Abstract: Isobutyl xanthate is a representative organic pollutant in mineral processing wastewater. Conventional treatment methods exhibit low degradation efficiency and may lead to secondary pollution. While photocatalytic technology effectively degrades pollutants, its implementation is constrained by the difficult recovery of nanocatalysts. Additionally, conventional magnetic supports require complex preparation processes and involve high costs. In this study, the magnetic γ-Fe₂O₃@SiO₂/BiOI (FSB) nanocomposites were synthesized by encapsulating natural magnetic hematite with a SiO₂ layer, followed by combining with BiOI. Photocatalytic degradation of isobutyl xanthate using FSB was evaluated, and the mechanisms behind the degradation of isobutyl xanthate were explored. The results indicate that within 90 minutes, the FSB composite material achieved a degradation efficiency of 99.22% for 100 mg/L of isobutyl xanthate with a Chemical Oxygen Demand (COD) removal rate of 76.04% and a Total Organic Carbon (TOC) removal of 52.29% within 90 min. FSB exhibited excellent stability and reusability, maintaining a stable degradation efficiency of 92.34% for isobutyl xanthate after 5 cycles, with a magnetic recovery rate of up to 82.41%. The sacrificial agent experiments and ESR tests confirmed that ∙O²⁻ is the dominant active radical responsible for the degradation of isobutyl xanthate. Furthermore, the reaction mechanism was elucidated through DFT calculations. This study not only provides an efficient and environmentally friendly strategy for treating xanthate wastewater, but also offers important theoretical and practical insights for developing novel photocatalysts based on natural magnetic materials. The developed technology demonstrates promising potential to treat industrial wastewater from the mineral processing sector.