- Email: [email protected]
Solvent extraction of cadmium from sulfate solution with di-(2-ethylhexyl) phosphoric acid diluted in kerosene
Hydrometallurgy 96 (2009) 230–234
Contents lists available at ScienceDirect
Hydrometallurgy j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / h yd r o m e t
Solvent extraction of cadmium from sulfate solution with di-(2-ethylhexyl) phosphoric acid diluted in kerosene Vinay Kumar a,⁎, Manoj Kumar a, Manis Kumar Jha b, Jinki Jeong b, Jae-chun Lee b,1 a b
Metal Extraction and Forming Division, National Metallurgical Laboratory, Jamshedpur-831007, India Minerals and Materials Processing Division, Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon, 305-350, Republic of Korea
a r t i c l e
i n f o
Article history: Received 18 June 2008 Received in revised form 9 September 2008 Accepted 20 October 2008 Available online 5 November 2008 Keywords: Solvent extraction Cadmium D2EHPA Sulfate solution
a b s t r a c t In the present paper, solvent extraction process has been used for extraction of cadmium from sulfate solution using di-(2-ethylhexyl) phosphoric acid (D2EHPA) with 1% isodecanol in kerosene diluent expected from industrial effluents or leaching of ores/secondary materials. Different process parameters such as pH, contact time, extractant concentration, O/A ratio etc. were investigated. Results demonstrated that quantitative extraction of cadmium was feasible from 4.45 mM cadmium feed solution in single stage at equilibrium pH 4.5, time 2 min and O/A ratio 1:1 with 0.15 mM D2EHPA. The extraction mechanism of cadmium from sulfate solution by D2EHPA in kerosene could be represented at equilibrium by Cd2+ + 3/2 (H2A2)org ⇔ CdA2(HA)org + 2H+. The loading capacity of 0.15 mM D2EHPA in sulfate solution was determined to be ∼8.9 mM cadmium. The loaded cadmium was effectively stripped using 180 g/L sulfuric acid. The metal or salt could be produced by electrolysis or crystallization from the stripped solution. © 2008 Published by Elsevier B.V.
1. Introduction Cadmium is an important metal which is extensively employed in solar battery, electronic, electroplating, metallurgical industries etc. (Arnzt et al., 1999). During production and also at the end-of-service life, waste material containing cadmium is generated in the form of solid and liquid effluents in these industries. The disposal of such materials causes not only the environmental pollution but loss of resources as cadmium and its compounds are highly toxic and carcinogenic in nature (Elyahyaoui and Bouhlassa, 2001; Agrawal and Sahu, 2006). Recovery and recycling of metals will conserve the natural resources to meet the future demand of materials and also reduce the environmental pollution. The processes usually employed for the recovery of metals are hydro/pyrometallurgical methods where material is first leached in acidic or alkaline solution to dissolve the metals directly or after thermal treatment. The leach solution contains cadmium along with other metallic constituents such as nickel, zinc etc. depending on waste material treated. The solution is subsequently processed to recover valuable constituents following precipitation, cementation, ion exchange, adsorption, electrolysis etc. (Mantuano et al., 2006; Agrawal et al., 2006). Among the available processing alternatives, solvent extraction is a technique that not only meets the strict environmental regulations and also high purity value added products could be produced (Safarzadeh et al., 2007). Different authors (Almela and Elizalde, 1995; Reddy et al., 2004; Gupta et al., ⁎ Corresponding author. Fax: +91 657 2270527. E-mail addresses: [email protected] (V. Kumar), [email protected] (J. Lee). 1 Fax: +82 42 8683705. 0304-386X/$ – see front matter © 2008 Published by Elsevier B.V. doi:10.1016/j.hydromet.2008.10.010
2001) studied the extraction of cadmium from the aqueous solutions using organic extractants such as di-(2-ethylhexyl) phosphoric acid (D2EHPA), di-2,4,4-trimethylpentyl phosphinic acid (Cyanex 272) etc. The process reported the extraction and separation of cadmium from aqueous leach solution of zinc sulfide concentrate, residue of zinc plant, beta cake, pot skimming, etc. The extraction of cadmium (II) from chloride solution of 1.0 M ionic strength by the bis(2,2,4-trimethylpentyl) thiophosphinic (Cyanex 302) (HR) extractant in kerosene has been studied over a range of pH and reagent concentrations (Almela and Elizalde, 1995). The results indicated that the extraction of cadmium (II) takes place with the formation of the species CdR2 (HR) and CdR2(HR)2. Solvent extraction of cadmium from sulfate solution was studied using organophosphorous based extractants viz. TOPS 99 (an equivalent of di-(2-ethylhexyl) phosphoric acid, obtained from Heavy water plant, Talchar, India), PC 88A (2-ethylhexylphosphonic acid mono-2-ethylhexyl ester) and Cyanex 272 (Reddy et al., 2004). The extraction of cadmium takes place by cation exchange mechanism with the formation of 1:3 metal to reagent complex. TOPS 99 has been found to be the best synergist for extraction with mixed extractant than PC 88A and Cyanex272. Gupta et al. (2001) explored the extraction of Cd(II) along with Al(III), Fe(III), In(III), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Hg(II) and Pb(II) from hydrochloric acid solution using Cyanex 923 (a mixture of different tri-n-octylphosphine oxide) and pointed out the separation of cadmium in the presence of various metallic ionic species. Gotfryd and Cox (2006) used an equimolar mixture diisopropylsalicylic acid and Cyanex 471X (tri-isobutylphosphine sulfide) (0.5 mol/L) diluted with Solvesso 150 as extractant to separate cadmium and zinc from the leach solution of cadmium carbonate or cadmium cementation sponge. The loaded cadmium from the organic
V. Kumar et al. / Hydrometallurgy 96 (2009) 230–234
231
in aqueous phase and the concentration of cadmium in the raffinate. 1.8 M H2SO4 was used for stripping of the cadmium from the loaded organic and satisfactory material balance was obtained in all the experiments. 3. Results and discussions 3.1. Selection of suitable extractant
Fig. 1. Cadmium extraction in sulfate solution at different equilibrium pH using feed solution 8.9 mM Cd with different organic extractants; O/A phase ratio= 1:1; time = 10 min.
