Adsorption-catalytic synergistic Fenton degradation of potassium butyl xanthate in flotation tailing wastewater by renewable iron-loaded sludge: performance, kinetics and mechanism

The renewable iron-loaded residual sludge heterogeneous catalyst (RLS-Fe) was prepared by impregnation-pyrolysis method and applied to the heterogeneous Fenton for the degradation of potassium butyl xanthate (BX-K) in flotation tailing wastewater. The rich pore structure and uniformly distributed iron oxides endowed the catalyst with excellent adsorption and catalytic capabilities. RLS-Fe exhibited maximum adsorption capacity of 86.47 mg/g, with surface concentration (C_s) of 2.88 mg/cm² and surface coverage (θ) exceeding 80 %. The interaction of monolayer-adsorbed BX-K with catalytically generated ·OH facilitated the Fenton reaction and enhanced the adsorption process, making the degradation and mineralization of BX-K more efficient, with the removal rate of 99.82 % in 80 min. Through the synergistic effects of adsorption and catalytic processes, H₂O₂ was efficiently decomposed and effectively utilized. The ·OH generated in the initial stage rapidly degraded the adsorbed BX-K and released the adsorption sites, while the ·O₂^– produced subsequently targeted the catalytic sites and restored their activity. The Langmuir-Hinshelwood (L-H) kinetic model confirmed that the mutual promotion of adsorption and catalysis elevated the apparent reaction rate constant and accelerated the mineralization of BX-K. Additionally, density functional theory (DFT), Fukui indices and Gibbs free energy calculations were employed to analyze the intermediates and degradation pathways of BX-K. The −C=S– bond was identified as the primary target for ·OH attack. The RLS-Fe catalyst prepared in this study presented excellent stability and renewability, offering new insights for the streamlined preparation of renewable catalysts and efficient treatment of tailings wastewater.