The efficient treatment of mineral-processing wastewater has attracted soaring interest recently. This study’s objective was to degrade xanthate from flotation tailings wastewater using a pyrite-catalyzed Fenton system. A sodium butyl xanthate (SBX) removal rate of more than 96% was achieved via the method under optimal conditions (a H₂O₂ concentration of 0.5 mM, a FeS₂ concentration of 0.5 g/L, an initial SBX concentration of 100 mg/L, and a natural pH of 9.36 ± 0.5), which is 12.85% higher than with a H₂O₂ system. An appropriate concentration of natural pyrite can act as a catalyst to significantly improve the oxidation capacity of H₂O₂. Additionally, the results of electron paramagnetic resonance and quenching measurements suggest that hydroxyl radicals (•OH) are the main active species in the H₂O₂-FeS₂ system. The possible reaction mechanism is proposed. The H₂O₂ adsorbs onto the pyrite surfaces and reacts with Fe²⁺, triggering the formation of •OH and Fe³⁺. The •OH most likely attacks the SBX that adsorbs on the pyrite surface or exists in the solution and promotes the transformation of the SBX anion (C₄H₉OCS₂⁻) into the intermediate butyl xanthate peroxide (BPX, C₄H₉OCS₂O⁻). Finally, BPX intermediates are likely further oxidized to smaller products such as SO₄²⁻, CO₂, and H₂O under the ongoing attack of •OH.

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