Overview

The Cuprex Metal Extraction Process: Recovering Copper from Sulfide Ores

R.F. Dalton, G. Diaz, R. Price and A.D. Zunkel

The Cuprex™ metal extraction process produces cathode-grade copper using a hy­drometallurgical process based on chloride leaching of sulfide ore concentrates. The process incorporates several novel steps to overcome the major problems associated with earlier chloride-based processes, including mild leaching conditions usingferric chloride as leachant and solvent extraction of copper using a novel reagent. This produces a highly concentrated cupric chloride electrolyte from which cathode-grade copper is electrowon in the Metclor cell. The technical viability and robustness of the core technology have been proven in a series of large-scale pilot trials. More recent work has concentrated on supplementary processes to convert the cop­per powder product to an article of commerce and to recover valuable by-products. A fully integrated scheme is now being developed with updated cost estimates.

INTRODUCTION

Recent years have seen a considerable increase in activity in the development of hydrometallurgical processes. There are a number of reasons for this increase. For example, hydrometallurgical pro­cesSes permit the recovery of metals from lower-grade feedstocks, are often more environmentally acceptable than con­ventional pyrometallurgy, and provide a means of processing complex concen­trates that cannot be handled simply or economically by pyrometallurgy. It is probably not without significance that most recent hydrometallurgical pro­cesses for the recovery of base metals from sulfide ores are based on chloride leaching systems, and that the majority of these processes are aimed primarily at, or at least include, the production of copper. Chloride hydrometallurgy has been described as a logical choice for treating unconventional concentrates that smelters cannot readily handle, 1 and the technology is regarded as particu­larly suitable for on-site, small-tonnage refining of copper in remote areas. In view of these positive attributes, it is not unreasonable to question why chloride hydrometallurgy has so far found very limited practical application.

CHLORIDE LEACHING PROCESSES

The history of chloride leaching dates back almost a century, and it has long been recognized as a highly efficient

1991 August. JOM

process capable of producing concen­trated leach solutions. Ferric chloride and cupric chloride solutions have been the favored leachants, particularly for chalcopyrite concentrates, because of their high leaching efficiency and the fact that sulfur is liberated in the elemen­tal form:1.2

CuFeS2 + 3CuCI2 -7

4CuCI + FeCI2 + 2S (1)

CuFeS2 + 4FeCI3 -7

CuCIz + 5FeCI2 + 2S (2)

Initially, chloride-based processes found little application because of the highly corrosive nature of the solutions, but these problems have been largely overcome with the advent of modern materials of construction such as fiber­reinforced plastic, polypropylene, butyl rubber and titanium.

Over the past 20 years, research and development work on chloride-based hydrometallurgical processes have bur­geoned, and at least 12 processes are said to have progressed beyond the "labora­tory beaker" stage of evaluation. These earlier processes have been reviewed and discussed in some detail in Refer­ences 2-8. Essentially, however, they can be broken down into three main classes: • Those such as the Canmet9,10

Minemet Recherchell,lz and Broken Hill Associated Smelters (BHAS)13 processes, in which copper is finally electrowon from sulfate solution. In these processes, copper is recovered by solvent extraction using an 0-

hydroxyaryloxime reagent, fol­lowed by stripping with sulfuric acid and conventional electrowin­ning from sulfate solution, Leach solutions in these processes are generally of lower copper concen­tration and acidity or steps have to be taken to adjust and control pH.

• Those such as Cyprus Metallurgi­cal's Cymet process,14,lS which em­ploy mixed ferric chloride and cu­pric chloride leachants to produce cuprous chloride that is then iso­lated from the reaction mixture. The precipitated cuprous chloride is re­duced to metallic copper using hy­drogen in a fluidized bed reactor.

