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U.S. Bureau of Mines Spol:ane Research CentQr E ~.~ u ", vl:J ",';'11 Ibe. Sppi,

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Recovery of From Spent Leach Solutions-Improved Elution and Impurity Removal Techniques, With Revised Process Economics

By P. G. Bennett and T. H. Jeffers

BUREAU OF MINES '

UNITED STATES DEPARTMENT OF THE INTERIOR Report of Investigations 9190

Recovery of Cobalt From Spent Copper Leach Solutions-Improved Elution and Impurity Removal Techniques, With Revised Process Economics

By P. G. Bennett and T. H. Jeffers

UNITED STATES DEPARTMENT OF THE INTERIOR Donald Paul Hodel, Secretary

BUREAU OF MINES T S Ary, Director Library of Congress Cataloging in Publication Data

Bennett, P. G. RecovelY of cobalt from spent copper leach solutions.

(Bureau of Mines Report of investigations ; 9190) I

Bibliography: p. 9.

Supt. of Docs. no.: I 28.23:9190.

1. Cobalt-. 2. . 3. Copper. 1. Jeffers, T. H. (Thomas 11.). II. Title. III. Sel'les: Report of investigations (Ullited States. Bureau of Mines) ; 9190.

TN23.U43 [TN799.C6] 622 S [669'.733J 88-600153 CONTENTS

Abstract...... 1 Introduction ...... • ...... 2 Elution studies ...... • ...... 2 Fixed-bed elution ...... 2 Pachuca reactor description ...... 3 Pachuca reactor operation ...... 3 Pachuca elution test conditions ...... r. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 4 Effect of contact time ...... 4 Effect of A-R ratio ...... 4 Effect of eluant concentration ...... 5 Complete Pachuca acid elution procedure ...... • ...... 5 Effect of ammonium eluant concentration ...... 5 SllD'!m?ry of Pachuca reactor operating procedure ...... 6 ReSin mventory ...... • ...... 6

Iron studies t...... ",.,.,,,,,...., , .. .. , • .. .. '" .. .. • • • J f .. .. " .. • • • .. • .. • .. .. • .. , .. " ...... • .. • .. .. " ...... • • • , • .. • " .. 6 Process econolnics ...... 7 Capital costs ...... 7 Operating costs ...... 7 Summary and conclusions ...... 8 References ...... 9 ILLUSTRATIONS

1. Pachuca reactor ...... 0 • • • • • 3 2. Cobalt extraction using as-received and aged solution ...... 7 TABLES

1. Effect of process variables on cobalt elution ...... •...... 4 2. and copper elution using two 5-min 4N NH40H contacts with a 2O-pct bleed stream ...... 5 3. Estimated capital costs ...... • ...... 7 4. Estimated alffiual operating costs ...... 8 " ., .... ", .j""", , .. ,

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

ft foot L liter ft3 cubic foot L/min liter per minute g gram Ib pound g/L gram per liter min minute gal gallon Mgal thousand gallons gpm gallon per minute MMBtu million British thermal units gpm/ft2 gallon per minute per square foot pct percent h hour ppm part per million in inch st short ton kW-h kilowatt hour yr year RECOVERY OF COBALT FROM SPENT COPPER LEACH SOLUTIONS-IMPROVED ELUTION AND IMPURITY REMOVAL TECHNIQUES, WITH REVISED PROCESS ECONOMICS

By P. G. Bennett1 and T. H. Jeffers2

ABSTRACT

The Bureau of Mines developed a process using ion exchange to recover cobalt from spent copper leach solutions. A preliminary economic evaluation of the process indicated that about one-third of the capital cost was attributed to the total resin inventory, and one-third of the operating cost was required for reagents to remove from the ion-exchange eluates. An agitated Pachuca elution system was investigated in place of a fIxed-bed elution system. The Pachuca system reduced the resin inventory by 27 pet when compared with the fiXed-bed elution system. Processing fresh spent copper leach solution reduced the resin inventory by 20 pct and resin iron loading by 80 pct. Reagent requirements for removing iron from the eluates were decreased because less iron was extracted. The Pachuca system, along with processing fresh spent copper leach solution, reduced the total resin inventory by 47 pct. A revised cost evaluation of the cobalt recovery process was obtained to determine the effects of these process modifIcations. The estimated total capital cost for a plant processing 10,000 gpm of spent copper leach solution containing 26 ppm Co was $23.1 million. With credits for nickel, , and copper byproducts, the estimated net operating cost was $5.10jlb of cobalt.

lChemical engineer. 2Supelvis01Y ehemical engineer. Salt Lake City Research Center, Bureau of Mines, Salt Lake City, UT. INTRODUCTION

