Mechanism investigation of food waste compost as a source of passivation agents for inhibiting pyrite oxidation

Pyrite oxidation causes the generation of acid mine drainage (AMD), posing significant challenges in the management of sulfide tailings. Passivation agents such as humic acid have been tested to prevent pyrite oxidation. The potential of using humate rich food waste compost as a source of passivation agents to suppress pyrite oxidation was explored in this study. Batch leaching tests were conducted at room temperature, involved oxidatively leaching a pure pyrite and a pyrite-containing coal refuse sample, respectively, with and without adding the compost at acidic pH. The involved passivation mechanisms were investigated by solution leaching tests and spectroscopic (XPS) and microscopic (SEM) analysis of the pure pyrite sample and its leaching residues. Compared to the control, adding the compost led to the increases in solution pH, removal of the Fe2+/Fe3+ ions from the solutions by adsorption, and remarkable decreases (≥58 %) in sulfur concentration in both samples. Both SEM and XPS analysis indicated that a coating layer was successfully established on pyrite surface after being leached in the presence of the compost. The coating layer comprised a mixture of organic species (e.g., O-CO and N-H/C groups) and phosphate, potentially improving the likelihood of providing antioxidant protection over acidic pH. As a low-cost material, food waste compost can benefit the source control of AMD not only in terms of its surface passivation, but also its intrinsic alkalinity, metal immobilization, and low environmental risk.