Modeling and response surface methodology optimization of reaction parameters for aqueous mineral carbonation by steel slag

CO₂ sequestration via mineralization of steel slag has received widespread attention due to its ability to achieve in-situ CO₂ sequestration in steel industries and high-value utilization of steel slag. The final CO₂ sequestration capacity of steel slag is closely related to the reaction parameters (i.e., reaction duration, reaction temperature, CO₂vol concentration, and liquid-solid ratios) of mineralization. The reaction parameters may have synergistic effects on the ability of steel slag to sequestrate CO₂. Therefore, the single-factor (one-factor-at-a-time) experimental strategy can't obtain optimal process parameters. Herein, response surface methodology and the Box-Behnken Design were employed in determining optimal conditions. It is found that the combined effects of CO₂ concentration in combination with reaction temperature and liquid-solid ratio significantly influence the sequestration process (P = 0.0082 and P < 0.0001, respectively). Conversely, the combined effects of reaction duration with liquid-solid ratio and CO₂ concentration were found to be less significant (P = 0.6905 and P = 0.6114, respectively). The reasons behind this observation can be ascribed to the focus of this research on the later stages of the reaction, during which it proceeds smoothly. Additionally, alterations in temperature, liquid-solid ratio, and CO₂ concentration not only affect the initial pH, CO₂ dissolution rate and quantity, and reaction kinetics but also alter the patterns of their collective impact on CO₂ sequestration. The CO₂ capture could reach 179.1 g-CO₂/kg-steel slag at the optimal condition (i.e., 56.14 °C reaction temperature, 6.66 ml/g liquid-solid ratio, 44.53 wt.% CO₂ concentration, and 286.73 mins reaction time), compared to single-factor stepwise optimization, which improves by about 9.84 %. Implementing this optimized mineralization process could enable the Chinese steel industry to capture an estimated 27.4 million tons of CO₂ annually, based on an annual production of 153 million tons of steel slag.