<p>ZnFe₂O₄ photocatalysts, known for narrow band gap, stable photochemical properties, and non-toxic composition, show great potential in the degradation of pollutants. In this study, spinel ZnFe₂O₄ nanoparticles were synthesized via a co-precipitation method, using blast-furnace slag from steelworks serving as the raw material, highlighting the value of industrial waste recycling. The optimal synthesis conditions for ZnFe₂O₄ were determined based on the photocatalytic degradation efficiency of Rhodamine B (Rh B). Subsequently, the optimized ZnFe₂O₄ nanoparticles were employed for the photocatalytic degradation of phenol in simulated wastewater. The results indicate that the photocatalytic performance of ZnFe₂O₄ nanoparticles, obtained by calcination at 650&#xa0;°C for 2&#xa0;h under the condition of a mass ratio of acid solution to blast-furnace slag of 9:1 and a reaction time of 8&#xa0;h, is superior. Under strong acidic conditions (pH = 1), the photocatalytic degradation rate of phenol reached 97.7% within 2&#xa0;h. After five consecutive cycles, the material exhibited excellent photochemical stability, preserving its structural and functional integrity. Furthermore, the photocatalytic degradation efficiency of phenol was found to be 72.0% within 2&#xa0;h. Based on the catalytic mechanism analysis, the active species sequence during the degradation of pollutants by ZnFe₂O₄ nanoparticles is as follows: ·O₂⁻ &gt; ·OH &gt; e⁻ &gt; h⁺, suggesting that superoxide radicals (·O₂⁻) and hydroxyl radicals (·OH) play dominant roles in the pollutant degradation.</p>