Lab‐scale atmospheric CO2 absorption for calcium carbonate precipitation in sand

The microbial‐induced calcite precipitation (MICP) process for ground improvement uses microorganisms to hydrolyze urea, producing carbonate ions to induce in situ calcium carbonate (CaCO3) precipitation in soil to improve its strength. This paper proposes using the hydroxide‐based absorption of CO2 instead to provide the carbonate ion source. This study utilizes direct air capture (DAC) to absorb atmospheric CO2 using potassium hydroxide (KOH) in a semi‐batch bubble absorption column. Potassium carbonate (K2CO3) was then injected into sand with calcium hydroxide (Ca(OH)2 as a calcium source to precipitate CaCO3 and regenerate KOH. Batch and continuous flow precipitation methods produced a poor distribution of CaCO3, with more CaCO3 precipitated on top, resulting in unconfined compressive strength (UCS) of 6.9 to 19.6 kPa. Sand pre‐mixed with Ca(OH)2 gave well distributed CaCO3, precipitated throughout the sample with 7.56 wt% and 6.87 wt% CaCO3 content and UCS of 39.2 and 35.3 kPa before failing for batch and continuous flow precipitation respectively. This differs from MICP strength improvement of 1000 kPa with 5.3 wt% CaCO3 due to poor binding of sand with the precipitated CaCO3 crystals. However, this application provides a stable sequestration source for atmospheric CO2 in soil.