EXTRACTION OF NICKEL FROMAMMONIACAL LEACH SOLUTIONS:

EXTRACTANT AND SOLUTIONCHEMISTRY ISSUES

by

Dr. J.M.W. Mackenzie

Henkel Australia Pty Ltd

and

Dr. M.J. Virnig, B.D. Boley, G.A. Wolfe

Henkel Corporation, MID

PRESENTED AT

ALTA 1998 Ni/Co Pressure Leaching & Hydrometallurgy Forum

May 25 28, 1998

EXTRACTION OF NICKEL FROM AMMONIACAL LEACHSOLUTIONS: EXTRACTANT AND SOLUTION CHEMISTRY

ISSUESby

Dr. J.M.W. MackenzieHenkel Australia Pty Ltd

andDr. M.J. Virnig, B.D. Boley, G.A. Wolfe

Henkel Corporation, MID

Table of Contents

1. INTRODUCTION 1

2. SOLVENT EXTRACTION OF NICKEL USING LIX 84-I AND XI-84-IT 4

3. EFFECT OF FREE AMMONIA CONCENTRATION, AMMONIUM IONCONCENTRATION, CARBONATE,SULFATE AND DILUENT ON EXTRACTION OFNICKEL AND AMMONIA BY LIX 84-I 5

4. AMMONIA TRANSFER ON XI-84-IT AND LIX 84-I 8

5. EFFECT OF CARBONATE, SULFATE AND DILUENT ON NICKEL EXTRACTIONKINETICS WITH LIX 84-I AND XI-84-IT 10

6. EFFECT OF TEMPERATURE ON NICKEL STRIP KINETICS WITH LIX 84-IAND XI-84-IT 13

7. EFFECT OF REAGENT CONCENTRATION ON INTERFACIAL SURFACETENSION AND ORGANIC PHASE VISCOSITY 15

8. REOXIMATION OF CIRCUIT ORGANIC 18

9. COBALT RECOVERY 19

10. SUMMARY 21

11. ACKNOWLEDGEMENTS 22

12. REFERENCES 34

11. INTRODUCTION

EVOLUTION NOT REVOLUTION aptly describes Henkels approach to thedevelopment of a hydrometallurgical process for the recovery of nickel fromlaterites. The first stage of the evolutionary process was the circuit shown inFigure 1 and first described in detail at the 1996 ALTA Nickel Conference1.This circuit, which has been successfully piloted on a laboratory scale at anumber of locations, is a part of the Cawse Nickel Project, which will go intoproduction this year. It is also the basis of a number of nickel feasibility studiescurrently underway .

In common with other hydrometallurgical groups around the world, Henkelwould have preferred to take the revolutionary step of developing an extractantand associated hydrometallurgical flowsheet to go directly from an acid leachsolution to nickel catholyte. Henkel however realized that development of aRevolution is extremely costly in terms of capital, manpower, and time2.Some of the issues which led Henkel to pursue the evolutionary road were: Acid leaching of laterites produces solutions which contain a very wide range

of elements, some of which are present in concentrations much higher thanthe nickel concentration. Unless a highly selective extractant can bedeveloped some of these elements will be co-extracted with the valuablemetal. An example of this is given in a recent paper by Soldenhoff et. al3,which shows that in the recovery of Co from a laterite based acid leachingsolution using Cyanex 272, Co occupied only 5% of the metal loadingcapacity of the organic. The remainder of the loading capacity was taken upby Mg, 72%, and Mn, 23%.

The chemistry of Ni does not suggest an obvious route for the developmentof a selective nickel extractant for acid leach solutions. Warshawsky hascommented on this in some detail4.

The development of a nickel extractant which will work in a conventional acidleach-SX-EW circuit is further complicated by the electrowinningrequirements of nickel which dictate that the pH of the strip solution whichforms the nickel catholyte must be in the range of 3.5 to 4. Since lateriteacid leach solutions contain 5-20 g/l of free acid with a resultant pH of 1-2,the electrowinning requirement adds to the difficulty of selecting a suitablefunctionality for a nickel extractant.

2 Some of the metals present in solutions produced by acid leaching oflaterites are capable of a number of valency states. Manipulation of thesevalencies in acid sulfate solution in such a manner in the hydrometallurgicalprocess that one can achieve separation from the nickel can be difficult.Examples of such metals are Co, Mn, and Cr. The latter two metals are alsocapable of forming the strongly oxidizing species, permanganate anddichromate, respectively. These strong oxidants can destroy both theextractant and the diluent used in the SX process. Oxidation of metals inammonia solutions can often be much more readily achieved than in acidsolutions. This facilitates both removal by precipitation as an oxide as in thecase of Mn or oxidation to a valency state which is not extracted as in thecase of Co. The circuit shown in Figure 1 can produce SX feed solutionscontaining less than 1.0 mg/l of Cr, Mn and Co(II).

Nickel laterites are relatively low-grade ores containing between about 1.0and 1.5% of nickel. In dollar terms, this is equivalent to a copper orecontaining about 2-5% Cu. Despite the existence of well developed SX-EWroutes for direct agitation leaching of ore containing these types of Cuvalues, it is not commonly practiced. Consideration of Ni hydrometallurgyconvinced Henkel of the advantages of a circuit which would involve somepreconcentration of the valuable metals prior to SX-EW. Acid leaching oflaterites typically produces solutions which contain 3-5 g/l of Ni after solid-liquid separation. The preconcentration of the metals in the hydroxide formsin the Henkel circuit can produce SX feed solutions containing in excess of20 g/l of Ni. In typical practice, the SX feed solution will be in the 12-14 g/lof Ni range.

As noted previously, development of a new extractant from scratch can be bothcostly and time consuming. In addition to the development costs, theregistration of a new molecule around the world can, in todays regulatoryenvironment, contribute significantly in terms of time and money to the costs ofintroducing such a material to the market. Given the need to develop ahydrometallurgical route for nickel within a reasonable time frame, Henkel feltthat the best route would be to tailor their existing technology to the needs ofthe industry.

