Effect and mechanism of steel slag composition on CO2 fixation rate under microbial and non-microbial

In this study, we used microorganisms and steel slag to reduce CO₂ emissions. The main objective is to investigate the influence and mechanisms of CO₂ fixation rate based on the composition of steel slag. In the absence of microorganisms, steel slag powders with higher C₂S content exhibit higher CO₂ fixation rate. The absolute content of C₂S decreases by 2.16–5.86 % and 3.43–14.21 % at 2 h and 48 h of carbon sequestration reaction, respectively. Under the action of microorganisms, the CO₂ fixation rate of different steel slags increases by more than two-fold, with increases in amount of CO₂ fixation at 2 h and 48 h of reaction being 142–169 % and 166–191 %, respectively. Microorganisms can enhance the reaction degree of C₂S, C₃S, and C₂F phases in different steel slags. The increase in amount of CO₂ fixation is particularly significant for steel slag powders with high C₂S and C₂F content. Enzymes secreted by microorganisms in the early stage of carbon sequestration can also increase the concentration of HCO₃^- and CO₃^2- in the liquid phase, but this is influenced by the pH value and Ca²⁺ concentration of different steel slag leachates. Steel slag powders with lower leachate pH values and containing small amounts of Ca²⁺ will be more conducive to microorganisms enhancing the early-stage CO₂ fixation rate.