Regulating water-salt transport in subsided soil reclamation: The mechanism of calcination-acid leaching activated coal gangue

Abstract

Gangue discharge and accumulation cause serious environmental issues. Activating gangue for subsided soil reclamation aids disposal and resource use. To address this, we used a 'calcination-acid leaching' activation method. XRD, FTIR, BET, and SEM-EDS assessed mineral changes, pore structure, and available silicon in calcined-acid-leached coal gangue (CA-CG) across different calcination temperatures and acid concentrations. Furthermore, soil column experiments measured water and salt transport, varying fly ash-to-gangue ratios, isolation layer thicknesses, and reclamation structures. Notably, at 700 °C, kaolinite completely dehydroxylates to metakaolinite, boosting silicon-aluminum reactivity. With 5 % acid leaching, amorphous silicon reacts rapidly with hydrogen ions, yielding 103 mg/kg accessible silicon. At this acid level, the CA-CG surface area was 28.81 % higher than at 1 % acid. As the ash-to-coal ratio increases, the water retention coefficient R first increases, then drops. Moreover, double-layer structures improve bottom desalination and reduce surface salt during evaporation. They resist upward ion migration better than single-layer structures. Finally, the control order for ion migration is: SO₄²⁻, Ca²⁺, Na⁺, Cl⁻.