The Bureau of Mines developed a process using ion included resin in the multiple-compartment ion-exchange exchange to extract cobalt from domestic spent copper (MCIX) extraction column and resin in the elution circuit. leach solutions (1-J).3 These solutions, which are Fixed-bed elution was utilized in earlier test work (2), and produced by heap or dump leaching of low-grade copper the preliminary cost evaluation was based on this elution with dilute , contain copper, cobalt, mode. Elution time was an important factor in the resin nickel, iron, zinc, and aluminum. Copper is generally inventory and associated costs. Reduced elution times removed from the solutions using cementation on scrap were necessary to minimize the elution circuit resin iron. Although the spent leach solutions typically contain inventory. Thus, several alternative elution procedures only 15 to 30 ppm Co, five domestic resources have been were evaluated in the laboratory. Those investigated identified with combined potential cobalt recoveries in included (1) fluidized-bed elution, (2) continuous fixed-bed excess of 2 million lb annually, or approximately 20 pct of elution, (3) stirred reactor elution, and (4) Pachuca air-lift the annual U.S. cobalt consumption. The United States elution. currently imports over 95 pct of its cobalt supply, much of The Pachuca reactor demonstrated the greatest it from Africa (:1). potential for reducing the elution time and was thus The cobalt recovery process consists of four major unit chosen for further study. Although Pachuca reactors have operations: (1) ion exchange (loading and elution) to been used for leaching gold (~-Q) and uranium ores (l-B), extract and concentrate the cobalt, (2) solvent extraction an extensive literature search did not indicate that they to remove coextracted impurities from the ion-exchange have been used for eluting ion-exchange resins. eluates, (3) a second solvent,· extraction operation to Reagent expenses fol' the removal of il'On from MCIX separate the cobalt and nickel and concentrate the cobalt, column eluates represented a significant cost of the cobalt and (4) cobalt to produce a final product. recovery operation. The resin used in this investigation, A preliminary economic evaluation of the cobalt while coextracting iron, had a higher afftnity for ferric than recovery process was prepared by the Bureau's Process ferrous iron. Eluates collected from the elution circuit Evaluation Group. The estimated capital cost for a plant contained about 6 g of ferric iron per liter of wet-settled processing 10,000 gpm of feed solution containing 26 ppm resin (WSR), and were processed in a solvent-extraction Co was $29.9 million. This plant would produce about circuit using di(2-ethylhexyl) phosphoric acid (DEHPA). 1 million Ib of cobalt annually at an operating cost of Sodium was used to strip iron from the $17.58/Ib of cobalt produced. Estimated byproduct credits DEHPA, and dextl'Ose chelated the iron and prevented for nickel carbonate, zinc oxide, copper-niekel residues, iron hydroxide precipitation. Although the DEHPA circuit and cobalt-magnesium carbonate offset much of the effectively removed the iron from the eluates, each gram operating cost, yielding a net operating cost of $9.36jlb of of ferric iron stripped required 15.9 g Na2C03 and 0.7 g cobalt. dextrose. Process modifications using fresh cementation Two m~jor contributors to the process costs were plant effluent were therefore investigated to determine if identified. About one-third of the capital cost was lower ferric iron loadings in the MCIX column could be attributed to the initial resin inventory, and one-third of achieved; thus, reducing the and the operating cost resulted from reagent requirements for dextrose reagent costs associated with iron removal from removing iron from the ion-exchange column eluates. The pl'Oduct eluates. resin inventory required for the cobalt recovery process

ELUTION STUDIES

FIXED-BED ELUTION 2. Two 20-min contacts with a recycled 30-g/L H2S04 eluant to elute a portion of the cobalt and nickel and a In earlier work G~), the fixed-bed elution procedure portion of the iron, zinc, and aluminum impurities. effectively resulted in a barren resin that was returned to 3. One 20-min contact with a fresh 30-g/L H2S04 eluant the MCIX column. The elution procedure consisted of to elute the remaining cobalt, the remainder of the iron, zinc, and aluminum impurities, and a portion of the nickel. 1. 011e 20-min contact with pH 3.0 wash water to 4. One 20-min contact with fresh water to remove remove a portion of the iron, zinc, and aluminum residual H2S04, impurities. 5. Three 20-min contacts with a recycled 3.5N NH40H eluant to elute copper and the remaining nickel.

