A validation experiment on indium recovery by electrowinning of aqueous electrolytes: Optimization of electrolyte composition

What is it about?

A batch-type and lab-scale indium recovery method was developed via electrowinning (EW) to prove mass production-capability and economic recovery of indium from InCl3 crystals precipitated from the solvent extraction using a suitable phosphoric acid-based extractant. More precisely, the InCl3 crystals thus precipitated were further dissolved in three different aqueous electrolyte mixtures for subsequent electrowinning experiments: 0.05 M InCl3 - 0.7 M LiCl; 0.05M InCl3; 0.05 M InCl3 – 0.7 M NaCl. The effect of adding LiCl and NaCl supporting electrolytes to InCl3 on overall EW efficiency was thus comprehensibly investigated. Direct electroreduction of InCl3 using 0.05 M InCl3 aqueous electrolyte resulted in the highest indium metal purity of 99.996 % deposited on the copper cathode. Thus, metallic contents obtained from the validation experiments were further characterized using various analytical tools such as inductively coupled plasma/atomic emission spectroscopy (ICP/AES), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray fluorescence (XRF).

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Why is it important?

Post-solvent extraction hydrated indium chloride precipitation was further dissolved into three different aqueous electrolyte mixtures: 0.05 M InCl3, 0.05 M InCl3 – 0.7 M LiCl and 0.05 M InCl3 – 0.7 M NaCl for subsequent electrowinning (EW) experiments, in which the effect of adding LiCl and NaCl supporting electrolytes to InCl3 on overall EW efficiency was comprehensively investigated. More rapid decrease of In3+ ions concentration in the InCl3 + LiCl and InCl3 + NaCl electrolytes is attributed to more efficient and facile electro-reduction of indium ions at the cathode via significantly increased electrolytic conductivity by addition of LiCl and NaCl. Direct electro-reduction of InCl3 using 0.05 M InCl3 aqueous electrolyte resulted in 99.996 % purity indium metal deposited on the copper cathode and further study is necessary to explain lower purity of the indium recovered from the 0.05 M InCl3 – 0.7 M LiCl. Overall, batch-type mass production- capable indium recovery process has been tested by lab-scale experiment and the feasibility of economic recovery of indium has been experimentally substantiated via validation experiments.