Indium is a crucial material and is widely used in high-tech industries, and electrodeposition is an efficient method to recover rare metal resources. In this work, the electrochemical behavior of In3+ was investigated by using different electrochemical methods in electrolytes containing sodium and indium sulfate. Cyclic voltammetry (CV), chronoamperometry (CA), and alternating current impedance (EIS) techniques were used to investigate the reduction reaction of In3+ and the electrocrystallization mechanism of indium in the indium sulfate system. The cyclic voltammetry results showed that the electrodeposition process is irreversible. The average charge transfer coefficient a of In3+ was calculated to be 0.116 from the relationship between the cathodic peak potential and the half-peak potential, and the H+ discharge occurred at a higher negative potential of In3+. The nucleation mechanism of indium electrodeposition was analyzed by chronoamperometry. The mechanism of indium at potential steps of −0.3 to −0.6 V was close to diffusion-controlled instantaneous nucleation with a diffusion coefficient of 7.31 × 10−9 cm2 s−1. The EIS results demonstrated that the reduction process of In3+ is subject to a diffusion-controlled step when pH = 2.5 and the applied potential was −0.5 V. SEM and XRD techniques indicated that the cathodic products deposited on the titanium electrode have excellent cleanliness and purity.
Electrorefining is an effective method for preparing high-purity indium. To realize the control of impurity Sn in crude indium electrolytic refining, electrochemical test methods, such as cyclic voltammetry (CV), and chronoamperometry (CA) were mainly used to study the electrochemical behavior of indium. The results show that when a few of SnSO 4 was added to the electrolyte containing indium sulfate, in the meantime, the Sn 2+ concentration reached 5000 ppm, in the electrolysis process, the impurity Sn in the cathode was appeared to precipitate before the indium precipitated. The electrodeposition of indium was irreversible, controlled by diffusion steps, and In 3+ reduction was carried out by fractional steps, transferring one electron at a time. The diffusion coefficient of In 3+ calculated by cyclic voltammetry was 1.02 × 10 −7 cm 2 /s, and the average charge transfer coefficient was 0.081. The nucleation mechanism of indium conformed to three-dimensional instantaneous nucleation. The results provide theoretical guidance for electrolytic refining of crude indium and electrochemical regulation of impurities.
The accumulation of spent carbide (YG8), not only pollutes the environment but also causes waste of tungsten, cobalt and other rare metal resources. To better address this issue, we proposed a combined electrochemical separation process of lowtemperature aqueous solution and high-temperature molten salt for tungsten and cobalt. H 2 WO 4 was obtained from spent carbide in an aqueous solution, and we calcined it to obtain WO 3 , which was used as a raw material to obtain tungsten by using molten salt electrodeposition. The influence of the current efficiency and the electrochemical behavior of the discharge precipitation of W(VI) were also studied. The calcination results showed that the morphology of WO 3 was regular and there were no other impurities. The maximum current efficiency of 82.91% was achieved in a series of electrodeposition experiments. According to XRD and SEM analysis, the recovered product was high purity tungsten, which belongs to the simple cubic crystal system. In the W(VI) reduction mechanism experiments, the electrochemical process of W(VI) in NaCl-Na 2 WO 4 -WO 3 molten salt was investigated using linear scanning voltammetry (LSV) and chronoamperometry in a three-electrode system. The LSV showed that W(VI) was reduced at the cathode in two steps and the electrode reaction was controlled by diffusion. The fitting results of chronoamperometry showed that the nucleation mechanism of W(VI) was an instantaneous nucleation mode, and the diffusion coefficient was 7.379×10 -10 cm 2 •s -1 .
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