VU11deJrlin,~d numbers in parentheses refer to items in the list of references at the end of this report. 3

6. One 15-min contact with fresh water to remove tube. Pressurized air was used to move the residual NH40H. loaded resin up through the center draft tube. Two perfo­ rated polyethylene disks were placed inside the Pachuca A total time of 180 min was required for complete resin reactor to center the draft tube in the reactor vessel. elution. One hundred seventy-five minutes was needed Approximately 5 in above the top of the center draft tube, for contacting the resin with the various eluants, and within the reactor, was a 3/8-in-ID by 27-in-high stainless approximately 5 min was required for resin transfer to and stool tube with three 1/8-in-OD by 6-in-high welded from the fixed-bed column. The elution time was based stainless steel support rods used to connect the upper and on an eluant flow rate of 1 gpm/ft2. lower portions of the draft tube. The openings between the rods allowed for resin-eluant overflow and circulation. PACHUCA REACTOR DESCRIPTION The upper section of the draft tube extended 4-1/2 in above the top of the reactor. An adjustable collar was A Pachuca reactor was designed, constructed, and permanently attached to the top of this section to prevent tested for eluting loaded resin from the 2-in-diam MCIX movement of the draft tube during operation. eolumn. The Pachuca reactor is illustrated in figure 1. A threaded 5-in-OD by 5-in-high polyethylene cap was The body of the reactor vessel was fabricated from a attached to the bottom of the Pachuca reactor. The cap 2-1/2-in-ID by 6-ft-high polymethylmethacrylate tube. The was fabricated with a 45° sloping floor that led to three center draft tube consisted of a 3/8-in-ID by 43-in-high 3/8-in-diam openings allowing for the air intake, resin drainage, and eluate drainage. The eluate drain line was fitted with a screen inside the cap to prevent the discharge of resin from the reaetor with the eluate solution.

Vacuum line PACHUCA REACTOR OPERATION

Eluant inlet During operation of the Paehuca reactor, loaded resin, discharged from the MCIX column, was rinsed with fresh water to remove entrained feed solution. The resin-rinse water slurry was then transferred to the Pachuca reactor. The eluate drainline valve was opened, and the rinse water was removed from the vessel. The drainline was then Rubber stopper closed, the appropriate amount of eluant was pumped into the reaetor, and airflow for agitation was initiated. Operation of the Pachuca was a batch operation and -2t-in-IO by required the brief application of vacuum through the draft 72-in-high tube to initiate resin circulation. An airflow rate of column 0.08 L/min was required for minimum resin circulation, while an airflow of 0.9 L/min or greater was needed for Perforated disk complete resin agitation. All tests were performed at an airflow rate of 1.3 L/min. Batch elution in the Pachuca reactor consisted of pumping fresh eluant to the reactor and contacting with 3 . b a-m- 10 y the resin for a specified amount of time. Upon completion 43-in-high of an eluant contact, the intake air was discontinued, and center draft vacuum was applied to the eluate line at the bottom of the tube reactor to assist ill draining the metal-rich eluate from the reactor. Fresh eluant was then pumped into the reactor, and the elution procedure was repeated. The complete Pachuca elution procedure, determined from preliminary tests, consisted of the following stcps:

1. One contact with an H2S04 eluant wash to remove a portion of the iron, zinc, and aluminum impurities. Cobalt losses were minimal. 2. Two contacts with an H2S04 eluant to elute cobalt, Resin outlet the remaining iron, zinc, and aluminum, and part of the -Air inlet nickel. 3. One contact with fresh water to remove residual FIGURE 1.-Pachuca reactor. H2S04, 4

