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A new membrane electro-deposition based process for tin recovery from waste printed circuit boards
Journal of Hazardous Materials 304 (2016) 409–416
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Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat
A new membrane electro-deposition based process for tin recovery from waste printed circuit boards Yang Jian-guang ∗ , Lei Jie, Peng Si-yao, Lv Yuan-lu, Shi Wei-qiang School of Metallurgy and Environment, Central South University, Changsha, Hunan 410083, China
h i g h l i g h t s • • • •
A process for tin recovery based on membrane electro-deposition is proposed. Tin can be recovered as the form of high purity cathode tin. Anolyte can be reused as leaching agent for leaching tin again after electrowinning. The optimum parameters for electro-deposition are introduced.
a r t i c l e
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Article history: Received 30 August 2015 Received in revised form 3 November 2015 Accepted 5 November 2015 Available online 10 November 2015 Keywords: WPCBs Tin recovery Chloride leaching Membrane electrodeposition
a b s t r a c t The current research investigated a process combining leaching, purification and membrane electrodeposition to recover tin from the metal components of WPCBs. Experimental results showed that with a solid liquid ratio of 1:4, applying 1.1 times of stoichiometric SnCl4 dosage and HCl concentration of 3.5–4.0 mol/L at a temperature of 60–90 ◦ C, 99% of tin can be leached from the metal components of WPCBs. The suitable purification conditions were obtained in the temperature range of 30–45 ◦ C with the addition of 1.3–1.4 times of the stoichiometric quantity of tin metal and stirring for a period of 1–2 h; followed by adding 1.3 times of the stoichiometric quantity of Na2 S for sulfide precipitation about 20–30 min at room temperature. The purified solution was subjected to membrane electrowinning for tin electrodeposition. Under the condition of catholyte Sn2+ 60 g/L, HCl 3 mol/L and NaCl 20 g/L, current density 200 A/m2 and temperature 35 ◦ C, a compact and smooth cathode tin layer can be obtained. The obtained cathode tin purity exceeded 99% and the electric consumption was less than 1200 kW h/t. The resultant SnCl4 solution generated in anode compartment can be reused as leaching agent for leaching tin again. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Printed circuit boards (PCBs) are typical and fundamental components of almost all electric and electronic equipment (EEE). With the rapid development of technology and the society, high-performance requirements and great demands in EEE make replacement of PCBs more frequent, resulting in large quantities of WPCBs that need to be disposed. Mechanical and pyrometallurgical methods are the current ways of recycling WPCBs, and pyrolysis process also attracts more and more attention nowadays [1,2]. Almost all waste EEE recycling enterprises in China use various mechanical methods to separate metals and non-metals from
∗ Corresponding author at: Department of Metallurgical Science and Engineering, Central South University, China. E-mail address: jianguang [email protected] (Y. Jian-guang). http://dx.doi.org/10.1016/j.jhazmat.2015.11.007 0304-3894/© 2015 Elsevier B.V. All rights reserved.
WPCBs. As a result, approximately 30 wt.% of the original mass, enriched multi-metal fraction (Cu, Sn, Pb, Fe, Zn, Sb, and so on) is separated from the non-metal components. At present the enriched multi-metal fraction is mainly sold to copper smeltery as copper smelting raw material, and the tin contained in multi-metal fraction is not only failed to get effective recovery, but also cause serious interference to the copper recovery. In addition, the existing pyrometallurgical and hydrometallurgical recovery processes generate pollution because of the release of dioxins and furans or high volume of effluents [3–6]. Hydrometallurgical treatments have more flexibility during the upscaling and control processes. Sulfuric, hydrochloric and nitric acid solutions are often used as leaching agents in hydrometallurgical technologies [7–9]. Bin et al., proposed a hydrometallurgical recovery process to recover copper and tin by constant-current and constant-voltage electrolysis from the leaching solution of tinned copper wastes [10]. Fogarasi et al., introduced two new cop-
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Table 1 Chemical composition of the enriched multi-metal fraction (wt.%). Elements
Content/%
Elements
Content/%
Sn Cu Pb Zn Fe
8.8 56.04 5.85 0.71 1.51
Al Ca Ni Ag Others
0.70 1.41 0.37 0.07 24.54
Table 2 Tin occurrence analysis of the enriched multi-metal fraction/%. Tin occurrence
Sn
SnO
Other
Content/% Proportion/%
8.63 98.1
0.09 1.02
<0.1 <1.0
per recovery processes from waste printed circuit boards [11,12], and Kim et al., investigated the leaching kinetics of copper from waste printed circuit boards by electro-generated chlorine in HCl solution [13]. The experimental results show that the elements could be deposited on the cathode in turns by different deposition potentials. García-Gabaldón et al., studied the performance of a two-compartment batch electrochemical reactor separated by a ceramic diaphragm for tin removal from the activating solutions [14,15]. However, even under optimized conditions, the tin leaching efficiency was proven to be incapable of reaching more than 90%, whereas the current efficiency cannot exceed 85%. The low tin recovery are the obvious disadvantages that limit the application. In our previous study [16,17], a process and related fundamental principle was proposed for the separation and recovery of antimony, bismuth from a concentrate using a membrane electrodeposition process. Further, a new process based on membrane electrodeposition for tin recovery from the metallic fraction of WPCBs is proposed. Thus leaching, purification and membrane electrodeposition to recover tin was investigated. This process has been applied for patent in China recently [18]. The current paper demonstrates that not only tin can be efficiently recovered from WPCBs, but also SnCl4 can be regenerated from the anode compartment and to be used as leaching agent again. 2. Experimental 2.1. Materials The metal components of WPCBs, obtained from Lv-yan Resource Recycle Co., China, were characterized for chemical composition and phase analysis. The dry screen used for the analysis was about 10 mesh (2 mm), and all samples were leached without further grinding. Chemical analysis of the enriched multi-metal fraction was conducted by atomic absorption spectroscopy, except for the copper, tin, lead and zinc contents were analyzed by chemical titration, and the results are given in Table 1. Tin occurrence analysis showed that tin was present mainly as metallic tin (>98%) and as stannous oxide (SnO) (<1%) in small quantity (Table 2). The other chemicals used were of reagent grade. The hydrochloric acid, stannic chloride, etc., were purchased from Changsha Shenghua, Inc., China, with no further purification introduced. 2.2. Method The WPCBs were first treated by using mechanical methods, such as multi-crushing, grinding, electrostatic separation, gravity separation, and magnetic separation to separate metals and non-metals from WPCBs. The schematic of the electrodepositon apparatus and procedure for leaching, purification and electrode-
Fig. 1. Schematic representation of the experimental apparatus for electrodepositon and experimental procedure.
