Inducing the formation of organic-inorganic carbonated composites via extracellular polymeric substances (EPS)-modified carbonation in low-calcium CO2 sequestration materials

Extracellular polymeric substances (EPS), mainly composed of polysaccharides and proteins, are high-molecular compounds secreted during the metabolic process of bacteria. This study primarily examined the modification effects and influencing factors of EPS on the carbonation of low-calcium CO₂ sequestration materials. The results indicate that EPS significantly enhanced the compressive strength of carbonated samples, from 2.21 MPa to 32.90 MPa, as well as the carbonation degree from 4.44 wt.% to 11.51 wt.%. Acidic amino acids in EPS can not only promote the leaching of Ca²⁺, but also adsorb free water in the system. Consequently, EPS may provide more nucleation sites, inducing the in-situ generation of amorphous calcium carbonate (ACC), and thus organic-inorganic carbonated composites were formed eventually, which improved the pore structure and carbonation degree of samples. The application of EPS has overcome the influence of unstable enzyme activity during the traditional microbial carbonation, achieving better and more stable carbonation effects.