Hydrometallurgy, 8 (1982) 197--222 197 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

EVALUATION AND SELECT ION OF EXTRACTANTS FOR THE SEPA- RAT ION OF COPPER AND ZINC FROM CHLORIDE LEACH L IQUOR

G.M. RITCEY, B.H. LUCAS and K.T. PRICE

Extractive Metallurgy Laboratory, Canada Centre for Mineral and Energy Technology, Ottawa KIA OG1 (Canada)

(Received April 24, 1981; accepted September 25, 1981)

ABSTRACT

Ritcey, G.M., Lucas, B.H. and Price, K.T., 1982. Evaluation and selection of extractants for the separation of copper and zinc from chloride leach liquor. Hydrometallurgy, 8: 197--222.

The paper describes the bench-scale studies on the solvent extraction separation of copper and zinc from chloride liquors resulting from the low temperature chlorination of a lead--zinc sulphide concentrate. Various possible extractants were evaluated and the selection of the most suitable reagent was based on the effect of total chloride and equilibrium pH on extraction and discrimination, scrubbing and stripping. Acorga P5300 was the most suitable extractant for copper and TBP was selected for zinc.

INTRODUCTION

The convent ional refining of zinc usually comprises a hydrometal lurgical route, alone or in combinat ion with pyrometal lurgy. Roasted concentrates are dissolved with di lute sulphuric acid to produce a solution containing zinc sulphate plus impurit ies. After a series of process steps to remove the impuri- ties, the zinc is recovered by electrolysis, and the depleted zinc sulphate solu- t ion and regenerated sulphuric acid are returned to the leaching step. How- ever, because of their mineralogy, some of the fine-grained and complex zinc- bearing ores do not respond to the product ion of concentrates. The complex sphalerite ores which are found in large quantit ies in Canada, Austral ia and Norway are very diff icult to concentrate by differential f lotat ion, and then only at considerable loss of values.

At CANMET*, the prob lem of treating such ores was recognized and a comprehensive R&D program commenced late in 1975. After examinat ion of the problem, one of the approaches selected was that of producing a bulk concentrate which would be chlor inated and brine leached, the metals sub- sequently being separated and recovered f rom the solution by solvent extrac- tion. Such a process would provide high metal recoveries, e l iminate the en-

*Canada Centre for Mineral and Energy Technology.

198

vironmental problem of sulphides in the tailings, and produce metals of high purity. Any chloride process would also have to provide for recycle of chlorine in order to make the process economically feasible.

Previous investigators have reported on the solvent extraction of metals from chloride solutions containing metals such as copper, lead and zinc [ 1 ]. The use of TBP has been proposed for the extraction and separation of zinc from cadmium [ 2--4 ]. The best separation of zinc from cadmium utilized 100% TBP [2,4], with the zinc recovered by stripping with sulphuric acid. The use of TOPO for zinc extraction from chloride liquors showed an in- crease in the E values compared to TBP [3]. Extraction data for the use of naphthenic acid [2,5,7] or Versatic 911 [4--7] have been reported for the extraction and separation of zinc from cadmium showing that extraction was pH-dependent and reached a maximum at pH 6. With respect to amines, al- though the primary amines preferentially extract zinc, the secondary, tertiary and quaternary amines were selective for cadmium [4]. The Espindesa pro- cess uses a secondary amine for zinc extraction, followed by scrubbing and then water stripping the zinc which is subsequently extracted with D2EPHA [1]. The extraction and separation of zinc from cadmium with D2EPHA is accomplished best in the pH range 0.5--1.0 [4]. Mixed extraction systems of Kelex 100 and Versatic 911 showed an increase in separation factor for zinc over cadmium [ 5,6].

The literature contains considerable information on the extraction of copper from chloride liquors. LIX 64N has been used in a pilot process by NIM in Johannesburg [8]. Others have demonstrated that chloride ion con- centrations up to 4 M for LIX 64N and 3 M for Kelex 100 do not hinder the extraction of copper in the presence of ferric iron [9,10] because the kinetics favour copper over iron. The same authors reported that small amounts of chloride were extracted by LIX 64N but that no chloride was extracted by LIX 65N, due to the presence of LIX 63 in the LIX 64N [11, 12]. In the Mini- met process [13] (a cupric chloride leach) copper is extracted with LIX 65N, chloride is removed by scrubbing with water or copper sulphate solution, and stripping is accomplished with spent electrolyte from conventional elec- trowinning of copper sulphate solution.

Although many data are therefore available on chloride systems, the type of solution that would result from the chlorination-leach of the complex galena--sphalerite--chalcopyrite could differ in extraction and separation characteristics. Also, the objective at CANMET was to produce high purity zinc by electrowinning of zinc chloride solutions, thereby returning chlorine to the circuit.

The initial research was concerned with the examination and comparison of possible extractants for copper and zinc extraction and for discrimination from each other as well as from iron and lead. The total chloride content in the leach liquor (as NaC1) was also studied for its effect on extraction and discrimination. The subsequent work covered firstly the comparison of three selected possible copper extractants with respect to equilibrium, kinetics,

199

metal discrimination, scrubbing and stripping, and finally the selection of the best extractant for copper optimization tests. Subsequent to the bench- scale test, optimization tests were conducted on continuous mixer settlers and an economic assessment was made [14]. The present work describes the selection of the extractants and the operating conditions leading to the continuous testing.

PROCEDURE

The majority of the tests were conducted on actual roast-leach liquor where the metal concentrations were adjusted to a desired value for testing. The tests were all conducted in separatory funnels, where the extraction parameters such as equilibrium pH, contact time, chloride concentration, scrubbing and stripping were varied. The extractant concentrations were also varied. Prior to extraction, all copper solvents were pre-equilibrated with 150 g HC1/L, O/A 5/1, followed by a water wash at A/O of 1. The pre- equilibration of the TBP was usually by 50 g HC1/L, O/A 5/1. The feed solution composition was approximately 30 g Zn/L, 0.4 g Cu/L, 0.4 g Pb/L, 0.002 g Fe 3/L, and the NaC1 concentration was varied in the range 1--5 M to deter- mine the effect of chloride concentration.