position tin from the enriched multi-metal fraction is shown in Fig. 1. Leaching was carried out in 500 mL glass flasks by adding a weighed amount of multi-metals powder, sodium chloride and stannic chloride to diluted HCl solution at the desired temperature with magnetic stirring at 250 r/min. The temperature of the system was controlled within 2 ◦ C on a hot plate. A condenser was attached to the flask to prevent vaporization losses. At the end of each experiment, the insoluble leach residue was filtered and washed with 1 mol/L HCl and then distilled water. The recovery of tin was calculated by mass balance using the analysis of the multi-metals powder and the leach residue. In the purification procedure, a weighed amount of tin powder and Na2 S was added to the stirred solution to remove Cu2+ and Pb2+ . After filtration, the degree of purification was calculated from analysis of Cu2+ and Pb2+ concentrations by and atomic absorption spectroscopy. In the electrowinning experiment, a two-compartment acrylic cell (90 × 120 × 150 mm) was used, where the anode and cathode compartments were separated by a widely used commercial quaternary-ammonium-hydroxy-type anion exchange membrane (HF-201, Beijing Enling Technology Co., Ltd., China). The applied HF-201 type anion exchange membrane has the anion selective permeability. The membrane only allows the chloride ion and water molecules to penetrate, while other ions are difficult to penetrate. The cathode plate was made of titanium and the anode was a graphite plate with the same surface area. The catholyte and anolyte contained Sn2+ (stannous chloride) and HCl. Both electrolytes are
Y. Jian-guang et al. / Journal of Hazardous Materials 304 (2016) 409–416 Table 3 Leaching and purification analyses under optimized conditions. Elements in solution −1
From leaching/g L After purification/g L−1
Table 4 Effect of different stannous ion concentration on the electro-deposition.
Sn2+
Cu2+
Pb2+
Fe2+
Sn4+
Sn2+ /g L−1
Cathode surface
Current efficiency/%
Cell voltage/V
58.6 59.9
0.20 0.02
0.95 0.03
2.11 2.09
0.19 –
20 40 60 80 100 120
powdery smooth smooth smooth smooth rough
88.1 97.0 99.6 99.0 99.1 99.7
1.67 2.10 2.24 2.39 2.47 2.23
stirred to reduce the concentration polarization in the cell compartments. During the experiment, the additional tin solution is filled in the cathode compartment at a rate according to the theory of tin electro-deposition to ensure the uniformity of the catholyte concentration. The relative cathode current efficiencies are calculated through the following Eq. (1). Where W1 represents actual mass of cathode product, W2 represents the theoretical mass of cathode tin. = (W 1 /W 2 ) ∗ 100%(1) At the cathode, the electrode reactions are: 2+
Sn
411
+ 2e− → Sn(mainreaction);
2H+ + 2e− → H2 ↑ (secondaryreaction); At the anode, the following reactions are possible, but no oxygen or chlorine was detected under the conditions used:
3.2. Purification results and discussions The major aim of purification was to produce a pure electrolyte for electrowinning. The most suitable purification conditions were obtained in the temperature 45 ◦ C with the addition of 1.1 times of the stoichiometric quantity of tin powder as reductant and stirring for a period of 1.0 h (Eqs. (5)–(6)); followed by 1.3 times of the stoichiometric quantity of Na2 S for sulfide precipitation about 30 min at 35 ◦ C (Eqs. (7)–(8)). Under these conditions, the tin concentration increased slightly while Cu2+ and Pb2+ were substantially lower as shown in Table 3. The reduction of copper and lead was >99% with little loss of tin. Sn4+ + Sn = 2Sn2+ (5)
Sn2+ → Sn4+ + 2e− (mainreaction); 2Cl− → Cl2 ↑ + 2e− (secondaryreaction). 3. Results and discussions 3.1. Leaching results During preliminary experiments, various leaching conditions were examined and the most suitable setting for tin extraction was obtained in the temperature range 40–45 ◦ C over two hours with 3.5–4.0 mol/L HCl and the 1.1 times stannic chloride of the stoichiometric quantity using a solid–liquid ratio of 1:3–1:4 with 250 r/min magnetically stirring, and all experiments were carried out using 100 g multi-metals powder per time. As shown in Table 3, the recovery of tin in the leach solution was substantially higher than that of the other metals. Through calculations and analysis of Sn2+ , Cu2+ , Pb2+ and Sn4+ in the leach solution and the leach residue, it was found that >99% Sn was leached from the multi-metals powders without leaching much of the other metals. This procedure yielded an enriched solution containing 58.6 g/L Sn2+ contaminated with about 2 g/L Fe and <1 g/L Cu and Pb. It can be calculated that the exact amount of tin dissolved in a leaching experiment and the amount added as SnCl4 were 8.72 g and 21.22 g, respectively. Under the proposed leaching conditions, most of the metallic tin can be leached into solution according to Eq. (2). It was also observed that after leaching experiment terminated, a new generated thin layer fine copper particle was covered on leach residue. The reason may be concluded that some copper can be dissolved by SnCl4 , but ultimately be reduced by metallic tin according to Eqs. (3) and (4). Therefore, it was deduced that some Cu–Sn alloy even Cu can be dissolved during the beginning of leaching period under the condition of intensive mechanical stirring. Sn + SnCl4 = 2SnCl2 (2) Cu + SnCl4 = CuCl2 + SnCl2 (3) CuCl2 + Sn = Cu + SnCl2 (4)
Sn + Cu2+ = Sn2+ + Cu(6) Cu2+ + S2− = CuS(7) Pb2+ + S2− = PbS(8)
3.3. Electrowinning of tin The tin electrowinning experiments in a divided cell were carried out in order to establish optimum tin electro-deposition parameters such as the effect of stannous ion and sodium chloride concentration in catholyte, temperature, cathode current density and acidity in the catholyte on the main cell performance parameters such as cathodic current efficiency and cell voltage. The resultant stannic chloride concentration in anolyte and the mass of deposited tin on the cathode were also determined. During electrowinning, some atmosphere protection measures (pumped into some N2 and inclosed cell) were applied for avoiding Sn2+ oxidation during electrowinning experiments. 3.3.1. Effect of stannous concentration in the catholyte Electrowinning was first conducted by varying the stannous ion concentration in the catholyte from 20 g/L to 120 g/L in the presence of 20 g/L NaCl and 3 mol/L HCl at temperature of 35 ◦ C and a current density of 200 A/m2 . And 3 mol/L HCl was proved effective to prevent Sn2+ from hydrolyzing during electrowinning. The experiment results are shown in Table 4. Clearly, the current efficiency increases with increasing stannous ion concentration, but at low tin concentrations powdery deposits were observed. At lower stannous ion concentrations, there was higher hydrogen evolution which not only results in lower current efficiencies, but also obtained powdery tin plates (Fig. 2(a)). When the stannous ion concentration lies in 40 (Fig. 2(b)) to 100 g/L (Fig. 2(c)), the cathode surfaces seem better, mostly smooth with metallic luster, and the current efficiency change little. Since no notable additional benefit was derived in going beyond a stannous ion of 100 g/L, this value was chosen as the optimum.
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Fig. 2. The optical images of the cathode tin under different stannous concentration in the catholyte (a)— [Sn2+ ] = 20 g L−1 ; (b)—[Sn2+ ] = 40 g L−1 ; (c)—[Sn2+ ] = 100 g L−1 .
