comparative study of chelating ion exchange resins for metal recovery from bioleaching of nickel...

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Minerals Engineering 19 (2006) 1280–1289

Comparative study of chelating ion exchange resins for metalrecovery from bioleaching of nickel laterite ores

A. Deepatana, J.A. Tang, M. Valix *

Department of Chemical Engineering, The University of Sydney, Sydney, NSW 2006, Australia

Received 9 December 2005; accepted 7 April 2006Available online 23 June 2006

Abstract

Heterotrophic fungi and their metabolic products have been used in extracting nickel and cobalt from low grade nickel lateritic ores.This study compared the potential of two commercial chelating resins based on iminodiacetate and aminophosphonate functional groups(Purolite S930 and S950) in recovering nickel and cobalt from pregnant bioleaching solutions. The sorption characteristics of these resinswere examined using various metal concentrations (from 15 to 2000 mg/L), chelating agents including citric, DL-malic and lactic acids, andsolution pH. The solution pH was varied by preparing metal solutions using 0.01 and 0.1 M of organic acids. Metals were recovered fromloaded resins using 2 M HNO3. To interpret the sorption behavior of the resins, the adsorption data were fitted to the Freundlich andLangmuir models. The results showed both nickel and cobalt organic complexes adsorptions were in a good agreement with the two empir-ical models suggesting that the adsorption mechanisms follow a combination of monolayer and multilayer. The adsorption performance ofthe aminophosphonate based resin (Purolite S950) was found to exceed that of the Purolite S930. Favourable adsorptions of nickel andcobalt complexes were achieved in weakly acidic solution. Purolite S950 also showed higher selectivity toward nickel and cobalt complexescompared to Purolite S930. The desorption efficiencies from Purolite S950 were about 90% for nickel and from 82% to 98% for cobalt.� 2006 Elsevier Ltd. All rights reserved.

Keywords: Oxide ores; Ion exchange; Bioleaching

1. Introduction

Current commercial extractions of nickel laterite oresincluding pyro- and hydrometallurgical processes areenergy intensive and operational costs are high. Despitethese difficulties, processing of laterite deposits continuesto grow as high grade sulfide minerals continue to bedepleted (Canterford, 1971; Caron, 1950; Valix et al.,2001a). Microbiological leaching offers a new ‘‘clean’’ tech-nology for extracting metals from these low grade ores withlow cost and low energy demand compared to conventionalpyrometallurgical and hydrometallurgical routes. This pro-cess has the potential to offer a much needed step-change inthe technology for processing laterite ores (Tzeferis and

0892-6875/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.mineng.2006.04.015

* Corresponding author. Tel.: +61 2 9351 5661; fax: +61 2 9351 2854.E-mail addresses: [email protected] (J.A. Tang), mvalix@

chem.eng.usyd.edu.au (M. Valix).

Agatzinin-Leonardou, 1994; Bosecker, 1985; Valix et al.,2001a). Bioleaching of low-grade nickel laterite is basedon the activity of the metabolites (organic acids) of hetero-trophic microorganisms such as Aspergillus and Penicilliumspecies to solubilise mineral oxide into metal–organic com-plexes (Valix et al., 2001a). A recent study has showed thatcitric, malic and lactic acids are among the various metab-olites that are found to be effective in dissolving the desiredmetals (Ni and Co) from nickel laterite ores (Tang, 2004).

This study is concerned with the recovery of dissolvednickel and cobalt from the resulting complex solutions gen-erated from the bioleaching process. Metals are currentlyrecovered from solution by various techniques includingprecipitation, electrowinning and adsorption. In this study,metals were recovered using ion exchange resins. Ionexchange has become an important method for separatingand extracting metals in hydrometallurgical processes(Rosato et al., 1984; Kononova et al., 2000; Mendes and

mailto:[email protected]

