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.

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