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Mass transport-enhanced electrodeposition for the efficient recovery of copper and selenium from sulfuric acid solution
Accepted Manuscript Mass transport-enhanced electrodeposition for the efficient recovery of copper and selenium from sulfuric acid solution Junling Su, Xiao Lin, Shili Zheng, Rui Ning, Wenbo Lou, Wei Jin PII: DOI: Reference:
S1383-5866(16)32869-6 http://dx.doi.org/10.1016/j.seppur.2017.03.056 SEPPUR 13644
To appear in:
Separation and Purification Technology
Received Date: Revised Date: Accepted Date:
27 December 2016 26 March 2017 27 March 2017
Please cite this article as: J. Su, X. Lin, S. Zheng, R. Ning, W. Lou, W. Jin, Mass transport-enhanced electrodeposition for the efficient recovery of copper and selenium from sulfuric acid solution, Separation and Purification Technology (2017), doi: http://dx.doi.org/10.1016/j.seppur.2017.03.056
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Mass transport-enhanced electrodeposition for the efficient recovery of copper and selenium from sulfuric acid solution
Junling Sua,b, Xiao Lin b, Shili Zhengb, Rui Ningc, Wenbo Loud, Wei Jinb,*
a
School of Chemical and Environmental Engineering, China University of Mining and Technology of Beijing, Beijing 100083, China b
National Engineering Laboratory for Hydrometallurgical Cleaner Production
Technology, Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China c
d
Daye Nonferrous Metal Co., Ltd., Huangshi, Hubei, 435005, China
School of Metallurgy, Northeastern University, Shenyang 110819, People's Republic of China *Corresponding author: E-mail: [email protected] (Wei Jin), Tel: +86 10 62584427.
Abstract: Recovery of selenium from copper-based sulfuric acid solution is of significant importance for the supply of this scattered metal. In order to overcome the drawbacks of high energy/reagents consumption and low recovery ratio in conventional processes, a cost-effective electrochemical recovery process of Se and Cu was first developed using low-cost stainless steel cathodes. It has been demonstrated that Se and Cu ions can be simultaneously electrodeposited, and the co-deposition is mass transport controlled quasi-reversible reaction. Consequently, a
cylinder turbulent cell with larger surface area cathode was employed for the extraction of metals from dilute solution (2.0 g/L Cu2+ and 0.3 g/L Se4+). Nanosized powder was obtained due to the excellent mass transport. 93.2% copper and 97.6% selenium was successfully extracted with a current efficiency of 81.3%. The as-prepared metal powder could be readily flushed and collected from the cell with water. This mass transport-enhanced approach may serve as a promising alternative to overcome the drawbacks of existing metal recovery and water purification.
Key words: Selenium, Electrodeposition, Mass transport, Stainless steel cathode, Copper
1. Introduction Selenium (Se) is widely used in semiconductor and electronics industries, such as solar panels, light emitting diodes and phase-change memory chips [1, 2]. However, Se is a typical scattered metals, which only accounts for 5×10-6 percent of the earth`s crust [3]. One of their primary sources is the anode slime produced during the electrolytic refining of copper, where the mass fraction of Se can reach 5-25% [4]. Consequently, many efforts have been developed for the recovery of copper (Cu) and Se from the slimes. Decopperization of anode slimes is the first stage of selenium recovery [5-7]. Generally, the slimes are dissolved by high temperature roasting-acidic leaching process, and then most of the copper can be recovered by crystallization or solvent
extraction. Subsequently, the selenium compounds can be reduced and recovered by SO2 or Na2SO3 (as shown in equation 1). However, this reduction is only efficient when the initial concentration of selenium is greater than 1 g/L [8]. Besides, the remaining Cu 2+ can be separated as copper powder by partial reduction and disproportionation (as shown in equation 2 and 3), while the recovery ratio of copper is limited (~30%) [9, 10]. SeO32- + H2O + 2SO2 → Se + 2H+ + 2SO42-
(1)
2Cu2+ + 2H2O + SO2 → 2Cu+ + 4H+ + SO42-
(2)
2Cu + → Cu2+ + Cu
(3)
Alternatively, electrodeposition is an efficient, cost-effective and readily adoptable method to recover metal ions in the corresponding metallic state [11-13]. By employing the clean reagent of “electron”, the process can be carried out with high selectivity and no extra chemicals are required. Considerable studies of electrochemical copper recovery have been reported [14-16]. Nevertheless, the Se electrodeposition mainly focuses on the semiconductor layer fabrications in electronic and optical devices, and the cathodic electrodes are usually expensive substrates of Au, Mo and Pt [17, 18]. More importantly, the concentration of Se in the leaching solution of anode slime is usually 0.2-4.0 g/L, resulting in the potential diffusion limitation during the electrochemical process [19]. It has been demonstrated that the mass transport of electrodeposition process can be significantly enhanced by the employment of electrode movement, large surface area electrode and high flow rate of electrolyte [20, 21]. In this regard, the aim of this
study is to develop a cost-effective electrochemical recovery process of Se and Cu from dilute solution. The co-deposition behavior of Se and Cu was systematically investigated with respected to the mass transport condition. This approach may serve as a promising alternative to overcome the drawbacks of existing metal recovery and water purification.
2. Materials and methods 2.1 Materials The chemical reagents used in the preparation of synthetic solutions used in this study were all of analytical grade purity and used as received from Sigma Aldrich, including sulfuric acid (95.0-98.0 wt.%), copper sulfate (99.99 wt.%) and sodium selenite (99.0 wt.%). A synthetic solution was prepared by dissolving the corresponding sulfuric acid and bismuth salt into ultrapure water (18 MΩ·cm) obtained from a water purification system.
2.2 Electrochemical studies To understand the basic electrochemistry of Cu and Se ions, linear sweep voltammetry (LSV) was performed at ambient temperature using a CHI760E workstation (CH Instruments, Shanghai). A typical three electrodes cell (500 mL) with a 316L stainless steel working electrode (active area of 2.0 cm2), an IrO2-Ta2O5 coated titanium counter electrode and a double junction Ag/AgCl (0.22 V vs. SHE) reference electrode was used. Prior to each experiment, the stainless steel plate was
successively polished using 180, 400 and 600 grit silicon carbide sandpaper to obtain a smooth electrode surface for deposition. Then, the electrode was washed and sonicated in purified water. Subsequently, the electrochemical measurements were performed in N2-purged solutions by potential cycling from 0.3 V to -0.7 V at various scan rates. All potentials are reported versus saturated calomel electrode (SCE) Chronopotentiometry (CP) was employed to investigate the electrodeposition behavior with same electrochemical cell and electrodes as described in the CV procedure. The current density was selected at 175 and 350 A/m2 with different stirring rate. Furthermore, a tubular cell (emew® system) with an IrO2-Ta2O5 coated titanium anode in the center and an annular stainless steel foil cathode outside of the tube was used to further improve the mass transport condition. The cell has a cathode area of 150 cm2 and cathodic current density was 350 A/m2. 2 liters of solution were used in each test, and the flow rate used was 3 L/min or 5 L/min.
