

mechanical cells, and alternate means of reducing flotation retention times by enhancing

flotation.

The Thiosalts Consortium was set-up to respond to the following needs: (1) early

identification of the potential for an ore to generate thiosalts and (2) identification of plant

conditions that would increase the production rates of thiosalts. In order to meet these needs,

CANMET proposed a two-phased study: (1) characterization of thiosalts generation in

experimental mill circuits and development of basic information on thiosalts formation and

(2) development of prediction tools, and prevention and control measures. This study reports

the findings of the first phase of the approach.

The principal objective of this study was to identify the processes, conditions and

mineralogical characteristics that may influence the production of thiosalts during milling of

sulphide ores.

Two types of ore were investigated: pyritic Cu-Zn ore from Louvicourt and pyrrhotite-rich

Cu-Ni ore from Strathcona. The Louvicourt mill sampling was carried out on September 17-

18, 1998. A total of 35 pulp samples representing the mill circuit were taken, and pH, Eh,

dissolved oxygen and conductivity measurements were made after filtering and before the

samples were frozen. Approximately 500 kg of fresh mill feed, process water and graded

balls for ball mill operation were obtained from the Louvicourt mill on October 1 and 10,

1998. The ore has been dried, crushed and prepared for testing at CANMET facilities. Ten

pulp samples from the plant were analyzed for total thiosalts, S2O3, S3O6, S4O6, SO42-, S,

Fe3+, Fe2+, Zn, Cu, Ca, Mg, Na, and K. Results are given in Appendix A. Original sampling

at the Strathcona mill planned for October 20, 1998 was cancelled because of an emergency


3

shutdown at the mill. Mill sampling was instead conducted on November 19-20, 1998. A

total of 28 pulp samples representing the mill were collected and analyzed on-site for pH, Eh,

dissolved oxygen and conductivity after filtering and before freezing the samples.

Approximately 450 kg of fresh rod mill feed, process water from Moose Lake and reclaim

water from the stock tank 129 were received from the mill plant on December 1, 1998. Ten

pulp samples from the plant were analyzed for total thiosalts S2O2-3, S3O2-

6, S4O2-6, SO4

2-, S,

Fe3+, Fe2+, Zn, Cu, Ca, Mg, Na, and K. Results are given in Appendix A.

BACKGROUND INFORMATION

Thiosalts or polythionates are a collective name for oxyanions such as S2O3

2-, S3O62-, S4O6

2-,

which are intermediate products of oxidation of S to SO42-. Although the thermodynamics of

oxidation suggests that SO42- is the only ultimate product, kinetic limitations in neutral and

alkaline media results in partially oxidized products. The oxidation route of sulphide

minerals is presented schematically in Figure 1. Equation 1 shows a more detailed sub

process of sulphide mineral oxidation (Bocharov, 1985).

2

/ 2S

2

-4e-

0

+S +2e +e0 -

SO

MS SO S O S O SO

S SO S O

S e e ne

e

e

42

22 2 2

2 32 2

4 62

42

2 632

2 32

2

2 2 40

−

− + + − − − − −

− − −

−

↑

⇒ → → →

↑ ↓

→

↓

− − −

− −

−

SO42−

Equation 1

Sulphide minerals are thermodynamically unstable in moisture. Their oxidation in aqueous

solutions can be considered as an electrochemical corrosion process for which the following

equation (Avdokhin and Abramov, 1989) applies.

∆Gτ = -nEτF < 0 Equation 2


4

where Gτ is isobaric-isothermal potential of corrosion process, n is number of gram-

equivalents of substance, F is the Faraday’s constant (9.648456.104 C/mole), and Eτ is the

difference in reversible potential of the cathode and anode processes (Eτ =ϕc -ϕa ).

The spontaneous occurrence of the electrochemical corrosion of minerals is determined by

the difference in the reversible potential of the mineral (anode), ϕa, and of any oxidizing

agent (cathode), ϕc, present in the solution. Process water used during grinding and flotation

always contains ample amount of dissolved oxygen whose reversible oxidation-reduction

potential is much more positive than the potential of any mineral. Consequently, Eτ will be

positive, making the expression ∆Gτ being less than zero, a prerequisite for spontaneous

oxidation of sulphide minerals.

Majority of sulphide minerals fall in the category of compounds with partial ionic bonding

and are frequently represented as MeS where Me stands for a metal. When in contact with

water, dissolved oxygen is adsorbed at the metal anion site as represented by Equation 3.

MeS O MeS O

MeS O H O MeS O OHdiss ads

ads

+

+ + +

↔↔ + −

2 2

2 2 322 22

( ) ( )

( )

. Equation 3

Elemental sulphur which is normally present on sulphide mineral surfaces may oxidize to

thiosalts in aqueous sulphite solution (Equation 4). The sulphite ion is also a product of

surface oxidation (Equation 5). Equations 5, 6 and 7 are various routes of sulphur oxidation

(Garshteyn, Illyvieva and Baron, 1987).

MS MSS SO S Oaq0

32

2 32+ → +− −

( ) Equation 4


5

MS MS

MS MS

MS MS

S O H O S O S OH

S OH SO S H O

S O SO

SO O SO

S SO S O

S SO H O H

aq

aq

aq aq aq

aq aq aq

aq aq

aq aq

aq

22 2 2 3

2 0

032 2

2

22 4

2

32

2 42

032

2 32

232

2

12

2

3 6 3

212

2 3 3

− − −

− − −

− −

− −

− −

− −

+ + → + +

+ → + + +

+ →

+ →

+ → +

+ + →

( )

( )

( ) ( ) ( )

( ) ( ) ( )

( ) ( )

( ) ( )

( )

200 3 6⇔ + −S OH

Equation 5

MSMS MS

S SO S O

S OH S SO S H O

SO O SO

aq aq

aq aq aq

aq aq aq

032

2 32

0 032 2

2

32

2 42

6 2 3

12

+ →

+ → + + +

+ →

− −

− − −

− −

( ) ( )

( ) ( ) ( )

( ) ( ) ( )

Sometimes: Equation 6

MS 2 2 2

2 4

022 2 2

2 32

2 632 2

2 32

32 2

42

2 32

4 62 4

42

0

0

S SO S O

S SO S O

SO SO

S O S O SO

e S

e e S

e

e

→ →

→ →

→

↔ →

− + + −

− − − + + −

− − −

− − − −

−

−

−

Equation 7

At relatively high concentrations, thiosulphate is complexed by Cu ions according to

Equation 8 (Skrinchenko and Shelkova, 1987):

2 6 222 3

22 3 2

34 6

2Cu S O Cu S O S O+ − − −+ → +[ ( ) ] Equation 8

All sulphide minerals are semi-conductors and, in a grinding and flotation environment, they

undergo galvanic corrosion. Galvanic corrosion or surface oxidation occurs when two (or

more) dissimilar sulphide minerals, just as in the case of metals, are brought into electrical

contact under water. When a galvanic couple forms, one of the minerals in the couple

becomes the anode and oxidizes faster than it would all by itself, while the other becomes the


6

cathode and oxidizes slower than it would alone. Neither of the minerals in the couple may

oxidize by itself in grinding and/or flotation pulp depending on other conditions.

Table 1. Galvanic series of sulphide minerals

(Natarajan, 1986, Abramov, 1989) pH 4 (Kosabag and Smith 1985) Chalcocite Pyrite Noble (Cathodic), slow oxidizing Bornite Marcasite Covellite Chalcopyrite Pyrite Sphalerite Chalcopyrite Covellite Galena Bornite Pentlandite Galena Pyrrhotite Sphalerite Stainless steel media Mild steel media Active (Anodic) fast oxidizing

The Galvanic Series shown in Table 1 is a list of sulphide minerals ranked in order of their

tendency to oxidize in grinding and flotation environments. This table can be used to predict

which mineral will become the anode and how fast it will oxidize relative to the other

minerals and the steel grinding media. When two minerals on the list are in physical contact

during grinding, conditioning or flotation, the one closer to the anodic (or active) end of the

series will become the anode and oxidizes faster than the one closer to the cathodic (or noble)

end.

Suppose that pyrite, with a rest potential (i.e. the potential reached spontaneously by a

mineral electrode in a given aqueous solution) of +660 mV, is attached to galena which has a

rest potential of +400 mV. In this case, pyrite will act as the cathode and the voltage

difference between the two minerals will be 260 mV. It is this voltage difference that drives

the current flow to accelerate oxidation of the anodic mineral, galena. With their joint

presence and contact with each other during comminution and flotation, the nobler mineral in

the galvanic series will be protected from oxidation by the less noble minerals.

There are two major factors affecting the severity of galvanic corrosion. These are the

voltage differences between the two minerals and the size of the exposed area of cathodic

mineral relative to that of the anodic mineral. If the particle size distribution of the two

minerals is similar, relative abundance of the two minerals controls the oxidation rate of the

anodic mineral and hence the thiosalts generation due to cathodic effects. Oxidation of the

anodic mineral increases as the voltage difference between the cathode and anode increases


7

(i.e. the further apart the minerals are in the galvanic series) and as the cathode area increases

relative to the anode area.

When two minerals in a galvanic couple are close together on the series, their voltage ranges

overlap, and either one can be the anode, depending on the exact exposure conditions. In the

case of complex ore where more minerals with different rest potentials come in contact with

each other, the situation becomes more complex and the oxidation pattern will depend on

surface area ratios of the sulphide minerals present in the ore. An electrical potential will

develop between the large area of the cathode mineral and the small area of the anode. Rapid

pitting of the active mineral occurs at the point of contact. A small sphalerite inclusion in a

larger pyrite particle for instance accelerates sphalerite oxidation thus mobilizing more

sulphur, which is a precursor to thiosalts formation. Lack of liberation may become a cause

for concern not only due to poor metallurgical performance but also from an environmental

point of view.

Chalcopyrite-pentlandite-pyrrhotite ore

The grinding mill (if not lined) and the steel rods produce steel debris during grinding. This

fine metallic debris may interact with the ground mineral particles. If the media is mild steel,

magnetic minerals such as pyrrhotite can be coated with the iron debris which may affect the

rate and extent of pyrrhotite oxidation by lowering the rest potential of the mineral. When it

comes in contact with chalcopyrite or pentlandite, the Fe-coated pyrrhotite may assume a

mixed potential and become more anodic and, accordingly, may oxidize faster. As a

consequence, oxidation of chalcopyrite and pentlandite may even slow down. On the other

hand, with a decrease in the difference of rest potentials of the Fe-coated pyrrhotite and

grinding media, the oxidation of pyrrhotite due to galvanic interactions becomes less severe.

Under certain operating conditions, coating of pyrrhotite with grinding media debris may be

insufficient to lower the rest potential of the mineral. Since the rest potential of mild steel is

lower than that of stainless steel, pyrrhotite may be more protected against oxidation by the

mild steel media. Oxygen depletion resulting from the oxidation of steel debris also causes

changes in the rest potential.


8

A reaction product on the surface of pyrrhotite may be of a non-soluble nature and could alter

the rest potential of pyrrhotite permanently. Mild steel depletes dissolved oxygen from the

solution. Overall, more thiosalts are likely to be generated by stainless steel than by mild

steel media.

The following are possible reactions during grinding of a pyrrhotitic ore (Pozzo and Iwasaki,

1987).

At the steel anode:

Fe Fe e→ ++ −2 2 Equation 9

At pyrrhotite cathode (Cheng and Iwasaki, 1992)

FeS H O Fe SO H eS S O SO

+ → + + +

→ →

+ − + −

− −2

24

2

02 3

24

2

8 8 Equation 10

At chalcopyrite cathode:

12

2 22 2O H O e OH+ + →− − Equation 11

Presence of chalcopyrite should enhance the oxidation of pyrrhotite and pentlandite.

However, the presence of the steel debris that is magnetically attached to pyrrhotite particles

lowers the rest potential. In the case of the Strathcona ore, there is a possibility that the

thiosalts generation rate increases in proportion to increases in certain sulphide mineral

content even if the overall sulphur content of the ore doesn’t change significantly.

Pyrite-chalcopyrite-sphalerite ore

In this case, the grinding media debris is less attracted by the non-magnetic sulphide

minerals. Pyrite could act as the cathode whereas sphalerite, chalcopyrite and steel debris act

as the anode.

At the contact of the grinding media (steel anode) with sphalerite, chalcopyrite and pyrite, the

following reaction takes place:

2e Fe Fe -2 += + Equation 12

At the sphalerite, chalcopyrite and pyrite cathodes, oxygen is reduced to hydroxide:


9

2OH 2e OH O 21 ,, --

2222 →++Surface

FeSCuFeSZnS Equation 13

On the other hand, if the minerals are in contact more with each other than with the grinding

media, the following changes occur. Pyrite becomes the cathode when it is in contact with

either sphalerite or chalcopyrite. Chalcopyrite becomes the cathode when it is in contact with

sphalerite only.

For pyrite in contact with either minerals the anodic reaction can be expressed as:

−+ ++→ eSZnZnS 202 Equation 14

For chalcopyrite in contact with sphalerite, the anodic reaction is:

−+ ++→ eSFeCuFeS 42 02

2 Equation 15

The corresponding cathodic reaction is the reduction of oxygen on the pyrite surface as

above.

THE INFLUENCE OF pH, TEMPERATURE AND RESIDENCE TIME ON THIOSALTS GENERATION

The effects of conditioning (grinding) pH, temperature and residence time were investigated

under controlled laboratory conditions for both sulphide ores. Besides aeration rate and

grinding media type, these three factors are known to have the capacity to influence thiosalts

generation (Cotton, Spira and Wheeland, 1977). To determine how these factors affect

thiosalts generation and investigate possible interactions between these factors, a 23-Factorial

design of experiments with centre-point replicate was set up. A statistical design of

experiments was selected since many unknown factors may affect interpretations of one-at-a-

time type of experiments and small changes in responses often result from changes in

uncontrolled operating parameters. Significance of such small changes can not be positively

determined unless they are subjected to statistical analysis. Ranges of the factors investigated

are pH 7.5 to 9.5; temperature: 10 to 25°C; and residence time: 10 to 30 minutes. Within the

factor space studied, residence time of up to 30 minutes increased thiosalts concentration

only marginally in the case of the pyrrhotitic ore. A change in pH from 7.5 to 9.5 had the


10

same effect as raising the pulp conditioning temperature from 10 to 25°C. There was no

significant interaction between the three factors.

Test Methodology

The set-up used for this investigation is shown in Figure 2. A 76x210 mm plexiglass tube

was used for the test. The bottom was fitted with a stainless steel plate of very fine porosity

through which air was fed. Air flow, pH and temperature were controlled by a PC. Air was

fed at a rate of 0.25 L/min through a mass flow controller. The pH control was on/off type

using two peristaltic pumps: one for lime addition and the other for acid. Temperature was

controlled using a U-shaped 4-mm stainless tube through which cold/hot water flows.

Temperature was measured using a thermocouple. Information about pH, temperature,

oxidation-reduction potential, air flow rate and conductivity of the pulp was collected on-line

by a PC.

Initial tests conducted indicated that it was difficult to obtain reproducible results on thiosalts

generation due to difficulties in monitoring and controlling certain process factors. For

instance, minor inconsistencies, such as grinding temperature, delays in collecting samples

and preparation for testing and minor changes in grinding pH, that are acceptable in standard

flotation tests, caused significant differences in the amount of thiosalts generated. Evidently,

normal procedures used for grinding of ores for flotation testing was not adequate. When a

positive identification of factor effects became difficult, an elaborate procedure for preparing

samples was worked out to provide a uniform feed for each test. The amount of sample used

for each test was scaled down from 1650 g to a manageable size of 300 g due to cost

considerations. The samples weighing 1650 g were ground with 840 mL of temperature-

adjusted tap water. The pulp was filtered immediately and the filtrate was aerated with

nitrogen until the dissolved oxygen concentration dropped to 0.5 ppm to prevent further

oxidation of thiosalts species. The filter cake was split into 5 portions and each portion was

vacuum-sealed in an aluminum bag for storing in freezer. Three batches of samples were

ground for each ore to prepare sufficient number of feeds. The filtrate from the three

grindings was mixed and split into 15 equal amounts of solution. Each sample was

transferred to 0.5 L plastic container purged with nitrogen, and instantly frozen with liquid

nitrogen and stored in freezer. Before testing, the aluminum bag containing frozen solid


11

sample and the bottle containing frozen solution, with its tight lid in place, were warmed up

in a temperature-controlled water bath. As soon as the working temperature was attained, the

solution and the solid samples were transferred to the cell where the temperature was

maintained automatically.