phase was effectively stripped with 1.10 mol/L H2SO4 solution in two stages. Owusu (1998) proposed a scheme for the separation of metals from Zn–Cd–Co–Ni sulfate solution using D2EHPA. Mellah and Benachour (2007) used tri-n butyl phosphate (TBP) in kerosene for separation of zinc(II), cadmium(II) and chromium(III) from phosphoric acid solutions whereas Nazari et al. (2005) employed Alamine 336 with iso-dodecanol in kerosene for cadmium extraction from wet process phosphoric acid. Distribution coefficients (D) of zinc(II), cadmium(II) and chromium(III) were also reported. In order to establish the condition for extraction of cadmium from the effluents/leach solutions expected from the waste materials viz. electronic scraps, spent batteries etc., the studies have been made using solvent extraction process. The optimum condition i.e. pH, time, extractant for cadmium extraction has been established. 2. Experimental 2.1. Reagent
Initially, the solvents 5% (v/v) diluted in kerosene viz. Cyanex 923, Cyanex 272 and D2EHPA studied for selection of a suitable extractant for extraction of cadmium from sulfate solution (Elyahyaoui and Bouhlassa, 2001; Mantuano et al., 2006). Isodecanol (1%) was added in 5% solution of D2EHPA to improve its phase separation in sulfate medium. Initially, extraction studies were made using aqueous feed containing 8.9 mM cadmium at different equilibrium pH with the organic extractants at 10 min contact time to ensure the complete equilibrium. Fig. 1 shows that acidic solvents D2EHPA and Cyanex 272 were found more efficient extractants and exhibited quantitative extraction of cadmium at equilibrium pH 4.5 and 6.0 respectively, whereas Cyanex 923 showed poor extraction (b20%) even at higher equilibrium pH 6.0. The order of extraction of cadmium was found to be D2EHPA NCyanex 272 N Cyanex 923 with pH. Extraction of cadmium is low up to equilibrium pH 2.0 with all three extractants and further increase in pH caused significant upsurge in extraction efficiency of D2EHPA and Cyanex 272, however, Cyanex 923 showed negligible improvement in extraction. The pH for 50% extraction of cadmium was found to be 3.0 and ∼4.3 for D2EHPA and Cyanex 272 respectively. Since, D2EHPA showed complete extraction at lower equilibrium pH as compared to Cyanex 272, thus it was selected for further extraction study to avoid precipitation of metal at higher equilibrium pH. 3.2. Effect of contact time The kinetics of cadmium extraction was studied by equilibrating aqueous solution containing 4.45 mM cadmium with 5% D2EHPA at aqueous pH 6.03. The results obtained are shown in Fig. 2. The extraction of cadmium (≈78.0%) was quite rapid and attained the equilibrium within a minute. It was also observed that prolong contact time had no adverse effect on extraction. However, to ensure equilibrium 5-minute contact time was maintained during the extraction studies.
The aqueous feed solution containing cadmium was prepared by dissolving appropriate amount of its sulfate salt in double distilled water. The sulfuric acid (H2SO4) and ammonium hydroxide solutions were used in order to maintain desired equilibrium pH of the solution during extraction. All chemicals used were of analytical grade reagent from E. Merck, Mumbai, India. Organic reagents viz. D2EHPA (di-(2-ethylhexyl) phosphoric acid, (Fluka, AG, Buchs), Cyanex 923 (a mixture of different tri-n-octylphosphine oxide, Cytec Ind Canada) and Cyanex 272 (di-2,4, 4-trimethylpentyl phosphinic acid, Cytec Ind., Canada) were employed for extraction without further purification. Commercial grade kerosene was used as diluent for organic extractant and 1% isodecanol mixed with D2EHPA in order to achieve better/quick phase separation and avoid third phase formation. 2.2. Procedure Solvent extraction studies were carried out by mixing equal volume (50 mL) each of cadmium solution and organic extractant using glass stirrer for specified time. After equilibration, the phases were allowed to separate and cadmium content to the raffinate was determined with the help of atomic absorption spectrometer (AAS) (GBC, Avanta). Concentration of cadmium in organic phase was deduced from the difference between initial concentration of cadmium
Fig. 2. Kinetics study of cadmium extraction with D2EHPA (0.15 M) and 1% isodecanol in kerosene; initial pH = 6.03; Cd = 4.45 mM; O/A ratio = 1:1.
232
V. Kumar et al. / Hydrometallurgy 96 (2009) 230–234
3.3. Determination of the metal–organic complex species In order to determine the formation of metal–organic complex during extraction of cadmium, a dimer state of D2EHPA has been considered as reported by various authors (Mellah and Benachour, 2006; Alamdari et al., 2004; Mansur et al., 2002a,b; Wang and Hoh, 1982; Golding and Barclay, 1988). Thus, the extraction mechanism of the metal ion (in this case cadmium) with D2EHPA in kerosene may be expressed as follows: Kex
Mnaq+ + ðn + pÞ=2 ðH2 A2 Þ org X
MAn ðHAÞp
org
+ + nHaq
ð1Þ
where (H2A2) extractant in dimeric form, M is metal, n is valence of the metal or metal complex ion and p number of molecules of extractant engaged in reaction. The equilibrium constant of the extraction reaction Kex, can be given as a function of molar concentration, provided that the ionic strength of the aqueous solution is constant. h i Kex = MAn ðHAÞp
org
+ n n + n + pÞ=2 H aq = M aq ½H2 A2 ðorg :
ð2Þ
The distribution coefficient, D, is defined as the ratio of metal concentration in organic phase to the metal concentration in aqueous phase at reaction equilibrium, and is substituted into the above equation. n + pÞ=2 + n D = Kex ½H2 A2 ðorg = H aq :
Fig. 4. Equilibrium pH vs. log D for 4.45 mM Cd-solution with extractant 0.15 M D2EHPA and 1%(v/v) isodecanol; O/A = 1:1.
