Extraction and Separation of Cadmium from the Chloride Solution of E-Waste Using Cyanex 923 Impregnated Amberlite XAD-7HP Resin

Nghiem Van Nguyen1,2, Jae-chun Lee3,4,+, Hai Trung Huynh2 and Jinki Jeong3,4

1Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, Sendai 980-8577, Japan 2School of Environmental Science and Technology, Hanoi University of Science and Technology (HUST), Vietnam 3Mineral Resources Research Division, Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon 305-350, Republic of Korea 4Resources Recycling, Korea University of Science and Technology (KUST), Daejeon 305-350, Republic of Korea

Cadmium(II) is not only hazardous but is also an impurity in the leachate of electronic waste which is processed during the extraction of valuable metals. This research focuses on the removal of cadmium from the leachate of e-waste containing Cu, Ni, Sn, Pb, Cd, Zn and Au using a solvent impregnated resin (SIR). The studies performed for the extraction of cadmium from the high acidity chloride solution showed the effective removal of cadmium forming solvation compound with Cyanex 923 impregnated Amberlite XAD-7HP resin. In the adsorption studies, the kinetics was found to be a second-order rate and followed a Langmuir isotherm. The results also showed that SIR comprising Cyanex 923 is effective for adsorption of zinc and gold from the leachate. The loaded metals on the SIR were separated by using selective eluents, water for Cd and Zn, whereas thiourea eluted Au. The remaining metals in the rafﬁnate could be further processed to recover valuables after removing cadmium and other metals by a suitable hydrometallurgical processes. [doi:10.2320/matertrans.M2015137]

(Received April 7, 2015; Accepted May 21, 2015; Published June 26, 2015) Keywords: cadmium(II), amberlite XAD-7HP resin, cyanex 923 extractant, solvent impregnated resin (SIR), leachate

