GB1007354A - Production of magnesium hydroxide - Google Patents

Abstract

Magnesium hydroxide is prepared by simultaneously introducing an aqueous magnesium chloride solution and a dolime slurry, which is made by slaking calcined dolomite with aqueous calcium chloride solution, into a reaction zone at a temperature below the boiling point of the aqueous solution in proportions to provide therein more than one mole of calcium hydroxide per mole of magnesium chloride. The reaction may be effected at 40 DEG to 80 DEG C. and in a continuous manner. Calcined dolomite may be staked in aqueous calcium chloride solution of specific gravity at 25 DEG C. of 1.07 or more. At least 90 wt. per cent of the particles in the slurry may be less than 0.84 mm. in diameter and the slurry may be introduced into the reactor within 90 minutes after staking. Magnesium chloride solutions of less than 3.5 wt. per cent may be added to the reactor at a rate to provide an average residence therein of at least 3 hours, whereas solutions of more than 3.5 wt. per cent may be added at a rate to provide an average residence therein of at least 2 hours. Part of the mixture leaving the reactor may be recycled to the slaker and magnesium hydroxide may be removed therefrom by sedimentation or filtration prior to recycling. The filtrate may be evaporated to recover dissolved salts, e.g. CaCl2 and the product, after water washing, may be ignited to form periclase.