2.3 Physical characterization The surface morphology and approximate composition of prepared products were characterized using a field-emission scanning electron microscopy (FE-SEM, JSM-7610F) with energy dispersive X-ray spectroscopy (EDS), while its crystalline structure was measured using a X-ray diffraction (XRD, Smartlab, Japan) with Cu Kα radiation. The inductivity coupled plasma-optical emission spectrometer (ICP-OES, Optima 5300DV, PerkinElimer, USA) was used to analyze the concentration of dissolved copper and selenium. The mean particle sizes and size distribution were
determined using a Microtrac S3500 particle size analyzer.
3. Results and discussion 3.1 Electrochemical reduction of Cu(II) and Se(IV) Linear sweep voltammetry (LSV) measurements were performed using the synthetic leaching solution of anode slime to determine the electrochemical reduction Cu(II) and Se(IV) at the stainless steel electrode. As shown in Fig. 1, a small reduction peak emerged at -0.43 V with a peak current density of 1.31 mA cm-2 in the 25 g/L H2SO4 solution, which is attributed to the surface reaction of stainless steel electrode [22]. The Cu2+ reduction peak appeared at -0.46 V with 15.70 mA cm-2 peak current density in the presence of 2.0 g/L Cu2+, in consistent with previous study [23]. Interestingly, there are two cathodic peaks at -0.14 V and -0.40 V in the presence of 0.3 g/L Se4+, in good agreement with the corresponding reduction behavior at SnO2 coated glass electrodes [24]. The peaks are corresponding to four-electron and six-electron reductions as shown in equation 4 and 5, respectively. It should be noted that the H2Se then proceeds conproportionation reaction to generate Se. Obviously, the selenium ions can undergo electrochemical reduction to Se at low-cost stainless steel electrodes, and the Se and Cu ions reduction potentials are very close. Consequently, a well-defined reduction peak at -0.45 V with a small wide reduction peak at around -0.13V are observed in the presence of 2.0 g/L Cu 2+and 0.3 g/L Se4+, which is due to the combination of Cu and Se reduction. SeO32- + 6H+ + 4e- → Se + 3H2O
(4)
SeO32- + 8H+ + 6e- → H2Se + 3H2O SeO32- + 3H2Se → 4Se + 3H2O
(5) (6)
3.2 Mass transport effect In order to further characterize the electrochemical reduction behavior, potential scans were performed at different rates ranging from 50 to 200 mV/s. As can be seen in Figure 2a, a negative shift of the cathodic peak potential with increasing scan rate is observed, which agrees with the theory of a quasi-reversible reaction [25, 26]. Besides, there are good linear relationships between the reduction peak currents and the square root of scan rate (v1/2) as seen in Figure 2b, indicating the reduction reaction of this system is diffusion-controlled [27]. In general, the peak current of a mass transport controlled quasi-reversible electrodeposition reaction at 298 K can be calculated by the following equation [28]:
I p = 367n 3 / 2 AD1/ 2Cv1/ 2
(7)
where Ip (A) is the peak current, n is the number of electrons, A (cm2) is the surface area of the working electrode, D (cm2·s-1) is the diffusion coefficient, C (mol·L-1) is the bulk concentration, and v (V·s-1) is the scan rate. Therefore, the diffusion coefficients of Cu2+ and Se4+ were estimated to be 2.37×10-5 cm2·s-1 and 2.93×10-6 cm2·s-1. Given the low concentration of Se4+ in solution and its lower diffusion coefficient, it is expected to overcome the diffusion issues for better recovery performance.
3.3 Electrochemical co-deposition To determine the electrochemical co-deposition behavior of Cu 2+ and Se4+, chronopotentiometry with different applied current and stirring rate was performed. As presented in Fig. 3, the obtained potential negatively shift from -0.35 V to -0.60 V with the increasing cathodic current, offering more driving force for the electrochemical reduction and deposition. Furthermore, the stirring rate (e.g. mass transport) plays an important role in the electrochemical behavior. As the stirring rate decreases, the potential negatively shift to the hydrogen evolution region with serious oscillation issues, possibly leading to the formation of unfavorable Cu2O products and the decrease of current efficiency [29]. Electrolytic metal recovery using the three-electrode cell was examined for 60 minutes, and a deposition foil was removed and collected. After the washing and drying, the deposited products were characterized by SEM, EDS and XRD. As shown in Fig. 4, compact electrodeposited film with relatively uniform grain size was obtained. And the EDS analyses indicate the film consisted of Cu and Se with small oxides present (see Fig. 5a), while XRD confirmed the presence of Cu, Cu2Se and Cu2O as shown in Fig. 5b. Consequent, the composition of the film was estimated by combining the XRD and EDS results in Table 1. The formation of Cu 2O is demonstrated to occur by the partial reduction of Cu2+ to Cu + followed by the precipitation of Cu + as Cu2O as shown in equation 8. It is common to see copper “burn” (e.g. Cu 2O formation) during high current density electrodeposition when the agitation or mass transport is not great enough [30]. Besides, the Cu2Se products
originate from the co-deposition of Se and Cu from the acidic sulfate solution as illustrated in equation 9 [31], which is quite different from the selenium-sulfate system mentioned above. As a result, 9.2% of the copper and 19.3% of the selenium was recovered from the solution by the 60 minute treatment at 350 A·m-2 and 1000 rpm, while the current efficiency of 27.1% is limited. It should be noted that the current efficiency was calculated with the equation 10 by considering the corresponding electron transfer numbers of different electrodeposited products: 2Cu2+ + H2O + 2e- → Cu2O + 2H+
(8)
2Cu2+ + SeO32- + 6H+ + 8e- → Cu 2Se + 3H2O
(9)
= ܧܥ
ଽସ଼ହ× ୧×୲
ಮ
×ౣ సభ
(10)
where the CE is current efficiency, 96485 C·mol-1 is the Faraday constant of electrolysis, n is the numbers of electron transfer, m and M are the corresponding weight and molar mass of electrodeposited products, respectively, i and t are the current and electrolysis time of the electrodeposition, respectively. In consistent with the above results of chronopotentiometric curves, the high current density and mass transport can significantly facilitate high Cu/Se recovery ratio, better total metal recovery and less Cu2O formation. However, the co-deposition performance of Cu and Se was not complete and particularly energy efficient in these conditions.
