Utilizing seawater and brine to simultaneously produce high-purity magnesium sulfate and vaterite-type calcium carbonate

Abstract

Previous studies on the utilization of seawater and brine have focused on either recovering Mg from seawater/brine using alkalis or extracting Ca from industrial byproducts using solvents. Therefore, the present study was aimed at recovering Mg and Ca simultaneously from simulated seawater/brine and slaked lime [Ca(OH)2] using a simple process, with seawater/brine employed both as a Mg source and as a solvent for extracting Ca from the Ca source. Manipulating the concentration of the sucrose additive and the ionic strength of seawater/brine enabled Mg and Ca recovery with high efficiency and purity. The highest Mg recovery from brine was 75 %, and ~ 100 % pure MgSO4 was produced; specifically, ~28 kg of MgSO4•7H2O was produced from 1 ton of brine. The impacts of sucrose concentration and seawater ionic strength on the Ca elution, carbonation efficiency, and size and shape of the resulting vaterite particles were analyzed. The purity of the vaterite produced was 94 %–100 %, and the maximum CaCO3 yield per ton of the Ca(OH)2 was estimated as 770 kg, with a carbonation efficiency of up to 92 %. Therefore, our cost-effective method—featuring the use of seawater/brine and Ca(OH)2—can concurrently produce economically demanding minerals such as MgSO4 and vaterite, thereby facilitating resource conservation.