Preparation activated tailings by pH swing process: Towards yielding cemented tailings backfill and in-situ CO2 mineralization

In-situ CO₂ mineralization of tailings holds great potential for large-scale CO₂ sequestration, but its development is seriously limited by the low CO₂ conversion rate. This study proposed an innovative pH swing process to produce activated tailings through magnesium extraction from raw tailings and subsequent leachate precipitation. By the combination of activated tailings and high-belite calcium sulfoaluminate cement, a new type of cemented activated tailings backfill (CATB) was developed. The results demonstrate that 82.33 % of magnesium is extracted from raw tailings and precipitates in the form of Mg(OH)₂ serving as the dominating carbonation active phase during the pH swing process. Besides the aragonite forms in the carbonated cemented raw tailings backfill (CRTB), carbonated CATB also contains calcite, nesquehonite, and hydromagnesite. Substituting activated tailings for raw tailings results in a higher CO₂ absorption capability (ranging from 8.88 % to 14.17 % with various binder-to-tailings ratios). These indicate that the activated tailings have a promising application scenario in large scale in-situ CO₂ mineralization.