Selective Reduction of Au(I) from a High-Concentration Thiosulfate Solution for Gold Recovery Using One-Step Heat-Treated High-Sulfur Coal

Abstract

It is challenging to economically, efficiently, and selectively recover Au(S2O3)23– from thiosulfate gold leaching solutions. This article reports an approach to effectively recover Au(S2O3)23– using a toxic material, high-sulfur coal (HSC). Calcined HSC (CHSC) obtained through the one-step calcination of HSC in an inert environment can effectively adsorb Au(S2O3)23– present in a high-concentration thiosulfate solution. While the adsorption process is dominated by chemical adsorption, the optimization of the adsorption conditions of Au(S2O3)23– suggested that pH and the concentration of thiosulfate can also exert influence on the adsorption process. The adsorption of Au(S2O3)23– by CHSC followed the Langmuir isotherm model, and the high correlation coefficient suggested that the reaction followed pseudo-second-order kinetics. X-ray diffraction (XRD) was conducted to characterize the phases of HSC before and after calcination. The XRD results indicated that the main phase of HSC changed from FeS2 (pyrite) to Fe8S9 (pyrrhotite) after calcination. The Fermi level and surface charge density of Fe8S9 were greater than those of FeS2, which facilitated the extraction of electrons from the surface of Fe8S9 during the reduction of Au(I). As a result of the formation of Fe8S9, the open-circuit potential is reduced from 0.08 V (HSC) to −0.023 V (CHSC). As such, CHSC has a greater reducing capability, which gives rise to the reduction of Au(I) present in the solution to elemental gold. These results were confirmed using an X-ray photoelectron spectrometer. This study not only converted toxic HSC to a valuable material but also provided a new method to adsorb Au(S2O3)23– from thiosulfate leaching solutions.