3.4 Efficient electrochemical recovery In order to improve the electrochemical recovery performance, a cylinder turbulent cell with larger cathode surface area was employed with a current of 350
A/m2 and different solution flow rate. It should be noted that 2 liters solution was treated in this section to better evaluate the practical implications. As shown in Table 1, 68.7% copper and 73.2% selenium was efficiently removed from the solution with a solution flow rate of 3 L/min. The current efficiency was determined to be 60.3%, which is much higher than the corresponding data of conventional cell. Clearly, the co-deposition behavior is substantially enhanced by changing the mass transport condition. Besides, the performance was further enhanced by increasing the flow rate to 5 L/min. 93.2% copper and 97.6% selenium was successfully extracted with a current efficiency of 81.3%, offering satisfied recovery for potential industrial applications. As compared to the thin film product in the conventional cell, electrodeposited nanosized powder was obtained in the cylinder turbulent cell due to the excellent mass transport (Fig. 6). And the Cu 2O formation in the products was also substantially reduced to 3% (Table 1), suggesting the electrochemical reduction was efficiently performed and the partial reduction to Cu 2O was well eliminated. As illustrated in Fig. 7, the mean particle size of 3 L/min and 5 L/min were 84 µm and 76µm, respectively. It should be noted that the as-prepared metal powder could be readily flushed and removed from the cell with water, which overcomes the drawback of product harvesting from a conventional cell. Consequently, the schematic diagram of mass transport-enhanced electrodeposition process is illustrated in Fig. 8, offering a more energy efficient process with high values metal products.
4. Conclusions An efficient mass transport-enhanced electrochemical recovery process of Se and Cu from sulfuric acid solution was first developed using low-cost stainless steel cathodes. It has been demonstrated that Se and Cu ions can be simultaneously electrodeposited, and the co-deposition is mass transport controlled quasi-reversible reaction. The diffusion coefficients of Cu 2+ and Se4+ were also estimated to be 2.37×10 -5 cm2·s-1 and 2.93×10-6 cm2·s-1, suggesting better diffusion properties are needed for the Se recovery. Compact electrodeposited film was obtained using the three-electrode cell, but the co-deposition performance of Cu and Se was not complete and particularly energy efficient. The high current density and mass transport can significantly facilitate better metal recovery and less Cu 2O formation. Consequently, a cylinder turbulent cell with larger surface area cathode was employed, and nanosized powder was obtained due to the excellent mass transport. 93.2% copper and 97.6% selenium was successfully extracted with a current efficiency of 81.3%. The Cu2O formation in the products was also substantially reduced to 3%, and the as-prepared metal powder could be readily flushed and collected from the cell with water. This mass transport-enhanced approach may serve as a promising alternative to overcome the drawbacks of existing metal recovery and water purification.
Acknowledgements W.J. acknowledges the funding support from National Natural Science Foundation of China under Grant No. 51604253 and “CAS Pioneer Hundred Talents
Program”. We acknowledged the support from the National Basic Research Program of China (973 Program) under Grant No. 2013CB632601 and 2013CB632605, and the National Natural Science Foundation of China under Grant No. 51274179.
References [1] R. M. Hodlur, M. K. Robinal, A new selenium precursor for the aqueous synthesis of luminescent CdSe quantum dots, Chem. Eng. J. 244 (2014) 82-88. [2] C. Li, F. Wang, J. C. Yu, Semiconductor/biomolecular composites for solar energy applications, Energy Environ. Sci. 4 (2011) 100-113. [3] W. F. Liu, T. Z. Yang, D. C. Zhang, L. Chen, Y. N. Liu, Pretreatment of copper anode slime with alkaline pressure oxidative leaching, Int. J. Miner. Process. 128 (2014) 48-54. [4] D. Li, X. Guo, Z. Xu, Q. Tian, Q. Feng, Leaching behavior of metals from copper anode slime using an alkali fusion-leaching process, Hydrometallurgy 157 (2015) 9-12. [5] Y. Kilic, G. Kartal, S. Timur, An investigation of copper and selenium recovery from copper anode slimes, Int. J. Miner. Process. 124 (2013) 75-82. [6] J. E. Hoffmann, Recovering selenium and tellurium from copper refinery slimes, JOM 41 (1989) 33-38. [7] C. Hu, Q. Chen, G. Chen, H. Liu, J. Qu, Removal of Se(IV) and Se(VI) from drinking water by coagulation, Sep. Purif. Technol. 142 (2015) 65-70. [8] A. Baral, C.K. Sarangi, B. C. Tripathy, I. N. Bhattacharya, T. Subbaiah, Copper
electrodeposition from sulfate solutions-Effects of selenium. Hydrometallurgy 146 (2014) 8-14. [9] T. Shibasaki, K. Kabe, H. Takeuchi, Recovery of tellurium from decopperizing leach solution of copper refinery slimes by a fixed bed reactor, Hydrometallurgy 29 (1992) 399-412. [10] S. Klas, D. W. Kirk, Understanding the positive effects of low pH and limited aeration on selenate removal from water by elemental iron. Sep. Purif. Technol. 116 (2013) 222-229. [11] J. P. Chen, L. L. Lim, Recovery of precious metals by an electrochemical deposition method. Chemosphere 60 (2005) 1384-1392. [12] Y. Huang, G. Han, J. Liu, W. Chai, W. Wang, S. Yang, S. Su, A stepwise recovery of metals from hybrid cathodes of spent Li-ion batteries with leaching-flotation-precipitation process, J. Power Sources 325 (2016) 555-564. [13] W. Jin, H. Du, S. Zheng, Y. Zhang, Electrochemical processes for the environmental remediation of toxic Cr(VI): A review. Electrochim Acta 191 (2016) 1044-1055. [14] A. Mecucci, K. Scott. Leaching and electrochemical recovery of copper, lead and tin from scrap printed circuit boards, J. Chem. Technol. Biotechnol. 77 (2002) 449-457. [15] D. N. Bennion, J. Newman, Electrochemical removal of copper ions from very dilute solutions, J. Appl. Electrochem. 2 (1972) 113-122.
[16] Z. Sun, H. Cao, P. Venkatesan, W. Jin, Y. Xiao. J. Sietsma, Y. Yang. Electrochemistry during efficient copper recovery from complex electronic waste using
ammonia
based
solutions,
Front.
Chem.
Sci.
Eng.
