According to Beitehu Chemical: Magnesium hydroxide is in the form of white amorphous powder or colorless hexagonal columnar crystals. Soluble in dilute acid and ammonium salt solutions, almost insoluble in water and alcohol. Easily absorbs carbon dioxide in humid environments. When heated to above 200°C in an alkaline solution, it becomes hexagonal crystal. Decomposes into magnesium oxide and water at 230°C. When the temperature is higher than 500℃, it loses water and turns into magnesium oxide. The aqueous solution is alkaline, pH 9.5~10.5.
The production method of magnesium hydroxide is as follows:
1. In industry, seawater and cheap calcium hydroxide solution (milk of lime) are often used. ) reaction to obtain magnesium hydroxide precipitate.
Brine-lime method: The lime milk made from pre-purified and refined brine and digested and deslagging lime is subjected to a precipitation reaction in the sedimentation tank, and the resulting slurry is Add flocculant to the mixture, mix thoroughly, enter the settling tank for separation, and then filter, wash, dry and crush to obtain the finished magnesium hydroxide. The chemical reaction equation is:
MgCl2+Ca(OH)2→CaCl2+Mg(OH)2↓
Brine-ammonia method: remove sulfate and carbon dioxide through purification treatment , brine with a small amount of boron and other impurities as the raw material, and ammonia as the precipitant to carry out the precipitation reaction in the reactor. Before the reaction, a certain amount of seed crystal is put in and stirred thoroughly. The ratio of brine to ammonia is 1: (0.9~0.93), and the temperature is controlled at 40°C. After the reaction is completed, a flocculant is added, and the precipitate is filtered, washed, dried, and pulverized to obtain the finished magnesium hydroxide. The chemical reaction equation is:
MgCl2+2NH3·H2O→Mg(OH)2↓+2NH4Cl
This test method needs to increase the yield, shorten the washing cycle, improve and perfect the production Craftsmanship. Magnesite ore is calcined with anthracite or coke in a vertical kiln using the magnesite-hydrochloric acid-ammonia method to produce magnesium oxide and carbon dioxide. The magnesium chloride solution is prepared by mixing the bitter soil powder into a slurry with water and then reacting with hydrochloric acid of a specified concentration. The magnesium chloride solution reacts with ammonia water of a certain concentration in a reactor, and the product is washed, settled, separated by filtration, dried, and pulverized to obtain magnesium hydroxide product. Surface treatment agents can be added as needed for surface treatment.
2. New process for preparing magnesium hydroxide from dolomite
Calcining dolomite at 950°C for 2.5 hours, digestion ratio 1:40, digestion temperature 70°C, digestion time is 50 minutes; the molar ratio of hydrochloric acid dosage to calcium ions in the first acid leaching is 2:1, and the molar ratio of sulfuric acid dosage to magnesium ions in the second acid leaching is 1:1; pH value of the solution during the precipitation process is 11. Under this process condition, the maximum yield of magnesium hydroxide can be obtained, the total yield reaches more than 85.20%, and flaky magnesium hydroxide with average purity and average dispersion can be obtained. Under the optimized conditions of the carbonization process, the magnesium extraction rate in the calcium and magnesium separation process reaches 90.02%, and the product yield in the magnesium hydroxide preparation process is 88.21%. The selected carbonization temperature is 30°C, and the precipitant is ammonia water, which can obtain better purity. It is a flaky magnesium hydroxide product with good dispersion.
微信扫一扫打赏
