Ion Exchange Processes for CO₂ Mineralization Using Industrial Waste Streams: Pilot Plant Demonstration and Life Cycle Assessment

An attractive technique for removing CO2 from the environment is sequestration within stable carbonate solids (e. g., calcite). However, continuous addition of alkalinity is required to achieve favorable conditions for carbonate precipitation (pH>8) from aqueous streams containing dissolved CO2 (pH<4.5) and Ca2+ ions. In this study, a pH-swing process using ion exchange was demonstrated to process 300 L of produced water brine per day for CO2 mineralization. Proton titration capacities were quantified for aqueous streams in equilibrium with gas streams at various concentrations of CO2 (pCO(2)=0.03-0.20 atm) and at various flow rates (0.5-2.0 L min(-1)). Energy intensities for the process were determined to be between 30 and 65 kWh per tonne of CO2 sequestered depending on the composition of the brine stream. A life cycle assessment was performed to analyze the net carbon emissions of the technology which indicated a net CO2 reduction for pCO(2)>= 0.12 atm (-0.06--0.39 kg CO2e per kg precipitated CaCO3) utilizing calcium-rich brines. The results from this study indicate the ion exchange process can be used as a scalable method to provide alkalinity necessary for the capture and storage of CO2 in Ca-rich waste streams.