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Preparation of magnesium hydroxide


(A): the industry often seawater and inexpensive solution of calcium hydroxide (lime) reaction, can be obtained magnesium hydroxide precipitate.

Brine a lime method previously purified brine digested slag lime lime treatment made from refined processing and precipitation reaction in the precipitation tank after adding flocculant, mixing the slurry obtained into the settling tank separation, and then filtered, washed, dried, pulverized to obtain a magnesium hydroxide products. The chemical reaction equation is:

MgCl2 + Ca (OH) 2 → CaCl2 + Mg (OH) 2 ↓

Brine - ammonia method with purified brine treatment to remove sulphate, carbon dioxide and a small amount of boron impurities such as raw materials and ammonia precipitation as a precipitating agent in a reaction vessel, prior to the reaction a certain amount of investment in the seed mixture was stirred sufficiently. The ratio of brine and ammonia is 1: (0.9 to 0.93), the temperature control at 40 ℃. After completion of the reaction flocculant added, the precipitate was filtered, washed, dried and pulverized to obtain a magnesium hydroxide product. The chemical reaction equation is:

MgCl2 + 2NH3 · H2O → Mg (OH) 2 ↓ + 2NH4Cl

The test methods to be improved yields, shorter wash cycle, improve and perfect the production process. Magnesite - hydrochloric acid - ammonia method magnesite and anthracite or coke in a shaft kiln calcination to produce magnesium oxide and carbon dioxide. Kutu powder slurried with water after the reaction of magnesium chloride solution with a predetermined concentration of hydrochloric acid. Its magnesium chloride solution with a concentration of ammonia in a reaction vessel, the resultant was washed, sedimentation, was isolated by filtration, dried and pulverized to obtain a magnesium hydroxide product. May be added as necessary surface treatment agent subjected to surface treatment.

Magnesium hydroxide is a good prospect of polymer matrix composites retardant inorganic filler. Like with aluminum hydroxide, magnesium hydroxide flame retardant chemical decomposition when heated to rely on absorbing and releasing water and play a flame retardant, it has a non-toxic, stable chemical properties of magnesium oxide and decomposes after a low-smoke, non- secondary pollution. However, compared with a halogen-containing organic flame retardant, flame retardant to achieve a considerable effect, fill level generally above 50%. Since magnesium is inorganic, surface and polymer binder poor compatibility, such a high filler content, if not its surface modification, after filling the polymer material, the composite result The mechanical properties decrease. Therefore, it must be surface modification to improve its compatibility with the polymer matrix material, so that the mechanical properties of the filler material does not drop, even the mechanical properties of some materials has increased.

Experiments show that the unmodified PP magnesium hydroxide in the form of aggregates exist, although the powder itself is fine, but because of the particle surface and PP matrix incompatibility exists between particle aggregates and PP matrix obvious limit or even empty. Due to brittle fracture when empty after the escape of magnesium hydroxide particles formed, indicating that unmodified magnesium hydroxide fire retardant padding just to play a role in the PP, and PP without chemical bonding. Surface-modified magnesium hydroxide dispersed in PP matrix, mostly in the form of primary particles-particles or small aggregates of particles dispersed in the material.

(B): Preparation of magnesium dolomite new technology, dolomite calcined at 950 ℃ 2.5 hours 1:40 digestion, digestion temperature of 70 ℃, the digestion time is 50mins; when once the amount of hydrochloric acid leaching of calcium ions Moore ratio of 2 to 1 molar ratio of twice the amount of acid leaching with sulfuric acid when the magnesium ions is 1 to 1; pH of the solution was 11 during precipitation. In this process conditions can be obtained magnesium hydroxide maximum yield, total yield of more than 85.20%, and the purity in general, the dispersion is generally flaky magnesium hydroxide. Carbonization process in the most optimal conditions, the extraction rate of magnesium, calcium and magnesium separation process reaches 90.02%, magnesium hydroxide preparation process product yield 88.21%, selected carbonization temperature 30 ℃, the precipitation agent is ammonia, can be better purity, good dispersion, and a sheet of magnesium hydroxide products. [4]


Magnesium hydroxide note:

Because magnesium hydroxide and alkali genus, the eyes, respiratory system and skin are irritating. It should be used to do the appropriate protection, gloves or goggles, after accidental contact with eyes, rinse immediately with plenty of water and seek medical advice.

Acute toxicity: oral, LD50 = 8500mg / kg (rat)

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