Mechanistic study of magnesium carbonate semibatch reactive crystallization with magnesium hydroxide and CO₂

This work investigates semibatch precipitation of magnesium carbonate at ambient temperature and pressure using Mg(OH)₂ and CO₂ as starting materials. A thermal analysis method was developed that reflects the dissolution rate of Mg(OH)₂ and the formation of magnesium carbonate. The method was successfully used to determine the composition of solids precipitated from the reaction. Concentration profiles of Mg²⁺ and total carbon over time were determined from the liquid phase. The influence of CO₂ flow rate and stirring rate on precipitation was analyzed based on comprehensive information from the liquid and solid phases. A stirring rate of 650 rpm was found to be the optimum speed as the flow rate of CO₂ was 1 L/min. Precipitation rate increased with gas flow rate, which indicates that mass transfer of CO₂ plays a critical role in this precipitation case. Magnesium carbonate trihydrate (nesquehonite) was formed as a bunch of needle-like primary crystals.