Fig. 3. The optical images of the cathode tin under different sodium chloride concentration in catholyte (a)—5 g L−1 ; (b)—20 g L−1 ; (c)—30 g L−1 .
Table 5 Effect of different concentration of sodium chloride on the electro-deposition.
Table 6 Effect of different temperature on the electro-deposition.
NaCl/g L−1
Current efficiency/%
Cell voltage/V
T/◦ C
Current efficiency/%
Cell voltage/V
Cathode surface
5 10 15 20 25 30
89.1 91.0 95.6 98.1 98.2 98.5
2.79 2.62 2.45 2.27 2.24 2.22
25 30 40 50
94.49 98.11 93.93 81.97
2.79 2.62 2.45 2.31
rough smooth smooth rough
3.3.2. Effect of sodium chloride concentration in catholyte The concentration of sodium chloride in the catholyte was varied from 5 g/L to 30 g/L in the presence of 100 g/L Sn2+ and 3 mol/L HCl at temperature of 35 ◦ C and a current density of 200 A/m2 . The aim of incorporation of sodium chloride into the electrolyte was to enhance the conductivity of the solution during tin electrowinning. The effect of sodium chloride concentration on the current efficiency and cell voltage is summarized in Table 5. Experiment results showed that varying sodium chloride concentration in catholyte from 5 to 30 g L−1 has little influence to cathode tin surface (Fig. 3(a) and (b)), while the current efficiency increases and the cell voltage decreases with NaCl addition up to 20 g/L, beyond which there is no obvious benefit. This may
be explained by increasing sodium chloride concentration only enhanced the conductivity of the electrolyte and lowered cell voltage as well as the cathodic overpotential required to obtain the desired current density. The decreased overpotential results in lower H2 evolution and higher efficiency for tin deposition. Therefore 20 g/L NaCl was chosen as the optimum sodium chloride concentration in the catholyte. 3.3.3. Effect of electrowinning temperature Table 6 shows the effect of temperature on the current efficiency and cell voltage at a current density of 200 A/m2 , using a catholyte composition of 100 g/L Sn2+ , 3 mol/L HCl and 20 g/L NaCl. When the temperature increased from 25 to 50 ◦ C, the current efficiency increased firstly and then decreased, and the cell voltage decreased along. Furthermore, the electro-deposition at low tem-
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413
Fig. 4. The optical images of the cathode tin under different electrowinning temperature (a)—25 ◦ C; (b)−35 ◦ C; (c)—50 ◦ C.
Table 7 Effect of different cathode current density on the electro-deposition.
Table 8 Effect of different acidity on the electro-deposition.
Current density/A m−2
Cathode surface
Current efficiency/%
Cell voltage/V
Acidity/mol L−1
Cathode surface
Current efficiency/%
Cell voltage/V
100 150 175 200 250 300
smooth smooth smooth smooth powdery powdery
95.24 99.00 98.03 99.99 99.08 99.47
1.19 1.69 2.33 2.42 2.67 3.11
0.5 1 2 3 4 6
dendritic powder smooth smooth rough rough
– 96.81 99.00 97.51 94.20 92.80
– 2.75 2.39 1.93 1.56 1.17
perature is easy to be rough, whisker on the edge (Fig. 4(a)). The tin deposit formed at temperatures at 30–40 ◦ C was smooth, uniform with metallic luster (Fig. 4(b)), while higher temperatures reduced both the quality and adherence. The higher current efficiency and deposit quality is obviously due to increased stannous ion mobilities and less H2 production. However, the increased temperature also results in water and HCl volatilization, hence a temperature of 35 ◦ C was selected for obtaining tin plates of good morphology. 3.3.4. Effect of cathode current density The effect of cathode current density on the current efficiency and cell voltage was conducted by varying the cathode current density from 100 A/m2 to 300 A/m2 in the presence of 100 g/L Sn2+ , 20 g/L NaCl and 3 mol/L HCl at 35 ◦ C. Table 7 shows that the current efficiency remained constant around 95–99%, while cell voltage increased steadily with cathode current density. At the same time, the quality of the deposit deteriorated from the good cathode surface at a low current density (Fig. 5(a) and (b)). With the increase of current density, the current efficiency and cell voltage increase, and the cathode surface becomes worse (Fig. 5(c)). The higher current density required an increase in the cathodic polarization, which resulted in more H2 evolution. This made the deposit at the edges become increasingly powdery and dendritic. Considering all these factors, 200 A/m2 was chosen as the optimum cathode current density. 3.3.5. Effect of acidity in the catholyte The effect of acidity on the cathode surface, current efficiency and cell voltage was studied, at 35 ◦ C, 200 A/m2 current density and the catholyte containing Sn2+ 100 g/L and 20 g/L NaCl. Results are shown in Table 8. The electro-deposition at low acidity cannot be processed for very bad cathode surface (Fig. 6(a)). With the increase of acidity, the current efficiency first increased and then decreased while the cell
Table 9 Main constituents of cathode tin, %. Bi
Fe
Zn
Pb
Cu
As
Sn
0.075
0.022
0.001
0.053
0.092
0.001
99.49
voltage decreased steadily, and the cathode surface became better, mostly smooth with metallic luster (Fig. 6(b)). With the acidity over 4 mol/L, the current efficiency and cell voltage decrease, and the cathode surface become rough,and high acidity resulted in more H2 evolution. Therefore, 3 mol/L acidity is selected for the electrodeposition.
3.4. Confirmation experiment Based on the above studies, the optimum conditions for the electro-deposition of tin from a chloride solution in a membrane cell were as follows: Sn2+ 100 g/L, NaCl 20 g/L, temperature 35 ◦ C, HCl 3 mol/L in catholyte and anolyte, cathode current density 200 A/m2 , cathode—anode distance of 5 cm. These conditions were then applied in a confirmation experiment to obtain tin metal sheets and stannic chloride solution (resultant stannic ions in anolyte are not precipitated by hydrolysis at 3 mol/L HCl). The tin leach solution was first purified according to the described optimized conditions and then subjected to electrowinning. In each case, a good quality tin plate and an anolyte suitable for recycling was obtained (98.6% of the Sn2+ in anolyte was converted into Sn4+ after electrowinning). Table 9 and Fig. 7 give the typical analysis, the optical and SEM pattern, XRD pattern of the obtained tin plate. All the XRD pattern peaks are indexed to pure metallic tin (JCPDS file No. 65-0296, Sn).
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Fig. 5. The optical images of the cathode tin under different cathode current density (a)—100 A m−2 ; (b)—200 A m−2 ; (c)—300 A m−2 .
Fig. 6. The optical images of the cathode tin under different acidity in the catholyte (a)—0.5 mol L−1 ; (b)—3 mol L−1 ; (c)—6 mol L−1 .
Table 10 Cost of tin recovery through the membrane electro-deposition process. No.
Raw material and manufacturing material
Cost (dollars/ton)
Note
1 2 3 4 5
Hydrochloric acid Sodium sulfide and additives Electricity Water Labour
35 22 200 30 250
*The market price of tin is about 21,600 dollars per ton while the market price of tin contained in multi-metal fraction of WPCBs is about 7600 dollars, the same as copper price.