By controlling the operating conditions in the chlorination--oxidation --~ leach sequence, of the ore or of the concentrate, a leach liquor containing

200

iron was anticipated to be almost completely eliminated during the roast-- oxidation--leach, no further work was directed towards iron removal.

Extraction of copper

Preliminary shake-out tests were conducted on several possible extractants including D2EPHA, LIX 64N, LIX 65N, LIX 70, Kelex 100 and Shell SME 529. These early tests, over the pH range 1--2 and 0--5 M NaC1 concentra- tion, indicated that the Shell SME 529 was the best extractant as to extrac- tion and metals discrimination. Subsequent tests were carried out, including the two Imperial Chemical Industries Acorga P5100 and P5300 reagents to- gether with Shell SME 529, Henkel's LIX 64N and LIX 65N. The extractants were as 10% solutions in kerosene, pre-equilibrated with 150 g/L HC1 at A/O 5/1 followed by a water wash at A/O 1/1. The feed to extraction contained, in g/L: 29.6 Zn, 0.41 Cu, 0.40 Pb, 0.0003 Fe. Extraction was varied over a pH range 1--5, NaC1 addition of 0--3 M, .and the retention time was 2 min at a phase ratio A/O of 7/1. The results indicated that the Acorga P5100 was the best extractant for copper, followed very closely by Acorga P5300. However, the P5300 possessed the best overall selectivity over Zn, Fe and Pb.

There was a trend towards an increase in metal selectivity with increase in pH or NaC1 concentration. At the lower pH values, LIX 65N was the next best extractant, while at pH 3--5 the SME 529 was the next best to the Acorga reagents. With 3 M NaC1, Acorga P5300 gave the best selectivity of Cu/Zn, Cu/Fe, although copper extraction was slightly lower compared to P5100 and SME 529. The results at a 3.0 M NaC1 concentration are given in Table 1. Subsequent tests were carried out to compare these three reagents as to extraction kinetic effects and equilibrium data as well as scrubbing and stripping properties.

Comparison of Acorga P5100, P5300 and Shell SME 529

Equilibrium data Equilibrium data were obtained on the Acorga reagents as well as the Shell

SME 529, at NaC1 concentrations of 0, 1 and 3 M for feed solutions contain- ing 0.4 and 5.0 g Cu/L. The contact time was 2 min. Although the three levels of NaC1 concentrations were run and all showed excellent equilibria, only the 3 M NaC1 concentration is compared and evaluated here. {This is the NaC1 concentration most likely to be used in the leaching of the chlorinated roast calcine.) In Figs. 1 and 2 are shown the results for Shell SME 529, Acorga P5100 and P5300 for the two levels of copper feed solution {P5100 is twice the concentration, in the as-received form, and therefore the reason for half-strength compared to the other two reagents}. Based on chemical equilibria, the P5100 and SME 529 appeared better than the P5300.

TABLE 1

Screening of extractants: Effect of equilibrium pH and chloride concentration on selectivity (10% extractant concentration)

201

Extractant Equil. NaCi. Selectivity (SF) Cu ext'n pH (M) (%)

Cu/Zn Cu/Fe Cu/Pb

LIX 64N 1 3.0 850 170 170 6.2 2 1400 280 560 11.5 3 1933 290 580 21.3 4 1575 630 630 23.1

LIX 65N 1 2500 375 938 27.5 2 2040 1020 2040 74.7 3 1295 1295 2590 94.9 4 633 1266 2811 92.7

SME 529 1 1300 93 650 23.8 2 518 207 2070 75.8 3 663 265 2650 97.1 4 518 288 2590 94.9

Acorga P5100 1 588 2350 2350 86.1 2 867 1300 2600 95.2 3 422 1265 2530 92.7 4 394 1380 2760 100.0

Acorga P5300 1 1550 1550 1550 56.8 2 1180 2360 2360 86.5 3 2967 2670 2670 97.8 4 1190 2380 2380 87.2

*P5100 is 5% (double strength as received).

0.3

O .Z ,

x x

| w

0 . I i I

202

4_ 0.8 z 0 .7

0 .6 ~ 0-5

0 .3

0 .2

0 .1

2

] I I L I I I I ] I I I I I L ] l [ I I I 02 -03 '04 -06 0"1 0"2 0"3 0"5 07 I '0 2"0 4 -0

RAFFINATE (g Cu/L)

Fig. 2. Equilibrium isotherms for P5100, P5300 and SME 529 (20C). Feed: Cu, 4.4 g/L; NaC1, 3 M; equilibrium pH, 3.5. * P5100 (5%); SME 529 (10%); A P5300 (10%).

Rate of phase separation Phase separation tests were carried out on the feed solutions, containing

0.4 or 5.0 g Cu/L, 0, 1, 3 M NaC1 and 30 g Zn/L, 0.4 g Pb/L, 0.002 g Fe3+/L, to compare the phase separation characteristics, mixing at room temperature, of SME 529, Acorga P5100 and P5300 diluted in Shell 140 kerosene. The contact time was 2 min in each test, and the A/O phase ratios were varied from A/O 5/1 to 20/1. Primary phase disengagement time is taken as the first distinct line that appears at the interface. Secondary phase disengage- ment time is when all of the organic reaches the interface line. A comparison of the primary phase disengagement times, at three levels of NaC1 concen- tration, is shown in Figs. 3 and 4 for 0.4 g Cu/L feed at A/O 7/1, and for the 5.0 g Cu/L at A/O of 1/1 (both phase ratios approximating saturation loading conditions}. The results in Fig. 3 indicate that SME 529 has the faster sepa- ration characteristics at the low NaC1 concentration in the feed. With NaC1 concentration up to 3.0 M, the P5100 and P5300 are equal and slightly in- ferior in rate of phase disengagement compared to the SME 529. The second- ary break time obtained for treating low-grade copper solutions at these con- ditions was also slightly better with the SME 529. At the higher feed concen- tration of 5 g Cu/L, the phase separation of SME 529 became steadily worse with increasing NaC1 concentration in the feed (Fig. 4). The phase separation rates for the two Acorga reagents were relatively constant over the NaC1 con- centration range, and faster than the SME 529 at the higher NaC1 concentra- tions. The secondary phase break time for SME 529 was slower by at least a factor of 2.