Feed Sample Compositions

Bulk chemical compositions of the ore samples are given in Table 2. The Strathcona ore

(ST1 and ST2) is characterized by high Fe, S and SiO2 concentrations. Average Cu and Ni

levels of the ore are 4.3 and 2.7% respectively. Sulphate concentration of the ore is 0.5% and

the CO2 level is below the detection limit of 0.05%. Solid samples that resulted from the

experiments do not display significant variations from these levels.

Table 2. Bulk chemical analysis of the Strathcona (ST)

and Louvicourt (LV) ore samples ST1 ST2 LV1 LV2 SiO2 28.24 28.67 32.94 34.23 TiO2 0.33 0.32 na na Al2O3 7.58 7.64 9.37 9.56 MnO 0.08 0.08 0.12 0.13 MgO 2.04 2.02 5.01 5.07 CaO 2.99 3.06 1.90 1.99 Na2O 1.73 1.78 0.32 0.36 K2O 0.58 0.57 0.65 0.65 CO2 <0.05 <0.05 4.17 4.17 SO4 0.48 0.47 0.25 0.28 Fe 28.88 28.81 20.27 20.66 Ni 2.70 2.66 na na Cu 4.29 4.25 3.92 4.04 Pb na na <0.03 <0.03 Zn na na 0.16 0.16 Ssul 20.17 19.52 18.36 18.31 Total 93.10 92.93 97.45 99.61 Results in wt %; Ssul: sulphide sulphur; na: not analyzed

The Louvicourt ore samples (LV1 and LV2) are characterized by high SiO2, Fe and S

concentrations. Aluminum concentrations (as Al2O3) are approximately 9.5%. MgO levels

are around 5%. Sulphate concentrations are lower than 0.3% and the CO2 levels are 4.2%.

Copper is approximately 4% and Zn is 0.16%.


12

Mineralogical Composition of the Strathcona Ore

The Strathcona ore consists predominantly of pyrrhotite, chalcopyrite, pentlandite, quartz,

muscovite and Ca-pyroxene (Table 3). Pyrrhotite is the dominant sulphide mineral in all the

samples. Pyrite, sphalerite, galena and bornite occur in trace quantities. Chlorite, K-feldspar,

amphibole, epidote and biotite are the other silicate minerals present in moderate to minor

quantities. In addition, magnetite, ilmenite, apatite, gypsum and Fe-oxyhydroxides are

present. A representative photomicrograph is given in Figure 3.

Table 3. Minerals identified, their relative abundances and particle

sizes in the Strathcona ore Mineral Abundance Particle size (µm)

Pyrrhotite +++ 1-1500 (25-300) Chalcopyrite +++ 1-1500 (25-200) Pentlandite ++ 1-1500 (25-150) Magnetite/Ilmenite ++ 1-1500 (100-400) Pyrite + 10-50 Sphalerite + 1-1500 (100-200) Galena + 1-150 (1-20) Bornite - 10-20 Quartz +++ 1-1500 (25-300) Potassium feldspar +++ 1-1500 (25-300) Pyroxene ++ 25-150 Muscovite + 20-125 Chlorite +++ 20-125 Amphibole ++ 20-150 Epidote ++ 20-100 Biotite + 20-50 Gypsum + 10-30 Iron oxyhydroxide + 25-50 Apatite + 5-10 +++ :major; ++: minor; +: trace; -: not present ; Numbers in brackets represent the size ranges of the majority of grains.

Pyrrhotite occurs as liberated grains and, less commonly, in association with chalcopyrite,

pentlandite and magnetite/ilmenite (Figure 4). Pyrrhotite-gangue associations were observed;

however, they are generally restricted to the fine-grained fraction. Coarse pyrrhotite grains

that are liberated frequently display exsolution flames of pentlandite. Chalcopyrite was

observed primarily as liberated grains and less commonly in association with pyrrhotite,

pentlandite, and gangue minerals. More rarely chalcopyrite occurs in the form of exsolution

blebs in sphalerite. Pentlandite exists primarily as liberated grains and as exsolution lamellae

or flames in pyrrhotite. Rare occurrences of pyrrhotite intergrown with chalcopyrite were


13

also observed. Pentlandite also occurs in association with feldspar and quartz. Galena was

observed as inclusions in chalcopyrite and to a lesser extent in sphalerite. Rare occurrences

of liberated galena were also observed. Pyrite, magnetite and ilmenite occur primarily as

liberated grains. Pyrite also occurs in association with pyrrhotite and chalcopyrite. Coarse

pyrrhotite and chalcopyrite grains sometimes display a relatively fine-grained rim that

consists of angular fragments mineralogically identical to the grain they surround (Figure 5).

The angular nature of the fragments that comprise the halo suggest that it is the result of a

mechanical process rather than being chemical. Major liberated sulphide grains (i.e.

pyrrhotite, chalcopyrite and pentlandite) range from less than 1 µm to 1.5 mm in size;

however, the majority of the grains fall between 40 and 200 µm.

Quartz, plagioclase feldspar, amphibole, epidote, pyroxene, chlorite and muscovite are the

most abundant gangue minerals in the ore sample. Gangue minerals often occur as

composite particles sometimes locking and encapsulating various sulphides.

Mineralogical Composition of the Louvicourt Ore

The Louvicourt ore mineralogy and average grain sizes of the minerals after grinding are

summarized in Table 4. Sulphide and gangue minerals occur in equal proportions. The

sample is made up of grains that range in size from less than 1 µm to 1.5 mm with the

majority falling in the 50 to 125 µm range (Figure 6). Pyrite occurs primarily as liberated

grains displaying subhedral outlines. Pyrite commonly occurs in association with

chalcopyrite. Composite particles of pyrite-chalcopyrite-gangue association are also present

(Figure 7). Less commonly, pyrite occurs as inclusions in chalcopyrite. In order of

decreasing abundance, chalcopyrite occurs as subhedral to anhedral liberated grains,

inclusions in pyrite, attached to pyrite, inclusions in gangue minerals and inclusions in

sphalerite. Sphalerite occurs as liberated grains, attached to chalcopyrite and gangue-

chalcopyrite composites, in order of decreasing abundance. Sphalerite may contain

exsolution blebs of chalcopyrite. Other sulphides listed in Table 4 are very rare and warrant

only a cursory mention. Galena, native bismuth, pyrrhotite and an unknown sulphosalt,

having an approximate mineral composition of Fe6Sb7S7, occur as fracture-fillings in

sphalerite-carbonate composites (Figure 8). A small gold grain measuring approximately

2 µm was found as encapsulated in pyrite.


14

Quartz, magnesian siderite, chlorite and muscovite are the most abundant gangue minerals.

Carbonate grains display subhedral to euhedral outlines, some of which have well-developed

crystal habit (Figure 9). Magnetite, ilmenite, and rutile occur as liberated grains.

Table 4. Minerals identified, their relative abundances and

particle sizes in the Louvicourt ore Mineral Abundance Particle size (µm)

Pyrite +++ <1500 (50-200) Chalcopyrite +++ <500 (50-200) Magnetite/Ilmenite + 25-50 Pyrrhotite + <100 (2-50) Sphalerite + 25-100 Galena + 1-10 Arsenopyrite + 25-40 Gold + 2 Native Bi + 10-15 Unknown Sulphosalt + 10-15 Quartz +++ 1-1500 (25-200) Mg-siderite ++ 2-1000 (25-200) Ankerite +++ 25-75 Calcite + 25-75 Dolomite + 25-75 Muscovite +++ 20-150 Chlorite +++ 1-500* Amphibole + 1-100 Potassium feldspar ++ 25-200 Plagioclase feldspar + 25-200 Rutile + 5-20 Apatite + 5-15 +++ :major; ++: minor; +: trace; -: not present ; Numbers in brackets represent the size ranges of the majority of grains;

Experiments on Thiosalts Generation

The amount of thiosalts generated, expressed as g/t of total thiosalts concentration for each

test, is given in Table 5.

Bulk chemical compositions of the Strathcona samples that resulted from the batch

experiments (LLL1, LLL2, MMM1 MMM2, HHH1 and HHH2) are given in Table 6. These

samples do not display significant variations from the feed composition.


15

Table 5. Test design parameters and results

Total Thiosalts Generated (g/t) TEST

ID Factor A

pH Factor B

Temperature (°C)

Factor C Residence time

(min) Louvicourt Strathcona

1 8.5 17.5 20.0 34 216 2 9.5 10.0 10.0 45 85 3 9.5 10.0 30.0 51 203 4 7.5 10.0 10.0 30 59 5 9.5 25.0 30.0 75 284 6 7.5 25.0 10.0 47 160 7 8.5 17.5 20.0 50 174 8 9.5 25.0 10.0 67 206 9 7.5 25.0 30.0 49 267 10 7.5 10.0 30.0 31 90 11 8.5 17.5 20.0 59

Table 6. Bulk chemical analysis of the experimental samples LLL1 LLL2 MMM1 MMM2 HHH1 HHH2 SiO2 29.09 28.88 29.52 28.88 29.09 29.52 TiO2 0.32 0.32 0.33 0.33 0.33 0.32 Al2O3 7.69 8.03 8.77 7.92 7.75 7.84 MnO 0.08 0.09 0.10 0.09 0.08 0.08 MgO 1.97 2.07 3.48 2.01 1.99 2.04 CaO 2.95 2.92 3.01 2.95 3.01 3.04 Na2O 1.82 1.81 1.86 1.82 1.86 1.85 K2O 0.58 0.59 0.59 0.59 0.59 0.59 CO2 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 SO4 0.33 0.32 0.29 0.28 0.28 0.26 Fe 27.68 29.09 24.85 28.37 27.37 28.00 Ni 2.57 2.69 1.43 2.64 2.56 2.61 Cu 3.99 4.19 4.06 4.08 3.99 4.04 Ssul 19.15 19.37 19.28 19.99 19.16 18.93 Total 91.67 93.49 92.09 93.22 91.51 92.47 Results in wt %; Ssul: sulphide sulphur


16

The Louvicourt samples that resulted from the experiments (LLL1, LLL2, MMM1, MMM2,

HHH1 and HHH2) are compositionally similar to the feed (Table 7).

Table 7. Bulk chemical analyses of the Louvicourt samples resulted from batch experiments

LLL1 LLL2 MMM1 MMM2 HHH1 HHH2

SiO2 34.44 34.66 34.87 35.30 34.23 34.66 Al2O3 9.77 9.75 9.47 9.56 9.54 9.47 MnO 0.13 0.13 0.13 0.13 0.13 0.13 MgO 4.92 4.98 4.92 4.87 4.86 4.91 CaO 1.85 1.86 1.86 1.90 1.87 1.89 Na2O 0.59 0.39 0.38 0.40 0.54 0.35 K2O 0.67 0.66 0.67 0.66 0.66 0.66 CO2 3.96 4.15 4.10 3.96 4.14 4.17 SO4 0.19 0.21 0.19 0.19 0.20 0.22 Ssul 17.86 17.75 18.12 17.13 17.96 17.67 Fe 19.60 19.97 19.67 19.51 19.68 19.86 Cu 3.65 3.73 3.65 3.66 3.65 3.70 Pb <0.03 <0.03 <0.03 <0.03 <0.03 <0.03 Zn 0.16 0.17 0.16 0.16 0.16 0.17 Total 97.80 98.41 98.19 97.44 97.63 97.85 Results in wt %; Ssul: sulphide sulphur

Mineralogical Composition of the Strathcona Samples

Similar to the feed mineralogy, the Strathcona samples that resulted from batch experiments

consist predominantly of pyrrhotite, chalcopyrite, pentlandite, quartz, muscovite and Ca-

pyroxene. Pyrrhotite is the dominant sulphide mineral in all the samples. Pyrite, sphalerite,

galena and bornite occur in trace quantities. Mineralogy of the Strathcona samples is

summarized in Table 8. This suite of Strathcona samples exhibits only minor differences in

the relative sulphide abundance from sample to sample.


17

Table 8. Minerals identified, their relative abundances and particle sizes in the Strathcona samples

abundance particle size (µm) Mineral

SAR4-LLL SAR7-MMM SAR5-HHH SAR4-LLL SAR7-MMM SAR5-HHH

Pyrrhotite +++ +++ +++ 1-125 (20-40) 1-125 (15-30) 1-150 (15-30) Chalcopyrite +++ +++ +++ 1-125 (20-40) 1-125 (15-30) 1-150 (15-30) Pentlandite ++ ++ ++ 1-125 (10-40) 1-125 (10-30) 1-75 (10-30) Magnetite/Ilmenite + + + 20-40 20-40 20-40 Pyrite + + + 10-25 10-25 10-20 Sphalerite + + + 20-40 20-40 20-40 Galena + - + 1-10 1-10 1-10 Bornite + - - 10-20 Quartz +++ +++ +++ 1-125 (25-75) 1-125 (25-50) 1-150 (25-50) Potassium feldspar +++ +++ +++ 1-125 (25-75) 1-125 (25-50) 1-75 (25-50) Pyroxene ++ ++ ++ 25-50 10-25 10-25 Muscovite + + + 20-50 20-50 25-50 Chlorite +++ +++ +++ 20-50 20-50 25-50 Amphibole ++ ++ ++ 20-75 20-75 25-100 Epidote ++ ++ ++ 25-50 25-50 25-50 Biotite + + + 10-40 10-30 10-40 Gypsum + - - 10-25 Iron oxyhydroxide + + + 25-50 25-40 25-50 Apatite + + + 5-10 5-10 5-10 +++ :major; ++: minor; +: trace; -: not present

SAR4-LLL

The descriptive mineralogy of this sample is similar to that of the ore sample. Sulphides

range in size from <1 µm to 120 µm; however, the majority of the grains are between 15 and

50 µm. Relatively coarse liberated sulphide grains occasionally display evidence of

mechanically created deformation halos similar to that observed in the ore sample.

Composite particles commonly consist of pyrrhotite, chalcopyrite and a variety of gangue

minerals. There is no apparent evidence of dissolution or alteration along grain margins or

microfractures in sulphides. Quartz, feldspar, amphibole, epidote, pyroxene, and muscovite

are the dominant silicates in this sample. Chlorite is a minor phase. Silicates are generally

anhedral to subhedral and show no evidence of alteration along their grain boundaries. Trace

amounts of liberated iron oxyhydroxide grains are present in this sample.


18

SAR7-MMM

This sample is mineralogically similar to SAR4-MMM. Sulphides range in size from 1 µm

to 100 µm; however, the vast majority of grains are between 10 and 50 µm. Sulphides are

anhedral to subhedral and show no apparent evidence of dissolution. In addition, grain

boundaries between different sulphide minerals show no evidence of alteration or

replacement. Quartz, plagioclase feldspar, amphibole, epidote, pyroxene and chlorite are the

dominant silicate phases in this sample. Biotite and muscovite are present as minor phases.

Silicate particles are generally anhedral and subhedral and devoid of apparent dissolution

features.

SAR5-HHH

Mineralogy of this sample is similar to those of SAR4-MMM and SAR7-LLL. Sulphides

appear to display a higher degree of liberation than that exhibited in the other samples (ORE,

SAR4-LLL, SAR7-MMM). Sulphide particles range from less than 1 µm to 100 µm with the

majority being between 15 and 30 µm. Fewer coarse-grained sulphides exhibit rims of

agglomerations of finer particles observed in the other samples (Figure 10). Sulphides do not

display any apparent evidence of alteration along the grain boundaries with other sulphides.

Silicate mineralogy is similar to that described for SAR7-HHH with the exception of minor

amounts of calcite. Feldspars are anhedral to subhedral with fresh particle boundaries.

Mineral Quantities

It is assumed that ilmenite is responsible for the bulk Ti concentrations. Accordingly,

ilmenite mode was calculated based on Ti and Fe tied to ilmenite and was subtracted from

total Fe before employing multiple regression techniques and mass balance calculations.

Only pyrrhotite, pentlandite and chalcopyrite, as sulphide minerals, were considered in the

calculations. Sulphide minerals that are present in trace or minor quantities were excluded

from the calculations. The following mineral compositions, based on theoretical mineral

formulas or semi-quantitative energy-dispersive microanalysis, were used in the calculations:

pyrrhotite: FeS; pentlandite: Ni4.5Fe4.5S8; chalcopyrite: CuFeS2; quartz: SiO2; muscovite:

K2Al6Si6O20(OH)4; chlorite: Mg4.6Fe5.4Al4.4Si5.8O20(OH)16; Ca-pyroxene:

Mg0.8Ca0.8Fe0.4Al0.1Si2O6; and epidote: Ca2FeAl2Si3O13.


