(662f) A Simulation Study of Mineral Carbonation through Electrolysis of Rejected Brine

Greenhouse gas emissions owing to the relentless burning of fossil fuels have negatively impacted the atmospheric environment. Global warming has caused abnormal phenomena such as ocean acidification, rise in sea levels and extreme climate changes. Among the six major greenhouse gases: carbon dioxide (CO₂), methane(CH₄), nitrous oxide(N₂O), hydrofluorocarbons (HFCs), sulfur hexafluoride(SF₆), perfluorocarbons(PFCs), carbon dioxide has the lowest global warming potential but has the greatest contribution to global warming due to its excessive production.

To build resilience against climate change, Carbon Capture and Utilization (CCU) technology has been employed as a viable solution. Our study proposes the simultaneous treatment process for both wastewater and air pollutant using desalinated rejected brine and their performances are evaluated within the simulated data. The high content of magnesium and calcium ions allows rejected brine to become a stable feedstock in the application of CCU technology.

The electrolysis of desalinated seawater is done to produce sodium hydroxide and is later applied in the carbon dioxide capture and ion separation processes. Throughout the process, above 90% of CO₂ is captured with the alkali absorbent in a form of ionic carbon dioxide such as carbonate and bicarbonate. Metal cations present in seawater rejected brine are extracted via electrolysis and then utilized to regenerate the CO₂-loaded absorbent and produce metal carbonates. Simulations for electrolysis were run in MATLAB2020a while the carbonation process was modeled in ASPEN PLUS simulation tool.

The mineral carbonation process is developed in favor of high metal ion content in the desalinated rejected brine. Using the different solubilities of magnesium and calcium ions at different pH, sodium hydroxide produced via electrolysis is applied in the metal ion separation process via the pH swing method. While magnesium ions precipitate into magnesium hydroxides at pH 11, the calcium ions precipitate into calcium hydroxide at pH 13. The results showed that 99% of calcium and 60% of magnesium recovered from seawater were converted to calcium carbonate and magnesium carbonate. The metal ions are selectively separated in the form of metal hydroxides for a faster reaction rate and higher yield of the final product. While calcium undergoes spontaneous reaction, magnesium ions have a lower conversion yield due to kinetic hindrance present caused by the hydrophilicity of the magnesium ion.

The proposed design process connects our previous studies based on mineral carbonation of carbon dioxide using metal ions present in desalinated rejected brine into the commercialization of the conceptual design. Our research team has previously studied a series of works based on mineral carbonation using desalinated rejected brine to enhance its efficiency with metal ion separation and purification of the final product through speculation study of its morphology. The simulation study has helped in identifying the optimal operating conditions for further scale-up studies. It is expected that our designed process serves as a cornerstone for a step forward in the commercialization of mineral carbonation of carbon dioxide and contributes to mitigation in global warming issues for sustainable development.