Inhibitory effects and mechanisms of smoldering combustion-derived biochar covers on pyrite oxidation and acid mine drainage formation.

The oxidation of sulfur-bearing minerals, particularly pyrite (FeS2), generates acid mine drainage (AMD) with low pH and high trace element concentrations, posing a significant global environmental challenge. To address the high cost and limited long-term effectiveness of conventional AMD source control methods, this study introduces an innovative strategy using smoldering-derived biochar as a pyrite cover material. The biochar was produced through a cost-effective, low-temperature smoldering combustion process. Besides, leaching experiments were conducted at room temperature (13-26 °C) to investigate the effectiveness of biochar-containing alkaline compounds and a multistage pore structure-as a cover layer for inhibiting pyrite oxidation. The results revealed that the inherent alkalinity of biochar neutralized acidic intermediates and promoted jarosite formation. Additionally, the 15 cm biochar cover increased the leachate pH, reduced redox potential, and suppressed trace element leaching, achieving reductions of 18.66 % for Fe, 61.87 % for Cu, and 41.66 % for Zn. The mechanism by which the biochar cover inhibited pyrite oxidation was extensively investigated via multiple characterization methods, and the analysis results revealed that the jarosite passivation layer and biochar pore barriers synergistically enhanced the long-term stability of oxidation inhibition and suppressed AMD formation at the pyrite surface. Our study proved that smoldering combustion-derived biochar exhibits strong potential as a cost-effective passivation cover for AMD source control under actual environmental conditions.