ð3Þ
By taking the logarithm of the above equation: log D = log Kex + ðn + pÞ=2 log ðH2 A2 Þ org −n log ½H +
ð4Þ
logD = logKex + ðn + pÞ=2 logðH2 A2 Þ org −npH:
ð5Þ
3.3.1. Plot of log D vs. equilibrium pH The experimental studies for cadmium extraction with equilibrium pH were carried out using aqueous feed concentrations of 0.89 mM, 4.45 mM, and 8.9 mM cadmium with a constant concentration of the
Fig. 3. Effect of equilibrium pH on extraction of cadmium with extractant 0.15 M D2EHPA and 1%(v/v) isodecanol using different cadmium feed concentrations; O/A ratio = 1:1; time = 5 min.
extractant D2EHPA i.e. 0.15 M with 1% (v/v) isodecanol in kerosene. The results show increase in cadmium extraction with the rise in equilibrium pH for each feed concentration (Fig. 3). Moreover, there is a shift in equilibrium pH towards higher pH value with increased feed concentration of cadmium. This may be attributed to the fact that at a particular pH a fixed amount of extractant can extract a certain quantity of metal ion. Further increase in concentration of metal ion in aqueous feed causes decrease in extraction of the metal. Hence, low feed concentration attains the equilibrium at low equilibrium pH as compared to the higher feed concentration (Ritcey and Ashbrook, 1984). The pH for 50% extraction of cadmium found to be 3.0, ∼2.4, and ∼1.9 for the concentration of metal in the aqueous feed 8.9 mM, 4.45 mM and 0.89 mM, respectively. A plot of log D values of metal extraction from aqueous feed of 4.45 mM was plotted against equilibrium pH of the aqueous solution. The results presented in Fig. 4 show a slope value, n = 1.91, support the charge value of cadmium ion i.e. 2 in the aqueous feed. 3.3.2. Plot of log D vs. log [H2A2]org In this investigation concentration of D2EHPA was varied in the range 0.04–0.20 mol/L (M) in kerosene using 1% isodecanol in each case during the cadmium extraction from 1.72 mM Cd aqueous feed concentration. Fig. 5 shows a plot between log D vs. log [H2A2]org
Fig. 5. Log–log plot between distribution ratio and extractant concentration (0.04– 0.20 M); Cd = 1.72 mM; equilibrium pH = 2.5; O/A ratio = 1:1; time = 5 min.
V. Kumar et al. / Hydrometallurgy 96 (2009) 230–234
233
extraction. At equilibrium pH 3.0, 77.6% cadmium was extracted at O/A ratio 1:1 in single contact. McCabe Thiele plot (Fig. 7) suggested the requirement of three stages for complete extraction of cadmium from the feed solution of 4.45 mM Cd at equilibrium pH 3.0 at O/A ratio one. 3.5. Loading capacity of D2EHPA To investigate the loading capacity of 5% (v/v) D2EHPA diluted in kerosene, extraction studies were carried out with two different aqueous feeds 3.56 mM and 1.78 mM Cd at 4.0 pH. The same organic was contacted with fresh aqueous feed maintaining O/A ratio one up to 13 stages in repeated contact mode. The extraction of cadmium presented in Fig. 8 shows almost the same loading capacity with 1004 mg/L and 1002 mg/L cadmium feed solution respectively for 50 mL of 5% D2EHPA. 3.6. Stripping of the loaded organic Fig. 6. Effect of O/A ratio variation on extraction of cadmium (4.45 mM) with extractant 0.15 M D2EHPA and 1%(v/v) isodecanol; equilibrium pH = 3.0; time = 5 min.
at equilibrium pH 2.5 which corresponds that the extraction of cadmium was linearly related with extractant concentration. The slope value {(n + p)/2} was determined to be ∼1.5 thus the p value becomes 1.0. The extraction mechanism for cadmium extraction may be represented as: 2+
Kex
+ Cdaq + 3=2ðH2 A2 Þ X CdA2 ðHAÞ + 2Haq :
ð6Þ
It indicates that cadmium is solvated with 1.5 molecule of dimeric D2EHPA with formation of CdA2 ðHAÞ org complex in the organic phase, provided when extracted compounds are not associated with each other. 3.4. Effect of organic to aqueous (O/A) ratio The effect of O/A ratio has been studied using aqueous feed containing 4.45 mM Cd with 0.15 M D2EHPA and 1% isodecanol in kerosene. The results presented in Fig. 6 indicate increase in cadmium extraction from 22% to almost total extraction with increase in O/A ratio from 0.2 to 3.0 with availability of reagent at high O/A ratio for cadmium
Fig. 7. McCabe Thiele plot to determine number of stages for extraction of cadmium at equilibrium pH 3.0 with extractant 0.15 M D2EHPA and 1%(v/v) isodecanol.
