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Enhanced anodic dissolution of cupronickel alloy scraps by electro-generated reactive oxygen species in acid media
Journal of Alloys and Compounds 806 (2019) 106e112
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Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Enhanced anodic dissolution of cupronickel alloy scraps by electrogenerated reactive oxygen species in acid media Yunting Wang a, Yudong Xue b, c, **, Chunhui Zhang a, * a
School of Chemical and Environmental Engineering, China University of Mining and Technology (Beijing), Beijing, 100083, China National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, CAS Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, China c University of Chinese Academy of Sciences, Beijing, 100049, China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 21 May 2019 Received in revised form 21 July 2019 Accepted 22 July 2019 Available online 23 July 2019
Recycling of the cupronickel alloy scraps not only solves environmental related issues but also realizes the extraction of valuable metals and saves consumption of primary ore resources. Oxidative dissolution is a critical step for the recycling of valuable metal from the alloy scraps. In order to improve the dissolution kinetics and efficiency, a novel integrated electrochemical dissolution strategy for the sustainable recycling of the cupronickel alloy scraps was first developed, where the in-situ electro-generated reactive oxygen species (ROS) were employed as the indirect oxidative mediator. Much higher dissolved concentration of Ni, Zn, and Cu was reached by the present integrated strategy than that of the direct anodic dissolution process, which is attributed to the in-situ produced oxidative H2O2 and $OH via oxygen reduction reaction and electro-Fenton-like reaction, respectively. Moreover, the large quantity of ROS can be electro-generated, thus achieving high dissolved concentration, under the optimum condition with the preset potential of 0.3 V (vs. Ag/AgCl) or current density of 2.54 mA/cm2, respectively. This novel synergistic strategy may serve as a promising and cost-effective technique for the alloy scraps recycle and valuable metal extraction. © 2019 Elsevier B.V. All rights reserved.
Keywords: Anodic dissolution Electrochemical oxidation Reactive oxygen species Electro-Fenton-like Alloy scraps
1. Introduction Cupronickel alloy is widely used in the marine industry, power industry, chemical engineering, precise instrument, and medical apparatus, due to its high corrosion resistance and superior electrical and thermal conductivity [1e4]. A large amount of cupronickel alloy scraps is generated from the production process and retired alloys. Cupronickel alloy scraps contain valuable metals in which the average content of Ni, Zn, and Cu is about 20%, 30%, and 50%, respectively [5]. Recycling of the cupronickel alloy scraps not only solves environmental related issues but also realizes the extraction of valuable metals and saves consumption of primary ore resources. Therefore, the recovery of valuable metals from
* Corresponding author. ** Corresponding author. National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, CAS Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, China. E-mail addresses: [email protected] (Y. Xue), [email protected] (C. Zhang). https://doi.org/10.1016/j.jallcom.2019.07.276 0925-8388/© 2019 Elsevier B.V. All rights reserved.
cupronickel alloy scraps has received much attention. Oxidative dissolution is an important step for the recycling of valuable metal from large-scale industrial wastes, such as alloy scraps, electronic scraps, metallurgical slags, and spent catalysts [6]. Conventionally, the dissolution process is performed using concentrated inorganic acids, such as HCl, H2SO4, and HNO3 [7]. However, the dissolution rate is limited by the poor oxidative capacity and sluggish kinetics, particularly in H2SO4 solution [8]. Therefore, considerable additional oxidants and complexing agents are required, significantly frustrating the cost-effectiveness and environmental compatibility [9]. Anodic dissolution process has been developed for the metal recovery due to the advantages of simple, inexpensive and energy efficiency [10]. By employing the clean oxidant “electrons” [11], Ni2þ and Zn2þ can be obtained from the anodic dissolution of Ni and Zn, respectively [12], while the anodic dissolution of Cu occurs in a step-wise pathway as shown in Eqs. (1) and (2) [13]. Industrially, high concentrated acid and elevated temperature are required to secure the dissolution rate and eliminate the anodic passivation [14]. Kim developed a membrane-assisted process in 1.0 M HCl solution at room temperature, where the electro-
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generation of chlorine gas and leaching of copper simultaneously take place in the anode compartment [15]. The leaching efficiency was enhanced by dissolving CuCl precipitate on the surface of copper anode. Nevertheless, the further dissolution improvement and the cost-effectiveness are limited by the solubility of gaseous Cl2 and the employment of membrane, respectively. Besides, when HNO3 solution used as an electrolyte, it also produces nitric oxide gas. Both HCl and HNO3 electrolytes have a big negative impact, causing serious environmental pollution and poor working conditions. Therefore, in view of engineering application, H2SO4 is a promising media for the dissolution process. Cu 4 Cuþ þ e
(1)
Cuþ 4 Cu2þ þ e (Rate-determining step)
(2)
Recently, electrochemical advanced oxidation processes (EAOPs) have been widely performed as an alternative method for environmental remediation, especially for waste treatment [16e18]. The H2O2 can be in-situ electro-generated by the twoelectron-pathway oxygen reduction reaction (ORR) [19] as shown in Eq. (3) on the cathode, followed by the transition metal catalyzed electro-Fenton or electro-Fenton-like to generate highly oxidative species of hydroxyl radicals ($OH) [16,20]. It has been demonstrated that the Cuþ ions are able to react with H2O2 to produce $OH (as shown in Eqs. (4) and (5)) [21,22], further enhancing the oxidative capability of the dissolution process. O2 þ 2Hþ þ 2e / H2O2
(3)
Cuþ þ H2O2 / Cu2þ þ OH þ $OH
(4)
Cuþ þ $OH / Cu2þ þ OH
(5)
