Degradation of cyanide contaminants in tailing residues by persulfate-based advanced oxidation processes: Coupling effects of alkali and heat

Cyanide tailings (CTs), hazardous solid waste from gold extraction, demand urgent detoxification to mitigate long-term environmental risks. This study develops an advanced oxidation process (AOP) combining persulfate, alkali, and heat (PDS/alkali/heat) that achieves 71.0 % degradation of cyanides (1580 → 458 mg/kg) and reduces cyanide leachability by >98 % (11.7 → 0.2 mg/L), resulting in treated residues exhibiting significantly reduced environmental risk. By optimizing the NaOH:PDS molar ratio to 0.5:1, we resolved the antagonism between alkaline-driven cyanide desorption and OH^--mediated suppression of sulfate radical (SO₄·^-) generation, enabling efficient decomplexation and degradation of metal-cyanide species. Mechanistic investigations confirm SO₄·^--mediated oxidation as the dominant pathway, transforming cyanides into low-toxicity nitrogenous products (e.g., CNO^-, NO₃^-, NH₄⁺) and directly explaining the 50-fold reduction in environmental mobility. The geochemical stability of treated residues ensures safe long-term storage in tailings ponds with minimal groundwater contamination potential. This technology provides a scalable solution for global management of cyanide-contaminated mine waste, reducing threats to freshwater ecosystems.