Abstract
Improving the efficiency of evaporative crystallization for salt production is expected to enhance not only salt production in Japan but also freshwater production. In this study, evaporative crystallization under high suspension density conditions was investigated. The relationships among agglomeration level, crystal growth, and NaCl crystal purity were examined in terms of the effects of coexisting ion concentration and suspension density, which influence supersaturation. This study focuses on coexisting potassium and magnesium ions as the major ions present in seawater, and these relationships were investigated experimentally. During the investigation, a method was developed to estimate the level of agglomeration through image analysis. The focus was on water content as an indicator of purity, based on the assumption that mother liquor is incorporated during agglomeration. The results clarified two main findings. First, the concentration ratio of coexisting ions affected the bulkiness of agglomerates, which in turn influenced the water content. Second, even at high suspension densities, specific impurity-ion concentration conditions were identified under which agglomeration and increased water content were not promoted, while crystal growth was neither suppressed nor associated with enhanced mother-liquor incorporation. These insights offer practical operational guidelines for evaporative crystallization in salt production.
