Process Monitoring of Gold Recovery from a Thiosulfate Leaching Solution Using Silicon Powder: Measurement of Gold Potential (Supporting Information)

We have developed a gold recovery method utilizing the thiosulfate leaching and cementation onto silicon (Si) powder. In this process, copper (oxidizing agent for gold dissolution) was also recovered after gold recovery. In this work, we tried to monitor the recovery behavior in order to improve selectivity of metals. For experimentation, an ammonium thiosulfate solution containing 1 mM (M: mol dm⁻³) sodium gold(I) sulfite and 5 mM copper(II) sulfate was prepared (pH 13). We immersed a gold wire in the solution and measured the rest potential during the recovery process using Si powder. The potential of gold wire shifted to negative direction at the start and end of gold and copper recovery. We discussed the potential shift by measuring polarization curves of gold wire in the ammonium thiosulfate solution under various conditions. The efficient recovery of high-purity gold would be achieved by monitoring the potential of gold.