19

Pyrrhotite quantities vary from about 29 to 33% (by weight) (Table 9). Chalcopyrite is the

second most abundant sulphide with quantities in the 13 to 15% range. Pentlandite occurs in

quantities varying from 7 to 9%. Quartz and muscovite together make up approximately

30% of the samples. Ca-pyroxene is present in concentrations that are approximately 9%

whereas epidote forms approximately 6% of the samples. These mineral quantities are

relatively uniform among the ores and the processed samples.

Table 9. Mineral quantities (wt%) of the feed and experimental samples

ORE1 ORE2 LLL1 LLL2 MMM1 MMM2 HHH1 HHH2 Quartz 15.2 15.4 16.4 15.1 14.0 15.8 16.3 16.2 Muscovite 14.4 14.1 14.7 14.9 19.6 15.2 14.9 14.7 Ca-pyroxene 9.5 9.5 9.2 9.5 14.9 8.9 9.3 9.6 chlorite 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 epidote 5.1 6.1 5.6 5.9 0.0 5.2 5.6 6.0 ilmenite 0.6 0.6 0.6 0.6 0.7 0.6 0.7 0.6 pyrrhotite 32.9 32.8 32.1 33.2 29.1 32.3 31.6 32.1 pentlandite 8.9 8.4 8.5 8.2 6.8 8.9 8.7 8.4 chalcopyrite 13.5 13.1 12.9 12.6 15.0 13.1 13.0 12.5 Total 100 100 100 100 100 100 100 100

Mineralogical Composition of the Louvicourt Samples

The mineralogy of the Louvicourt samples and average grain sizes of the minerals are

summarized in Table 10. There is no significant mineralogical difference among the

samples.

LVR5-LLL

Mineralogy of this sample is similar to that of the ore sample. Sulphide and gangue minerals

occur in roughly equal proportions. Sulphide minerals range in size from approximately 1 to

120 µm; however, the majority of the grains fall in the 10 to 30 µm range. Liberated grains

of pyrite and chalcopyrite exhibit no apparent evidence of alteration along their grain margins

(Figure 11). Grain boundaries between pyrite and chalcopyrite are pristine and show no

evidence of reaction. Similarly, pyrrhotite and sphalerite particles do not display any

evidence of oxidation. Carbonates do not show any apparent evidence of significant

dissolution (Figure 12). This is evidenced by the preservation of rhombohedral crystal

boundaries exhibited by many of the magnesian siderite particles.


20

Table 10. Minerals identified, their relative abundances and particle sizes in the Louvicourt samples

abundance particle size (µm) Mineral

LVR5-LLL LVR7-MMM LVR6-HHH LVR5-LLL LVR7-MMM LVR6-HHH

Pyrite +++ +++ +++ <200 (20-50) <150 (25-75) <200 (25-75) Chalcopyrite +++ +++ +++ <100 (10-40) <100 (25-50) <125 (25-50) Magnetite/Ilmenite + + + 15-30 20-75 25-100 Pyrrhotite - + + <20 10-30 10-40 Sphalerite + + + 2-20 25-75 25-100 Galena + - - 1-5 - - Arsenopyrite - - - - - - Gold - - - - - - Native Bi - - - - - - Unknown Sulphosalt - - - - - - Quartz +++ +++ +++ 1-120 (10-50) 1-150 (25-75) 1-200 (25-75) Mg-siderite ++ ++ ++ 1-100 (5-50) 1-150 (25-50) 1-150 (25-75) Ankerite +++ +++ +++ 5-25 10-50 10-50 Calcite + + + 5-25 10-50 10-50 Dolomite + + + 5-25 10-50 10-50 Muscovite +++ +++ +++ 5-50 5-75 10-100 Chlorite +++ +++ +++ 5-50 5-75 10-100 Amphibole 5-25 5-50 5-50 Potassium feldspar ++ ++ ++ 5-100 10-100 10-125 Plagioclase feldspar + + + 5-100 10-100 10-125 Rutile + + + - - - Apatite + - - - - - +++ :major; ++: minor; +: trace; -: not present; Numbers in brackets represent the size ranges of the majority of grains;*: as part an agglomerate


21

LVR7-MMM

Mineralogy of this sample is similar to LVR-ORE and LVR5-LLL. Only the differences are

described here. Pyrite and chalcopyrite particles range in size from approximately 1 to

125 µm; however, the majority of particles are between 10 and 40 µm. Particle surfaces

reveal no evidence of oxidation. Similarly, the mutual grain boundaries between pyrite and

chalcopyrite show no discernible evidence of reaction (Figure 13). Of the gangue minerals

listed in Table 10, the carbonates are considered to be the best measure of degree of reactivity

or dissolution. Carbonates are similar to those observed in LRV5-LLL and show no evidence

of significant dissolution; however, some grains display somewhat ragged edges, which may

be interpreted as an indication of the initial stages of dissolution.

LVR6-HHH

Sulphide mineralogy is similar to that described for LVR5-LLL and LVR7-HHH. The

majority of pyrite and chalcopyrite particles ranges from 10 to 40 µm; however grains as

large as 120 µm were observed. Sulphides show no obvious evidence of dissolution along

the grain edges or boundaries with other sulphides. Carbonate minerals have maintained

their subhedral to euhedral form, although some rugged edges may be due to dissolution.

Mineral Quantities

It is assumed that chalcopyrite is the only Cu-bearing mineral and all the Zn is tied to

sphalerite. Following the calculation of chalcopyrite (based on its theoretical formula

CuFeS2) and sphalerite, assuming that it does not contain Fe (i.e. ZnS), the remaining S is

assigned to pyrite. Iron that is tied to pyrite was subtracted from the bulk Fe concentrations

and the residual Fe and other elements were used in the calculation of the other minerals

present in the samples by MODAN (Paktunc, 1998). The following mineral compositions,

based on either theoretical mineral formulas or semi-quantitative energy-dispersive X-ray

microanalysis, were used in the calculations: quartz: SiO2; muscovite:

K1.7Na0.2Fe0.1Al5.8Si6O20(OH)4; plagioclase: Ca0.05Na0.95Al1.05Si2.95O8; chlorite:

Mg6Fe3.4Al5.2Si5.4O20(OH)16; magnesian siderite: Fe0.38Mg0.62CO3; ankerite:

Ca0.5Mg0.38Fe0.12CO3; and magnetite: Fe3O4. The results are given in Table 11.


22

Table 11. Mineral quantities (wt%) of the feed and experimental samples recalc ORE1 ORE2 LLL1 LLL2 MMM1 MMM2 HHH1 HHH2

quartz 22.9 23.0 22.6 23.2 24.3 24.4 22.9 24.0 muscovite 13.7 13.2 13.4 14.0 13.6 13.5 13.5 13.8 plagioclase 5.2 5.4 7.7 6.0 5.7 5.9 7.3 5.5 chlorite 20.6 20.4 20.2 19.8 19.9 19.9 19.4 19.6 Mg-siderite 2.7 2.3 2.5 2.7 2.7 2.1 2.8 2.7 ankerite 7.6 7.6 7.2 7.2 7.3 7.4 7.3 7.4 magnetite 0.9 1.5 0.6 1.3 0.4 1.6 0.7 1.3 pyrite 18.4 18.2 18.3 18.0 18.6 17.5 18.4 18.0 chalcopyrite 7.9 8.1 7.4 7.6 7.4 7.5 7.4 7.5 sphalerite 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

Statistical Analysis and Discussion of Effects of Parameters Studied on Thiosalts Generation The results are statistically analyzed to determine the most significant effects. Three main

effects (pH, temperature and residence time), three 2-Factor interaction effects (pH vs

temperature, pH vs residence time, temperature vs residence time), and one 3-Factor

interactions (pH vs temperature vs residence time) can be determined from this series of tests

(Table 12).

Table 12. Contributions by factors and their interactions to thiosalts generation when factor settings change from low to high levels investigated

Effect of changing From low to high

setting

Contribution % Model Coefficient

Term Pyritic

ore Pyrrhotitic

ore Pyritic

ore Pyrrhotitic

ore Pyritic

ore Pyrrhotitic

ore Intercept 81.54 236.44pH [A] 33.44 70.55 48.02 10.03 16.72 35.27Temperature [B] 33.44 167.64 48.02 56.66 16.72 83.82Residence time [C] 7.02 116.65 2.12 27.43 3.51 58.32pH X Temperature 4.54 -26.54 0.89 1.42 2.27 -13.27pH X Residence time 4.54 20.26 0.89 0.83 2.27 10.13Temperature X Residence time 1.24 12.57 0.07 0.32 0.62 6.29pH X Temp. X Residence time 0.41 -40.51 0.01 3.31 0.21 -20.26


23

Table 13 and 14 show the results of statistical analysis of factor and factor-interaction effects

and their contributions to thiosalts generation. From this, it is evident that only the main

effects are significant and not even a single interaction effect exists in both cases. In the case

of the pyritic ore, changes in residence time did not significantly affect the thiosalts

generation. All the significant effects have positive signs implying that, within the studied

factor space, all three factors contribute to thiosalts generation. The extent to which each

factor contributes to the total amount of thiosalts is sufficiently independent of the levels of

the remaining two factors. In other words, whether it is in the winter (where in-mill water

temperature is around 10°C) or in the summer, the effect of change in pH or change in

residence time will remain about the same all other conditions being similar. For mill

temperatures below 10°C and above 25°C there may be some differences. Tables 13 and 14

show statistical details of variance analysis for the factors of significant influence. From

Table 13, it is evident that the generation of thiosalts can be adequately expressed in terms of

only pH and temperature variations. Temperature and pH variations contributed 96% of the

total thiosalts generated, each have equal contribution in the case of the pyritic ore. The

effects are linear in nature (note that curvature with a probability of greater than 0.7 is not

significant) implying that increasing pH beyond 9.5 and temperature beyond 25°C would

increase the thiosalts generation at a similar rate. This linearity of the effects of all the three

factors investigated is also confirmed in Table 13.

Thiosalts generation by the pyrrhotitic Cu-Ni ore is significantly affected by all three factors,

temperature being the largest contributor (56.7%) followed by residence time (27.4%) and

pH (10%). The effects of these factors on thiosalts generation are linear as in the previous

case.

The pyrrhotitic ore appears to be more sensitive to pulp temperature than the pyritic ore while

the pyritic ore is more sensitive to pH than the pyrrhotitic ore (Figures 14, 15 16 and 17).

Unlike its effect in the tailings pond, elevated temperatures may not contribute to thiosalts

degeneration during the relatively short residence time in the processing plant. Pulp

residence time, which has a negligible effect on thiosalts generation in the case of pyritic Cu

ore, has however a significant contribution in the case of pyrrhotitic Cu-Ni ore.


24

Table 13. ANOVA for Selected Factorial Model (Pyritic Cu ore) Source Sum of

Squares DF Mean Square F Value Prob > F

Model 4473.79 2 2236.89 14.78 0.0031

Curvature 17.37 1 17.37 0.11 0.7447

Residual 1059.07 7 151.30

Lack of Fit 184.45 5 36.89 0.084 0.9873

Pure Error 874.62 2 437.31

Cor Total 5550.22 10

Root MSE 12.30 R-Squared 0.8086 Dep Mean 80.77 Adj R-Squared 0.7539 C.V. 15.23 Pred R-Squared 0.5604 PRESS 2440.08 Adeq Precision 9.018 Desire > 4

Table 14. ANOVA for Selected Factorial Model (Cu-Ni pyrrhotitic ore) Source Sum of

Squares DF Mean Square F Value Prob > F

Model 93370.68 3 31123.56 14.69 0.0036

Curvature 96.07 1 96.07 0.045 0.8384

Residual 12713.21 6 2118.87

Lack of Fit 5828.23 4 1457.06 0.42 0.7898

Pure Error 6884.98 2 3442.49

Cor Total 1.062E+05 10

Root MSE 46.03 R-Squared 0.8802 Dep Mean 238.25 Adj R-Squared 0.8202 C.V. 19.32 Pred R-Squared 0.6345

PRESS 38804.11 Adeq Precision 11.434 Desire > 4


25

The total thiosalts generated may be expressed with the following equations: Pyritic ore:

C = 16.72 * pH + 2.23 * T - 99.61 Equation 16

Pyrrhotitic ore:

C = 35.27 * pH + 11.18 * T + 4.17 * t - 375.6 Equation 17

where C is the total thiosalts (TTS) concentration in ppm, T is temperature in oC and t is

residence time in minutes.

Figures 14 and 15 show the adequacy of these models to estimate the amount of TTS

generated under various conditions. Within the factor-space studied, the average TTS

generated by the pyritic ore is 81.5 g/t (Figure 20). On average, the pyrrhotitic ore generates

236.4 g/t TTS (Figure 21). Raising the pH from 8.5 to 9.5 would result in an increase of

these values by 16 g/t and 35 g/t respectively assuming that the temperature and residence

time remains constant.

All other conditions remaining constant, a change in pulp temperature by 1°C would result in

an increase by 2.2 g/t and 11.2 g/t in TTS for the pyritic and pyrrhotitic ores respectively. An

increase in residence time by 1 minute has the effect of increasing total thiosalts generation

by about 4 g/t for the pyrrhotitic ore while there is no significant change occurring in the case

of the pyritic ore.


26

INFLUENCE OF GRINDING MEDIA ON THIOSALTS GENERATION

Test Methodology

Samples weighing 1.65 kg were ground at 66% solids to a targeted grind size by using 100%

stainless steel, 100% mild steel and a 50%:50% mixture of stainless steel and mild steel rods

(equal in number of rods and similar in weights and diameters). No reagents were used

during grinding. The mill discharge was allowed to settle and the clear solution was analyzed

for total thiosalts.

Results and Discussion

The physical parameters of testing and the results are presented in Table 15 and Figures 22,

23 and 24. From Figure 24 it is evident that the pyritic ore produces more thiosalts than the

pyrrhotitic ore regardless of the grinding media composition. It is however necessary to

determine if this is the case for all pH values within the range of interest. Lime is the major

reagent used to control pH in most sulphide ore processing plants. The change in pH of mill

discharge, as a function of lime addition rate, is shown in Figure 25. The resulting pulp

conditions are shown in Table 16. Stainless steel media was used in this series of tests. The

pyrrhotitic ore consumes at least three-times more lime than the pyritic ore to obtain similar

pH.

Table 15. Experimental conditions and results of grinding media effect study

Pyritic ore (Louvicourt) Pyrrhotitic ore (Strathcona) Grinding media

100% MS SS/MS mix 100% SS 100% MS SS/MS MIX 100% SS

Temperature (0C) 19.1 19.00 22.0 20.3 22.00 22.1

Dissolved oxygen conc. (mg/L) 1.38 4.24 1.09 2.42 0.42 4.23

pH 6.6 7.05 6.31 6.03 6.88 5.31

Conductivity (µs) 36.9 20.3 2.4 56.3 3.2 4.6

Thiosalts concentration. (ppm) 22 40 104 16 11 66

Thiosalts generated (g/t of ore) 11 21 53 8 6 34

Note: MS: Mild steel, SS: Stainless steel


27

Table 16. Effects of pulp pH (lime addition) on thiosalts generation during grinding with stainless steel

Pyritic ore (Louvicourt) Pyrrhotitic ore (Strathcona)

Lime (g/t) 152 455 909 152 455 909 1818 2424 3212

pH 0.81 6.64 4.64 0.56 1.5 5.3 1.5 2.0 4.5

Conductivity (µs) 1262 1590 1497 3350 2280 3360 1852 2760 4480

Temperature (0C) 7.04 7.96 9.44 6.67 6.83 7.4 7.14 8.03 9.14

Dissolved oxygen conc. (mg/L) 24.8 24.6 26.4 28.6 25.2 23.9 26.5 22.5 24.5

Thiosalts concentration (ppm) 146 228 366 13 18 134 55 107 256

Thiosalts generated (g/t of ore) 72 114 183 7 9 67 28 55 130

The effects of pulp pH (as controlled by lime addition) on thiosalts generation is shown in

Figure 26 for both ore types. Unlike the flotation stage (see Figures 16, 17 and 19), the

pyritic ore produces more thiosalts than the pyrrhotitic ore within the range of grinding pH

investigated. The linearity of the relationship and the similarity of the slopes for the two

curves representing the two ores may provide a simple predictive tool.

