Using recycled gangue to capture CO2 and prepare alkali-activated backfill paste: Adsorption and microevolution mechanisms

Abstract

Gangue is a type of coal-based solid waste that can be used to prepare mine backfill and CO2 capture materials. However, the CO2 capture ability and activity of gangue are limited by its natural unreactive minerals and dense micro-structure. This study developed a novel chemical modification approach to modify recycled gangue and enhance its CO2 capture and hydration properties. Moreover, a new type of recycled gangue-based backfill paste was prepared to capture CO2. Multiple experiments were conducted to characterize the CO2 capture ability, mineral composition, and specific surface area of the modified gangue, as well as the hydration and microstructure of the alkali-activated modified gangue-based paste (ACM). The results reveal that the CO2 adsorbed ability and compressive strength of ACM can be significantly improved via acetic acid (AA) modification, and the optimum dosage of AA is 2 wt% of the gangue. At this dosage, the CO2 capture ability of gangue reaches 0.30 mmol/g, and the 3 d compressive strength of the ACM is doubled. This is because of the following reasons: 1) AA reacts with kaolinite and muscovite to generate acetate, which increases gangue activity; 2) the modification reduces the particle size and increases the specific surface area of the gangue, both of which are crucial for improving the CO2 capture capacity of the gangue. 3) More gels are generated in ACM, and the dense microstructure contributes to an increase in the compressive strength. This study develops an effective approach to improve the activity and CO2 capture ability of recycled gangue and thus provides guidance for backfill mining, recycled gangue utilization, and CO2 capture.