mailto:mvalix@

Table 1Properties of commercial chelating resins

Purolite S930 Purolite S950

Matrix Macroporousstyrene-divinylbenzene

Macroporousstyrene-divinylbenzene

Functional group Iminodiacetic acid Aminophosphonicacid

Particle size (mm) 0.3–1.0 0.3–1.2Bed density (g/L) 710–745 710–745Particle density (g/cm3) 1.17 1.13Moisture content (%) 55–65 60–68Operating temperature,

max (�C)70 90

pH range (operating) H+ form 2–6, Na+

form 6–11H+ form 2–6, Na+

form 6–11Total capacity

(meq/g wet)H+ form 1.52, Na+

form 1.29H+ form 2.40, Na+

form 1.20

A. Deepatana et al. / Minerals Engineering 19 (2006) 1280–1289 1281

Martins, 2005). This is associated with advantages pre-sented by using ion exchange resins in dilute solution andthe development of new selective chelating resins for metalrecovery (Albollino et al., 1990; Ersoz et al., 1995) fromstable complexes, which include the solutions of interestin this study. The use of resins in metal recovery fromleaching solutions generated in bioleaching of nickel later-ite ores appears scarce and at present limited to internalindustrial studies (Duyvesteyn and Omofoma, 1997).

The aim of this study is to examine the potential of twocommercial chelating resins based on iminodiacetate andaminophosphonate functional groups (Purolite S930 andS950) in recovering nickel and cobalt from the pregnantsolutions derived from bioleaching of nickel laterite ores.The use of resins in bioleaching processes will require agreater knowledge of equilibrium metal binding and itsdependence on resin structure and medium conditions.This study thus included an investigation of the roles ofcomplexing agents, solution pH and metal concentrationsin the adsorption equilibria and stripping of nickel andcobalt complexes from S930 and S950 chelating resins.

2. Experimental section

2.1. Resins

The chelating resins Purolite S930 and S950 (PuroliteInternational Co., LTD) were used in this study. PuroliteS930 and S950 are chelating ion exchange resins character-ized by iminodiacetate and aminophosphonate functionalgroups respectively. These groups are bound in a macropo-rous polystyrene matrix (see Fig. 1). The physical proper-ties of these two resins, as reported by the suppliers, areshown in Table 1. Both resins were shipped in sodiumform. To convert the resin to the hydrogen form, the resinswere washed with 2 M HCl followed by deionized waterrinse. The resins were then dried and kept at room temper-ature for future use.

2.2. Metal complexes

All synthetic bioleaching solutions were prepared fromanalytical grade reagents. Metal solutions with concentra-

Fig. 1. Structure of Purolite S930 (a) and Purolite S950 (b).

tions from 15 to 2000 mg/L were prepared using Ni(NO3)2 Æ6H2O and Co(NO3)2 Æ6H2O salts in 0.01 and 0.1 M organic(citric, DL-malic and lactic) acids. These acid concentra-tions are typical of those produced by the heterotrophicor fungi microorganisms used in bioleaching nickel lateriteores (Valix et al., 2001a,b).

2.3. Batch adsorption

The sorption of single metals was studied by the batchtechnique. Adsorption tests were carried out at room tem-perature in 250-mL tank reactor. The general method ofadsorption involved adding and equilibrating two gramsof dry resins with 100-mL of metal–organic complex ofvarious concentrations. Adsorption was carried out in athermally controlled shaker. The reactors were agitated inan incubator shaker for 24 h which was found to be suffi-cient to attain adsorption equilibrium. The metal concen-trations in solution were measured before and afteradsorption by atomic absorption spectroscopy (VarianSpectroAA). The amount of metal adsorbed per unit masswas calculated as follows:

Qe ¼Ci � Ce

mV ð1Þ

where Ci and Ce are the initial and equilibrium concentra-tions (mg/L), m is the mass of resins (g), and V is the vol-ume of the metal organic complex solutions (L).

