Method for improving adsorption capacity of gold(I) thiosulfate complex on mercapto-functionalized silica gel by masking copper with ethylenediamine

The thiosulfate method is a cyanide-free hydrometallurgical method for gold extraction, but the existence of copper ion in Cu²⁺–NH₃–S₂O₃^2- system is not conducive to the subsequent gold(I) recovery. This paper describes a process for improving the gold(I) adsorption capacity of mercapto-functionalized silica gel (MP-SG) by using ethylenediamine (en) as an additive to mask copper(II). The effects of en/Cu²⁺ molar ratio, contact time, and pH on adsorption were investigated. The results showed that the addition of en increased the adsorption capacity of MP-SG to gold by more than 70%. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirmed that the valence states of gold and copper on the adsorbent were both + 1, which confirmed the occurrence of competitive copper(II) adsorption. This could be inhibited by the addition of en without affecting the interfacial properties of MP-SG. UV–vis spectroscopy and the distribution of copper species revealed that addition of en changed the composition of the solution, forming a more stable Cu(en)₂²⁺ complex, the fraction of Cu(en)₂²⁺ increased with en content, thus reducing the competitive adsorption of Cu(II) to gold (I). The recovery rate of gold in the actual thiosulfate leaching solution was up to 92.35%, and en has almost no influence on the recycling process of the recovered leaching liquor, which proves the feasibility of this method in practical application. (author)