• Those processes such as Duval's copper leach, electrolysis and re­generation (CLEAR) process,1.2,S,16,17

the U.S. Bureau of Mines (USBM) process18,19 and the Dextec process20 in which copper is produced di­rectly by electrolysis. The CLEAR and USBM processes were de­veloped primarily for the treatment of chalcopyrite concentrates, the principal leachants being cupric chloride and ferric chloride, re­spectively. Both processes produce cuprous chloride solutions from which copper is electrowon in dia­phragm cells and leachant regen­eration takes place in the anode compartment. The overall cell reac­tions for the CLEAR process and the USBM process are given in Equation 3 and Equation 4, respec­tively,

2CuCI -7 Cu + CuCI2 (3)

CuCI + FeCI2 -7 Cu + FeCI3 (4)

The Dextec process involves the anodic dissolution of copper from a chalcopyrite concentrate in a brine solution in the presence of oxygen. The reaction is carried out in a di­aphragm cell and the copper is de­posited at the cathode,

A number of these processes pro­gressed well beyond the laboratory de­velopment stage and some, such as the CLEAR process, advanced to full-scale production. Like so many of the other early chloride-based processes, however, the CLEAR process was not a commer­cial success; and the 30,000 t/y experi­mental plant at Sierrita, Arizona closed in 1981 for various technical and eco­nomic reasons. S

Notably, very few of the processes outlined above permit the direct pro­duction of high-purity copper, even when applied mainly to clean chal­copyrite concentrates. In most cases, fur­ther expensive fire refining and electro­refining are necessary to produce wire bar- or cathode-grade material. For ex­ample, the CLEAR process produced only blister-grade copper and, similar to the Cymet process, contained all the silver present in the original leach solu­tion, thus necessitating further electro­refining.s

The very efficiency of chloride leach­ing brings its own problems. Many other base metals, minor metals and metal­loids which are present as reactive sul-

51

fides (e.g., Zn, Pb, Ag, As, Sb, Bi, Cd and Hg) are all leached very effectively in chloride media:

Ag2S + 2FeCl3 ~ 2AgCl + 2FeCl2 + S (5)

ZnS + 2FeCl3 ~ ZnCl2 + 2FeCl2 + S (6)

PbS + 2FeCl3 ~ PbC~ + 2FeCl2 + S (7)

This is a factor that cannot be overlooked since, without a purification stage, the presence of these metals has a very se­rious effect on the quality of the copper produced.21

Chloride-based processes that pro­duce pure copper by means of solvent extraction using o-hydroxyaryloxime reagents are constrained by the per­formance of these extraction agents.

Cu2+ (aq.) + 2RH (org.) f--)

RzCu (org.) + 2H+ (aq.) (8)

Since Equation 8 (where RH is the 0-

hydroxyaryloxime extractant) is gov­erned by hydrogen ion concentration, the practical result is that only relatively dilute copper solutions can be treated (as in the Canmet process), or careful pH control or adjustment is necessary (as in the Minemet Recherche process). This negates one of the very attractive features of chloride leaching-its ability to pro­duce very concentrated copper solutions. It is therefore clear that, while solvent extraction has a great deal to offer because high-purity copper can be produced di­rectly, the o-hydroxyaryloximes are far from being ideally suited for this task and are, at best, a compromise choice dictated by their availability.

Cu Concentrates

FeO'OH + Other Metals

Bleed to Effluent Treatment

NEW SOLVENT EXTRACTION TECHNOLOGY

Recognizing the need for an extrac­tant capable of capitalizing on the at­tractions of chloride leaching of copper concentrates, Imperial Chemical Indus­tries (lCI) (Manchester, United Kingdom) embarked on a program of research aimed at devising such a reagent. The successful outcome of this was the novel extractant DS5443,6,7,22 a commercial formulation of which is now available as Acorga™ CLX50 from ICI Specialties. This reagent is ideally suited for the extraction of copper from chloride me­dia, since the loading and stripping op­erations are governed by the con­centration of chloride ion in the aqueous phase (Equation 9, where L represents the extractant DS5443).

Cu2+ (aq.) + 2Cl- (aq.) + 2L (org.) ~ L2CuCl2 (org.) (9)

Thus, the extraction process takes place at the high chloride ion concentration encountered in chloride leach solutions, and the stripping process takes place at low chloride ion concentration. Further, Acorga CLX50 meets all the other re­quirements for a successful solvent ex­traction reagent (viz., high selectivity for copper, fast extraction and strip kinetics, good phase-disengagement properties, and high stability).