Although both grinding and flotation result in increases of thiosalts for both ore types, the

extent to which milling and flotation affect each ore type appears to be different. Since pyrite

produced more thiosalts than pyrrhotite during grinding while it produced less during

aeration flotation (see Figure 17), an explanation is ought to be found. It could be that the

mechanism of oxidation during grinding where there is a galvanic influence of a grinding

media is more intensive for the pyritic ore. It could also be that, due to the surface coating by

oxidation products formed during grinding, the rate of oxidation is slower in the case of the

pyritic ore than it is for the pyrrhotitic ore during aeration (flotation). Due to grinding in a

closed mill, the oxygen demand may not have been met for the pyrrhotitic ore compared to

the pyritic ore. It requires characterization of surface oxidation products to validate the

above mentioned hypothesis.

The following preliminary conclusions were drawn from the test results:

• The amount of thiosalts generated during grinding strongly depends on the type of

grinding media.

• As anticipated, the stainless steel produced more thiosalts than mild steel grinding media

did. Switching from 100% mild steel to 100% stainless steel media increased the amount


28

of total thiosalts generated during grinding by 5-fold for the pyritic ore and 4-fold for the

pyrrhotitic ore.

• Grinding the pyrrhotitic ore with a 50:50 mix of stainless steel and mild steel media

generated slightly less thiosalts than the 100% mild steel media. Grinding the pyritic ore

under similar conditions doubled the amount of thiosalts generated during grinding.

• The change in trend of dissolved oxygen consumption during grinding, in response to

changes in grinding media composition, is unique for both ore types. The highest

consumption of oxygen for the pyritic ore occurred during grinding with 100% stainless

steel and the lowest consumption occurred during grinding with the 50:50 mix. The

opposite is true for the pyrrhotitic ore. In general, where 100% stainless steel or mild

steel grinding media is used, oxygen is stripped from the solution faster by the pyritic ore

than the pyrrhotitic ore.

• Conductivity of grinding mill discharge solution is higher for the mild steel media than

the stainless steel media.

• The pyritic ore is oxidized faster than the pyrrhotitic ore during grinding regardless of the

grinding media type. During flotation, the opposite appears to be true. Less thiosalts are

generated by the pyritic ore than by the pyrrhotitic ore at pH values normally used for

flotation.

• The solution becomes more acidic with increase in proportion of stainless steel in the

media.

Being influenced by both ore mineralogy and grinding media composition, oxidation of

sulphide ore during grinding, and the resulting thiosalts generation, is a complex process.

The environment in an autogenous (or semi-autogenous) mill can be expected to be more

oxidizing (or non-reducing) than in conventional mill in which active media is used and this

results in the formation of higher concentration of S2O3- (Forrssberg et al., 1993).


29

STUDY OF THIOSALTS FORMATION UNDER SIMULATED SULPHIDE ORE PROCESSING PLANT CONDITIONS

Continuous and semi-batch-type flotation tests were conducted in the laboratory to

investigate thiosalts generation by simulating operations of the Louvicourt and Strathcona

mills. Prior to these tests, the processing plants were sampled to determine the levels of

thiosalts concentrations in major streams. Based on a preliminary investigation, it was

decided to use batch-type laboratory flotation tests to study the nature of thiosalts generation

in the processing plants. Data obtained from laboratory simulations correspond to the

measurements made on the samples obtained from the plants. The amount and rate of

thiosalts generation in the process streams are influenced mainly by sulphide mineral

quantities and types of reagents used, pH, temperature and residence time.

Neither Strathcona mill nor Louvicourt mill was able to provide the proposed amount of ore,

dried and crushed to minus 10 mesh size required to process 180 kg of ore per hour. In view

of this, a small-flow continuous grinding, classification and flotation circuit capable of

processing 200 g/min was proposed as an alternate approach. SAG mill feed from the

Louvicourt mill and rod mill feed from the Strathcona mill were sampled dried and crushed

at CANMET. The Louvicourt ore was tested by both continuous and semi-batch modes

whereas the Strathcona ore was tested on semi-batch mode only.

Continuous Testing of Thiosalts Generation for the Louvicourt Ore

Figure 27 shows the configuration of the small-flow continuous grinding, classification and

flotation experimental set-up capable of processing 200 g/min of ore. The grinding circuit

consists of a rod mill in closed circuit with a 160 µm sieve. The flotation circuit was

configured to allow pre-aeration, collector conditioning, and Cu rougher-scavenger and

3-stage closed circuit cleaning of Cu concentrate. The Zn circuit is comprised of activation

stage, collector conditioning, pH adjustment, Zn roughing, scavenging and 3-stage cleaning

of Zn concentrate. Main flotation conditions are summarized in Table 17.


30

Table 17. Flotation conditions for the Louvicourt ore

Unit operation/conditions Conditions Remarks

Grinding size 100% passing 160 micron

Grinding pH 8 to 8.5

Aeration time 10 min 2 L/min airflow

Cu Collector type Combination of KAX 20 g/t, 3 min conditioning

pH of Cu flotation 8.5 to 9

Rougher and scavenger residence time 30 min

Zn activation pH > 8.5

CuSO4.5H2O 280 g/t of feed

SIPX 30 g/t of feed

SIPX conditioning pH 10-11

Zn Flotation pH 10-11

Zn rougher and scavenger residence time 30 minutes

Table 18. Thiosalts generation in the experimental grinding and flotation circuit Water flow (mL/min) Total thiosalts

(mg/L) g/min g/min/t of feed

ST1 Mill Feed 0.0059 29.5 ST2 Mill discharge 200 52 0.0104 ST2-ST1 Grinding 0.0045 22.5 ST3 Post aeration 300 39 0.0117 ST3-ST2 Aeration 0.0013 6.5 ST4 Cu concentrate stream 60 70 0.0042 ST5 Cu tailings stream 290 71 0.0206 ST4+ST5 Cu circuit 0.0131 65.5 ST7 Zn concentrate stream 20 77 0.0015 ST8 Zn tailings stream 300 68 0.0204 6.8 ST7+ ST8 Zn circuit 0.0014 Total 0.0261 The distribution of thiosalts generation in the circuit is shown in Table 18 and Figure 28. The

amount of total thiosalts generated in the mill discharge includes the thiosalts originally

contained in the feed sample. An estimated 23% of the thiosalts measured in the mill

discharge originated from the feed.

With 50% of the total thiosalts generated, Cu circuit is the biggest contributor followed by

grinding (17%). Owing to the addition of CuSO4, which reduces the amount of total thiosalts

concentration in the solution, the amount of thiosalts generated within the Zn circuit is only

5% despite the alkalinity of the circuit which was maintained at pH of about 11. Aeration

contributed only 5%.


31

Semi-batch Testing of Thiosalts Generation for Louvicourt Ore

Stabilization and control of the small flow continuous testing system described in the

preceding section was fast and easy. However, changing the flow conditions to less than

200 g/min solids was ineffective and higher than 200 g/min of solids flow resulted in coarse

grinding. Changing the residence time in the flotation and conditioning circuits was also

difficult. In view of this, a semi-batch flotation setup was assembled for more accurate

measurements of flow and other physical and chemical conditions.

Test Methodology

This setup consists of an automated and instrumented flotation cell based on

Denver laboratory flotation machine (Figure 29). The equipment allows automated

measurement and/or control and recording of various parameters such as airflow rate, pH,

oxidation reduction potential (ORP), dissolved oxygen concentration, temperature, froth

depth and pulp level. Froth is picked up automatically and pumped to a filtration funnel.

Both solids and froth water weight are monitored and recorded during flotation. Two modes

of flotation are available: one with addition of pH-adjusted water for pulp level control and

the other is without water addition. In the latter case, there is no need to maintain constant

pulp level with water. The froth pick-up mechanism is designed to automatically track the

pulp/froth interface at a predetermined distance (froth depth). This eliminates the undue

dilution of flotation pulp and reagent concentrations. The whole setup minimizes

intervention by the operator and ensures consistently reproducible results, which are critical

when using statistical design and analysis of results.

The rougher and scavenger flotation stages were conducted under controlled temperature, pH

and airflow rate. Cleaning of concentrates was done in a similar but smaller flotation setup

but without control on temperature. The complete flowsheets indicating sampling points are

shown in Figure 30. Selective Cu and Zn flotation procedure was used, although there was

very little Zn in the ore, to better simulate plant procedure.


32

Grinding

• grinding was carried out in a rod mill with 46 lbs. mild steel rods at 66% solids.

• no excess water was used to wash down the pulp from the mill. Volume of the pulp,

when transferred to the flotation cell, was less than that of the cell. No water was

removed from the pulp to preserve the composition of the pulp solution.

• the pulp was diluted in the flotation cell to 40% solids.

Aeration

• pH was adjusted with lime addition to 8.5

• pulp was aerated to ORP of = -100 mV (SCE vs Au electrode)

• collector conditioning for Cu Rougher flotation

• PAX was added at pH 8 - 8.5

• duration of conditioning was 3 minutes

Cu Rougher Flotation

• Cu was floated at 2.5 L/min. airflow, 1600 RPM, and at a pH of 8.5.

• frother amount was just about sufficient and was added gradually in a diluted form.

• froth removal was gentle and uniform. The targeted concentrate weight was

recovered over a period of 10 minutes.

Cu Scavenger Flotation

• airflow was temporarily stopped and the required amount of collector was injected

deep into the pulp for a thorough mixing before turning on the air.

• froth removal was gentle. The targeted concentrate weight was recovered over a

period of 10 minutes.

Zn Flotation

• Zn activation with CuSO4 was for about 1 minute and was carried out before pH

adjustment for Zn flotation.

• pH was adjusted to 11 before collector (sodium isopropyl xanthate) addition

• collector conditioning was for 3 minutes.

Zn Rougher Flotation

• pH of 11 was maintained

• airflow rate was 2.5 L/min.




33

Zn Scavenger Flotation

• airflow was temporarily stopped and the required amount of reagent(s) was injected

deep into the pulp for a thorough mixing before turning on the air. A pH of 11 was

maintained.



Concentrate Cleaning

• both Cu and Zn concentrates cleaning were carried out in a small cell with a gentle

airflow.

• Cu cleaning was at pH 6 to 6.5. Zn cleaning was at pH 10.5 to 11

• froth removal was gentle and slow.

• the targeted concentrate weight was recovered over a period of 3 minutes.

Results and Discussions (Louvicourt)

The bulk chemistry and mineralogical composition of the flotation products are summarized

in Table 19. In Table 20, metal recovery, in separate mill products, is shown. Table 21

shows the overall grade and recovery of Zn if the separate products were combined. Ignoring

the amount of Zn in the products allows considering the two separate concentrates as

belonging to only Cu. In this case, the recovery of Cu is 91.9% at 23.7% Cu grade or 93.5%

at 19.1% Cu grade. These values are comparable to that of the plant grade and recovery.

Figure 31 shows the amount of total thiosalts generated in major process circuits by each ton

of feed ore. Evidently, 14% of the total thiosalts comes with the feed ore. Approximately

one-third of the total thiosalts was generated during grinding. Cu conditioning contributed

only 5%. Cu rougher/scavenger/cleaner circuit produced 23%. Zn conditioning stage,

particularly the addition of CuSO4, results in minor reduction of thiosalts concentration. Zn

rougher/flotation/cleaner produced 26% of the total thiosalts. Cu cleaning stage alone

contributed half of the total amount generated by Cu rougher/scavenger/cleaner circuits. The

same applies to Zn circuit. This can be explained by the similar quantities of sulphide

minerals present in both circuits. Due to the insignificance of Zn content in the ore, both

circuits can be technically considered as Cu circuits. In this test, Zn flotation was carried out

not to recover Zn but to monitor the effects of Zn processing factors on thiosalts generation.


34

Table 19. Bulk chemistry and mineralogical quantification of the flotation products (Louvicourt) Assays % Mineral distribution

Stream Weight(g)Cu Fe Zn S CuFeS2 ZnS FeS2 Others

Cu concentrate 95.7 30.6 30.1 0.51 34.68 88.29 0.76 6.87 4.08Cu cleaner tailings 7.1 11.3 22.5 0.50 25.98 32.60 0.75 26.96 39.69Cu circuit tailings 22.9 0.9 18.2 0.13 20.88 2.51 0.19 37.40 59.90Zn cleaner concentrate 72.0 23.1 29.7 1.90 34.91 66.65 2.84 20.15 10.36Zn cleaner tailings 52.0 1.7 18.3 0.16 21.01 4.76 0.24 36.14 58.86Zn scavenger tailings 1377.9 0.2 17.9 0.06 20.51 0.69 0.09 37.94 61.28Head Sample (assayed) 1650.0 3.5 19.2 0.19 22.06 10.21 0.28 34.51 54.99

Table 20. Flotation test results (separate Cu and Zn concentrates)

Weight Cu Fe Zn (g) % Assay Cumulative

dist'n Assay Cumulative dist'n Assay Cumulative

dist'n Cu concentrate 95.7 5.88 30.60 57.33 30.10 9.23 0.51 17.24Cu cleaner tailings 102.8 6.32 29.27 58.90 29.58 9.74 0.51 18.49Cu circuit tailings 125.7 7.72 24.09 59.29 27.50 11.08 0.44 19.54Zn cleaner concentrate 72.0 4.42 23.10 32.56 29.70 6.85 1.90 48.32Zn cleaner tailings 124.0 8.85 14.10 34.24 24.92 9.90 1.17 51.26Final tailings 1377.9 84.66 0.240 6.5 17.90 79.0 0.060 29.2Head Sample (assayed) 1627.6 100 3.14 100 19.18 100 0.17 100Head Sample (calculated) 26.8 3.54 19.20 0.19

Table 21. Flotation Test Results (Combined Cu and Zn concentrates)

Weight Cu Fe Zn (g) % Assay Cumulative

dist'n Assay Cumulative dist'n Assay Cumulative

dist'n Cu concentrate 95.7 5.88 30.60 57.33 30.10 9.23 0.51 17.24Cu cleaner tailings 102.8 6.32 29.27 58.90 29.58 9.74 0.51 18.49Cu circuit tailings 125.7 7.72 24.09 59.29 27.50 11.08 0.44 19.54Zn cleaner concentrate 197.7 12.15 23.73 91.85 28.30 17.93 0.97 67.86Zn cleaner tailings 249.7 15.34 19.13 93.53 26.22 20.98 0.80 70.80Final tailings 1377.9 84.66 0.240 6.5 17.90 79.0 0.060 29.2Head Sample (assayed) 1627.6 100 3.14 100 19.18 100 0.17 100Head Sample (calculated) 26.8 3.54 19.20 0.19


35

Semi-batch Testing of Thiosalts Generation for Strathcona Cu-Ni ore

The same equipment and procedures used in the investigation of Louvicourt ore were used in

testing the Strathcona ore with a slight difference in the flowsheet. In the case of Strathcona,

in which the plant flowsheet was simulated, no attempt was made to separate Cu from Ni.

The flowsheet, which is similar to the Strathcona Mill flowsheet, is shown in Figure 32.

Results and Discussions (Strathcona) The bulk chemistry and mineralogical quantities of the flotation products are given in

Table 22. The ore contains about 12.6% chalcopyrite, 3.7% pentlandite and 35.9%

pyrrhotite. Pyrrhotite is the predominant sulphide mineral in all streams except in Cu circuit

streams and in the non-magnetic stream where chalcopyrite dominates. Metal distribution in

the flotation products is shown in Table 23. The flotation process employed was adequate

and resulted in 97% overall recovery of Cu at a grade of 9.7% Cu, and 87.9% recovery of Ni

at a grade of 4.9% Ni.

The operation of the simulated circuit resulted in the production of 579 g thiosalts per ton of

feed. The amount of thiosalts generated by each ton of feed ore in various circuits is shown

in Figure 33. The 3-minute conditioning with potassium amyl xanthate contributed the

highest amount of thiosalts (i.e. 29.3%). The primary conditioning circuits contributed most

of the remaining thiosalts. It is evident that collector conditioning has a major effect on

thiosalts generation followed by the regrinding of flotation products in the pyrrhotite

rejection circuit. These two areas appear to be paramount from the point of view of

controlling the production of thiosalts.


36

Table 22. Bulk chemistry and mineralogical composition of the flotation products

(Strathcona) Sulphide mineral distribution (wt%)

Weight (g) Chalcopyrite Pentlandite Pyrrhotite Total

Head 1626 12.6 3.7 35.9 52.2Cu-Ni con 65.1 90.9 4.3 17.5 112.7Cu-Ni cleaner tailings 26.6 41.0 11.2 35.2 87.4Cu cleaner feed 91.7 76.5 6.5 14.3 97.2Pyrrhotite rejection cleaner concentrate 151.7 13.6 7.2 83.7 104.5

Pyrrhotite rejection cleaner concentrate tailings 2

142.7 14.7 5.9 92.4 113.1


139.9 12.1 6.3 97.5 115.9

Non-magnetics 71.7 66.6 2.9 34.2 103.8Final tailings 1029 0.5 0.6 11.9 12.9Note: The total sulphide mineral abundance adds to more than 100% in most cases due to the assumption that the Ni, Cu, Fe and S analyzed in the products are contained by only these three minerals.

