*3.2. Effect of the Molar Ratio of SiO<sup>2</sup> to CaCl<sup>2</sup>*

Figure 3 shows the effect of the molar ratio of SiO<sup>2</sup> to CaCl<sup>2</sup> on the Co volatilization percentage in the CoO–SiO2–Fe2O3–CaCl<sup>2</sup> system. When the molar ratio of CaCl<sup>2</sup> to CoO is 8.3, the Co volatilization percentage increases significantly, as the molar ratio of SiO<sup>2</sup> to CaCl<sup>2</sup> rises from 0 to 1, and remains almost constant when the molar ratio of SiO<sup>2</sup> to CaCl<sup>2</sup> increases from 1 to 8 at all the desired temperatures. Similar trends are observed when the molar ratio of CaCl<sup>2</sup> to CoO is 16.6 at 1273 K and 1373 K. The Co volatilization percentage increases significantly and remains almost constant when the critical molar ratio of SiO<sup>2</sup> to CaCl<sup>2</sup> is two. However, it increases significantly as the molar ratio of SiO<sup>2</sup> to CaCl<sup>2</sup> is amplified at 1173 K.

**Figure 3.** Effect of the molar ratio of SiO<sup>2</sup> to CaCl<sup>2</sup> on the Co volatilization percentage.

Equation (5) is initially promoted with an increase in the molar ratio of SiO<sup>2</sup> to CaCl<sup>2</sup> from zero. The enhancement becomes weaker when the molar ratio of SiO<sup>2</sup> to CaCl<sup>2</sup> is large enough. As shown in Equation (6), SiO<sup>2</sup> plays an important role in the generation of

Cl2, by the decomposition of CaCl2. This result is consistent with the works of Liu et al. [18], Zhu et al. [19], and Ding [20]. The Co volatilization percentage is very low when the molar ratio of SiO<sup>2</sup> to CaCl<sup>2</sup> is zero. Most of the CaCl<sup>2</sup> is lost in the form of volatilization in this case. This also means that the role of Fe2O<sup>3</sup> in the generation of Cl2, by the decomposition of CaCl2, is much weaker than that of SiO2. More Cl<sup>2</sup> is released when the molar ratio of SiO<sup>2</sup> to CaCl<sup>2</sup> is increased, which leads to an increase in the Co volatilization percentage. There is sufficient Cl<sup>2</sup> at a high molar ratio of SiO2, resulting in a constant Co volatilization percentage.
