Hebei Messi Biology Co., Ltd. stated that anhydrous magnesium carbonate exists in the form of magnesite in nature, and MgCO3 and FeCO3 can form a complete isomorphism, that is, Mg2+ and Fe2+ in the crystal structure can replace each other due to similar properties, and its crystal physical properties change linearly with the amount of the two elements. The unit cell structure and chemical bonds remain unchanged, Mg2+ and Fe2+ can be miscible with each other in proportion, and can form isomorphic mixtures with different contents. Natural magnesite generally contains Fe and is difficult to remove. In addition, there are impurities such as Ca, Mn, and Si. Therefore, products directly ground and processed by minerals are usually of low purity and poor quality.
Anhydrous magnesium carbonate can replace basic magnesium carbonate or trihydrate magnesium carbonate as an additive for advanced glass, fine ceramics, fire retardant coatings, daily necessities and pharmaceutical products, and can play a role in reinforcement, wear resistance, and flame retardancy. In addition, the most important application of anhydrous magnesium carbonate is as a new inorganic flame retardant. The decomposition temperature of anhydrous magnesium carbonate is between 300-500℃, and a large amount of CO2 is produced during decomposition. The process is an endothermic reaction, and the unit reaction heat absorption is 864J/g. No harmful substances are produced during the decomposition process, and the product CO2 can isolate the air and block the oxygen source. In theory, it can achieve very good flame retardant effect, especially suitable for fire retardant of electrical materials with relatively high temperature requirements.
The research on anhydrous magnesium carbonate is still in the exploratory stage. A few anhydrous magnesium carbonates used in industry are prepared from high-quality magnesite through physical processing (such as grinding, graded crushing, etc.).
As early as 2008, pure phase MgCO3 crystals were prepared at 150℃ using basic magnesium carbonate 3MgCO3·Mg(OH)2·3H2O as raw material and CO2 continuously introduced into ethylene glycol solvent; MgCO3 gel was generated through a series of reactions using magnesium powder, methanol and CO2; pure phase MgCO3 was generated using magnesium chloride and CO2 under sealed conditions of 120℃ and 3bar pressure;
The research on the preparation of anhydrous magnesium carbonate mainly focuses on the hydrothermal method. Different magnesium sources were used to react with urea at 160℃ for hydrothermal reaction, and rhombohedral microcrystalline particles with a particle size of about 10um were generated after 30h; magnesium acetate, sodium sulfate, and hexamethylenetetramine were placed in the hydrothermal system, and magnesium carbonate crystals with a particle size of about 30um were generated after reacting at 160℃ for 24h, and their optical properties were studied; magnesium salts reacted with ammonium carbonate to generate the intermediate ammonium magnesium carbonate, and then low-temperature calcination was performed to obtain whisker-like anhydrous magnesium carbonate products. This method avoids the traditional high temperature and high pressure environment treatment, reduces production costs, and the product can be used as a flame retardant in actual production; a hydrothermal treatment process was adopted, with MgCl2 as the magnesium source and urea as the precipitant, sodium citrate and chitosan were added to the hydrothermal system, and three-dimensional flower-shaped products with a particle size of 15um and spherical products with a particle size of 20um were prepared under different conditions.
Overall, the preparation of anhydrous magnesium carbonate is mostly concentrated under high temperature and high pressure conditions, which may be determined by the characteristics of the material itself. Existing preparation studies generally have harsh reaction environments, long reaction times, and large crystal particle sizes. As an inorganic powder material, good dispersibility and uniform fine particle size are important criteria for evaluating product quality. Therefore, one of the important research directions for anhydrous magnesium carbonate is to prepare powders with good dispersibility, uniform particle size and industrial application. In addition, the reaction time should be shortened as much as possible to improve the reaction efficiency. On the other hand, the morphology of inorganic powders often affects their own properties. Therefore, the preparation of inorganic powders with special morphology can expand their application fields in actual production.
In order to solve the shortcomings of the prior art, a method for preparing anhydrous magnesium carbonate with special morphology based on hydrothermal carbonization reaction is provided. The method has simple process and mild conditions, and the prepared anhydrous magnesium carbonate has good dispersibility and diverse morphology. The method for preparing anhydrous magnesium carbonate with special morphology based on hydrothermal carbonization reaction, the steps are as follows:
The initial pH of the aqueous solution is adjusted to 5.5-14.0, magnesium salt is added, and the mixture is placed in a reactor after stirring. The reaction temperature is 120-250°C, the reaction time is 1-12h, and after post-treatment, pure phase anhydrous magnesium carbonate is obtained. The concentration of the aqueous solution is 10-200mg/ml. The magnesium salt is one of magnesium sulfate, magnesium chloride, magnesium hydroxide, magnesium oxide or magnesium acetate. The magnesium salt is added to control the concentration of Mg2+ in the reaction solution to be 0.5-3.0 mol/l. The initial pH value of the ascorbic acid aqueous solution is adjusted with NaOH or KOH. The reaction temperature is 150-250°C.
The process flow is simple, no additional CO2 is required, the conditions are mild, the required equipment is simple and easy to operate. It is energy-saving and efficient, and anhydrous magnesium carbonate with good dispersibility, uniform particle size and diverse morphology can be prepared in a relatively short time.