A novel rapid and selective microbially thiosulfate bioleaching of precious metals from discarded telecommunication printed circuited boards (TPCBs)

In this study for the first time, microbe-produced thiosulfate is considered as a new lixiviant in bioleaching of precious metals from discarded TPCBs. The effects of significant parameters for the selective over bio-production of thiosulfate (S₂O₃²⁻) and sulfate (SO₄²⁻) were investigated. The cultivation of Acidithiobacillus thiooxidans in the 9K medium with inhibitor (3.2 mg/L KCN) by pH adjustment, led to the overproduction of thiosulfate up to 350 mg/L and significantly decreased sulfur oxidation rate to sulfate to 6%. In contrast, without inhibitor and pH adjustment considerably increased amounts of sulfate to 26000 mg/L by 83% of sulfur oxidation rate to sulfate. A 100% copper dissolution was obtained at optimum condition (Sulfate: 26000 mg/L; pH 0.5;H₂O₂: 5% (v/v); 20 g/L TPCBs; 24 h) prior thiosulfate bioleaching. In the next stage, at 10 g/L TPCBs, 31% (0.11 mg/gTPCB) gold and 40% (1.23 mg/gTPCB) silver after 48 h were successfully recovered by thiosulfate bioleaching.