Stripping of cadmium from the loaded organic was conducted using 180 g/L sulfuric acid (H2SO4). Mixing the loaded organic with the stripping agent 180 g/L H2SO4 for 5 min at O/A ratio 1:1 resulted almost complete stripping (99.9%) of the loaded metal in single stage and satisfactory mass balance was obtained. The stripped solvent showed similar extraction efficiency when reused under the same experimental condition even up to 10 cycles of extraction. 4. Conclusions The following conclusions are drawn from solvent extraction studies of cadmium from sulfate solution: ➞ On comparing the performance for extraction of cadmium with different extractants, the extraction was found to be in the following order with pH D2EHPA NCyanex 272 N Cyanex 923. ➞ The total cadmium can be quantitatively extracted at equilibrium pH 4.5 with 5% D2EHPA (v/v) in kerosene in single contact, however, it requires three stages at lower equilibrium pH 3.0 from 4.45 mM cadmium solution. ➞ The extraction studies showed the formation of CdA2(HA)org species in the organic feed. Loading capacity of 5% D2EHPA was found to be ∼ 1000 mg/L Cd at equilibrium pH 3.0. The loaded metal could be stripped with 180 g/L H2SO4 at O/A ratio 1:1.
Fig. 8. Determination of loading capacity of 5% (v/v) D2EHPA using two different feed concentrations; O/A ratio = 1:1; time = 5 min; pH = 4.0.
234
V. Kumar et al. / Hydrometallurgy 96 (2009) 230–234
Acknowledgements The authors wish to thank the Director, National Metallurgical Laboratory, Jamshedpur, India for giving the permission to publish this article. The work reported in this paper was made under the project funded by the Korea Institute of Geo-science and Mineral Resources (KIGAM), Korea. The financial support is gratefully acknowledged. References Agrawal, A., Sahu, K.K., 2006. Kinetics and isotherm studies of cadmium adsorption on manganese nodule residue. J. Hazard. Mater. B137, 915–924. Agrawal, A., Kumar, V., Pandey, B.D., 2006. A review of remediation options for the treatment of electroplating and leather tanning effluent containing chromium. Miner. Process. Extr. Metall. Rev. 27, 99–130. Almela, A., Elizalde, M.P., 1995. Solvent extraction of cadmium (II) from acidic media by Cyanex 302. Hydrometallurgy 37, 47–57. Alamdari, E.K., Moradkhani, D., Darvish, D., Askari, M., Behnian, D., 2004. Synergistic effect of MEHPA on co-extraction of zinc and cadmium with DEHPA. Miner. Eng. 17, 89–92. Arnzt, Y., Chambron, J., Dumitresco, B., Eclancher, B., Prat, V., 1999. A portable cadmium telluride multidetector probe for cardiac function monitoring. Nucl. Instrum. Methods Phys. Res. A 428, 150–157. Elyahyaoui, A., Bouhlassa, S., 2001. Extraction of cadmium and iodocadmat species by di (2-ethylhexyl) phosphoric acid from perchloric and phosphoric media. Appl. Radiat. Isotopes 54, 921–926. Golding, J.A., Barclay, C.D., 1988. Equilibrium characteristics for the extraction of cobalt and nickel into di(2-ethylhexyl)phosphoric acid. Can. J. Chem. Eng. 66, 970–979. Gotfryd, L., Cox, M., 2006. The selective recovery of cadmium (II) from sulfate solutions by a counter current extraction stripping process using a mixture of diisoporpylsalicylic acid and Cyanex®-471X. Hydrometallurgy 81, 226–233.
Gupta, B., Deep, A., Malik, P., 2001. Extraction and recovery of cadmium using Cyanex 923. Hydrometallurgy 61, 65–71. Mansur, M.B., Slater, M.J., Biscaia, E.C., 2002a. Kinetic analysis of the liquid–liquid test system ZnSO4/D2EHPA/n-heptane. Hydrometallurgy 63, 107–116. Mansur, M.B., Slater, M.J., Biscaia, E.C., 2002b. Equilibrium analysis of the liquid–liquid test system ZnSO4/D2EHPA/n-heptane. Hydrometallurgy 63, 117–126. Mantuano, D.P., Dorella, G., Elias, R.C.A., Mansur, M.B., 2006. Analysis of a hydrometallurgical route to recover base metals from spent rechargeable batteries by liquid–liquid extraction with Cyanex 272. J. Power Sources 159, 1510–1518. Mellah, A., Benachour, D., 2006. The solvent extraction of zinc and cadmium from phosphoric acid solution by di-2-ethylhexyl phosphoric acid in kerosene diluent. Chem. Eng. Process. 45, 684–690. Mellah, A., Benachour, D., 2007. The solvent extraction of zinc, cadmium and chromium from phosphoric acid solutions by tri-n butyl phosphate in kerosene diluent. Sep. Purif. Technol. 56, 220–224. Nazari, K., Ghadiri, A., Babaie, H., 2005. Elimination of cadmium from wet process phosphoric acid with Alamine 336. Miner. Eng. 18, 1233–1238. Owusu, G., 1998. Selective extraction of Zn and Cd from Zn–Cd–Co–Ni sulfate solution using di-2-ethylhexyl phosphoric acid extractant. Hydrometallurgy 47, 205–215. Reddy, B.R., Priya, N.D., Kumar, J.R., 2004. Solvent extraction of cadmium(II) from sulfate solution using TOPS 99, PC 88A, Cyanex 272 and their mixtures. Hydrometallurgy 74, 277–283. Ritcey, G.M., Ashbrook, A.W., 1984. Solvent Extraction: Principles and Applications to Process Metallurgy, Part-I. Elsevier, Amsterdam. Safarzadeh, M.S., Bafghi, M.S., Moradkhani, D., Ilkhchi, M.O., 2007. A review on hydrometallurgical extraction and recovery of cadmium from various resources. Miner. Eng. 20, 211–220. Wang, C.H., Hoh, Y.C., 1982. The effect of pH on cadmium extraction by LIX-34. Hydrometallurgy 8, 161–171.