In essence, Acorga CLX50 is capable of transferring large amounts of copper with no need for pH adjustment or control and with very high selectivity over a wide range of metals and metal­loids. Thus, the reagent can produce pure cupric chloride solutions from highly

.--.S

Figure 1. The flow sheet for the Cuprex metal extraction process.

52

impure, concentrated chloride leach so­lutions. The extraction behavior of Acorga CLX50 is quite sensitive to tem­perature. Thus, extraction at ambient temperature (25°C) gives high copper recoveries, while stripping at 6Q-65°C facilitates the attainment of very concen­trated pregnant copper electrolyte so­lutions (>90 gil Cu) with a completely stripped organic phase using only two extraction and three strip stages.

NEW CHLORIDE ELECTROWINNING

TECHNOLOGY

Another development which led to improvements in chloride hydromet­allurgy is the electrowinning of copper from chloride solution in the Metclor cell, developed by Tecnicas Reunidas (Madrid, Spain). 23,24 For this cell, the pure concentrated cupric chloride electrolyte produced by Acorga CLX50 is an ideal feed.

Traditionally, copper is electrowon or electrorefined from a sulfate solution; such processes are well understood, relatively easy to carry out, and in com­mon practice worldwide. By comparison, electrowinnhtg of copper from chloride solution is not such a common practice and, though well researched, is recog­nized as carrying with it certain inherent technological difficulties. These arise mainly from the existence of two stable oxidation states of copper in chloride solution, the existence of copper in so­lution as complex anionic chloro species such as CUCl32-, the liberation of chlorine rather than oxygen at the anode, and the production of a powder or dendritic form of copper rather than smooth sheet

r--------------. Cu

Depleted Brine

Solid Residue

JOM • August 1991

15.00 125.00

r-f .-I ""- ..... t7'I 12.00 t7'1100.00 0 CIJ

:::J C 0 CIS

9.00 Q)

C)

a/A 2.2 :::J 75.00 a/A B.O ~ c-o « c c ~ 6.00 .~ 50.00 Q) a. a. a. a 0 0 u

3.00 U '25.00

0.00 -fI'----r--....--....,......---r-0.00 B.OO 16.00 24.00 32.00

Copper in Aqueous gil

O.OO--f"-----,----.-----r--~-

0.00 2.50 5.00 7.50 10.00 Copper in Organic gil

a b Figure 2. Isotherms for (a) extraction (25°C) and (b) stripping (65°C) of copper by 50% Acorga CLX50. Feed: 25 gIl Cu, 5.5 M CI. Strip: 5 gIl HC!.

cathodes at anything other than low current densities.

The Metclor cell is a two-compart­ment deSign, the cathode and anode compartments being separated by a re­inforced cation-selective ion-exchange membrane such as Dupont's Nafion™ 417. It utilizes coated, dimensionally stable anodes to facilitate chlorine evo­lution at minimum voltage and a unique design of perforated hollow titanium cathode through which catholyte is pumped so as to create high agitation and good mass transfer at the cathode surface.

THE CUPREX METAL EXTRACTION PROCESS-CORE

TECHNOLOGY

Following the highly encouraging preliminary studies conducted by ICI and T echnicas Reunidas, Nerco Minerals Company (Vancouver, Washington) be­came interested in the development of a hydrometallurgical process for the treatment of sulfidic copper ores that incorporated the two key technical ad­vances. This led initially to a small-scale pilot trial (750 glh copper) jointly oper­ated by the three companies. This small­scale trial had the objective of demon­strating the compatibility of the three main sections of the process-leaching, solvent extraction and electrowinning­and the ability to produce top quality copper directly. The outcome was suffi­ciently encouraging for the three com­panies to form a joint venture partner­ship, known as Hydrometals IV, to de­velop what is now known as the Cuprex™ metal extraction process (CMEP).

1991 August • JOM

The next stage in the development was the construction and operation o(a larger scale demonstration pilot plant (12 kg/h) to prove the technical and economic viability of the process. This objective has now been accomplished.

