Sustainable brine management: Unlocking magnesium and calcium for improved carbonation in the modified Solvay process

Abstract

The extensive utilization of Reverse Osmosis (RO) in water desalination has led to the production of high-salinity brine, which poses significant environmental and societal challenges. This study presents an effective approach for the recovery of calcium and magnesium from real local RO brine. This method, serving as the initial step in a multi-treatment process, aims to efficiently manage brine and mitigate CO2 emission. Experimental outcomes demonstrate that a decarbonization pre-treatment, achieved through acidification, utilizes a near-stoichiometric ratio of sodium hydroxide to magnesium (2:1). This process, along with gradual addition of alkaline solution and adequate settling time, effectively removes more than 98 % of magnesium. Additionally, it precipitates high-purity magnesium hydroxide solids with large particles sizes (193.6 µm). In the subsequent soda ash stage, more than 97 % of calcium is successfully removed, yielding calcium carbonate with 95 % purity. Preliminary assessments of revenue generated from these products offer economic justifications for Zero Liquid Discharge implementation. Furthermore, Aspen Plus simulation for the carbonation process using the modified Solvay process revealed the significant benefits of the pretreatment process. This enhances sodium conversion efficiency, improves the production of sodium bicarbonate, and reduces impurities. These findings underscore the importance of Ca2+ and Mg2+ separation steps in improving the carbonation process.