1. Introduction tions.12) The impregnation of an extractant in a resin, which allows to maintain their high recovery efficiency, and prevent With the technological innovations, there has been their dispersion in the aqueous solution, and the presence of upsurge/increase in the production of high-tech electrical the resin significantly facilitates the extraction of the ionic and electronic equipment (EEE) worldwide, thus generating species from the solution.13) large quantities of obsolete and discarded materials contain- Several research works have been studied for the ing various valuable and hazardous metallic and non-metallic extraction of cadmium using SIR/EIR from various solutions constituents.1,2) Their disposal as dump and landfills is containing sulfate, chloride, nitrate, phosphate ions, etc.1418) creating environmental pollution as well as loss of natural The separation of cadmium, zinc, and lead from sulfate resources. The recovery of e-waste will not only conserve the solutions was investigated using ISPE-302,14) which was resources but also meet the future demand of materials for prepared by attachment of bis (2,4,4-trimethyl)monothio- sustainable growth. However, it requires a development of phosphonic acid on a functionalized silica surface. ISPE-302 specific processing options depending on different metallic exhibited the selectivity series following the order cad- constituents and its concentrations. The electronic compo- mium > lead > zinc. For removal of cadmium from phos- nents particularly printed circuit boards (PCBs) contains phoric acid solutions, Cyanex 301 impregnated Amberlite hazardous and valuable metals. A process has been XAD-7 was found more efficiently than Cyanex 301 developed for the recovery of metals from e-wastes by impregnated Amberliter XAD-2 about 67 times.16) The physical beneficiation followed by leaching with electro- investigation on the adsorption of Pb(II), Cd(II) and Zn(II) generated chlorine to dissolve their metallic values in our cations in nitrate solution has been done recently using laboratory.3,4) The leachate contains different metals such as carboxyphenylresorcinarene-impregnated resin.18) The results copper, cadmium, lead, tin, zinc, gold, etc. in the chloride was reported the selectivity order of extracted metal ions as solutions. Pb(II) º Cd(II), Zn(II). The values of correlation coefficients Cadmium, one the hazardous metals having adverse effect (R2) indicated that the Langmuir isotherm model well- on human health,5) is also present in low concentration in the described the sorption equilibrium. leach solution. Their recovery from dilute solution could As the chloride solutions is extensively employed in be achieved by hydrometallurgical processes consisting of hydrometallurgy, the studies have also been reported for the solvent extraction,6,7) ion exchange,8,9) extractant/solvent extraction of cadmium ions in the presence of other ionic impregnated resins (EIR/SIR),10,11) etc. Although the solvent species by extractant/solvent impregnated resins (EIR/ extraction process is efficient for the recovery of metals from SIR).1923) 1-Hexyl-4-ethyloctyl isopropyl-phosphonic acid the aqueous solution using organic extractants, it is not (HEOPPA) impregnated in the resin was used in the feasible to recover the metals particularly from dilute extraction of cobalt(II), nickel(II), zinc(II), cadmium(II), solutions containing low metallic content. In these processes, and copper(II) in chloride solution.20) The reaction mechan- polymers-supported organic extractants are promising for the ism was proposed by the formation of complex ML2(HL)q, extraction and separation of metal ions from dilute solu- and adsorption isotherm was followed Freundlich’s model. Navarro and his research group21) studied the extraction of +Corresponding author, E-mail: [email protected] cadmium from chloride by Cyanex 921 (tri-octyl phosphine Extraction and Separation of Cadmium from the Chloride Solution of E-Waste Using Cyanex 923 Impregnated Amberlite XAD-7HP Resin 1295 oxide, TOPO) impregnated in Amberlite XAD-7 (EIR). The Table 1 Composition of leachate of electronic scraps. / ¹ sorption capacity was found to be 13 mg Cd g, for EIR with Elements Concentration, C/mg·dm 3 366 mg Cyanex 921/g in a 3.0 mol/dm3 HCl solution Cu 14940 containing 60 mg Cd/dm3, in which equilibrium was reached Ni 560 within 28,800 s contact time. The extraction mechanism Sn 125 involved various solvating reactions with neutral CdCl 2 Pb 80 and ion pairs (involving associations between protons and Zn 5.6 anionic cadmium chloro-species). Cadmium can be effi- Au 5.5 ciently desorbed using a diverse range of eluents and the Cd 0.5 possibility of re-using the resin was demonstrated over four cycles. In view of the above, solvent/extractant impregnated resin (SIR), Cyanex 923 impregnated Amberlite XAD-7HP resin has been studied for the extraction of cadmium along with the 2.2 Preparation of solvent impregnated resin (SIR) other associated metals in the leachate of electronic wastes. beads The organic extractant, Cyanex 923 (a mixture of four trialkyl In this research, the dry impregnation method has been phosphine oxide with general formula R3PO [(R = employed for preparation of SIR beads because it is simple CH3(CH2)7 or CH3(CH2)5)]) has been chosen due to its and easy to determine the amount of extractant loaded in the attractive properties such as low solubility in solutions, resin. The dilute Cyanex 923 was prepared by mixing a effectiveness at high acidity and easy stripping.24,25) As the known amount of extractant and acetone. The dry Amberlite Cyanex 923 impregnated Amberlite XAD-7HP resin not only XAD-7HP resin was added in known dilute Cyanex 923, and removes cadmium(II) from the aqueous solutions but also the mixture was shaken at 298 K for 86,400 s. The solid beads loads other metals such as gold and zinc present in the leach were then separated by using Buchner filter, and put in liquor. Therefore, separation of the metals such as cadmium, vacuum oven at 333 K for 43,200 s to evaporate acetone. The zinc and gold loaded on the SIR by the selective elution solvent impregnated resin containing 0.375 g Cyanex 923 in method has also been investigated in the present paper for 1.0 g SIR has been used in subsequent studies for cadmium effective regeneration of SIR for subsequent recycling. The extraction under the different experimental conditions. closed-loop process for removal of cadmium(II) and other associated metals from the leachate of electronic scraps will 2.3 Methods be proposed after obtaining the optimum experimental The experimental studies on the adsorption and elution of conditions. cadmium(II) by the SIR were performed in batch test. The batch experiments were carried out using a conical flask in a 2. Experimental shaking water bath under atmospheric conditions. The percentage adsorption was calculated following 2.1 Materials equation: The leachate obtained by the elecro-generated chlorine ðC C Þ leaching of e-waste contains different metals in mg/dm3 ð Þ¼ o t ð Þ Adsorption % C 100 1 14940 Cu, 560 Ni, 125 Sn, 80 Pb, 5.6 Zn, 5.5 Au and 0.5 Cd o 3 4) (Table 1) with acidity of 2.0 mol/dm (HCl). The synthetic Where Co is the initial concentration of metal in the feed and 3 3 solutions containing cadmium 0.5200 mg/dm were pre- Ct is concentration of metal in raffinate at time t (mg/dm ). pared similar to the composition of the leach liquor of The amount of metal adsorbed on the adsorbent (q,mg/g) e-scraps, by dissolving cadmium chloride in distilled water. was determined by equation: The chemicals viz. cadmium chloride, hydrochloric acid, ðC C Þ sodium hydroxide, thiourea, acetone, etc. were laboratory q ¼ o t V ð Þ M 2 grade reagents. Amberlite XAD-7HP resin supplied by Rohm and Hass Where M is the dry mass of adsorbent (g) and V is the volume was treated with 1.0 mol/dm3 HCl in 21,600 s at 298 K to of the test solution (dm3). remove impurities and organics. The resin was washed The distribution ratio of a metal between an aqueous phase several times with de-ionized water and then dried for and an organic is known as the extraction coefficient, D and 43,200 s in an oven at 323 K before use. is defined as: The extractant, Cyanex 923 is a mixture of four trialkyl ½Morg phosphine oxide with general formula: R3PO (14%), R2RAPO D ¼ ð3Þ ½Maq (42%), RRA2PO (31%)andRA3PO (8%), in which R denotes n-octyl and RA stands for n-hexyl group [(R = CH3(CH2)7 Where, [M]org is the concentration of metal in organic (mg/ 3 and RA = CH3(CH2)5)] with the average molecular mass dm ) and [M]aq is the concentration of metal in the aqueous 348 g/mol.26) The principal advantage of Cyanex 923 is its phase (mg/dm3). very low solubility in water and ease in stripping of the The metal content of the samples was analyzed by Atomic loaded metal. Cyanex 923 is supplied by Cytec company Absorption Spectrometry (A Analyst 400, Perkin Elmer, (USA). The properties of both Amberlite XAD-7HP resin USA) to determine cadmium and other metals concentration and Cyanex 923 extractant are reported elsewhere.27,28) in the leachate before and after contacting with SIR. 1296 N. Van Nguyen, J. Lee, H. T. Huynh and J. Jeong