TABLE 1. - Effect of process variables on cobalt elution 4. Two contacts with an NH40H eluant to clute copper and the remaining nickel. A·A Contact Total Co eluted, pet, 5. One contact with fresh water to remove residual ratio time, min at H2S04 concentration of- NH40H. 30 giL 40 PACHUCA REACTOR 2 C Barren resin was drained from the reactor and returned 1: 1 ... 5 35 62 78 to the MCIX column. Samples of the barren resin were 10 38 68 88 15 36 65 90 taken after each completed elution and thoroughly stripped 20 41 64 93 of any remaining metal values to monitor the progress of the elution and provide data for comparison with previous 2:1 ... 5 71 95 96 96 ftxed-bed elution procedures. 10 75 93 97 98 15 76 94 97 97 20 77 94 98 98 PACHUCA ELUTION TEST CONDITIONS 3:1 ... 5 88 94 98 96 Loaded resin discharged from the MCIX column was 10 91 94 98 98 15 91 93 97 98 used for all elution testing in the Pachuca reactor (;2). The 20 89 96 96 loaded resin contained, in grams per liter of WSR, 0.78 Co, 1.40 Ni, 2.74 Cu, 6.33 Fe, 5.0 Zn, and 0.15 AI. 3:1 ... 15 81 NO 20 96 96 NO NO The variables investigated were (1) resin-eluant contact NO Not determined. time, (2) aqueous-to-resin (A-R) ratio, and (3) eluant concentration. The most signiftcant information from this research was Preliminary results indicated that a minimum sulfuric obtained when comparing the contact time required for the acid concentration of 30 giL was required to attain fLXed~bed elution with the Pachuca reactor elution. The reasonable cobalt elution. Therefore, test work was fLXed-bed elution results in table 1 show that three IS-min performed to determine the effects of acid concentrations contacts using 30- and 4O-g/L H2S04 eluted only 66 and of 30 giL H2S04 or greater on cobalt elution. 81 pct of the cobalt, respectively, while three 20-min Two-contact acid elution tests were conducted in the contacts using 30- or 4O-g/L HJS04 eluted 96 pct of the Pachuca reactor with 30-, 40-, 45-, and 50-giL H2S04 at cobalt. Similar results were obtained with the Pachuca A-R ratios of 1:1, 2:1, and 3:1. Eluate samples reactor at several operating conditions, and only two 5-min representing 0.5 pct of the total eluant volume we~e contacts were required. For example, 98 pct of the cobalt withdrawn from the reactor at 5-, 10-, 15-, and 20-mm was eluted llsing two 5-min contacts with 45 giL H2S04 at intervals to monitor the progress of the elution. Two an A-R ratio of 3:1. The reduced contact time achieved separate contacts were necessary because acid was with the Pachuca reactor will reduce the total resin neutralized during the elution, and the remaining acid inventory because the resin will spend less time in the concentration was insufftcient to effectively elute the metal elution circuit and more time in the MCIX column values from the resin. The ftrst acid contact was a extracting metal values. recycled solution collected as the eluate from a previous contact. The recycled eluant acid concentration was EFFECT OF A-R RATIO adjusted with sulfuric acid to the corresponding fresh acid eluant concentration by comparing the pH's of the two The data in table 1 also show the effect of A-R ratios solutions. After the initial contact with recycled eluant, the on the cobalt elution. When the higher A-R ratios were resin was eluted with a fresh acid eluant contact. Table 1 used cobalt elution increased. Overall, 94 pct or greater presents the cobalt eluted when using the Pachuca reactor of the cobalt was eluted with an A-R ratio of 2:1 or 3:1 or the fLXed-bed column at various operating conditions. when using 40-, 45-, or 50-giL H2S04, However, Lhe cobalt concentration in the product eluates decreased with EFFECT OF CONTACT TIME increased A-R ratio. This was due to dilution associated with the greater volume of eluant. For example, after one One of the objectives of this work was to determine the elution using two 5-min contacts with a 4O-g/L H2S04 minimum contact time required to effectively elute the eluant, 62, 95, and 94 pct of the cobalt was eluted at A-R cobalt. Results from table 1 show that cobalt elution in ratios of 1:1, 2:1, and 3:1, respectively, while product the Pachuca reactor did not appreciably increase with an eluates collected from the ftrst acid contact, contained increase in contact time as the elution approached the 0.42, 0.38, and 0.35 giL Co, respectively. Eluates collected target range of 95 to 100 pct. For example, with the 40- from the test series with the 2:1 A·R ratio contained 95 pct giL H2S04 eluant at an A-R ratio of 2:~, cobal~ elution of the cobalt and were similar to the results obtained from varied from 93 to 95 pct as the contact tIme vaned from the test series using the 3:1 A-R ratio. The A-R ratio of 5 to 20 min. The elution rate for other metals on the resin 2:1 was the preferred A-R ratio because the acid require­ such as nickel iron and zinc showed similar trends. Thus, ment was 33 pct less than the acid required with the 3:1 5 min appear~d to 'be sufftcient contact time to effectively A-R ratio. elute the loaded resin. 5

