Structural properties of clays and their effect on the recovery of copper sulphides by flotationLina Uribe1, Leopoldo Gutierrez1, Oscar Jerez 2

1 Departament of Metallurgical Engineering, Universidad de Concepción, Concepción, Chile2 Instituto de Geología Económica Aplicada (GEA), Universidad de Concepción, Concepción, Chile

Outline› Background› Objectives› Experimental methodology› Results› Conclusions

Background› The grades of the major copper deposits in Chile have decreased

which has caused that the treatment of more complicated ores containing high levels of complicated gangue is more common today. Clay minerals are the most typical.

› The presence of clay minerals affects several stages in the mineral processing chain, i.e., grinding, froth flotation, thickening, dewatering and final disposal.

Background

Background1. Slime coating on the mineral surfaces

Hydrophilic coating

Hydrophobic particle

Less hydrophobic

particle

Fine clays

Valuableparticle Bubble

Background2. Changes in pulp rheology, higher viscosity (h) and yield stress (to)

vp vb

h, t0

Slurry

Background3. Changes in froth stability

Zona de colección

Zona de limpieza

Burbuja

Particula valiosa hidrofóbica

Particula no valiosa (Ganga)

Froth

If the froth is unstable froth recovery decreases.

Background4. Non specific reagent consumption.

The lower the particle size, the higher the specific surface area. This could lead to higher non specific reagent consumptions.

1L Cube

1L Cube

10 cm

10 cm

10 cm

0.5 mm (500 microns)

8 x 106 particles

12 m2 surface area

10 cm

10 cm

10 cm

0.01 mm (10 microns)

1 x 1012 particles

600 m2 surface area

Bubble

Background5. Coating of air bubbles with fine clay particles

Hydrophobicbubble

Less hydrophobic

bubble

Fine clays

Hydrophilic coating

Bubble

Background

Although there is evidence that validates the aforementioned mechanisms, there is still a lack of understanding on the effect of clays on the process of flotation of copper sulphide minerals.

A better solution can be obtained

ObjectivesSpecific objectives

To study the effect of fine particles of kaolinite and montmorillonite on:

› Floatabilty of copper sulphide minerals

› Induction time

› Slime coating

› Reagent consumption

Experimental methodologySamples and reagents

Sample Quantitative XRD mineralogy(Chipera and Bish, 2001)

CECcmol/kg

BET(Kelm and

Helle, 2001)

kaolinite 96% kaolinite, 3% anatase, 1% other traces 0.7 180

Montmorillonite 75% montmorillonite, 16% feldspar, 8% quartz, 1% other traces 100 117

Chemical analysis Calculated mineralogical compositionCu % 23.6 Sb % 0.1 CuFeS2 % 68.1Fe % 30.1 As % 0.2 FeS2 % 20.2

Mo % 0.1 Bi % 0.0 MoS2 % 0.08Zn % 1.2 S % 36.1 Quartz % 11.61Ag % 0.0 Insols % 8.5Pb % 0.1

-Copper sulphide sample: copper concentrate sample

-Kaolinite and montmorillonite: Clay Minerals Society.

Experimental methodologyClay samples

Figure 1. Kaolinita. Figure 2. Esmectita. Kaolinite montmorillonite

Mean size, microns

Top size, microns

Kaolinite 4.4 21Montmorillonite 3.9 19

Copper concentrate 119 206

Experimental methodologyMicro-flotation tests

› 130 mL Patridge and Smith glass cell 20 mL/min N2, 2 minutes flotation. › The flotation feed was prepared mixing known amounts of the copper concentrate sample with fine clay

particles at different proportions (0, 300, 400, 500, and 1,000 ppm or mg of clay per litre of water). › PAX and MIBC were used at concentrations of 400 and 200 ppm respectively.

Experimental methodologyInduction time measurements

Bed of particles

(1)(2)

(3)

Solution

(a) (b)

Idea developed by Glembotsky (1953). › A bubble is contacted with a bed of particles for measured and controlled contact times. Then the bubble

is observed through a microscope to determine whether attachment occurred during the contact time or not.

