GB595284A - Process for production of magnesium carbonate - Google Patents

Abstract

Magnesium carbonate MgCO3 3H2O (of 200 micron or greater particle size) is produced by carbonating a slurry containing magnesium oxide and/or hydroxide under controlled conditions so that the rate of conversion into neutral MgCO3 is not in excess of 0.12 mols per gallon per hour and separating from the other material. The process may be applied to calcined dolomite, magnesite, brucite, serpentine, to carbothermic magnesium process residues containing unreacted magnesia and carbon, or to magnesia precipitated from brines with lime or calcined dolomite. The brine may be pretreated with lime to precipitate calcium bicarbonate as carbonate and some magnesium as hydroxide, which is processed as above, and the residual brine treated with lime or calcined dolomite to precipitate further magnesium hydroxide. When the slurry contains calcium as well as magnesium it may be treated prior to carbonation with sodium or potassium carbonate to convert the calcium to carbonate. The magnesium carbonate produced may after separation be reacted with sodium hydroxide produced from the sodium carbonate, and the resulting magnesium hydroxide, after washing, treated by the process of the invention. Alternatively the calcium may be leached out with water. When the calcined dolomite is granular, the slurry after pretreatment with sodium carbonate may be submitted to preliminary classification to a fine overflow fraction, which is treated by the process of the invention, and a coarse underflow fraction which is converted by fast carbonation to small size magnesium carbonate, which after separation from other material is added to the large carbonate crystals produced by the main process. The combined carbonates may be treated with sodium hydroxide and the magnesium hydroxide produced carbonated by the main process. Batch or continuous processes may be used for the main carbonation. Flue gas may be used. The total CO3 + HCO3 ion concentration should be kept between 0.02 and 0.05 mol/litre. The solids concentration of the slurry may be 0.5-1.5 mols/litre. A retention period of 36-48 hours is desirable at 10-30 DEG C. Hydraulic or centrifugal separation or classification methods may be used. The hydrated carbonate may be converted to basic carbonate or oxide. Specifications 467,543 and 554,760 and U.S.A. Specification 734,030/03 are referred to.ALSO:In a cyclic carbothermic magnesium process, the residues containing unreacted magnesia and carbon are recycled to the slurry of magnesium oxide and/or hydroxide, made, e.g. from calcined dolomite or magnesite, which is then carbonated under controlled conditions so that the rate of conversion into neutral MgCo33H2O is not in excess of 0.12 mols. per gallon per hour, and the large-sized magnesium carbonate produced separated from the other material, calcined to magnesia, briquetted with carbon and submitted to the carbothermic process to produce magnesium. Batch or continuous processes may be used for the main carbonation. Flue gas may be used. The total CO3+HCO3 ion concentration should be kept between 0.02 and 0.05 mol./litre. The solids concentration of the slurry may be 0.5-1.5 mols. per litre. A retention period of 36-48 hours is desirable at 10-30 DEG C. Hydraulic or centrifugal separation or classification methods may be used. Specifications 467,543 and 554,760, [Group III], and U.S.A. Specification 734,030/03 are referred to.