2.4. Metal stripping

At the completion of the adsorption test, the resins wereseparated by filtration. Metals were then eluted from theresin with 100-mL of 2 M nitric acid with a contact timeof 3 h. Desorption was conducted under conditions whichare similar to batch adsorption. The stripping efficiencywas calculated from the mass of metal desorbed (Mdesorbed)over the mass of metal adsorbed onto the resins (Madsorbed):

% Efficiency ¼ Mdesorbed

Madsorbed

� 100 ð2Þ

1282 A. Deepatana et al. / Minerals Engineering 19 (2006) 1280–1289

3. Results and discussion

3.1. Equilibrium models for nickel and cobalt organic

complexes

In this study, two empirical adsorption models wereconsidered, the Langmuir and Freundlich models. TheLangmuir equation (1918) is the most widely used twoparameter equation commonly expressed as

Qe ¼QmbCe

1þ bCe

ð3Þ

The parameter b is a direct measure for the intensity of theadsorption process (L/g) and Qm is the constant related tothe area occupied by a monolayer of adsorbate, reflectingthe adsorption capacity (mg/g). From a plot of 1/Qe versus1/Ce, the corresponding parameters Qm and b can be deter-mined from its slope and intercept. The Freundlich iso-therm (1906) is an empirical equation and shown to besatisfactory for low concentrations. The equation is com-monly given as

Qe ¼ AC1=ne ð4Þ

The corresponding parameter A can be defined as theadsorption or distribution coefficient and represents thequantity of metal adsorbed onto resin adsorbents (mg/g).The constant 1/n, varies between 0 and 1, and is a measureof adsorption intensity or surface heterogeneity. Adsorp-tion becomes more heterogeneous as its value gets closerto zero. A value for 1/n above one indicates unfavorableadsorption. A plot of logQe versus log Ce yields a straightline and the empirical constants A and 1/n are derived fromthe intercept and slope of the plot by linear regression.

Nickel adsorption isotherms of various organic acidcomplexes onto the two resins, Purolite S930 and S950,are compared in Figs. 2–4. The data were fitted to theLangmuir and Freundlich models. The corresponding

(a)

0

2

4

6

8

10

12

14

16

18

0 500 1000 1500 2000Ce (mg/L)

Qe (

mg

Ni/g

resi

ns)

Exp data for Purolite S930


Fig. 2. Adsorption of nickel citrate onto Purolite S930 and

model parameters are reported in Tables 2 and 3. Theextent of fit to the experimental data was measured usingthe coefficient of determination (R2).

The R2 values from the linear fit of both Langmuir andFreundlich are high (R2 > 0.90). This suggests that thenickel–organic complexes adsorption onto the two resinsagrees with the two isotherm models and indicates thatnickel complexes are adsorbed by a combination of mono-layer and multilayer mechanisms. The small 1/n value alsosuggest that nickel adsorption onto these chelating resinsare favorable. In addition, it appears that the functionalgroups of the two resins influence adsorption of nickel–organic complexes. Purolite S930 based on iminodiaceticfunctional groups provided poorer adsorption comparedto S950 with the aminophosphonic groups (see Figs. 2–4). This is also reflected by the higher empirical modelparameters; Qm and A-values, shown in Tables 2 and 3.Nickel–organic acid complexes tend to be bulky. Theselarge complexes allow a better fit into the rather rigid struc-ture of the P–O bond of the phosphonate group, whereas inthe iminodiacetate resin, the two –COO– groups may bothbind onto the metals as follows:

CH2-COO

R-N Ni-Cit

CH2-COO

The greater affinity of the nickel complexes to the ami-nophophonic resin may be associated with the reduced ste-ric hindrance in comparison to that provided by theiminodiacetate resin. Comparison of the adsorption ofnickel–organic complexes onto the resins in this study tothose of nickel chloride (1.5 mg/g dry resin) (Fernandezand Dıaz, 1992) on iminodiacetic acid resins suggests thatfavorable metal adsorption is obtained from organic acidcomplexes. However, adsorption of nickel from an aqueous

(b)

0

2

4

6

8

10

12

14

16

0 500 1000 1500 2000Ce (mg/L)

Qe (

mg

Ni/g

resi

ns)



Purolite S950 in citric acid at (a) 0.01 M and (b) 0.1 M.