Obviously, it is highly desirable to investigate the synergistic effect between the anodic dissolution and the indirect oxidation via the electro-generated reactive oxygen species (ROS) mediator from the cathode. In this regard, the aim of this study is to develop an integrated direct and indirect electrochemical oxidation approach for enhancing the anodic dissolution of cupronickel alloy scraps under mild conditions (dilute H2SO4 solution and room temperature), which is completed by simply introducing the oxygen atmosphere into the single cell electrolyzer. 2. Experimental 2.1. Materials H2SO4 (98%), C4K2O9Ti$2H2O (98.5%), 5,5-dimethyl-1-pyrroline (DMPO), acetone (99.5%), and tert-butanol (t-BA, 99%) were purchased from Alfa Aesar. The electrolyte was provided by dissolving the corresponding sulfuric acid into ultrapure water (18 MU cm) obtained from a water purification system. High purity N2 and O2 (99.99%) were supplied by Beijing Qianxi Gas Co., Ltd., China. Cupronickel alloy scrap electrode (2 cm 6 cm) was polished with alumina powder, then rinsed with alcohol and deionized water to remove the surface impurities, and dried at 80 C for 5 min. The active carbon fiber electrode (5.0 cm 2.0 cm 0.5 cm) was cleaned in an ultrasonic bath with acetone for 30 min and immersed for 24 h, then rinsed with deionized water, dried at 80 C for 24 h and heated at 150 C for 2 h. 2.2. Experimental procedures The electrochemical experiments were conducted in a standard
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three-electrode system and controlled by a CHI760E workstation (CH Instruments Inc., Shanghai). Cupronickel alloy scrap electrode and active carbon fiber electrode were used as the working electrode and counter electrode, respectively. The reference electrode is Ag/AgCl electrode (the supporting solution is the saturated KCl solution). The linear sweep voltammetry (LSV) experiment was conducted in N2 and O2-saturated 100 mL 0.01 mol/L H2SO4 electrolyte at 25 C by potential cycling in the scan rate of 100 mV s1. The chronoamperometry was performed with vigorous electrolyte stirring and the applied potential was set at 0.3 V (vs. Ag/AgCl) to offer enough reaction driving force. Chronoamperometry experiments were conducted at 0.1, 0.2, and 0.3 V. Chronopotentiometry experiments were conducted at 0.83, 1.67, and 2.54 mA/cm2. The composition of the cupronickel alloy scrap electrode and the dissolution concentration of different elements were calculated by measuring the dissolved metal ions using ICP-OES (Optima 5300DV, PerkinElmer, USA). Each experiment was carried out at least in triplicate, and error bars in figures represent one standard deviation [23]. 2.3. Analysis The H2O2 concentration generated in the electrochemical system was determined by a UVevisible spectrophotometer (Labtech model 9100b), using potassium titanium (IV) oxalate as a colored indicator. The hydroxyl radical generated in the process was detected by electron spin resonance (ESR) with 5,5-dimethyl-1pyrroline (DMPO) by a JEOL spectrometer (JES-FA200) at room temperature. The surface morphology of the active carbon fiber electrode and cupronickel alloy scrap electrode were measured by FE-SEM (JSM-7610F). The unambiguous topographic information of the metallic electrode surface was provided by atomic force microscope (AFM, FastScan Bio, Bruker). 3. Results and discussion In order to analyze the elemental composition in the cupronickel alloy scraps, ICP is used in this study. As shown in Table 1, the results indicated that Cu, Ni, and Zn are the three main elements in the alloys. The compositions are consisting of 54.45% Cu, 17.6% Ni, 27.6% Zn, and 0.35% impurities. Therefore, recovery of valuable elements, especially Ni, Zn, and Cu, in the cupronickel alloy scraps is the main goal for the oxidative dissolution process. To construct a high-efficient electrochemical dissolution system, ROS generated on the cathode was coupled with the anodic dissolution process. Active carbon fiber is applied as the cathode, due to its intrinsic ROS generation properties, low cost, desirable long-term stability, and superior electrochemical properties [24]. The microstructure of active carbon fiber electrodes is illustrated by the FE-SEM, as shown in Fig. 1a, in which the diameter of carbon microfilaments was observed to be around 20 mm. Moreover, it can be observed that active carbon fiber presents a three-dimensional structure to provide a large surface area, thus introducing a large amount of oxygen reduction catalytic active sites on the active carbon fiber surface. As shown in Fig. 1b, a broad reduction wave was commenced at 0.14 V (vs. RHE) in the N2-saturated electrolyte, which is attributed to the charging electrochemical double-layer of carbon materials
Table 1 Element composition of cupronickel alloy scraps tested by ICP-OES (%). Cu
Ni
Zn
Fe
Ag
Ca
Na
Sn
Co
54.45
17.60
27.60
0.209
0.002
0.048
0.018
0.033
0.005
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Fig. 1. (a) FE-SEM image of the active carbon fiber electrode. (b) CV curves of active carbon fiber electrode in N2-purged and O2-saturated 0.01 M H2SO4 solutions, scan rate: 5 mV s1 (inset: CV curves of active carbon fiber electrode, scan rate: 5 mV s1).
[25]. In contrary, much higher current density was obtained in the O2-saturated electrolyte, attributing to the oxygen reduction peak. The onset potential of ORR is 0.24 V (vs. RHE), and the iORR at 0.31 V (vs. RHE) was 3.27 mA/cm2 approximately, which was calculated by taking the difference of current density in O2 and N2 saturated electrolytes. Besides, as seen the CV curves of active carbon fiber electrode in the inset of Fig. 1b, a well-defined oxygen reduction peak occurs in the O2-saturated electrolyte, while no significant reduction peak was observed at the same applied potential in the N2-saturated electrolyte, indicating that the oxygen reduction reaction happened on the active carbon fiber surface in the O2-saturated electrolyte [26]. Oxygen reduction dominantly proceeds two-electron pathway on the active carbon fiber to generate H2O2 [27]. To determine the in-situ generated H2O2 concentration, the chronoamperometry technique was employed at 0.3 V (vs. Ag/AgCl) in O2-saturated electrolyte. The production of H2O2 was quantified by UVevis using potassium titanium (IV) oxalate as a colored indicator. As shown in Fig. 2a, the absorbance value was increased gradually. Furthermore, there is a linear relationship between H2O2 concentration and reaction time, as shown in Fig. 2b, and the H2O2 yield can reach above 1.7 mM after 90 min electrochemical reaction. After introducing the ROS into the anodic dissolution system, we discussed the dissolution behavior of Ni, Zn, and Cu from the cupronickel alloy scrap electrode. The electrochemical dissolution behavior was investigated by using different cathodes under
Fig. 2. (a) UVevis spectra of electro-generated H2O2 at different times in 0.01 M H2SO4 solution, (b) Corresponding linear fit plots of H2O2 concentration versus time.
different gaseous environments. As presented in Fig. 3, the dissolved concentrations of Ni, Zn, and Cu in N2-saturated electrolyte are 12.95, 18.63, and 31.12 mg/L, respectively. Compared with the results of the N2-saturation condition, the dissolved concentrations of Ni, Zn, and Cu in electrolyte without gas saturation was almost maintained with a slight increase (0.35, 0.37, 0.86 mg/L). When the
Fig. 3. Comparison of the electrochemical dissolution behavior of Ni, Zn, and Cu in N2 and O2 saturated 0.01 M H2SO4 solutions. ACF: active carbon fiber; SS: stainless steel.