6 7 8
Equipment amortization Taxation expense Others Total
82 25 40 684
*The leached residue can be sold to copper smeltery as the same price of multi-metal fraction.
Table 11 Comparisons between the proposed process and traditional ‘fuming process’. Process Membrane electro-deposition process ‘Fuming process’
Tin recovery rate /% >98 <50
3.5. Economical aspects of the process Based on the pilot scale plant test (one ton tin per day) in Lvyan Corporation, Miluo, China, the cost of tin recovery from multimetal fraction of WPCBs through the proposed process is shown in
Cost per ton tin /$ <700 >6000
Environmental impact Friendly Bad
Table 10. In comparison, the current tin recovery process, called the ‘fuming process’ which involves pyrochemical volatilization tin in fuming furnace, always results in serious environmental pollution and in higher energy consumption. The comparisons between the proposed membrane electro-deposition process and the ‘fuming
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Fig. 7. The optical image and SEM images and the XRD pattern of the cathode tin obtained in the confirmation experiment.
process’ are listed in Table 11, indicating that the proposed process has cost advantages over traditional methods. 4. Conclusions A comprehensive procedure based on membrane electrodeposition was developed for the separation and recovery of tin from multi-metals powders of waste printed circuit boards. All the process conditions, including SnCl4 –HCl leaching; purification and electrowinning of tin, were optimized. Selective leaching of tin from multi-metals powders was achieved using SnCl4 as agent, and copper and lead impurities were removed by replacement and sulfide precipitation. By using an electrolytic cell fitted with an anion exchange membrane separator, pure tin plate (99.49%) was obtained from the catholyte with >98% current efficiency. Some chloride ion migrated through the membrane into the anolyte and 98.6% of the Sn2+ was oxidized to Sn4+ which can be recycled to the leach. Economic evaluation of the process when scaled up at pilot scale showed that the cost per ton tin recovery from WPCBs was only $ 684.0, far less than that of tradition process (more than $ 6000.0). WPCBs contain plenty of valuable resources and hazardous materials, considered both an attractive secondary resource and an environmental contaminant. At present, most of the research on
metal recovery from WPCBs are mainly focused on copper or gold, silver recovery. There are few research reports about the selective separation and recovery tin from the enriched multi-metal components of WPCB. Considering that the amount of tin and the corresponding value contained in WPCBs are quite abundant, and that its current disposal methods represent resources waste and a potential risk to living beings, the proposed method would allow for the effective detinning of WPCBs metal components for use as copper smelting raw material. In this sense, this paper could be potentially interesting and contribute to the development of WPCBs disposal and could be relevant to this journal. Acknowledgments Project (51574294, 51174237) supported by the National Nature Science Foundation of China. Project (2012FJ1010) supported by Major science and technology projects of Hunan Province. Project (2015CX001) supported by Innovation Driven Plan of Central South University. References [1] Y. Zhou, W. Wu, K. Qiu, Recovery of materials from waste printed circuit boards by vacuum pyrolysis and vacuum centrifugal separation, Waste Manage. 30 (2010) 2299–2304.
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[2] G. Bidini, F. Fantozzi, P. Bartocci, B. D’Alessandro, M. D’Amico, P. Laranci, E. Scozza, M. Zagaroli, Recovery of precious metals from scrap printed circuit boards through pyrolysis, J. Anal. Appl. Pyrol. 111 (2015) 140–147. [3] H.M. Veit, A.M. Bernardes, J.Z. Ferreira, J.A.S. Tenorio, C.D.F. Malfatti, Recovery of copper from printed circuit boards scraps by mechanical processing and electrometallurgy, J. Hazard. Mater. 137 (2006) 1704–1709. [4] K. Huang, J. Guo, Z. Xu, Recycling of waste printed circuit boards: a review of current technologies and treatment status in China, J. Hazard. Mater. 164 (2009) 399–408. [5] K. Huang, J. Guo, Z. Xu, Recycling of non-metallic fractions from waste printed circuit boards: a review, J. Hazard. Mater. 168 (2009) 567–590. [6] Z. Yihui, Q. Keqiang, A new technology for recycling materials from waste printed circuit boards, J. Hazard. Mater. 175 (2010) 823–828. [7] T. Havlik, D. Orac, M. Petranikova, A. Miskufova, F. Kukurugya, Z. Takacova, Leaching of copper and tin from used printed circuit boards after thermal treatment, J. Hazard. Mater. 183 (2010) 866–873. [8] K. Yuchuang, L. I-hsien, C. Jiaming, Heavy metal extraction from PCB wastewater treatment sludge by sulfuric acid, J. Hazard. Mater. 177 (2010) 881–886. [9] S. Roy, R. Buckle, The recovery of copper and tin from waste tin stripping solution: Part II: kinetic analysis of synthetic and real process waste, Sep. Purif. Technol. 68 (2009) 185–192. [10] L. Bin, P. De-an, J. Yi-hui, T. Jian-jun, Z. Shengen, Z. Kun, Recovery of copper and tin from stripping tin solution by electrodeposition, Rare Met. 3 (2014) 1–5. [11] S. Fogarasi, F. Imre-Lucaci, P. Ilea, A. Imre-Lucaci, The environmental assessment of two new copper recovery processes from waste printed circuit boards, J. Clean. Prod. 54 (2013) 264–269.
[12] S. Fogarasi, F. Imre-Lucaci, A. Egedy, A. Imre-Lucaci, P. Ilea, Eco-friendly copper recovery process from waste printed circuit boards using Fe3+ /Fe2+ redox system, Waste Manage. 40 (2015) 136–143. [13] E.Y. Kim, M.S. Kim, J.C. Lee, J. Jeong, B.D. Pandey, Leaching kinetics of copper from waste printed circuit boards by electro-generated chlorine in HCl solution, Hydrometallurgy 107 (2011) 124–132. ˜ [14] M. García-Gabaldón, V. Pérez-Herranz, J. García-Antón, J.L. Guinón, Electrochemical recovery of tin and palladium from the activating solutions of the electroless plating of polymers: potentiostatic operation, Sep. Purif. Technol. 45 (2005) 183–191. ˜ [15] M. García-Gabaldón, V. Pérez-Herranz, J. García-Antón, J.L. Guinón, Electrochemical recovery of tin from the activating solutions of the electroless plating of polymers: galvanostatic operation, Sep. Purif. Technol. 51 (2006) 143–149. [16] Y. Jianguang, T. Chaobo, Y. Shenghai, H. Jing, T. Motang, The separation and electrowinning of bismuth from a bismuth glance concentrate using a membrane cell, Hydrometallurgy 100 (2009) 5–9. [17] Y. Jianguang, Y. Shenghai, T. Chaobo, The membrane electrowinning separation of antimony from a stibnite concentrate, Metall. Mater. Trans. B 41 (2010) 527–534. [18] Y. Jianguang, L. Jinyuan, Y. Shenghai, H. Jing, T. Chaobo, C. Yongming, A kind of new solder stripper agent based on HCl -tin salt and a new process for tin recovery from spent solder stripper, (2014), Chinese patent, CN201410011267.0.
