Removing Sulfate Ions from ED Brine by Reactive Crystallization of Calcium Sulfate with Adding Calcium Chloride

摘要

In Japan, during the salt manufacturing process, electrodialysis (ED) brine is obtained by concentrating seawater via electrodialysis by using ion-exchange membranes. A method that enables the elimination of SO4~(2-) from the ED brine by the reactive crystallization of calcium sulfate (CaSO4) has been developed to utilize ED brine as a raw material in the electrolytic alkali industry and improve the efficiency of the salt manufacturing process by minimizing scale formation during evaporative concentration and crystallization. Powdered calcium chloride (CaCl2) was added to the simulated ED brine containing inorganic ions (Na~+, K~+, Ca~(2+), Mg~(2+), Cl~-, SO4~(2-), and Br ) in concentrations identical to those in the actual ED brine, and CaSO4 was crystallized for 18 days at a reaction temperature of 303 K The concentration of added CaCl2 ((CCaCl2) add) was used as a variable operating parameter, and the effects of CaCl2 addition on the reduction in SO4~(2-) ion concentration in the simulated ED brine were investigated. When (CCaCl2) add was higher than 0.297 mol/L, a decrease in the concentration of SO4~(2-) ions (CSO4) was induced by the crystallization of CaSO4 with increasing reaction time, and CSO4 became approximately constant six days after CaCl2 addition. After six days, CSO4 decreased with increasing (CCaCl2) add; however, the decreasing trend in CSO4 with increasing (CCaCl2) add was less significant when (CCaCl2) add was higher than 1.0 mol/L. When (CCaCl2) add was set to 1.0 mol/L, CSO4 can be reduced to 0.002 mol/L. Thus, the addition of powdered CaCl2 can be considered effective for reducing the SO42~ ion concentration in the ED brine produced during salt production in Japan.