Feasibility study of net CO₂ sequestration using seawater desalination brine with profitable polyproduction of commodities

We present a profitable pathway from desalination waste brines to negative CO2 emissions. The method, termed ‘brine to bricks’ (BtB), mineralizes CO2 as nesquehonite (MgCO3･3H2O) using the Mg content of brines. Fresh water, gypsum (CaSO4･2H2O), halite (NaCl), mirabilite (Na2SO4･10H2O), sylvite (KCl), and hydrochloric acid are concurrently produced. To prevent ‘carbon leakage’, BtB does not rely on external chemicals, fossil fuel-derived heat and power, or captured CO2. BtB selectively precipitates CaSO4･2H2O, NaCl, and Na2SO4･10H2O by evaporative concentration and temperature-control. The remaining Na⁺ and K⁺ ions are separated as NaCl and KCl from the magnesium chloride slurry by hydrochloric acid-based precipitation. Super-azeotropic hydrochloric acid is regenerated from the slurry using a novel method: low hydration magnesium chloride addition. Purified magnesium chloride is decomposed to amorphous MgO prior to reaction with ambient CO2. The current NET potential of BtB, including the CO2 emissions from desalination, is 136 MtCO2/y. In the current market, BtB can operate at a profitability up to $266/t-CO2, dependent primarily on the availability of waste heat and the local performance of renewable energy. Based on current desalination adoption projections, BtB could remove 0.350-1.784 GtCO2/y by 2050 while providing substantial increases in fresh water, construction materials, and chemicals that are of use to other negative emission technologies.