2016,
DOI:
10.1007/s11705-016-1587-x. [17] M. F. Cabral, H. B. Suffredini, V. A. Pedrosa, S. T. Tanimoto, S. A. S. Machado. Electrodeposition and characterization of thin selenium films modified with lead ad-atoms, Appl. Surf. Sci. 254 (2008) 5612-5617. [18] S. Saha, N. Tachikawa, K. Yoshii, Y. Katayama, Electrodeposition of selenium in a hydrophobic room-temperature ionic liquid, J. Electrochem. Soc. 163 (2016) D259-D64. [19] L. Thouin, S. Rouquette-Sanchez, J. Vedel, Electrodeposition of copper-selenium binaries in a citric acid medium, Electrochim. Acta 38 (1993) 2387-2394. [20] D. Pletcher, F. C. Walsh, Industrial electrochemistry, Chapman and Hall, London. 1990. [21] F. C. Walsh, Electrochemical technology for environmental treatment and clean energy conversion, Pure Appl. Chem. 73 (2001) 1819-1837. [22] Y. Xue, W. Jin, H. Du, S. Wang, S. Zheng, Y. Zhang, Tuning α-Fe2O3 nanotube arrays for the oxygen reduction reaction in alkaline media, RSC Adv. 6 (2016) 41878-41884. [23] D. Grujicic, B. Pesic, Electrodeposition of copper: the nucleation mechanisms, Electrochim. Acta 47 (2002) 2901-2912. [24] Y. Lai, F. Liu, J. Li, Z. Zhang, Y. Liu, Nucleation and growth of selenium
electrodeposition onto tin oxide electrode, J. Electroanal. Chem. 639 (2010) 187-192. [25] W. Jin, H. Du, S. Zheng, H. Xu, Y. Zhang, Comparison of the oxygen reduction reaction between NaOH and KOH solutions on Pt electrode: the electrolyte-dependent effect, J. Phys. Chem. B 114 (2010) 6542-6548. [26] W. Jin, M. S. Moats, S. Zheng, H.Du, Y. Zhang, J. D. Miller, Modulated Cr(III) oxidation in
KOH
solutions at
a
gold
electrode: Competition
between
disproportionation and stepwise electron transfer, Electrochim. Acta 56 (2011) 8311-838. [27] W. Jin, M. S. Moats, S. Zheng, H. Du, Y. Zhang, J. D. Miller, Indirect Electrochemical Cr(III) Oxidation in KOH Solutions at an Au Electrode: The Role of Oxygen Reduction Reaction, J. Phys. Chem. B 116 (2012) 7531-7537. [28] T. Berzins, P. Delahay, Oscillographic polarographic waves for the reversible deposition of metals on solid electrodes, J. Am. Chem. Soc. 75 (1953) 555-559. [29] P. E. de Jongh, D. Vanmaekelbergh, J. J. Kelly, Cu 2O: Electrodeposition and characterization, Chem. Mater., 1999, 11, 3512-3517. [30] Y. Yang, Y. Li, M. Pritzker, Control of Cu2O film morphology using potentiostatic pulsed electrodeposition, Electrochim. Acta 213 (2016) 225-235. [31] L. Zhang, W. He, X. Chen, Y. Du, X. Zhang, Y. Shen, F. Yang, Nanocrystallized Cu2Se grown on electroless Cu coated p-type Si using electrochemical atomic layer deposition, Surf. Sci. 2015, 631, 173-177.
Figures and Captions: Fig. 1 CV curves of stainless steel electrodes in the synthetic 25 g/L H2SO4 leaching solution, scan rate: 100 mV·s-1 Fig. 2 Electrochemical reduction behavior as a function of scan rate on stainless steel: (a) cyclic voltammograms of Cu2+ reduction with increasing scan rate (50-200 mV/s ); (b) variation of the reduction peak currents as a function of the square root of the scan rate in 2.0 g/L Cu 2+, 0.3 g/L Se4+ ( peak at -0.14 V), Cu2+ and Se4+ containing 25 g/L H2SO4 solutions Fig. 3 Chronopotentiometric curves using a stainless steel electrode with different current densities and stirring rate Fig. 4 SEM images of electrodeposited film from copper and selenium based solutions at 1000 rpm and 350 A·m-2. Fig. 5 (a) EDS and (b) XRD spectra with crystallographic plane indices of electrodeposited film from copper and selenium based solutions at 1000 rpm and 350 A·m-2. Fig. 6 (Left) Photo of stainless steel cathode after deposition and (right) SEM image of electrodeposited powder from copper and selenium based solutions at 5 L/min and 350 A·m-2. Fig. 7 Particle size distribution of electrodeposited powder from cylinder electrochemical cell. Fig. 8 Schematic diagrams of mass transport-enhanced electrodeposition for the recovery of Cu and Se
Table 1 The comparison of electrochemical recovery performance with different parameters
-2
Current density / mA cm
0 -4 -8 blank 2+ 2.0 g/L Cu 4+ 0.3 g/L Se 2+ 4+ Cu + Se
-12 -16 -20 -0.8
-0.6
-0.4
-0.2
0.0
Potential / V vs. SCE Fig. 1
0.2
0.4
0
Current density / mA cm
-2
a
-4 -8 50 mV/s 75 mV/s 100mV/s 125mV/s 150mV/s 200mV/s
-12 -16 -20 -24 -0.8
-0.6
-0.4
-0.2
0.0
Potential / V vs. SCE
Current density/ mA cm
-2
2+
24
Cu 4+ Se 2+ 4+ Cu +Se
b
20 16 12 8 4 0 6
8
10 1/2
12 1/2
-1/2
V / mV s Fig. 2
14
0.2
Potential / V vs. SCE
-0.2 -0.4 -0.6 -0.8 -2
-1.0
175 A/m 1000 rpm -2 350 A/m 200 rpm -2 350 A/m 600 rpm -2 350 A/m 1000 rpm
-1.2 0
200
400
600
Time / s Fig. 3
800
1000
1200
Fig. 4
Fig. 5
Intensity/a.u.
Intensity / a.u.
Cu
Cu 10
Se
A Cu B Cu2O
12
80
B(311) A(220)
C Cu2Se
60
B(220)
8
A(200) B(211)
6
A(111)
a
B(111) B(200)
4
C(090)
Energy / keV
40
2θ / degree
C(250) C(410) B(110)
Cu
O
20
2
Se
b
C(030)
Fig. 6
6
3 L/min 5 L/min
Volume / %
5 4 3 2 1 0 0
300
600
900
Particle size / µm Fig. 7
1200
1500
Fig. 8
Table 1 Current -2
(A· m ) # 175
Mass transport
Time (min)
Product weight (g)
Current efficiency
Cu recovery
Se recovery
Product composition
1000 rpm
60
0.08
30.4%
4.3%
11.9%
33% Cu2O, 23% Cu, 38% Cu2 Se 10% Cu2O, 51% Cu, 39% Cu2 Se 16% Cu2O, 47% Cu, 37% Cu2 Se 20% Cu2O, 42% Cu, 38% Cu2 Se 7% Cu2O, 73% Cu, 20% Cu2 Se 3% Cu2O, 81% Cu, 15% Cu2 Se
#
350
1000 rpm
60
0.14
27.1%
9.2%
19.3%
#
350
600 rpm
60
0.12
19.2%
7.3%
16.2%
#
350
200 rpm
60
0.10
15.2%
5.3%
12.1%
*
350
3 L/min
60
3.23
60.3%
68.7%
73.2%
*
5 L/min
60
4.11
81.3%
93.2%
97.6%
350
# *
Three-electrode cell Cylinder tubular cell
Highlights: • Novel electrochemical recovery process of Se and Cu was first reported. • Se and Cu ions can be simultaneously electrodeposited at low-cost stainless steel from dilute solutions. • An efficient recovery of Se and Cu was obtained via the mass transport-enhanced electrodeposition.
