Carbonation curing of magnesium-coal slag solid waste backfill material: Study on properties of flow, mechanics and carbon sequestration

To expedite the achievement of the ''30-60 double carbon'' goal, it is imperative to create a novel, low-carbon, cost-effective, and sustainable backfill material for mining purposes. Against this background, this paper investigates the workability, carbonation performance and carbon sequestration capacity of coal gangue (CG), magnesium slag (MS) and fly ash (FA) as magnesium coal slag solid waste backfill material. The results of the study show that: (1) The rheological properties of the CFM fresh slurry conform to the Herschel-Balkley (H-B) model, and its flowability meets the requirements of mine backfill transport. With increasing MS content, the yield stress, apparent viscosity, thixotropy and shear thickening of CFM fresh slurry increase, and the micro-slump and diffusion diameter decrease. (2) Carbonation curing can effectively improve the early UCS of CFM. The highest UCS of CFM was 8.854 MPa after 7 days of carbonation curing, which was 27.84 times higher than that of standard curing. In addition, the UCS of CFM increased with the increase of curing age and MS content. (3) CFM produces a large number of carbonation products such as calcium carbonate after carbonation curing, which makes its microstructure denser. (4) CFM can absorb up to 14.55% of CO2 after carbonation. (5) The volume stability of CFM is significantly improved after carbonation curing. In summary, CFM is not only a new type of low-cost, low-carbon and sustainable solid waste backfill material, but its practical application in the field of mine backfilling also has great potential for the realisation of magnesium coal slag solid waste resource utilisation and CO2 sequestration.