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oxygen atmosphere introduced to the system and the active carbon fiber applied, the dissolved concentrations of Ni, Zn, and Cu are 22.76, 35.29, and 40.46 mg/L, respectively. There are nearly 75.8%, 89.4%, and 30.0% enhancement of the Ni, Zn, and Cu dissolution, respectively, in O2-saturated solution than the corresponding one in N2-purged solution, which is possibly resulting from the contribution of the in-situ electro-generated ROS on the cathode. In this study, active carbon fiber and stainless steel (SS) cathode were used for comparing the effect of in-situ ROS generation properties. It should be noted that the dissolved concentrations of Ni, Zn, and Cu using SS cathode are lower than that of active carbon fiber due to the limited oxygen reduction performance on the SS electrode. The above results indicated that high ROS concentration is desired for improving the valuable metal dissolution. Furthermore, it is significant to control the potential and current density in the electrochemical experiments. In order to investigate the effect of potential and current density, further experiments were conducted for the Ni, Zn, and Cu dissolution in O2-saturated solution. Fig. 4 shows the effect of different potentials on the dissolved copper with time. The dissolved Ni, Zn, and Cu are monotonically linear with the reaction time. An increasing trend can be observed that the dissolved concentration of valuable metal would increase with high potential. The dissolution of Ni, Zn, and Cu (120 min) increased to 23.76, 35.30, and 41.46 mg/L at 0.3 V, which is much higher than that of 0.1 and 0.2 V. It is suggested that the amount of ROS is high at 0.3 V for the dissolution process. Fig. 5 presents the effect of applied current density on the metal dissolution with electrolysis time. As can be seen, the dissolved Ni, Zn, and Cu increased with the enhancement of the current density. When the applied current density set at 0.83 mA/cm2, the dissolved concentrations of Ni, Zn, and Cu were 10.64, 15.46, and 28.12 mg/L, respectively. While the applied current density increased to 2.54 mA/cm2, the dissolved concentrations of Ni, Zn, and Cu were increased to 27.76, 38.30, and 52.28 g/L, respectively, which also experienced an obviously increase due to the presence of oxygen to produce more ROS for the dissolution process. The hydrogen peroxide was produced on the cathode during the ORR. The standard electrode potential (E0) of Cu2þ/Cuþ is 0.15 V/ SHE, thus causing Cu is easier to dissolve than other metals in the cupronickel alloy scraps. Hydroxyl radicals can be continuously insitu electro-generated by the Fenton-like reaction of H2O2 and Cuþ to enhance anodic dissolution. To investigate the mechanism in the present enhanced electrochemical dissolution process, the dissolution experiment was carried out with selective $OH scavenger of t-BA [9]. As presented in Fig. 6a, the dissolved Ni, Zn, and Cu in the N2-purged atmosphere were well maintained at 12.96, 18.65, and 31.11 mg/L, respectively, when t-BA was added, indicating that $OH was not generated in this system. In contrast, the addition of corresponding t-BA in the O2-saturated environment leads to the decline of dissolved Ni, Zn, and Cu from 22.76, 35.30, and 40.46 mg/ L to 14.69, 23.36, and 33.70 mg/L, respectively, suggesting that the $OH is mainly responsible for the accelerated dissolution process. The contribution of anodic effect accounted for 56.9% of Ni, 52.7% of Zn, and 76.9% of Cu. It is calculated that the effect of $OH on anodic dissolution accounts for 35.5%, 33.8%, and 16.7% of the total dissolved amount of Ni, Zn, and Cu, respectively, while the H2O2 contribution to anodic dissolution for Ni, Zn, and Cu is 7.6%, 13.5%, and 6.4%, respectively. Besides, it was calculated that the $OH is dominant, which account for 82.3% of Ni, 71.8% of Zn, and 72.4% of Cu in the indirect electrochemical oxidation (ROS including H2O2 and $OH). By the addition of the quenching agent, the contributions of the reactive species (H2O2 and $OH) for the dissolution process are well distinguished. Therefore, when the ROS introduced to the present electrochemical system, the anodic dissolution rate was greatly increased.
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Fig. 4. Dissolved Ni (a), Zn (b), and Cu (c) with time at the varying potentials in the O2saturated 0.01 M H2SO4 solutions.
Furthermore, $OH generated in this integrated electrochemical process was detected by the electron spin resonance (ESR) spectra in Fig. 6b [28e30]. When DMPO added into the electrochemical cell, evident signals assigned to $OH were found in the oxygensaturated system, while no corresponding signal was observed in the nitrogen-purged system. Based on the above analysis and previous studies, the $OH is generated by the Cuþ-catalyzed activation of H2O2 in this Electro-Fenton-like system as shown in Eq.
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Fig. 6. (a) Electrochemical dissolution of metal ions in the presence and absence of tBA; (b) ESR spectra of the active free radicals detected in the presence and absence of oxygen (DMPO was used as a trapping agent).
Fig. 5. Dissolved Ni (a), Zn (b), and Cu (c) with time at varying current densities in the O2-saturated 0.01 M H2SO4 solutions.
(4) [31e33]. Subsequently, the formed $OH offers further oxidative stress for the dissolution of Ni and Zn, which is responsible for the enhanced anodic dissolution performance. To further illustrate the effect of ROS on the anodic dissolution, the early stages of the cupronickel alloy scrap electrode at different atmospheres were also investigated by FE-SEM and AFM. As illustrated in Fig. 7a and b, most of the alloy surface is smooth. A small amount of grain boundary corrosion appears in the N2
environment. In contrast, significant grain boundary corrosion is visible in the corresponding O2 environment, as shown in Fig. 7c. Due to the presence of ROS in the O2-rich environment, the cupronickel alloy scrap anode surface is strong attacked by the integration of H2O2 and $OH. The copper dissolution is promoted by the synergistic effect between the anodic dissolution and the cathodic indirect oxidation. On the contrary, the copper was dissolved simply by the effect of anodic dissolution with the absence of ROS in the N2 environment. Similarly, the cupronickel alloy exhibits a relatively uniform surface due to the stable anodic dissolution as shown in the threedimensional image of Fig. 8a under N2 atmosphere. Unlikely, a disordered surface is presented in Fig. 8b under O2 atmosphere, where a series of long mountains and valleys are observed due to the strong attack of ROS. This discrete dissolution behavior stems from the complex reaction mechanism and multiple contributions from different oxygen species, which is very similar to the phenomenon of “localized corrosion” owing to the accelerated attach from the corrosive environment [34]. Consequently, the schematic diagram of the enhanced anodic dissolution process of copper by electro-generated ROS in acidic solution is illustrated in Fig. 9, offering a promising and cost-effective technique for valuable metal recovery from the alloy scraps. The hydrogen peroxide was in-situ electro-generated by the 2e reduction of the dissolved molecular oxygen on the surface of active carbon fiber electrode. Then, the
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111
Fig. 8. Three-dimensional AFM images of the cupronickel alloy scrap electrode surface after 20 min electrochemical treatment in the absence (a) and presence (b) of oxygen atmosphere.
Fig. 7. FE-SEM images of the cupronickel alloy scrap electrode surface before (a) and after 20 min electrochemical treatment in the absence (b) and presence (c) of oxygen atmosphere.
H2O2 decomposition can be catalyzed by transition metals with the redox couple Cu2þ/Cuþ to generate highly oxidative species of $OH during the electro-Fenton-like process, which further enhances the anodic dissolution of cupronickel alloy scraps. 4. Conclusions In this study, enhanced anodic dissolution of cupronickel alloy scraps by electro-generated reactive oxygen species (ROS) was developed, where the ROS were readily in-situ electro-generated and employed as the indirect oxidative mediator. By simply introducing the oxygen atmosphere, much higher dissolved concentrations of Ni, Zn, and Cu were obtained than that of direct anodic dissolution in a nitrogen-purged environment. The optimum applied potential and the current density are 0.3 V (vs. Ag/AgCl) and 2.54 mA/cm2, respectively, so in this case, a large amount of ROS is
Fig. 9. Schematic diagrams of enhanced anodic dissolution of cupronickel alloy scraps by electro-generated reactive oxygen species in acidic solution.