Contents lists available at ScienceDirect
Hydrometallurgy j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / h yd r o m e t
Solvent extraction of cadmium from sulfate solution with di-(2-ethylhexyl) phosphoric acid diluted in kerosene Vinay Kumar a,⁎, Manoj Kumar a, Manis Kumar Jha b, Jinki Jeong b, Jae-chun Lee b,1 a b
Metal Extraction and Forming Division, National Metallurgical Laboratory, Jamshedpur-831007, India Minerals and Materials Processing Division, Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon, 305-350, Republic of Korea
a r t i c l e
i n f o
Article history: Received 18 June 2008 Received in revised form 9 September 2008 Accepted 20 October 2008 Available online 5 November 2008 Keywords: Solvent extraction Cadmium D2EHPA Sulfate solution
a b s t r a c t In the present paper, solvent extraction process has been used for extraction of cadmium from sulfate solution using di-(2-ethylhexyl) phosphoric acid (D2EHPA) with 1% isodecanol in kerosene diluent expected from industrial effluents or leaching of ores/secondary materials. Different process parameters such as pH, contact time, extractant concentration, O/A ratio etc. were investigated. Results demonstrated that quantitative extraction of cadmium was feasible from 4.45 mM cadmium feed solution in single stage at equilibrium pH 4.5, time 2 min and O/A ratio 1:1 with 0.15 mM D2EHPA. The extraction mechanism of cadmium from sulfate solution by D2EHPA in kerosene could be represented at equilibrium by Cd2+ + 3/2 (H2A2)org ⇔ CdA2(HA)org + 2H+. The loading capacity of 0.15 mM D2EHPA in sulfate solution was determined to be ∼8.9 mM cadmium. The loaded cadmium was effectively stripped using 180 g/L sulfuric acid. The metal or salt could be produced by electrolysis or crystallization from the stripped solution. © 2008 Published by Elsevier B.V.
1. Introduction Cadmium is an important metal which is extensively employed in solar battery, electronic, electroplating, metallurgical industries etc. (Arnzt et al., 1999). During production and also at the end-of-service life, waste material containing cadmium is generated in the form of solid and liquid effluents in these industries. The disposal of such materials causes not only the environmental pollution but loss of resources as cadmium and its compounds are highly toxic and carcinogenic in nature (Elyahyaoui and Bouhlassa, 2001; Agrawal and Sahu, 2006). Recovery and recycling of metals will conserve the natural resources to meet the future demand of materials and also reduce the environmental pollution. The processes usually employed for the recovery of metals are hydro/pyrometallurgical methods where material is first leached in acidic or alkaline solution to dissolve the metals directly or after thermal treatment. The leach solution contains cadmium along with other metallic constituents such as nickel, zinc etc. depending on waste material treated. The solution is subsequently processed to recover valuable constituents following precipitation, cementation, ion exchange, adsorption, electrolysis etc. (Mantuano et al., 2006; Agrawal et al., 2006). Among the available processing alternatives, solvent extraction is a technique that not only meets the strict environmental regulations and also high purity value added products could be produced (Safarzadeh et al., 2007). Different authors (Almela and Elizalde, 1995; Reddy et al., 2004; Gupta et al., ⁎ Corresponding author. Fax: +91 657 2270527. E-mail addresses: [email protected] (V. Kumar), [email protected] (J. Lee). 1 Fax: +82 42 8683705. 0304-386X/$ – see front matter © 2008 Published by Elsevier B.V. doi:10.1016/j.hydromet.2008.10.010
2001) studied the extraction of cadmium from the aqueous solutions using organic extractants such as di-(2-ethylhexyl) phosphoric acid (D2EHPA), di-2,4,4-trimethylpentyl phosphinic acid (Cyanex 272) etc. The process reported the extraction and separation of cadmium from aqueous leach solution of zinc sulfide concentrate, residue of zinc plant, beta cake, pot skimming, etc. The extraction of cadmium (II) from chloride solution of 1.0 M ionic strength by the bis(2,2,4-trimethylpentyl) thiophosphinic (Cyanex 302) (HR) extractant in kerosene has been studied over a range of pH and reagent concentrations (Almela and Elizalde, 1995). The results indicated that the extraction of cadmium (II) takes place with the formation of the species CdR2 (HR) and CdR2(HR)2. Solvent extraction of cadmium from sulfate solution was studied using organophosphorous based extractants viz. TOPS 99 (an equivalent of di-(2-ethylhexyl) phosphoric acid, obtained from Heavy water plant, Talchar, India), PC 88A (2-ethylhexylphosphonic acid mono-2-ethylhexyl ester) and Cyanex 272 (Reddy et al., 2004). The extraction of cadmium takes place by cation exchange mechanism with the formation of 1:3 metal to reagent complex. TOPS 99 has been found to be the best synergist for extraction with mixed extractant than PC 88A and Cyanex272. Gupta et al. (2001) explored the extraction of Cd(II) along with Al(III), Fe(III), In(III), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Hg(II) and Pb(II) from hydrochloric acid solution using Cyanex 923 (a mixture of different tri-n-octylphosphine oxide) and pointed out the separation of cadmium in the presence of various metallic ionic species. Gotfryd and Cox (2006) used an equimolar mixture diisopropylsalicylic acid and Cyanex 471X (tri-isobutylphosphine sulfide) (0.5 mol/L) diluted with Solvesso 150 as extractant to separate cadmium and zinc from the leach solution of cadmium carbonate or cadmium cementation sponge. The loaded cadmium from the organic
V. Kumar et al. / Hydrometallurgy 96 (2009) 230–234
231
in aqueous phase and the concentration of cadmium in the raffinate. 1.8 M H2SO4 was used for stripping of the cadmium from the loaded organic and satisfactory material balance was obtained in all the experiments. 3. Results and discussions 3.1. Selection of suitable extractant
Fig. 1. Cadmium extraction in sulfate solution at different equilibrium pH using feed solution 8.9 mM Cd with different organic extractants; O/A phase ratio= 1:1; time = 10 min.