During the past two years, Henkel has worked closely with a number of nickellaterite projects. Based on that experience as well as experience gained indealing with recovery of copper from spent ammoniacal etchants from theprinted circuit industry along with consideration of potential operatingconstraints of a circuit such as that outlined in Figure 2a and 2b, Henkel hascarried out their own internal investigations of factors such as:

1. Effect of Ammonia and Ammonium Ion Concentration on AmmoniaTransfer

2. Effect of Ammonia and Ammonium Ion Concentration on Ni Extraction

3. Selectivity of LIX 84-I for Ni over other Metals

34. Development of an Improved Reagent Formulation, XI-84-IT

5. Ni Extraction Kinetics

6. Ni Strip Kinetics

7. Effect of Reagent Concentration on Organic Phase Behavior

8. Reoximation Procedures for Extractant Damaged during ReductiveStripping of Co(III) from the Organic.

This paper describes some of the evolutionary steps taken by Henkel since theHenkel approach to Ni laterite hydrometallurgy was first described two yearsago at this conference.

42. SOLVENT EXTRACTION OF NICKELUSING LIX 84-I AND XI-84-IT

The active extractant in LIX84-I is 2-hydroxy-5-nonylacetophenone oxime,which is dissolved in a dearomatized hydrocarbon carrier such as Exsol D-80,Shellsol D-70 or Escaid 110. The structure of 2-hydroxy-5-nonylacetophenoneoxime is shown in Figure 3. It is commonly referred to as a ketoxime. Figure 3also shows the structure of the other major phenolic oxime type metalextractants, the salicylaldoximes, which are commonly referred to in theindustry as aldoximes.

Studies on the effects of modifiers on the co-extraction of ammonia with thenickel led to the development of XI-84-IT, a developmental reagent for theextraction of Cu and Ni from ammoniacal leach solutions. XI-84-ITincorporates the use of a modifier with 2-hydroxy-5-nonylacetophenone oxime.As shown by the extraction isotherms in Figure 4, XI-84-IT is a slightly weakerextractant than LIX 84-I.

Extraction of Ni from ammoniacal solution proceeds, depending upon theammonia complex speciation, as follows:

Tetramine

Hexamine

R= Ketoxime

These reactions are equilibrium reactions and can be driven in either directiondepending upon the concentrations of the various species involved in thereaction. Increasing the ammonia or ammonium ion concentration in theaqueous phase will result in less extraction of nickel. At very highconcentrations of ammonia and ammonium ion, nickel can be effectivelystripped as practiced by Queensland Nickel5. Nickel can also be effectivelystripped by weak acid as follows:

Ni(NH3)6+2(aq) + 2RH(org) R2Ni(org) +4NH3(aq)+ 2NH4+(aq)

Ni(NH3)4+2(aq) + 2RH(org) R2Ni(org) +2NH3(aq)+ 2NH4+(aq)

R2Ni(org) + 2H+(aq) + SO4-2 2RH(org) + Ni+2(aq) + SO4-2(aq)

53. EFFECT OF FREE AMMONIA CONCENTRATION, AMMONIUMION CONCENTRATION, CARBONATE,SULFATE AND DILUENT

ON EXTRACTION OF NICKEL AND AMMONIA BY LIX 84-I

Henkel has carried out a series of investigations aimed at exploring the effect ofammonia concentration, ammonium ion concentration, carbonate, sulfate anddiluent on extraction of nickel and ammonia by LIX 84-I. Solutions wereprepared containing 30% (v/v) of the reagent in a diluent having an aromaticcontent of 22% (Flash Point - 65.6C), typical of many of the diluents incommercial use in solvent extraction plants, and in a low aromatics solventextraction diluent (Flash Point - 77C) having an aromatic content of 5% or less.The reagent concentrations were adjusted to give equivalent max loads.Concentrated aqueous solutions were prepared to contain 30 g/l Ni and 2 g/l Znin either a sulfate or carbonate system. In the case of the sulfate system, therequired amount of nickel sulfate, zinc sulfate and ammonium sulfate weredissolved in DI water, then concentrated ammonium hydroxide was added, andfinally the solution was diluted to the mark. The final concentrated solutionscontained 30 g/l Ni, 2 g/l Zn and 65 g/l NH3 with either 50, 100, or 200 g/l ofammonium sulfate. In the case of the carbonate system, the required amountof nickel carbonate and ammonium carbonate were placed in DI water andallowed to stir overnight before adding the ammonium hydroxide to give a clearsolution. Dissolving zinc carbonate proved to be extremely difficult in thissystem. In order to get the zinc into the carbonate solutions, a concentratedsolution of zinc sulfate in DI water was prepared and then added to theammoniacal solution of nickel carbonate. The zinc immediately precipitatedupon addition to the ammonia solution but then quickly redissolved. Theresultant solution was then diluted to volume to give the final concentrate.Final concentrated solutions were prepared containing 30 g/l Ni, 2 g/l Zn, and65 g/l NH3 with either 40, 100 or 200 g/l of ammonium carbonate. Portions ofthese concentrated solutions were then diluted with water and solutions ofammonium hydroxide, ammonium carbonate or ammonium sulfate to give finalsolutions containing 15 g/l Ni and 2 g/l Zn with varying amounts of NH3,ammonium carbonate, or ammonium sulfate. These solutions were thencontacted by shaking at an O/A =1 for 30 minutes with the desired organicphase. After 30 minutes, the phases were separated, the organic was filteredthrough phase separation paper and a portion assayed for ammonia6. Asecond portion was assayed for Ni and Zn.