The CMEP flow sheet is shown in Figure 1. In the process, sulfidic ore concentrate is leached at atmospheric pressure with ferric chloride solution at about 95°C to produce a solution in which all the copper is in the divalent oxidation state (Equations 10 and 11) and reactive sulfides are converted to elemental sul­fur (Equation 12).

CuFeS2 + 4FeCl3 -7

CuCl2 + 5FeCl2 + 2S (10)

Cu2S + 4FeC13 -7

2CuCl2 + 4FeCl2 + S (11)

MilS + 2FeCl3

-7

MI!C1z + 2FeC1z + S (12)

The reaction mixture is then cooled, passed to a thickener, and filtered. The leach residue, which filters easily, con­sists of gangue, pyrite and up to 65% sulfur, depending upon the grade of concentrate used. It also contains any gold or molybdenite present in the original ore.

The pregnant leach solution is cooled to 25°C, and any sulfate introduced with the concentrate is removed by the con­trolled addition of calcium chloride to precipitate gypsum. The clarified preg­nant liquor containing copper, iron and minor impurities (mainly zinc, lead and silver) and 5.5 M to 6 M chloride ion is sent to the extraction stage of the sol vent extraction circuit. In this stage, it is con­tacted at ambient temperature with a

kerosene solution of Acorga CLX50, and the copper is transferred selectively to the organic phase. The loaded organic solution is scrubbed with spent anolyte to remove traces of impurities and is then stripped in accordance with Equa­tion 13 by contacting with water at 65°C to produce an aqueous solution con­taining over 100 gil copper.

L2CuC1z (org.) -4

2L (org.) + Cu2+ (aq.) + 2Cl- (aq.) (13)

Typical isotherms and McCabe-Thiele diagrams for the extraction and stripping of copper with Acorga CLX50 are shown in Figure 2.

The chloride ion content of the aque­ous extract is increased by the addition of sodium chloride to enhance its con­ductivity and to minimize the possibil­ity of precipitation of cuprous chloride. It is then sent to the electrolysis section as catholyte.

The mode of operation of the Metclor cell and the way in which it is integrated with the appropriate sections of the sol­vent extraction circuit are diagramed in Figure 3. Copper deposition takes place in the cathode compartment and the electronic balance in the catholyte is maintained by transfer of sodium ions from the anolyte through the ion-ex­change membrane. The copper is re­moved continuously from the cells, washed, and processed to an article of commerce. The spent catholyte, which contains copper in the cuprous and cu­pric oxidation states and sodium chloride (corresponding to that added to the aqueous extract and the deposited cop­per), is sent to the reforming stage.

In the reforming stage, monovalent

53

FEED ---,

EXTRACTION

RAFFINATE TO----' REGENERATION

Solvent

NaCI

H20

NaCI Solution

CuCI2 + NaCI

Figure 3. The simplified flow circuit for the Metclor cell.

copper in the spent catholyte is oxidized to the divalent oxidation state using some of the chlorine produced in the anode compartment of the cell. The reformed spent catholyte then passes to the deple­tion stage of the solvent extraction circuit, where it is contacted with organic solvent from the stripping stage.

In two stages of depletion carried out at a high organic-to-aqueous phase ratio (8:1), the copper concentration in the reformed spent catholyte is reduced to approximately 0.1 gil. The copper-de­pleted aqueous solution is fed to the electrolysis cell as anolyte. The organic solvent phase, now containing a small amount of copper, is advanced to the extraction stage of the solvent extraction circuit.

Silver present in the concentrate is leached and reports in the raffinate from the solvent extraction stage. Since the copper concentration in this solution is very low, silver may be recovered by cementation. Excess iron present in the leach raffinate resulting from leaching of chalcopyrite is removed as goethite (FeO·OH) in a pressure oxidation stage that simultaneously regenerates part of the leachant (Equation 14). The remain­der of the leachant is regenerated using chlorine from the electrolysis stage (Equation 15).

6FeCl2 + 1.502 + Hp ~ 2FeO·OH + 4FeCl3 (14)

2FeCl2 + Cl2 ~ 2FeC13

(15)

Copper in the scrubbing and washing liquors may be precipitated as copper sulfide and returned to the leaching stage. Other metal cations may be precipitated by a combination of liming and sulfide treatment to produce environmentally acceptable solid and liquid effluents.

