Calcined High-Sulfur Coal for Highly Efficient Adsorption of Au(S2O3)23-from a Gold Thiosulfate Leaching Solution Using an External Reduction Potential

High-sulfur coal cannot be directly burned and used; moreover, its long-term stacking can easily pollute the surrounding soil and water. Previous studies have determined that high-sulfur coal calcined under an inert gas atmosphere is reducible and can be used to recover Au(S2O3)(2)(3-) from thiosulfate solutions. However, calcined high-sulfur coal (CHSC) cannot effectively adsorb Au(S2O3)(2)(3-) from gold thiosulfate leaching solutions containing copper and ammonia owing to the presence of oxidant Cu(NH3)(4)(2+). In this study, we demonstrated that the adsorption capacity of CHSC can be increased from 5 to 92% after the conversion of Cu(NH3)(4)(2+) into Cu(S2O3)(3)(5-) using an external reduction potential. After adsorption was completed, the Cu(S2O3)(3)(5-) in the solution was spontaneously converted into Cu(NH3)(4)(2+) under an air atmosphere to recycle the leachate. The reduction method using an external potential prevented the irreversible transformation of Cu(NH3)(4)(2+) caused by the addition of reducing agents. In addition, Au-loaded CHSC was subjected to a dense-medium separation method via centrifugal sedimentation to separate Au from other substances in CHSC. Au and carbon were enriched in the light products, facilitating the subsequent recovery of Au via roasting. It was determined that the optimal experimental conditions for the recovery of 96% of Au from Au-loaded CHSC were as follows: a density of the heavy medium of 2.3 g/cm(3), rotation speed of 2000 rpm, and centrifugation time of 8 min. This work proposes a new method for recovering Au(S2O3)(2)(3-) from thiosulfate leaching solution based on sorbents prepared from solid waste high-sulfur coal.