Preparation of high-purity calcium solution by closed mechanical activation leaching of carbide slag.

Calcium carbide slag is an alkaline hazardous waste generated in industrial production processes. Utilizing the slag for CO₂ solidification will help achieve the "carbon peak and carbon neutrality" goal as soon as possible. In alkaline environments, ammonium chloride leaching agents can selectively leach Ca, separating Ca from other impurities in carbide slag to prepare the high-purity calcium-containing solution. Then, the obtained calcium-rich solution is reacted with CO₂ to prepare high-purity calcium carbonate, achieving solid waste resource utilization. Using ammonium chloride as the leaching agent and a ball mill as the leaching reaction equipment, a closed mechanical activation method was employed to investigate the effects of process parameters such as leaching agent dosage, mechanical stirring speed, reaction time, and liquid-solid ratio on the Ca leaching rate in carbide slag. The results show that under the optimal reaction conditions of 1.1 times the theoretical amount of ammonium chloride, a ball mill speed of 500 r/min, a reaction time of 10 min, and a liquid-solid ratio of 4:1, the Ca leaching rate could reach 89.76%, and the Ca concentration in the filtrate could reach as high as 79.4 g/L, which could be used for subsequent experiments. Compared to conventional leaching method, the closed mechanical activation method can increase the Ca leaching rate by 3 percentage points and significantly reduces ammonia volatilization, ensuring a good operating environment. [ABSTRACT FROM AUTHOR]