Preparation of calcium carbonate nanoparticles from waste carbide slag based on CO2 mineralization

This study proposes a novel method for simultaneously dealing with the waste carbide slag (WCS) and CO2 mitigation. In addition, the ultrafine vaterite CaCO3 with high economic value was produced under mild conditions of 25 °C and 0.1 MPa. Ammonium sulfate ((NH4)2SO4) was employed to efficiently extract calcium from WCS into the solid phase calcium sulfate dehydrate (CaSO4·2H2O). Subsequently, it was subjected to “dropwise carbonation” leading to the formation of a calcium carbonate with controllable particle size between 100 nm–1 μm through multiple crystalline phase transformations. The results showed that nano-sized CaCO3 with nearly 90% purity and whiteness was prepared at 25 °C, CO2-500 mL/min, and NH4+/Ca2+ = 2.4 conditions. Results of TG and FTIR analyses confirmed that CaCO3 polymorphs with vaterite and metastable were formed. Based on the calcium conversion ratio of the entire process, treatment with 1 ton of WSC captured ∼0.5 tons of CO2 and yields about 1.15 tons of nano-sized CaCO3 per each cycle operation. This study provides a valuable method for identifying potential application for scale preparation of vaterite nanoparticles from low cost but abundant calcium resource such as WCS and gypsum.