Eco-friendly and selective separation of nickel and copper from low-grade nickel sulfide ore via sulfur fixation roasting with MgCO3 followed by sulfuric acid leaching

Based on the demand for nickel sulfate for batteries and environmental pollution control, this work proposed a novel and clean magnesium carbonate roasting process for sulfur fixation followed by acid leaching for efficient extraction of Ni and Cu. The effect of some key factors, including mass ratio of MgCO3 to ore, roasting temperature, and roasting time in the MgCO3 roasting process, also leaching time, leaching temperature, acid concentration, and liquid-to-solid ratio in the leaching process, on the transformation of metals was investigated. An optimal roasting and leaching conditions were determined and 98.5 % nickel and 99.0 % copper were converted into metal sulfate into the leaching solution. In the roasting process, magnesium carbonate plays a major role in sulfur fixation by transforming into MgO, and the Mg element contained in the ore plays a minor role in sulfur fixation, and the sulfur element involved in the reaction is transferred to magnesium sulfate in the ore to avoid gas emission. And the magnesium carbonate can be recycled with almost no loss. The kinetic model of metal transformation in leaching process was determined by Sharp method and the results show that the transformation of metal is controlled by diffusion of solid product layer, the apparent activation energies and the influence index of the initial sulfuric acid concentration are determined to be 25.64 kJ & sdot;mol-1 and 1.26 (for nickel), 18.34 kJ & sdot;mol-1 and 1.43 (for copper), 15.36 kJ & sdot;mol-1 and 0.87 (for iron), respectively. From an economic and environmental perspective, this process has strong feasibility and broad application prospects for treating low-grade nickel sulfide ore.