Preparation of magnesium hydroxide crystallization kinetics and in situ modification

As an important chemical material, magnesium hydroxide is widely used in medicine, chemical industry, environmental protection, aerospace and food, etc. It is often used as flame retardant for polymer, neutralizer for acidic waste liquid of environmental protection and raw material for magnesium oxide production. Among many applications, magnesium hydroxide is most often used as a flame retardant for polymeric materials, but the prepared magnesium hydroxide flame retardant in China still suffers from uneven particle size distribution, high production cost, high specific surface free energy, and serious agglomeration between particles, resulting in its poor dispersion in organic materials. Therefore, it is a hot spot to explore new methods to produce inorganic flame retardants with good performance of magnesium hydroxide.

In this paper, magnesium hydroxide was prepared by direct liquid-phase precipitation using sodium hydroxide as the base source, magnesium nitrate hexahydrate as the magnesium source, and polyethylene glycol (PEG) as the modifier. The crystallization kinetics of magnesium hydroxide in low concentration solution was investigated by concentration monitoring method. The effects of reaction temperature, initial concentration of raw material, type and amount of modifier on the kinetic parameters during the nucleation and growth of crystals were investigated according to the relationship between the kinetic parameters. The nucleation induction period of the crystallization process under different conditions was investigated by monitoring the changes of conductivity in the solution.

The results showed that the induction period decreased and the nucleation and growth rates increased when the concentration and temperature increased; the higher the amount of polyethylene glycol added, the longer the induction period and the smaller the nucleation and growth rates; the higher the molecular weight of polyethylene glycol, the longer the induction period and the smaller the nucleation rate, and the growth rate tended to decrease and then increase, and the nucleation rate was much larger than the growth rate during the reaction crystallization process.