Table 23. Flotation Test Results (Strathcona ore) Weight

Cumulative distribution

Assay (%)

Cumulative distribution (%) Each

product (g) (g) % Cu Ni Cu Ni

Cu-Ni concentrate 65.1 65.1 4.00 31.50 2.80 34.19 5.50Cu-Ni tailings 26.6 91.7 5.63 26.48 4.10 40.48 11.33Pyrrhotite rejection cleaner concentrate 151.7 243.4 14.95 12.92 4.44 52.44 32.60


142.7 386.1 23.72 10.04 4.22 64.60 49.13


139.9 526.0 32.32 8.48 4.18 74.37 66.26

non-magnetic fraction 71.7 597.7 36.72 9.74 4.88 97.08 87.89

Rougher/scavenger tailings 1029 1029.9 63.28 0.170 0.39 2.9 12.1

HEAD (calculated) 1627.6 100 3.69 2.04 197 100HEAD (assayed) 3.54 2.34


37

EFFECTS OF MINERALOGY ON THIOSALTS GENERATION DURING MILLING AND FLOTATION

Mineralogical composition of sulphide ores influences the amount and rate of thiosalts

formation in mill feed, during grinding and flotation. An examination of ore samples with

variable quantities of sulphide minerals and corresponding amounts of thiosalts generated

under similar conditions allows estimation of the contributions of grinding and sub-processes

in flotation to the formation of thiosalts. The Strathcona and Louvicourt ores were subjected

to batch-type grinding and flotation simulation experiments as shown in Figures 34 and 35.

Each ore sample was processed to prepare variable head grade samples to simulate possible

variation in mineralogical composition. Magnetic separation was used to prepare the

pyrrhotitic Cu-Ni ore samples whereas gravity separation was used to prepare the pyritic Cu-

Zn ore samples. The samples were mineralogically characterized to investigate relationships

between the level of total thiosalts generation and the changes in mineralogical composition.

Louvicourt Ore

Sample Preparation and Testing Methodology

The pyritic ore sample was crushed to 100% passing 1650 µm and scrubbed under nitrogen

atmosphere with deoxygenated water to remove any residual thiosalts in the sample. The

sample was then ground at 66% solids with a stainless steel media in deoxygenated water to

reduce oxidation. The mill discharge was further diluted with deoxygenated water and

subjected to gravity separation on a shaking table. The middling and the concentrate,

containing mostly sulphide and other metallic minerals, separated in this manner, were

pressure filtered under nitrogen and preserved in the freezer. Equal amounts of sample were

taken from the concentrate and the middling to mix with a 1.65 kg of freshly ground sample.

Each of the four tests conducted contained the same amount of original ore but variable

amounts of gravity concentrate and middling. The mixing proportion of solids for each test is

given in Table 24.


38

Table 24. Louvicourt experimental samples

Test ID Original sample

(%)

Table concentrate and middling

(%)

Total sample weight

(g) LVT 1 96 4 1710 LVT 2 93 7 1770 LVT 3 90 10 1830 LVT 4 87 13 1890

Bulk chemical compositions of the samples are given in Table 25. The head sample (LVT1)

has 19.5% Fe, 18.4% S (sulphide), 3.3% Cu and 0.14% Zn. LVT2 and LVT3 do not display

significant variations from the head sample. LVT4 has higher sulphide S and Fe

concentrations.

Table 25. Bulk chemical analysis of the samples

prepared by gravity separation LVT1 LVT2 LVT3 LVT4

SiO2 35.94 34.87 34.66 33.80 Al2O3 8.88 8.69 8.88 8.69 MnO 0.12 0.11 0.11 0.12 MgO 4.48 4.31 4.48 4.48 CaO 1.54 1.54 1.54 1.82 Na2O 0.31 0.32 0.30 0.32 K2O 0.63 0.61 0.66 0.58 CO2 3.60 3.54 3.51 3.75 SO4 0.34 0.33 0.33 0.34 Ssul 18.41 18.41 19.40 20.62 Fe 19.50 19.90 19.60 20.10 Cu 3.29 3.54 3.86 3.69 Pb na na na na Zn 0.14 0.15 0.15 0.14 Total 97.17 96.33 97.47 98.44 na: not analysed

Mineralogy

Mineralogy of the three process samples and grain sizes are summarized in Table 26.

Variations in mineralogy and textural relationships among the three samples are not

significant. Representative photomicrographs illustrating the salient textures and mineral

associations are presented in Figures 6, 7, 8, 9, 11, 12, 13, 36 and 37.


39

Table 26. Minerals identified, relative abundances and particle sizes in the Louvicourt experimental samples

Abundance particle size (µm) Mineral LVT2-H LVT3-H LVT4-H LVT2-H LVT3-H LVT4-H

Pyrite +++ +++ +++ <125 (25-75) <125 (25-75) <125 (25-75) Chalcopyrite ++ ++ ++ <125 (25-60) <125 (25-60) <125 (25-60) Magnetite/Ilmenite + + + 25-100 25-100 25-100 Pyrrhotite + + + <75 (10-60) <75 (10-60) <75 (10-60) Sphalerite + + + <25 (5-10) <25 (5-10) <25 (5-10) Galena + + - <10 <10 <10 Arsenopyrite + - + <10 <10 <10 Quartz +++ +++ +++ 1-150 (25-100) 1-150 (25-100) 1-150 (25-100) Mg-siderite ++ ++ ++ 1-125 (25-75) 1-125 (25-75) 1-125 (25-75) Ankerite ++ ++ ++ 1-125 (25-75) 1-125 (25-75) 1-125 (25-75) Calcite + + + 25-75 25-75 25-75 Dolomite + + + 25-75 25-75 25-75 Muscovite ++ ++ ++ 10-75 10-75 10-75 Chlorite +++ +++ +++ 10-75 10-75 10-75 Amphibole + + + 10-60 10-60 10-60 Potassium feldspar + + + 1-150 (25-100) 1-150 (25-100) 1-150 (25-100) Plagioclase feldspar + + + 1-150 (25-100) 1-150 (25-100) 1-150 (25-100) Rutile + + + - - 5-20 Apatite - - + +++ :major; ++: minor; +: trace; -: not present

Sulphide and Oxide Minerals

Pyrite and chalcopyrite account for over 90% of sulphide and oxide minerals observed in

these samples. The remainder consists of magnetite, pyrrhotite, sphalerite, galena and

arsenopyrite in order of decreasing abundance. Pyrite and chalcopyrite occur primarily as

liberated inclusion-free grains; however, very fine-grained pyrite and chalcopyrite was

observed attached to various gangue minerals. More rarely fine-grained chalcopyrite was

observed as attached to relatively coarse pyrite. All the sulphide mineral particles display

sharp edges and show no evidence of dissolution or reaction.

Gangue Minerals

Quartz, chlorite, ankerite and magnesian siderites are the dominant gangue minerals in order

of decreasing abundance in each of the three samples studied. Quartz is by far the most

abundant gangue mineral. Quartz, along with chlorite and carbonates represents

approximately 80% of all the gangue minerals. Some of the carbonate mineral grains show

corroded-looking grain edges; however, this texture shows no preference for a particular

mineral or sample. As a result, a sample may contain particles with sharp outlines and

particles with rugged edges. This suggests that dissolution is more a function of degree of

exposure than mineralogy. In addition to carbonates, some feldspar grains exhibit features

which may have resulted from dissolution. Similar to the carbonates, feldspar dissolution


40

features were observed on a grain to grain basis, not a sample to sample basis. None of the

other silicate or oxide minerals display any definitive evidence of dissolution.

Polymineralic agglomerations were observed in all the samples. Gangue minerals dominate

the mineralogy of agglomerates but small quantities of pyrite and chalcopyrite are almost

always present. Agglomerations can range in size from 100 to 1000 µm.

Mineral Quantities

Mineral quantities as determined by MODAN are listed in Table 27.

Table 27. Mineral quantities (wt %) of the Louvicourt

experimental samples LVT1 LVT2 LVT3 LVT4

quartz 27.3 26.6 26.3 25.5 muscovite 13.4 13.5 14.6 14.6 plagioclase 5.1 5.3 5.3 6.0 chlorite 18.7 18.2 17.5 16.0 Mg-siderite 2.7 2.6 1.9 0.9 ankerite 6.2 6.3 6.9 8.5 magnetite 0.2 1.0 0.0 0.0 pyrite 19.4 19.1 19.6 21.1 chalcopyrite 6.7 7.1 7.7 7.2 sphalerite 0.2 0.2 0.2 0.2 Total 100 100 100 100

Test Results and Discussion Scrubbing of the feed sample prior to grinding under non oxidizing nitrogen atmosphere

removed all the thiosalts originally present in the ore which was estimated to be 42 g/t.

Grinding of the ore in enclosed laboratory mild steel rod mill produced 31 g/t of total

thiosalts. It appears that a good portion of the total thiosalts in mill effluents originates from

the mine and not all is produced in the processing plant. Thiosalts are known to be formed

especially in stockpiles. Table 28 shows a comparison of particle size distribution of the

samples tested. The d80 grind size for the original ore is 52 µm. With the addition of gravity

concentrate and middling, the d80 shifts to a lower value indicating that the combination of

gravity concentrate and middling has a lower d80 value than the original ore grind size.

Generally, the higher the proportion of the gravity concentrates in the mixture the lower the

d80 size is. The concentration of total thiosalts in successive water samples, taken at


41

predetermined time intervals, is reported in Table 29. To determine the dynamics of thiosalts

formation rate, the results were analyzed by time intervals and are shown in Figure 38.

Table 28. Louvicourt experimental sample size distributions

original ore LVT1 LVT2 LVT3 LVT4

d80 grinding size (µm) 52 44 47 43 40

Table 29. Test results

Total thiosalts generated (g/t) Process step

Cumulative residence time (min) LVT1 LVT2 LVT3 LVT4

5' pulp conditioning without air 5 33 39 46 20 15' aeration 15 41 48 50 33 35' aeration 35 52 69 65 59 55' aeration 55 73 97 92 94 75' aeration 75 96 127 121 124 10' min conditioning with KAX 85 116 142 138 130

The rate of thiosalts generation appears to be higher during grinding and the first few minutes

of conditioning than the first 5 to 20 minutes of flotation. The rate of thiosalts production

gradually increases for the first hour for all four samples. There is at least one-fold increase

in thiosalts production rate during this period. After that, the rate appears to be levelling off.

The increase in rate with time can be due to dissolution of oxide coatings on sulphide

particles, which may have developed during initial conditioning. This exposes more sulphide

surfaces for further oxidation to form thiosalts.

The instant reduction in the rate of thiosalts generation as aeration starts may be partly

explained by the oxidation of thiosalts to sulphate due to an increase in the abundance of

dissolved oxygen concentration. Figure 39 shows that the pulp oxidation-reduction potential

(ORP) for LVT4, which is highly reducing at the beginning, quickly becomes oxidizing in

the first 5 minutes of conditioning and levels off after 30 minutes. The dissolved oxygen

concentration follows a similar pattern, but the increase is much slower because it is partially

used up during oxidation or oxygen transfer into solution is slower.


42

The pulp oxidation-reduction potential change with residence time for all the samples

(Figure 40) indicates that with an increase in the proportion of the sulphide minerals in the

pulp, the oxidation potential becomes more reducing. Only LVT1 does not follow this

pattern, probably owing to its relatively low sulphide mineral content.

To establish a relationship between pH and total thiosalts generation rate, pulp pH is plotted

against cumulative residence time (Figure 41). During the first 5 minutes of conditioning, the

pH drops sharply. With aeration, the pH begins to rise again for a period of about 10

minutes. After 10 minutes of aeration, the pH begins to gradually decrease. LVT4 and

LVT3 are generally less acidic than LTV1 and LTV2.

Conductivity also increased with an increase in abundance of sulphide minerals in the pulp

(Figure 42). Only LVT2 does not appear to follow this general pattern. The conductivity of

LTV1 (sample with the lowest amount of sulphide minerals) is the weakest, and non-

proportionally low.

Strathcona Ore

Sample Preparation, Sample Mineralogy and Test Methodology

To obtain a series of variable feed compositions for grinding and simulation of flotation

processes, the Strathcona ore was first crushed to 100% passing 1650 µm. The sample was

then separated into a magnetic and a non-magnetic fraction using a low intensity drum

magnetic separator (Eriez Magnetics Model 15DIA”X” 12’) operating at a medium speed.

The split was 53% magnetic and 47% non-magnetic fractions. Obviously some amount of

magnetic and non-magnetic particles would report into the other component by entrapment.

For simplicity, we would refer to the two products as magnetic and non-magnetic fractions.

The amount of material used in each test was 1.65 kg. The proportions used to prepare the

samples are listed in Table 30.


43

Table 30. Strathcona experimental samples

Sample No Magnetic fraction (wt%) Description SAMM-H na original Sample SAMM7 0 experimental sample SAMM1 10 “ SAMM 2 30 “ SAMM 5 50 “ SAMM 3 70 “ SAMM 4 90 “ SAMM 6 100 “

Table 31. Bulk chemical analysis of the samples prepared from magnetic and non-magnetic fractions

SAMM-H SAMM7 SAMM1 SAMM2 SAMM5 SAMM3 SAMM4 SAMM6 SiO2 34.87 53.91 50.27 44.28 36.37 32.09 26.10 24.39 TiO2 0.42 0.47 0.47 0.47 0.47 0.48 0.48 0.48 Al2O3 8.13 12.47 11.72 10.77 9.07 7.75 6.43 5.86 MnO 0.11 0.12 0.13 0.12 0.12 0.11 0.12 0.11 MgO 2.30 3.27 3.00 2.75 2.49 2.27 2.12 2.04 CaO 3.46 5.21 5.00 4.46 3.95 3.43 3.06 2.92 Na2O 2.51 3.90 3.55 3.15 2.66 2.22 1.87 1.73 K2O 0.89 1.37 1.19 1.06 0.93 0.78 0.69 0.63 CO2 <0.03 <0.03 <0.03 <0.03 <0.03 <0.03 <0.03 <0.03 SO4 0.44 0.07 0.11 0.14 0.17 0.25 0.31 0.33 Fe 24.00 8.38 11.40 16.90 22.90 28.20 33.60 35.20 Ni 1.82 0.92 1.01 1.35 1.58 1.74 2.01 2.11 Cu 3.27 1.31 1.49 1.52 1.37 1.16 1.25 1.07 Ssul 15.33 4.34 5.98 9.74 13.47 16.92 20.32 21.90 Total 92.45 93.50 92.81 93.85 92.58 94.51 95.10 95.59 Results in wt %; Ssul: sulphide sulphur

Bulk chemical compositions of the samples are given in Table 31. The head sample

(SAMM-H) has 24% Fe, 15.3% S (sulphide), 3.3% Cu and 1.8% Ni. Iron, Ni, S and SO4

concentrations display a steady increase from the non-magnetic sub-sample (SAMM7) to the

magnetic sub-sample (SAMM6). These increases are counter balanced by decreases in SiO2,

Al2O3, MgO, CaO, Na2O and K2O concentrations. Mineralogy and the grain sizes of the

minerals present are summarized in Tables 32 and 33. The samples exhibit differences in

sulphide quantities as anticipated.