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Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat
A new membrane electro-deposition based process for tin recovery from waste printed circuit boards Yang Jian-guang ∗ , Lei Jie, Peng Si-yao, Lv Yuan-lu, Shi Wei-qiang School of Metallurgy and Environment, Central South University, Changsha, Hunan 410083, China
h i g h l i g h t s • • • •
A process for tin recovery based on membrane electro-deposition is proposed. Tin can be recovered as the form of high purity cathode tin. Anolyte can be reused as leaching agent for leaching tin again after electrowinning. The optimum parameters for electro-deposition are introduced.
a r t i c l e
i n f o
Article history: Received 30 August 2015 Received in revised form 3 November 2015 Accepted 5 November 2015 Available online 10 November 2015 Keywords: WPCBs Tin recovery Chloride leaching Membrane electrodeposition
a b s t r a c t The current research investigated a process combining leaching, purification and membrane electrodeposition to recover tin from the metal components of WPCBs. Experimental results showed that with a solid liquid ratio of 1:4, applying 1.1 times of stoichiometric SnCl4 dosage and HCl concentration of 3.5–4.0 mol/L at a temperature of 60–90 ◦ C, 99% of tin can be leached from the metal components of WPCBs. The suitable purification conditions were obtained in the temperature range of 30–45 ◦ C with the addition of 1.3–1.4 times of the stoichiometric quantity of tin metal and stirring for a period of 1–2 h; followed by adding 1.3 times of the stoichiometric quantity of Na2 S for sulfide precipitation about 20–30 min at room temperature. The purified solution was subjected to membrane electrowinning for tin electrodeposition. Under the condition of catholyte Sn2+ 60 g/L, HCl 3 mol/L and NaCl 20 g/L, current density 200 A/m2 and temperature 35 ◦ C, a compact and smooth cathode tin layer can be obtained. The obtained cathode tin purity exceeded 99% and the electric consumption was less than 1200 kW h/t. The resultant SnCl4 solution generated in anode compartment can be reused as leaching agent for leaching tin again. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Printed circuit boards (PCBs) are typical and fundamental components of almost all electric and electronic equipment (EEE). With the rapid development of technology and the society, high-performance requirements and great demands in EEE make replacement of PCBs more frequent, resulting in large quantities of WPCBs that need to be disposed. Mechanical and pyrometallurgical methods are the current ways of recycling WPCBs, and pyrolysis process also attracts more and more attention nowadays [1,2]. Almost all waste EEE recycling enterprises in China use various mechanical methods to separate metals and non-metals from
∗ Corresponding author at: Department of Metallurgical Science and Engineering, Central South University, China. E-mail address: jianguang [email protected] (Y. Jian-guang). http://dx.doi.org/10.1016/j.jhazmat.2015.11.007 0304-3894/© 2015 Elsevier B.V. All rights reserved.
WPCBs. As a result, approximately 30 wt.% of the original mass, enriched multi-metal fraction (Cu, Sn, Pb, Fe, Zn, Sb, and so on) is separated from the non-metal components. At present the enriched multi-metal fraction is mainly sold to copper smeltery as copper smelting raw material, and the tin contained in multi-metal fraction is not only failed to get effective recovery, but also cause serious interference to the copper recovery. In addition, the existing pyrometallurgical and hydrometallurgical recovery processes generate pollution because of the release of dioxins and furans or high volume of effluents [3–6]. Hydrometallurgical treatments have more flexibility during the upscaling and control processes. Sulfuric, hydrochloric and nitric acid solutions are often used as leaching agents in hydrometallurgical technologies [7–9]. Bin et al., proposed a hydrometallurgical recovery process to recover copper and tin by constant-current and constant-voltage electrolysis from the leaching solution of tinned copper wastes [10]. Fogarasi et al., introduced two new cop-
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Table 1 Chemical composition of the enriched multi-metal fraction (wt.%). Elements
Content/%
Elements
Content/%
Sn Cu Pb Zn Fe
8.8 56.04 5.85 0.71 1.51
Al Ca Ni Ag Others
0.70 1.41 0.37 0.07 24.54
Table 2 Tin occurrence analysis of the enriched multi-metal fraction/%. Tin occurrence
Sn
SnO
Other
Content/% Proportion/%
8.63 98.1
0.09 1.02
<0.1 <1.0
per recovery processes from waste printed circuit boards [11,12], and Kim et al., investigated the leaching kinetics of copper from waste printed circuit boards by electro-generated chlorine in HCl solution [13]. The experimental results show that the elements could be deposited on the cathode in turns by different deposition potentials. García-Gabaldón et al., studied the performance of a two-compartment batch electrochemical reactor separated by a ceramic diaphragm for tin removal from the activating solutions [14,15]. However, even under optimized conditions, the tin leaching efficiency was proven to be incapable of reaching more than 90%, whereas the current efficiency cannot exceed 85%. The low tin recovery are the obvious disadvantages that limit the application. In our previous study [16,17], a process and related fundamental principle was proposed for the separation and recovery of antimony, bismuth from a concentrate using a membrane electrodeposition process. Further, a new process based on membrane electrodeposition for tin recovery from the metallic fraction of WPCBs is proposed. Thus leaching, purification and membrane electrodeposition to recover tin was investigated. This process has been applied for patent in China recently [18]. The current paper demonstrates that not only tin can be efficiently recovered from WPCBs, but also SnCl4 can be regenerated from the anode compartment and to be used as leaching agent again. 2. Experimental 2.1. Materials The metal components of WPCBs, obtained from Lv-yan Resource Recycle Co., China, were characterized for chemical composition and phase analysis. The dry screen used for the analysis was about 10 mesh (2 mm), and all samples were leached without further grinding. Chemical analysis of the enriched multi-metal fraction was conducted by atomic absorption spectroscopy, except for the copper, tin, lead and zinc contents were analyzed by chemical titration, and the results are given in Table 1. Tin occurrence analysis showed that tin was present mainly as metallic tin (>98%) and as stannous oxide (SnO) (<1%) in small quantity (Table 2). The other chemicals used were of reagent grade. The hydrochloric acid, stannic chloride, etc., were purchased from Changsha Shenghua, Inc., China, with no further purification introduced. 2.2. Method The WPCBs were first treated by using mechanical methods, such as multi-crushing, grinding, electrostatic separation, gravity separation, and magnetic separation to separate metals and non-metals from WPCBs. The schematic of the electrodepositon apparatus and procedure for leaching, purification and electrode-
Fig. 1. Schematic representation of the experimental apparatus for electrodepositon and experimental procedure.
