Selective complexation leaching of copper from copper smelting slag with the alkaline glycine solution: An effective recovery method of copper from secondary resource

•Introducing a novel separation method of copper from copper smelting slag with the glycine solution.•Efficient complex leaching of copper was realized in alkaline glycine solution.•Complexation mechanism of Cu2+ and Gly− was analyzed by freeze–drying of leaching solution. In the process of copper smelting, amounts of copper droplets inevitably enter the copper smelting slag (CSS), resulting in a high loss of copper. As the grade of exploitable copper ore decreases gradually, the recovery of copper from copper slag is very important to ensure the safe supply of copper. In this study, a new method was proposed to recover copper via selective complexation leaching process by using the alkaline glycine solution. Various leaching parameters, including initial pH, particle size, stirring speed, liquid-solid ratio, temperature and glycine concentration were investigated. Under the optimum leaching conditions, the copper extraction of 86.40 % was achieved, while the other valuable metal elements were barely leached. The results of leaching kinetics indicated that the mixed control, a combination of internal diffusion and interfacial chemical reaction, was the rate-limiting step in the leaching process, where the apparent activation energy was calculated to be 34.66 kJ/mol. After leaching process, the leaching solution rich in copper–glycine complex was obtained, and the copper grade in the leaching residue was 0.22 wt%, while the unseparated copper was tightly wrapped by gangue minerals. Therefore, glycine was successfully used as the leaching agent to extract copper from CSS with high efficiency and selectivity, which provided a prospective method for the green recovery of CSS.