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[3211-22-08] Gold precipitation onto co-existing metals during ammonium thiosulfate leaching of waste printed circuit boards

^○Sanghee Jeon¹, Mayumi Ito¹, Naho Kitajima¹, Rong Pongsumrankul¹, Sinya Tanaka¹, Hirotaka Takahasi¹, Carlito Baltazar Tabelin¹, Naoki Hiroyoshi ¹ (1. Hokkaido University)

司会: 芳賀一寿（秋田大学）

Keywords:Gold, Ammonium thiosulfate leaching, waste printed circuit boards, Precipitation

Cyanide leaching is a conventional method to extract gold (Au). Due to the toxicity of cyanide, however, ammonium thiosulfate leaching has been developed as an alternative method to extract Au. This study investigated the factors affecting the extraction of Au in ammonium thiosulfate leaching of waste printed circuit boards (PCBs), and found that the liquid-to-solid ratio is an important factor, that is, extraction of Au decreased when liquid-to-solid ratio increased. Gold extraction was 86% at liquid-to-solid ratio of 100, but Au extraction was under 9% at liquid-to-solid ratio of 20. Calculation based on the experimental results at this liquid-to-solid ratio indicated that, there was enough thiosulfate for Au extraction in the aqueous phase. This means that the low Au extraction is not due to the lack of thiosulfate. SEM-EDX observations of the leaching residues showed that Au was preferentially deposited on the surfaces of Cu and Al particles. This indicate that the extracted Au is re-precipitated on these co-existing metals