position tin from the enriched multi-metal fraction is shown in Fig. 1. Leaching was carried out in 500 mL glass flasks by adding a weighed amount of multi-metals powder, sodium chloride and stannic chloride to diluted HCl solution at the desired temperature with magnetic stirring at 250 r/min. The temperature of the system was controlled within 2 ◦ C on a hot plate. A condenser was attached to the flask to prevent vaporization losses. At the end of each experiment, the insoluble leach residue was filtered and washed with 1 mol/L HCl and then distilled water. The recovery of tin was calculated by mass balance using the analysis of the multi-metals powder and the leach residue. In the purification procedure, a weighed amount of tin powder and Na2 S was added to the stirred solution to remove Cu2+ and Pb2+ . After filtration, the degree of purification was calculated from analysis of Cu2+ and Pb2+ concentrations by and atomic absorption spectroscopy. In the electrowinning experiment, a two-compartment acrylic cell (90 × 120 × 150 mm) was used, where the anode and cathode compartments were separated by a widely used commercial quaternary-ammonium-hydroxy-type anion exchange membrane (HF-201, Beijing Enling Technology Co., Ltd., China). The applied HF-201 type anion exchange membrane has the anion selective permeability. The membrane only allows the chloride ion and water molecules to penetrate, while other ions are difficult to penetrate. The cathode plate was made of titanium and the anode was a graphite plate with the same surface area. The catholyte and anolyte contained Sn2+ (stannous chloride) and HCl. Both electrolytes are
Y. Jian-guang et al. / Journal of Hazardous Materials 304 (2016) 409–416 Table 3 Leaching and purification analyses under optimized conditions. Elements in solution −1
From leaching/g L After purification/g L−1
Table 4 Effect of different stannous ion concentration on the electro-deposition.
Sn2+
Cu2+
Pb2+
Fe2+
Sn4+
Sn2+ /g L−1
Cathode surface
Current efficiency/%
Cell voltage/V
58.6 59.9
0.20 0.02
0.95 0.03
2.11 2.09
0.19 –
20 40 60 80 100 120
powdery smooth smooth smooth smooth rough
88.1 97.0 99.6 99.0 99.1 99.7
1.67 2.10 2.24 2.39 2.47 2.23
stirred to reduce the concentration polarization in the cell compartments. During the experiment, the additional tin solution is filled in the cathode compartment at a rate according to the theory of tin electro-deposition to ensure the uniformity of the catholyte concentration. The relative cathode current efficiencies are calculated through the following Eq. (1). Where W1 represents actual mass of cathode product, W2 represents the theoretical mass of cathode tin. = (W 1 /W 2 ) ∗ 100%(1) At the cathode, the electrode reactions are: 2+
Sn
411
+ 2e− → Sn(mainreaction);
2H+ + 2e− → H2 ↑ (secondaryreaction); At the anode, the following reactions are possible, but no oxygen or chlorine was detected under the conditions used:
3.2. Purification results and discussions The major aim of purification was to produce a pure electrolyte for electrowinning. The most suitable purification conditions were obtained in the temperature 45 ◦ C with the addition of 1.1 times of the stoichiometric quantity of tin powder as reductant and stirring for a period of 1.0 h (Eqs. (5)–(6)); followed by 1.3 times of the stoichiometric quantity of Na2 S for sulfide precipitation about 30 min at 35 ◦ C (Eqs. (7)–(8)). Under these conditions, the tin concentration increased slightly while Cu2+ and Pb2+ were substantially lower as shown in Table 3. The reduction of copper and lead was >99% with little loss of tin. Sn4+ + Sn = 2Sn2+ (5)
Sn2+ → Sn4+ + 2e− (mainreaction); 2Cl− → Cl2 ↑ + 2e− (secondaryreaction). 3. Results and discussions 3.1. Leaching results During preliminary experiments, various leaching conditions were examined and the most suitable setting for tin extraction was obtained in the temperature range 40–45 ◦ C over two hours with 3.5–4.0 mol/L HCl and the 1.1 times stannic chloride of the stoichiometric quantity using a solid–liquid ratio of 1:3–1:4 with 250 r/min magnetically stirring, and all experiments were carried out using 100 g multi-metals powder per time. As shown in Table 3, the recovery of tin in the leach solution was substantially higher than that of the other metals. Through calculations and analysis of Sn2+ , Cu2+ , Pb2+ and Sn4+ in the leach solution and the leach residue, it was found that >99% Sn was leached from the multi-metals powders without leaching much of the other metals. This procedure yielded an enriched solution containing 58.6 g/L Sn2+ contaminated with about 2 g/L Fe and <1 g/L Cu and Pb. It can be calculated that the exact amount of tin dissolved in a leaching experiment and the amount added as SnCl4 were 8.72 g and 21.22 g, respectively. Under the proposed leaching conditions, most of the metallic tin can be leached into solution according to Eq. (2). It was also observed that after leaching experiment terminated, a new generated thin layer fine copper particle was covered on leach residue. The reason may be concluded that some copper can be dissolved by SnCl4 , but ultimately be reduced by metallic tin according to Eqs. (3) and (4). Therefore, it was deduced that some Cu–Sn alloy even Cu can be dissolved during the beginning of leaching period under the condition of intensive mechanical stirring. Sn + SnCl4 = 2SnCl2 (2) Cu + SnCl4 = CuCl2 + SnCl2 (3) CuCl2 + Sn = Cu + SnCl2 (4)
Sn + Cu2+ = Sn2+ + Cu(6) Cu2+ + S2− = CuS(7) Pb2+ + S2− = PbS(8)
3.3. Electrowinning of tin The tin electrowinning experiments in a divided cell were carried out in order to establish optimum tin electro-deposition parameters such as the effect of stannous ion and sodium chloride concentration in catholyte, temperature, cathode current density and acidity in the catholyte on the main cell performance parameters such as cathodic current efficiency and cell voltage. The resultant stannic chloride concentration in anolyte and the mass of deposited tin on the cathode were also determined. During electrowinning, some atmosphere protection measures (pumped into some N2 and inclosed cell) were applied for avoiding Sn2+ oxidation during electrowinning experiments. 3.3.1. Effect of stannous concentration in the catholyte Electrowinning was first conducted by varying the stannous ion concentration in the catholyte from 20 g/L to 120 g/L in the presence of 20 g/L NaCl and 3 mol/L HCl at temperature of 35 ◦ C and a current density of 200 A/m2 . And 3 mol/L HCl was proved effective to prevent Sn2+ from hydrolyzing during electrowinning. The experiment results are shown in Table 4. Clearly, the current efficiency increases with increasing stannous ion concentration, but at low tin concentrations powdery deposits were observed. At lower stannous ion concentrations, there was higher hydrogen evolution which not only results in lower current efficiencies, but also obtained powdery tin plates (Fig. 2(a)). When the stannous ion concentration lies in 40 (Fig. 2(b)) to 100 g/L (Fig. 2(c)), the cathode surfaces seem better, mostly smooth with metallic luster, and the current efficiency change little. Since no notable additional benefit was derived in going beyond a stannous ion of 100 g/L, this value was chosen as the optimum.
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Fig. 2. The optical images of the cathode tin under different stannous concentration in the catholyte (a)— [Sn2+ ] = 20 g L−1 ; (b)—[Sn2+ ] = 40 g L−1 ; (c)—[Sn2+ ] = 100 g L−1 .
Fig. 3. The optical images of the cathode tin under different sodium chloride concentration in catholyte (a)—5 g L−1 ; (b)—20 g L−1 ; (c)—30 g L−1 .
