Strategies to control product characteristics in simultaneous crystallization of NaCl and KCl from aqueous solution

Abstract

In this work we developed an approach for the simultaneous crystallization of NaCl and KCl from their aqueous solution by concomitantly seeding both salts. Experiments were designed based on the ternary system phase diagram. The mother liquor concentration was chosen near the eutonic condition at its boiling temperature. The seeds for each compound had different sizes but the amounts were calculated to provide nearly equal surface areas for each material. Elementary phenomena were assessed and the chemical composition in different particle size ranges within the products was analysed. Despite the presence of seeds from each component in the suspension under crystallization, the formation of mixed composition polycrystalline particles was observed. A seeding protocol involving much larger KCl than NaCl seeds resulted in an easily separable product with two distinct populations. In general, segregation of the salts through the size ranges followed the trend induced by seeding, highlighting the possibility of retrieving relatively pure solid fractions of each salt.