Sustainable CO2 utilization and calcium carbonate recovery from calcium carbide wastewater

The hydration of calcium carbide for acetylene production generates calcium carbide residue (CCR), primarily as a calcium hydroxide slurry, often disposed of in ponds, increasing soil alkalinity and CCR wastewater. This study, thus, explores converting CCR wastewater into calcium carbonate (CaCO₃) via CO₂ carbonation with triethanolamine (TEA). After initial carbonation and filtration, the carbonated CCR solutions were heated to 80°C to remove CO₂ and the solution underwent three cycles of dissolution and carbonation, promoting resource sustainability. TEA enhanced cubic calcite formation, but only non-TEA solutions successfully precipitated CaCO₃ upon reuse. Successive recycling rounds reduced CCR dissolution and CaCO₃ formation due to impurity buildup. Maximum CaCO₃ yields were 23.0% for heated solution and 36.6% for non-heated solution. To enhance process sustainability, dilution with raw water is recommended to counter impurity accumulation and optimize recycling conditions.