3. Results and Discussion 1.0

At first the adsorption of cadmium carried out with the 0.8 fresh Amberlite XAD-7HP resin with varying concentration / 3 Cd+2 of cadmium 0.5 200 mg Cd dm in the acidity range of 0.6 +1 / 3 / CdCl 0.003 2.0 mol dm HCl showed no adsorption extraction of CdCl2 CdCl - metal on the resin. This may be due to the presence of major 3 0.4 CdCl -2 amount of neutral CdCl2 species in the chloride solution 4 Molar fraction which are not interacting on the resin surface. Thus SIR results are not influenced by the surface properties of 0.2 Amberlite. Initially, the solvent extraction studies carried out for the extraction of cadmium from the chloride solutions 0.0 containing 100 mg Cd/dm3 and 2.0 mol/dm3 HCl with 0.043 0246810 . -3 mol/dm3 Cyanex 923 diluted in kerosene showed the 96% [HCl], C/ mol dm metal extraction by solvation of the cadmium chloride. This Fig. 1 Speciation diagram of cadmium in chloride medium. behavior is correlated with the formation of cadmium chloro- 2¹n complexes in solution, of which general formula is CdCln Eh (Volts) Cd - Cl - H2O - System at 25.00 C and their relative concentration depends on HCl concen- 2.0 tration in solution. At low HCl concentration, the most 1.5 abundant species are Cd2+ and CdCl+, which could not be extracted by the solvating extractant.21) At high concentration 1.0 Cd(OH)2 of HCl, the neutral complex (CdCl2) and the ionic complexes 0.5 CdCl2(a) ¹ 2¹ (CdCl3 and CdCl4 ) are dominant. These species can be extracted by Cyanex 923 depending on HCl concentration: 0.0 ¹ ¹2 the neutral complex CdCl2, and CdCl3 or CdCl4 -0.5 associated with protons can form ion pairs. The relationship between distribution coefficient and extractant concentration -1.0 3 Cd at 2 mol/dm HCl was found to followed linear equation -1.5 y = 1.98x + 3.54, suggesting the involvement of two mole- -2.0 cules (slope 1.98) of Cyanex 923 in the formation of the 0 2 4 6 8 10 12 14 extracted cadmium species. The similar results were reported C:\HSC6\EpH\CdCl25.iep pH in several papers.29,30) Fig. 2 EhpH diagram of cadmium in CdClH2O system at high chloride concentration. 3.1 Effect of pH and concentration of chloride solution In the hydrometallurgical processing of metals, both acidity and chloride concentration play an important role in solution of 0.5 mg Cd/dm3. The distribution coefficient of the formation of metals species in aqueous solution, and thus cadmium (D) increases with increasing the chloride activity affects the extraction and separation of metals under the in the solution, and the result is given in Fig. 3. The effect of different conditions. The speciation diagram of cadmium acidity of the solution on the adsorption efficiency from three with varying concentration of hydrochloric acid is presented different cadmium concentrations of 0.5, 10, 200 mg Cd/dm3 2+ + in Fig. 1 shows the presence of Cd , CdCl and CdCl2, etc. using SIR is presented in Fig. 4. With increasing HCl in the solution. The presence of Cd2+ and CdCl+ species concentration from 0.1 to 2.0 mol/dm3, the extraction of decreased with increase in chloride concentration (hydrochlo- cadmium increased from 19.2, 8.5, 5.0% to 95.0, 89.4, 88.3% ric acid concentration) whereas the cadmium as a neutral for the solution containing 0.5, 10, 200 mg Cd/dm3, respec- 3 species (CdCl2) increased and is dominant at 1.0 mol/dm tively. The extraction of cadmium in chloride system depends of HCl concentration. The EhpH diagram of cadmium on both acidity of solution and chloride concentration presented in Fig. 2 also clearly shows that the presence of because at high acidity and chloride concentration, the ¹ 2¹ cadmium species strongly depends on the chloride concen- species of cadmium like CdCl2 or CdCl3 and CdCl4 could tration, and the dominant species of cadmium is neutral be dominant in the solution, and react with Cyanex 923 3 CdCl2 at high chloride concentration (1.0 mol/dm HCl). The molecules as a proposing equation: ¹ ¹2 species CdCl3 and CdCl4 increases with increasing HCl 2n CdCln þ mHCl þ pCyanex 923 concentration. , • ð Þ ð Þ The adsorption of cadmium on SIR under the different HmCdCl2þm Cyanex 923 p 4 condition of acidity and chloride ion concentration, were The extraction capacity of extractant in SIR for cadmium carried out with 1.0 g SIR (0.375 g Cyanex 923/g SIR) at was found to be lower than that of extractant itself in solvent aqueous to resin ratio of 25 cm3/g resin at 298 K and extraction process. This may be explained by several reasons 0.3 mol/dm3 HCl showed the increase in the percentage including a steric hindrance effect: that not all the reactive adsorption with sodium chloride concentration. The extrac- sites were involved in the uptake. At high loading, tion increased from 65.4% to 90.6% with chloride concen- crystallization of the extractant inside the porous network tration 0.3 mol/dm3 to 1.5 mol/dm3 from the aqueous feed may occur and limit accessibility to the reaction sites.21) Extraction and Separation of Cadmium from the Chloride Solution of E-Waste Using Cyanex 923 Impregnated Amberlite XAD-7HP Resin 1297