Figures 5 through 8 summarize the effects of ammonium salt concentration andammonia concentration along with that of diluent on nickel extraction andammonia loading on the organic phase with LIX 84-I. The nickel andammonia data are plotted against the starting ammonia or ammonium ionconcentrations in the aqueous. The results can be summarized as follows:

6 Figure 5 shows the nickel loading and ammonia loading on the organic as afunction of increased ammonia level while holding the ammonium sulfatelevel constant at 25 g/l. Figure 6 shows the equivalent data for thecarbonate system with the ammonium carbonate being held constant at 20g/l. At 32.5 g/l ammonia, there is sufficient ammonia to have 6 g/l of freeammonia present after forming the metal amine complexes. From Figures 5and 6, increasing the free ammonia concentration depresses nickelextraction and increases ammonia loading on the organic as one wouldexpect. The effect is more pronounced in the sulfate system then in thecarbonate system. In terms of nickel extraction, the 22% aromatics diluentshows slightly better nickel extraction than does the aliphatic diluent. It alsotends to load a slightly higher level of ammonia than does the aliphaticdiluent. The effect of diluent on nickel extraction is a bit surprising. In typicalcopper from acid systems, increasing the aromatic content of the diluentresults in the organic phase behaving as a slightly weaker extractant due tothe fact that the aromatics can act as a thermodynamic modifier. In the caseof nickel extraction from ammoniacal solutions, the better solvency power forextracted species of diluents containing aromatics appears to outweigh thepotential thermodynamic modification effect. The results for the sulfatesystem are consistent with the findings of Flett and Melling7. They found thatincreased aromatic content in the diluent increased ammonia loading on theorganic phase. As the nickel concentration on the organic increases, thenickel takes up sites that were associating with the ammonia resulting incrowding of the ammonia off of the organic phase. In an operating plant, theammonia concentration on the organic will be at its highest in E3 where it willbe carrying the lowest level of nickel and it will be in contact with an aqueousphase containing high levels of free ammonia liberated by extraction ofnickel in stages E1 and E2. The loaded organic exiting E1 will have thelowest level of ammonia loading. It will be very close to max loaded withnickel due to the fact that it will be in contact with a feed having lots of nickelavailable for extraction and low levels of free ammonia.

Figures 7 and 8 show the equivalent data where in this case the ammoniaconcentration is held constant at 32.5 g/l and the ammonium ionconcentration is varied by adding either ammonium sulfate or ammoniumcarbonate. While the data is plotted in terms of increasing ammonium ionconcentration, the sulfate or carbonate level is also being increased at thesame time. From Figures 7 and 8, increasing the ammonium ionconcentration has a similar effect as increasing the ammonia concentrationon nickel extraction. Again, the effects are greater in the sulfate system thanin the carbonate system. The organic prepared with the aromatic containingdiluent also tends to extract more nickel than does that prepared with thealiphatic diluent. The differences between the sulfate and carbonatesystems suggest that there are two different nickel amine complexesinvolved, Ni(NH3)6+2 in the carbonate system and Ni(NH3)6SO4 in thesulfate system. See additional comments in Section 4.0.

7 One interesting point is that there seems to be a significant difference in thebehavior of the carbonate system as compared to the sulfate system withregard to ammonia loading on the organic phase depending upon thearomatic content of the diluent. Compare the data in Figures 5 and 7 withthat in Figures 6 and 8. This area requires further exploration. One possibleexplanation may be as follows: In the sulfate system, the use of thearomatic diluent always results in higher loadings of ammonia on the organicphase than if an aliphatic diluent is used. In the carbonate system, thepicture is not so clear. At low ammonia concentrations, the aromatic diluentfavors lower ammonia loading than does the aliphatic diluent, while thereverse is true at higher ammonia concentrations. At low free ammoniaconcentrations, the aromatics may actually be binding with the extractantpreventing ammonia loading on the organic phase. Under these conditions,the aromatic is acting as an equilibrium modifier. At high ammoniaconcentrations, this effect is possibly being overpowered and the more polarcharacter of the aromatics is helping to solvate the ammonia in the organicphase. Under these conditions, the aromatic content is acting as anammonia solvent. This is further suggested by the results where theammonium sulfate or carbonate are being increased while the ammonialevel is held constant. The sulfate system is relatively clean. Sulfatebehaves simply as an anion and does not effect the overall position of theammonia/ammonium equilibrium. In the case of the carbonate system, theammonia/ammonium equilibrium is probably also influenced by thecarbonate/bicarbonate equilibria. Given equivalent levels of ammonia andammonium ions in solution, there is effectively more free ammonia in thesulfate system than there is in the carbonate system.

Zinc loadings on the organics were very low, in the range of 1-3 ppm. Thezinc level was highest at the lowest level of nickel loading on the organic.

In operating a circuit, one will want to minimize the level of free ammonia inthe incoming feed to insure high recoveries of nickel and minimize extractionof ammonia and other metals. One will also need to monitor the level ofammonium sulfate or ammonium carbonate buildup in the aqueous phase.High levels of ammonium ions will also suppress nickel extraction, increaseammonia extraction and result in poorer selectivity.

84. AMMONIA TRANSFER ON XI-84-IT AND LIX 84-I

Solutions of XI-84-IT and LIX84-I were prepared in the aliphatic diluent at30% (v/v) concentration resulting in organics having copper max loads of 14.68and 14.92 respectively. These were contacted at 25C by shaking for 30minutes with a solution containing 15 g/l Ni, 1 g/l Zn, 32.5 g/l ammonia andeither 25 g/l ammonium sulfate or 20 g/l ammonium carbonate in DI water.After loading, the organic phase was assayed for nickel and ammonia. Theresults are summarized in Table 1.

TABLE 1 AMMONIA LOADING ON XI-84-IT AND LIX84-I

Reagent Ammonium Carbonate Ammonium Sulfate[NH3] (g/l) [Ni] (g/l) [NH3] (g/l) [Ni] (g/l)

84-I 0.448 13.7 0.409 13.7

84-IT 0.375 13.5 0.299 13.4

As illustrated in the Table, XI-84-IT transfers less ammonia on the organicphase than does LIX 84-I. The differences shown in these static tests aresmaller than what one might expect to see in a dynamic circuit. Due to thelevel of nickel extracted, the organic is in contact with an aqueous containinghigh levels of free ammonia. In an actual circuit, the loaded organic would be incontact with the E1 aqueous which would contain significantly lower ammountsof free ammonia. This is illustrated in Table 2 where the organic was contactedtwice with the aqueous feed, which was sulfate based in this case and alsocontained magnesium, zinc, and cobalt. As can be seen from the data, asecond contact with the feed solution results in slightly more nickel loading onthe organic and a significant reduction in ammonia loading in both cases with adecided advantage for XI-84-IT in terms of lower ammonia loading. The dataalso shows a decided advantage for XI-84-IT in terms of selectivity for nickelover cobalt in this test. Magnesium and zinc were not detectable on theorganic in this trial.

