Study Of The Electrodeposition Behaviour And Nucleation Mechanism Of Indium In Acidic Solutions

Indium is a typical rare metal with strategic value in the fields of optoelectronic semiconductors,low temperature solders,catalysts and wear resistant anti-corrosion coatings.Current indium resources are mainly derived from intermediate products of metal smelting processes such as zinc and lead as well as electronic waste containing indium.Methods of separating and extracting indium include ion exchange,solvent extraction,leaching,vacuum metallurgy and electrochemical metallurgy.Electrodeposition is the preferred process for the separation and extraction of indium due to its simplicity of operation,mild production conditions and ease of industrial dissemination.An in-depth understanding of the nucleation mechanism of the indium electrodeposition process and its influencing factors can provide theoretical guidance for the optimal design of the indium electrolysis process.The electrochemical reduction and oxidation behaviour of indium in acidic aqueous solutions is complex,and the electrodeposition process is accompanied by hydrogen evolution reaction,which makes the electrochemical study of indium difficult.The electrochemical study of indium in acidic aqueous solution is mostly limited to the process level,but there is a lack of systematic and in-depth explanation of the underlying electrochemical redox behaviour and nucleation mechanism of electrodeposition.In this work,the electrochemical quartz microcrystalline balance（EQCM）was used to investigate the redox behaviour of indium in acidic aqueous solutions and the nucleation mechanism of electrodeposition by combining cyclic voltammetry,linear voltammetry,chronoamperometry and electrochemical impedance with its ability to monitor current and electrode mass changes in real time.The main work and research results of this paper are as follows:（1）The electrochemical redox mechanism of indium in acidic aqueous solution is revealed.The reduction process of indium mainly involves the conversion of In（III）to In（0）with an initial reduction potential of about-0.8 V;the oxidative dissolution of indium starts at about-0.68V,and the conversion from In（0）to In（III）occurs first in the oxidation process,and there is a reaction in which In（0）is oxidised to the low-valent In（I）at a higher overpotential,and In（I）can be In（I）can be further oxidized to In（III）at the electrode,which also diffuses into the solution and disproportionates to produce In（0）and In（III）.In the oxidation process,when the solution p H is high,indium is easily passivated to produce In（OH）₃or In₂O₃film layer covering the indium surface,and the indium oxidation process is a coupled electrochemical-chemical reaction mechanism.（2）The kinetics of indium electrodeposition and the growth mechanism of electrocrystalline nucleation have been investigated.The SH model shows that the nucleation of indium at both platinum and glassy carbon electrodes is progressive and that hydrogen evolution can mask the shape of the overlapping nucleation and nucleation diffusion zones in the indium current transient,thus deviating from the typical metal electrodeposition current transient.The nucleation parameters of the indium electrodeposition process were obtained by modelling the experimental current transient and fitting it nonlinearly.（3）The effects of electrolysis temperature,chloride ions and substrate electrodes on the nucleation of indium electrodeposition were investigated.The increase of electrodeposition temperature will lead to a positive shift of indium electrodeposition potential,accelerating the deposition rate of indium and making the grains more coarse;chloride ion has a significant activation effect on the electrodeposition of indium.On the amorphous glassy carbon electrode,the indium deposit has a lamellar structure,the layer is loose and easy to peel off,and the growth process appears to be selectively oriented,while on the polycrystalline platinum electrode,the indium deposit is more closely bonded to the substrate,the indium growth direction varies,and the selective orientation does not appear.