Dynamic Leaching of Iron and Manganese from Coal Gangue under Periodic Infiltration

Abstract

A dynamic column leaching experiment was conducted to characterize the release behavior of Fe and Mn from coal gangue under periodic infiltration. Leachate samples were collected daily for 11 days and analyzed for Fe, Mn, pH, and total dissolved solids (TDS), while scanning electron microscopy (SEM) was used to compare the microstructures of raw and leached gangue. Both metals showed strong early-stage release followed by progressive attenuation. Fe concentration decreased from 387 mg/L on day 1 to 71.5 mg/L on day 6, whereas Mn declined from 24.709 mg/L to 1.70 mg/L over the same period, with a transient rebound on day 3. Meanwhile, pH increased from 5.49 to 7.84 and TDS decreased from 2700 to 444 mg/L, indicating strong coupling between metal release and hydrochemical evolution. SEM observations showed surface roughening, crack development, layer detachment, and improved pore connectivity after leaching, which created more reactive interfaces for mineral dissolution and metal migration. The cumulative release masses reached 388.65 mg for Fe and 23.04 mg for Mn by the end of the test. Kinetic fitting showed that Fe was best described by the Elovich equation (R² = 0.993), whereas Mn was better represented by a polynomial model (R² = 0.929). These results indicate that Fe release was dominated by rapid dissolution of readily available surface-associated phases followed by site depletion, while Mn release was controlled by multiple coupled processes and was more sensitive to changes in the leaching environment.