CaCO3 Precipitation Kinetics in the System CaCl2–CO2–Mg(OH)2–H2O for Comprehensive Utilization of Soda Production Wastes

The precipitation of CaCO 3 and its kinetics for the CaCl 2 –CO 2 –Mg(OH) 2 –H 2 O system were systematically studied to develop a novel process for eliminating solid and liquid waste from the Solvay soda process. The effects of operating conditions including temperature, CaCl 2 concentration, flow rate of CO 2, and stirring speed on the reaction kinetics were experimentally determined. The results revealed that low temperature, high CO 2 flow rate, and fast stirring speed can accelerate the reaction rate, and the mass transfer of CO 2 is the controlling step. An MSMPR crystallizer was used to obtain the experimental crystal size distribution (CSD). A simplified population balance equation (PBE) was used to correlate the parameters on the basis of supersaturation. The soda solid and liquid wastes discharged from the Solvay industry were used as raw material to test the new process and validate the methodology. The precipitated CaCO 3 consists of calcite or aragonite with high purity and uniform CSD. A double-effect evaporative-cooling crystallization process to recover MgCl 2 ·6H 2 O and NaCl was simulated with help of Aspen plus and the electrolyte-NRTL (ELENRTL) model, suggesting economic benefits.