EFFECT OF ACID ELUANT CONCENTRATION to a strong acid elution for each cycle. This contact eluted approximately 90 pct of the nickel and prevented the The results presented in table 1 also show the effect of buildup of nickel on the resin. Approximately 50 pct of the sulfuric acid eluant concentrations on cobalt elution. this eluate was used to adjust the recycled solutions to 40- In general, as the acid concentration increased, the amount giL H~SO 4 for the next series of four elutions. The of cobalt eluted from the resin also increased. Cobalt remainmg eluate, along with fresh 250-g/L H2S04, was elution was greater than 95 pct with two 5-min contacts at used as the next 250-g/L H2S04 eluant contact. The 250- an A-R ratio of 2:1 and acid concentrations of 4O-g/L giL H2S04 eluate used to adjust the recycled acid eluant H2S04 or higher. The 4O-g/L H2S04 eluant required 11.1 to 4O-g/L H2S04 resulted in excess eluant when main­ and 20.0 pct less H2S04 than the 45- and 50-giL H2S04 taining an A-R ratio of 2:1. The excess AO-g/L H2S04 eluants, respectively. eluant was removed from the system, blended with fresh Although the 4O-g/L H2S04 eluant used in the Pachuca 4O-g/L H2S04, and used for the first elution contact in the system effectively eluted the resin, the acid requirements next series of four elutions. were approximately twice the acid requirements of the fIXed-bed elution system using 30-g/L H2S04, Thus, when EFFECT OF AMMONIUM HYDROXIDE compared with the fIXed-bed elution system, the increased ELUANT CONCENTRATION acid requirement in the Pachuca system will result in a higher annual acid operating cost. However, the Pachuca Following the acid elution, the resin was contacted with system will reduce the resin inventory, a major capital cost. ammonium hydroxide to eluate the copper and the remaining nickel. Earlier elution test results indicated a COMPLETE PACHUCA ACID minimum concentration of 4N NH40H was sufficient to ELUTION PROCEDURE elute essentially all of the copper and a portion of the remaining nickel. Twenty percent of the NH40H eluant Preliminary test work indicated that downstream was removed after each cycle contact and replenished with solvent-extraction processing of the product eluates was an equivalent volume of SN NH40H. This ensured that more efficient when these solutions contained a cobalt NH40H was available for further copper and nickel concentration higher than that achieved after one elution. removal in subsequent elutions. The 20-pct bleed stream Therefore, recycling the acid eluant for several elutions was processed for copper, nickel, and recovery. was investigated. Table 2 summarizes results obtained using two 5-min An elution scheme employing two 4O-g/L HZS04 eluant contacts with the 4N NH40H eluant at A-R ratios of 1:1, contacts at an A-R ratio of 2:1 for four elutions was 2:1, and 3:1. Copper elution was essentially complete at determined to be an acceptable operating procedure for the higher A-R ratios, while only a portion of the residual increasing the cobalt concentration of the eluate. The nickel was eluted. At an A·R ratio of 2:1,95 pct Cu and complete elution scheme for four elutions used 1 L of 32 pct Ni was eluted, while at an A-R ratio of 3:1, 95 pct WSR per elution. The first elution produced 2 L of eluate Cu and 40 pct Ni was eluted. Though 8 pcl more nickel per liter of WSR and contained, in grams per liter, was eluted when using an A-R ratio of 3:1 than was eluted 0.38 Co, 0.15 Ni, 0.005 Cu, 1.9 Fe, 1.S Zn, and 0.02 AI. when using an A-R ratio of 2:1, the former required 33 pet After the fourth elution, 4 L of product eluate, obtained more NH40H eluant. Therefore, the ammonium hydrox­ from the second contact of the third elution along with the ide elution was performed at an A-R ratio of 2:1, because first contact from the fourth elution, was collected. The less NH40H was required and the subsequent add elution eluate contained, in grams per liter, 0.74 Co, 0.42 Ni, with the 250-g/L H2S04 would prevent a buildup of nickel 0.009 Cu, 6.0 Fe, 4.2 Zn, and 0.035 AI. This product on the resin. In addition, economic evaluation indicated eluate contained a sufficient cobalt concentration for that a nickel carbonate byproduct obtained from the acid efficient downstream solvent-extraction processing. eluate was four times more valuable, $3.10/Ib versus Although the cobalt concentration in the product eluate $0.79/Ib, than the nickel residue collected from the did not increase proportionally with each elution, the NH40H eluate (~). Therefore, it would be more eco­ second acid contact per elution ensured that the remaining nomical for the nickel to be collected in the acid eluates cobalt was eluted. than in the NH40H solution. The Pachuca operating procedure utilizing four elutions sufficiently eluted the metal values from the loaded resin, TABLE 2. - Niokel and copper elution using two 5-mln 4N NH40H contacts with a 20-pot with the exception of nickel. The nickel elution was bleed stream, percent incomplete, and after 10 to 15 loading and eluting cycles, the nickel buildup on the resin was sufficient to interfere with the cobalt extraction. A H S0 eluant was 250-g/L 2 4 2:1 ...... 32 95 used as the second contact of the fourth elution to improve 3:1 ...... 40 95 the nickel elution, thus 25 pet of the resin was subjected 6

