Sequential carbonate mineralization of desalination brine for CO2 emission reduction

Desalination brine is a potential source for CO2 mineralization aimed at reducing CO2 emissions, because the concentration of Ca and Mg in brine is almost twice that of ordinary seawater. However, the previously achieved conversion ratio of CO2 to carbonate minerals is too low for commercial application, as Ca and Mg compete and interfere with each other during precipitation. In this study, we tested the separate and sequential mineralization of Ca and Mg in brine, enhancing the CO2 conversion ratio to 57% from 12%. We also tested the use of 15% CO2 gas (the typical concentration of actual combustion gas), and it was observed that 69% of injected CO2 was precipitated as Ca and Mg carbonate minerals and 99% of Ca and 69% of Mg in the initial brine were precipitated. In addition, the volume of NaOH solution required was reduced by 76%. This revised method is more material- and reagent-efficient which would likely have lower operation costs; moreover, as no further additives are required, environmental impact of brine release is also likely to be reduced. The findings of this study can help address environmental problems caused by large seawater desalination plants and thermal power plants.