203

60

50 '

v

N 4o

N

~ 30

20

I I 1.0 2.0

NACL CONCENTRATION (M)

=x

o

I 30

Fig. 3. Effect of NaC1 concentrat ion on phase separat ion (20 C). Feed: 0.4 g Cu/L; equi l ibr ium pH, 4.0; A/O, 7/1 ; retent ion time, 2 rain. o SME 529 (10%); P5100 (5%); A P5300 (10%).

90

80

70

A A

30 ~ x

x-

~_ 60

50

40

20

I I I I 2 3

NaCl ,!M)

Fig. 4. Effect of NaC1 concentrat ion on phase separat ion (20C). Feed: 5.0 g Cu/L; equi l ibr ium pH, 3.5; A/O, 1/1; retent ion time, 2 rain. o SME 529 (10%); X P5100 (5%); ~ P53oo (lO%).

204

Kinetics and selectivity The three chelating extractants were compared as to their relative extrac-

tion kinetic differences. Extraction was from the leach feed liquor contain- ing 0.38 g Cu/L at A/O of 7/1, with the NaC1 concentration varying at 0, 1 and 3 M. The results indicated that an increase in NaC1 concentration from 0 to 3 M resulted in an increase in the rate of extraction of copper, which reached a maximum after about two minutes. At 3 M NaC1 concentration, comparing the 10% extractant concentration of P5300 and SME 529 with 5% P5100 (because the latter is the more concentrated as-received and capable of twice the copper loading compared to the other two reagents), the order of the rate of extraction is P5100 > P5300 > SME 529 (Fig. 5). The P5100

I0,000

I000

I00

I0

o

x

x ~ X ~ -x"

/

J

I I I I I I 60 120 180 240 300 T)me (min)

Fig. 5. Comparison of E values and extraction rate. Feed: 0.38 g Cu/L; equilibrium pH, 4.0; A/O, 7/1. x SME 529 (10%); * Acorga P5300 (10%); o Acorga P5100 (5%).

is several orders of magnitude faster in reaching a given level of extraction. The results at equilibrium pH 4.0 are shown in Table 2 and Fig. 5. The per cent extractions relative to time for the three extractants are shown in Fig. 6.

Table 3 shows the comparison of the reagents for discrimination over Zn, Pb and Fe. The results, as measured by the ratios in the loaded solvent, indi- cate that Shell SME 529 holds a slight edge over the Acorga extractants for zinc discrimination while the reverse is true for discrimination over lead. How- ever, the discrimination over iron is far superior for the Acorga reagents.

TABLE 2

Compar ison of rates of extract ion for Acorga P5100, P5300, Shell SME 529 (0.38 g Cu/L, A/O 7/1)

205

NaC1 conc. Time Cu extract ion coeff ic ient (E) (M) (s)

SME529 P5300 P5100 10% 10% 5%

0 5 3.5 7.5 10 7.0 20.2 30 10.2 36.5 6O 2O.2 74.6

120 35.6 90.9 300 40.8 171.1

1.0 5 4.4 12.6 15 7.9 33.5 30 16.3 81.7 60 20.3 159.0

120 35.4 303.0 300 41.6 350.0

3.0 5 6.3 14.6 15 13.3 59.5 30 22.4 120.0 60 29.7 260.0

120 36.4 260.0 300 46.1 260.0

25.1 179.0 259.0

1850.0 3000.0 3000.0

I00

90

8O

L~

v 70

~ 60 Ld

50

~x f ' f x

4O I I I ] I 60 120 180 240 :300

T ime (rain)

Fig. 6. Compar ison of extract ion kinetics (20C). Feed: 0.38 g Cu/L; equi l ibr ium pH, 4.0; 3 M NaC1; A/O, 7/1. X SME 529 (10%); P5300 (10%); o P5100 (5%).

206

TABLE 3

Pur i ty rat iosAn loaded so lvent , 3 M NaC1 system

Ref . t ime 10% SME 529 10% P5300 (s)

5% P5100

Cu/Zn Cu/Pb Cu/Fe Cu/Zn Cu/Pb Cu/Fe Cu/Zn Cu/Pb Cu/Fe

5 258 1842 9.2 62 1800 2000 27 2080 3467 15 447 1790 11.9 264 2644 2645 213 1280 2560 30 520 2080 13.9 585 5850 1170 199 5180 3700 60 737 3157 14.7 647 5180 2878 883 4417 3312

120 1145 3816 16.4 - - 5140 2570 867 6500 3714 300 1185 3385 15.8 800 3418 2400 5320 5320 4433

Scrubbing of chloride and stripping Thus, although the data suggested that the Acorga P5100 is superior as re-

gards (1) equilibrium (and therefore stage efficiency), (2) phase disengagement or coalescence and (3) kinetics, nevertheless purity of the feed electrolyte to electrowinning would still be a major factor in the ultimate reagent choice. The P5300 was shown to be more selective for copper in the presence of zinc, iron and lead.

Because the extraction would be from chloride media, there existed the possibility of chloride-carryover with the loaded solvent into the subsequent

TABLE 4

Chloride scrubbing of loaded solvents followed by stripping

Scrub feed solution

Acorga P5100 Acorga P5300

Cu scrubbed Scrub sol'n Phase sep'n (s) Cu scrubbed (%) (%)

Cu C1 Prim. Sec. (g/L) (rag/L)

1% H:SO 4 20.6 2.68 120 42 25 25.7 50 g/L (NH4)~SO 4 0 0.004 45 38 18 10.9 50 g/L Na2SO 4 0 0.0001 22 40 20 8.3

Scrub feed Cu stripped Strip liquor Phase sep'n (s) Cu stripped (%) (%)

Cu C1- Prim. Sec. (g/L) (rag/L)

10/1 38.9 37.2 17 35 25 48.0 5/1 46.8 32.9 22 20 15 61.8

H2SO4 3/1 50.6 32.1 4 25 15 67.1 1/1 53.7 30.2 7 10 15 69.8

(NH4)2SO 4 5/1 56.0 36.5 24 30 20 63.3 Na2SO 4 5 / l 41/5 34.8 46 25 18 64.0

207

stage of stripping with sulphuric acid return copper electrolyte, prior to elec- trowinning for copper recovery. The ease of scrubbing the chloride from the loaded solvent had therefore to be determined. Solvents (5% P5100, 10% P5300, 10% SME 529) in Shell 140 diluent were contacted for 5 min with a 5 g Cu/L solution in 3.0 M NaC1 at pH 3.5. The phases were separated, and the loaded solvent was filtered prior to carrying out the subsequent tests.