(a)

0

2

4

6

8

10

12

14

16

18

20

0 500 1000 1500 2000Ce (mg/L) Ce (mg/L)

Qe (

mg

Ni/g

resi

ns)



(b)

0

2

4

6

8

10

12

14

16

0 500 1000 1500 2000

Qe (

mg

Ni/g

resi

ns)



Fig. 4. Adsorption of nickel lactate onto Purolite S930 and Purolite S950 in lactic acid at (a) 0.01 M and (b) 0.1 M.

Table 2Langmuir parameters for nickel in organic acids

Organicacid

Modelparameters


0.01 M 0.1 M 0.01 M 0.1 M

Citric Qm (mg/g) 10.43 9.02 18.42 14.51b (L/g) 6.5 · 10�3 2.3 · 10�3 3.0 · 10�3 5.1 · 10�3

R2 0.95 0.99 0.96 0.93

DL-Malic Qm (mg/g) 15.15 9.80 14.45 11.83b (L/g) 5.2 · 10�3 3.4 · 10�3 6.2 · 10�2 2.0 · 10�2

R2 0.98 0.98 0.92 0.95

Lactic Qm (mg/g) 12.97 9.23 19.42 14.84b (L/g) 1.1 · 10�2 6.4 · 10�3 3.9 · 10�3 4.5 · 10�3

R2 0.93 0.93 0.92 0.95

Table 3Freundlich parameters for nickel in organic acids

Organic acid Model parameters Purolite S930 Purolite S950

0.01 M 0.1 M 0.01 M 0.1 M

Citric A (mg/g) 0.46 0.10 2.51 0.951/n 0.44 0.60 0.24 0.37R2 0.98 0.99 0.96 0.99

DL-Malic A (mg/g) 0.53 0.23 2.79 1.721/n 0.47 0.50 0.25 0.28R2 0.97 0.99 0.99 0.99

Lactic A (mg/g) 0.86 0.38 3.26 2.131/n 0.39 0.46 0.22 0.25R2 0.99 0.98 0.98 0.99

(a)

0

2

4

6

8

10

12

14

16

18

20

0 500 1000 1500 2000Ce (mg/L)

Qe (

mg

Ni/g

resi

ns)



(b)

0

2

4

6

8

10

12

14

16

0 500 1000 1500 2000Ce (mg/L)

Qe (

mg

Ni/g

resi

ns)

Exp data for Puroilte S930


Fig. 3. Adsorption of nickel malate onto Purolite S930 and Purolite S950 in DL-malic acid at (a) 0.01 M and (b) 0.1 M.


solution onto IRN77 cation-exchange resin with sulfonicacid functional group showed Freundlich isotherm withan A value of 81.82 mg/g and 1/n of 0.17 (Rengaraj

et al., 2002). These higher parameters clearly suggest thatmetal adsorption onto sulfonic acid resins is higher. Boththe nickel chloride and Ni2+ from an aqueous solution


are small molecules compared to the nickel citrate com-plex. This suggests that the affinity of the metal for the par-ticular functional groups is also important in theadsorption of metals onto the resins. It appears the orderof affinity of nickel ion and complexes towards the variousfunctional groups are –SO�3 (sulfonate); –PO�3 (phospho-nate); –COO– (carboxylate).

Similarly, the adsorption of cobalt–organic complexesonto the two resins, Purolite S930 and S950 are comparedin Figs. 5–7. The empirical Langmuir and Freundlichparameters are shown in Tables 4 and 5. The extent of fitto the experimental data, reflected by the coefficient ofdetermination (R2) shows a good variability for all fitteddata (R2 > 0.90).

