Effect of Triethanolamine as a New and Efficient Additive on Thiosulfate-Copper-Ammonia System Leaching of Gold

A new and efficient additive, triethanolamine (TEA), was used on pure gold leaching in a thiosulfate-copper-ammonia system. An appropriate TEA concentration enhanced the gold dissolution rate and reduced thiosulfate consumption. The beneficial effect became most pronounced in the case of MTEA:Mcopper = 1:1, where the gold dissolution rate increased by approximately 50% and thiosulfate consumption decreased by approximately 10%. The possible mechanisms of TEA are as follows: TEA combines with cupric and ammonia, which enhances the catalytic oxidation ability of Cu(II). Meanwhile, TEA can reduce the consumption of thiosulfate caused by the oxidation of Cu(II) and hence decreases the formation of passivation layers on the gold surface. Furthermore, the deprotonated ethanolic oxygen atoms of [Cu(NH3)x(TEA)y] act as bridging ligands, which could form an “electronic bridge” that benefits the electron transfer from Au0 to Cu2+. In addition, the actual main reaction complex in the cupric-ammonia-TEA complex ([Cu(NH3)x(TEA)y]) was [Cu(NH3)3TEA]2+.