Gold recovery from cyanidation residue by chloride leaching and carbon adsorption – Preliminary results from CICL process

There is a vast amount of globally underutilized low-grade mine tailings and leach residues, including those from primary processing of gold. In this research, the target is to recover the remaining gold (10.9 g/t) from weathered refractory iron-rich residue that had previously been subject to autoclave oxidation, subsequent cyanidation in a conventional carbon-in-leach (CIL) circuit as well as storage at tailings area. Chloride leaching has been considered as one of the most promising cyanide-free gold leaching methods and it has shown positive outcomes in treating primary gold ores, concentrates, and flotation tailings. Therefore, in the current study, the iron-rich residue investigated was subjected to chloride leaching combined with simultaneous carbon adsorption. The investigated parameters included leaching time (2–8 h), chloride concentration ([Cl⁻] = 0.2–5 M), type and concentration of oxidant ([Cu²⁺]/[Fe³⁺] = 0.1–1 M), as well as type and concentration of activated carbon (14–25 g/L), whereas S/L ratio (100 g/L), acidity (pH = 1), and temperature (90 °C) were kept constant. Leaching results indicate that up to 40% of the remaining gold could still be recovered from the investigated residue with optimized chloride leaching. According to the results, the most important parameter for gold recovery was the leaching time. Moreover, of the studied oxidants, cupric ions were shown to contribute more to gold recovery when compared to ferric ions (35% vs. 24% at [Cu²⁺]/[Fe³⁺] = 0.1 M). Nevertheless, an increase of cupric concentration from 0.1 M (low-concentrated) to 0.5 M, resulted in only a slight increase in gold recovery (from 36% to 40%), whereas no further improvement in gold recovery was achieved with a 1 M cupric concentration. Two studied activated carbon products showed equal effectiveness in gold adsorption. In-situ carbon adsorption was shown to occur effectively in chloride media, as all dissolved gold could be detected in the activated carbon, and the concentration of remaining gold in the pregnant leach solution was minimal (< 0.02 mg/L). These findings indicate that low-concentrated chloride leaching of leach residues from industrial gold processes can allow an enhanced recovery of gold from previously mined and treated raw materials.