44

Table 32. Minerals identified in the Strathcona samples

Mineral SAMM-H SAMM1 SAMM2 SAMM3 SAMM4 SAMM5 SAMM6 SAMM7

Pyrrhotite +++ ++ +++ +++ +++ +++ +++ ++

Chalcopyrite ++ ++ ++ ++ ++ ++ ++ ++

Pentlandite ++ ++ ++ ++ ++ ++ ++ +

Magnetite/Ilmenite ++ ++ ++ ++ ++ ++ ++ ++

Pyrite + + ++ ++ + + + ++

Sphalerite + + + + + + + +

Galena + + + + + + + -

Bornite - + + + - + + -

Cubanite - - + - + + -

Millerite + - - - - - - -

Quartz +++ +++ +++ +++ +++ +++ +++ +++

Feldspar +++ +++ +++ +++ +++ +++ +++ +++

Pyroxene +++ +++ +++ +++ ++ ++ ++ ++

Muscovite + + + + + + + +

Chlorite +++ ++ +++ +++ +++ +++ +++ +++

Amphibole ++ + ++ ++ ++ ++ ++ ++

Epidote ++ ++ ++ ++ ++ ++ ++ ++

Biotite + + + + + + + +

Iron oxyhydroxide + + + + - - - -

Apatite + + - + + + + +

+++ :major; ++: minor; +: trace; -: not present


45

Table 33. Grain sizes (µm) of the minerals identified in the Strathcona samples

Mineral SAMM-HEAD SAMM7-H SAMM1-H SAMM2-H SAMM5-H SAMM3-H SAMM4-H SAMM6-H

Pyrrhotite <125 (50-100) <100 (25-50) <125 (50-100) <125 (50-100) <125 (50-100) <100 (25-50) <100 (50-75) <125 (50-100)

Chalcopyrite <125 (25-75) <100 (25-50) <125 (25-75) <125 (25-75) <125 (50-75) <100 (25-50) <100 (25-75) <125 (50-75)

Magnetite/Ilmenite 50-125 10-100 (25-50) 50-125 50-125 50-75 5-100 (25-50) 5-100 (50-100) 50-75

Pentlandite <75 (10-50) <75 (10-25) <75 (10-50) <75 (10-50) <75 (25-50) <75 (10-25) <25 (5-15) <75 (25-50)

Pyrite <125 (60-100) <50 (20-40) <125 (60-100) <125 (60-100) <100 (50-75) <50 (20-40) <75 (50-50) <100 (50-75)

Sphalerite <100 (25-50) <25 (5-10) <100 (25-50) <100 (25-50) <50 (25-50) <25 (5-10) <25 (5-10) <50 (25-50)

Galena <10 <10 <10 <10 <10 <10 <10 <10

Arsenopyrite - - - - - <10 - -

Cubanite 5-25 - 5-25 5-25 5-25 - 5-25 5-25

Millerite 5-25 - 5-25 5-25 5-25 - - 5-25

Quartz 1-125 (50-100) 1-150 (25-100) 1-125 (50-100) 1-125 (50-100) 1-150 (50-100) 1-150 (25-100) 1-125 (25-75) 1-150 (50-100)

Mg-siderite 1-125 (25-75) 1-125 (25-75) 1-125 (25-75) 1-125 (25-75) 1-100 (25-75) 1-125 (25-75) 1-100 (25-75) 1-100 (25-75)

Ankerite 1-125 (25-75) 1-125 (25-75) 1-125 (25-75) 1-125 (25-75) 1-100 (25-75) 1-125 (25-75) 1-100(25-75) 1-100 (25-75)

Calcite 25-75 25-75 25-75 25-75 25-75 25-75 25-75 25-75

Dolomite 25-75 25-75 25-75 25-75 25-75 25-75 25-75 25-75

Muscovite 5-75 10-75 5-75 5-75 5-75 10-75 10-75 5-75

Chlorite 10-100 10-75 10-100 10-100 10-125 (50-100) 10-75 10-100 10-125 (50-100)

Amphibole 10-50 10-60 10-50 10-50 10-50 10-60 10-50 10-50

Potassium feldspar 1-125 (50-100) 1-150 (25-100) 1-125 (50-100) 1-125 (50-100) 1-125 (50-75) 1-150 (25-100) 1-100 (25-75) 1-125 (50-75)

Plagioclase feldspar 1-125 (50-100) 1-150 (25-100) 1-125 (50-100) 1-125 (50-100) 1-125 (50-75) 1-150 (25-100) 1-100 (25-75) 1-125 (50-75)

Apatite - 5-20 - - - 5-20 5-20 -


46

Sulphide and Oxide Minerals

Pyrrhotite, chalcopyrite and pentlandite are the dominant sulphide minerals in each of the

eight samples studied. Magnetite is the most common oxide mineral in the samples. Minor

and trace sulphides and oxides include pyrite, sphalerite, cubanite, millerite, bornite, and

rutile. Their relative abundance and average grain sizes are summarized in Tables 32 and 33.

Pyrrhotite, chalcopyrite and magnetite occur primarily as liberated grains (Figures 43 and

44). Pentlandite often occurs as exsolution flames enclosed in coarse pyrrhotite grains but it

also forms liberated grains. Chalcopyrite was also observed as encapsulated grains in various

gangue minerals (Figure 45) and more rarely as attached grains to pyrrhotite. Magnetite

occurs exclusively as liberated grains with no inclusions. Galena occurs almost exclusively

as inclusions in various sulphides (e.g. chalcopyrite) and silicates (e.g. amphibole). Trace

sulphides such as cubanite, bornite and millerite were all observed as relatively small and

liberated grains.

The majority of the sulphide grains show little or no significant evidence of oxidation.

Coarse particles of pyrrhotite from each of the eight samples studied display a rim of

agglomeration of very fine-grained pyrrotite (Figure 46). This rim may contain minor

quantities of other sulphides, usually chalcopyrite or pentlandite. In some cases, this texture

appears to be gradational with grain size increasing away from the host pyrrhotite

(Figure 47). Coarse-grained pentlandite rarely displays a thin rim. Unfortunately, this rim is

too thin to be accurately resolved by the electron beam (approximate diameter 1µm). Other

sulphide grains show no evidence of oxidation.

Gangue Minerals

Quartz, chlorite, epidote, plagioclase, potassium feldspar, Ca-pyroxene and amphibole are the

major gangue minerals in the samples (Table 32). The majority of gangue minerals occur as

liberated grains (Figure 45). They may contain fine-grained inclusions of the dominant

sulphides. Polymineralic agglomerations made up of gangue minerals and various sulphides,

and ranging in size from 200 to 1000 µm occur in all the samples. None of the gangue

minerals display any apparent evidence of dissolution.


47

Mineral Quantities

Mineral quantities were determined using a similar technique as the one described previously

for the Strathcona samples. Mineral quantities of the process samples are given in Table 34.

Table 34. Mineral quantities (wt%) of the samples resulting

from magnetic separation SAMM-H SAMM7 SAMM1 SAMM2 SAMM5 SAMM3 SAMM4 SAMM6 quartz 20.9 33.9 31.9 27.0 21.2 18.3 13.6 12.6muscovite 14.2 21.1 18.3 17.4 15.5 14.2 12.3 11.9Ca-pyroxene 10.1 13.1 10.6 10.1 10.6 10.9 11.3 11.3chlorite 3.4 6.5 7.8 5.8 4.1 1.9 0.7 2.9epidote 7.2 12.9 14.0 11.8 9.3 6.3 4.2 0.0ilmenite 0.8 0.9 0.9 0.9 0.9 1.0 0.9 0.9pyrrhotite 27.0 3.1 7.5 16.9 28.0 37.4 46.0 49.0pentlandite 6.0 3.6 3.7 4.8 5.5 5.9 6.6 7.2chalcopyrite 10.4 4.9 5.3 5.3 4.9 4.1 4.3 4.2Total 100 100 100 100 100 100 100 100

Grinding and flotation simulation conditions

The following grinding and simulated flotation conditions were used for each test (Table 35).

Table 35. Grinding and simulated flotation conditions

Grinding Conditions Louvicourt Strathcona Grinding media: mild steel rods stainless steel rods

Grinding time: 32 minutes variable Initial water temperature: 18°C 21.6ºC

Pulp density: 66% solids 66% solids Pulp temperature after grinding: 22ºC 24.5ºC

Conditions of flotation simulation Airflow rate: 2.5 L/min. 2.5 L/min.

Pulp equilibration: 5 minutes 5 minutes Residence time: 15, 35, 55, 75 minutes 15, 35, 55, 75 minutes

Pulp density: 32% solids 32% solids Pulp temperature 26ºC 25ºC

Test Results and Discussion

The d80 particle size for the original and composite samples is shown in Table 36. The d80

particle size decreases with an increase in the magnetic component from 10% to 90%.

Table 36. Strathcona experimental sample grain size distribution

Original sample

SAMM7 SAMM1 SAMM2 SAMM5 SAMM3 SAMM4 SAMM6

Magnetic component 0% 10% 30% 50% 70% 90% 100% d80 particle size (µm) 53 57 83 65 57 51 46 63


48

Table 37. Thiosalts concentrations (g/t) generated during experiments

Total thiosalts generated (g/t) SAMM7 SAMM1 SAMM2 SAMM5 SAMM3 SAMM4 SAMM6

Unit operation Cumulative residence time (min)

Original sample 0% 10% 30% 50% 70% 90% 100%

Scrubbing N/A 30 10 30 30 36 36 49 42 Grinding N/A 7 58 45 53 60 47 48 43 5 min. pulp conditioning without air

5 20 84 60 68 66 64 80 64

15 min. aeration

15 112 104 94 144 188 218 278 238

35 min. aeration

35 216 128 132 196 264 320 420 336

55 min. aeration

55 282 152 138 218 292 380 500 438

75 min. aeration

75 350 170 174 252 358 438 570 514

10 min. condit. with KAX

85 384 164 164 252 376 452 614 524

The original sample and the samples with 10 and 30% magnetic fraction, contained equal

amounts of thiosalts in dry form. Scrubbing of these samples under nitrogen atmosphere in

deoxygenated water indicated that they all contained 30 g/t of total thiosalts. The samples

with 70 and 90% magnetic fraction contained 36 g/t and 49 g/t thiosalts respectively. The

sample with 100% magnetic minerals component, however, contained about 42 g/t total

thiosalts, 7 g/t less than the sample with 90% components. The sample without the magnetic

fraction (SAMM7) contained only 10 g/t of total thiosalts, one-fourth the amount contained

by the 100% magnetic minerals component sample (SAMM6).

Thiosalts in the feed sample appear to be associated with the magnetic fraction because the

amount of residual thiosalts removed from the test samples generally increased with an

increase in magnetic fractions as shown in Table 37.

The cumulative change in total thiosalts concentration with an increase in residence time is

shown in Figure 48. Evidently, all the experimental samples with the exception of the

original sample, produced similar amounts of total thiosalts during conditioning. The

original sample produced the least amount of total thiosalts during conditioning and the first

15 minutes of aeration. This sample ultimately produced the same amount of total thiosalts


49

as the composite sample with 50:50 magnetic and non-magnetic fractions. The 50:50

composite, and the original sample, contained similar amounts of pyrrhotite and pentlandite,

but the 50:50 composite contained only one-half of the original chalcopyrite. Why the

original sample had a lower level of thiosalts at the beginning may be explained by the fact

that the composite sample was subjected to a sample preparation process. In general terms,

the higher the magnetic mineral component in the sample, the higher the amount of total

thiosalts produced during flotation. Particle size distribution appears to be affecting this

general trend. The sample with 100% magnetic fractions produced lower thiosalts compared

to the sample with 90% magnetic fractions. The 100% magnetic fraction has a finer particle

size than that of the 90% magnetic fraction (Table 36).

The average rate of thiosalts production was calculated by intervals and plotted on Figure 49

to see if such rate is consistent with sulphide mineral abundances in the experimental

samples. The rate of thiosalts generation during conditioning appears to be erratic. During

the simulated flotation stages, there is a general trend, which shows that samples with higher

amounts of sulphide mineral, release more thiosalts. The first 10 minutes of aeration marks

the highest rate of thiosalts generation which is followed by a gradual decrease with

increasing residence time. The specific rate of thiosalts generation, expressed as g/t/min., is

plotted in Figure 50 against the total quantities of pentlandite, chalcopyrite and pyrrhotite.

The rate appears to increase linearly with increases in the total amount of sulphide mineral

quantities. The rate is higher at the preliminary processing steps and decreases steadily with

increase in residence time. From Figures 51 and 52, it is evident that the coefficient of

correlation between the rate of thiosalts generation and mineral quantities does not change

significantly if the quantities of pentlandite and chalcopyrite are considered unimportant

compared to the amount of pyrrhotite. The specific thiosalts generation rate is further plotted

against the bulk sulphur assays shown in Table 31 (excluding SAMM7 and SAMM1). It

appears that there is an exponential relationship between the rate of thiosalts generation and

the sulphur content of the test samples (Figure 53). With an increase in sulphur content of

the samples, the difference in rates of thiosalts generation in successive processing stages

also increases.

The initial rapid rate of thiosalts generation coincides with the rapid increase in pulp

oxidation-reduction potential from a highly reducing to a more oxidizing condition, leveling


50

off within 5 minutes (Figure 54). The time interval for the rapid thiosalts production rate

coincides with a small but rapid decrease in pulp pH (Figure 55) at the early stage of

flotation.

EFFECTS OF REAGENTS ON THIOSALTS GENERATION

Effect of Xanthate on Thiosalt Generation by the Pyrrhotitic Cu-Ni ore

Xanthates are the most commonly used class of sulphide mineral collectors, the potassium

amyl form being the number one (Frank, Aplan and Chander, 1987). Laboratory flotation

test results of the Strathcona ore revealed high concentration of thiosalts in the solution

during conditioning of the pulp with potassium amyl xanthate for a relatively short period of

three minutes. An estimated 29.3% of the total amount generated during the entire test was

attributed to this conditioning stage (Figure 33). A series of tests were conducted to obtain

some understanding of the mechanisms by which xanthate influenced the increase in thiosalts

concentration in the solution. The minus 10 mesh test sample was scrubbed in deoxygenated

water of pH 2 (adjusted with HCl) at a temperature of 20°C. HCl is known to clean sulphides

resulting in S-rich mineral surface (Pratt and Nesbitt, 1997). The apparatus shown in

Figure 2 was used for the experiment. In Figure 56, the amount of thiosalts generated per

tonne of ore is plotted against the amount of potassium amyl xanthate used. This confirms

the previous observation that xanthate has a major impact on thiosalts generation (Frank

et al., 1987).

It has been suggested that collector molecules have the capacity to remove from the mineral

surfaces most oxidized products which include fine oxidized sulphide particles, colloidal

metal hydroxide particles, and oxidized sulphide layers (Smart, 1991). Thus, there are two

possible mechanisms by which the influence of xanthate on thiosalts concentration in the

pulp solution has been manifested. The first mechanism involves the transfer of thiosalts

compounds from the surface to solution as a result of the surface cleaning action of xanthate.

The second cause for increased thiosalts concentration could be the result of more surface

sulphur exposure to oxidation.

It has been shown by (Avdokhin and Abramov, 1989) that the most probable electrochemical

reactions leading to the formation of Cu-, Pb-, and Zn-xanthate by oxidation of chalcocite,

covellite, galena and sphalerite are:


51

Equation 18

where Kx: Potassium amyl Xanthate.

In all cases, thiosulphate ion is a major electrochemical reaction product. It is assumed that

this same mechanism is responsible for the major thiosalts generation during conditioning of

the Strathcona ore.

Effects of Sulphur Dioxide on Thiosalt Generation by the Pyritic Cu-Zn Ore

Sulphur dioxide is a reactive gas widely used as a depressant to promote selectivity between

Cu/Pb and Zn minerals. It is believed that recoveries of Au-, Ag- and Cu-minerals are

improved when sulphur dioxide is used instead of other depressants such as cyanide and

starch. The probable mechanism is assumed to be the substantial reduction of cupric ions

(activator for sphalerite) to cuprous and the complexing of the latter with sulphite ions which

lowers the activation of sphalerite.

Aqueous solution of SO2 consists of HSO3-, SO3

- and H3O (hydrated H+) ions (Chander

1987). The reaction sequence may be written as:

SO H O SO H HSO

HSO SO Hg aq2 2 2 3

3 32

( ) ( )+ ⇔ + +

⇔ +

+ −

− − + Equation 19

If elemental sulphur is present and conditions in the pulp (i.e. time alkalinity and

temperature) are favourable, the reaction between elemental sulphur and sulphite ion

proceeds to form thiosulphate (Wasserlauf and Dutrizac, 1982). Based on Equation 5, the

reaction between the two species may be written as:

Cu S H O Kx CuKx S O H e

CuS H O Kx CuKx S O H e

PbS H O Kx PbKx S O H e

ZnS H O Kx ZnKx S O H e

2 2 2 32

2 2 32

2 2 32

2 2 32

3 4 6 8

3 2 2 6 6

3 4 2 6 8

3 4 2 6 8

+ + ⇔ + + +

+ + ⇔ + + +

+ + ⇔ + + +

+ + ⇔ + + +

− − +

− − +

− − +

− − +


52

MS MSS SO S Oaq aq0

32

2 32+ → +− −

( ) ( ) Equation 20

If this is the case, then sulphur dioxide contributes to the total thiosalts generated in a

flotation pulp. Results presented by Noranda Mining and Exploration-Brunswick Mining

Division at the Thiosalts Workshop (Montreal, June 5, 1996) however indicated that

investigators did not find any specific unit process or reagent (including SO2) that generated

more thiosalts than others. To generate more information on the effect of SO2 on thiosalts

generation, SO2-conditioning tests were conducted for the pyritic Cu-Zn ore from Louvicourt.