› The final result of the test is a plot of percentages of successful contacts (N sc) versus the measured contact time (tc). In this work, the induction time was obtained by determining the contact time at which 50 % of the contacts were successful.

0 100 200 300 400Contact time, ms

0

10

20

30

40

50

60

70

80

90

100

Perc

enta

ge o

f suc

cess

ful c

onta

cts,

%

45.4 ms

Experimental methodologySlime coating

If slime coating occursthen T2<T1

Suspension Clay

Turbidity=T1

Suspension Clay+Chalcopyrite

Turbidity=T2

(a) (b)

ResultsMicro-flotation experiments

0 200 400 600 800 1000 1200Additions of kaolinite, ppm

70

75

80

85

90

95

100

Conc

entra

te y

ield

, %

K aolinitepH 9.5pH 10.5

200 400 600 800 1000 1200Additions of montmorillonite, ppm

MontmorillonitepH 9.5pH 10.5

ResultsInduction time

0 100 200 300 400Contact time, ms

0

102030405060708090

100

Perc

enta

ge of

succ

essf

ul co

ntac

ts, %

pH 9.5pH 9.5 (Equation 1)pH 10.5pH 10.5 (Equation 1)

45.4 ms

68.3 ms

0 200 400 600 800 1000Clay content, ppm

0

50

100

150

200

250

300

350

400

Indu

ctio

n tim

e, m

s

Kaolinite (pH 9.5)Kaolinite (pH 10.5)Montmorillonite (pH 9.5)Montmorillonite (pH 10.5)

Results

Bubble coated by clay particles. tc = 500 ms, PAX 40 ppm, pH=9.5.

Bubble coated by clay particles. tc = 1000 ms, PAX 40 ppm, pH=9.5.

Fine clays Copper concentrate

particles Fine clays

Copper concentrate

particles

Coating of air bubbles with fine clay particles.

These pictures were taken during the induction time measurements. They show that fine clay particles adsorb on the bubble surfaces.

ResultsSlime coating

0 200 400 600 800 1000 1200Additions of kaolinite, ppm

0

200

400

600

Turb

idity

, %

Kaolinite, pH 8.5Without CpyWith Cpy

0 200 400 600 800 1000 1200Additions of kaolinite, ppm

0

200

400

600

Turb

idity

, %

Kaolinite, pH 9.5Without CpyWith Cpy

0 200 400 600 800 1000 1200Additions of kaolinite, ppm

0

200

400

600

Turb

idity

, %

Montmorillonite, pH 8.5Without CpyWith Cpy

0 200 400 600 800 1000 1200Additions of kaolinite, ppm

0

200

400

600

Turb

idity

, %

Montmorillonite, pH 9.5Without CpyWith Cpy

If slime coating occursthen T2<T1

Suspension Clay

Turbidity=T1

Suspension Clay+Chalcopyrite

Turbidity=T2

(a) (b)

Conclusions› The presence of clay particles reduced the floatability of a

copper concentrate sample. These results agree with the induction time data.

› Among the mechanisms that explain this type of behavior are slime coating and coating of bubbles with fine clay particles.

› Its seems that the phenomenon of coating of valuable particles with fine clays becomes more relevant on the process of flotation only when the clay concentration is above 500 ppm.

› When sea water was used the general trends were similar but with some important deviations (montmorillonite).

Conclusions› Currently, the solutions used to treat minerals with high clay

contents relate to dilute the pulp, blending, mineral or simply discarding.

› The following lines of action are proposed to find solutions to the problem of altered minerals with high clay contents:× Process design including desliming or removal of fines (In development

Dimet-UdeC).

× Development of flotation reagents which avoid the negative effects of phyllosilicates (In development Dimet-UdeC).

ACKNOWLEDGEMENTS Professor Ursula Kelm of the GEA Institute of the

University of Concepcion. Water research center for agriculture and mining

(CHRIAM center UdeC-Fondap). Proyecto Fondecyt Iniciación N°11140184. The University of Concepcion, project VRID

N°214.095.089-1.0.

THANKS!