9TABLE 2: EFFECT OF REPETITIVE CONTACTS ON AMMONIA LOADINGWITH XI-84-IT AND LIX 84-I.

Contact XI-84-IT LIX 84-I[NH3](g/l)

[Ni](g/l)

[Co](g/l)

[NH3](g/l)

[Ni](g/l)

[Co](g/l)

#1 0.236 14.0 0.050 0.389 13.8 0.120

#2 0.150 14.4 0.078 0.199 14.2 0.200

The lower ammonia loadings observed for XI-84-IT for the nickel system aresupported by data from copper extraction systems. In a circuit trial with anammoniacal copper sulfate leach solution, XI-84-IT transferred only 38% of theammonia that LIX 84-I did based on acid consumption (kg acid/kg Cutransferred) in the wash stage. Entrainments were equivalent in both cases.

10

5. EFFECT OF CARBONATE, SULFATE AND DILUENTON NICKEL EXTRACTION KINETICS

WITH LIX 84-I AND XI-84-IT

The nickel extraction kinetics tests were carried out using a stirred box at 25C.The procedure was similar to Henkels standard Performance Test procedure8.Samples of the emulsion were removed at 0.5, 1, 1.5, and 5 minutes. Thephases were allowed to separate, the organic was filtered through phaseseparation paper, and then assayed for Ni and Zn. The aqueous feed solutionsconsisted of the following, all in DI water:A. 15 g/l Ni, 1 g/l Zn, 32.5 g/l NH3, and 25 g/l ammonium sulfate

B. 15 g/l Ni, 1 g/l Zn, 32.5 g/l NH3, and 100 g/l ammonium sulfate

C. 15 g/l Ni, 1 g/l Zn, 32.5 g/l NH3, and 25 g/l ammonium carbonate

D. 15 g/l Ni, 1g/l Zn, 32.5 g/l NH3, and 100 g/l of ammonium carbonate

The organic phase consisted of 30% (v/v) LIX 84-I dissolved in either 22%aromatic diluent or aliphatic diluent and the XI-84-IT was dissolved in the 22%aromatic diluent. The results are summarized in Tables 3 and 4.

TABLE 3. SUMMARY OF EXTRACTION KINETICS DATA AT 25 C.

Solution Diluent C Reagent E30* (%) E60* (%) E90* (%)

A Aliph. 25 84-I 84 91.7 95.8

22% Arom. 25 84-I 84.9 93.2 96.6

25 84-IT 84.5 91.5 95.8

40 84-I 99.2 99.3 99.5

40 84-IT 98 99 99.8

B 22% Arom. 25 84-I 74.4 84.8 90.4

25 84-IT 71.4 81.0 88.1

C Aliph. 25 84-I 93.1 96.5 98.6

22% Arom. 25 84-I 91.6 96.5 98.6

25 84-IT 90.3 95.5 97.0

D 22% Arom 25 84-I 83.1 91.5 95.4

25 84-IT 79.8 89.1 93.8

* E30, E60 and E90 are the 30, 60 and 90 second extraction points. % is based on E300 point.

From the data, the following conclusions can be drawn:

11

Extraction from carbonate systems is always faster than from sulfatesystems. This phenomena has been observed consistently by Henkel in awide range of testwork and also by other investigators including Nilsen et al9.It is interesting to speculate on the reasons for these slower extractionkinetics which, perhaps not coincidentally, are mirrored by indications of aslower Co(2) to Co(3) oxidation in sulfate systems. There are some potentialchemical speciation differences between the Ni-NH3-SO4 and the Ni-NH3-CO3 systems. The sulfate systems have the capability of forming theNi(NH3)6SO4 double salts and the preponderance diagrams for thesespecies are available10. These diagrams and the stability constants fromwhich they were derived suggest a strong association between the nickelamine complex and the sulfate anion. It is possible that this association isresponsible for the slower chemical kinetics observed in the sulfate system.For the carbonate system, the CO3 anion may behave more as a freecounter ion than as an associated anion. This would be consistent with thepreponderance diagrams which do not show Ni(NH3)6CO3 salt formation.Consideration of the differences in the aqueous chemistry and solventextraction behavior of the sulfate and the carbonate systems is not idle. Inthe flowsheet shown in Figure 1, there are two potentially commerciallyuseful hydroxides for the precipitation of the base metal hydroxides; MgOand CaO. Where MgO is available at a reasonable price, it is the alkali ofchoice as the base metal precipitates will readily redissolve in anammonia/ammonium carbonate liquor. At some locations, CaO is the onlyeconomically attractive alkali available. For a base metal hydroxide derivedfrom CaO precipitation, ammonium sulfate rather than ammonium carbonatereleaching is required. In this paper, Henkel will show that both alkalis areviable alternatives but that the SX plant design criteria may differ slightlydepending on the leach liquor being treated.

Increasing the amount of ammonium carbonate or ammonium sulfate resultsin slower extraction kinetics and a fall off in overall extraction as previouslynoted. By copper solvent extraction standards, the extraction kinetic resultsare slow at 25oC, especially at the higher salt concentration. In actualoperation, solvent extraction plants are expected to be operated at 40oC. Atthe higher temperature, extraction is much faster. Given the potential impactof low temperatures and the effect of the higher salt concentrations onextraction kinetics, it is recommended that mixers be conservatively sized togive a 3-4 minute mixer retention time to provide some additional flexibility inthe solvent extraction plant.

There is no significant difference between the diluents and the reagents interms of extraction kinetics.

At 25C, phase separation times were quite slow but at 40oC, phaseseparation times averaged 98 seconds under organic continous mixingconditions.