S1383-5866(16)32869-6 http://dx.doi.org/10.1016/j.seppur.2017.03.056 SEPPUR 13644
To appear in:
Separation and Purification Technology
Received Date: Revised Date: Accepted Date:
27 December 2016 26 March 2017 27 March 2017
Please cite this article as: J. Su, X. Lin, S. Zheng, R. Ning, W. Lou, W. Jin, Mass transport-enhanced electrodeposition for the efficient recovery of copper and selenium from sulfuric acid solution, Separation and Purification Technology (2017), doi: http://dx.doi.org/10.1016/j.seppur.2017.03.056
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Mass transport-enhanced electrodeposition for the efficient recovery of copper and selenium from sulfuric acid solution
Junling Sua,b, Xiao Lin b, Shili Zhengb, Rui Ningc, Wenbo Loud, Wei Jinb,*
a
School of Chemical and Environmental Engineering, China University of Mining and Technology of Beijing, Beijing 100083, China b
National Engineering Laboratory for Hydrometallurgical Cleaner Production
Technology, Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China c
d
Daye Nonferrous Metal Co., Ltd., Huangshi, Hubei, 435005, China
School of Metallurgy, Northeastern University, Shenyang 110819, People's Republic of China *Corresponding author: E-mail: [email protected] (Wei Jin), Tel: +86 10 62584427.
Abstract: Recovery of selenium from copper-based sulfuric acid solution is of significant importance for the supply of this scattered metal. In order to overcome the drawbacks of high energy/reagents consumption and low recovery ratio in conventional processes, a cost-effective electrochemical recovery process of Se and Cu was first developed using low-cost stainless steel cathodes. It has been demonstrated that Se and Cu ions can be simultaneously electrodeposited, and the co-deposition is mass transport controlled quasi-reversible reaction. Consequently, a
cylinder turbulent cell with larger surface area cathode was employed for the extraction of metals from dilute solution (2.0 g/L Cu2+ and 0.3 g/L Se4+). Nanosized powder was obtained due to the excellent mass transport. 93.2% copper and 97.6% selenium was successfully extracted with a current efficiency of 81.3%. The as-prepared metal powder could be readily flushed and collected from the cell with water. This mass transport-enhanced approach may serve as a promising alternative to overcome the drawbacks of existing metal recovery and water purification.
Key words: Selenium, Electrodeposition, Mass transport, Stainless steel cathode, Copper
1. Introduction Selenium (Se) is widely used in semiconductor and electronics industries, such as solar panels, light emitting diodes and phase-change memory chips [1, 2]. However, Se is a typical scattered metals, which only accounts for 5×10-6 percent of the earth`s crust [3]. One of their primary sources is the anode slime produced during the electrolytic refining of copper, where the mass fraction of Se can reach 5-25% [4]. Consequently, many efforts have been developed for the recovery of copper (Cu) and Se from the slimes. Decopperization of anode slimes is the first stage of selenium recovery [5-7]. Generally, the slimes are dissolved by high temperature roasting-acidic leaching process, and then most of the copper can be recovered by crystallization or solvent
extraction. Subsequently, the selenium compounds can be reduced and recovered by SO2 or Na2SO3 (as shown in equation 1). However, this reduction is only efficient when the initial concentration of selenium is greater than 1 g/L [8]. Besides, the remaining Cu 2+ can be separated as copper powder by partial reduction and disproportionation (as shown in equation 2 and 3), while the recovery ratio of copper is limited (~30%) [9, 10]. SeO32- + H2O + 2SO2 → Se + 2H+ + 2SO42-
(1)
2Cu2+ + 2H2O + SO2 → 2Cu+ + 4H+ + SO42-
(2)
2Cu + → Cu2+ + Cu
(3)
Alternatively, electrodeposition is an efficient, cost-effective and readily adoptable method to recover metal ions in the corresponding metallic state [11-13]. By employing the clean reagent of “electron”, the process can be carried out with high selectivity and no extra chemicals are required. Considerable studies of electrochemical copper recovery have been reported [14-16]. Nevertheless, the Se electrodeposition mainly focuses on the semiconductor layer fabrications in electronic and optical devices, and the cathodic electrodes are usually expensive substrates of Au, Mo and Pt [17, 18]. More importantly, the concentration of Se in the leaching solution of anode slime is usually 0.2-4.0 g/L, resulting in the potential diffusion limitation during the electrochemical process [19]. It has been demonstrated that the mass transport of electrodeposition process can be significantly enhanced by the employment of electrode movement, large surface area electrode and high flow rate of electrolyte [20, 21]. In this regard, the aim of this
study is to develop a cost-effective electrochemical recovery process of Se and Cu from dilute solution. The co-deposition behavior of Se and Cu was systematically investigated with respected to the mass transport condition. This approach may serve as a promising alternative to overcome the drawbacks of existing metal recovery and water purification.
2. Materials and methods 2.1 Materials The chemical reagents used in the preparation of synthetic solutions used in this study were all of analytical grade purity and used as received from Sigma Aldrich, including sulfuric acid (95.0-98.0 wt.%), copper sulfate (99.99 wt.%) and sodium selenite (99.0 wt.%). A synthetic solution was prepared by dissolving the corresponding sulfuric acid and bismuth salt into ultrapure water (18 MΩ·cm) obtained from a water purification system.
2.2 Electrochemical studies To understand the basic electrochemistry of Cu and Se ions, linear sweep voltammetry (LSV) was performed at ambient temperature using a CHI760E workstation (CH Instruments, Shanghai). A typical three electrodes cell (500 mL) with a 316L stainless steel working electrode (active area of 2.0 cm2), an IrO2-Ta2O5 coated titanium counter electrode and a double junction Ag/AgCl (0.22 V vs. SHE) reference electrode was used. Prior to each experiment, the stainless steel plate was
successively polished using 180, 400 and 600 grit silicon carbide sandpaper to obtain a smooth electrode surface for deposition. Then, the electrode was washed and sonicated in purified water. Subsequently, the electrochemical measurements were performed in N2-purged solutions by potential cycling from 0.3 V to -0.7 V at various scan rates. All potentials are reported versus saturated calomel electrode (SCE) Chronopotentiometry (CP) was employed to investigate the electrodeposition behavior with same electrochemical cell and electrodes as described in the CV procedure. The current density was selected at 175 and 350 A/m2 with different stirring rate. Furthermore, a tubular cell (emew® system) with an IrO2-Ta2O5 coated titanium anode in the center and an annular stainless steel foil cathode outside of the tube was used to further improve the mass transport condition. The cell has a cathode area of 150 cm2 and cathodic current density was 350 A/m2. 2 liters of solution were used in each test, and the flow rate used was 3 L/min or 5 L/min.