5 1.0 y = 1.0973x + 0.8202 R2 = 0.98 4 0.8 -1

D 0.6 3 10 mg Cd/dm3 log 50 mg Cd/dm3 0.4 3

, C /mg·g 200 mg Cd/dm t 2 q

0.2 1

0.0 -0.6 -0.4 -0.2 0.0 0.2

log aCl- 0 0 5 10 15 20 25 30 35 Fig. 3 Effect of chloride concentration on adsorption of cadmium. Time, t /s

Fig. 5 Effect of contact time on adsorption of cadmium using SIR.

100 Table 2 Rate constant for pseudo ﬁrst- and second-order kinetics of cadmium adsorption on SIR. 80 Constants of kinetic expression Initial cadmium Pseudo ﬁrst-order rate 60 concentration, ¹3 C/mg·dm ¹ Calculated q , Empirical q , k , t/s 1 e e R2 1 m/mg·g¹1 m/mg·g¹1 40 0.5 mg Cd/dm3 10 0.214 0.054 0.235 0.945 Adsorption (%) 3 10 mg Cd/dm 50 0.151 0.269 1.210 0.978 200 mg Cd/dm3 20 Pseudo second-order rate

/ ¹1 ¹1 Calculated qe, Empirical qe, 2 k2, m g·mg ·s / ¹1 / ¹1 R 0 m mg·g m mg·g 0.0 0.5 1.0 1.5 2.0 10 2.319 0.226 0.235 0.998 HCl concentration, C/ mol·dm-3 50 2.443 1.112 1.210 0.999 Fig. 4 Effect of acidity of solution on adsorption of cadmium(II) using SIR.

Where qe and q are the amounts of cadmium (mg Cd/g resin) adsorbed on the resin at equilibrium and at time t, ¹1 3.2 Adsorption kinetics of cadmium(II) respectively, and k1 is the rate constant (s ). The effect of contact time on the adsorption of The pseudo-second-order reaction is mostly concerned cadmium(II) was studied by varying time from 120 s to with the amount of metal on the adsorbent’s surface and the 3,600 s using 1.0 g of SIR and 25 cm3 of solutions containing amount of metal adsorbed at equilibrium.32) The pseudo- 10, 50 and 200 mg Cd/dm3, and 2.0 mol/dm3 acidity in second-order reaction is presented by the equation: different stoppered flasks at 298 K. The effect of time on t 1 1 adsorption of cadmium using the SIR is presented in Fig. 5. ¼ þ t ð Þ q h q 6 The adsorption of cadmium was found to increase with time e and the equilibrium extraction was achieved in 1,500 s with Where k2 is the rate constant of the pseudo-second-order 2 maximum loading of cadmium on SIR as 4.68 mg Cd for sorption (g/mg·s), h = k2 qe is the initial sorption rate. solution containing 200 mg Cd/dm3, respectively. The ki- The rate constants and coefficient of determinations for netics of cadmium adsorption on SIR by the impregnated the pseudo-first- and second-order kinetics are presented in Cyanex 923 is a heterogeneous reaction between solid and Table 2. Apparently, the second-order kinetic was found fluid and affected by diffusion of ions through the liquid film more suitable than the first-order because coefficient of surrounding the particle, diffusion of ions through the determination (R2) for the second-order rate was found to be polymeric matrix of the resin and chemical reaction with near to 1 as compared to lower R2 values for the first-order extractant in the resin. The pseudo first and second order rate reaction. Figure 6 depicts the plots of second order rate laws were used to investigate the kinetic adsorption of expressions for the adsorption of cadmium on SIR with cadmium by the SIR. coefficient of determination values near ³1.0 for both the The pseudo-first-order rate expression is described:31) solutions containing 10 and 50 mg Cd/dm3 at 298 K.