Scrubbing tests on the loaded solvents were performed using Na2SO4, (NH4)2SO4 and H2SO4, at O/A 5/1, for a 5 min contact time. The scrubbed solvents were stripped with a solution containing 30 g Cu/L and 150 g H2SOJL. The H2SO4-scrubbed solvents were stripped at varying phase ratios, while the other two scrubbed solvents were stripped at O/A 5/1. Contact time for stripping was 2 min.

The results in Table 4 indicate that, for scrubbing, both the Acorga rea- gents are similar in effectiveness for chloride removal and in the time re- quired for coalescence to take place. The Shell reagent required a consider- ably longer time for coalescence. The strip results indicate that a range of 4--22 mg/L chloride was achieved with the H2SO 4 scrub of Acorga P5100, compared to a range of 2--15 mg/L for Acorga P5300 and 12--40 mg/L for Shell SME 529. (NH4)2SO4 and Na2SO4 scrubbing were less effective than the use of H2SO4 (with (NH4)2SO4 Na2SO4), but the 1% H2SO4 scrub removed a considerable quantity of copper (26%). Again the coalescence times were equal for the Acorga reagents, while the Shell reagent required a longer period of coalescence. The most effective copper stripping occurred with the Acorga

Shell SME 529

Scrub sol'n Phase sep'n (s) Cu scrubbed Scrub sol'n Phase sep'n (s) (%)

Cu C1- Prim. Sec. Cu C1- Prim. Sec. (g/L) (rag/L) (g/L)

3.51 0.11 44 35 26.7 3.32 1.12 g/L 135 65 0.016 49 25 20 0.39 0.021 58 mg/L 50 40 0.087 2.4 28 18 0.78 0.087 1.88 mg/L :>180 :>180

Strip liquoz Phase sep'n (s) Cu stripped Strip liquor Phase sep'n (s) (%)

Cu Cl- Prim. Sec. Cu C1- Prim. Sec. (g/L) (rng/L) (g/L) (rag/L)

39.5 15 18 18 27.3 31.8 40 50 35 35.0 2 15 10 54.0 31.8 26 65 80 34.5 9 30 20 77.0 31.4 20 120 50 31.3 10 22 12 76.5 29.8 12 60 30 38.8 19 17 15 57.9 31.9 14 55 45 38.5 20 24 18 66.8 32.9 710 45 35

208

P5300 extractant. Although the Acorga P5100 has much in its favour for ex- traction, the P5300 had a slight edge in the important aspects of selectivity, scrubbing and stripping effectiveness. Therefore, all further work was with the latter extractant, P5300.

Equilibrium data for P5300 Subsequent stripping tests on the loaded P5300 solvent indicated that the

solvent, after stripping, still contained about 0.6 g Cu/L. (See later Section 'Stripping of copper from P5300'.) To recycle such a load to extraction is not a serious situation, and it was decided to incorporate this into the flow-sheet. Figure 7 shows the typical equilibrium data obtained by taking a stripped

S

C2

0-!

I-0

X- -X

I J I I I I I 001 "002 "004 007 "01 0"1 0 '2 0"3

RAFFINATE (g Cu/L)

Fig. 7. Equil ibrium isotherms for Acorga P5300 (20C). Feed: 0.38 g Cu/L; solvent, 10% Acorga P5300 in Solvesso 150. x solvent containing 0.64 g Cu/L prior to extraction; A fresh solvent to loading.

solvent of 10% Acorga P5300, containing a residual 0.64 g Cu/L, and con- tacting a feed solution at various phase ratios for 2 min at an equilibrium pH of 4. The feed solution contained 0.4 g Cu/L, 30 g Zn/L, 0.4 g Pb/L, 0.002 g Fe3+/L and 3 M NaC1. Prior to extraction, the solvent was pre-equilibrated with 150 g HC1/L, at O/A 5/1, followed by a water wash. The results show a comparison of the extraction isotherm obtained from the partially-loaded (0.64 g Cu/L) solvent with that of a fresh solvent. At this time no explana- tion can be given for the difference in saturation loading values obtained be- tween the fresh and the re-used solvent.

Stage-wise extraction (P5300) Ten successive contacts of 10% Acorga P5300 were made with a feed solu-

tion containing 0.4 g Cu/L, 30 g Zn/L, 0.4 g Pb/L, 0.002 g Fe3/L and 3.0 M NaC1 at pH 3.5--4.0 in order to determine scrubbing effectiveness with multi-

209

stage extraction. The phase ratio was A/O 7/1, and the contact time was 2 min. The ratios in the loaded solvent, after the successive contacts, were Cu/Zn 2800, Cu/Pb 2800, Cu/Fe 350. No intermediate analyses were made and all the copper (99.8%) was extracted in the first stage, therefore high purity would result after a very limited number of stages.

Scrubbing of chloride and effect of temperature (,1>5300) The results of scrub-strip tests for chloride removal, using additional scrub

solutions to those shown previously, are given in Table 5, indicating that

TABLE5

Scrubbing of chloride from P5300 followed by stripping; O/A 5/1, room temperature

Scrub solution Chloride in strip solution (mg/L)

Phase disengagement on stripping (s)

Primary Secondary

Water 10 5 3 50 g/L (NH4)2SO4 12 7 5 50 g/L Na2SO 4 10 8 7 pH 2.5 H2SO 4 9 12 10 pH 4.5 H~SO 4 8 12 10 pH 7.5 NaOH 8 12 10 pH 8.5 NaOH 23 12 10 15 g/L NH4OH 21 10 8 No scrubbing 75

relatively low chloride levels were repeatedly achieved at room temperature. Water or Na2SO4 appear suitable for the removal of chloride from P5300.

Another series of tests, where the loaded solvent was scrubbed at 20C, 35C and 50C with 50 g/L Na2SO4 followed by stripping at 20C, is shown in Table 6, indicating room temperature to be more effective for scrubbing.

