Process for preparing high-purity magnesium hydroxide by ammonia method using brine.

MgCl₂+2NH₃・H₂O==2NH4CI+Mg(OH)₂

The magnesium hydroxide product obtained by this method has a relatively high purity and is suitable for preparing high-purity magnesia. In the preparation of magnesium hydroxide flame retardant products, the particle size distribution of the obtained magnesium hydroxide product is relatively wide, while the yield is relatively low. Moreover, due to the strong volatility of ammonia water, the operating environment is relatively harsh, and there are yield and environmental protection issues.

Although this method has the above problems, it can obtain magnesium hydroxide products with relatively high purity, and the mother liquor of the obtained product can be recycled. To prepare high-purity magnesium hydroxide by this method, further research must be strengthened on issues such as the sedimentation conditions of magnesium hydroxide, hydration treatment technology, the yield of magnesium ions, and the operating environment of the production workshop. This method is a very promising method and is suitable for preparing flame retardant magnesium hydroxide products from brines with high magnesium content.

Using brine and bittern blocks as raw materials, a magnesium hydroxide flame retardant is prepared by a two-step method, namely ammonia precipitation-hydrothermal treatment process. The flame retardant magnesium hydroxide product prepared by the two-step method is hexagonal flake, relatively thin, with good dispersion, an average particle size of 200nm product, and high purity.

For preparing magnesium hydroxide flame retardant by ammonia method-hydrothermal reaction method, the magnesium hydroxide synthesized at room temperature by ammonia water method is modified by hydrothermal treatment. The particles are transformed from an irregular amorphous structure to a regular hexagonal flake structure, and the particle size distribution tends to be uniform, the particle size obviously grows, and the average particle size is about between 0.35μm and 0.6μm. The specific surface area is greatly reduced. Moreover, prolonging the hydrothermal time significantly reduces the proportion of small particle sizes, the particle size distribution becomes more uniform, the particle size increases, and the hexagonal flakes thicken and the specific surface area decreases.