Table 5 Effect of different concentration of sodium chloride on the electro-deposition.
Table 6 Effect of different temperature on the electro-deposition.
NaCl/g L−1
Current efficiency/%
Cell voltage/V
T/◦ C
Current efficiency/%
Cell voltage/V
Cathode surface
5 10 15 20 25 30
89.1 91.0 95.6 98.1 98.2 98.5
2.79 2.62 2.45 2.27 2.24 2.22
25 30 40 50
94.49 98.11 93.93 81.97
2.79 2.62 2.45 2.31
rough smooth smooth rough
3.3.2. Effect of sodium chloride concentration in catholyte The concentration of sodium chloride in the catholyte was varied from 5 g/L to 30 g/L in the presence of 100 g/L Sn2+ and 3 mol/L HCl at temperature of 35 ◦ C and a current density of 200 A/m2 . The aim of incorporation of sodium chloride into the electrolyte was to enhance the conductivity of the solution during tin electrowinning. The effect of sodium chloride concentration on the current efficiency and cell voltage is summarized in Table 5. Experiment results showed that varying sodium chloride concentration in catholyte from 5 to 30 g L−1 has little influence to cathode tin surface (Fig. 3(a) and (b)), while the current efficiency increases and the cell voltage decreases with NaCl addition up to 20 g/L, beyond which there is no obvious benefit. This may
be explained by increasing sodium chloride concentration only enhanced the conductivity of the electrolyte and lowered cell voltage as well as the cathodic overpotential required to obtain the desired current density. The decreased overpotential results in lower H2 evolution and higher efficiency for tin deposition. Therefore 20 g/L NaCl was chosen as the optimum sodium chloride concentration in the catholyte. 3.3.3. Effect of electrowinning temperature Table 6 shows the effect of temperature on the current efficiency and cell voltage at a current density of 200 A/m2 , using a catholyte composition of 100 g/L Sn2+ , 3 mol/L HCl and 20 g/L NaCl. When the temperature increased from 25 to 50 ◦ C, the current efficiency increased firstly and then decreased, and the cell voltage decreased along. Furthermore, the electro-deposition at low tem-
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413
Fig. 4. The optical images of the cathode tin under different electrowinning temperature (a)—25 ◦ C; (b)−35 ◦ C; (c)—50 ◦ C.
Table 7 Effect of different cathode current density on the electro-deposition.
Table 8 Effect of different acidity on the electro-deposition.
Current density/A m−2
Cathode surface
Current efficiency/%
Cell voltage/V
Acidity/mol L−1
Cathode surface
Current efficiency/%
Cell voltage/V
100 150 175 200 250 300
smooth smooth smooth smooth powdery powdery
95.24 99.00 98.03 99.99 99.08 99.47
1.19 1.69 2.33 2.42 2.67 3.11
0.5 1 2 3 4 6
dendritic powder smooth smooth rough rough
– 96.81 99.00 97.51 94.20 92.80
– 2.75 2.39 1.93 1.56 1.17
perature is easy to be rough, whisker on the edge (Fig. 4(a)). The tin deposit formed at temperatures at 30–40 ◦ C was smooth, uniform with metallic luster (Fig. 4(b)), while higher temperatures reduced both the quality and adherence. The higher current efficiency and deposit quality is obviously due to increased stannous ion mobilities and less H2 production. However, the increased temperature also results in water and HCl volatilization, hence a temperature of 35 ◦ C was selected for obtaining tin plates of good morphology. 3.3.4. Effect of cathode current density The effect of cathode current density on the current efficiency and cell voltage was conducted by varying the cathode current density from 100 A/m2 to 300 A/m2 in the presence of 100 g/L Sn2+ , 20 g/L NaCl and 3 mol/L HCl at 35 ◦ C. Table 7 shows that the current efficiency remained constant around 95–99%, while cell voltage increased steadily with cathode current density. At the same time, the quality of the deposit deteriorated from the good cathode surface at a low current density (Fig. 5(a) and (b)). With the increase of current density, the current efficiency and cell voltage increase, and the cathode surface becomes worse (Fig. 5(c)). The higher current density required an increase in the cathodic polarization, which resulted in more H2 evolution. This made the deposit at the edges become increasingly powdery and dendritic. Considering all these factors, 200 A/m2 was chosen as the optimum cathode current density. 3.3.5. Effect of acidity in the catholyte The effect of acidity on the cathode surface, current efficiency and cell voltage was studied, at 35 ◦ C, 200 A/m2 current density and the catholyte containing Sn2+ 100 g/L and 20 g/L NaCl. Results are shown in Table 8. The electro-deposition at low acidity cannot be processed for very bad cathode surface (Fig. 6(a)). With the increase of acidity, the current efficiency first increased and then decreased while the cell
Table 9 Main constituents of cathode tin, %. Bi
Fe
Zn
Pb
Cu
As
Sn
0.075
0.022
0.001
0.053
0.092
0.001
99.49
voltage decreased steadily, and the cathode surface became better, mostly smooth with metallic luster (Fig. 6(b)). With the acidity over 4 mol/L, the current efficiency and cell voltage decrease, and the cathode surface become rough,and high acidity resulted in more H2 evolution. Therefore, 3 mol/L acidity is selected for the electrodeposition.
3.4. Confirmation experiment Based on the above studies, the optimum conditions for the electro-deposition of tin from a chloride solution in a membrane cell were as follows: Sn2+ 100 g/L, NaCl 20 g/L, temperature 35 ◦ C, HCl 3 mol/L in catholyte and anolyte, cathode current density 200 A/m2 , cathode—anode distance of 5 cm. These conditions were then applied in a confirmation experiment to obtain tin metal sheets and stannic chloride solution (resultant stannic ions in anolyte are not precipitated by hydrolysis at 3 mol/L HCl). The tin leach solution was first purified according to the described optimized conditions and then subjected to electrowinning. In each case, a good quality tin plate and an anolyte suitable for recycling was obtained (98.6% of the Sn2+ in anolyte was converted into Sn4+ after electrowinning). Table 9 and Fig. 7 give the typical analysis, the optical and SEM pattern, XRD pattern of the obtained tin plate. All the XRD pattern peaks are indexed to pure metallic tin (JCPDS file No. 65-0296, Sn).
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Fig. 5. The optical images of the cathode tin under different cathode current density (a)—100 A m−2 ; (b)—200 A m−2 ; (c)—300 A m−2 .
Fig. 6. The optical images of the cathode tin under different acidity in the catholyte (a)—0.5 mol L−1 ; (b)—3 mol L−1 ; (c)—6 mol L−1 .
Table 10 Cost of tin recovery through the membrane electro-deposition process. No.
Raw material and manufacturing material
Cost (dollars/ton)
Note
1 2 3 4 5
Hydrochloric acid Sodium sulfide and additives Electricity Water Labour
35 22 200 30 250
*The market price of tin is about 21,600 dollars per ton while the market price of tin contained in multi-metal fraction of WPCBs is about 7600 dollars, the same as copper price.