2.3 Physical characterization The surface morphology and approximate composition of prepared products were characterized using a field-emission scanning electron microscopy (FE-SEM, JSM-7610F) with energy dispersive X-ray spectroscopy (EDS), while its crystalline structure was measured using a X-ray diffraction (XRD, Smartlab, Japan) with Cu Kα radiation. The inductivity coupled plasma-optical emission spectrometer (ICP-OES, Optima 5300DV, PerkinElimer, USA) was used to analyze the concentration of dissolved copper and selenium. The mean particle sizes and size distribution were
determined using a Microtrac S3500 particle size analyzer.
3. Results and discussion 3.1 Electrochemical reduction of Cu(II) and Se(IV) Linear sweep voltammetry (LSV) measurements were performed using the synthetic leaching solution of anode slime to determine the electrochemical reduction Cu(II) and Se(IV) at the stainless steel electrode. As shown in Fig. 1, a small reduction peak emerged at -0.43 V with a peak current density of 1.31 mA cm-2 in the 25 g/L H2SO4 solution, which is attributed to the surface reaction of stainless steel electrode [22]. The Cu2+ reduction peak appeared at -0.46 V with 15.70 mA cm-2 peak current density in the presence of 2.0 g/L Cu2+, in consistent with previous study [23]. Interestingly, there are two cathodic peaks at -0.14 V and -0.40 V in the presence of 0.3 g/L Se4+, in good agreement with the corresponding reduction behavior at SnO2 coated glass electrodes [24]. The peaks are corresponding to four-electron and six-electron reductions as shown in equation 4 and 5, respectively. It should be noted that the H2Se then proceeds conproportionation reaction to generate Se. Obviously, the selenium ions can undergo electrochemical reduction to Se at low-cost stainless steel electrodes, and the Se and Cu ions reduction potentials are very close. Consequently, a well-defined reduction peak at -0.45 V with a small wide reduction peak at around -0.13V are observed in the presence of 2.0 g/L Cu 2+and 0.3 g/L Se4+, which is due to the combination of Cu and Se reduction. SeO32- + 6H+ + 4e- → Se + 3H2O
(4)
SeO32- + 8H+ + 6e- → H2Se + 3H2O SeO32- + 3H2Se → 4Se + 3H2O
(5) (6)
3.2 Mass transport effect In order to further characterize the electrochemical reduction behavior, potential scans were performed at different rates ranging from 50 to 200 mV/s. As can be seen in Figure 2a, a negative shift of the cathodic peak potential with increasing scan rate is observed, which agrees with the theory of a quasi-reversible reaction [25, 26]. Besides, there are good linear relationships between the reduction peak currents and the square root of scan rate (v1/2) as seen in Figure 2b, indicating the reduction reaction of this system is diffusion-controlled [27]. In general, the peak current of a mass transport controlled quasi-reversible electrodeposition reaction at 298 K can be calculated by the following equation [28]:
I p = 367n 3 / 2 AD1/ 2Cv1/ 2
(7)
where Ip (A) is the peak current, n is the number of electrons, A (cm2) is the surface area of the working electrode, D (cm2·s-1) is the diffusion coefficient, C (mol·L-1) is the bulk concentration, and v (V·s-1) is the scan rate. Therefore, the diffusion coefficients of Cu2+ and Se4+ were estimated to be 2.37×10-5 cm2·s-1 and 2.93×10-6 cm2·s-1. Given the low concentration of Se4+ in solution and its lower diffusion coefficient, it is expected to overcome the diffusion issues for better recovery performance.
3.3 Electrochemical co-deposition To determine the electrochemical co-deposition behavior of Cu 2+ and Se4+, chronopotentiometry with different applied current and stirring rate was performed. As presented in Fig. 3, the obtained potential negatively shift from -0.35 V to -0.60 V with the increasing cathodic current, offering more driving force for the electrochemical reduction and deposition. Furthermore, the stirring rate (e.g. mass transport) plays an important role in the electrochemical behavior. As the stirring rate decreases, the potential negatively shift to the hydrogen evolution region with serious oscillation issues, possibly leading to the formation of unfavorable Cu2O products and the decrease of current efficiency [29]. Electrolytic metal recovery using the three-electrode cell was examined for 60 minutes, and a deposition foil was removed and collected. After the washing and drying, the deposited products were characterized by SEM, EDS and XRD. As shown in Fig. 4, compact electrodeposited film with relatively uniform grain size was obtained. And the EDS analyses indicate the film consisted of Cu and Se with small oxides present (see Fig. 5a), while XRD confirmed the presence of Cu, Cu2Se and Cu2O as shown in Fig. 5b. Consequent, the composition of the film was estimated by combining the XRD and EDS results in Table 1. The formation of Cu 2O is demonstrated to occur by the partial reduction of Cu2+ to Cu + followed by the precipitation of Cu + as Cu2O as shown in equation 8. It is common to see copper “burn” (e.g. Cu 2O formation) during high current density electrodeposition when the agitation or mass transport is not great enough [30]. Besides, the Cu2Se products
originate from the co-deposition of Se and Cu from the acidic sulfate solution as illustrated in equation 9 [31], which is quite different from the selenium-sulfate system mentioned above. As a result, 9.2% of the copper and 19.3% of the selenium was recovered from the solution by the 60 minute treatment at 350 A·m-2 and 1000 rpm, while the current efficiency of 27.1% is limited. It should be noted that the current efficiency was calculated with the equation 10 by considering the corresponding electron transfer numbers of different electrodeposited products: 2Cu2+ + H2O + 2e- → Cu2O + 2H+
(8)
2Cu2+ + SeO32- + 6H+ + 8e- → Cu 2Se + 3H2O
(9)
= ܧܥ
ଽସ଼ହ× ୧×୲
ಮ
×ౣ సభ
(10)
where the CE is current efficiency, 96485 C·mol-1 is the Faraday constant of electrolysis, n is the numbers of electron transfer, m and M are the corresponding weight and molar mass of electrodeposited products, respectively, i and t are the current and electrolysis time of the electrodeposition, respectively. In consistent with the above results of chronopotentiometric curves, the high current density and mass transport can significantly facilitate high Cu/Se recovery ratio, better total metal recovery and less Cu2O formation. However, the co-deposition performance of Cu and Se was not complete and particularly energy efficient in these conditions.
