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

Abstract

The precipitation of CaCO3 and its kinetics for the CaCl2–CO2–Mg(OH)2–H2O 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, CaCl2 concentration, flow rate of CO2, and stirring speed on the reaction kinetics were experimentally determined. The results revealed that low temperature, high CO2 flow rate, and fast stirring speed can accelerate the reaction rate, and the mass transfer of CO2 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 CaCO3 consists of calcite or aragonite with high purity and uniform CSD. A double-effect evaporative-cooling crystallization process to recover MgCl2·6H2O and NaCl was simulated with help of Aspen plus and the electrolyte-NRTL (ELENRTL) model, suggesting economic benefits.