Messi Biology states that preparing magnesium silicate using magnesium carbonate as the magnesium source is an economically viable process route with excellent product performance. It is particularly suitable for the production of adsorption-type porous magnesium silicate. However, the appropriate reaction method must be chosen, and the calcination temperature and magnesium-to-silicon ratio must be strictly controlled according to the crystal form and specific surface area requirements of the target product.
Magnesium carbonate (MgCO₃) easily decomposes upon heating, starting decarboxylation at around 350°C and completely converting into reactive magnesium oxide and carbon dioxide at around 700°C. Therefore, whether using a dry method or a wet method, the core reaction pathway for magnesium carbonate to participate in the formation of magnesium silicate involves first releasing highly active MgO or Mg²⁺, which then combines with the silicon source (commonly sodium silicate Na₂SiO₃ or quartz SiO₂):
- Dry solid-state reaction: MgCO₃ first decomposes into
MgO, andMgOreacts with SiO₂ at high temperatures to generate forsterite-type magnesium silicate (Mg₂SiO₄). Research shows that when the Mg/Si molar ratio is approximately 2∶1.2 and pre-calcined in air above 1200°C for 3 hours, single-phase Mg₂SiO₄ can be synthesized. After sintering into ceramics at 1280–1340°C for 2 hours, the dielectric constant is about 7.05, and the bulk density is about 3.1g/cm³. - Wet precipitation-hydrothermal reaction: Magnesite (natural MgCO₃) undergoes light-burning, hydration, and carbonation to yield a heavy magnesium water (Mg(HCO₃)₂) solution with a concentration of about 0.3 mol/L, which is then mixed with a 1mol/L sodium silicate solution at a magnesium-to-silicon molar ratio of 1:1.5. The system’s pH is adjusted to 10.0 using CO₂, and the reaction proceeds at 25°C for 65 minutes to obtain amorphous magnesium silicate with a specific surface area as high as 167.3m²/g. Taking the wet method as an example, the process chain is clear and controllable: magnesite
→→hydration→→carbonation to produce heavy magnesium water→→co-precipitation with sodium silicate→→aging→→filtration and washing→→drying (optional low-temperature calcination activation). Researchers systematically compared the effects of hydrothermal conditions on product morphology: under the conditions of a Mg²⁺ concentration of 0.2mol/L, a Si/Mg molar ratio of 3:2, precipitation at 70°C, and hydrothermal treatment at 150°C for 12 hours, three-dimensional flower-ball-shaped porous magnesium silicate with a specific surface area of 539.9m²/g can be prepared. When the calcination temperature rises above 300°C, the porous structure disintegrates into particle aggregates, and the specific surface area plummets. This data clearly highlights the sensitivity of the temperature window.
Magnesium silicate prepared via the magnesium carbonate route performs outstandingly in fields such as adsorption, flame retardancy, and pharmaceutical carriers. Mechanically, the CO₂ released by the decomposition of magnesium carbonate acts as a “pore-forming agent” in the reaction system, which is conducive to the formation of a porous structure coexisting with micro- and meso-pores. Meanwhile, its dissolution and decomposition rates are milder than those of magnesium oxide, avoiding agglomeration caused by local supersaturation and resulting in a more uniform particle size distribution. Adsorption experiments show that the multi-porous magnesium silicate activated by calcination at 200°C has a saturated adsorption capacity for Cu²⁺ of up to 232.25mg/g, which is a 37.7% increase compared to the unactivated sample; the removal rate of free fatty acids in vegetable oil by the sample activated at 300°C reaches 19.3%. In addition, the dry-process product Mg₂SiO₄ is an excellent refractory material candidate due to its high melting point of up to 1890°C and excellent thermal stability.
Overall, magnesium carbonate is one of the ideal magnesium sources for preparing adsorption-type, medical-grade, and cosmetic-grade magnesium silicate. As long as the calcination temperature (avoiding excessive sintering above 300°C), the magnesium-to-silicon ratio (typically in the range of 1∶1.5 to 2∶1.2), and the system pH (preferably 9 to 10) are well controlled, magnesium silicate products with excellent performance can be stably obtained.