generated during the oxidative dissolution process. Based upon the selective scavenger experiment and ESR measurement, the ROS (including H2O2 and $OH) formation and their effect towards metal dissolution were systematically illustrated. This novel synergistic
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strategy may serve as a promising and cost-effective technique for valuable metal recovery and solid waste treatment. Acknowledgement We acknowledge the financial support of the Research Fund of Major Science and Technology Program for Water Pollution Control and Treatment, China (2017ZX07402001). References [1] H.J. Kim, Y. Kim, J.H. Jeong, J.H. Choi, J. Lee, D.G. Choi, A cupronickel-based micromesh film for use as a high-performance and low-voltage transparent heater, J. Mater. Chem. A 3 (2015) 16621e16626. [2] V. Subramanian, P. Chandramohan, M.P. Srinivasan, S. Velmurugan, S.V. Narasimhan, Corrosion of cupronickel alloy in permanganate under acidic condition, Corros. Sci. 49 (2007) 620e636. [3] Z. Hajdari, H.O. Curkovi c, V. Cade z, S. Segota, Corrosion protection of cupronickel alloy by self-assembled films of fatty acids, J. Electrochem. Soc. 163 (2016) C145eC155. [4] V.S.C., P. Yadavalli, R.P. George, M.C. K M U, Development of hydrophobic cupronickel surface with biofouling resistance by sandblasting, Surf. Coat. Technol. 345 (2018) 89e95. [5] W.D. Riley, H.V. Makar, Impurity effects in secondary copper alloys, Conserv. Recycl. 9 (1986) 315e323. [6] L. Rocchetti, F. Veglio, B. Kopacek, F. Beolchini, Environmental impact assessment of hydrometallurgical processes for metal recovery from WEEE residues using a portable prototype plant, Environ. Sci. Technol. 47 (2013) 1581e1588. [7] P. Jochen, Heap leaching as a key technology for recovery of values from lowgrade ores e a brief overview, Hydrometallurgy 165 (2016) 206e212. [8] A. Behnamfard, M.M. Salarirad, F. Veglio, Process development for recovery of copper and precious metals from waste printed circuit boards with emphasize on palladium and gold leaching and precipitation, Waste Manag. 33 (2013) 2354e2363. [9] Z. Wang, R.T. Bush, J. Liu, Arsenic(III) and iron(II) co-oxidation by oxygen and hydrogen peroxide: divergent reactions in the presence of organic ligands, Chemosphere 93 (2013) 1936e1941. [10] S. Yang, H. He, D. Wu, D. Chen, X. Liang, Z. Qin, M. Fan, J. Zhu, P. Yuan, Decolorization of methylene blue by heterogeneous Fenton reaction using Fe3xTixO4 (0x0.78) at neutral pH values, Appl. Catal. B Environ. 89 (2009) 527e535. [11] D.K.Y. wong, B.A.W. coller, D.R. macfarlane, A kinetic model for the dissolution mechanism of copper in acidic sulfate solutions, Electrochim. Acta 38 (1993) 2121e2127. [12] V.V. Ekilik, A.G. Berezhnaya, E.A. Tugolukova, Dissolution of Ni-Zn alloys in sulfate solutions, Prot. Met. 41 (2005) 191e200. [13] A. Moreira, A. Benedetti, P. Cabot, P. Sumodjo, Electrochemical behaviour of copper electrode in concentrated sulfuric acid solutions, Electrochim. Acta 38 (1993) 981e987. [14] A. Owais, M.A.H. Gepreel, E. Ahmed, Effect of thermal treatment of copper anodes on electrorefining process, Hydrometallurgy 152 (2015) 55e60. [15] E.Y. Kim, M.S. Kim, J.C. Lee, K. Yoo, J. Jeong, Leaching behavior of copper using electro-generated chlorine in hydrochloric acid solution, Hydrometallurgy 100 (2010) 95e102.
[16] Y. Xue, W. Jin, H. Du, S. Zheng, Z. Sun, W. Yan, Y. Zhang, Electrochemical Cr(III) oxidation and mobilization by in situ generated reactive oxygen species in alkaline solution, J. Electrochem. Soc. 163 (2016) H684eH689. [17] C.A. Martinez-Huitle, S. Ferro, Electrochemical oxidation of organic pollutants for the wastewater treatment: direct and indirect processes, Chem. Soc. Rev. 35 (2006) 1324e1340. [18] E. Brillas, I. Sires, M.A. Oturan, Electro-fenton process and related electrochemical technologies based on Fenton's reaction chemistry, Chem. Rev. 109 (2009) 6570e6631. [19] L. Guo, K. Liang, K. Marcus, Z. Li, L. Zhou, P.D. Mani, H. Chen, C. Shen, Y. Dong, L. Zhai, K.R. Coffey, N. Orlovskaya, Y.H. Sohn, Y. Yang, Enhanced photoelectrocatalytic reduction of oxygen using Au@TiO2 plasmonic film, ACS Appl. Mater. Inter. 8 (2016) 34970e34977. [20] Y. Xue, S. Zheng, H. Du, Y. Zhang, W. Jin, Cr(III)-induced electrochemical advanced oxidation processes for the V2O3 dissolution in alkaline media, Chem. Eng. J. 307 (2017) 518e525. [21] S.O. Ganiyu, M. Zhou, C.A. Martínez-Huitle, Heterogeneous electro-Fenton and photoelectro-Fenton processes: a critical review of fundamental principles and application for water/wastewater treatment, Appl. Catal. B Environ. 235 (2018) 103e129. [22] L. Zhang, D. Xu, C. Hu, Y. Shi, Framework Cu-doped AlPO4 as an effective Fenton-like catalyst for bisphenol A degradation, Appl. Catal. B Environ. 207 (2017) 9e16. [23] Y. Xue, Y. Wang, S. Zheng, Z. Sun, Y. Zhang, W. Jin, Efficient oxidative dissolution of V2O3 by the in situ electro-generated reactive oxygen species on Ndoped carbon felt electrodes, Electrochim. Acta 226 (2017) 140e147. [24] Q. Ye, T.X. Shan, P. Cheng, Thermally induced evolution of dissolved gas in water flowing through a carbon felt sample, Int. J. Heat Mass Transf. 108 (2017) 2451e2461. [25] H.J. Zhang, H.L. Li, C.C. Deng, B. Zhao, J.H. Yang, Electrocatalysis of oxygen reduction reaction on carbon nanotubes modified by graphitization and amination, ECS Electrochem. Lett. 4 (2015) H33eH37. [26] Y. Xue, W. Jin, H. Du, S. Wang, S. Zheng, Y. Zhang, Tuning a-Fe2O3 nanotube arrays for the oxygen reduction reaction in alkaline media, RSC Adv. 6 (2016) 41878e41884. [27] C. Zhang, Y. Jiang, Y. Li, Z. Hu, L. Zhou, M. Zhou, Three-dimensional electrochemical process for wastewater treatment: a general review, Chem. Eng. J. 228 (2013) 455e467. [28] Y. Xue, S. Zheng, Z. Sun, Y. Zhang, W. Jin, Alkaline electrochemical advanced oxidation process for chromium oxidation at graphitized multi-walled carbon nanotubes, Chemosphere 183 (2017) 156e163. [29] Z. Wang, W. Ma, C. Chen, H. Ji, J. Zhao, Probing paramagnetic species in titaniabased heterogeneous photocatalysis by electron spin resonance (ESR) spectroscopyda mini review, Chem. Eng. J. 170 (2011) 353e362. [30] Y. Xue, Y. Zhang, Y. Zhang, S. Zheng, Y. Zhang, W. Jin, Electrochemical detoxification and recovery of spent SCR catalyst by in-situ generated reactive oxygen species in alkaline media, Chem. Eng. J. 325 (2017) 544e553. [31] A.N. Pham, G. Xing, C.J. Miller, T.D. Waite, Fenton-like copper redox chemistry revisited: hydrogen peroxide and superoxide mediation of copper-catalyzed oxidant production, J. Catal. 301 (2013) 54e64. [32] L. Zhang, Y. Nie, C. Hu, J. Qu, Enhanced Fenton degradation of Rhodamine B over nanoscaled Cu-doped LaTiO3 perovskite, Appl. Catal. B Environ. 125 (2012) 418e424. [33] F. Chen, X. Zhao, H. Liu, J. Qu, Enhanced destruction of Cu(CN)2 3 by H2O2 under alkaline conditions in the presence of EDTA/pyrophosphate, Chem. Eng. J. 253 (2014) 478e485. [34] R.E. Melchers, Bi-modal trend in the long-term corrosion of aluminium alloys, Corros. Sci. 82 (2014) 239e247.
