Production of high-purity MgSO4 from seawater desalination brine

Abstract

In this study, we developed a technology to recover Mg from seawater desalination brine in the form of high-purity MgSO4 that did not contain Ca impurities. The MgSO4 recovery consisted of pre-precipitation of Mg(OH)2 using alkali, concentration of Mg using sulfuric acid, and precipitation of MgSO4 using ethanol. The removal of Ca impurities by adding ethanol twice into the Mg concentrate in the precipitation process was subtle but a highly beneficial novelty. The first dosage of ethanol was added to the Mg concentrate by adjusting the quantity such that only Ca (without Mg) was precipitated in the form of CaSO4. Then, the ethanol was further added to the Ca-free Mg concentrate to precipitate high-purity MgSO4. This two-step ethanol addition ensures effective removal of Ca impurities without Mg loss using the difference in the solubility of CaSO4 and MgSO4 in ethanol. As the purity of the recovered MgSO4 was up to 99.8%, it could be used to re-mineralize fresh water after the seawater desalination process. According to the cost assessment, high-purity MgSO4 produced from seawater desalination brine is expected to be preferred over other products in pharmaceutical and food markets that require high purity and economic feasibility.