US8021442: Process for the preparation of common salt of high purity from brines in solar salt pans

The process of the invention is an improvement over the existing process of producing salt of high purity from alum-treated brine disclosed in the prior art. More particularly, the invention rectifies the ratio of Ca2+ to Mg2+ from a value <1 to a value in the range of 2-3 desired by chlor-alkali and soda ash industries. The improved process involves the adjustment of pH of clarified brine with aqueous HCl so as to carry out salt crystallization at a pH of 6.5 instead of at the natural pH of 7. The pH adjustment reduces the Mg2+ impurity in salt while slightly raising the Ca2+ impurity in the salt and thereby achieving the desired ratio.