Recycling and utilization of calcium carbide slag - current status and new opportunities

Coal is the dominant fuel in China to provide primary energy, and 70% of polyvinyl chloride is produced from coal-based CaC2. CaC2 reacts with water to produce acetylene and calcium carbide slag (CCS) as a solid waste for polyvinyl chloride production. Approximate 40 million tons of dry CCS are generated annually in China, among which only a small part is used in cement and as desulfurization agents. In contrast, most of the CCS is accumulated, occupying land and posing environmental risks. For the chlor-alkali industry, CCS can regenerate massive CaO through purification, molding, calcination. Thus, CCS can be used as raw material for CaC2 production, thereby realizing renewable and sustainable utilization of calcium resources. Therefore, the recycling of CCS decreases the need for limestone extraction, leading to reduced CO2 emission, energy consumption, and solid waste pollution. For example, if CaO is produced by CCS instead of natural limestone, 20 million tons of CO2 emissions can be reduced each year. While the massive CaO with high thermal strength is crucial for the CaC2 production in the electric arc furnace, enabling CCS recycling and sustainable utilization.