Proposing a circular economy for mine tailings: using them as catalysts in the treatment of landfill leachate

Mine tailings (MT), a significant by-product of the mining industry, pose environmental risks due to their metal content and social hazards when they are located near urban areas. However, their mineral composition, rich in feldspars, quartz, phyllosilicates, and TiO₂, offers potential for reuse within a circular economy framework. In this context, this study evaluates the catalytic application of MT in a sonophotocatalytic process to treat mature landfill leachate (LL), a recalcitrant effluent with low biodegradability. Using a full factorial design, the effects of catalyst load, hydrogen peroxide concentration, and pH of the solution on the removal of total organic carbon (TOC), Chemical Oxygen Demand and aromatic compounds (Abs254) of the landfill leachate were assessed. Optimal conditions (2000 mg/L MT, 3000 mg/L H₂O₂, pH 3) led to 29.8 % and 50.2 % removal of TOC and aromatic compounds, respectively. Under these optimized physicochemical conditions applied for 3 h of treatment, the removal of TOC, COD, and aromatic compounds was 84.9 %, 69.6 %, and 88.7 %, respectively.

The biodegradability of treated landfill leachate improved significantly, exceeding 80 % in the Zahn-Wellens test, with no detectable leaching of metals from the catalyst. These findings demonstrate the feasibility of repurposing MT as photocatalysts for landfill leachate treatment, offering a sustainable solution to two pressing waste streams.