54

PILOT TESTING AND PROCESS OPTIMIZATION

All of the steps comprising the core technology of CMEP-namely leaching, solvent extraction, electrowinning, leachant regeneration and treatment of liquid effluents-have been tested in a continuous demonstration pilot plant at the Tecnicas Reunidas Research Center in Torrejon, Spain.

The plant, with the capacity to process one tonne of concentrate per day, was operated round the clock during a series of trials, each of which lasted up to three weeks. The plant was highly automated and contained as much on-line instru­mentation as would be required in a commercial scale plant. All instrument readings were fed to a master control computer. A second computer was used for continuous logging of data.

The plant employed a single-stage leaching operation comprising five re­actors arranged in series. The pilot op­erations were carried out using a south­western U.s. chalcopyrite concentrate of composition shown in Table 1.

Copper leach efficiencies of greater than 96-97% were obtained with a resi­dence time of 9-10 hours at 95-100DC, leading to an overall copper recovery in the process of greater than 96%. Flocculant was added to the pulp from the leaching operation, which separated readily in the thickener. The underflow from the thickener passed to a drum filter where final separation and wash­ing of the leach residue was accom­plished without problems.

In the pilot plant operations the preg­nant leach solution was cooled to 25°C, and calcium chloride was added in a stirred vessel to precipitate sulfate intro­duced with the concentrate as gypsum.

DEPLETED BRINE

The solution then passed to a second preCipitation vessel and on to a thick­ener, from which some of the underflow was returned to the first stirred vessel to seed the gypsum precipitation. The clari­fied pregnant leach solution was for­warded to solvent extraction containing approximately 25 gil copper, 120 gil iron and 6 M in chloride ion.

The solvent extraction circuit com­prised two extraction, two scrub, four strip and two ~epletion stages and em­ployed a 50 vol. % solution of Acorga CLXSO in Escaid 1 00. Extraction raffinates containing less than 0.5 gil copper were consistently obtained, and the use of four strip stages produced advanced aqueous electrolytes containing up to 110 gil copper. The solvent extraction circuit proved to be robust and rela­tively insensitive to fluctuations in con­ditions. Neither decomposition nor de­terioration in the performance of the extraction reagent was detected during the entire period of operations.

Table I. Composition of Concentrate Used in Demonstration Pilot Plant Runs

Element Cu Fe Zn Pb As Sb Bi Mo Ag Hg Ca Mg SiOz S (total) 504 Moisture

Amount

27.5wt.% 26.1 wt.% 0.26wt.% 0.08wt.% 235 ppm 110ppm 25 ppm

140 ppm 90 ppm 10 ppm 0.5 wt.%

0.12 wt.% 12.0wt.% 28.5wt.% 3.0wt.% 1.8 wt.%

JOM • August 1991

Electrowinning was carried out in three full-size cells with some oppor­tunity taken to experiment with slight design variations. The cells were of a multiple two-compartment design, the anodes and cathodes being separated by a reinforced, cation-selective, ion-ex­change membrane such as Nafion 417. Cathodes were titanium and anodes were coated titanium rods.

Electrowinning operated well, with copper being electrowon at a current efficiency greater than 94% and current density of 1.5 kA/m2. Mean power con­sumption in the cells during the demon­stration plant trials was 2.66 kWh per kilogram of copper produced.

No problems were encountered in the depletion and regeneration stages, and excess iron was successfully removed from the extraction raffinate as a filter­able goethite precipitate. Similarly, no problems were encountered in liming and sulfide precipitation of metals from effluent streams.

The pilot trials achieved the initial objective of demonstrating the technical viability of the process and its ability to produce cathode-grade copper. A typi­cal copper analysis, produced under normal operating conditions but fol­lowing copper powder washing and drying, is shown in Table II.

In summary, the pilot trial demon­strated the mutual compatibility of the four main sections of CMEP: leaching, solvent extraction, electrowinning and leachant regeneration. Inevitably, prob­lems were encountered, but satisfactory splutions were found and implemented during the course of the demonstration plant operations. Possibly the most important result to emerge from the pi­lot operation was the ability of CMEP to produce copper of a quality matching that of the highest standards in the in­dustry when operating under optimum conditions.

