The Formation of Hard-to-Dissolve Matter in Dry Salt

Change of Chemical Composition in Mother Liquor on Surface of Cornmon Salt on Drying (Part 2)

Abstract

We investigated the process of production of hard-to-dissolve matter, which was caused by the decomposition of magnesium chloride hydrate on drying and was formed in dry salt, and the preventive measure of hard-to-dissolve matter.
As the results, magnesium chloride hydroxide(Mg₂(OH)₃Cl·4H₂O, Mg₃(OH)₅Cl·4H₂O)was formed by storing under the moisture absorption environment after heating MgCl₂·6H₂O at high temperature which forms MgOHCl. Calcium carbonate was also formed when the dry salt was stored for a long time. From these results, it was considered that magnesium chloride hydroxlde was resolved by proton from CO₂ absorbed in moisture, and calcium carbonate was formed from Ca dissolved in moisture and CO₃^2-increased by the decomposition. The alkalinity(pH 4.8)of dry salt which did not form magnesium chloride hydroxide and calcium carbonate was under 1mg-eq./kg.
Therefore, it was considered that the production of hard-to-dissolve matter in dry salt was to be prevented by the control of alkalinity in the salt after drying.