Ten successive scrubs with 50 g/L Na2SO4 resulted in a level of about 5 mg/L chloride in the strip solution.

TABLE 6

Comparison of temperature for scrubbing--stripping

Temp. (C) Cu stripped (%) Strip liquor chloride (mg/L)

20 67.6 4 35 66.2 18 50 64.7 27

210

Stripping of copper from P5300 The loaded solvent is readily stripped with a solution of 30 g/L Cu con-

taining 150 g/L H2SO4. A room temperature stripping isotherm is shown in Fig. 8 for the removal of 3 g Cu/L from the loaded solvent. The data indicates that three stages are required to produce a recycle solvent containing 0.2 g/L. Also indicated is a strip electrolyte feed to electrowinning of 50 g Cu/L, also containing 0.005 g Zn/L, 0.005 g Pb/L and 0.09 g Fe/L.

50.0

40.0

v 30.0

~o.o

I00

OC 0

/

/"/5 /

/

/

I I I 0"2 0"4 0 '6 0'8

1511 OIA

/

/

I I I I I ~ f I'0 1.2 1.4 1"6 16 2"0 3"0

STRIPPED SOLVENI ~ (g Cu/L)

Fig. 8. Stripping isotherm for copper (10% P5300). Feed solvent: 3.0 g Cu/L; strip solu- tion: 150 g H2SO4/L + 30 g Cu/L.

Scrubbing of S04 from P5300 solvent After stripping the loaded solvent with the acidified CuSO4 solution to re-

cover copper, the stripped solvent would possibly carry back to the extrac- tion circuit some quantities of sulphate. With repeated recycle, the sulphate would be released from the solvent to the aqueous phase and would build up in the chloride leach solution. Therefore, scrub tests were carried out to determine the best scrub condition. The loaded solvent was treated by three stages of scrubbing with Na2SO4 solution to remove chloride; copper was stripped with acidified copper prior to scrubbing for sulphate removal. Scrubbing with water, O/A 5/1, was the most effective for sulphate removal, and room temperature was better than 50C. The results are shown in Table 7.

Subsequent tests, using a water scrub and varying the O/A ratio, indicated little or no emulsion tendency at O/A 3/1, compared to 1/3 where emulsion

TABLE 7

Scrubbing for sulphate removal

211

Reagent for scrubbing SO 4 in scrub aqueous (g/L)

Room temp. 50C

water 0.88 0.030 50 g/L NaCl 0.27 0.063 175 g/L NaCl 0.21 0.064 50 g/L CaC12 0.13 0.037

was a problem. For example, the phase separation time was 25 s in the for- mer, compared to 75 s in the latter. No additional sulphate was removed by adding more scrub stages.

Zinc extraction from copper raffinate

Screening of extractants The summary of screening tests on some selected extractants for zinc from

the chloride solution are shown in Table 8. The extractants were contacted at a high A/O ratio of 6/1 with a feed solution containing, in g/L: 0.5 Fe,

TABLE 8

Screening tests for extract ion of Zn f rom Cu raff inate; 3 M NaCl, equil, pH 2.0

Loaded solvent (g/L) Zn /Fe Fe Zn Pb solvent

5% LA 3 0.002 0.14 0.006 -- 5% Adogen 368 0.13 2.60 0.002 -- 5% Adogen 383 0.55 1.81 0.001 3.3

(18) (1.2) 5% Adogen 464 0.14 3.28 0.002 --

(2.2) 5% D2EPHA 2.42 1.49 0.001 0.62

(80.6) (1) 5% TOPO 0.39 3.18 0.001 8.2

(13) (2.1) 5% TOPO (not 0.35 3.18 0.002 --

equil.) 100% TBP 1.16 27.2 0.010 23.4

(52) (18.1) 75% TBP 0.74 17.6 0.006 23.8

(24.7) (11.7)

() indicates % extract ion

212

25 Zn, 0.4 Pb. The NaC1 was varied from 0--3 M and the equilibrium pH at 1 and 2. Very little difference was found with change in pH of extraction. Metals extraction increased with increase in NaC1 concentration from 0--3 M. The values in Table 8 are shown for extraction at an equilibrium pH of 2.0. All solvents were pre-equilibrated with 150 g HC1/L, A/O 5/1, except where noted otherwise. The diluent for all solvent mixtures was Shell 140. TBP was the best of the extractants evaluated, both for loading and discrimination over iron.

Extraction of zinc with TBP As a result of the screening tests, 100% TBP was selected for further Zn

extraction studies. The solvent was acid equilibrated with 150 g HC1/L, A/O 5/1 before use. Contact time was 5 min at an arbitrary phase ratio A/O of 1/1 Extraction was varied at an equilibrium pH 1--5 on a solution containing, in g/L: 0.5 Fe, 0.39 Pb, 25.2 Zn. The NaC1 content was varied from 0--3 M. The results indicated little increase in extraction of zinc by either increase in equilibrium pH or increase in NaC1 concentration. The best phase disengage- ments were generally at pH 4 and 5. Although there was an improvement with increasing NaC1 concentration, the phase disengagement was not good.

A similar series of tests was repeated using 75% TBP in Shell 140. Essen- tially the same results as above were obtained but with lower Zn extraction. Again, phase disengagement was poor. Subsequently, the diluent was changed

TABLE 9

Effect of NaCI concentrat ion and equi l ibr ium pH on the extract ion with 75% TBP in Solvesso 150

NaCladded Equil. Loadedso lvent (g /L ) Ext rac t ion(%) (M) pH

Zn Fe Pb Zn Fe Pb

0 1.0 5.94 0.002 0.014 33.0 0.55 4.6 2.0 5.84 0.002 0.012 33.8 0.55 4.0 3.0 6.28 0.002 0.014 37.6 0.55 4.6 4.0 6.34 0.002 0.012 39.7 0.55 4.0 5.0 6.31 0.001 0.008 35.1 0.22 2.7

1.0 1.0 9.44 0.018 0.012 52.5 4.9 4.0 2.0 9.44 0.007 0.012 52.5 1.9 4.0 3.0 9.66 0.003 0.012 53.8 0.83 4.0 4.0 9.78 0.003 0.011 54.4 0.83 3.7 5.0 9.69 0.002 0.010 53.8 0.55 3.3