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Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Enhanced anodic dissolution of cupronickel alloy scraps by electrogenerated reactive oxygen species in acid media Yunting Wang a, Yudong Xue b, c, **, Chunhui Zhang a, * a
School of Chemical and Environmental Engineering, China University of Mining and Technology (Beijing), Beijing, 100083, China National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, CAS Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, China c University of Chinese Academy of Sciences, Beijing, 100049, China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 21 May 2019 Received in revised form 21 July 2019 Accepted 22 July 2019 Available online 23 July 2019
Recycling of the cupronickel alloy scraps not only solves environmental related issues but also realizes the extraction of valuable metals and saves consumption of primary ore resources. Oxidative dissolution is a critical step for the recycling of valuable metal from the alloy scraps. In order to improve the dissolution kinetics and efficiency, a novel integrated electrochemical dissolution strategy for the sustainable recycling of the cupronickel alloy scraps was first developed, where the in-situ electro-generated reactive oxygen species (ROS) were employed as the indirect oxidative mediator. Much higher dissolved concentration of Ni, Zn, and Cu was reached by the present integrated strategy than that of the direct anodic dissolution process, which is attributed to the in-situ produced oxidative H2O2 and $OH via oxygen reduction reaction and electro-Fenton-like reaction, respectively. Moreover, the large quantity of ROS can be electro-generated, thus achieving high dissolved concentration, under the optimum condition with the preset potential of 0.3 V (vs. Ag/AgCl) or current density of 2.54 mA/cm2, respectively. This novel synergistic strategy may serve as a promising and cost-effective technique for the alloy scraps recycle and valuable metal extraction. © 2019 Elsevier B.V. All rights reserved.
Keywords: Anodic dissolution Electrochemical oxidation Reactive oxygen species Electro-Fenton-like Alloy scraps
1. Introduction Cupronickel alloy is widely used in the marine industry, power industry, chemical engineering, precise instrument, and medical apparatus, due to its high corrosion resistance and superior electrical and thermal conductivity [1e4]. A large amount of cupronickel alloy scraps is generated from the production process and retired alloys. Cupronickel alloy scraps contain valuable metals in which the average content of Ni, Zn, and Cu is about 20%, 30%, and 50%, respectively [5]. Recycling of the cupronickel alloy scraps not only solves environmental related issues but also realizes the extraction of valuable metals and saves consumption of primary ore resources. Therefore, the recovery of valuable metals from
* Corresponding author. ** Corresponding author. National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, CAS Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, China. E-mail addresses: [email protected] (Y. Xue), [email protected] (C. Zhang). https://doi.org/10.1016/j.jallcom.2019.07.276 0925-8388/© 2019 Elsevier B.V. All rights reserved.
cupronickel alloy scraps has received much attention. Oxidative dissolution is an important step for the recycling of valuable metal from large-scale industrial wastes, such as alloy scraps, electronic scraps, metallurgical slags, and spent catalysts [6]. Conventionally, the dissolution process is performed using concentrated inorganic acids, such as HCl, H2SO4, and HNO3 [7]. However, the dissolution rate is limited by the poor oxidative capacity and sluggish kinetics, particularly in H2SO4 solution [8]. Therefore, considerable additional oxidants and complexing agents are required, significantly frustrating the cost-effectiveness and environmental compatibility [9]. Anodic dissolution process has been developed for the metal recovery due to the advantages of simple, inexpensive and energy efficiency [10]. By employing the clean oxidant “electrons” [11], Ni2þ and Zn2þ can be obtained from the anodic dissolution of Ni and Zn, respectively [12], while the anodic dissolution of Cu occurs in a step-wise pathway as shown in Eqs. (1) and (2) [13]. Industrially, high concentrated acid and elevated temperature are required to secure the dissolution rate and eliminate the anodic passivation [14]. Kim developed a membrane-assisted process in 1.0 M HCl solution at room temperature, where the electro-
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generation of chlorine gas and leaching of copper simultaneously take place in the anode compartment [15]. The leaching efficiency was enhanced by dissolving CuCl precipitate on the surface of copper anode. Nevertheless, the further dissolution improvement and the cost-effectiveness are limited by the solubility of gaseous Cl2 and the employment of membrane, respectively. Besides, when HNO3 solution used as an electrolyte, it also produces nitric oxide gas. Both HCl and HNO3 electrolytes have a big negative impact, causing serious environmental pollution and poor working conditions. Therefore, in view of engineering application, H2SO4 is a promising media for the dissolution process. Cu 4 Cuþ þ e
(1)
Cuþ 4 Cu2þ þ e (Rate-determining step)
(2)
Recently, electrochemical advanced oxidation processes (EAOPs) have been widely performed as an alternative method for environmental remediation, especially for waste treatment [16e18]. The H2O2 can be in-situ electro-generated by the twoelectron-pathway oxygen reduction reaction (ORR) [19] as shown in Eq. (3) on the cathode, followed by the transition metal catalyzed electro-Fenton or electro-Fenton-like to generate highly oxidative species of hydroxyl radicals ($OH) [16,20]. It has been demonstrated that the Cuþ ions are able to react with H2O2 to produce $OH (as shown in Eqs. (4) and (5)) [21,22], further enhancing the oxidative capability of the dissolution process. O2 þ 2Hþ þ 2e / H2O2
(3)
Cuþ þ H2O2 / Cu2þ þ OH þ $OH
(4)
Cuþ þ $OH / Cu2þ þ OH
(5)
Obviously, it is highly desirable to investigate the synergistic effect between the anodic dissolution and the indirect oxidation via the electro-generated reactive oxygen species (ROS) mediator from the cathode. In this regard, the aim of this study is to develop an integrated direct and indirect electrochemical oxidation approach for enhancing the anodic dissolution of cupronickel alloy scraps under mild conditions (dilute H2SO4 solution and room temperature), which is completed by simply introducing the oxygen atmosphere into the single cell electrolyzer. 2. Experimental 2.1. Materials H2SO4 (98%), C4K2O9Ti$2H2O (98.5%), 5,5-dimethyl-1-pyrroline (DMPO), acetone (99.5%), and tert-butanol (t-BA, 99%) were purchased from Alfa Aesar. The electrolyte was provided by dissolving the corresponding sulfuric acid into ultrapure water (18 MU cm) obtained from a water purification system. High purity N2 and O2 (99.99%) were supplied by Beijing Qianxi Gas Co., Ltd., China. Cupronickel alloy scrap electrode (2 cm 6 cm) was polished with alumina powder, then rinsed with alcohol and deionized water to remove the surface impurities, and dried at 80 C for 5 min. The active carbon fiber electrode (5.0 cm 2.0 cm 0.5 cm) was cleaned in an ultrasonic bath with acetone for 30 min and immersed for 24 h, then rinsed with deionized water, dried at 80 C for 24 h and heated at 150 C for 2 h. 2.2. Experimental procedures The electrochemical experiments were conducted in a standard
