Abstract: A process for controlling the concentration of aluminum in the brine of a membrane chlor-alkali cell is disclosed wherein the brine has its calcium carbonate settler solids digested in the calcium chloride flow stream by the addition of an inorganic mineral acid to bring the pH to about 2.0 to about 3.0 to solubilize the aluminum in the brine. The brine has the pH adjusted upwardly to reprecipitate the aluminum onto carrier particles and then removes the reprecipitated aluminum and carrier particles from the brine by filtration or centrifugation.

Abstract: A process for purifying an alkali metal halide brine containing aluminum as an impurity which comprises adjusting the pH of the alkali metal halide brine to the range of from about 8.5 to about 9.5 and contacting the alkali metal halide brine with an ion exchange resin having a phosphonic acid group.Using the novel process of the present invention, high purity alkali metal halide brines may be produced for use in electrolytic membrane cells which have concentrations of aluminum reduced to a level which will not cause damage to a cation exchange membrane or affect the membranes ability to transport cations or water molecules.

Abstract: 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.