phase was effectively stripped with 1.10 mol/L H2SO4 solution in two stages. Owusu (1998) proposed a scheme for the separation of metals from Zn–Cd–Co–Ni sulfate solution using D2EHPA. Mellah and Benachour (2007) used tri-n butyl phosphate (TBP) in kerosene for separation of zinc(II), cadmium(II) and chromium(III) from phosphoric acid solutions whereas Nazari et al. (2005) employed Alamine 336 with iso-dodecanol in kerosene for cadmium extraction from wet process phosphoric acid. Distribution coefficients (D) of zinc(II), cadmium(II) and chromium(III) were also reported. In order to establish the condition for extraction of cadmium from the effluents/leach solutions expected from the waste materials viz. electronic scraps, spent batteries etc., the studies have been made using solvent extraction process. The optimum condition i.e. pH, time, extractant for cadmium extraction has been established. 2. Experimental 2.1. Reagent
Initially, the solvents 5% (v/v) diluted in kerosene viz. Cyanex 923, Cyanex 272 and D2EHPA studied for selection of a suitable extractant for extraction of cadmium from sulfate solution (Elyahyaoui and Bouhlassa, 2001; Mantuano et al., 2006). Isodecanol (1%) was added in 5% solution of D2EHPA to improve its phase separation in sulfate medium. Initially, extraction studies were made using aqueous feed containing 8.9 mM cadmium at different equilibrium pH with the organic extractants at 10 min contact time to ensure the complete equilibrium. Fig. 1 shows that acidic solvents D2EHPA and Cyanex 272 were found more efficient extractants and exhibited quantitative extraction of cadmium at equilibrium pH 4.5 and 6.0 respectively, whereas Cyanex 923 showed poor extraction (b20%) even at higher equilibrium pH 6.0. The order of extraction of cadmium was found to be D2EHPA NCyanex 272 N Cyanex 923 with pH. Extraction of cadmium is low up to equilibrium pH 2.0 with all three extractants and further increase in pH caused significant upsurge in extraction efficiency of D2EHPA and Cyanex 272, however, Cyanex 923 showed negligible improvement in extraction. The pH for 50% extraction of cadmium was found to be 3.0 and ∼4.3 for D2EHPA and Cyanex 272 respectively. Since, D2EHPA showed complete extraction at lower equilibrium pH as compared to Cyanex 272, thus it was selected for further extraction study to avoid precipitation of metal at higher equilibrium pH. 3.2. Effect of contact time The kinetics of cadmium extraction was studied by equilibrating aqueous solution containing 4.45 mM cadmium with 5% D2EHPA at aqueous pH 6.03. The results obtained are shown in Fig. 2. The extraction of cadmium (≈78.0%) was quite rapid and attained the equilibrium within a minute. It was also observed that prolong contact time had no adverse effect on extraction. However, to ensure equilibrium 5-minute contact time was maintained during the extraction studies.
The aqueous feed solution containing cadmium was prepared by dissolving appropriate amount of its sulfate salt in double distilled water. The sulfuric acid (H2SO4) and ammonium hydroxide solutions were used in order to maintain desired equilibrium pH of the solution during extraction. All chemicals used were of analytical grade reagent from E. Merck, Mumbai, India. Organic reagents viz. D2EHPA (di-(2-ethylhexyl) phosphoric acid, (Fluka, AG, Buchs), Cyanex 923 (a mixture of different tri-n-octylphosphine oxide, Cytec Ind Canada) and Cyanex 272 (di-2,4, 4-trimethylpentyl phosphinic acid, Cytec Ind., Canada) were employed for extraction without further purification. Commercial grade kerosene was used as diluent for organic extractant and 1% isodecanol mixed with D2EHPA in order to achieve better/quick phase separation and avoid third phase formation. 2.2. Procedure Solvent extraction studies were carried out by mixing equal volume (50 mL) each of cadmium solution and organic extractant using glass stirrer for specified time. After equilibration, the phases were allowed to separate and cadmium content to the raffinate was determined with the help of atomic absorption spectrometer (AAS) (GBC, Avanta). Concentration of cadmium in organic phase was deduced from the difference between initial concentration of cadmium
Fig. 2. Kinetics study of cadmium extraction with D2EHPA (0.15 M) and 1% isodecanol in kerosene; initial pH = 6.03; Cd = 4.45 mM; O/A ratio = 1:1.
232
V. Kumar et al. / Hydrometallurgy 96 (2009) 230–234
3.3. Determination of the metal–organic complex species In order to determine the formation of metal–organic complex during extraction of cadmium, a dimer state of D2EHPA has been considered as reported by various authors (Mellah and Benachour, 2006; Alamdari et al., 2004; Mansur et al., 2002a,b; Wang and Hoh, 1982; Golding and Barclay, 1988). Thus, the extraction mechanism of the metal ion (in this case cadmium) with D2EHPA in kerosene may be expressed as follows: Kex
Mnaq+ + ðn + pÞ=2 ðH2 A2 Þ org X
MAn ðHAÞp
org
+ + nHaq
ð1Þ
where (H2A2) extractant in dimeric form, M is metal, n is valence of the metal or metal complex ion and p number of molecules of extractant engaged in reaction. The equilibrium constant of the extraction reaction Kex, can be given as a function of molar concentration, provided that the ionic strength of the aqueous solution is constant. h i Kex = MAn ðHAÞp
org
+ n n + n + pÞ=2 H aq = M aq ½H2 A2 ðorg :
ð2Þ
The distribution coefficient, D, is defined as the ratio of metal concentration in organic phase to the metal concentration in aqueous phase at reaction equilibrium, and is substituted into the above equation. n + pÞ=2 + n D = Kex ½H2 A2 ðorg = H aq :
Fig. 4. Equilibrium pH vs. log D for 4.45 mM Cd-solution with extractant 0.15 M D2EHPA and 1%(v/v) isodecanol; O/A = 1:1.