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three-electrode system and controlled by a CHI760E workstation (CH Instruments Inc., Shanghai). Cupronickel alloy scrap electrode and active carbon fiber electrode were used as the working electrode and counter electrode, respectively. The reference electrode is Ag/AgCl electrode (the supporting solution is the saturated KCl solution). The linear sweep voltammetry (LSV) experiment was conducted in N2 and O2-saturated 100 mL 0.01 mol/L H2SO4 electrolyte at 25 C by potential cycling in the scan rate of 100 mV s1. The chronoamperometry was performed with vigorous electrolyte stirring and the applied potential was set at 0.3 V (vs. Ag/AgCl) to offer enough reaction driving force. Chronoamperometry experiments were conducted at 0.1, 0.2, and 0.3 V. Chronopotentiometry experiments were conducted at 0.83, 1.67, and 2.54 mA/cm2. The composition of the cupronickel alloy scrap electrode and the dissolution concentration of different elements were calculated by measuring the dissolved metal ions using ICP-OES (Optima 5300DV, PerkinElmer, USA). Each experiment was carried out at least in triplicate, and error bars in figures represent one standard deviation [23]. 2.3. Analysis The H2O2 concentration generated in the electrochemical system was determined by a UVevisible spectrophotometer (Labtech model 9100b), using potassium titanium (IV) oxalate as a colored indicator. The hydroxyl radical generated in the process was detected by electron spin resonance (ESR) with 5,5-dimethyl-1pyrroline (DMPO) by a JEOL spectrometer (JES-FA200) at room temperature. The surface morphology of the active carbon fiber electrode and cupronickel alloy scrap electrode were measured by FE-SEM (JSM-7610F). The unambiguous topographic information of the metallic electrode surface was provided by atomic force microscope (AFM, FastScan Bio, Bruker). 3. Results and discussion In order to analyze the elemental composition in the cupronickel alloy scraps, ICP is used in this study. As shown in Table 1, the results indicated that Cu, Ni, and Zn are the three main elements in the alloys. The compositions are consisting of 54.45% Cu, 17.6% Ni, 27.6% Zn, and 0.35% impurities. Therefore, recovery of valuable elements, especially Ni, Zn, and Cu, in the cupronickel alloy scraps is the main goal for the oxidative dissolution process. To construct a high-efficient electrochemical dissolution system, ROS generated on the cathode was coupled with the anodic dissolution process. Active carbon fiber is applied as the cathode, due to its intrinsic ROS generation properties, low cost, desirable long-term stability, and superior electrochemical properties [24]. The microstructure of active carbon fiber electrodes is illustrated by the FE-SEM, as shown in Fig. 1a, in which the diameter of carbon microfilaments was observed to be around 20 mm. Moreover, it can be observed that active carbon fiber presents a three-dimensional structure to provide a large surface area, thus introducing a large amount of oxygen reduction catalytic active sites on the active carbon fiber surface. As shown in Fig. 1b, a broad reduction wave was commenced at 0.14 V (vs. RHE) in the N2-saturated electrolyte, which is attributed to the charging electrochemical double-layer of carbon materials
Table 1 Element composition of cupronickel alloy scraps tested by ICP-OES (%). Cu
Ni
Zn
Fe
Ag
Ca
Na
Sn
Co
54.45
17.60
27.60
0.209
0.002
0.048
0.018
0.033
0.005
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Fig. 1. (a) FE-SEM image of the active carbon fiber electrode. (b) CV curves of active carbon fiber electrode in N2-purged and O2-saturated 0.01 M H2SO4 solutions, scan rate: 5 mV s1 (inset: CV curves of active carbon fiber electrode, scan rate: 5 mV s1).
[25]. In contrary, much higher current density was obtained in the O2-saturated electrolyte, attributing to the oxygen reduction peak. The onset potential of ORR is 0.24 V (vs. RHE), and the iORR at 0.31 V (vs. RHE) was 3.27 mA/cm2 approximately, which was calculated by taking the difference of current density in O2 and N2 saturated electrolytes. Besides, as seen the CV curves of active carbon fiber electrode in the inset of Fig. 1b, a well-defined oxygen reduction peak occurs in the O2-saturated electrolyte, while no significant reduction peak was observed at the same applied potential in the N2-saturated electrolyte, indicating that the oxygen reduction reaction happened on the active carbon fiber surface in the O2-saturated electrolyte [26]. Oxygen reduction dominantly proceeds two-electron pathway on the active carbon fiber to generate H2O2 [27]. To determine the in-situ generated H2O2 concentration, the chronoamperometry technique was employed at 0.3 V (vs. Ag/AgCl) in O2-saturated electrolyte. The production of H2O2 was quantified by UVevis using potassium titanium (IV) oxalate as a colored indicator. As shown in Fig. 2a, the absorbance value was increased gradually. Furthermore, there is a linear relationship between H2O2 concentration and reaction time, as shown in Fig. 2b, and the H2O2 yield can reach above 1.7 mM after 90 min electrochemical reaction. After introducing the ROS into the anodic dissolution system, we discussed the dissolution behavior of Ni, Zn, and Cu from the cupronickel alloy scrap electrode. The electrochemical dissolution behavior was investigated by using different cathodes under
Fig. 2. (a) UVevis spectra of electro-generated H2O2 at different times in 0.01 M H2SO4 solution, (b) Corresponding linear fit plots of H2O2 concentration versus time.
different gaseous environments. As presented in Fig. 3, the dissolved concentrations of Ni, Zn, and Cu in N2-saturated electrolyte are 12.95, 18.63, and 31.12 mg/L, respectively. Compared with the results of the N2-saturation condition, the dissolved concentrations of Ni, Zn, and Cu in electrolyte without gas saturation was almost maintained with a slight increase (0.35, 0.37, 0.86 mg/L). When the
Fig. 3. Comparison of the electrochemical dissolution behavior of Ni, Zn, and Cu in N2 and O2 saturated 0.01 M H2SO4 solutions. ACF: active carbon fiber; SS: stainless steel.