6 7 8
Equipment amortization Taxation expense Others Total
82 25 40 684
*The leached residue can be sold to copper smeltery as the same price of multi-metal fraction.
Table 11 Comparisons between the proposed process and traditional ‘fuming process’. Process Membrane electro-deposition process ‘Fuming process’
Tin recovery rate /% >98 <50
3.5. Economical aspects of the process Based on the pilot scale plant test (one ton tin per day) in Lvyan Corporation, Miluo, China, the cost of tin recovery from multimetal fraction of WPCBs through the proposed process is shown in
Cost per ton tin /$ <700 >6000
Environmental impact Friendly Bad
Table 10. In comparison, the current tin recovery process, called the ‘fuming process’ which involves pyrochemical volatilization tin in fuming furnace, always results in serious environmental pollution and in higher energy consumption. The comparisons between the proposed membrane electro-deposition process and the ‘fuming
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Fig. 7. The optical image and SEM images and the XRD pattern of the cathode tin obtained in the confirmation experiment.
process’ are listed in Table 11, indicating that the proposed process has cost advantages over traditional methods. 4. Conclusions A comprehensive procedure based on membrane electrodeposition was developed for the separation and recovery of tin from multi-metals powders of waste printed circuit boards. All the process conditions, including SnCl4 –HCl leaching; purification and electrowinning of tin, were optimized. Selective leaching of tin from multi-metals powders was achieved using SnCl4 as agent, and copper and lead impurities were removed by replacement and sulfide precipitation. By using an electrolytic cell fitted with an anion exchange membrane separator, pure tin plate (99.49%) was obtained from the catholyte with >98% current efficiency. Some chloride ion migrated through the membrane into the anolyte and 98.6% of the Sn2+ was oxidized to Sn4+ which can be recycled to the leach. Economic evaluation of the process when scaled up at pilot scale showed that the cost per ton tin recovery from WPCBs was only $ 684.0, far less than that of tradition process (more than $ 6000.0). WPCBs contain plenty of valuable resources and hazardous materials, considered both an attractive secondary resource and an environmental contaminant. At present, most of the research on
metal recovery from WPCBs are mainly focused on copper or gold, silver recovery. There are few research reports about the selective separation and recovery tin from the enriched multi-metal components of WPCB. Considering that the amount of tin and the corresponding value contained in WPCBs are quite abundant, and that its current disposal methods represent resources waste and a potential risk to living beings, the proposed method would allow for the effective detinning of WPCBs metal components for use as copper smelting raw material. In this sense, this paper could be potentially interesting and contribute to the development of WPCBs disposal and could be relevant to this journal. Acknowledgments Project (51574294, 51174237) supported by the National Nature Science Foundation of China. Project (2012FJ1010) supported by Major science and technology projects of Hunan Province. Project (2015CX001) supported by Innovation Driven Plan of Central South University. References [1] Y. Zhou, W. Wu, K. Qiu, Recovery of materials from waste printed circuit boards by vacuum pyrolysis and vacuum centrifugal separation, Waste Manage. 30 (2010) 2299–2304.
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[2] G. Bidini, F. Fantozzi, P. Bartocci, B. D’Alessandro, M. D’Amico, P. Laranci, E. Scozza, M. Zagaroli, Recovery of precious metals from scrap printed circuit boards through pyrolysis, J. Anal. Appl. Pyrol. 111 (2015) 140–147. [3] H.M. Veit, A.M. Bernardes, J.Z. Ferreira, J.A.S. Tenorio, C.D.F. Malfatti, Recovery of copper from printed circuit boards scraps by mechanical processing and electrometallurgy, J. Hazard. Mater. 137 (2006) 1704–1709. [4] K. Huang, J. Guo, Z. Xu, Recycling of waste printed circuit boards: a review of current technologies and treatment status in China, J. Hazard. Mater. 164 (2009) 399–408. [5] K. Huang, J. Guo, Z. Xu, Recycling of non-metallic fractions from waste printed circuit boards: a review, J. Hazard. Mater. 168 (2009) 567–590. [6] Z. Yihui, Q. Keqiang, A new technology for recycling materials from waste printed circuit boards, J. Hazard. Mater. 175 (2010) 823–828. [7] T. Havlik, D. Orac, M. Petranikova, A. Miskufova, F. Kukurugya, Z. Takacova, Leaching of copper and tin from used printed circuit boards after thermal treatment, J. Hazard. Mater. 183 (2010) 866–873. [8] K. Yuchuang, L. I-hsien, C. Jiaming, Heavy metal extraction from PCB wastewater treatment sludge by sulfuric acid, J. Hazard. Mater. 177 (2010) 881–886. [9] S. Roy, R. Buckle, The recovery of copper and tin from waste tin stripping solution: Part II: kinetic analysis of synthetic and real process waste, Sep. Purif. Technol. 68 (2009) 185–192. [10] L. Bin, P. De-an, J. Yi-hui, T. Jian-jun, Z. Shengen, Z. Kun, Recovery of copper and tin from stripping tin solution by electrodeposition, Rare Met. 3 (2014) 1–5. [11] S. Fogarasi, F. Imre-Lucaci, P. Ilea, A. Imre-Lucaci, The environmental assessment of two new copper recovery processes from waste printed circuit boards, J. Clean. Prod. 54 (2013) 264–269.
[12] S. Fogarasi, F. Imre-Lucaci, A. Egedy, A. Imre-Lucaci, P. Ilea, Eco-friendly copper recovery process from waste printed circuit boards using Fe3+ /Fe2+ redox system, Waste Manage. 40 (2015) 136–143. [13] E.Y. Kim, M.S. Kim, J.C. Lee, J. Jeong, B.D. Pandey, Leaching kinetics of copper from waste printed circuit boards by electro-generated chlorine in HCl solution, Hydrometallurgy 107 (2011) 124–132. ˜ [14] M. García-Gabaldón, V. Pérez-Herranz, J. García-Antón, J.L. Guinón, Electrochemical recovery of tin and palladium from the activating solutions of the electroless plating of polymers: potentiostatic operation, Sep. Purif. Technol. 45 (2005) 183–191. ˜ [15] M. García-Gabaldón, V. Pérez-Herranz, J. García-Antón, J.L. Guinón, Electrochemical recovery of tin from the activating solutions of the electroless plating of polymers: galvanostatic operation, Sep. Purif. Technol. 51 (2006) 143–149. [16] Y. Jianguang, T. Chaobo, Y. Shenghai, H. Jing, T. Motang, The separation and electrowinning of bismuth from a bismuth glance concentrate using a membrane cell, Hydrometallurgy 100 (2009) 5–9. [17] Y. Jianguang, Y. Shenghai, T. Chaobo, The membrane electrowinning separation of antimony from a stibnite concentrate, Metall. Mater. Trans. B 41 (2010) 527–534. [18] Y. Jianguang, L. Jinyuan, Y. Shenghai, H. Jing, T. Chaobo, C. Yongming, A kind of new solder stripper agent based on HCl -tin salt and a new process for tin recovery from spent solder stripper, (2014), Chinese patent, CN201410011267.0.