One-Step Activation-Synthesized Coal-Based Activated Carbon and its Adsorption Performance for Gold Thiosulfate Complexes

Abstract

Difficulties associated with recovering gold from leaching solutions restrict the wide applicability of the thiosulfate system. In this study, we developed a facile one-step activation strategy for the synthesis of coal-based activated carbon from inexpensive and readily available bituminous coal precursors; the activated carbon was subsequently used to adsorb gold from thiosulfate solutions. We investigated the optimum conditions for synthesizing coal-based activated carbon and the effects of pH, temperature, and the initial gold concentration on [Au(S2O3)2]3− adsorption by the coal-based activated carbon. We also analyzed the structure and surface properties of the material before and after gold adsorption, which revealed that the initially smooth surface morphology of the raw coal was porous following activation, and that the surface was loaded with -SCN groups. The adsorption process follows pseudo-second-order kinetics and is described by the Freundlich model. [Au(S2O3)2]3−-adsorption by the coal-based activated carbon is a very fast endothermic process, with adsorption equilibrium reached within 60 min at a gold concentration of 10 mg/L. Ligand exchange between the [Au(S2O3)2]3− ions in solution and the -SCN groups on the surface of the coal-based activated carbon occurs during gold adsorption, which ultimately leads to the surface of the activated carbon adsorbing the Au(Ⅰ) in solution. This study provides theoretical guidance and a practical basis for the adsorption of gold from thiosulfate leaching solutions using coal-based activated carbon, while also facilitating the clean and high-value utilization of coal resources.

Keywords: Coal-based activated carbon, thiourea, bituminous coal, one-step activation strategy, gold thiosulfate complex.