Magnesium hydroxide production

In neutral and alkaline environments, the magnesium hydroxide product can form a surface film which offers considerable protection to the pure metal or its common alloys. Electron diffraction studies of the film formed ia humid air iadicate that it is amorphous, with the oxidation rate reported to be less than 0.01 /rni/yr. If the humidity level is sufficiently high, so that condensation occurs on the surface of the sample, the amorphous film is found to contain at least some crystalline magnesium hydroxide (bmcite). The crystalline magnesium hydroxide is also protective ia deionized water at room temperature. The aeration of the water has Httie or no measurable effect on the corrosion resistance. However, as the water temperature is iacreased to 100°C, the protective capacity of the film begias to erode, particularly ia the presence of certain cathodic contaminants ia either the metal or the water (121,122). 

Seawater distillation, 15 834, 21 648-650 dispersant applications, 8 688-689 Seawater-dolime magnesium hydroxide production, 15 399... 

Impurities in natural sources can result in poor color, lower retention of physical properties on long-term heat aging, and reduction in electrical properties with the presence of electrolytes. Therefore, fine precipitated ATH and magnesium hydroxide are favored as particle size can be controlled to a nominal 1 pm size with low surface area and they contain very low impurity levels. Magnesium hydroxide production processes, by manufacturer, have considerably more variation than ATH but both metal hydrates are considered products by process, which in many cases results in the need to qualify alternate sources or in some cases to reformulate around filler selection. 

In neutral and alkaline environments the magnesium hydroxide product can form a surface film that offers considerable... 

Calcination of limestone Decomposition of magnesium hydroxide Production of carbon disulfide Chlorination of rutile to titanium tetrachloride Gasification of carbon Decomposition of ammonium chloride Decompositions of ammonium sulfate Mond process for nickel production Oxidation of silicon tetrachloride to silicon dioxide... 

Preparation and Manufacture. Magnesium chloride can be produced in large quantities from (/) camalhte or the end brines of the potash industry (see Potassium compounds) (2) magnesium hydroxide precipitated from seawater (7) by chlorination of magnesium oxide from various sources in the presence of carbon or carbonaceous materials and (4) as a by-product in the manufacture of titanium (see Titaniumand titanium alloys). 

Chemica.1 Properties. The reactivity of magnesium hydroxide is measured primarily by specific surface area in units of /g and median particle size in p.m. Reactivity ranges from low, 1-2 /g, 5 p.m, eg, Kyowa s product to high, 60-80 /g, 5—25 pm, eg, Barcroft s CPS and CPS-UF... 

Calcium chloride in the spent brine includes the residual quantity in the raw brine plus CaCl2 produced in equation 14. Approximately 0.84 kg of by-product calcium chloride are produced per kg of magnesium hydroxide via the brine-dolime process. 

Production and Shipment. Magnesium hydroxide is produced and shipped in aqueous slurry or as dry powder. 

Analytical and Test Methods. Many of the procedures for technical analyses of magnesium hydroxide are readily available from the principal producers. These procedures should be carefully reviewed. Site-specific variations in procedure steps and mechanics, especially for chemical activity, can bias results and inadvertantiy disqualify an otherwise acceptable product. 

Slurry Viscosity. Viscosities of magnesium hydroxide slurries are determined by the Brookfield Viscometer in which viscosity is measured using various combinations of spindles and spindle speeds, or other common methods of viscometry. Viscosity decreases with increasing rate of shear. Fluids, such as magnesium hydroxide slurry, that exhibit this type of rheological behavior are termed pseudoplastic. The viscosities obtained can be correlated with product or process parameters. Details of viscosity deterrnination for slurries are well covered in the Hterature (85,86). 

Uses. The principal use of magnesium hydroxide is in the pulp (qv) and paper (qv) industries (52). The main captive use is in the production of magnesium oxide, chloride, and sulfate. Other uses include ceramics, chemicals, pharmaceuticals, plastics, flame retardants/smoke suppressants, and the expanding environmental markets for wastewater treatment and SO removal from waste gases (87). 

Dead Seas Periclase Ltd., on the Dead Sea in Israel, uses yet another process to produce magnesium oxide. A concentrated magnesium chloride brine processed from the Dead Sea is sprayed into a reactor at about 1700°C (127,128). The brine is thermally decomposed into magnesium oxide and hydrochloric acid. To further process the magnesia, the product is slaked to form magnesium hydroxide which is then washed, filtered, and calcined under controlled conditions to produce a variety of MgO reactivity grades. A summary of MgO purities, for the various processes is given in Table 20. 

The finely divided yellow sulfide polymer formed is then allowed to settle and the reaction liquor is separated by decantation. The product is washed by decantation five times with water and finally filtered by suction. The moist cake of polymer is then air dried. The yield is 988 parts including approximately 75 parts of magnesium hydroxide. 

Example 3. The solubility product of magnesium hydroxide is 3.4 x 10-11 mol3 L 3. Calculate its solubility in grams per L. 

The relative molecular mass of magnesium hydroxide is 58.3. Each mole of magnesium hydroxide, when dissolved, yields 1 mole of magnesium ions and 2 moles of hydroxyl ions. If the solubility is xmolL-1, [Mg2 + ] = x and [OH-] = 2x. Substituting these values in the solubility product expression ... 

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