Combined scheme for conditioning circulating cyanide solutions

Due to the specific features of hydrometallurgical processing, where cyanide solutions are used, the composition of the leaching solution undergoes periodic changes referred to in the literature as “fatigue.” This adversely affects the rate of gold recovery and cementation, and therefore the overall efficiency of cyanide leaching technology. One of the most important markers determining the “fatigue” of the solution is copper. This study examined the possibility of applying a combined scheme for the purification of circulating cyanide solutions with high concentrations of copper (1196 mg/dm 3 ), iron (111 mg/dm 3 ), arsenic (19 mg/dm 3 ), and sodium cyanide (0.94 g/dm 3 ). A two-stage technology (reverse osmosis + chemical precipitation) was developed for the reduction of treated solution volumes and the removal of impurities. At the first stage, the solution was separated in a reverse osmosis unit equipped with LP22-8040 membranes, producing permeate and concentrate in a 1 : 1 ratio. The permeate (12 mg/dm 3 Cu and 0.01 mg/dm 3 Fe, pH = 11.13) was returned to the process cycle. At the second stage, the concentrate, which contained 99 % of the initial impurities, was further purified by the stepwise addition of a CuSO 4 solution (70 g/dm 3 Cu) in 1–11 cm 3 doses under stirring (500 rpm, 10 min). The results showed that the optimal CuSO 4 dose (11 cm 3 ) provided removal of more than 86 % of Cu from the initial solution, as well as 100 % of Fe and more than 96 % of As. The precipitate obtained in the process consisted of 68.3 % copper, with CuCN and Cu(OH) 2 as the main components.