The corresponding model parameters for the adsorp-tion of cobalt from Tables 4 and 5 and Figs. 5–7 indicate

(a)

0

1

2

3

4

5

6

0 50 100 150Ce (mg/L)

Qe (

mg

Co/

g re

sins

)



Fig. 5. Adsorption of cobalt citrate onto Purolite S930 and

(a)

0

1

2

3

4

5

6

7

8

0 50 100 150 200Ce (mg/L)

Qe (

mg

Co/

g re

sins

)



Fig. 6. Adsorption of cobalt malate onto Purolite S930 and P

that the adsorption of cobalt–organic complexes ontoS950 was favorable in comparison to S930. As shown inTable 5, the values of Freundlich constant; 1/n of typi-cally close to 1, suggest the cobalt adsorption onto Puro-lite S930 is unfavorable (1/n � 1). It is apparent thatcobalt adsorption follows these two empirical models.This suggests that cobalt–organic complexes are adsorbedonto Purolite S950 as a combination of monolayer andmultilayer forms. Previous adsorption of cobalt fromaqueous solution onto IRN77 cation-exchange resins withsulfonic acid functional gave Freundlich model parame-ters of A 75.63 mg/g and 1/n of 0.15 (Rengaraj et al.,2002). These results are consistent with the adsorptionof nickel complexes and indicate that both steric effectsand the affinity of the metals for certain functional groupsaffect metal adsorption onto the resins.

(b)

0

1

2

3

4

5

6

7

0 50 100 150 200Ce (mg/L)

Qe (

mg

Co/

g re

sins

)



Purolite S950 in citric acid at (a) 0.01 M and (b) 0.1 M.

(b)

0

1

2

3

4

5

6

7

8

0 50 100 150 200Ce (mg/L)

Qe (

mg

Co/

g re

sins

)



urolite S950 in DL-malic acid at (a) 0.01 M and (b) 0.1 M.

(a)

0

1

2

3

4

5

6

7

8

9

10

0 50 100 150 200Ce (mg/L)

Qe (

mg

Co/

g re

sins

)



(b)

0

1

2

3

4

5

6

7

8

9

0 50 100 150 200Ce (mg/L)

Qe (

mg

Co/

g re

sins

)



Fig. 7. Adsorption of cobalt lactate onto Purolite S930 and Purolite S950 in lactic acid at (a) 0.01 M and (b) 0.1 M.

Table 4Langmuir parameters for cobalt in organic acids

Organicacid

Modelparameters


0.01 M 0.1 M 0.01 M 0.1 M

Citric Qm (mg/g) 3.86 3.47 5.39 7.31b (L/g) 3.8 · 10�3 2.2 · 10�3 3.9 · 10�1 5.1 · 10�2

R2 0.97 0.99 0.99 0.99

DL-Malic Qm (mg/g) 2.99 1.88 7.54 7.38b (L/g) 5.7 · 10�3 2.3 · 10�3 3.4 · 10�1 8.2 · 10�2

R2 0.99 0.99 0.95 0.99

Lactic Qm (mg/g) 6.78 2.76 10.48 7.43b (L/g) 2.8 · 10�3 7.0 · 10�3 2.6 · 10�1 2.5 · 10�1

R2 0.98 0.99 0.99 0.99

Table 5Freundlich parameters for cobalt in organic acids

Organicacid

Modelparameters


0.01 M 0.1 M 0.01 M 0.1 M

Citric A (mg/g) 1.0 · 10�2 8.0 · 10�3 2.00 0.551/n 1.05 0.95 0.28 0.67R2 0.99 0.99 0.95 0.99

DL-Malic A (mg/g) 1.2 · 10�2 1.9 · 10�3 2.08 0.811/n 0.97 1.18 0.39 0.54R2 0.94 0.99 0.96 0.98

Lactic A (mg/g) 0.02 0.01 2.81 2.141/n 0.90 1.02 0.35 0.34R2 0.99 0.99 0.97 0.97

1 Technical data for Purolite S930 and S950, Purolite International Co.,LTD.


3.2. The effects of solution pH on the adsorption of nickel

and cobalt organic acids

The effects of solution pH were investigated by using0.01 and 0.1 M of organic acids. These concentrations aretypical of the metabolic acid concentrations produced by

