Recovery of Valuable Metals from Nickel Slag: A Descriptive Study

Abstract

Nickel slag (NS), generated mainly during nickel (Ni) smelting, and classified as a potentially harmful solid waste, is an important secondary resource containing not only valuable metals, such as Ni, Cu, Fe, and Co, but also hazardous elements, such as As and Pb. Hence, in response to its potential economic performance and environmental benefits, NS needs to be subjected to further recycling instead of being dumped without treatment. Flotation can be used to recover valuable metals Ni and Cu from NS. However, the crystalline state of Ni-bearing minerals and Cu-bearing minerals in NS are not conducive to flotation, which limits the recovery of Ni and Cu. Current study, the crystalline state of NS was optimized by sulfurization–reduction in order to maximize the recovery of Ni and Cu from NS. The mineralogical characteristics of NS were analyzed in detail, and the experiments on flotation recovery of Ni and Cu from raw slag and modified slag were carried out. The sulfurization–reduction mechanism was assessed based on thermodynamics and elements' phase distributions. Mineralogical characteristic analysis results show that the NS contains 0.88% Ni and 0.31% Cu. The metal minerals containing Ni or Cu in the NS are dispersed in silicate minerals with micron-sized fine particles, which makes it difficult to recover Ni and Cu by flotation. Chemical phase analysis shows that sulfurization–reduction modification can increase the distribution of Ni and Cu in metal state and sulfide state, and decrease the distribution of them in silicate. Compared with the direct flotation of raw slag, the flotation recoveries of Ni and Cu increased from 24.61% to 66.61% and from 38.77% to 80.00%, respectively. Overall, flotation is an effective method to recover nickel and copper from NS, and the flotation recovery of Ni and Cu can be improved by sulfurization–reduction modification.