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 (pCO₂=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 pCO₂≥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.