Scale-free process for purifying concentrated alkali metal halide brines containing sulfate ions as an impurity

摘要

A process for reducing sulfate ion concentrations in an alkali metal halide brine to be electrolyzed in an electrolytic cell comprises feeding the alkali metal halide brines to a reaction zone containing a slurry of gypsum crystals having a concentration of at least 5 weight percent of solids to form a brine-containing slurry. An aqueous solution of a brine soluble calcium salt is admixed with the brine-containing slurry in an amount sufficient to reduce the sulfate ion concentration to a desired level. The brine-containing slurry is agitated at a pumping velocity of at least about 1.0 meters per second to release solution supersaturation by gypsum crystal formation. A desulfated alkali metal halide brine having a reduced sulfate ion concentration is passed from the reaction zone to a settling zone, the residence time in the reaction zone being at least 30 minutes, the settling zone residence time based on rise rate to prevent crystal carryover being at least 10 feet per hour, and the desulfated alkali metal halide brine recovered.