A Novel Ammonium Chloride Roasting Approach for the High-Efficiency Co-sulfation of Nickel, Cobalt, and Copper in Polymetallic Sulfide Minerals

In this study, we propose a novel temperature-programmed ammonium chloride (NH4Cl) roasting–water-leaching process to extract nickel (Ni), cobalt (Co), and copper (Cu) from polymetallic sulfide minerals in a synchronous, efficient, and environment-friendly manner. During the roasting process, several vital parameters were investigated to achieve the high co-sulfation of Ni, Co, and Cu. The dosage of NH4Cl was drastically reduced, and chlorine-free calcine was obtained using a chlorination–sulfation roasting schedule. The results suggest that the water-leaching yields of Ni, Co, and Cu reached ~ 97, ~ 95, and ~ 99 pct, respectively, whereas that of iron was ~ 1 pct under the following optimized conditions: the first roasting step temperature was 250 °C, the heating rate was 2 °C/min, the dosage of the NH4Cl additive was 80 mg/g(ore), the holding times at 250 °C and 650 °C were 120 and 60 minutes, respectively, and the particle size of the NH4Cl additive was smaller than 75 μm. The phase evolution as well as the chlorination and sulfation mechanisms during the three-step roasting process were examined by the roasting–leaching experiments and the X-ray diffraction, energy-dispersive X-ray spectroscopy, and thermodynamic calculations. The results indicate that sulfide chlorination occurred because of the NH4Cl additive and the formed intermediates, including metal chlorides and chlorine gas. The chlorides of Ni, Co, and Cu were successfully transformed into sulfates. The temperature-programmed NH4Cl roasting–water-leaching process considerably improves the selective sulfation of the nonferrous metals. Furthermore, this is a promising technique for separating and extracting nonferrous metals from iron-based sulfide materials.