3.0 1.0 9.88 0.24 0.006 55.0 66.5 2.0 2.0 9.63 0.043 0.006 53.6 11.9 2.0 3.0 9.94 0.004 0.006 55.3 1.11 2.0 4.0 9.69 0.002 0.006 53.9 0.55 2.0 5.0 10.1 0.005 0.005 56.2 1.4 1.7

213

to Solvesso 150, resulting in much better phase separat ion over the pH and NaC1 concentrat ion ranges tested. The results are shown in Table 9. The feed solut ion contained, in g/L: 23.9 Zn, 0.48 Fe 3, 0.40 Pb; the tests were at an A/O of 0.75/1. The test results showed a significant increase in the loading (extract ion) of zinc with an increase in the chloride concentrat ion. The ex- tract ion of lead tended to decrease as the chloride content was increased f rom 0--3 M NaC1. The results tended towards increased iron extract ion as the chloride concentrat ion was increased, provided the pH was low. Change of equi l ibr ium pH had no apparent ef fect on the extract ion of Zn and Pb at 1.0 and 3.0 M NaC1. Lower Zn extract ion occurred when no NaC1 was added.

Effect of TBP concentration The TBP concentrat ion was varied at 20, 30, 40, 50 and 60% in Solvesso

150 di luent and the equi l ibr ium pH was adjusted at pH 1.0 and 2.0. Extrac- t ion tests were with a feed solut ion containing 25.1 g Zn/L, 0.45 g Fe3/L, 0.39 g Pb/L and 1.0 M NaC1. As the solvent concentrat ion was increased, the A/O ratio was equally changed to compensate for the extra sites available. The results of the tests again indicated no effect on extract ion due to change in pH. The results of the tests, at equi l ibr ium pH 2, are shown in Table 10.

TABLE 10

Effect of solvent concentration on extraction of zinc and discrimination over iron and lead

Solvent O/A conc. ratio v/o TBP

Loaded solvent (g/L) Extraction (%)

Zn Fe Pb Zn/Fe Zn/Pb Zn Fe Pb

20 5.0 0.69 0.001 0.002 690 345 13.7 1.09 2.56 30 3.3 1.58 0.002 0.003 790 527 21.0 1.43 - 40 2.5 2.91 0.0007 0.004 4157 727 29.0 - 2.56 50 2.0 4.88 0.001 0.006 4880 813 38.9 -- 3.07 60 1.7 6.50 0.003 0.008 2166 812 43.0 1.08 3.40 75 1.3 9.44 0.007 0.012 1348 787 52.5 1.9 4.0

Al though the zinc extract ion, and therefore loading, was increased by in- crease in solvent concentrat ion, that of iron and lead remained relatively constant. Thus the discr imination of Zn over Fe and Pb was increased with increasing TBP concentrat ion. This is shown in Fig. 9. The results indicate max imum selectivity of Zn over Fe and Pb at a TBP concentrat ion of 40-- 50%, beyond which higher solvent concentrat ion results in a decrease in metals selectivity.

Pre-equilibration of TBP The extract ion of zinc could probably be ef fected with the TBP in several

ways with respect to pre-condit ioning. Tests were therefore carried out to determine the ef fect of the pre-equi l ibrat ion solut ion concentrat ions and

214

~ooc ~--w 300C

>~ 0 100C

w 0 500

Q ~ooi o 100

~ Zn/Fe Zn/Pb

3 "~-c 10 ~ Z n ~ 50 ~ 30 w ~ 1.0

~ o5

s ~o 1o 20 ~o ;o

TBP CONCENTRATION [VOL %) 9o ~o

Fig. 9. Effect of TBP concentrat ion on Zn extract ion and discr iminat ion over Fe and Pb.

solution types on the extraction of zinc at equilibrium pH levels 1--4 and NaC1 concentrations of 0, 1 and 3 M NaC1. The results in Table 11 using 75% TBP in Solvesso 150, at A/O 0.83/1, indicate the following:

(a) At NaC1 concentrations of I and 3 M, there was no change in zinc ex- traction with: pH over the range 1--4, acid concentration, or the use of 150 g/L NaC1 solution for pre-equilibration.

(b) At 0 M concentration of NaC1 in the feed liquor, by increasing the acid pre-equilibration from 50 to 150 g/L HC1, the zinc loading (and therefore the zinc extraction) was increased.

(c) An increase in extraction of zinc results by increasing the NaC1 concen- tration from 0 to 3 M in the feed solution.

Thus, if 3 M NaC1 feed solution is used, pre-equilibration can be with salt or acid, and the equilibrium pH in the range 1--4 has no effect on extraction of zinc.

Solvent concentration As the TBP concentration was increased to 75%, the coalescence time re-

quired after extraction or stripping increased. Therefore, it was decided to evaluate 50%, 60% and 75% TBP. Tests were therefore carried out at the three solvent concentrations in contact with the leach solution containing 29.5 g Zn/L, 0.4 g Pb/L, 0.002 g Fe 3/L in 3 M NaC1. The tests were at room temperature, for 2 min contact time, and the phase ratios were varied in order to plot equilibrium curves, shown in Fig. 10. Although there may be some advantages in using the more dilute solvent, the higher concentration would

TABLE 11

Pre-equilibration of TBP

215

NaC1 Equil. pH Pre-equil. Solvent (g/L) % Zn Ext'd (M) Zn

0 1.0 150 g/L HCI 8.06 32.3 2.0 7.69 30.8 3.0 7.63 30.5 4.0 7.81 31.3

1.0 50 g]L HCl 6.25 25.0 2.0 6.25 25.0 3.0 6.25 25.0 4.0 6.25 25.0

1.0 150 g]L NaC1 6.25 25.0 2.0 6.03 24.1 3.0 6.06 24.2 4.0 5.98 23.9

1.0 1.0 150 g]L HC1 11.1 46.9 2.0 11.4 47.2 3.0 10.9 46.7 4.0 11.5 47.3

1.0 50 g]L HCI 10.6 44.8 2.0 11.1 45.9 3.0 10.4 43.6 4.0 11.1 45.5

1.0 150 g/L NaCl 10.9 46.0 2.0 10.9 45.1 3.0 10.6 45.4 4.0 11.1 45.6

3.0 1.0 150 g]L HC! 12.5 50.4 2.0 12.1 50.7 3.0 12.3 50.9 4.0 12.4 50.0

1.0 50 g]L HC1 12.9 52.0 2.0 12.7 52.9 3.0 12.7 52.6 4.0 12.8 51.6

1.0 150 g/L NaC1 12.8 50.4 2.0 13.0 54.2 3.0 12.9 53.4 4.0 12.8 51.6

requi re fewer theoret ica l stages. F igure 11 shows the re la t ionsh ip between TBP concent ra t ion and so lvent loading. A concent ra t ion above 20% is re- qu i red and the load ing increases steeply with increase in so lvent concent ra - t ion to 75% TBP.