12

As a consequence of the slower nickel extraction from sulfate media, insulfate systems more zinc is being extracted and then slowly crowded off theorganic as shown in Table 4. Crowding of the Zn from the organic by Ni isconsistent with observations from continuous circuits where the raffinatestage will show higher Zn loading than the loaded organic stage. In the 0-30second interval, Zn loads up to approximately 10 mg/l but by 300 seconds,the Zn loading is reduced to about 1 mg/l. While the sulfate systems tend tofavor initial extraction of Zn, there is no significant difference in Zn levels onthe organic between carbonate and sulfate systems at equilibrium. The twoHenkel extractants LIX 84-I and XI-84-IT show similar Ni extraction and Zncrowding kinetics in this type of batch test. However in continuous circuits,there is some evidence that XI-84-IT extracts a little less zinc, particularly inthe E2 and E3 stages than does LIX 84-I. Although the XI-84-IT is moreselective for nickel over zinc, the crowding kinetics of zinc are sufficientlyfast for both extractants to offer similar zinc loadings in E1. In general,selectivity for nickel over zinc appears to be governed by the extent to whichthe reagent will load nickel under the given conditions of free ammonia andammonium ion concentration. Under conditions where less nickel extractionoccurs, small amounts of zinc will be extracted.

TABLE 4.CROWDING OF ZINC BY NICKEL IN EXTRACTION KINETICS TESTS AT 25C.

Solution Reagent Metal Time (Secs)0 30 60 90 300

C 84-I Ni (g/l) 0 13.1 13.8 14.1 14.3

Zn (mg/l) 0 5.6 2.2 1.7 1.2

84-IT Ni (g/l) 0 12.1 12.8 13.0 13.4

Zn (mg/l) 0 5.5 2.8 2.1 1.5

A 84-I Ni (g/l) 0 12.4 13.6 14.1 14.6

Zn (mg/l) 0 13.5 3.8 2.2 1.0

84-IT Ni (g/l) 0 12.0 13.0 13.6 14.2

Zn (mg/l) 0 9.5 3.3 2.0 1.0

B 84-I Ni (g/l) 0 9.3 10.6 11.3 12.5

Zn (mg/l) 0 9.3 3.8 2.3 1.0

84-IT Ni (g/l) 0 9.0 10.2 11.1 12.6

Zn (mg/l) 0 9.4 4.2 2.6 1.2

13

6. EFFECT OF TEMPERATURE ON NICKEL STRIP KINETICSWITH LIX 84-I AND XI-84-IT

Stripping tests were carried out in a similar fashion to the extraction kinetics asdescribed in Henkels Standard Performance test procedure8. The mixer boxwas replaced with a jacketed baffled beaker arrangement11. Organic solutionscontaining 30% (v/v) reagent, were prepared in either 22% aromatic diluent oraliphatic diluent. The solutions were loaded by contacting them with a 15 g/l Ni,1 g/l Zn, 32.5 g/l NH3 and 25 g/l ammonium sulfate solution in DI water. Theloaded ammonia was scrubbed off the loaded organic by contacting at anO/A=1 with a pH = 5, 50 g/l sodium sulfate solution. The scrubbed organic wasthen filtered through phase separation paper. The resultant loaded organicswere then stripped by contacting them with an aqueous solution containing 59.6g/l Ni, 100 g/l Na2SO4, and 29.4 g/l H2SO4 at either 40C or 60C. The datais summarized in Table 5 and Table 6.

TABLE 5. STRIPPING KINETIC DATA AT 40C.

Diluent Reagent Strip Points (Min)5 (% Str) 10(% Str) 15 (% Str) 20 (% Str)

Aliph. 84-I 70.9 93.1 98.4 99.5

22% Arom. 84-I 69.0 91.6 97.7 99.3

84-IT 71.8 92.6 98.3 99.5

TABLE 6. STRIPPING KINETIC DATA AT 60C.

Diluent Reagent Strip Points (Min)3 (% Str) 6 (% Str) 9 (% Str) 12(%Str) 15(%Str)

Aliph. 84-I 89.8 98.4 99.4 99.5 99.5

22% Arom 84-I 90.6 98.6 99.5 99.6 99.6

84-IT 91.1 98.6 99.5 99.6 99.6

The following conclusions can be drawn: Temperature is the key variable. At 40, ten minutes was required to

achieve 90% stripping. At 60C, the same level of stripping is achieved in 3minutes. To achieve adequate stripping, mixer retention times should be inthe range of 5-7 minutes at temperatures of 50 - 60C.

14

Phase separation required on average 65 seconds at 60C and 90 secondsat 40C with either reagent. Tests were carried out aqueous continuous.

Limited testwork at 40oC indicated loading the organic from either a sulfatesolution or a carbonate solution had no effect on strip kinetics.

There is no significant difference between diluents and reagents in terms ofstrip kinetics.

Due to the advantages of running at higher temperatures, the flash point ofthe diluent may, for safety reasons, be more significant than the chemicalaspects of the diluents.

15

7. EFFECT OF REAGENT CONCENTRATION ON INTERFACIALSURFACE TENSION AND ORGANIC PHASE VISCOSITY

7.1 VISCOSITY

Solutions of 30% (v/v) of LIX 84-I and XI-84-IT were prepared in 22%aromatic diluent. A portion of each was loaded to approximately 12.1 g/l Ni(90% of max load) by contact with an ammoniacal feed solution. The kinematicviscosities of samples of the barren reagent and the loaded reagent were thendetermined at various temperatures. The results are summarized in Table 7.

TABLE 7. KINEMATIC VISCOSITY DATA

Temperature (C) Barren Organic Loaded OrganicLIX 84-I XI-84-IT LIX 84-I XI-84-IT

20 4.27 cst 4.12 cst 4.45 cst 4.46 cst

30 3.33 cst 3.16 cst 3.46 cst 3.61 cst

40 2.65 cst 2.57 cst 2.76 cst 2.89 cst

50 2.19 cst 2.12 cst 2.27 cst 2.37 cst

Due to the high reagent concentrations, the viscosity of the organic phase isquite high at lower temperatures. Most copper solvent extraction plants operateat reagent concentrations between 10 and 20% (v/v) at a temperature around25C. The viscosity of these organics is in the region of 2.4 - 3.0 cst. With thehigher reagent concentration, you need to operate in the 40C range in order tohave a similar organic viscosity to that in current copper solvent extractionplants. At colder temperatures, there will be problems with phase separation asevidenced by high entrainments and with achieving adequate mixing,necessitating slowing the flows.

