Coupling kinetics of high-temperature carbothermal reduction of copper slag under carbon dioxide atmosphere

Industrial recovery of valuable elements in copper slag is the key to treat copper slag and protect the environment. However, the results of the industrial reduction of copper slag are not ideal at present, mainly because the oxidation problem caused by excess oxygen is not considered. In this study, the properties of three carbonaceous materials and the coupling reaction behavior of copper slag + C under CO2 atmosphere were investigated by thermogravimetric and thermokinetic analyses. The results showed the activity of the three carbonaceous materials to be in the order of coke > anthracite > coal. Coke was more conducive to the reduction of copper slag under Ar atmosphere, whereas anthracite was more conducive under CO2 atmosphere. The reduction amount and rate of copper slag under CO2 atmosphere were higher than those under Ar atmosphere within a certain temperature range. Moreover, the carbon burning loss increased significantly so that CO2 could re-oxidize the reduced metal elements after heating to 1300 degree celsius. The limiting steps of the reduction reaction of copper slag under Ar atmosphere mainly followed the three-dimensional diffusion (ZLT) model. On the other hand, under CO2 atmosphere, the limiting steps of some of the reactions changed due to the influence of the coupling reaction. Overall, we observed that the activation energies of the reduction and oxidation reactions under coupling conditions were higher.