Preparation background of magnesium carbonate and overview of calcium bicarbonate
The chemical formula of magnesium carbonate is MgCO3·3H2O, and the formula weight is 138.38. Colorless and shiny tiny needle-like crystals with a density of 3.04g/cm3. They form into small balls or clusters and gradually weather in the air. When heated to 100℃, it loses CO2. When boiling this product with water, it also loses carbon dioxide and is insoluble in water. Used in magnesium salt manufacturing, pharmaceutical industry, advanced glass manufacturing, etc. Use basic magnesium carbonate to heat to 150-220℃ and pass in dry carbon dioxide until a white loose powder is formed and reaches a constant weight, and this product is obtained. It exists in nature as magnesite. Colorless to white trigonal rhombohedral crystal. Brittle slabs or powders.
In addition to anhydrate, there are also mono-, tri- and pentahydrates. Trihydrate salt is a colorless orthorhombic needle-shaped crystal, which is easily weathered in the air and has a relative density of 1.850. The commercially available product is a methylpyridine-free aqueous product. The relative density of anhydrate is 3.037. Melting point 550℃ (decomposition). Boiling point 900°C (removes carbon dioxide and turns into magnesium oxide). Almost insoluble in water (0.0106 at 20°C), acetone and ethanol, soluble in acid and carbon dioxide aqueous solution.
Magnesium carbonate is an important inorganic chemical material with good filling, dispersion and flame retardancy. Adding it to engineering plastics can significantly improve the flame retardant properties of engineering plastics. At the same time, it can also be used as refractory materials, insulation materials for boilers and pipes, and in the manufacture of magnesium salts, magnesium oxide, inks, glass, toothpaste, etc. The so-called magnesium carbonate products currently on the market are mostly hydrated basic magnesium carbonate except natural magnesite magnesium carbonate.
Preparation product standards for magnesium carbonate
Preparation and Application of Magnesium Carbonate
Magnesium carbonate can be used as a raw material for the manufacture of magnesium salts, magnesium oxide, glass, and ceramics; used as a bulking agent and alkaline agent for food additives; used as a mineral supplement for feed additives; it can be produced during thermal decomposition Light magnesium oxide can be used in toothpaste, cosmetics, plastics, inks, rubber, fire retardant coatings, perfume powder, etc. It can also be used as an acid suppressor in medicine and a carbon dioxide absorber in spacecraft.
An example of its application is as follows: preparing a heat-insulating refractory castable containing magnesium carbonate. It is composed of the following raw materials: mullite, zirconia fiber, magnesium carbonate, alumina hollow spheres, alumina powder, silica powder, and sodium silicate. Among them, mullite, alumina hollow spheres, and zirconia fiber are bones. Material, magnesium carbonate, alumina powder, silica powder, sodium silicate as the matrix; the weight parts of the above raw materials are: 20 to 30 parts of mullite, 10 to 20 parts of zirconia fiber, 5 to 10 parts of magnesium carbonate , 20 to 25 parts of alumina hollow spheres, 20 to 25 parts of alumina powder, 1 to 5 parts of silica powder, and 1 to 5 parts of sodium silicate.
The alumina hollow balls in the castable aggregate have a special surface structure and are hollow inside. The surface is uneven, which increases the contact specific surface area and makes the aggregate firmly bond with the alumina powder and silica powder in the matrix. It not only improves the fire resistance, but also increases the strength and insulation effect of the material. Magnesium carbonate decomposes under high temperature conditions to produce carbon dioxide gas. The carbon dioxide gas is discharged from the coated castable to form pores in the castable. At the same time, the zirconia fiber can The thermal shock resistance of the castable is guaranteed, and magnesium oxide reacts with aluminum oxide powder to form magnesia-aluminum spinel.
Preparation of magnesium carbonate
Method 1: Mix magnesite (MgCO3) with coke and then roast it to obtain magnesium oxide. After adding water to form a mud, CO2 is introduced to obtain carbonic acid. Magnesium hydride, after filtration, heat the filtrate to obtain alkaline carbonate precipitation.
Method 2: Heat dolomite (MgCO3·CaCO3) over a low fire to decompose only the magnesium carbonate and then pulverize it, then use it under 5 to 6 atmospheres. With the action of water and CO2, magnesium oxide turns into magnesium bicarbonate and dissolves, leaving calcium carbonate, which is obtained by filtering and heating.
Method 3: Dissolve equal amounts of crystallized magnesium sulfate and crystallized sodium carbonate in 10 times the amount of water, heat to 60 ℃ ~ 80 ℃ and mix thoroughly. When CO2 gas is generated, Precipitation occurs at the same time. Filter out the precipitate, mix it with hot water at 70 ℃ ~ 80 ℃, filter again, precipitate, and dry at 50 ℃ ~ 60 ℃ after sufficient washing.
Method 4: Preparation from brine after salt production. Add sulfuric acid to the brine, pass in hydrogen, heat to remove the bromine, then add sodium carbonate, stir, and react. At this time, basic magnesium carbonate precipitates are generated. Filter, wash with water, and then dry above 50°C. Precipitated magnesium carbonate (heavy magnesium carbonate) is produced.
Method 5: A method for producing anhydrous magnesium carbonate by carbonization, including the following steps:
S1: Use magnesium hydroxide and deionized water to prepare a reaction slurry;
S2: Pour the reaction slurry described in step S1 into the carbonization tower, add a phase transfer catalyst into the carbonization tower, and then introduce carbon dioxide gas to perform the carbonization reaction to obtain anhydrous magnesium carbonate slurry; the phase transfer catalyst is Salt solution of soluble metal chloride;
S3: Filter the anhydrous magnesium carbonate slurry described in step S2 to obtain anhydrous magnesium carbonate solid filter cake and filtrate;
S4: Convert any information mentioned in step S3�The solid filter cake of magnesium carbonate is dried to obtain anhydrous magnesium carbonate.