SUMMARY OF PACHUCA REACTOR 3. One S-min contact with 250-g/L H2S04, OPERATING PROCEDURE 4. One S-min contact with fresh water. 5. One 5-min contact with recycled 4N NH40H eluant The complete Pachuca reactor elution procedure with a 20-pct bleed stream. consisted of the following steps. An A-R ratio of 2:1 was 6. One S-min contact with fresh 4N NH40H. used for all contacts. One liter of fresh resin was used for 7. One 2-min contact with fresh water. each elution. Total elution time with the Pachuca reactor was First Elution approximately 50 min per elution. Thh;ty-twominutes was required for contacting the resin with the various eluants, 1. One 5-min contact with lO-g/L H2S04, and approximately 18 min was required for eluant transfer, 2. One 5-min contact with 40-gjL H2S04 recycled eluant drainage, and resin drainage at the end of an eluant. elution. The lS-min drain time was sufficient for this 3. One 5-min contact with fresh 4O-g/L H2S04, particular operation; however, in a scaled-up operation, the 4. One 5-min contact with fresh water. drain time could vary. The resulting barren resin 5. One 5-min contact with 4N NH40H recycled eluant contained, in grams per liter WSR, 0.03 Co, 0.4 Ni, 0.1 Cu, with a 20-pct bleed stream. 0.01 Fe, 0.04 Zn, and 0.001 AI. Barren resin collected 6. One 5-min contact with fresh 4N NH40H. from the fixed-bed elution column, which required about 7. One 2-min contact with fresh water. 180 min, contained, in grams per liter WSR, 0.01 Co, 0.3 Ni, 0.3 Cu, 0.001 Fe, 0.01 Zn, and 0.001 AI. Second Elution RESIN INVENTORY 1. One 5-min contact with 10-g/L H2S04, 2. Two 5-min contacts with 4O-g/L H2S04 recycled The MCIX column required a resin inventory of 10,400 eluant. ft3 of WSR to process a 10,000-gpm stream containing 3. One S-min contact with fresh water. 0.026 giL Co. The resin inventory for the fixed-bed 4. Two S-min contacts with recycled 4N NH40H eluant elution system was 6,100 ft3 of WSR, and when operated with a 20-pct bleed stream. in conjunction with the MCIX column, 16,500 ft3 of WSR 5. One 2-min contact with fresh water. was required. The resin inventory for the Pachuca reactor elution Third Elution system was only 1,700 ft3 of WSR, and a total resin inventory of 12,100 ft3 of WSR was required when the Same the second elution. Pachuca reactor was operated in series with the MCIX column. Fourth Elution The Pachuca reactor reduced the resin inventory in the elution system by 72 pct when compared with the fIXed­ 1. One S-min contact with 10-g/L H2S04, bed elution column, and the total resin inventory was 2. One 5-min contact with 4O-gjL H2S04 recycled reduced by 27 pct. eluant.

IRON STUDIES

The feed solution used in the cobalt recovery iron from the eluates produced ill the Pachuca elution unit, investigation was copper cementation plant effluent. The tests were conducted using fresh, as-received cementation solution was obtained in 5,000-gal batches and stored in plant effluent containing a high proportion of ferrous iron. open-air tanks until used. Although 90 to 95 pct of the The as-received effluent contained about 2.0 giL of total iron in the as-received solution was in the ferrous state, iron; 91 pct of the iron was in the ferrous state. the iron oxidized as it aged; solution processed in the Continuous tests in a lO-compartment MCIX column MCIX column generally contained a high proportion of using flow rates of 5 to 6 gpm/ft2 and an A-R flow ratio ferric iron. As the resin used for cobalt extraction had a of 40:1 yielded resin with iron loadings of only 0.7 to greater affinity for ferric rather than ferrous iron (2), more 1.2 giL ofWSR. Cobalt extractions were enhanced during iron was extracted as the solution aged. the tests because fewer resin sorption sites were occupied Crowding effects also contributed to increased iron by iron, and essentially complete cobalt extractions were extraction as the solution aged. Laboratory results achieved in only eight compartments. The resin inventory indicated that cobalt ions in the feed solution readily for a 10-compartment MCIX column was 10,400 ft3, and crowded ferrous iron off the resin. However, ferric iron reducing the column size to eight compartments resulted was slowly crowded off the resin by cobalt ions. Because in a 20-pct reduction in the resin inventory to 8,320 ft3. of the significant reagent cost associated with removing Figure 2 illustrates these results. Thus, the optimum 7

100 therefore decreased. Total sodium carbonate consumption was lowered by 40 pct, and dextrose consumption was reduced by 70 pct. .... 80 () 0- TABLE 3 •• Estimated capital costs z" 0 Fixed oapltal: i= 60 - Primary lon·exchange section ...... $7,478,200 ~ Ammonia recovery section ...... 277,500 0:: f- Zinc solvent-extraction section ..•.....•...... 1,085,400 ?:J 40 KEY Cobalt solvent-extraotion section ...... 283,600 • As-received solution Cobalt electrowlnnlng section ...... 812,200 «~ • Aged solution Byproduct reoovery section ...... •...... 1,059,800 CD Steam plant •.••....•...... •...... ,",. 519,400 0 u 20 Subtotal ." .. , ...... , .. " ...... 11,516,100 Plant facilities, 5 pct of above subtotal ...... , .. 575,800 Plant utilities, 6 pct of above subtotal ...... 691,000 Basic plant cost , ...... • ...... 12,782,900 0 Resin and solvent Inventory ...... 5,413,600 I 2 4 5 6 7 8 9 10 Escalation costs during construction ...... 416,400 COMPARTMENT Total plant cost ...... 18,612,900 Land cost ...... o FIGURE 2.-Cobalt extraction using as-received and aged Subtotal ...... 18,612,900 solution. Interest during construction period ...... 994,700 Fixed capital cost ...... 19,607,600 Working capital: Raw materials and supplies ...... 460,900 column size was reduced from 10 to 8 compartments, and Product and in-process Inventory ...•...... 1,025,200 a proportional reduction in the resin inventory was Accounts receivable ...... 1,025,200 realized. The resin with a low iron content was eluted, Available cash ...... , .... . 787,900 Working capital cost ...... ~99,200 and the resulting eluates contained about 1 giL ferric Fe, Capitalized startup costs ...... 196,100 considerably lower than the 6-g/L Fe eluates obtained in Subtotal , ...... , ...... 3.495300 earlier work using aged solution. Reagent consumptions Total capital cost ...... 23,102,900 in the impurity-removal solvent-extraction circuit were