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oxygen atmosphere introduced to the system and the active carbon fiber applied, the dissolved concentrations of Ni, Zn, and Cu are 22.76, 35.29, and 40.46 mg/L, respectively. There are nearly 75.8%, 89.4%, and 30.0% enhancement of the Ni, Zn, and Cu dissolution, respectively, in O2-saturated solution than the corresponding one in N2-purged solution, which is possibly resulting from the contribution of the in-situ electro-generated ROS on the cathode. In this study, active carbon fiber and stainless steel (SS) cathode were used for comparing the effect of in-situ ROS generation properties. It should be noted that the dissolved concentrations of Ni, Zn, and Cu using SS cathode are lower than that of active carbon fiber due to the limited oxygen reduction performance on the SS electrode. The above results indicated that high ROS concentration is desired for improving the valuable metal dissolution. Furthermore, it is significant to control the potential and current density in the electrochemical experiments. In order to investigate the effect of potential and current density, further experiments were conducted for the Ni, Zn, and Cu dissolution in O2-saturated solution. Fig. 4 shows the effect of different potentials on the dissolved copper with time. The dissolved Ni, Zn, and Cu are monotonically linear with the reaction time. An increasing trend can be observed that the dissolved concentration of valuable metal would increase with high potential. The dissolution of Ni, Zn, and Cu (120 min) increased to 23.76, 35.30, and 41.46 mg/L at 0.3 V, which is much higher than that of 0.1 and 0.2 V. It is suggested that the amount of ROS is high at 0.3 V for the dissolution process. Fig. 5 presents the effect of applied current density on the metal dissolution with electrolysis time. As can be seen, the dissolved Ni, Zn, and Cu increased with the enhancement of the current density. When the applied current density set at 0.83 mA/cm2, the dissolved concentrations of Ni, Zn, and Cu were 10.64, 15.46, and 28.12 mg/L, respectively. While the applied current density increased to 2.54 mA/cm2, the dissolved concentrations of Ni, Zn, and Cu were increased to 27.76, 38.30, and 52.28 g/L, respectively, which also experienced an obviously increase due to the presence of oxygen to produce more ROS for the dissolution process. The hydrogen peroxide was produced on the cathode during the ORR. The standard electrode potential (E0) of Cu2þ/Cuþ is 0.15 V/ SHE, thus causing Cu is easier to dissolve than other metals in the cupronickel alloy scraps. Hydroxyl radicals can be continuously insitu electro-generated by the Fenton-like reaction of H2O2 and Cuþ to enhance anodic dissolution. To investigate the mechanism in the present enhanced electrochemical dissolution process, the dissolution experiment was carried out with selective $OH scavenger of t-BA [9]. As presented in Fig. 6a, the dissolved Ni, Zn, and Cu in the N2-purged atmosphere were well maintained at 12.96, 18.65, and 31.11 mg/L, respectively, when t-BA was added, indicating that $OH was not generated in this system. In contrast, the addition of corresponding t-BA in the O2-saturated environment leads to the decline of dissolved Ni, Zn, and Cu from 22.76, 35.30, and 40.46 mg/ L to 14.69, 23.36, and 33.70 mg/L, respectively, suggesting that the $OH is mainly responsible for the accelerated dissolution process. The contribution of anodic effect accounted for 56.9% of Ni, 52.7% of Zn, and 76.9% of Cu. It is calculated that the effect of $OH on anodic dissolution accounts for 35.5%, 33.8%, and 16.7% of the total dissolved amount of Ni, Zn, and Cu, respectively, while the H2O2 contribution to anodic dissolution for Ni, Zn, and Cu is 7.6%, 13.5%, and 6.4%, respectively. Besides, it was calculated that the $OH is dominant, which account for 82.3% of Ni, 71.8% of Zn, and 72.4% of Cu in the indirect electrochemical oxidation (ROS including H2O2 and $OH). By the addition of the quenching agent, the contributions of the reactive species (H2O2 and $OH) for the dissolution process are well distinguished. Therefore, when the ROS introduced to the present electrochemical system, the anodic dissolution rate was greatly increased.
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Fig. 4. Dissolved Ni (a), Zn (b), and Cu (c) with time at the varying potentials in the O2saturated 0.01 M H2SO4 solutions.
Furthermore, $OH generated in this integrated electrochemical process was detected by the electron spin resonance (ESR) spectra in Fig. 6b [28e30]. When DMPO added into the electrochemical cell, evident signals assigned to $OH were found in the oxygensaturated system, while no corresponding signal was observed in the nitrogen-purged system. Based on the above analysis and previous studies, the $OH is generated by the Cuþ-catalyzed activation of H2O2 in this Electro-Fenton-like system as shown in Eq.
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Fig. 6. (a) Electrochemical dissolution of metal ions in the presence and absence of tBA; (b) ESR spectra of the active free radicals detected in the presence and absence of oxygen (DMPO was used as a trapping agent).
Fig. 5. Dissolved Ni (a), Zn (b), and Cu (c) with time at varying current densities in the O2-saturated 0.01 M H2SO4 solutions.
(4) [31e33]. Subsequently, the formed $OH offers further oxidative stress for the dissolution of Ni and Zn, which is responsible for the enhanced anodic dissolution performance. To further illustrate the effect of ROS on the anodic dissolution, the early stages of the cupronickel alloy scrap electrode at different atmospheres were also investigated by FE-SEM and AFM. As illustrated in Fig. 7a and b, most of the alloy surface is smooth. A small amount of grain boundary corrosion appears in the N2
environment. In contrast, significant grain boundary corrosion is visible in the corresponding O2 environment, as shown in Fig. 7c. Due to the presence of ROS in the O2-rich environment, the cupronickel alloy scrap anode surface is strong attacked by the integration of H2O2 and $OH. The copper dissolution is promoted by the synergistic effect between the anodic dissolution and the cathodic indirect oxidation. On the contrary, the copper was dissolved simply by the effect of anodic dissolution with the absence of ROS in the N2 environment. Similarly, the cupronickel alloy exhibits a relatively uniform surface due to the stable anodic dissolution as shown in the threedimensional image of Fig. 8a under N2 atmosphere. Unlikely, a disordered surface is presented in Fig. 8b under O2 atmosphere, where a series of long mountains and valleys are observed due to the strong attack of ROS. This discrete dissolution behavior stems from the complex reaction mechanism and multiple contributions from different oxygen species, which is very similar to the phenomenon of “localized corrosion” owing to the accelerated attach from the corrosive environment [34]. Consequently, the schematic diagram of the enhanced anodic dissolution process of copper by electro-generated ROS in acidic solution is illustrated in Fig. 9, offering a promising and cost-effective technique for valuable metal recovery from the alloy scraps. The hydrogen peroxide was in-situ electro-generated by the 2e reduction of the dissolved molecular oxygen on the surface of active carbon fiber electrode. Then, the
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Fig. 8. Three-dimensional AFM images of the cupronickel alloy scrap electrode surface after 20 min electrochemical treatment in the absence (a) and presence (b) of oxygen atmosphere.
Fig. 7. FE-SEM images of the cupronickel alloy scrap electrode surface before (a) and after 20 min electrochemical treatment in the absence (b) and presence (c) of oxygen atmosphere.
H2O2 decomposition can be catalyzed by transition metals with the redox couple Cu2þ/Cuþ to generate highly oxidative species of $OH during the electro-Fenton-like process, which further enhances the anodic dissolution of cupronickel alloy scraps. 4. Conclusions In this study, enhanced anodic dissolution of cupronickel alloy scraps by electro-generated reactive oxygen species (ROS) was developed, where the ROS were readily in-situ electro-generated and employed as the indirect oxidative mediator. By simply introducing the oxygen atmosphere, much higher dissolved concentrations of Ni, Zn, and Cu were obtained than that of direct anodic dissolution in a nitrogen-purged environment. The optimum applied potential and the current density are 0.3 V (vs. Ag/AgCl) and 2.54 mA/cm2, respectively, so in this case, a large amount of ROS is
Fig. 9. Schematic diagrams of enhanced anodic dissolution of cupronickel alloy scraps by electro-generated reactive oxygen species in acidic solution.