Test Methodology

1.65 kg of ore was ground at 66% solids in a stainless steel mill. The sample was filtered and

rinsed with water while still on the filter paper. Subsequently it was conditioned for 5

minutes with deoxygenated water of pH 2 (adjusted using HCl). The sample was filtered and

rinsed and then split into 5 equal parts, vacuum-sealed in aluminum bag and kept frozen for

24 hours before testing. The rinse water did not contain thiosalts.

Three conditioning tests were conducted at 20°C, and at pH of 4, 5 and 6 adjusted with SO2.

Two control tests were conducted at pH 4 and 5 adjusted with buffer solutions instead of

SO2. The apparatus with automatic pH and temperature control shown in Figure 2 was used

for these tests.


53

Test Results and Discussion

Results given in Table 38 indicate that S3O6 2- is the predominant thiosalt species in SO2

experiments. Evidently, decrease in pH (increase in SO2 in this case) increases the

concentrations of S3O6. S4O62- was detected only in the pulp conditioned with a buffer

solution. In test LVS O6, SO2 solution (without solids in it) was stirred for 5 minutes to

determine if there is a significant amount of thiosalts originating from SO2 itself. Evidently,

all three species are less than 5 ppm. Hence, it can be concluded that, there is a significant

amount of thiosalts generated as a result of mineral-SO2 interaction.

Table 38. Effects of SO2 conditioning on thiosalts generation

Test Conditions S2O3 S3O6 S4O6 Thiosalt Total

Sample Name

pH pH adjusted with: [ppm] [ppm] [ppm] [ppm] LVS 01 6 SO2 12 34 0 46 LVS 04 5 SO2 23 77 0 100 LVS 03 4 SO2 22 90 0 112 LVS 02 5 buffer 11 10 12 33 LVS 05 4 buffer 12 6 11 29 LVS 06 4 SO2 Solution, no solids. <1 <5 <5

CONCLUSIONS

Thiosalts generation in processing plants is controlled by the abundances of sulphide

minerals in the ore, pulp pH, temperature, residence time, grinding media type and reagents

such as xanthates and sulphur dioxide. The effects of pulp temperature, residence time and

pH on thiosalts generation appear to be linear. The pyrrhotitic ore appears to be more

sensitive to pulp temperature whereas the pyritic ore is more sensitive to changes in pH. Pulp

residence time has a negligible effect on thiosalts generation during processing of the pyritic

ore whereas the pyrrhotitc ore is significantly affected.

A good portion of the thiosalts in the mill circuit comes with the ore in dry form. Scrub

washing under inert atmosphere results in total removal of thiosalts contained in the feed ore.


54

The amount of thiosalts generated during grinding strongly depends on the type of grinding

media. The stainless steel produces more thiosalts than mild steel grinding media. The

pyritic ore generated more thiosalts than the pyrrhotitic ore during grinding regardless of the

grinding media type and grinding media composition. The use of more active media or semi-

autogenous grinding would generate less thiosalts than inert media or autogenous grinding.

Thiosalts generation is influenced by sulphide mineralogy. Thiosalts generally increase with

sulphide mineral content of the ore. Thiosalts generation rate appears to be linearly

dependent on the abundance of sulphide minerals in the ore.

Flotation of the pyrrhotitic ore produced more thiosalts than the pyritic ore at pH values

typical for flotation. Continuous testing results on the pyritic ore indicated that an estimated

23% of the overall thiosalts originated from the feed while grinding, aeration, copper circuit

flotation, and Zn circuit flotation contributed 17%, 5%, 50% and 5% respectively.

Semi-batch testing results on the pyritic ore indicated that approximately one-third of the

total thiosalts was generated during grinding. Copper rougher/scavenger/cleaner circuit

produced 23% of the total thiosalts generated with Cu cleaning stage being responsible for

approximately half of this amount. Zinc rougher/flotation/cleaner produced 26% of the total

thiosalts.

Semi-batch testing results of the pyrrhotitic ore indicated that the collector (potassium amyl

xanthate) conditioning contributed the highest amount of thiosalts generated in the circuit.

This is followed by the regrinding of flotation products in the pyrrhotite rejection circuit.

The amount of thiosalts in pulp solution appears to increase with the amount of collector

used.

The rate of thiosalts generation is the highest during the first few minutes of conditioning

including aeration. Conditioning of pulp with SO2 affects thiosalts generation. The amount

of thiosalts increases with an increase in SO2.


55

RECOMMENDATIONS

new process flowsheet development (stockpiling procedure, flotation circuit

configuration, selection of grinding mill and grinding media, selection of reagents and

reagent addition points) has to be based not only on metallurgical performance but also

based on the resulting level of thiosalts generation.

the characteristics of thiosalts on mineral surfaces before and after grinding, and in

flotation circuits (before and after reagent additions), should be examined in light of the

thiosalts species in the solutions, to allow appropriate changes to the process to inhibit

thiosalts generation.

some of the samples from the bench-scale testwork should be analysed by X-ray

photoelectron spectrometry (XPS) and synchrotron-based X-ray absorption spectrometry

(XAS) for the determination of sulphur speciation and oxidation features on the surfaces

of sulphide grains. These studies of chemistry of mineral surfaces at the mineral-solution

interface are required to develop an understanding of thiosalts formation in mill circuits.

Chemical reactions that control the production and evolution of thiosalts in process

streams will be governed by the behavior of elements at the mineral-solution interface. If

we understand the reactions at the mineral-solution interfaces, then we can look into

developing prediction and prevention techniques to passivate or demote such reactions

from occurring.

ACKNOWLEDGEMENTS

Participation and help of Dr. Peter Wells, Joseph Fyfe, Mike Wiebe and Noel Mejia of

Falconbridge Ltd., and Yves Desrosiers of the Louvicourt mill at various stages of the project

are greatly appreciated. Bob Campbell and Micheline Boisclair of CANMET are

acknowledged for sample preparation, assembling experimental setups, calibration of

instruments and conducting tests. Pierre Groulx of CANMET performed polished section

preparation work. Chemical analyses were carried out by the Analytical Services Group of

CANMET. John Graham’s timely and efficient response for thiosalts analyses and guidance

for sample preservation are greatly appreciated. The report was reviewed by Dr. Allen Pratt

Orlando Dinardo and Raymond Gaëtan.


56

REFERENCES

1. Bocharov, V.A. et al., (1985), Characteristics of sulphide oxidation during selective

flotation of pyritic ore, Svetnye Metalu No. 10.

2. Avdokhin, V.M. and Abramov, A.A., (1989), Oxidation of sulphide minerals during

the process of enrichment, Moscow “Nedra”.

3. Kosabag, D. and Smith, M.R., (1985), The effect of grinding media and galvanic

interactions upon the flotation of sulphide minerals, In Complex Sulphides. Ed.

Zunkel, A.D., Borman, R.S., Moris, A.E., Wesley R.J. pp. 55-82. The Metallurgical

Society, Inc.

4. Natarajan, K.A., (1988), “Electrochemical aspects of bioleaching multisulfide

minerals,” Minerals and Metallurgical Processing, Vol. 5, No. 2, pp. 61-65.

5. Pozzo, R.L. and Iwasaki, I., (1987), “Effect of pyrite and pyrrhotite on corrosive wear

of grinding media,” Minerals and Metallurgical Processing, Vol. 4, No. 3, pp. 166-

171.

6. Cheng, X. and Iwasaki, I., (1992), “Effect of Chalcopyrite and pyrrhotite interaction

on flotation separation,” Minerals and Metallurgical Processing, Vol. 9, No. 2,

pp. 73-79.

7. Paktunc, A.D., (1998) MODAN: An interactive computer program for estimating

mineral quantities based on bulk composition. Computers and Geosciences, 24:425-

431.

8. Rolia, E. and Tan, K.G., (1985), The generation of thiosalts in mills processing

comlex sulphide ores; Canadian Metallurgical Quarterly 24:293-302.

9. Wasserlauf, M. and Dutrizac, J.E., (1985), The chemistry, generation and treatment

of thiosalts in milling effluents – A non-critical summary of CANMET investigations

1976-1982; CANMET Report 82-4E, 91p.

10. Frank, F., Aplan, and Chander, S., (1987), Reagents in Mineral Technology; ed.

Somasundran, P. and Moudgil Brij, M., 335-369.

11. Forrssberg, K.S.E., Subrahmsanyam, T.V., Leif, K.N., (1993), Influence of grinding

method on complex sulphide ore flotation. Int. J. Miner. Process., 38:157-175.

12. Skrinchenko, M.L. and Shelkova, C.A., (1987), Interaction of thiosulphate complexes

of Cu with sulphide minerals. Svetnye Metalu. 3:94-97.


57

13. Pratt, A.R. and Nesbitt, H.W., (1997), Pyrrhotite leaching in acid mixtures of HCl

and H2SO4. American Journal of Earth Science, Vol. 297, October, 1997, pp. 807-

828.

14. Illyvieva, A.E., Garshteyn, G.V. and Baron, I.U., (1986), On Evaluation of

Mechanisms of chemical changes during aeration of complex sulphide pulp. Svetnye

Metalu. 2:80-82.


APPENDIX A FIGURES


Figure 1. Metal sulphide oxidation to sulphate generalized path.

SO4=

Polythionates

S=

S=

MS M=

M=


Figure 2. Experimental set-up for the thiosalts generation studies.

Acid

Lime

Mass flowcontroler

Air

To drain

Hot waterCold water

Solenidvalves

Stainlesssteel coil

Sampling valve

Stirrer

Poroussteel plate

pH OR

PC

ondu

ctiv

ity

DO

Tem

p .

Data Acquisition and Control System


Figure 3. Representative backscattered electron (BSE) photomicrograph of SAR-Ore (F).

po

qtz

pe

po

pe

cp

pe

Mag

MagMag

po

po

po

po

po

po po

po

po

po

cp

cp

pe

pe

pe

pe

pe

cp

fsp

fsp

fsp

fsp

fsp

fsp

fsp

qtz

qtz

amph

musc

qtz

fsp cpfsp

cp


Figure 4. BSE photomicrograph of SAR-Ore (F).

Figure 5. BSE photomicrograph of SAR-Ore.

Po

Pe

cp


Figure 6. Representative BSE photomicrograph of various sulphides and gangue minerals in LVR-Ore.

py py

py

pypy

py

py py

py

py

py

py

cp

cp

cp sid

sid

sid

sid chl

chl

chl

Fe Dol qtz

qtz appo

py

py

py

biot

chlpy


Figure 7. BSE photomicrograph of a composite particle made of pyrite, chalcopyrite and

quartz.

py

cp

qtz

sp

Mg-sidpo

ga

unknown


Figure 8. Backscattered electron (BSE) photomicrograph of an unknown sulfosalt (white) in sphalerite (light gray), magnesian siderite (medium gray) and

quartz (dark gray).


Figure 9. BSE photomicrograph of a rhombohedral magnesian siderite grain.


Figure 10. BSE photomicrograph of liberated pyrrhotite displaying variable sizes.

Figure 11. BSE photomicrograph of liberated pyrite and chalcopyrite grains LVR5-LLL.

Py

py

cp

py py


Figure 12. BSE photomicrograph of carbonate grains in LVR5-LLL.

Mg-sid

Mg-sid

dol


Figure 13. BSE photomicrograph showing chalcopyrite attached to an anhedral pyrite

grain in LVR7-MMM.

py

cp


40

50

60

70

80

90

100

110

120

40 50 60 70 80 90 100 110 120

Actual Value (g/t)

Pre

dict

ed V

alue

(g/t)

Figure 14. Total thiosalts prediction model adequacy for the pyritic ore.

75

125

175

225

275

325

375

425

475

75 125 175 225 275 325 375 425 475

Actual Value (g/t)


Figure 15. Total thiosalts prediction model adequacy for the pyrrhotitic ore.

0

50

100

150

200

250

300

350

7 12 17 22 27

Temperature, 0C

Pyritic Cu-Zn ore Pyrrhotitic Cu-Ni ore

Figure 16. Effect of pulp temperature on thiosalts generation.


0

50

100

150

200

250

300

7 7.5 8 8.5 9 9.5 10

pH


Figure 17. Effect of pH on thiosalts generation during flotation under

constant temperature and residence time.


Figure 18. Effect of pH and temperature on thiosalts generation for residence time of 22

minutes

pH

7.5 8.0 8.5 9.0 9.5 10.0

13.8

17.5

21.2

25.0

59

70

82

93

104

Tem

pera

ture


0

50

100

150

200

250

300

7 12 17 22 27 32

Residence tme, min.


Figure 19. Effect of residence time on thiosalts generation.


Figure 20. Overall effect of pH, temperature and residence time on total thiosalts generation

(pyritic ore).

pH

Residence time

A- A+B-

B+

C-

C+

50

51

78

81

74

84

111

124

Temperature


Figure 21. Overall effect of pH, temperature and residence time on total thiosalts generation

(pyrrhotitic ore).

pH

Residence time

A- A+B-

B+

C-

C+

82

126

224

373

119

284

288

397

Temperature


0

10

20

30

40

50

60

100% MS (50:50) SS/MS MIX 100% SS

Grinding media composition

0

1

2

3

4

5

6

7

8

Conductivity TTS DO pH

Figure 22. Effect of grinding media composition on total thiosalt generation by the

pyritic ore at natural pH.


0

10

20

30

40

50

60

70

100% MS (50:50) SS/MS MIX 100% SS


0

1

2

3

4

5

6

7

8

Conductivity TTS DO pH

Figure 23. Effect of grinding media composition on total thiosalt generation

by the

pyrrhotitic ore at natural pH.


Grinding media effect on total thiosalt (TTS) generation

0

20

40

60

80

100

120

100% MS SS/MS MIX 100% SS


Pyritic ore (Louvicourt)Pyrrhotitic ore (Strathcona)

Figure 24. Comparison of grinding media effects on pyritic and pyrrhotitic ores based on total

thiosalts generation at natural pH.

Change in grinding mill discharge pH

6.06.57.07.58.08.59.09.5

10.0

0 1000 2000 3000 4000

lime (g/t)

Pyritic orePyrrhotitic ore


Figure 25. Change in grinding mill discharge pH as a function of lime addition rate.


TTS (g/t) = 46pH - 254.07

TTS(g/t) = 49pH - 323.87

0

20

40

60

80

100

120

140

160

180

200

6.5 7 7.5 8 8.5 9 9.5 10

Mill discharge solution pH

Pyritic ore (Louvicourt)Pyrrhotitic ore (Strathcona)

Figure 26. Effect of lime controlled grinding pH on thiosalts generation.


Tailings

68 ppm

300

20

Aeration

Cu/Rghr/Scvr

Cu Concentrate

Zn rougher

3-stage Zn

Cleaner

Zn Concentrate

3-stage Cu

Cleaner

Zn Scavenger

52 ppm

39 ppm

70 ppm 68 ppm

71 ppm

200

100

50

L/ i

60

50 mL/min. water

20 mL/min

290

mL/min

50 mL/min

Conditioning

Classificati

Rod

Mill


Figure 27. Experimental continuous grinding, classification and flotation circuit (200 g/min

throughput).

Figure 28. Distribution of the total thiosalts among the major process and the ore.

23

17

5

50

5

0

10

20

30

40

50

60

Mill Feed Grinding Aeration Cu circuit Zn circuit

Circuit

Estim

ated

con

trib

utio

n [%

]


125 g

pH adjusted

Conc. recovery

controlling balance

In-line

concentrate

filtering funnel

Automatic froth

take-off assembly

Air

Automatic froth level

controller assembly

pH, ORP, DO

and T sensors

Flotation cell

3 L/min Air

Air flow controller

Pump

Vacuum

pump

Pulp zone

Froth

100 g

Concentrate

t i hi

Vacuum

pump

PC based data acquisition and

froth

depth

diffuser


Figure 29. The PC controlled automatic flotation cell.


tap water

-10 mesh

sample

AerationConditioning

Activation with CuSO4Conditioning

with SIPX

Grinding Circuit

Primary conditioning

Cu Flotation Circuit

Zn conditioning circuit

Zn Flotation Circuit

Stainless

steel rod

Zn rougher flotation

Zn Scavenger

Zn cleaner flotation

Cu rougher flotation

Cu Scavenger flotation

Cu cleaner flotation

ST ST

ST

ST ST

ST tap

water ST ST

ST

ST 10

ST ST 12

ST 13 tap

water ST 14

ST 14

ST 16

ST 15

Zn cleaner tails

Zn concentrate Final tails

Cu concentrate


Figure 30. Semi-batch test flowsheet used to investigate thiosalts generation in various

circuits (Louvicourt).