16

Given the high viscosities, it is important to emphasize that the overall solventextraction plant design should be conservative. Evaporation of diluent from theorganic phase will result in an increase in the viscosity of the organic phasecompounding operating problems such as entrainment. Increasing theviscosity could have an impact on mixer efficiences. In extraction, Henkelexpects that E2 and E3 will show high mixer efficiences (+95%) and that E1could show a lower efficiency due to the fact that the organic entering E1 isalready close to max loaded with nickel resulting in low driving force for furtherextraction. Increased organic phase viscosity due to either colder temperaturesor diluent evaporation will effect mixing efficiency resulting in potentially lowernickel extraction. On the strip side, Henkel would expect that only a smallamount of nickel will be stripped in S1 (the stage receiving the loaded organic).Most of the acid in the lean electrolyte entering stripping will have beenconsumed by the time the aqueous enters S1. S1 acts as a pH adjustmentstage. Its function is to raise the pH of the exiting preg electrolyte to about 3.5.The low incoming acid, which reduces the overall driving force in S1, will resultin overall low stripping efficiency under normal conditions. Increasing theviscosity of the organic phase may result in additional lowering of the mixerefficiency in S1, hence lowering the stripping efficiency even further, and resultin a higher acid level in the preg electrolyte entering the electrowinningtankhouse.

7.2 INTERFACIAL SURFACE TENSION

The organic phases used for the kinematic viscosity experiments were alsoused for interfacial surface tension measurements against solutions of 50 g/lammonium carbonate and 50 g/l ammonium sulfate in DI water at pH 9.0 and10.0. The pH of the solution was adjusted with ammonium hydroxide. Themeasurements were made at 40C. The results are summarized in Table 8.

The data highlights the fact that the interfacial surface tensions in these nickelextraction plants will be quite low. This is primarily due to the high reagentconcentration. In current operating copper solvent extraction plants treatingacidic leach solutions with organic phases containing 10-20% (v/v) reagent,interfacial surface tensions are typically in the range of 23-26 dynes/cm. Atinterfacial surface tensions of 20 dynes/cm, we would expect to see problemswith entrainment and phase separation in the copper plants. In view of the lowinterfacial surface tension values which will be encountered, solvent extractionplants designed to treat ammoniacal nickel solutions should be designedconservatively with regard to agitation and settler area. Agitators should be ofthe low shear type. In terms of settler area, work should be carried out with theexpected plant solutions to determine the actual settler area required. Settlerflows of 3.5-4 m3/m2/hr have been suggested.

17

TABLE 8. SUMMARY OF INTERFACIAL SURFACE TENSION DATA AT 40C

Organic Reagent pH = 9.0 pH = 10.00Carbonate1 Sulfate1 Carbonate1 Sulfate1

Barren 84-I 16.9 16.9 18.2 17.5

84-IT 18.2 17.1 17.2 18.7

Loaded 84-I 16.9 16.4 15.2 16.6

84-IT 16.1 15.0 15.2 16.61Values are given in dynes/cm.

18

8. REOXIMATION OF CIRCUIT ORGANIC

Stability of the reagents in the Henkel circuit is expected to be quite good. Theprimary degradation route of oximes is acid catalyzed hydrolysis to give theketone. Acid levels in strip (45 g/l) are much lower than in Cu solvent extractioncircuits which use 180 g/l acid. Alternatively, the oxime function can beconverted to an imine by reaction with high concentrations of ammonia. Theimine can then be relatively easily hydrolyzed to the ketone upon exposure toweak acid. The level of ammonia to which the reagent is exposed in theHenkel circuit is significantly lower than in the Queensland Nickel circuit whichuses ~280 g/l ammonia in stripping. Given the mild conditions, reagent stabilityis not expected to be an issue.

One key point in preparation of the ammoniacal feed solution is to oxidize thecobalt that is present to the +3 oxidation state. Any Co(+2) present in theincoming feed solution will be extracted by the organic and once loaded on theorganic will tend to oxidize to the +3 oxidation state. Once it is converted to the+3 state on the organic, the cobalt can only be stripped by contacting theorganic with strong acid while generating nascent hydrogen by the reaction ofan active metal such as zinc or iron with the acid. The nascent hydrogenreduces the Co(+3) to the Co(+2) which will strip. At this point, it is difficult toestimate the overall effect of these conditions on the overall stability of theorganic given the paucity of actual long term operating data.

At some point in time, the level of ketone in the organic phase may reachsufficiently high levels to warrant reoximating the organic to convert this ketoneback to the active oxime extractant. Henkel has developed a reoximationprocedure for the organic phase similar to that used in our manufacturingprocess. The resultant reoximated organic has typically shown good physicaland metallurgical properties.

The reoximation process would be incorporated into the overall solventextraction circuit in the following fashion. An organic bleed stream would beremoved from the circuit. Preferably, the metal content of the organic shouldbe reduced as low as possible. A potentially good stream might be that comingfrom Co stripping since it should be well stripped at that point. The organicshould be filtered to remove any particulates and then transferred toreoximation where it is reacted with hydroxylamine sulfate or some otherhydroxylamine salt in the presence of an alkali. The resultant reoximatedorganic is then thoroughly washed with water and can then simply be returnedto the circuit.

19

9. COBALT RECOVERY

There are a couple of potential routes for recovering the cobalt from theaqueous raffinate exiting the nickel extraction circuit. One method is to simplyprecipitate the cobalt by treatment with sulfide. Another possibility is to extractthe cobalt as suggested by Nilsen and co-workers12 with XI-51, a fluorinatedbeta-diketone. It is unique in that cobalt does not tend to oxidize to the +3oxidation state when loaded on the organic.

