Gypsum crystallization and potassium chloride regeneration by reaction of calcium chloride solution with potassium sulfate solution or solid

Abstract

Abstract Gypsum crystallization along with the simultaneous regeneration of KCl was investigated by the reaction of CaCl 2 solution with K 2SO 4. Well developed sheet structure gypsum crystals were produced when K 2SO 4 solution was added into the CaCl 2 solution by slow titration or in multiple stages over 2–8 h followed by 2 h equilibration. In order to regenerate KCl solution as concentrated as possible, K 2SO 4 solid was added into the given CaCl 2 solution instead of K 2SO 4 solution, obtaining gypsum crystals with almost the same quality by multistage addition with [SO 4 2–]/[Ca 2+] molar ratio no larger than 0.8. However, impurity of K 2SO 4·CaSO 4·H 2O was detected by XRD and was further confirmed by SEM-EDS in the produced crystals when the [SO 4 2–]/[Ca 2+] ratio increased to 1.1. It is proved that appearance of the double sulfate is attributed to the relatively high concentration of K 2SO 4. So, it is essential to properly control the [SO 4 2–]/[Ca 2+] ratio and make sure [Ca 2+] in excess to suppress the solubility of CaSO 4 even at the expense of low calcium removal rate.