216

20

15

d 5

0

o /5% TBP

x-

~" .K '~r /x / 3M NACL ~ x ~ [QUIL, PH 4,O

I I I I I f 5 I0 15 20 25 30

RAFFINATE (g ZN/L)

Fig. 10. Equilibrium data for 50, 60 and 75% TBP. 3 M NaC1; equilibrium pH, 4.0.

20- - x

15

5

0 - - x . -x=x~x L l 25 5,0 75

SOLVENT CONCENTRATION (% IBP)

Fig. 11. Solvent concentration and Zn loading. Room temperature, 3 M NaC1.

Equilibrium isotherms for the 75% TBP -- 3 M NaCI--ZnCl2 system A series of tests was performed at 3 M NaC1 feed concentration containing

29 g Zn/L, 0.0018 g Fe/L and 0.40 g Pb/L. The feed was contacted at various phase ratios, for 2 min at room temperature, at an equilibrium pH 4.0, with 75% TBP in Solvesso 150. Pre-equilibration was with 150 g NaC1/L, O/A 5/1 in one series; in the other series no pre-equilibration was used. The results are shown in Table 12 and Fig. 12. Table 12 indicates that there is essentially no significant difference in zinc and lead extraction between pre-equilibrated or non-equilibrated solvents.

Scrubbing for removal of copper and lead Scrubbing of impurities from loaded solvents often takes place during

stage-wise extraction. A number of scrub solutions were examined as to their relative value in removing co-extracted Cu and Pb from a Zn-loaded solvent. These solutions included water, Na2 SO4, H2SO4 and NaOH. Although all scrub solutions were effective in the removal of Cu and Pb, appreciable amounts of

TABLE 12

Extraction and effect of non-equilibration

217

Phase ratio % Zn % Fe A/O

Non-equil. Pre-equil. Non-equil. Pre-equil.

% Pb

Non-equil. Pre-equil.

1/5 83.8 84.6 25.0 11.1 6.1 8.7 1/3 74.1 75.6 50.0 33.3 4.4 5.3 1/1 46.7 46.7 35.0 38.8 1.5 1.7 3/1 20.1 20.1 11.6 11.1 0.5 0.6 5/1 12.8 12.9 5.0 10.0 0.3 0.3

2O J

W

C3 W CI

j 5

x

0 I I I I I I 0 5 IO 15 20 25 30

RAFFINATE (g Zn/L)

Fig. 12. Equilibrium isotherm for the 75% TBP--3 M NaCl--ZnC12 system (20C). 75% TBP in Solvesso 150; 3 M NaCl; equilibrium pH, 4.0. o pre-equilibrated with 150 g NaC1/L; no pre-equilibration.

Zn were also stripped. However, with a scrub solution of 25 g Zn/L in 3 M NaC1 at pH 3.5--4.0, the Cu and Pb were scrubbed without a loss of Zn. The results of single-stage scrubbing at two phase ratios are shown in Table 13. Phase separation time was about 24 s.

TABLE 13

Scrubbing of TBP; loaded solvent: 0.021 g Cu/L, 0.056 g Pb/L, 75% TBP; scrub solution: 25 g Zn/L in 3 M NaC1, pH 3.5--4.0

Phase ratio O/A

Scrubbed solvent (g/L)

Cu Pb

1/5 0.0003 0.001 1/1 0.0005 0.002

218

Stripping of zinc Water was used to strip the zinc from the loaded solvents. Stripping iso-

therms for 60% TBP (room temperature) and 75% TBP (room temperature and 50C) were prepared from the data obtained by contact of loaded sol- vents {12.5 and 18.4 g Zn/L respectively} at various phase ratios for 2 min. These results are shown in Fig. 13.

50

'~ 40

z 3O Q

~ 2o

10

~ o / / / / / / /~

I I ] I I I I 2 4 6 8 I0 12 14

STRIPPED SOLVENT (g Zn /L )

Fig. 13. Water stripping of Zn (50C). o 75% TBP in Solvesso 150; ~ 60% TBP in Solvesso 150.

Subsequent evaluation of the electrolyte, for electrowinning, indicated that a water strip would probably not be fully satisfactory and that a better medi- um would be 15 g Zn/L at pH 1.0 in HC1 [3]. Loaded solvents were prepared by first equilibrating the 60% and 75% TBP extractants in Solvesso 150 dilu- ent with 50 g HC1/L at O/A 5/1, followed by extraction at A/O 5/1 using a feed consisting of 30 g Zn/L, 0.4 g Pb/L, 0.002 g Fe3/L in 3 M NaC1 at pH 4.0. The data, in Fig. 14, indicated only slightly better results with the 75% compared to the 60% solvent. However, the rate of coalescence was faster with the 60% TBP. A stripped solvent of 1.76 g Zn/L was obtained with the 60% solvent, compared to 3.75 g Zn/L with the 75% solvent. The loading-- stripping sequence with the 60% solvent provided better discrimination over Pb and Fe as compared with the 75% TBP. The purity results are shown in Table 14.

DISCUSSION

The programme of evaluation of numerous possible extractants for the selective separation and recovery of copper and zinc from brine solutions has resulted in the choice of Acorga P5300 for copper and TBP for zinc. The solvent extraction process is not a simple procedure of finding an extractant for a metal. Other factors enter into the selection, such as dispersion and coal-

50,

4O

~ 3O

~ 20

I0

/o

j /

0 I I I I 0 5 iO 15 20

STRIPPED SOLVENT (g ZN/L)

Fig. 14. Stripping of Zn with ZnC12--HC1. Strip feed: 15 g Zn/L; pH 1.0 (HC1). o 75% TBP (loaded at 20.9 g Zn/L); X 60% TBP (loaded at 14.6 g Zn/L).