Table II. Copper Product Quality Under Normal Operating Conditions

Impurity Element Content (ppm)*

Al Sb As Bi Cd Cr Co Fe Pb Mg Mn Ni Se Si Ag Te Sn Zn

0.42 3.7 0.3 ND 0.05 ND 0.7 3.2 ND 3.7

0.36 ND ND ND 0.5 0.5 ND ND

II- Spark emission analysis. NO-Not detected.

1991 August • JOM

ASTM Standard B115 (ppm)

5 5 2

12 8

8 4

25 2 10

THE ENHANCEMENT PROGRAM

As indicated previously, the main emphasis of the pilot plant runs was on a successful demonstration of the core technology of the process. Supplemen­tary processes to produce a copper article of commerce and to recover valuable by­products from copper concentrates were not fully developed at this time. Recog­nizing that a fully integrated process had to be demonstrated technically and environmentally, and that capital and operating costs for the integrated process had to be developed, the Hydrometals joint venture has since undertaken an enhancement program. Good progress is being made on the enhancement pro­gram, and final technical results and cost estimates for the integrated CMEP are expected by the end of 1991. The main thrusts of the work are as follows:

Recovery of Sulfur and By-Products

Processes are being developed by a Canadian technology vendor for the re­covery of sulfur, molybdenite and unleached chalcopyrite from the leach residue by a combination of flotation and melt filtration, and for the recovery of gold by cyanidation.

Copper Powder Processing

This work is aimed at the production of an article of commerce from the electrowon copper powder. Washing, drying, briquetting, melting and direct conversion of copper powder to copper wire and copper rod are being evalua ted by several process development con­tractors and equipment vendors in the United States and the United Kingdom. The key challenge is to maintain the cathode quality of the copper through to the final article of commerce.

Silver Recovery

Tecnicas Reunidas has developed a cementation procedure for recovery of silver from solvent extraction raffinate with iron powder. This is now being integrated into the process flow sheet.

Environmental Assessments

Process residues such as goethite and sludges from lime precipitation have been subjected to toxicity tests at an en­vironmental laboratory in the United States. They have been found to meet u.s. Resource Conservation and Recov­ery Act criteria and are not considered hazardous wastes. The liquid effluents are being evaluated to confirm their ad­herence to U.S. standards.

Technology Integration and Cost Estimation

The peripheral technologies and the recovery and recycle of salt from the depleted brine are being integrated with

the core technology by a Canadian engi­neering contractor. The capital and op­erating costs for the integrated process are being estimated for five locations worldwide-the southwestern United States, the Iberian Peninsula, western Canada, Chile and Australia.

On the basis of data accumulated dur­ing the demonstration plant trials, the estimates shown in Tables III and IV have been made for units of consumption of reagents and utilities for the particu­lar ore concentrate used. The particular case study was based on recovery of salt in the process by forced steam evapora­tion. (In the southwestern United States and other warm arid locations, solar evaporation may be viable and less ex­pensive.) The consumptions listed may vary, depending upon the mineralogy of the particular ore concentrate, though they are not expected to vary widely. Precise estimates can be made on the basis of laboratory-scale leaching trials and a computed mass balance for the process circuit. Clearly, actual operating costs will be very dependent on local factors, particularly the cost and avail­ability of reagents, utilities and man­power. Table V gives estimated staffing levels for a 30,000 t/y CMEP copper production facility.