heterotrophic fungi (Valix et al., 2001a,b). Tables 2–5 sug-gest the order of adsorption capacity based on the organicacid at both 0.01 and 0.1 M acid is lactic > malic > citricfor both S930 and S950. The results suggest that nickeland cobalt complexes adsorptions are favorable at thelower acid concentration for all acid used. The reducednickel and cobalt uptake at the lower pH (0.1 M acids) isproposed to be associated with the higher affinity of hydro-gen ion toward the resins (Sengupta et al., 1991) and theadsorption of anions (Matejka and Weber, 1990). As theacid concentration is increased the competition betweenhydrogen ion and nickel–organic complexes for adsorptionsites also rises (Sengupta et al., 1991; Kiefer and Holl, 2001;Outola et al., 2001). Both S930 and S950 are weakly acidicchelating exchangers that rarely dissociate hydrogen ion inacidic solution. These resins have been found to effectivelytake up metals (Zn, Ni, Cu and Cd) from aqueous solutionat pH between 2 and 6 (Outola et al., 2001). The technicaldata1 for both resins provided by Purolite Internationalsuggest the selectivity for Purolite S930 is H+ > Ni2+�Co2+ and Purolite S950: H+ > Ni2+ P Co2+. The reduc-tion in uptake of metal–organic complexes on the two res-ins can also be attributed to the adsorption of anions. Theadsorption of pure organic acids onto the two resins (seeTable 6) was shown to result in greater acidity. This sug-gests that dissociated anions are taken up by the resinand leaves a higher concentration of hydronium ions(H+) in solution. The higher H+ released from PuroliteS930 in solution reflects the greater affinity of this resinto anions in comparison to Purolite S950. The selectivityof Purolite S930 towards anions may further explain itslower metal uptake.

Table 6The pH of solution of organic acids before and after adsorption

Organicacids

[M] Purolite S930 Purolite S950

pH beforeadsorption

pH afteradsorption

H+ released(·103 M)

pH beforeadsorption

pH afteradsorption

H+ released(·103 M)

Citric 0.01 2.50 1.85 11.0 2.50 2.18 3.440.1 1.94 1.50 20.1 1.94 1.58 14.8

DL-Malic 0.01 2.63 1.93 9.40 2.63 2.37 1.920.1 2.11 1.64 15.1 2.11 1.78 8.83

Lactic 0.01 2.73 1.94 9.62 2.73 2.47 1.530.1 2.23 1.71 13.6 2.23 1.90 6.70

(a)

0

20

40

60

80

100

120

100 500 1000 1500 2000Concentration of Nickel (mg/L)

% E

ffici

ency

(b)

0

20

40

60

80

100

120


% E

ffici

ency

Purolite S950Purolite S930

Fig. 9. The effect of metal concentrations prepared in 0.01 M (a) and 0.1 M (b) DL-malic acid on the regeneration efficiency of nickel from Purolite S930and S950.

(a)

0

20

40

60

80

100

120


% E

ffici

ency

(b)

0

20

40

60

80

100

120


% E

ffici

ency


Fig. 8. The effect of metal concentrations prepared in 0.01 M (a) and 0.1 M (b) citric acid on the regeneration efficiency of nickel from Purolite S930 andS950.



3.3. Metal regeneration

Desorption studies were carried out in 2 M HNO3 toremove metals complexed with citrate, lactate and malateadsorbed on the resins. The regeneration efficiencies Puro-lite S930 and S950 are compared in Figs. 8–10 for nickeland Figs. 11–13 for cobalt. The metal concentrations usedin this study cover the maximum leachable concentrationsof nickel and cobalt from low grade nickel laterite ores(Tang, 2004).

High regeneration efficiencies were achieved for nickelcomplexes adsorbed in both Purolite S930 and S950 (about90%). This is with the exception of adsorbed nickel–citrate

(a)

0

20

40

60

80

100

120


% E

ffici

ency

Fig. 10. The effect of metal concentrations prepared in 0.01 M (a) and 0.1 M (bS950.

(a)

0

20

40

60

80

100

120

15 50 100 200Concentration of Cobalt (mg/L)

% E

ffici

ency

Fig. 11. The effect of metal concentrations prepared in 0.01 M (a) and 0.1 M (bS950.

complexes onto Purolite S930 which showed a regenerationefficiency of less than 80% (see Figs. 8–10).

