GB621619A - Process for production of magnesium carbonate - Google Patents

Abstract

Solid neutral magnesium carbonate is produced by reacting a hydrous slurry containing calcium and magnesium hydroxides with magnesium bicarbonate to convert at least a substantial part of the calcium to calcium carbonate, subjecting the resulting slurry, preferably after thickening, to controlled carbonation to convert magnesium hydroxide to magnesium carbonate of particle size greater than about 200 microns, and removing the bulk of the magnesium carbonate as an underflow by hydraulic separation. Carbonation, e.g. with flue gas, is controlled so that the rate of conversion of magnesia to carbonate does not exceed 0.03 mols. per litre per hour and that the carbonate and bicarbonate concentration is maintained within the limits of about 0.02 to 0.05 mols. per litre. Dolomite may be calcined, slaked, diluted and classified to remove silica, to produce the original slurry. The overflow containing calcium carbonate and some magnesium carbonate may be rapidly carbonated with 25-30 per cent CO2 flue gas to dissolve all the magnesium as bicarbonate, and the filtrate from calcium carbonate recycled to the main process. The magnesium carbonate may be heated to form basic carbonate or the oxide batch or continuous carbonation with or without seeding may be used. A continuous centrifuge may be used for separation. Specification 595,284 is referred to.