Dynamic leaching behaviors of heavy metals from recycled coal gangue aggregate under loading conditions during solid backfill mining☆

In solid backfill coal mining, recycled coal gangue aggregate (RCGA) is subject to the combined effects of overlying strata stress and leaching by mine water in the goaf. This process causes heavy metals to be leached and released from RCGA, which can lead to groundwater contamination. In this study, the release patterns of heavy metals in RCGA under the coupled effects of stress, solution pH, and solution flow rate were investigated, and the interactions between RCGA and the surrounding environment were explored. The findings indicate that: (1) The combined action of effective stress and mine water promotes the leaching of heavy metals. Specifically, the leaching of Pb, Zn, and Mn of RCGA is primarily influenced by the pH value of the leaching solution, while the leaching of Cu and Cr of RCGA is more closely related to the stress level; (2) Acidic environments accelerate the release of carbonate-bound fraction (CAR) in elements, facilitating the transformation of Fe/Mn oxide-bound fraction (XXI) into soluble forms; (3) The leaching ratios (Lr) of heavy metals follow the order: L-rZn > L-rPb > L-rMn > L-rCu > L-rCr. This research provides guidance for the safe application of RCGA in solid backfill coal mining.