Advanced Strategies for Recycling Calcium Carbide Slag in Industry

Abstract

As a strong alkaline industrial waste generated in the process of acetylene production, calcium carbide slag has a huge annual output and prominent environmental risks. This paper systematically reviews the disposal and resource utilisation technology system of calcium carbide slag, reveals that its main component is calcium hydroxide (82%-90%) with silica-aluminium-iron impurities, and demonstrates the environmental urgency of industrial utilisation. By comparing the process characteristics of traditional physical disposal (reclamation pile, natural sedimentation) and chemical comprehensive utilisation (cement/lime/lightweight bricks), it is pointed out that landfill method has land encroachment and pollution potential, while the existing resource technology has significant limitations in terms of calcium carbide slag consumption (15%-50%), energy consumption control (calcination process up to 900-1000℃) and added value of the product. Focusing on the innovative path of calcium carbonate preparation from calcium carbide slag: breaking through the limitation of calcium hydroxide solubility, adopting ammonium chloride leaching-CO₂ carbonation recycling process to achieve the utilisation rate of calcium carbide slag to be increased to more than 80%, and the purity of the light calcium carbonate produced reaches 99.2%, whiteness > 93%, and its economic feasibility is verified by 50kt/a industrialised production line. Research shows that the leaching method reduces energy consumption by 15%-20% compared with the traditional calcination method, and the synergistic CO₂ capture can reduce emissions by 21kg CO₂/t of calcium carbide slag, which promotes the formation of a closed-loop resource chain of ‘calcium carbide slag-calcium carbonate’. The future needs to develop high value-added product development, intelligent purification process and cross-industry coupling technology to break through the bottleneck of industrialisation.