An Innovative Approach to Prepare Calcium Oxide from Calcium Carbide Slag Based on Sequential Mineral Transformation

Calcium carbide slag (CS) is an industrial solid waste produced via the coal-based poly(vinyl chloride) process, and its main component is calcium hydroxide (Ca(OH)2) (85–95 wt %). CS can be used instead of calcium carbonate (CaCO3) to produce calcium oxide (CaO), reducing carbon dioxide (CO2) emissions. Our group has reported that CaO can be prepared at lower temperatures using CS compared with existing processing temperature, where the calcination temperature decreases from 1000 to 700 °C when CaCO3 is replaced with CS during CaO production. A comparison of the carbon emissions of CS and CaCO3-based CaO preparation processes show that using CS to produce CaO reduces CO2 emissions by 977.62 kg/t. Herein, the CS-based CaO is explained by controlling the CS calcination temperature and mineral transformation. CS completely decomposes into CaO at 492 °C. The calcination temperature of CS is between 400 and 600 °C, where CaCO3 is formed via the reaction of carbon and Ca(OH)2 and water in CS. Furthermore, when the carbon content in CS is >4%, CaCO3 is formed. When the calcination temperature is 700 °C, CaCO3 decomposes into CaO. As the temperature increases, the metallurgical activity of CS increases, and its strength decreases. When the temperature is 700 °C, the compressive strength of CaO is 21.94 MPa, its metallurgical activity is 379.85 mL, and the CaO content is 95.14%. This study provides a new method for preparing CaO to simultaneously reduce carbon emissions and in-situ recycle CS.