Mineral sequestration of CO2 using saprolite mine tailings in the presence of alkaline industrial wastes

This study investigate the feasibility of sequestering CO2 via mineral carbonation of calcium-rich alkaline industrial wastes, such as steel slag (SS) and coal fly ash (FA) in acidic mine tailings. Mine tailings are treated with SS and FA at various liquid-to-solid ratios (15 and 30 ml/g) to extract metal components present in FA and SS to supplement the Ca2+ and Mg2+ content of the tailings and to partially neutralize the mine tailings. This remediation step has the benefit of reducing the consumption of neutralizing reagent, such as NaOH, required for pH adjustment to induce mineral carbonation. Compared with FA, it is found that SS with higher MgO and CaO content shows greater neutralizing effect. The ICP-AES analysis of the treated tailing shows its Ca2+ content significantly increased from 111 mg L−1 to 1100 mg L−1; which can proportionally increase the CO2 capture capacity. The highest carbonation efficiencies are observed at carbonation pH of 9 as confirmed by Total Carbon (TC) analyzer and TGA analysis. Mineralogical phase analysis of the carbonated products using TGA-DTG, XRD, and FTIR shows the carbonated solids precipitated at pH 7 and 8 are mainly nesquehonite, while hydromagnesite is the main constituent of carbonates that precipitated at pH 9. The insights from this study direct effort towards sustainable process development focused on remediation of alkaline industrial wastes and the utilization of anthropogenic CO2 emissions.