PROCESS ECONOMICS

Utilizing the data on reductions in resin inventory and utilized to process as-received COR per cementation plant reagent consumptions, a revised cost analysis of the cobalt effluent at a flow rate of 5 gpm/ft and an A-R flow ratio recovery operation was obtained from the Bureau's of 40:1. A summary of the capital cost is presented in Process Evaluation Group. As in the preliminary table 3. evaluation (;2), the capital and operating costs were based on processing a 10,000-gpm stream containing 26 ppm Co. OPERATING COSTS

CAPITAL COSTS Operating costs were also based on an average of 330 days of operation per year, and include direct, indirect, The capital cost estimate was of the general type called and fixed costs as detailed in table 4. The estimated a study estimate by Weaver and Bauman (10). This type annual operating cost for the plant was $13.2 million, of cost estimate is usually within 30 pct of the cost to build which is equivalent to a cost of $13.76/1b of cobalt the described plant; however, factors such as changes in recovered. However, byproduct credits for a copper-nickel material costs can have a significant impact on the residue, zinc carbonate, nickel carbonate, and cobalt­ accuracy. The estimated total capital cost for a magnesium carbonate amounted to $8.67 lIb of cobalt, commercial-scale cobalt recovery plant was $23.1 million, yielding a net operating cost of $S.10/Ib of cobalt. At the based on third quarter 1986 costs (Marshall and Swift current published price of cobalt, $7.00/Ib, the rate of index of 798.3). The plant was designed to operate three return on investment would be about 4 pct. A selling price shifts per day, 7 days per week, and 330 days per year. of about $10.20/Ib of cobalt would yield a 13-pet rate of MCIX columns containing eight compartments were return on the investment. 8

TABLE 4•• Estimated annual operating costs

Annual cost Costs per pound eleotrolytlo oobalt Direot costs: Raw materials: Sulfuric acid at $40/st •••...... ••...... •.••.•....•...... •. $1,453.500 $1.518 Ammonia at $0.14/lb ...... ••...... •...... 91,100 .095 Sodium carbonate, 58 pct at $83/st .•...... ••..•...•...•••...... •...... 3,122,500 3.261 Dextrose at $O.26/lb ....• '3' ...... ••...... •...... ••....•..... 457,700 .478 lon-exchange resin at $600/ft ...... ••....•...... •...... • 944,500 .986 DEHPA solvent at $3.60/gal ...... •...... ••...•...... •...... •...... 21,500 .022 Cyanex 272 solvent at $15/gal •...... •...... •••....•.....•.••....• 89,600 .094 Chemicals for steamplant H20 treatment ...... •...... • - 5,900 .006 Total ...... •..•.•...... •...... •...... ••...... ••..• 6,1§~,aQQ MOO Utilities: .. Eleotric power at $0.047/kWo h ••.•••.•...... •...•..•...•••.... , .•••••...••. 535,500 .559 Process water at $0.25/Mgal ...•...... •••••.•...•.•...... 59,500 .062 Raw water at $0.05/Mgal .....••....••...... •.•.....•.••...... •...•.• 1,000 .001 Natural gas at $6.00/MMBtu ...•...... •.•••..•.•...... ••...... 1,615,600 1.687 Total ...... •...... ••...... •.•...... •....•••.... 2,211,6QQ 2,~09 Direct labor: Labor at $9/h .•...... •...... , •...... •....•...... •.....•..•. 636.500 .665 Supervision. 15 pct of labor ...... ••.•....•.....••.•....•...•.•...... 95,500 .100 Total .••...... ••...... •..••.....••.•.....•.....•...... •.•..... -.n~,OOQ .765 Plant maintenance: Labor ...••••...... •••.•...... •..•...... •....•..•.....•• 297,000 .310 Supervision,2O pet of maintenance labor ..••.....•••••...••.••....•...... 59,400 .062 Materials ...... ••...... •...... •...... •..• 297,000 .31Q Total ...... •...... •...... 653,400 .682 Payroll overhead, 35 pot of above payroll •...... •..•...... •....•••.. 380,900 .398 Operating supplies, 20 pet of plant maintenance ...... •...... 130,700 .136 Total direct cost , ...... •...... •....•.•..•...... •... 10,294,900 10.750 Indlreot cost, 40 pot of direct labor and maintenance •.•••...•...... •..•... 554,200 .579 Fixed cost: Taxes, 1 pet of total plant cost ...... •••..•.•.•...... •... 186,100 .194 Insurance. 1 pet of total plant cost ....•...... •...... •...... ••.. 186.100 .194 Depreciation, 10-yr life ....•.•...... •...... •.....•...... 1,960,800 2.047 Total operating cost ...... ••...••...... •.•...... •. L~,1a2,100 -13.764 Credit: Copper-nickel residue at $0.79/lb ...... •....•...... •...• 3.265 Zinc oarbonate at $0.24/lb ...... •...... •...... •... 2.416 Nickel oarbonate at $3.10/lb ..•...... •...... 2.933 Cobalt-Manganese carbonate at $2.70/lb ...... •.....•...... •...•...... 055 rotal ..••...... ••..•...... •.•• 8.66 Net operating cost ...... •...... ••... , .. , ..... 5.095 SUMMARY AND CONCLUSIONS