k1 logðqe qÞ¼logðqeÞ t ð5Þ 3.3 Adsorption isotherms 2:303 The loading capacity of SIR containing Cyanex 923 was 1298 N. Van Nguyen, J. Lee, H. T. Huynh and J. Jeong

60 Table 3 Parameters of Langmuir and Freundlich isotherm for adsorption of 10 mg Cd/dm3 cadmium on SIR. 50 50 mg Cd/dm3 Extractant in Freundlich isotherm Langmuir isotherm 1 g SIR, m/g 2 ¹1 2 y= 2.079x + 0.502 nkf R qm, m/mg·g kl R 40 2 R =0.998 0.375 2.570 3.311 0.946 24.39 0.030 0.991

30 t/q y= 693x + 0.330 R2=0.999 20 0.25

10 0.20 y= 1.362x + 0.041 0 R2=0.991 0 5 10 15 20 25 30 Time, t /s 0.15 e q

Fig. 6 Pseudo second-order kinetics for adsorption of cadmium on SIR. 1/ 0.10 studied using 1.0 g sample of adsorbent which was contacted 0.05 with 25 cm3 aqueous feed solution containing 200 mg/dm3

Cd(II) for 1,800 s at 298 K by maintaining the acidity of the 0.00 feed solution at ³2.0 mol/dm3. The repeated contacts with 0.00 0.02 0.04 0.06 0.08 0.10 0.12 the same cadmium-loaded SIR were made with fresh aqueous 1/Ce solutions until a maximum adsorption of cadmium was achieved. The maximum adsorption of cadmium by the SIR Fig. 7 Langmuir isotherm for adsorption of cadmium using SIR. was found to be 20.1 mg Cd/g resin. The data obtained in the experiments was subsequently applied to determine adsorp- Table 4 Effect of eluents for elution of cadmium(II) from the loaded SIR tion phenomena by using the Langmuir and Freundlich (loaded SIR, 4.68 mg Cd/g SIR; A/R ratio, 25 cm3/g; contact time, isotherms. 1,800 s; mixing speed, 120 rpm; temperature, 298 K). The Freundlich model assumes that the uptake or Eluents Elution (%) adsorption of metal ions occurs on a heterogeneous surface 0.1 mol/dm3 HCl 80.6 by monolayer adsorption. The model can be described as 0.1 mol/dm3 NaCl 89.8 follows:33,34) H2O 91.4 q ¼ 1 C þ k ð Þ log n log e log f 7

Where kf and n are the Freundlich constants for adsorption than Freundlich isotherm. The empirical loading capacity capacity and adsorption intensity, respectively. of SIR for adsorption of cadmium was found to be 20.1 According to the Langmuir model, the uptake of metal ions mg Cd/g SIR while the value of loading capacity of SIR occurs on a homogeneous surface by monolayer adsorption obtained from plot of Langmuir isotherm was 24.39 mg Cd/g without any interaction between the adsorbed ions. The SIR. Therefore, the Langmuir isotherm provides a better fit model can be presented in a linear form:28,35) to the experimental data for cadmium than the Freundlich model, and presented in Fig. 7. 1 ¼ 1 1 þ 1 ð Þ q k q C q 8 1 m e m 3.4 Elution of cadmium(II) where Ce is equilibrium concentration of metal in solution For the removal of cadmium from loaded SIR, the elution (mg/dm3), q is amount of metal adsorbed on the resin at of cadmium was carried out by three eluents HCl, NaCl and equilibrium (mg/g), kl is equilibrium constant related to the H2O in the batch test. The loaded SIRs containing 4.68 mg affinity of the binding sites for the metals or the Langmuir Cd were eluted at aqueous to resin ratio of 25 cm3/g constant, and qm is the resin capacity (possible maximum maintaining a 1,800 s contact time with mixing rate of amount of metal ions adsorbed per unit mass of adsorbent, 120 rpm. The results presented in Table 4 show that mg/g). percentage elution of cadmium was found to be 80.6, 89.1 3 3 Plots of 1/Ce vs. 1/q and log Ce vs. log q were examined and 91.4 with 0.1 mol/dm HCl, 0.1 mol/dm NaCl and H2O to validate the experimental data with Langmuir and respectively. The water was found to be the most suitable Freundlich isotherms. The coefficient of determinations of among the eluents. Therefore, water was considered for the Langmuir and Freundlich isotherms for cadmium removal of cadmium from the loaded SIR throughout this adsorption on the resin are presented in Table 3. The study. coefficient of determination, R2 in the Langmuir isotherm is closer to 1 in the both types of SIR. This shows that 3.5 Adsorption of the other metals by the SIR adsorption of cadmium follows Langmuir isotherm rather After establishing the condition for the removal of Extraction and Separation of Cadmium from the Chloride Solution of E-Waste Using Cyanex 923 Impregnated Amberlite XAD-7HP Resin 1299