Figure 31. Distribution of thiosalts generated among sub-processes.

14

33

14

11 12

-1

13 13

-505

1015202530354045

Mill Fee

d

Grindin

g

10 m

in eq

uilibr

ation

6 min

aerat

ion

Cu Rou

gher+

Sca

veng

er

Cu Clea

ning

Zn con

dition

ing

Zn RGHR+S

CAVENGER

Zn Clea

ning

Sub-process

Thio

salts

[%]

Conditioning

Cu circuit flotation

Zn circuit flotation


Figure 32. Semi-batch test flowsheet used to investigate thiosalts generation in various

circuits (Strathcona).

tap water

-10 mesh sample

10 min6 min

Magnetic Separation

Grinding Circuit

Primary conditioning

Cu-Ni Flotation

Pyrrhotite Rejection Circuit

Rod mill

Stainless

PO Rejection

Scavenger

PO Rejection Rougher

Cu-Ni Rougher I flotation

Cu-Ni Rougher II flotation

Cu-Ni cleaner flotation

ST

ST

ST

ST

ST

ST

CuSO4

ST 12

ST

ST 17

ST 18ST 16

ST 14

ST 15

Pyrrhotite tailings

Cu-Ni Concentrate

ST

3 min

Cu-Ni Scavenger flotation

ST 10 ST 11

ST 13

ST

tap water

tap water

tap water

Magnetic

Nonmagnetic

Ball mill

Mild steel


6.3 7.4

15.9 16.5

29.3

4.51.6

4.56.2

0

5

10

15

20

25

30

35

Sub processes

Figure 33. Proportion of total thiosalts generated in various process circuits.


15 min. 20 min. 20 min.20 min.

Air 2.5 L/min.

Nitrogen gas

FreezerConcentrate Middlings

tap waterFiltrate (discarded)

Wermco Scrubber

10 min. conditioningwith Xanthate

deoxygenated tap water

Pressure filter -10 mesh sample

Table concentrate


Figure 34. Sample preparation, grinding and flotation simulation of Louvicourt pyritic Cu-

Zn ore.

5 min. conditioning No air, no reagent

15 min. 20 min. 20 min. 20 min.

Air

2 5 L/min

Nitrogen gas

Eriez Drum Magnetic Separator

Freezer Non Mag Mag

tap water Filtrate (discarded)

Wermco Scrubber

10 min. conditioningwith Xanthate

deoxygenated tap water

Pressure filter


Figure 35. Sample preparation, grinding and flotation simulation of Strathcona pyrrhotitic Cu-Ni ore.


Figure 36. BSE photomicrograph of pyrite grains attached to and encapsulated in gangue

(chlorite, quartz and muscovite).

Figure 37. BSE photomicrograph of a pyrite grain attached to and encapsulated in gangue.

Note the sharp grain boundaries on exposed surfaces of pyrite grains.

py

chl

musc+qtz

py

chl

mag


Figure 38. Effect of mineralogical composition of Louvicourt ore on total thiosalts

generation rate.

Change in rate of total thiosalts generation with time

0.0

0.4

0.8

1.2

1.6

2.0

Time interval (min.)

LVT1 0.89 0.51 0.58 1.06 1.16

LVT2 1.06 0.62 1.03 1.40 1.49

LVT3 1.24 0.26 0.77 1.34 1.44

LVT4 0.53 0.92 1.28 1.77 1.47

32 min. grinding, 5 min.

conditioning 5-20 20-40 40-60 60-80

Aeration


Figure 39. Dissolved oxygen concentration and pulp oxidation-reduction potential data for LVT4.

-300

-200

-100

0

100

200

300

0 10 20 30 40 50 60 70 80 90

Residence time [min.]

Oxi

datio

n R

educ

tion

Pot

entia

l [m

V, P

t vs.

SC

E]

0

2

4

6

8

10

12

Dis

solv

ed O

xyge

n C

once

ntra

tion

[mg/

L]

ORP [mV, Pt vs. SCE]

Dissolved Oxygen [mg/L]


-240

-200

-160

-120

-80

-40

0

40

80

120

160

200

240

280

0 10 20 30 40 50 60 70 80 90 100


Pulp

Oxi

datio

n re

duct

ion

pote

ntia

l (m

V, S

CE)

LVT1LVT2LVT3LVT4

Figure 40. Change in pulp oxidation-reduction potential with residence time.


8.1

8.2

8.3

8.4

8.5

8.6

8.7

8.8

8.9

9

0 10 20 30 40 50 60 70 80


pH

LVT1

LVT2

LVT3

LVT4

LVT3LVT1

LVT2

LVT4

Figure 41. Louvicourt test. Change in pH with residence time.


100

150

200

250

300

350

400

0 20 40 60 80 100


LVT1LVT2LVT3LVT4

Figure 42. Pulp conductivity


Figure 43. Representative BSE photomicrograph of various sulphides from SAMM-HEAD.

mag

cubpo

po

po

cp

cp

pe

po po

po po

popo

pe

cp

cp

po


Figure 44. Representative BSE photomicrograph of various sulphides in SAMM6

Figure 45. Representative BSE photomicrograph of various gangue minerals in SAMM5.


Figure 46. BSE photomicrograph of pyrrhotite surrounded by fine particles of pyrrhotite.

fsp

fsp

fsp

fsp

fsp

cpx

qtz pe

chl

cp


Figure 47. Representative BSE photomicrograph of pyrrhotite SAMM5.

po

po

po

po

pomag

Po+mag


Figure 48. Effect of mineralogical composition of Strathcona ore on total thiosalts

generation rate.

Effect of mineralogical composition on total thiosalts generation

0

100

200

300

400

500

600

700

0 5 15 35 55 75 85Residence time [min.]

Cum

ulat

ive

thio

salts

gen

erat

ed [g

/t]

Originalsample0%

10%

30%

50%

70%

90%

100%

Magnetic fraction


Figure 49. Change in rate [g/t/min] of total thiosalts generation (Strathcona ore).

Change in rates of total thiosalts generation with time

0

2

4

6

8

10

12

14

Time interval

Ave

rage

rate

of T

TS g

ener

atio

n (g

/t/m

in)

SAH [Head] 4.12 2.13 5.20 3.30 3.40

SAMM7 [0%] 5.23 1.33 1.20 1.20 0.90

SAMM1 [10%] 2.93 2.27 1.90 0.30 1.80

SAMM2 [30%] 3.07 5.07 2.60 1.10 1.70

SAMM [50%] 1.21 8.13 3.80 1.40 3.30

SAMM3 [70%] 3.31 10.27 5.10 3.00 2.90

SAMM 4 [90%] 6.41 13.20 7.10 4.00 3.50

SAMM6 [100%] 4.25 11.60 4.90 5.10 3.80

0-5 (no air) 5-20 20-40 40-60 60-80


Total thiosalts generation rate as a function of total metallic mineral components

0

2

4

6

8

10

12

14

0 20 40 60 80

Total metallic mineral component [%]

5-20

20-40

40-60

60-80

Time interval [min]

Figure 50. Thiosalts generation rate as a function of residence time interval and sulphide

mineral

content of samples.


R2 = 0.97

R2 = 0.98

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

0 10 20 30 40 50 60 70

Mineral Abundance [%]

Spoe

cific

thio

salts

pro

duct

ion

rate

[g/t/

min

]

Pyrrhotite + Chalcopyrite + PentlanditePyrrhotite

Figure 51. Comparison of correlations between initial thiosalts generation rate

(g/t/min.)

and mineral quantities (first 15 minutes of processing).


R2 = 0.89

R2 = 0.88

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0 10 20 30 40 50 60 70

Mineral Abundance [%]

Thio

salts

pro

duct

ion

rate

[g/t/

min

]

Pyrrhotite + Chalcopyrite + PentlanditePyrrhotite

Figure 52. Comparison of correlations between initial thiosalts generation rate (g/t/min.)

and mineral quantities (last 20 minutes of processing).


y = 0.6447e0.1057x

R2 = 0.99

y = 0.6027e0.1446x

R2 = 0.98

y = 0.6717e0.0782x

R2 = 0.86

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

0 5 10 15 20 25

Bulk sulphur assay [%]

5-20 min.20-40 min.60-80 min.

Time Interval

Figure 53. Thiosalts generation rate (g/t/min.) as a function of bulk sulphur assays (%).


-250

-200

-150

-100

-50

0

50

100

150

200

250

0 10 20 30 40 50 60 70 80 90 100


Oxi

datio

n-R

educ

tion

Pote

ntia

l (m

V vs

. SC

E)

Magnetic

Non Magnetic

Figure 54. Change in pulp oxidation-reduction potential (SAMM6, magnetic and

SAMM7

non-magnetic samples).


7.8

8

8.2

8.4

8.6

8.8

9

9.2

0 20 40 60 80 100 120


pH

MagneticNon Magnetic

Figure 55. Change in pulp pH (SAMM6, magnetic and SAMM7 non-magnetic samples).


320

330

340

350

360

370

380

390

0 20 40 60 80

Potassium amyl xanthate (g/t)

Thio

salts

(g/t)

Figure 56. Effect of Xanthate addition rate on thiosalts generation.


APPENDIX B PULP SAMPLES COLLECTED AT THE MILLS

AND MEASUREMENTS


B-1

Appendix B

Louvicourt Mill

Field ID Lab ID T

(ºC) pH ORP Conductivity

(µ) DO

(mg/L) #1 LC1 21.1 6.6 151 1476 5.3#2 LC2 23.7 11.1 -59 23300 1.56#3 LC3 24.4 10.6 -35.4 172 3.3#4 LC4 26.5 10.7 -27 2060 1.8#5 LC5 25.4 10.6 -23 2060 3.5#6 LC6 22.4 9.7 22.8 1584 4#7 LC7 24.8 10.4 -18.3 2070 1.2#8 LC8 22.9 9.7 22.5 1653 2.3#9 LC9 24.0 9.5 16 2130 2.1#10 LC10 22.7 9.4 39.5 1898 2.8#11 LC11 24.2 9.9 21 1998 1.2#12 LC12 Sampled with #10 #1012 LC1012 23.0 9.3 61.5 1909 2.61#13 LC13 24.4 9.6 20 2230 1.3#14 LC14 21.6 9.1 35 1693 4.6#15 LC15 22.5 9.3 36.4 1719 3.3#16 LC16 22.2 9.6 39.4 1636 2.2#SP1 LC17 20.6 9.4 56 1518 3.6#18 LC18 23.5 9.0 19 1823 1.2#19 LC19 20.4 9.0 79 904 5.1#20 LC20 23.3 9.4 44 1833 2.4#21 = #32 LC21 21.6 9.3 50 1629 5.1#22 LC22 25.0 10.8 -24 2200 1.5#23 Sampled with #23 #24 Sampled with #24 #2324 LC2324 20.0 9.3 64 1587 4.7#25 LC25 23.0 10.0 18 2200 2.5#26 LC26 19.9 9.2 55 1334 5.58#27 LC27 22.0 9.6 40 1508 3.9#28 LC28 19.6 9.2 72.7 1298 6#29 LC29 18.2 8.5 128 1197 7.3#30 LC30 19.5 9.0 100 1495 5.6#31 LC31 21.9 9.3 60 1492 4.0#SP3 LC32 21.5 10.6 -6.9 1630 2.9#33 LC33 21.7 8.4 120 1134 0.7#34 LC34 23.7 9.8 -17 2210 1.65#35 LC35 Same as #21 #36 LC36 21.6 11.8 -68 3000 3.92Tap water LC36 22.8 6.5 215 335 5.2


B-2

Appendix B

Strathcona Mill

Sample ID ORP DO

(mg/L) T

(ºC) pH Conductivity

(µs)

Tap Water 233 11.5 6.8 170 23 135 4.47 12.3 6.28 2570 26 -87 1.00 15.7 10.65 2930 19 72 4.86 14.9 8.32 3160 62 -62.7 6.20 12.4 12.14 6840 20 65.3 4.71 15.2 8.65 3240 2 2.8 1.04 16.1 9.84 3400 27 -92.4 1.42 16.7 10.64 2910 3 -28.3 4.20 17.3 9.56 3800 57 -17.8 2.39 15.2 8.77 2600 56 +111.92 9.00 11.2 7.84 1845 35 +27 6.52 13.6 9.25 2590 25 +84.3 6.49 13.7 8.38 2400 36 +15 5.06 15.3 8.72 2890 16 +56.5 6.7 15.2 8.08 3370 43 -19 5.0 13.4 9.29 2180 4 +85.8 3.8 13.7 8.68 2600 15 +39.2 6.9 15.2 7.79 3290 24 +84.5 4.92 13.3 8.01 2440 68 -76.6 4.51 13.2 12.20 8140 54 +50.4 7.85 14.5 9.50 2590 48 -38.1 7.81 14.2 11.61 2740 18 +63.4 4.8 15.5 8.90 2700 55 -25 6.4 14.9 10.40 2720 49 -79 7.0 14.9 12.08 8070 ST13-2 -61 5.6 13.8 11.93 4600 ST-27 -26 9.7 13.7 11.45 2360 ST-15 +147 8.9 13.7 8.98 2560 ST-13-4 -53 6.8 13.5 11.93 4920 ST-28 -14.7 2.74 13.2 11.33 2330 ST-21 78 7.3 13.8 9.33 2930 ST-1 +190 9.70 12.7 8.04 1766 ST-14A None ST-19B +12.4 8.56 13.4 10.81 2790 ST-20 +72.5 8.6 14.4 9.56 2890 ST-30 -30.4 3.1 13.1 10.73 2750 ST-29 +13.5 9.3 12.7 10.20 2680 ST-14B -111.7 5.6 14.0 10.97 2460


APPENDIX C THIOSALTS (INDIVIDUAL SPECIES

AND TOTAL THIOSALTS)

ANALYSIS OF THE PULP SAMPLES


C-1

Strathcona Mill ST1 ST2 A ST7 ST9 ST10 ST11A ST11B ST12 ST23 ST26

Fe+2 ppm <1 <1 <1 <1 <1 <1 <1 <1 <1 <1

SO4 ppm 670 1138 802 1081 738 750 769 689 583 721

S2O3 ppm 3 255 417 232 583 431 523 238 50 213

Thiosalt mg/L 13 599 556 564 706 535 624 318 60 301

S3O6 ppm 10 277 108 206 9 85 87 52 10 23

S4O6 ppm <5 5 52 58 <5 <5 44 28 <5 <5

Ca ppm 205 328 213 311 332 289 277 240 374

Cu ppm 0.78 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2

Mg ppm 13.2 2.06 2.95 9.72 0.14 0.18 2.72 5.95 <0.06 <0.06

S ppm 192 407 358 415 1179 820 580 435 216 321

Zn ppm 0.24 0.038 0.027 0.032 0.03 0.014 0.033 0.033 0.031 0.038

Fe ppm 0.06 <0.13 <0.13 <0.13 <0.13 <0.13 <0.13 0.13 <0.13 <0.13

Na mg/L 106 77 44.4 99.7 83.9 76 58.2 90.8 98.7 90

K mg/L 24.1 37.1 17.4 56.2 32.5 27.1 18.1 23.2 22.7 30.2


C-2

Louvicourt Mill LC1 LC4 LC6 LC13 LC20 LC21 LC22 LC25 LC29 LC31

Fe+2 ppm < 1 < 1 < 1 < 1 < 1 < 1 < 1 < 1 < 1 < 1

SO4 ppm 88 103 123 145 231 149 273 187 78 172

S2O3 ppm 21 < 5 < 5 < 5 5 < 5 9 6 23 9

Thiosalt mg/L 292 421 323 436 500 349 449 445 210 260

S3O6 ppm 558 595 574 538 452 548 564 501 402 596

S4O6 ppm 44 27 44 33

Ca ppm 23 37.7 26.6 32.4 26.7 26 30.4 29.3 17.3 21.1

Cu ppm 36.5 58.9 41.7 50 40.9 39.3 47.8 45.7 29.2 31.9

Mg ppm 348 429 373 430 404 378 424 418 249 366

S ppm <0.2 <0.2 0.47 <0.2 0.41 0.24 <0.2 0.25 2.53 2.07

Zn ppm <0.09 <0.09 <0.09 <0.09 <0.09 <0.09 <0.09 <0.09 <0.09 <0.09

Fe ppm 4.01 0.31 3.01 2.48 2.67 3.57 0.57 1.26 3.81 2.79

Na mg/L 404 923 470 829 629 510 844 1006 315 422

K mg/L <0.06 <0.06 <0.06 <0.06 <0.06 <0.06 <0.06 0.07 0.09 <0.06

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