A Pachuca air~lift reactor reduced the overall resin transfer, eluant drainage, and resin drainage at the end of inventory of a cobalt recovery process by 27 pct and the a completed elution. elution resin inventory by 72 pct when compared with a Processing fresh cementation plant effluent resulted in flXed-bed elution column. Total elution time was reduced product eluates containing approximately 1 giL Pe; from about 180 min using the fixed~bed column to approx~ whereas, those obtained from aged feed solution contained mately 50 min utilizing the Pachuca reactor. Six 5-min 6 giL Fe. Lower iron concentrations in the eluates contacts employing one 10-g/L H2S04 scrub, two 4O-g/L reduced reagent consumptioll for impurity removal. Total H2S04 eluant contacts with a 250-g/L H2S04 eluant as the sodium carbonate consumption was reduced by 40 pct alld second contact of the fourth elution, one water wash, two dextrose consumption by 70 pct. Resin inventory was 4N NH40H eluant contacts with a 20-pct bleed stream, reduced by 20 pct using the eight-compartment MCIX and one 2-min water wash effectively eluted the loaded column. resin. Approximately 18 min was required for eluant Utilizing the eight-compartment MCIX loading column thus reducing the reagent cost for iron removal. along with the Pachuca reactor for resin elution resulted Implementing the Pachuca elution system and processing in a decrease in the total resin inventory by 47 pct; thus, a fresh feed solution resulted in a net operating cost of reduction in the capital cost. The processing of fresh feed $5.10/lb of cobalt. This value included byproduct credits. solution lowered iron concentrations in the eluates, REFERENCES

1. Jeffers, T. H., and M. R. Harvey. Cobalt Recovery 6. Geldard, D., and L. D. Mann. The Introduction and From Copper Leach Solutions. BuMines RI 8927, 1985, Application of Carbon-in-Pulp in a Heap Leach Project. 12 pp. Australasian. Inst. Min. and Metall., v. 7, 1982, pp. 13-15. 2. Jeffers, T. H., K. S. Gritton, and P. G. Bennett. 7. Jose, J. M., J. L. Merino, and P. Gasos. The Use of Recovery of Cobalt From Spent Copper Leach Solution Pachuca Tanks in . Rev. Metal. (Madrid), Using Continuous Ion Exchange. Paper in Recycle and v. 3(1), 1967, pp. 48-57. Secondary Recovery of Metals, ed. by P. R. Taylor, H. V. 8. Cloete, F. L. D. The Relix Process for the Carbon­ Sohn, and N. Jarrett (Proc. Int. Symp. on Recycle and in-Pulp Recovery of Uranium. J. S. Afr. Inst. Min. and Secondary Recovery of Metals, TMS-AIME, Ft. Lauder­ Metall., v. 3, 1981., pp. 66-73. dale, FL, Dec. 1-4, 1985). Metall. Soc. AIIME, 1985, 9. Grinstead, R. R. Selective Absorption of Copper, pp. 609-621. Nickel, Cobalt, and Other Transition Metal Ions From 3. Jeffers, T. H., K. S. Gritton, P. G. Bennett, and D. C. Sulfuric Acid Solutions With the Chelating Ion Exchange Seidel. Recovery of Cobalt From Spent Copper Leach Resin XFS 4195. Hydrometallurgy (Amsterdam), v. 12, Solution Using Continuous Ion Exchange. BuMines 1984, pp. 387-400. RI 9084, 1.987, 17 pp. 10. Weaver, J. B., and H. C. Bauman. Cost and 4. Kirk, W. Cobalt. Sec. in BuMines Mineral Profitability Estimation. Sec. 25 in Chemical Engineers' Commodity Summaries, 1986, pp. 38-39. Handbook, ed. by R. H. Perry and C. H. Chilton. 5. Hallet, C. J., A. J. Monhemium, and D. G. C. McGraw-Hill, 5th ed., 1973, p. 47. Ropertson. Paper in '81. Inst. Min. and Metall., London, 1981, pp. 308-320.

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