3.4 Efficient electrochemical recovery In order to improve the electrochemical recovery performance, a cylinder turbulent cell with larger cathode surface area was employed with a current of 350
A/m2 and different solution flow rate. It should be noted that 2 liters solution was treated in this section to better evaluate the practical implications. As shown in Table 1, 68.7% copper and 73.2% selenium was efficiently removed from the solution with a solution flow rate of 3 L/min. The current efficiency was determined to be 60.3%, which is much higher than the corresponding data of conventional cell. Clearly, the co-deposition behavior is substantially enhanced by changing the mass transport condition. Besides, the performance was further enhanced by increasing the flow rate to 5 L/min. 93.2% copper and 97.6% selenium was successfully extracted with a current efficiency of 81.3%, offering satisfied recovery for potential industrial applications. As compared to the thin film product in the conventional cell, electrodeposited nanosized powder was obtained in the cylinder turbulent cell due to the excellent mass transport (Fig. 6). And the Cu 2O formation in the products was also substantially reduced to 3% (Table 1), suggesting the electrochemical reduction was efficiently performed and the partial reduction to Cu 2O was well eliminated. As illustrated in Fig. 7, the mean particle size of 3 L/min and 5 L/min were 84 µm and 76µm, respectively. It should be noted that the as-prepared metal powder could be readily flushed and removed from the cell with water, which overcomes the drawback of product harvesting from a conventional cell. Consequently, the schematic diagram of mass transport-enhanced electrodeposition process is illustrated in Fig. 8, offering a more energy efficient process with high values metal products.
4. Conclusions An efficient mass transport-enhanced electrochemical recovery process of Se and Cu from sulfuric acid solution was first developed using low-cost stainless steel cathodes. It has been demonstrated that Se and Cu ions can be simultaneously electrodeposited, and the co-deposition is mass transport controlled quasi-reversible reaction. The diffusion coefficients of Cu 2+ and Se4+ were also estimated to be 2.37×10 -5 cm2·s-1 and 2.93×10-6 cm2·s-1, suggesting better diffusion properties are needed for the Se recovery. Compact electrodeposited film was obtained using the three-electrode cell, but the co-deposition performance of Cu and Se was not complete and particularly energy efficient. The high current density and mass transport can significantly facilitate better metal recovery and less Cu 2O formation. Consequently, a cylinder turbulent cell with larger surface area cathode was employed, and nanosized powder was obtained due to the excellent mass transport. 93.2% copper and 97.6% selenium was successfully extracted with a current efficiency of 81.3%. The Cu2O formation in the products was also substantially reduced to 3%, and the as-prepared metal powder could be readily flushed and collected from the cell with water. This mass transport-enhanced approach may serve as a promising alternative to overcome the drawbacks of existing metal recovery and water purification.
Acknowledgements W.J. acknowledges the funding support from National Natural Science Foundation of China under Grant No. 51604253 and “CAS Pioneer Hundred Talents
Program”. We acknowledged the support from the National Basic Research Program of China (973 Program) under Grant No. 2013CB632601 and 2013CB632605, and the National Natural Science Foundation of China under Grant No. 51274179.
References [1] R. M. Hodlur, M. K. Robinal, A new selenium precursor for the aqueous synthesis of luminescent CdSe quantum dots, Chem. Eng. J. 244 (2014) 82-88. [2] C. Li, F. Wang, J. C. Yu, Semiconductor/biomolecular composites for solar energy applications, Energy Environ. Sci. 4 (2011) 100-113. [3] W. F. Liu, T. Z. Yang, D. C. Zhang, L. Chen, Y. N. Liu, Pretreatment of copper anode slime with alkaline pressure oxidative leaching, Int. J. Miner. Process. 128 (2014) 48-54. [4] D. Li, X. Guo, Z. Xu, Q. Tian, Q. Feng, Leaching behavior of metals from copper anode slime using an alkali fusion-leaching process, Hydrometallurgy 157 (2015) 9-12. [5] Y. Kilic, G. Kartal, S. Timur, An investigation of copper and selenium recovery from copper anode slimes, Int. J. Miner. Process. 124 (2013) 75-82. [6] J. E. Hoffmann, Recovering selenium and tellurium from copper refinery slimes, JOM 41 (1989) 33-38. [7] C. Hu, Q. Chen, G. Chen, H. Liu, J. Qu, Removal of Se(IV) and Se(VI) from drinking water by coagulation, Sep. Purif. Technol. 142 (2015) 65-70. [8] A. Baral, C.K. Sarangi, B. C. Tripathy, I. N. Bhattacharya, T. Subbaiah, Copper
electrodeposition from sulfate solutions-Effects of selenium. Hydrometallurgy 146 (2014) 8-14. [9] T. Shibasaki, K. Kabe, H. Takeuchi, Recovery of tellurium from decopperizing leach solution of copper refinery slimes by a fixed bed reactor, Hydrometallurgy 29 (1992) 399-412. [10] S. Klas, D. W. Kirk, Understanding the positive effects of low pH and limited aeration on selenate removal from water by elemental iron. Sep. Purif. Technol. 116 (2013) 222-229. [11] J. P. Chen, L. L. Lim, Recovery of precious metals by an electrochemical deposition method. Chemosphere 60 (2005) 1384-1392. [12] Y. Huang, G. Han, J. Liu, W. Chai, W. Wang, S. Yang, S. Su, A stepwise recovery of metals from hybrid cathodes of spent Li-ion batteries with leaching-flotation-precipitation process, J. Power Sources 325 (2016) 555-564. [13] W. Jin, H. Du, S. Zheng, Y. Zhang, Electrochemical processes for the environmental remediation of toxic Cr(VI): A review. Electrochim Acta 191 (2016) 1044-1055. [14] A. Mecucci, K. Scott. Leaching and electrochemical recovery of copper, lead and tin from scrap printed circuit boards, J. Chem. Technol. Biotechnol. 77 (2002) 449-457. [15] D. N. Bennion, J. Newman, Electrochemical removal of copper ions from very dilute solutions, J. Appl. Electrochem. 2 (1972) 113-122.
[16] Z. Sun, H. Cao, P. Venkatesan, W. Jin, Y. Xiao. J. Sietsma, Y. Yang. Electrochemistry during efficient copper recovery from complex electronic waste using
ammonia
based
solutions,
Front.
Chem.
Sci.
Eng.