generated during the oxidative dissolution process. Based upon the selective scavenger experiment and ESR measurement, the ROS (including H2O2 and $OH) formation and their effect towards metal dissolution were systematically illustrated. This novel synergistic
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strategy may serve as a promising and cost-effective technique for valuable metal recovery and solid waste treatment. Acknowledgement We acknowledge the financial support of the Research Fund of Major Science and Technology Program for Water Pollution Control and Treatment, China (2017ZX07402001). References [1] H.J. Kim, Y. Kim, J.H. Jeong, J.H. Choi, J. Lee, D.G. Choi, A cupronickel-based micromesh film for use as a high-performance and low-voltage transparent heater, J. Mater. Chem. A 3 (2015) 16621e16626. [2] V. Subramanian, P. Chandramohan, M.P. Srinivasan, S. Velmurugan, S.V. Narasimhan, Corrosion of cupronickel alloy in permanganate under acidic condition, Corros. Sci. 49 (2007) 620e636. [3] Z. Hajdari, H.O. Curkovi c, V. Cade z, S. Segota, Corrosion protection of cupronickel alloy by self-assembled films of fatty acids, J. Electrochem. Soc. 163 (2016) C145eC155. [4] V.S.C., P. Yadavalli, R.P. George, M.C. K M U, Development of hydrophobic cupronickel surface with biofouling resistance by sandblasting, Surf. Coat. Technol. 345 (2018) 89e95. [5] W.D. Riley, H.V. Makar, Impurity effects in secondary copper alloys, Conserv. Recycl. 9 (1986) 315e323. [6] L. Rocchetti, F. Veglio, B. Kopacek, F. Beolchini, Environmental impact assessment of hydrometallurgical processes for metal recovery from WEEE residues using a portable prototype plant, Environ. Sci. Technol. 47 (2013) 1581e1588. [7] P. Jochen, Heap leaching as a key technology for recovery of values from lowgrade ores e a brief overview, Hydrometallurgy 165 (2016) 206e212. [8] A. Behnamfard, M.M. Salarirad, F. Veglio, Process development for recovery of copper and precious metals from waste printed circuit boards with emphasize on palladium and gold leaching and precipitation, Waste Manag. 33 (2013) 2354e2363. [9] Z. Wang, R.T. Bush, J. Liu, Arsenic(III) and iron(II) co-oxidation by oxygen and hydrogen peroxide: divergent reactions in the presence of organic ligands, Chemosphere 93 (2013) 1936e1941. [10] S. Yang, H. He, D. Wu, D. Chen, X. Liang, Z. Qin, M. Fan, J. Zhu, P. Yuan, Decolorization of methylene blue by heterogeneous Fenton reaction using Fe3xTixO4 (0x0.78) at neutral pH values, Appl. Catal. B Environ. 89 (2009) 527e535. [11] D.K.Y. wong, B.A.W. coller, D.R. macfarlane, A kinetic model for the dissolution mechanism of copper in acidic sulfate solutions, Electrochim. Acta 38 (1993) 2121e2127. [12] V.V. Ekilik, A.G. Berezhnaya, E.A. Tugolukova, Dissolution of Ni-Zn alloys in sulfate solutions, Prot. Met. 41 (2005) 191e200. [13] A. Moreira, A. Benedetti, P. Cabot, P. Sumodjo, Electrochemical behaviour of copper electrode in concentrated sulfuric acid solutions, Electrochim. Acta 38 (1993) 981e987. [14] A. Owais, M.A.H. Gepreel, E. Ahmed, Effect of thermal treatment of copper anodes on electrorefining process, Hydrometallurgy 152 (2015) 55e60. [15] E.Y. Kim, M.S. Kim, J.C. Lee, K. Yoo, J. Jeong, Leaching behavior of copper using electro-generated chlorine in hydrochloric acid solution, Hydrometallurgy 100 (2010) 95e102.
[16] Y. Xue, W. Jin, H. Du, S. Zheng, Z. Sun, W. Yan, Y. Zhang, Electrochemical Cr(III) oxidation and mobilization by in situ generated reactive oxygen species in alkaline solution, J. Electrochem. Soc. 163 (2016) H684eH689. [17] C.A. Martinez-Huitle, S. Ferro, Electrochemical oxidation of organic pollutants for the wastewater treatment: direct and indirect processes, Chem. Soc. Rev. 35 (2006) 1324e1340. [18] E. Brillas, I. Sires, M.A. Oturan, Electro-fenton process and related electrochemical technologies based on Fenton's reaction chemistry, Chem. Rev. 109 (2009) 6570e6631. [19] L. Guo, K. Liang, K. Marcus, Z. Li, L. Zhou, P.D. Mani, H. Chen, C. Shen, Y. Dong, L. Zhai, K.R. Coffey, N. Orlovskaya, Y.H. Sohn, Y. Yang, Enhanced photoelectrocatalytic reduction of oxygen using Au@TiO2 plasmonic film, ACS Appl. Mater. Inter. 8 (2016) 34970e34977. [20] Y. Xue, S. Zheng, H. Du, Y. Zhang, W. Jin, Cr(III)-induced electrochemical advanced oxidation processes for the V2O3 dissolution in alkaline media, Chem. Eng. J. 307 (2017) 518e525. [21] S.O. Ganiyu, M. Zhou, C.A. Martínez-Huitle, Heterogeneous electro-Fenton and photoelectro-Fenton processes: a critical review of fundamental principles and application for water/wastewater treatment, Appl. Catal. B Environ. 235 (2018) 103e129. [22] L. Zhang, D. Xu, C. Hu, Y. Shi, Framework Cu-doped AlPO4 as an effective Fenton-like catalyst for bisphenol A degradation, Appl. Catal. B Environ. 207 (2017) 9e16. [23] Y. Xue, Y. Wang, S. Zheng, Z. Sun, Y. Zhang, W. Jin, Efficient oxidative dissolution of V2O3 by the in situ electro-generated reactive oxygen species on Ndoped carbon felt electrodes, Electrochim. Acta 226 (2017) 140e147. [24] Q. Ye, T.X. Shan, P. Cheng, Thermally induced evolution of dissolved gas in water flowing through a carbon felt sample, Int. J. Heat Mass Transf. 108 (2017) 2451e2461. [25] H.J. Zhang, H.L. Li, C.C. Deng, B. Zhao, J.H. Yang, Electrocatalysis of oxygen reduction reaction on carbon nanotubes modified by graphitization and amination, ECS Electrochem. Lett. 4 (2015) H33eH37. [26] Y. Xue, W. Jin, H. Du, S. Wang, S. Zheng, Y. Zhang, Tuning a-Fe2O3 nanotube arrays for the oxygen reduction reaction in alkaline media, RSC Adv. 6 (2016) 41878e41884. [27] C. Zhang, Y. Jiang, Y. Li, Z. Hu, L. Zhou, M. Zhou, Three-dimensional electrochemical process for wastewater treatment: a general review, Chem. Eng. J. 228 (2013) 455e467. [28] Y. Xue, S. Zheng, Z. Sun, Y. Zhang, W. Jin, Alkaline electrochemical advanced oxidation process for chromium oxidation at graphitized multi-walled carbon nanotubes, Chemosphere 183 (2017) 156e163. [29] Z. Wang, W. Ma, C. Chen, H. Ji, J. Zhao, Probing paramagnetic species in titaniabased heterogeneous photocatalysis by electron spin resonance (ESR) spectroscopyda mini review, Chem. Eng. J. 170 (2011) 353e362. [30] Y. Xue, Y. Zhang, Y. Zhang, S. Zheng, Y. Zhang, W. Jin, Electrochemical detoxification and recovery of spent SCR catalyst by in-situ generated reactive oxygen species in alkaline media, Chem. Eng. J. 325 (2017) 544e553. [31] A.N. Pham, G. Xing, C.J. Miller, T.D. Waite, Fenton-like copper redox chemistry revisited: hydrogen peroxide and superoxide mediation of copper-catalyzed oxidant production, J. Catal. 301 (2013) 54e64. [32] L. Zhang, Y. Nie, C. Hu, J. Qu, Enhanced Fenton degradation of Rhodamine B over nanoscaled Cu-doped LaTiO3 perovskite, Appl. Catal. B Environ. 125 (2012) 418e424. [33] F. Chen, X. Zhao, H. Liu, J. Qu, Enhanced destruction of Cu(CN)2 3 by H2O2 under alkaline conditions in the presence of EDTA/pyrophosphate, Chem. Eng. J. 253 (2014) 478e485. [34] R.E. Melchers, Bi-modal trend in the long-term corrosion of aluminium alloys, Corros. Sci. 82 (2014) 239e247.