XI-51 is an experimental product from Henkel. In contrast to XI-84-IT, which issimply a mixture of known materials, XI-51 is a new chemical which mayrequire additional development work.

To recover cobalt from the raffinate from the nickel extraction, the cobalt mustbe reduced back to the +2 oxidation state. This can be accomplished bycontacting the solution with cobalt metal. The chemistry of cobalt extractionand stripping by XI-51 is shown below:

Extraction

Stripping

R= XI-51

XI-51 appears to be a relatively strong extractant for cobalt from the nickelraffinate as can be seen from the extraction isotherm in Figure 9. The aqueousfeed solution for the extraction isotherm was obtained by treating a sample ofan actual ammoniacal nickel raffinate from a pilot plant trial with cobalt powderfor 30 minutes to reduce the cobalt (+3). It contained 1.73 g/l of cobalt. Theorganic phase consisted of 5% (v/v) of XI-51, 15% (v/v) isotridecanol, and theremainder, aliphatic diluent. Extraction and strip kinetics are also very fast asseen from the data in Table 9. The extraction and strip phase separations were74 and 56 seconds respectively. The aqueous feed for extraction wasprepared in a similar fashion to that for the extraction isotherm. It contained3.90 g/l of cobalt. The strip aqueous contained 73 g/l of cobalt as the sulfateand 15 g/l of sulfuric acid.

Co(NH3)6+2(aq) + 2RH(org) R2Co(org) + 4NH3(aq) + 2NH4+(aq)

R2Co(org) + 2H+(aq) + SO4-2(aq) 2RH(org) + Co+2(aq) + SO4-2(aq)

20

TABLE 9. COBALT EXTRACTION AND STRIP KINETICS WITH XI-51

Time (Sec.) Extraction Stripping[Co]Org (g/l) % [Co]Org (g/l) %

30 3.12 101 0.25 92

60 3.12 101 0.04 98

90 3.14 102 0.02 99

300 3.06 100 0.01 99

21

10. SUMMARY

The chemistry of extraction of nickel from ammoniacal solutions generated byacid pressure leach of nickel laterites followed by precipitation of the metalvalues by alkali and releach of the hydroxide cake with ammonia/ammoniumsulfate or carbonate has been explored. There are differences between sulfateand carbonate based systems that should be kept in mind when developing aflow sheet and designing a plant.

XI-84-IT is a developmental reagent that shows promise as an alternatereagent in this application due to the fact that it will transfer less ammonia thanLIX 84-I. Since it is a slightly weaker extractant that LIX84-I, it may also insome instances give better extraction selectivity than does LIX 84-I. This hasbeen observed in some preliminary trials by other laboratories.

Recovery of cobalt from the nickel raffinate by XI-51 has been demonstrated.This is a very interesting approach requiring additional development.

22

11. ACKNOWLEDGEMENTS

The authors wish to acknowledge the helpful discussions with the many peopleinvolved in testing and further development of the Henkel flowsheet for nickellatterites. This includes the personnel of Oretest, MIM Hydromet, LakefieldResearch, and Hazen Laboratories.

The authors would also like to acknowledge the permission of Henkel to publishthis paper as well as special thanks to Goyce Wolfe for her help in actuallydoing some of the laboratory work.

23

AutoclaveAcid LeachORE

Fe2(SO

4)3 disproportionates

to Fe2O3 plus H2SO4

SL S/L Sep

HydroxidePrecipitation

pH 5.0

HydroxidePrecipitation

pH 9.0

NH3 Leach

Oxidation

Ni SXLIX 84-I

Co RecoveryH2S ppt or

Cyanex 272

MgO/CaO

SL S/L SepFe and some Mn, Cr

MgO (or CaO)

SL Mg2+ S/L Sep

NH3/CO2 Ambient Pressureor

NH3/(NH4)2SO4Air/O 2

SLMn S/L Sep

SteamSteam sparged pachucato oxidise residual Mn,strip free NH3

Ni EWCu & Co bleed stream strippossible reoximation

Possible Znrecovery/removal Figure 1

24

L.O.WASHpH 6-7

200 gpl H2SO4

E 1 E 2 E 3 S.O.WASHS 4

pH 0.5-0.8S 3

pH 0.9-1.0S 2

pH 2.0S 1

pH 4.0

CuSTRIP(Bleed)

Cu

E.W.

pH Control Circuit

L.O.

NH3/CO3 NiPLS RAFFINATE

Ni TankhouseSpent

Ni TankhouseAdvance

200 gplH2SO4

Delta Ni 25 gplDelta H2SO4 42 gpl

Figure 2a.

25

Figure 2b.

Extraction Wash StripNumber of

Stages3 2 (L.O & S.O.) 4

Mixer Residence 3-4 Minutes 2-3 Minutes 5-7 MinutesO/A Throughput 1-3 10-20 +/- 2

O/A Mixer 1 1 1Temperature 40C 40C 50-60CSpecific Flow 3.5-4.0 m3/m2-

hr3.5-4.0 m3/m2-

hr4.0 m3/m2-hr

Extractant 30% (v/v)LIX84-I

30% (v/v)LIX84-I

30% (v/v)LIX84-I

pH 9.0-10.0 +/- 6.0 0.5-4.0graduated

PLSg/l Ni 10 - 30g/l Co 0.5 3.0g/l Cu 0.5 1.0

Preg Electrolyteg/l Ni 95-100g/l Co 0.001-0.020g/l Cu 0.01-0.03g/l Zn Trace

Spent Electrolyteg/l Ni 70-85

g/l H2SO4 42

27

Figure 3

OH

R

A

NOH

General Chemical Structure of the Hydroxy OximesUsed Commercially for Copper Recovery

R = C9H19 or C12H25

Salicylaldoximes A = H

Ketoximes A = CH3

28

Figure 4Nickel Extraction Isotherms for LIX 84-I and XI-84-IT

Ni (gpl in Aqueous)0 2 4 6 8 10 12 14 16

N

i

(

g

p

l

i

n

O

r

g

a

n

i

c

)

