Accelerated chemical conversion of metal cations dissolved in seawater-based reject brine solution for desalination and CO₂ utilization

A new desalination and carbon utilization method was developed using all of three major cations dissolved in seawater-based industrial wastewater (i.e., calcium, magnesium, and sodium). Here, three types of metal-based inorganic substances could be produced and utilized without additional energy requirements for precipitation reactions. Calcium and magnesium were separated in the form of hydroxide precipitates. Using a 30 wt% aqueous monoethanolamine (MEA) solution, carbon dioxide was captured and reacted with the hydroxides to produce calcium carbonate and magnesium carbonate. After Ca²⁺ and Mg²⁺ separation, sodium chloride was used to produce sodium bicarbonate based on the characteristics of primary alkanolamines mixed with a high concentration of sodium ions. The entire process produced 0.3819, 0.2549, and 0.4579 mol of calcium carbonate, magnesium carbonate, and sodium bicarbonate, respectively. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were conducted to investigate their crystal structure. Moreover, FT-IR spectroscopy was utilized to investigate the ionic species under Na⁺-rich conditions.