219

TABLE 14

Purity in strip solutions

O/A Zn/Pb Zn/Fe ratio

60% TBP 75% TBP 60% TBP 75% TBP

10/1 1700 1200 91600 4500 5/1 2500 1800 132000 8250 3/1 3400 2600 169000 12000 1/1 6000 5000 240000 12600 1/5 20900 16900 55600 18800 1/10 30800 25500 77000 38250

escence, kinetics, chemical equil ibrium, discr imination, ease of scrubbing and removal of impurit ies, and stripping characteristics, all of which must be compat ib le with subsequent stages such as electrowinning. Thus the process of reagent choice has involved many interactions.

F lowsheets for the two circuits that were subsequent ly technical ly and economical ly verif ied are shown in Figs. 15 and 16, based on a leach feed containing, in g/L, 30 Zn, 0.4 Cu, 0.4 Pb, 0.002 Fe, in 3.0 M NaC1 at pH 4.0 [14] .

Extract ion of copper is in 4 stages of mixer-sett lers, using 5% Acorga P5300 in an al iphatic kerosene di luent such as Shellsol LX 154. At an A/O ratio of 3.5/1, the solvent will load to 1.4 g Cu/L. The retent ion t ime in the mixer is 0.5 min. Fol lowing extract ion, the solvent is scrubbed with water in 6 stages, at an O/A ratio of 5/1, to remove chloride f rom the solvent. The mixing t ime

220

mou LE/~:H RAFEINATE TO ZINC RIEC, OV~RY CIRCUIT

r ~ r = SOLVENT keN(E-UP

ST SOLVENT S I~ IR~

EXTR~'~rlON-4 STAGES

~17 ,r 7 I--] r lR~- . . . . ~'1

WASTE I ~ L J l ' l~2 Jk ' HeO

CHLORIDE SCRUBBING * 6 STAGES

CATHUO[ Cu - ELECTROWl NNIN( COPPER

I

I

r l '

L J t SULPHATE I SC RU(mIND I "3 STAGES l

I

. . . . . . 1

. . . . . . . . . oJ

Fig. 15. Copper recovery circuit.

RAFFINATE RAFFINATE COPPER TO LE:ACH leiTH BLFJEU TO

CIRCUIT IX m0~t METAL CLEAR-UP |

SOLVENT MAKE-UP

LEACH r~ F I r~ r~ ~-- i

I ULJ L JL J U~-___ i EXTRACTION-S STAGES I I ZeC l f - -~ 1 ~, Noct I~.)

CIRCUIT EX I~K)N I

SC~UgOING - F

. . . . . . . . ~ . . . . 4.1 PRE- f ~L,eRA- I : ~ . r l ~r I F ] i

~ ~U SO,

lEE Zn CV

CATHOOE ZINC

Fig. 16. Zinc recovery circuit.

221

is 1 min. The copper is recovered from the solvent by stripping in 3 stages with return electrolyte from the electrowinning cells, containing 30 g Cu/L and 150 g H2SO4/L, at an O/A ratio of 6/1 and with a retention time in the mixer of 1 min. Sulphate remaining on the solvent after stripping is removed in 3 stages of water scrubbing at an O/A of 8/1 for 1 min. All settlers were de- signed on a basis of 4.4 m3/m 2 h (1.5 Iml~. gal/min ft 2) settler area.

I

Zinc circuit

Zinc extraction is accomplished in 6 stages at an O/A ratio of 2.2/1 with 60% TBP in Solvesso 150 aromatic diluent. A retention time of 1.8 min is used in the mixer. The solvent is scrubbe~l in 3 stages at an O/A of 3/1, for 1 min, with a solution consisting of 25 g ~nC12/L in 3 M NaC1. Zinc was re- covered from the solvent by 6 stages of stripping using return electrolyte containing 15 g Zn/L at pH 1.0 in HClat an O/A of 2.5/1 for 1.8 min. Prior to recycling the stripped solvent to ~xtraction, the solvent was acid equilibrated with 50 g HC1 at an O/A of ~/1 for 1.8 min.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the work of E.W. Wong of the Process Metallurgy Section for conducting the te~ts, and to the Chemical Laboratory for the numerous analyses.

Crown copyrights reserved.

REFERENCES

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2 Fletcher, A.W., Flett, D.S., Pegler, J.L., Pep~vorth, D.P. and Wilson, J.C., 1967. In: Advances in Extractive Metallurgy, Inst. of Mining and Metallurgy Syrup., London, pp. 686--711.

i 3 Forrest, V.M.P., Scargill, D. and Splckernell! D.R., 1969. J. Inorg. Nucl. Chem., 31: 187--197.

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345. 6 Lakshmanan, V.I. and Lawson, G.J., 1974. Proc. of International Solvent Extraction

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vent Extraction Conf., ISEC '74, Lyon, Soc. Chem. Ind., London, Voi. 1, p. 685. 10 Lakshmanan, V.I., Lawson, G.J. and Nyholm, P.S., 1974. Proc. of International

Solvent Extraction Conf., ISEC '74, Lyon, Soc. Chem. Ind., London, Vol. 1, p. 699. 11 Christie, P.G., Lakshmanan, V.I. and Lawson, G.J., 1976. Hydrometallurgy, 2 (2) 105.

222

12 Lakshmanan, V.I., Carpentar, J.C., Christie, P.G., Lawson, G.J. and Nyholm, P.S., 1976. Proc. Int. Syrup. on Copper Extraction and Refining, AIME, Las Vegas, February, p. 1025.

13 Demarthe, J.M., Gandon, L. and Georgeaux, A., 1976. In: Extractive Metallurgy of Copper -- Hydrometallurgy and Electrowinning, Vol. 2, Proc. of International Syrup. AIME, Port City Press, Baltimore, U.S.A., pp. 825--848.

14 Ritcey, G.M., Lucas, B.H. and Price, K.T., 1980. Proc. of International Solvent Ex- traction Conf., ISEC '80, Liege, Belgium, September, Vol. 3, Paper 80-71.