Modeling and Feasibility Assessment of Mineral Carbonation Based on Biological pH Swing for Atmospheric CO Removal.

Mitigating climate change requires both the reduction of greenhouse gas emissions and the removal of CO from the atmosphere. This study investigates a novel biological pH swing strategy for mineral carbonation at ambient conditions as a potential option for atmospheric CO removal. Through mathematical modeling, we evaluated a mineral carbonation system that utilized and to achieve alternating sulfur reduction and oxidation, respectively, with the cyclic process to effect pH swing for promoting the dissolution of a silicate mineral and the subsequent precipitation of a carbonate mineral to store CO. Sulfur cycles employing two reduced compounds, namely, hydrogen sulfide and thiosulfate, were compared. Our simulation results predicted that it is feasible to use the sulfur cycles to achieve the intended pH swing in a range of 1-10 and hence the acceleration of CO removal from the air. Despite the implementation of the pH swing, gas-liquid mass transfer and mineral dissolution remained rate-limiting compared to biological conversion. Dissolving 35 kg of forsterite in a 1 m reactor takes between 250 and 300 h, leading to the removal of approximately 22 kg of CO through MgCO precipitation, which requires about 180 h. Between the two forms of reduced sulfur, thiosulfate would offer considerable operational advantages over hydrogen sulfide. This theoretical exploration also identified key areas to be investigated to further establish the potential of the sulfur-cycle-based carbonation approach to CO removal.