Table 5 Elution of gold from loaded SIR using different types of eluents Table 6 The adsorption of metals in the leachate by Cyanex 923 (loaded SIR, 4.51 mg Au/g SIR; A/R ratio, 25 cm3/g; contact time, impregnated Amberlite XAD-7 HP resin (SIR, 1 g; A/R: 25 cm3/g; 1,800 s; mixing speed, 120 rpm; temperature, 298 K). acidity of the leachate, 2 mol/dm3 HCl; contact time, 1,800 s; mixing speed, 120 rpm; temperature, 298 K). Eluent Elution (%) Elements Adsorption (%) 0.1 mol/dm3 HCl 0

H2O 0.01 Cu 0 0.1 mol/dm3 NaOH 0.03 Ni 0 0.1 mol/dm3 thiourea 98.7 Sn 0 Pb 0 Au 99.5 Zn 98.1 cadmium from the chloride solution, the subsequent studies Cd 98.5 have been made for the extraction and separation of remaining metals viz. Cu, Ni, Sn, Pb, Zn and Au in / 3 2.0 mol dm HCl. The solution containing metals without Cd Electronic scraps has been prepared similar with leachate, which is presented HCl in Table 1. The preliminary studies were carried out to Electro-generated determine the adsorption behavior of these metals with the Chlorine Leaching SIR (0.375 g Cyanex 923 in 1.0 g SIR) at aqueous to resin ratio 25 cm3/g for 1,800 s. The results indicated that among these metals only gold and zinc are adsorbed by the SIR Solid-Liquid Separation leaving other metals in aqueous solution. This can be Residue explained by taking in to account the fact that Cu, Ni, Sn Leachate and Pb exist as cationic species at 2.0 mol/dm3 HCl concentration whereas gold and zinc exist in complex forms Adsorption using SIR which are adsorbed by Cyanex 923 as reported.24,33,36) For exploring the separation condition between gold and Water Cd-removed Leachate zinc, the adsorption study of gold has been carried out Elution of Cd & Zn separately from its synthetic solution containing 5 mg Au/ Recovery of Thiourea Cd & Zn valuable metals dm3 at 2.0 M acidity. The results showed that almost gold (99.5%) was adsorbed on SIR within 1,800 s and ratio Elution of Au 3 25 cm /g (aqueous/resin). Attempts were made to elute gold Regenerated SIR Au solution from the loaded SIR using various eluents such as dilute hydrochloric acid, water, dilute sodium hydroxide and Fig. 8 Proposed process flow sheet for extraction and separation of thiourea. The results presented in Table 5 indicate that only cadmium, and recovery of the valuable metals from the leachate of thiourea among these eluents was effective for removing gold e-waste using solvent impregnated resin (SIR) technique. from the loaded SIR (98.7%), and the other eluents are negligible effect for elution of gold. The adsorption of zinc by SIR was also examined separately using 1.0 g SIR metals loaded on the SIR. The selective elution of metals (0.375 g Cyanex 923 in 1.0 g SIR) while contacting it with were carried out to remove Cd and Zn from loaded SIR 5mg/dm3 Zn(II) at 2.0 M acidity of solution at liquid/solid containing Au, Zn, and Cd by water at aqueous to resin ratio ratio of 25 (cm3/g). Almost total zinc was adsorbed by SIR of 25 cm3/g in 1,800 s time leaving gold in the resin. Finally, within 1,800 s. Zinc on loaded SIR was eluted by both water gold on the SIR was eluted completely by 0.1 mol/dm3 and dilute hydrochloric acid (0.1 mol/dm3). Results showed thiourea solution. Metallic gold can be obtained from the that 96% and 90% of zinc were eluted by water and the dilute eluted solution by precipitation or electro-winning. The hydrochloric acid in the first stage of elution, respectively. process for adsorption of metals from the leachate of e-waste Therefore, water was selected as an eluent for elution of zinc using SIR is given in Fig. 8 where the selective elution from loaded SIR. could be achieved by different eluents to separate metals from the loaded SIR. The remaining metals Cu, Ni, Sn and 3.6 Removal of metals from the leach solution Pb in the raffinate could be recovered by suitable hydro- On establishing the optimum condition for the extraction metallurgical processing. The extraction of cadmium and and separation of metals from the leach liquor of e-wastes, other metals in chloride media by SIR have been reported by the studies were carried out with real solution as given in several authors, and their performance are listed in Table 7, Table 1 using Cyanex 923 impregnated resin at aqueous to in which shows that the extraction of cadmium takes place 3 resin ratio of 25 cm /g for 1,800 s. The results presented in by forming CdCl2 complex with the Cyanex 923 in the Table 6 to show that almost total Cd, Zn and Au metals are present study. adsorbed simultaneously by SIR leaving Cu, Ni, Sn and Pb in the raffinate as obtained above. 4. Conclusions Further studies were directed towards achieving selective elution for separating cadmium, gold, and zinc from the Based on studies carried out on the extraction of metals 1300 N. Van Nguyen, J. Lee, H. T. Huynh and J. Jeong

