Hebei Messi Biology Co., Ltd. stated that hydrated basic magnesium carbonate, also known as light magnesium carbonate, is white crystals or powders with loose texture and stable existence in the air. Its chemical composition varies slightly due to different preparation methods and conditions. Its relative density is small and it can be used as an additive for rubber and plastic products. At the same time, it has the characteristics of non-combustion and can be used as fireproof and thermal insulation materials and flame retardants. It is also widely used in the fields of medicine and health, daily chemicals, and fine chemical products. After thermal decomposition, it can be used to prepare magnesium oxide, and food-grade basic magnesium carbonate can be used as a flour improver. At present, basic magnesium carbonate is mainly used as an intermediate raw material to prepare high-purity magnesium oxide.
For the precipitation and crystallization process of generating insoluble substances, it is generally believed that there is a nucleation induction period in the reaction. Nucleation induction (tind) refers to the time interval from the establishment of a supersaturated solution of the target product to the formation of a critical crystal nucleus. A variety of methods are used to determine the nucleation induction period of the target product, including solution conductivity method and laser detection method. The solution conductivity method is widely used because of its convenient operation and high stability.
Using heavy magnesium water (Mg2+ concentration of 0.271mol/L) as raw material, the relationship between the reaction temperature and induction period of heavy magnesium water was determined by solution conductivity method, and the precipitation and crystallization process of magnesium carbonate and the formation mechanism of basic magnesium carbonate were preliminarily explored.
Using heavy magnesium water as experimental raw material, changing the reaction temperature and pressure, the thermal decomposition efficiency of heavy magnesium aqueous solution was improved. Basic magnesium carbonate with different morphologies was prepared, and the product met HG/T2959-2010. Conclusions:
1) At 70℃, 0.10MPa, and 0.5h reaction, the decomposition rate of heavy magnesium water was 66.4%, while at 70℃, 0.03MPa, and 0.5h reaction, the decomposition rate of heavy magnesium water reached 91.2%. At the same reaction temperature, reducing the reaction pressure, the decomposition rate of heavy magnesium water increased, and the reaction induction period decreased; at 0.10MPa, the specific surface area first increased and then decreased with increasing temperature; at 0.03MPa, the specific surface area decreased with increasing temperature. The product morphology changes with increasing temperature as follows: rod-shaped-flaky particles-flower-ball-shaped crystals.
2) As the pyrolysis reaction temperature increases, the number of crystal water contained in the product molecules gradually decreases. The final product is: 4MgCO3·Mg(OH)2·4H2O, which first removes crystal water during thermal decomposition to generate the intermediate product 4MgCO3·Mg(OH)2; then continues to decompose to generate CO2 and structural water, with a total mass loss of 56.81%, and the final remaining product is MgO.