Placing reclamation covers is an effective method to mitigate nitrate (NO 3 ⁻) release from coal gangue. This study considered the impacts of different reclamation covers on the contributions and release of NO 3 ⁻ from explosive and exchangeable NH 4 ⁺ (NH 4 ⁺-ex) sources in coal gangue using column experiments. The δ 18 O-NO 3 ⁻ values were measured to identify the sources of NO 3 ⁻ in coal gangue, and the calibrated and validated hydraulic and solute parameters were used to simulate NO 3 ⁻ release for all treatments (without cover, CK; 30-cm sandy loess, T1; 30-cm Pisha sandstone, T2; 30-cm mixed soil, T3; 15-cm Pisha sandstone overlying 15-cm sandy loess, T4; and 15-cm sandy loess overlying 15-cm Pisha sandstone, T5). Results indicated that SEEP/W and CTRAN/W with optimized parameters accurately simulated water movement and NO 3 ⁻ transport. The contribution of the explosive source was 80, 81, 86, 82, 84, and 84 % and of the NH 4 ⁺-ex source was 20, 19, 14, 18, 16, and 16 % for CK, T1, T2, T3, T4, and T5, respectively. Compared to CK, the five covered treatments reduced total NO 3 ⁻ cumulative mass released from the coal gangue by 5.59, 20.95, 7.41, 14.61, and 14.36 %, respectively. Reclamation covers significantly reduced NO 3 ⁻ release primarily by decreasing NO 3 ⁻ derived from the NH 4 ⁺-ex source, with the most significant effect noted for the 30-cm Pisha sandstone cover. This reduction was attributed to limited oxygen diffusion under the cover, which decreased nitrifying bacterial activity and thus NO₃⁻ production. Future studies should further validate these findings under real-world field conditions through the optimization of model parameters. • Explosive and NH 4 + -ex sources contributed 80 % and 20 % respectively to NO 3 - in coal gangue. • Covers inhibited NO 3 ⁻ release mainly by reducing the contribution of NH 4 + -ex source. • Limited O 2 diffusion under covers decreased nitrifying activity and NO 3 ⁻ production. • Model parameters derived from site-specific data require further field validation.
Liu et al. (Fri,) studied this question.