Table 7 Salient results of the extraction of metals from the chloride solution using solvent impregnated resins.

Solvent Aqueous Salient results on extraction of metals from impregnated resins References solution the chloride solution (SIR) Cyphos IL-101 Exchange mechanism involves Cd(II) in chloride immobilized in a phosphoniumcation and CdCl 2¹. 11) solutions 4 Amberlite XAD-7 Kinetics: Resistance to intra-particle diffusion. Metal complexes in the resin: MCl L , (HL) S Mixtures of DEHPA t p q s Zn(II), Cu(II) and where p, t, s and q take different values (HL) and TOPO (S) 19) Cd(II) in chloride depending on the metal and the extractant in Amberlite XAD2 concentration. Co(II), Ni(II), 1-Hexyl-4-ethyloctyl Extracted species in the resin phase takes place Zn(II), Cd(II), isopropyl phosphonic with the formation metal complex: ML (HL)q. 20) and Cu(II) in acid (HEOPPA) as an 2 Freundlich’s isotherm chloride solution extractant in resin Extraction of metals takes place by solvating Cd(II) from Cyanex 921 reactions with neutral CdCl2 and ion pairs. concentrated impregnated in Langmuir adsorption equation and sorption 21) chloride solution Amberlite XAD-7 kinetics are controlled by intraparticle diffusion. Kinetics controlled by: Pseudo-second-order Activated carbons Cd(II) in chloride model, impregnated with 22) solution Adsorption mechanism: Freundlich adsorption anionic surfactants isotherm Cyphos IL-101, IL- Extraction Cd takes place as chloroanionic 105, IL-109, and IL- Cd(II) in chloride species (CdCl 2¹) with counteranion of the IL. 111 immobilized in 4 23) solutions Kinetics of adsorption: Resistance to intra- composite particle diffusion. biopolymer capsules Cyanex 923 SIR effectively adsorbs cadmium(II) forming Cd, Zn, Au, Cu, impregnated in CdCl solvation compound with Cyanex 923. PRESENT Ni, Pb and Sn in 2 Amberlite XAD-7 Langmuir isotherm and second-order kinetics WORK chloride solutions HP resin followed

