Hebei Meixi Biotechnology said that anhydrous magnesium carbonate (MGC3) is a single crystal of MGC3 normal salt, which mainly exists in the form of magnesite in nature, and belongs to the calcite structure and trigonal crystal system. Because anhydrous magnesium carbonate has the advantages of high thermal decomposition temperature, large heat absorption, decomposition to produce a large amount of carbon dioxide (CO2), high activity of magnesium oxide (MGO), flame retardant, etc., it has great application prospects in the fields of thermal insulation, high temperature resistance, fire and thermal insulation materials. At the same time, anhydrous magnesium carbonate crystal morphology is diverse, cost-effective, is a multi-functional fine inorganic material, often used as an additive for functional ceramics and carbon anodes and other materials, a template for the synthesis of porous carbon and other hierarchical structure materials, an excellent carrier for drugs and adsorption materials, a refiner for magnesium alloys, and as a catalyst, sintering agent, template agent, inorganic pore agent, etc., which has important industrial application value and has attracted much attention in the field of new materials.
Irregular flower-like and spherical anhydrous magnesium carbonate crystals with an average particle size of 15 20 m were synthesized by hydrothermal reaction at a temperature of 180 m for 24 h at a temperature of 180 m, with magnesium chloride as the magnesium source, urea as the precipitant and sodium citrate as the additive, but only the evolution of the crystal morphology under the action of sodium citrate was preliminarily explained. The slurry prepared with a particle size of 200 300nm magnesium hydroxide is used as the magnesium source, and potassium citrate is used as an additive, at a temperature of 120 150 and a pressure of 03~0.Under the condition of 7MPa, the continuous introduction of CO gas and hydrothermal reaction for 6 h resulted in rhombohedral massive anhydrous magnesium carbonate crystals with an average diameter of 2 4 m, and it was confirmed that potassium ions had a promoting effect on crystal growth, but the raw material particle size was required to be high. Magnesium sulfate, urea, and sodium hydroxide are heated by microwave to obtain anhydrous magnesium carbonate, which can be used to obtain anhydrous magnesium carbonate with regular shape and uniform size in one step.
The rod-shaped magnesium trihydrate (MGC3·3H2O) precursor was synthesized from magnesium chloride hexahydrate and ammonium bicarbonate as raw materials, and anhydrous magnesium carbonate was prepared by hydrothermal reaction of MGC3·3H2O and ammonium chloride (NH, CI) using MGCo·3H2O as raw materials. MgCO3·3Ho is mixed with a mixed solution of water and ethylene glycol, and CO2 is introduced at a temperature of 150 to prepare anhydrous magnesium carbonate, which is simple and easy to operate. Ultrafine MGC3·3HO was prepared by stator or rotor reactor, and hydrothermal reaction was carried out as raw material to obtain anhydrous magnesium carbonate crystals. Magnesium sulfate was prepared from lightly burned magnesite powder and ammonium sulfate solution, and then magnesium sulfate was mixed with ammonium carbonate solution to obtain the intermediate product magnesium ammonium tetrahydrate; Anhydrous magnesium carbonate whiskers were prepared from low-temperature pyrolysis intermediates, and the whole cycle process was adopted, and the product purity was high, but the preparation process was complex. Anhydrous magnesium carbonate powder was prepared by hydrothermal reaction of urea with different magnesium source compounds such as magnesium metal powder, magnesium hydroxide, magnesium chloride and magnesium sulfate at a temperature of 160 for 30 hours, but the reaction time was longer.
At present, the preparation of anhydrous magnesium carbonate crystals at home and abroad is mainly based on soluble magnesium salts and carbonate and other analytical pure chemical reagents as raw materials, which has problems such as high synthesis cost, low economy, and environmental pollution caused by by-products. The preparation of anhydrous magnesium carbonate crystals from natural magnesite minerals has the advantages of wide range of raw materials and low cost, has the potential of industrial amplification and can greatly improve the added value of magnesite minerals. MgCO3·3Ho is a metastable phase in thermodynamics, and is often used as an intermediate product for the production of basic magnesium carbonate (4mgCO3·mg(OH)·4H0). The effects of hydrothermal temperature, hydrothermal time, solid-liquid mass ratio (m(mgCO3·3HO): m(deionized water)) and other conditions on the microscopic morphology and phase composition of the products were analyzed, and the formation mechanism of anhydrous magnesium carbonate assisted by NH4Cl was analyzed.