For securing noble metal resources, recovery of noble metals from urban mines is a key technology. Recently, ammonium thiosulfate solution has attracted attention as a safe and low-cost solution for gold leaching. We previously reported a noble metal recovery process using electroless displacement deposition onto silicon powder. In this study, we tried to use silicon powder to recover gold from an ammonium thiosulfate leaching solution. For experimentation, we added silicon powder to a simulated ammonium thiosulfate leaching solution containing 1 mM（M: mol dm－3）sodium gold（I）sulfite and copper（II）sulfate（oxidizing agent for gold dissolution）. In the cases that the copper（II）sulfate concentration was 5 mM or higher, gold was not recovered even after 24 h treatment. However, we recovered gold successfully in 3 h by decreasing the copper（II）sulfate concentration to 2 mM or less. We also recovered gold in 3 h by changing the pH from 10 to 13 of the solution containing 5 mM copper（II）sulfate.
To clarify effects of Zn and Zn-Ni alloy electroplating on the hydrogen embrittlement of SK85 steel sheets with different hardnesses, a method of using three-point bending tests to evaluate hydrogen embrittlement was investigated. Because specimens are easy to prepare and because no notch is required, three-point bending tests are effective as a simple method of evaluating hydrogen embrittlement of zinc-based electroplated high-strength steel sheets.