A study has been conducted to understand how the cobalt and nickel ions affect the dissolution behavior of gold and thiosulfate consumption in the thiosulfate-ethylenediamine (en)-Cu2+ system. The cobalt and nickel ions enhance gold dissolution within the concentration range used in this experiment, but there was almost no additional thiosulfate consumption. The concentration of the copper(II) complex with en decreases in the presence of the Co2+. The redox/mixed potentials (E-pt and E-AU) are measured using platinum and gold electrodes immersed in a gold leaching system. The test results show that the additional Co2+ and Ni2+ increase the EAU but do not significantly change the Ept. The leached gold foils were analyzed by XPS. The results show that the additional metallic ions could change the morphology of the gold surface such that passivated products containing sulfur would decrease and the gold could be easily dissolved. (C) 2015 Elsevier Ltd. All rights reserved.