2016,
DOI:
10.1007/s11705-016-1587-x. [17] M. F. Cabral, H. B. Suffredini, V. A. Pedrosa, S. T. Tanimoto, S. A. S. Machado. Electrodeposition and characterization of thin selenium films modified with lead ad-atoms, Appl. Surf. Sci. 254 (2008) 5612-5617. [18] S. Saha, N. Tachikawa, K. Yoshii, Y. Katayama, Electrodeposition of selenium in a hydrophobic room-temperature ionic liquid, J. Electrochem. Soc. 163 (2016) D259-D64. [19] L. Thouin, S. Rouquette-Sanchez, J. Vedel, Electrodeposition of copper-selenium binaries in a citric acid medium, Electrochim. Acta 38 (1993) 2387-2394. [20] D. Pletcher, F. C. Walsh, Industrial electrochemistry, Chapman and Hall, London. 1990. [21] F. C. Walsh, Electrochemical technology for environmental treatment and clean energy conversion, Pure Appl. Chem. 73 (2001) 1819-1837. [22] Y. Xue, W. Jin, H. Du, S. Wang, S. Zheng, Y. Zhang, Tuning α-Fe2O3 nanotube arrays for the oxygen reduction reaction in alkaline media, RSC Adv. 6 (2016) 41878-41884. [23] D. Grujicic, B. Pesic, Electrodeposition of copper: the nucleation mechanisms, Electrochim. Acta 47 (2002) 2901-2912. [24] Y. Lai, F. Liu, J. Li, Z. Zhang, Y. Liu, Nucleation and growth of selenium
electrodeposition onto tin oxide electrode, J. Electroanal. Chem. 639 (2010) 187-192. [25] W. Jin, H. Du, S. Zheng, H. Xu, Y. Zhang, Comparison of the oxygen reduction reaction between NaOH and KOH solutions on Pt electrode: the electrolyte-dependent effect, J. Phys. Chem. B 114 (2010) 6542-6548. [26] W. Jin, M. S. Moats, S. Zheng, H.Du, Y. Zhang, J. D. Miller, Modulated Cr(III) oxidation in
KOH
solutions at
a
gold
electrode: Competition
between
disproportionation and stepwise electron transfer, Electrochim. Acta 56 (2011) 8311-838. [27] W. Jin, M. S. Moats, S. Zheng, H. Du, Y. Zhang, J. D. Miller, Indirect Electrochemical Cr(III) Oxidation in KOH Solutions at an Au Electrode: The Role of Oxygen Reduction Reaction, J. Phys. Chem. B 116 (2012) 7531-7537. [28] T. Berzins, P. Delahay, Oscillographic polarographic waves for the reversible deposition of metals on solid electrodes, J. Am. Chem. Soc. 75 (1953) 555-559. [29] P. E. de Jongh, D. Vanmaekelbergh, J. J. Kelly, Cu 2O: Electrodeposition and characterization, Chem. Mater., 1999, 11, 3512-3517. [30] Y. Yang, Y. Li, M. Pritzker, Control of Cu2O film morphology using potentiostatic pulsed electrodeposition, Electrochim. Acta 213 (2016) 225-235. [31] L. Zhang, W. He, X. Chen, Y. Du, X. Zhang, Y. Shen, F. Yang, Nanocrystallized Cu2Se grown on electroless Cu coated p-type Si using electrochemical atomic layer deposition, Surf. Sci. 2015, 631, 173-177.
Figures and Captions: Fig. 1 CV curves of stainless steel electrodes in the synthetic 25 g/L H2SO4 leaching solution, scan rate: 100 mV·s-1 Fig. 2 Electrochemical reduction behavior as a function of scan rate on stainless steel: (a) cyclic voltammograms of Cu2+ reduction with increasing scan rate (50-200 mV/s ); (b) variation of the reduction peak currents as a function of the square root of the scan rate in 2.0 g/L Cu 2+, 0.3 g/L Se4+ ( peak at -0.14 V), Cu2+ and Se4+ containing 25 g/L H2SO4 solutions Fig. 3 Chronopotentiometric curves using a stainless steel electrode with different current densities and stirring rate Fig. 4 SEM images of electrodeposited film from copper and selenium based solutions at 1000 rpm and 350 A·m-2. Fig. 5 (a) EDS and (b) XRD spectra with crystallographic plane indices of electrodeposited film from copper and selenium based solutions at 1000 rpm and 350 A·m-2. Fig. 6 (Left) Photo of stainless steel cathode after deposition and (right) SEM image of electrodeposited powder from copper and selenium based solutions at 5 L/min and 350 A·m-2. Fig. 7 Particle size distribution of electrodeposited powder from cylinder electrochemical cell. Fig. 8 Schematic diagrams of mass transport-enhanced electrodeposition for the recovery of Cu and Se
Table 1 The comparison of electrochemical recovery performance with different parameters
-2
Current density / mA cm
0 -4 -8 blank 2+ 2.0 g/L Cu 4+ 0.3 g/L Se 2+ 4+ Cu + Se
-12 -16 -20 -0.8
-0.6
-0.4
-0.2
0.0
Potential / V vs. SCE Fig. 1
0.2
0.4
0
Current density / mA cm
-2
a
-4 -8 50 mV/s 75 mV/s 100mV/s 125mV/s 150mV/s 200mV/s
-12 -16 -20 -24 -0.8
-0.6
-0.4
-0.2
0.0
Potential / V vs. SCE
Current density/ mA cm
-2
2+
24
Cu 4+ Se 2+ 4+ Cu +Se
b
20 16 12 8 4 0 6
8
10 1/2
12 1/2
-1/2
V / mV s Fig. 2
14
0.2
Potential / V vs. SCE
-0.2 -0.4 -0.6 -0.8 -2
-1.0
175 A/m 1000 rpm -2 350 A/m 200 rpm -2 350 A/m 600 rpm -2 350 A/m 1000 rpm
-1.2 0
200
400
600
Time / s Fig. 3
800
1000
1200
Fig. 4
Fig. 5
Intensity/a.u.
Intensity / a.u.
Cu
Cu 10
Se
A Cu B Cu2O
12
80
B(311) A(220)
C Cu2Se
60
B(220)
8
A(200) B(211)
6
A(111)
a
B(111) B(200)
4
C(090)
Energy / keV
40
2θ / degree
C(250) C(410) B(110)
Cu
O
20
2
Se
b
C(030)
Fig. 6
6
3 L/min 5 L/min
Volume / %
5 4 3 2 1 0 0
300
600
900
Particle size / µm Fig. 7
1200
1500
Fig. 8
Table 1 Current -2
(A· m ) # 175
Mass transport
Time (min)
Product weight (g)
Current efficiency
Cu recovery
Se recovery
Product composition
1000 rpm
60
0.08
30.4%
4.3%
11.9%
33% Cu2O, 23% Cu, 38% Cu2 Se 10% Cu2O, 51% Cu, 39% Cu2 Se 16% Cu2O, 47% Cu, 37% Cu2 Se 20% Cu2O, 42% Cu, 38% Cu2 Se 7% Cu2O, 73% Cu, 20% Cu2 Se 3% Cu2O, 81% Cu, 15% Cu2 Se
#
350
1000 rpm
60
0.14
27.1%
9.2%
19.3%
#
350
600 rpm
60
0.12
19.2%
7.3%
16.2%
#
350
200 rpm
60
0.10
15.2%
5.3%
12.1%
*
350
3 L/min
60
3.23
60.3%
68.7%
73.2%
*
5 L/min
60
4.11
81.3%
93.2%
97.6%
350
# *
Three-electrode cell Cylinder tubular cell
Highlights: • Novel electrochemical recovery process of Se and Cu was first reported. • Se and Cu ions can be simultaneously electrodeposited at low-cost stainless steel from dilute solutions. • An efficient recovery of Se and Cu was obtained via the mass transport-enhanced electrodeposition.