The regeneration efficiencies for cobalt complexes areshown in Figs. 11–13. Purolite S950 showed high regener-ation efficiencies (up to 98%) from malate and lactateacids. However, only 82% of cobalt was desorbed fromthe cobalt citrate complexes adsorbed. In contrast, regen-eration efficiencies for Purolite S930 were from 32% in0.1 M citric acid to 88% in 0.01 M DL-malic acid. Theregeneration efficiencies also decreased as the acid concen-tration increased.

In summary, the regeneration efficiencies from PuroliteS950 were about 90% for nickel complexes and from 82%

(b)

0

20

40

60

80

100

120


% E

ffici

ency


) lactic acid on the regeneration efficiency of nickel from Purolite S930 and

(b)

0

20

40

60

80

100

120


% E

ffici

ency


) citric acid on the regeneration efficiency of cobalt from Purolite S930 and

(a)

0

20

40

60

80

100

120


% E

ffici

ency

(b)

0

20

40

60

80

100

120


% E

ffici

ency


Fig. 12. The effect of metal concentrations prepared in 0.01 M (a) and 0.1 M (b) DL-malic acid on the regeneration efficiency of cobalt from Purolite S930and S950.

(a)

0

20

40

60

80

100

120


% E

ffici

ency

(b)

0

20

40

60

80

100

120


% E

ffici

ency


Fig. 13. The effect of metal concentrations prepared in 0.01 M (a) and 0.1 M (b) lactic acid on the regeneration efficiency of cobalt from Purolite S930 andS950.


to 98% for cobalt complexes. These results suggest the nat-ure of the complexes generated as a result of leaching con-ditions and efficiency (the extent of metal dissolution) haslittle effect on the efficiency of metal desorption from Pur-olite S950.

4. Conclusions

The investigation of metal recovery from bioleaching ofnickel laterite ores using two commercial chelating resins,Purolite S930 and S950, with iminodiacetic and amino-

phosphonic acid functional groups, respectively, can beconcluded as follows:

1. Purolite S950 showed a greater performance in compar-ison to Purolite S930 in recovering both nickel andcobalt from synthetic bioleaching solutions. Adsorp-tions of nickel and cobalt organic complexes onto Puro-lite S950 are in good agreement with both Langmuir andFreundlich isotherm models. The mechanism for metaluptake follows a combination of monolayer and multi-layer adsorption. Multilayer adsorption of nickel is


likely to be associated with the competitive adsorptionamong the metal complexes, hydrogen ion and anions.It appears that the nature of the functional groups andsteric hindrance affects the adsorption behavior ontothe resin. The aminophosphonic based resin providesless steric hindrance in comparison to the iminodiaceticacid resin.

2. The adsorption capacity of nickel and cobalt complexesonto Purolite S950 is lower in comparison to adsorptionof metals from aqueous solution. These are reflectedfrom the model parameters, A value from the Freund-lich model and Qm value from the Langmuir model fit-ted to the adsorption data for nickel and cobaltorganic complexes. The significant difference was attrib-uted to the steric effect of the bulkier metal organic com-plexes compared to the hydrated nickel and cobalt ions.This remains a challenging aspect of recovering nickeland cobalt from the bioleach solutions.

3. The adsorption capacity of nickel and cobalt decreasesas the bioleach solution becomes more acidic. Acidicconditions promote the adsorption of both the hydro-gen ions and organic acid anions onto the resins. Opti-mal adsorptions of nickel and cobalt organic complexesonto Purolite S950 are achieved under weakly acidiccondition.

4. The regeneration efficiency suggests that Purolite S950provided high efficiency for both nickel about 90% andcobalt from 82% to 98%. It also appears that the natureof the metal complexes derived from typical bioleachingconditions do not have a significant effect on the overallregeneration efficiency.

Acknowledgements

The authors gratefully acknowledge the scholarship sup-port of the Royal Thai Government and the Australian Re-search Council for the financial support toward this study.

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comparative study of chelating ion exchange resins for metal recovery from bioleaching of nickel...

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