ð3Þ
By taking the logarithm of the above equation: log D = log Kex + ðn + pÞ=2 log ðH2 A2 Þ org −n log ½H +
ð4Þ
logD = logKex + ðn + pÞ=2 logðH2 A2 Þ org −npH:
ð5Þ
3.3.1. Plot of log D vs. equilibrium pH The experimental studies for cadmium extraction with equilibrium pH were carried out using aqueous feed concentrations of 0.89 mM, 4.45 mM, and 8.9 mM cadmium with a constant concentration of the
Fig. 3. Effect of equilibrium pH on extraction of cadmium with extractant 0.15 M D2EHPA and 1%(v/v) isodecanol using different cadmium feed concentrations; O/A ratio = 1:1; time = 5 min.
extractant D2EHPA i.e. 0.15 M with 1% (v/v) isodecanol in kerosene. The results show increase in cadmium extraction with the rise in equilibrium pH for each feed concentration (Fig. 3). Moreover, there is a shift in equilibrium pH towards higher pH value with increased feed concentration of cadmium. This may be attributed to the fact that at a particular pH a fixed amount of extractant can extract a certain quantity of metal ion. Further increase in concentration of metal ion in aqueous feed causes decrease in extraction of the metal. Hence, low feed concentration attains the equilibrium at low equilibrium pH as compared to the higher feed concentration (Ritcey and Ashbrook, 1984). The pH for 50% extraction of cadmium found to be 3.0, ∼2.4, and ∼1.9 for the concentration of metal in the aqueous feed 8.9 mM, 4.45 mM and 0.89 mM, respectively. A plot of log D values of metal extraction from aqueous feed of 4.45 mM was plotted against equilibrium pH of the aqueous solution. The results presented in Fig. 4 show a slope value, n = 1.91, support the charge value of cadmium ion i.e. 2 in the aqueous feed. 3.3.2. Plot of log D vs. log [H2A2]org In this investigation concentration of D2EHPA was varied in the range 0.04–0.20 mol/L (M) in kerosene using 1% isodecanol in each case during the cadmium extraction from 1.72 mM Cd aqueous feed concentration. Fig. 5 shows a plot between log D vs. log [H2A2]org
Fig. 5. Log–log plot between distribution ratio and extractant concentration (0.04– 0.20 M); Cd = 1.72 mM; equilibrium pH = 2.5; O/A ratio = 1:1; time = 5 min.
V. Kumar et al. / Hydrometallurgy 96 (2009) 230–234
233
extraction. At equilibrium pH 3.0, 77.6% cadmium was extracted at O/A ratio 1:1 in single contact. McCabe Thiele plot (Fig. 7) suggested the requirement of three stages for complete extraction of cadmium from the feed solution of 4.45 mM Cd at equilibrium pH 3.0 at O/A ratio one. 3.5. Loading capacity of D2EHPA To investigate the loading capacity of 5% (v/v) D2EHPA diluted in kerosene, extraction studies were carried out with two different aqueous feeds 3.56 mM and 1.78 mM Cd at 4.0 pH. The same organic was contacted with fresh aqueous feed maintaining O/A ratio one up to 13 stages in repeated contact mode. The extraction of cadmium presented in Fig. 8 shows almost the same loading capacity with 1004 mg/L and 1002 mg/L cadmium feed solution respectively for 50 mL of 5% D2EHPA. 3.6. Stripping of the loaded organic Fig. 6. Effect of O/A ratio variation on extraction of cadmium (4.45 mM) with extractant 0.15 M D2EHPA and 1%(v/v) isodecanol; equilibrium pH = 3.0; time = 5 min.
at equilibrium pH 2.5 which corresponds that the extraction of cadmium was linearly related with extractant concentration. The slope value {(n + p)/2} was determined to be ∼1.5 thus the p value becomes 1.0. The extraction mechanism for cadmium extraction may be represented as: 2+
Kex
+ Cdaq + 3=2ðH2 A2 Þ X CdA2 ðHAÞ + 2Haq :
ð6Þ
It indicates that cadmium is solvated with 1.5 molecule of dimeric D2EHPA with formation of CdA2 ðHAÞ org complex in the organic phase, provided when extracted compounds are not associated with each other. 3.4. Effect of organic to aqueous (O/A) ratio The effect of O/A ratio has been studied using aqueous feed containing 4.45 mM Cd with 0.15 M D2EHPA and 1% isodecanol in kerosene. The results presented in Fig. 6 indicate increase in cadmium extraction from 22% to almost total extraction with increase in O/A ratio from 0.2 to 3.0 with availability of reagent at high O/A ratio for cadmium
Fig. 7. McCabe Thiele plot to determine number of stages for extraction of cadmium at equilibrium pH 3.0 with extractant 0.15 M D2EHPA and 1%(v/v) isodecanol.