from the chloride leach solution of e-waste using SIR, REFERENCES Cyanex 923 impregnated Amberlite XAD-7HP resin, the following conclusions can be drawn: 1) A. Tuncuk, V. Stari, A. Akcil, E. Y. Yaxici and H. Deveci: Miner. Eng. 25 (2012) 2837. (1) SIR effectively adsorbs cadmium(II) forming CdCl2 2) V. Kumar, J.-c. Lee, J. Jeong, M. K. Jha, B. S. Kim and R. Singh: Sep. solvation compound with Cyanex 923 and it follows Purif. Technol. 111 (2013) 145154. the Langmuir isotherm and second-order kinetics at 3) E. Y. Kim, M. S. Kim, J.-c. Lee and B. D. Pandey: J. Hazard. Mat. 198 high acidity from chloride solution. (2011) 206215. 4) E. Y. Kim, M. S. Kim, J.-c. Lee, J. Jeong and B. D. Pandey: (2) The loading capacity of SIR for adsorption of cadmium / Hydrometallurgy 107 (2011) 124 132. was found to be 20.1 mg Cd g SIR for the 0375 g 5) G. F. Nordberg: Toxicol. Appl. Pharmacol. 238 (2009) 192200. Cyanex 923 impregnated Amberlite XAD-7HP resin. 6) B. R. Reddy and D. N. Priya: J. Power Sources 161 (2006) 14281434. (3) SIR simultaneously adsorbs cadmium, zinc, and gold 7) M. K. Jha, V. Kumar, J. Jeong and J.-c. Lee: Hydrometallurgy 111112 from the leachate of e-waste containing various metals. (2012) 19. (4) The solution obtained after extraction of Cd, Zn, Au, 8) S. Gomez-Salazar, J. S. Lee, J. C. Heydweiller and L. L. Tavlarides: Ind. Eng. Chem. Res. 42 (2003) 34033412. could be processed for recovery of the valuable metals 9) K. Bedoui, I. Bekri-Abbes and E. Srasra: Desalination 223 (2008) 269 such as copper, nickel, tin, lead, etc. using suitable 273. hydrometallurgical processing. 10) W. W. Yang, G. S. Luo and X. C. Gong: Hydrometallurgy 80 (2005) 179185. Acknowledgements 11) A. Arias, I. Saucedo, R. Navarro, V. Gallardo, M. Martinez and E. Guibal: React. Funct. Polym. 71 (2011) 10591070. 12) A. N. Pustam and S. D. Alexandratos: React. Funct. Polym. 70 (2010) This paper is based on the work supported by the Korea 545554. International Cooperation Agency (KOICA). The authors 13) D. Muraviev, M. Oleinikova and M. Valiente: Langmuir 13 (1997) gratefully acknowledge the Korea International Cooperation 49154922. Agency (KOICA) for providing ﬁnancial support for this 14) N. V. Deorkar and L. L. Tavlarides: Ind. Eng. Chem. Res. 36 (1997) 399406. research project. Authors are very grateful to Dr. Vinay 15) D. Muraviev, L. Ghantous and M. Valiente: React. Funct. Polym. 38 Kumar for his constructive comments for the improvement of (1998) 259268. manuscript. 16) L. H. Reyes, I. M. Saucedo, M. R. Navarro, J. R. Vazquez, M. A. Extraction and Separation of Cadmium from the Chloride Solution of E-Waste Using Cyanex 923 Impregnated Amberlite XAD-7HP Resin 1301

Rodriguez and M. Guibal: Ind. Eng. Chem. Res. 40 (2001) 14221433. USA (1991). 17) M. Benamor, Z. Bouariche, T. Belaid and M. T. Draa: Sep. Purif. 27) B. Gupta, N. Mudhar, Z. Begum and I. Singh: Hydrometallurgy 87 Technol. 59 (2008) 7484. (2007) 1826. 18) I. Zawierucha, J. Kozlowska, C. Kozlowski and A. Trochimczuk: 28) N. V. Nguyen, J. Jeong, M. K. Jha, J.-c. Lee and K. O. Asare: Desalin. Water Treat. 52 (2014) 314323. Hydrometallurgy 105 (2010) 161167. 19) J. L. Cortina, N. Miralles, A. M. Sastre and M. Aguilar: Hydro- 29) B. Gupta, A. Deep and P. Malik: Hydrometallurgy 61 (2001) 6571. metallurgy 37 (1995) 301322. 30) A. M. Rodriguez, D. G. Limon and F. J. Alguacil: J. Chem. Technol. 20) Q. Jia, Z. H. Wang, D. Q. Li and J. C. Niu: Sep. Sci. Technol. 38 (2003) Biotechnol. 80 (2005) 967972. 20252037. 31) M. K. Jha, R. R. Upadhyay, J.-c. Lee and V. Kumar: Desalination 228 21) R. Navarro, I. Saucedo, A. Nunez, M. Avila and E. Guibal: React. (2008) 97107. Funct. Polym. 68 (2008) 557571. 32) P. Saha and S. K. Sanyal: Desalination 259 (2010) 131139. 22) K. C. Ahn, D. Parka, H. S. Woo and M. J. Park: J. Hazard. Mat. 164 33) P. A. Amoyaw, M. Williams and X. R. Bu: J. Hazard. Mat. 170 (2009) (2009) 11301136. 2226. 23) E. Guibal, A. Figuerola, P. M. Ruiz, T. Vincent, C. Jouannin and A. M. 34) M. S. Mansour, M. E. Ossman and H. A. Farag: Desalination 272 Sastre: Sep. Purif. Technol. 45 (2010) 19351949. (2011) 301305. 24) S. F. Alguacil and H. Tayibi: Desalination 180 (2005) 181187. 35) S. Samatya, N. Kabay, U. Yuksel, M. Arda and M. Yuksel: React. 25) A. Agrawal, C. Pal and K. K. Sahu: J. Hazard. Mat. 159 (2008) 458 Funct. Polym. 66 (2006) 12061214. 464. 36) F. J. Alguacil and S. Martinez: J. Chem. Technol. Biotechnol. 76 (2001) 26) American Cyanamid Company: CYANEX 923 Extractant, Wayne, 298302.