Hexaamminecobalt(III) catalyzed thiosulfate leaching of gold from a concentrate calcine and gold recovery from its pregnant leach solution via resin adsorption

Abstract

Co(II) is effective in catalyzing gold thiosulfate leaching, but Co(III) has seldom been adopted directly as the catalyst. This paper examined the effect of hexaamminecobalt(III) on the thiosulfate leaching of gold from a concentrate calcine and the gold recovery via resin adsorption from the leach solution. Under the leaching solution conditions, the Co(NH3)63+/Co(NH3)x2+ (x = 4, 5) redox couple is thermodynamically formed playing the catalytic role. Experimental results verify the catalysis of Co(NH3)63+, which is better than that of Co(II) and Cu(II) in thiosulfate leaching of gold. Replacing Cu(II) by Co(NH3)63+ or Co(II), the thiosulfate consumption was significantly reduced and the complex two-stage gold elution process was simplified to a low-cost one-stage process. Compared with Co(II), Co(NH3)63+ that is already the oxidant could shorten the leaching time from 8 h to 6 h without affecting the gold extraction (~80%). In addition, the thiosulfate consumption was further lowered from 18.8 kg·t-1ore to 15.0 kg·t-1ore under the catalysis of Co(NH3)63+, which was confirmed by the X-ray photoelectron spectroscopy (XPS) analysis. Based on the thermodynamic analysis, the decrease of thiosulfate consumption may result from the formation of a lower concentration of the mixed-ligand Co(III) complexes such as Co(NH3)x(S2O3)+ (x = 4, 5). Gold recovery results suggested that, comparing Co(NH3)63+ with Co(II), the gold in the Co(NH3)63+ catalyzed leaching solution could be recovered more efficiently by resin adsorption. Therefore, Co(NH3)63+ is a catalyst more efficient than Co(II) and has promise to replace Cu(II) in the extraction and recovery of gold from its ores by thiosulfate leaching and resin adsorption.