| Summary: | The role of silica in the chlorination–volatilization of cobalt oxide, using calcium chloride, is investigated in this paper. It is found that the Co volatilization percentage of the CoO–Fe<sub>2</sub>O<sub>3</sub>–CaCl<sub>2</sub> system is not larger than 12.1%. Silica plays an important role in the chlorination–volatilization of cobalt oxide by using calcium chloride. In the CoO–SiO<sub>2</sub>–Fe<sub>2</sub>O<sub>3</sub>–CaCl<sub>2</sub> system, the Co volatilization percentage is initially positively related to the molar ratio of SiO<sub>2</sub> to CaCl<sub>2</sub>, and remains almost constant when the molar ratio of SiO<sub>2</sub> to CaCl<sub>2</sub> rises from zero to eight. The critical molar ratios of SiO<sub>2</sub> to CaCl<sub>2</sub> are 1 and 2 when the molar ratios of CaCl<sub>2</sub> to CoO are 8.3 and 16.6, respectively. The Co volatilization percentage remains almost constant with the increase in CaO concentration, and decreases when Al<sub>2</sub>O<sub>3</sub> and MgO are added. Ca<sub>2</sub>SiO<sub>3</sub>Cl<sub>2</sub> is determined after roasting at 1073 K and 1173 K, and disappears at temperatures in excess of 1273 K in the calcines from the CoO–SiO<sub>2</sub>–CaCl<sub>2</sub> system. CaSiO<sub>3</sub> always exists in the calcines at temperatures in excess of 973 K.
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