FEATURES OF CMEP

Long operating experience and analy­sis of the pilot-plant data leads to the conclusion that the technical viability of

Table III. Reagent Consumption

Reagent

Chlorine HCl (33%) NaCl CaCl2 Ca(OH)2 NaHS Oxygen Scrap Iron Flocculant Acorga CLX50 Kerosene

Consumption (per tonne Cu)

0.20 tonnes 0.608 tonnes 0.203 tonnes 0.072 tonnes 0.265 tonnes 0.031 tonnes 0.329 tonnes 0.118 tonnes

0.242 kg 1.00 kg 5.00 kg

Table IV. Utilities Consumption

Utility

Power Steam Process Water Cooling Water

Consumption (per tonne Cu)

4.00MWh 7.41 tonnes

33m3

321 m3

Table V. Estimated Labor Requirements

Salaried Personnel

Senior Mgt. and Admin. Laboratory Staff Operations /Engineers

Hourly Personnel

Foremen/Lead Operators Operators Maintenance/Electricians

Number

8 8 7

6 28 29

55

CMEP has been clearly demonstrated; indeed, it may prove to be particularly attractive in a number of situations. The particularly attractive features may be classified as both physical and chemical and are listed below.

Physical Features

• Lower capital costs than a smelter and refinery of eqUivalent capacity.

• Economically viable for both large and small operations, down to 10,000-30,000 t/y.

• Permits mine site production of copper in small operations in re­mote locations. This in turn elimi­nates concentrate shipping, cuts inventory costs, and gives mine operators the option of marketing their own copper with added value for their final product.

• Modular construction is possible, allowing design flexibility and plant portability.

Chemical Features

• Efficient leaching reactions give high copper recovery at moderate tem­peratures and pressures.

• The process is environmentally clean since elemental sulfur is pro­duced rather than sulfur dioxide.

• Production and marketing of sul­furic acid is avoided.

• Pyrite, gold and molybdenite are not leached.

• The process is capable of treating many feed materials, including "dirty" and low-grade concentrates. This reduces penalties for undesir­ables in concentrates, eliminates the need for cleaner flotation, and gives better metal recoveries.

• The process can be extended to in­clude most major metals found in complex, copper-bearing deposits.

ACKNOWLEDGEMENTS The authors express their appreciation for

the contributions and help of numerous col­leagues in their respective organizations and in organizations assisting with work on the enhancement program in bringing about the successful demonstration of the technical viability and evaluating the economics of the Cuprex metal extraction process, and in en­abling this paper to be written. Thanks are also due to the managements of Imperial Chemical Industries, Tecnicas Reunidas and Nerco Minerals Company for their permis­sion to present this paper.

References 1. D.C McLean, "Chloride Leaching of Copper Concen­trates, Practical Operational Aspects," presented at the AIME Annual Meeting, Dallas, TX (February 14-18, 1982). 2. E. Peters, N Application of Chloride Metallurgy to Treat­ment of Sulphide Minerals," Chloride Metallurgy (Brussels: Benelux Metallurgie, 1977), p. 1. 3. K.J. Edmiston, "An Update on Chloride Hydrometal­lurgical Processes for Sulphide Concentrates," SME T echni­cal Paper 84-114 (Golden, CO: SME, 1984). 4.0.5. Flett, J. Melling and R. Derry, "Chloride Metallurgy for the Treatment of Complex Sulphide Ores," report LR461 (ME), (Stevenage, UK: Warren Spring Laboratory, 1983). 5. A.W. Fletcher, "Future Potential for Chloride Metallurgy," paper presented at SME Annual Meeting, New Orleans, LA (March 3-5, 1986). 6. R Price, P.M. Quan and B. Townson, "Novel Solvent Extractants for Copper from Chloride Media-Their Appli­cation in the Processing of Complex Base Metal Concen­trates," presented at the Joint EEC-Canada Seminar on the Treatment of Complex Minerals, Ottawa, Canada (October 12-14,1982). 7. RF. Dalton et aI., "Novel Solvent Extractants for Recovery of Copper from Chloride Leach Solutions Derived from Sulphide Ores," Reagents in the Minerals Industry (London: IMM, 1984), p. 181. 8. R.F. Dalton et al, "The CUPREX Process-A New Chloride Based Hydrometallurgical Process for the Recovery of Cop­per fromSulphidicOres," Separation Proc. in Hydrometall., ed. G.A. Davies (London: Ellis Horwood, 1987), pp. 466-476. 9. G.M. Ritcey, B.H. LucasandKT. Price, "Evaluation and Se­lection of Extractants for the Separation of Copper and Zinc from Chloride Leach Liquor, Hydrometallurgy (1982), p. 197. 10. G.M. Ritcey, B.H. Lucas and K T. Price, "Extraction of Copper and Zinc from Chloride Leach Liquors Resulting from Chlorination Roast Leach of Fine-Grained Sulphides," Proc. ISEC'SO, vol. 3, (Liege, Belgium: Association des In­genieurs Sortis de I'Universite de Liege, 1980), paper 80-71. 11. J,M. Demarthe, L. Gandon and A. Georgeaux, "A New Hydrometallurgical Process for Copper," Extractive Metal­lurgy of Copper, ed. J.C Yannopoulus and J.C Agarwal (Warrendale, PA: TMS, 1976), p. 825. 12. J.M. Oemarthe,A. Sonntag and A. Georgeaux, U.S. Patent no. 4,023,964 (1977). 13. N.E. Meadows and M. Valenti, 'The BHASCopper Lead Matte Treatment Plant," Proc. Non Ferrous Smelting Sympo-

