Gold Recovery via Silicon Powder Cementation from a Thiosulfate Leaching Solution after Gold Metal Dissolution (Supporting Information)

Thiosulfate leaching of gold is a promising alternative to cyanidation due to its low toxicity and reduced environmental impact. We proposed displacement deposition (cementation) onto silicon powder for gold recovery from ammonium thiosulfate leaching solutions. However, the overall process from the leaching of solid gold to the separation of recovered gold has not been demonstrated. In this study, we present the leaching of a commercially available gold foil (94.43 wt% gold, 4.90 wt% silver, and 0.66 wt% copper) as a model of gold metal, the cementation of gold onto silicon powder in the pregnant solution, and the dissolution of silicon to separate the gold deposits. The gold metal dissolved completely in the leaching solution, and 100 % of dissolved gold was recovered via silicon powder cementation, while avoiding the co-recovery of copper used as an oxidizing agent for gold dissolution. The silicon powder was removed by potassium hydroxide treatment, yielding metal particles mainly composed of gold with minor silver originating from the gold foil. We further investigated silver deposition behavior using both gold and silver foils, indicating the formation of gold-silver mixed particles. This study demonstrates the applicability of a clean and sustainable gold recovery process from urban mine resources.