0

2

4

6

8

10

12

14

16

84-I (M.L. = 14.45)84-IT (M.L. = 14.29)

Feed: 15.39 g/l Ni, 1.06 g/l Zn, 25 g/l (NH4)2SO4, 32.5 g/l NH3

29

10

11

12

13

14

15

30 50 700

1

2

3

[NH3] Aliphatic

[NH3] 22%Aromatic

[Ni] 22% Aromatic

[Ni] Aliphatic

[NH3] (gpl in Feed)

[NH

3 ] (gpl in Organic)

[

N

i

]

(

g

p

l

i

n

O

r

g

a

n

i

c

)

Figure 5Effect of [NH3] on NH3 and Ni Loading of Organic Phase

25 gpl (NH4)2SO4

30

Figure 6Effect of [NH3] on NH3 and Ni Loading of Organic Phase

20 gpl (NH4)2CO3

10

11

12

13

14

15

30 50 700

1

2

3

[NH3] Aliphatic

[NH3] 22%Aromatic

[Ni] 22% Aromatic

[Ni] Aliphatic

[

N

i

]

(

g

p

l

i

n

O

r

g

a

n

i

c

)

[NH

3 ] (gpl in Organic)

[NH3] (gpl in Feed)

31

10

11

12

13

14

15

5 15 25 350

1

2

3

[NH3] Aliphatic

[NH3] 22%Aromatic

[Ni] 22% Aromatic

[Ni] Aliphatic

N

i

(

g

p

l

i

n

O

r

g

a

n

i

c

)

[NH

3 ] ( gpl in Organic)

[NH4+] (gpl in Feed)

Figure 7Effect of [NH4+] on NH3 and Ni Loading of Organic Phase

32.5 gpl NH3 in SO4

32

10

11

12

13

14

15

5 15 25 350

1

2

3

[NH3] Aliphatic

[NH3] 22%Aromatic

[Ni] 22% Aromatic

[Ni] Aliphatic

[

N

i

]

(

g

p

l

i

n

O

r

g

a

n

i

c

)

[NH

3 ] ( gpl in Organic)

[NH4+] (gpl in Feed)

Figure 8Effect of [NH4+] on NH3 and Ni Loading of Organic Phase

32.5 gpl NH3 in CO3

33

Figure 9XI-51 Cobalt Extraction Isotherm

Co (g/l in Aqueous)0.0 0.5 1.0 1.5

C

o

(

g

/

l

i

n

O

r

g

a

n

i

c

)

0

1

2

3

Feed: Nickel Pilot Plant Raffinate Reduced with Cobalt Metal

34

12. REFERENCES

1 Mackenzie, J.M.W., and Virnig, M.J., Recovery of Nickel from Ammoniacal Solutions Using LIX84-I, Proceedings of ALTA Nickel/Cobalt Pressure Leaching & Hydrometallurgy Forum, , May 1996,Perth, Western Australia.

2 Virnig, M.J., and Kordosky, G.A., Reagent Development in the 90's - A Perspective, Reagents forBetter Metallurgy, ed. P.S. Mulukutia, AIME, 1994, 311-317.

3 Soldenhoff, K., Hayward, N. and Wilkins, D., Direct Solvent Extraction of Cobalt and Nickel fromLaterite-Acid Pressure Leach Liquors, EPD Congress 1998, ed. B. Mishra (The Minerals, Metals, andMaterials Society, AIME) 1998, p 153-165.

4 Warshawsky, A., The Liquid-Liquid Extraction of Nickel: A Review., Minerals Sci. Engineering, Vol5 (No. 1), January 1973, p 35-52.

5 Price, M.J., and Reid, J.G., Separation and Recovery of Nickel and Cobalt in Ammoniacal Systems:Process Development, Proceedings ISEC 93, SCI, London, 1993, p 159.

6 Determination of NH3 in Solutions of LIX Reagents, Henkel Red Line Bulletin

7 Flett, D.S., and Melling, J., Extraction of Ammonia by Commercial Copper Chelating Extractants,Hydrometallurgy, 4, 1979, p 135-146.

8 Standard Henkel Quality Control Test for LIX Oxime Reagents, Henkel Red Line Bulletin

9 Nilsen, D.N. et al, Solvent Extraction of Nickel and Copper from Laterite-Ammoniacal Leach Liquors,USBM RI 8605, 1982.

10 Osseo-Asare, K., and Asihere, S.W., Heterogeneous Equilibria in ammonia/Laterite LeachingSystems, International Laterite Symposium, ed. Evans, D.J.I., Shoemaker, R.S., and Veltman, H., SME,New York, 1979, p 585-609.

11 Standard Henkel Quality Control Test for LIX54-100 and LIX 54, Henkel Red Line Bulletin

12 Nilsen, D.N., Siemens, R.E., and Rhoads, S.C., Solvent Extraction of Cobalt From Laterite-Ammoniacal Leach Liquors, USBM, RI 8419, 1980.

IINTRODUCTIONSOLVENT EXTRACTION OF NICKELUSING LIX 84-I AND XI-84-ITTetramineHexamine

EFFECT OF FREE AMMONIA CONCENTRATION, AMMONIUM ION CONCENTRATION, CARBONATE,SULFATE AND DILUENT ON EXTRACTION OF NICKEL AND AMMONIA BY LIX 84-IAMMONIA TRANSFER ON XI-84-IT AND LIX 84-IEFFECT OF CARBONATE, SULFATE AND DILUENTON NICKEL EXTRACTION KINETICSWITH LIX 84-I AND XI-84-ITEFFECT OF TEMPERATURE ON NICKEL STRIP KINETICS WITH LIX 84-I AND XI-84-ITEFFECT OF REAGENT CONCENTRATION ON INTERFACIAL SURFACE TENSION AND ORGANIC PHASE VISCOSITYVISCOSITYINTERFACIAL SURFACE TENSION

REOXIMATION OF CIRCUIT ORGANICCOBALT RECOVERYExtractionStripping

SUMMARYACKNOWLEDGEMENTSREFERENCES