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are you planning a move? To notify both TMS and ASM International of your new address, just telephone (216) 338-5151 and ask for the Member Service Center.

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siurn (Victoria, Australia: AusIMM, 1989), p. 153. 14. J.H. McNamara et aI., "A Hydrometallurgical Process for Copper," paper presented at the AIME Annual Meeting, Denver, CO (February 26-March 2,1978). 15. W.C Hazen, for Cyprus Metallurgical Process Corpo­ration, USA. Canadian Patents nos. 1,012,089 (1977) and 1,028,651 (1978). 16. F.W. Schweitzer and R Livingstone, "Duval's CLEAR Hydrometallurgical Process," paper presented at the AlME Annual Meeting, Dallas, TX (February 14-18, 1982). 17. C.E. Atwood and CH. Curtis for Duval Corporation, U.S. Patents nos. 3,785,944 (1974) and 3,879,272 (1975). 18. TA. Phillips, "Economic Evaluation of a Process for Ferric Chloride Leaching of Chalcopyrite Concentrate," Rl 7474 (Washington, D.C.: U.S. Bureau of Mines, 1971). 19. F.P. Haver, RD. Baker and M.M. Wong, "Improvements in Ferric Chloride Leaching of Chalcopyrite Concentrates," Rl8007 (Washington, D.C: U.S. Bureau of Mines, 1975). 20. P.K. Everett, 'The DEXTEC Copper Process," Ex/raction Metallurgy'S1 (London, U.K: IMM, 1981), p. 149. 21. E. Anderson et aI., "Production of Base Metals from ComplexSulphideConcentratesbytheFerricChlorideRoute ina Small Continuous Pilot Plant," Complex Su/phideOres,ed. M.J. Jones (London, U.K: IMM, 1980), pp. 186-192. 22. RF. Dalton, R. Price and P.M. Quan, "Novel Solvent Extractants for Chloride Leach Systems," Proc. In/. Solvent Extraction Conference, [SEC 'S3, Denver, CO (1983), p. 189. 23. E.D. Nogueira, "Recent Advances in the Development of Hydrometallurgical Processes for the Treatment of Base Metal Sulphides," Int. Conf. on Mineral Science Technology (South Africa: M1NTEK, 1984). 24. E. Hermana Tezanos, U.s. Patent no. 4,776,941 (1988).

ABOUT THE AUTHORS ____ _

R.F. Dalton received his Ph.D. in chemisty from the University of Manchester, United Kingdom, in 1969. He is currently senior sci­entist at ICI Specialties Research Centre.

G. Diaz received his graduate degree in in­dustrial chemistry from the University of Valladolid, Spain, in 1975. He is currently director of the R&D Center at Technicas Reunidas.

R. Price received his Ph.D. in chemistry from the University of Nottingham in 1960. He is currently a consultant at Ray Price Consult­ants, Shropshire, United Kingdom. Dr. Price is also a member of TMS.

A.D. Zunkel received his D.Sc. in metal­lurgical engineering from the Colorado School of Mines in 1967. He is currently president of A.D. Zunkel Consultants. Dr. Zunkel is also a past president of TMS.

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JOM • August 1991