Stripping of cadmium from the loaded organic was conducted using 180 g/L sulfuric acid (H2SO4). Mixing the loaded organic with the stripping agent 180 g/L H2SO4 for 5 min at O/A ratio 1:1 resulted almost complete stripping (99.9%) of the loaded metal in single stage and satisfactory mass balance was obtained. The stripped solvent showed similar extraction efficiency when reused under the same experimental condition even up to 10 cycles of extraction. 4. Conclusions The following conclusions are drawn from solvent extraction studies of cadmium from sulfate solution: ➞ On comparing the performance for extraction of cadmium with different extractants, the extraction was found to be in the following order with pH D2EHPA NCyanex 272 N Cyanex 923. ➞ The total cadmium can be quantitatively extracted at equilibrium pH 4.5 with 5% D2EHPA (v/v) in kerosene in single contact, however, it requires three stages at lower equilibrium pH 3.0 from 4.45 mM cadmium solution. ➞ The extraction studies showed the formation of CdA2(HA)org species in the organic feed. Loading capacity of 5% D2EHPA was found to be ∼ 1000 mg/L Cd at equilibrium pH 3.0. The loaded metal could be stripped with 180 g/L H2SO4 at O/A ratio 1:1.
Fig. 8. Determination of loading capacity of 5% (v/v) D2EHPA using two different feed concentrations; O/A ratio = 1:1; time = 5 min; pH = 4.0.
234
V. Kumar et al. / Hydrometallurgy 96 (2009) 230–234
Acknowledgements The authors wish to thank the Director, National Metallurgical Laboratory, Jamshedpur, India for giving the permission to publish this article. The work reported in this paper was made under the project funded by the Korea Institute of Geo-science and Mineral Resources (KIGAM), Korea. The financial support is gratefully acknowledged. References Agrawal, A., Sahu, K.K., 2006. Kinetics and isotherm studies of cadmium adsorption on manganese nodule residue. J. Hazard. Mater. B137, 915–924. Agrawal, A., Kumar, V., Pandey, B.D., 2006. A review of remediation options for the treatment of electroplating and leather tanning effluent containing chromium. Miner. Process. Extr. Metall. Rev. 27, 99–130. Almela, A., Elizalde, M.P., 1995. Solvent extraction of cadmium (II) from acidic media by Cyanex 302. Hydrometallurgy 37, 47–57. Alamdari, E.K., Moradkhani, D., Darvish, D., Askari, M., Behnian, D., 2004. Synergistic effect of MEHPA on co-extraction of zinc and cadmium with DEHPA. Miner. Eng. 17, 89–92. Arnzt, Y., Chambron, J., Dumitresco, B., Eclancher, B., Prat, V., 1999. A portable cadmium telluride multidetector probe for cardiac function monitoring. Nucl. Instrum. Methods Phys. Res. A 428, 150–157. Elyahyaoui, A., Bouhlassa, S., 2001. Extraction of cadmium and iodocadmat species by di (2-ethylhexyl) phosphoric acid from perchloric and phosphoric media. Appl. Radiat. Isotopes 54, 921–926. Golding, J.A., Barclay, C.D., 1988. Equilibrium characteristics for the extraction of cobalt and nickel into di(2-ethylhexyl)phosphoric acid. Can. J. Chem. Eng. 66, 970–979. Gotfryd, L., Cox, M., 2006. The selective recovery of cadmium (II) from sulfate solutions by a counter current extraction stripping process using a mixture of diisoporpylsalicylic acid and Cyanex®-471X. Hydrometallurgy 81, 226–233.
Gupta, B., Deep, A., Malik, P., 2001. Extraction and recovery of cadmium using Cyanex 923. Hydrometallurgy 61, 65–71. Mansur, M.B., Slater, M.J., Biscaia, E.C., 2002a. Kinetic analysis of the liquid–liquid test system ZnSO4/D2EHPA/n-heptane. Hydrometallurgy 63, 107–116. Mansur, M.B., Slater, M.J., Biscaia, E.C., 2002b. Equilibrium analysis of the liquid–liquid test system ZnSO4/D2EHPA/n-heptane. Hydrometallurgy 63, 117–126. Mantuano, D.P., Dorella, G., Elias, R.C.A., Mansur, M.B., 2006. Analysis of a hydrometallurgical route to recover base metals from spent rechargeable batteries by liquid–liquid extraction with Cyanex 272. J. Power Sources 159, 1510–1518. Mellah, A., Benachour, D., 2006. The solvent extraction of zinc and cadmium from phosphoric acid solution by di-2-ethylhexyl phosphoric acid in kerosene diluent. Chem. Eng. Process. 45, 684–690. Mellah, A., Benachour, D., 2007. The solvent extraction of zinc, cadmium and chromium from phosphoric acid solutions by tri-n butyl phosphate in kerosene diluent. Sep. Purif. Technol. 56, 220–224. Nazari, K., Ghadiri, A., Babaie, H., 2005. Elimination of cadmium from wet process phosphoric acid with Alamine 336. Miner. Eng. 18, 1233–1238. Owusu, G., 1998. Selective extraction of Zn and Cd from Zn–Cd–Co–Ni sulfate solution using di-2-ethylhexyl phosphoric acid extractant. Hydrometallurgy 47, 205–215. Reddy, B.R., Priya, N.D., Kumar, J.R., 2004. Solvent extraction of cadmium(II) from sulfate solution using TOPS 99, PC 88A, Cyanex 272 and their mixtures. Hydrometallurgy 74, 277–283. Ritcey, G.M., Ashbrook, A.W., 1984. Solvent Extraction: Principles and Applications to Process Metallurgy, Part-I. Elsevier, Amsterdam. Safarzadeh, M.S., Bafghi, M.S., Moradkhani, D., Ilkhchi, M.O., 2007. A review on hydrometallurgical extraction and recovery of cadmium from various resources. Miner. Eng. 20, 211–220. Wang, C.H., Hoh, Y.C., 1982. The effect of pH on cadmium extraction by LIX-34. Hydrometallurgy 8, 161–171.