Degradation of printing and dyeing wastewater pollutant reactive black 5 via pyrite activated persulfate: Efficacy and application impact assessment

To address the significant wastewater discharge from the printing and dyeing industry today, this study employed pyrite-activated persulfate (PS/pyrite) to induce advanced oxidation for the degradation of a representative azo dye, Reactive Black 5 (RB5), and conducted a comprehensive analysis of pertinent influencing factors. Leveraging pyrite's pH self-regulation capabilities, the pyrite/PS system demonstrated robust RB5 degradation across a broad pH spectrum of 3–9, achieving a degradation rate of approximately 96 %. Interestingly, due to the photocatalytic properties of pyrite, the degradation efficiency can be enhanced by 21 % with pyrite under illumination. Subsequently, the degradation of RB5 under illumination is further enhanced in PS/pyrite system, ultimately achieving a degradation rate of almost 100 %. The system maintained an acidic milieu and sustained the release of Fe2+, thereby fostering an optimal Fe2+/Fe3+ cycle. In a simulated wastewater environment, the pyrite/PS system exhibited resilience against interference from NH4+, NO3−, and humic acid (HA), while exhibiting a synergistic catalytic effect with Fe2+ and enhancing Fe2+/Fe3+ cycling at elevated Cu2+ concentrations. Electron paramagnetic resonance (EPR) tests and quenching experiments confirmed the generation of both hydroxyl radicals (OH) and sulfate radicals (SO4−), with SO4− serving as the primary radical species. Scanning electron microscopy (SEM) analysis identified rough microparticles as the primary sites for Fe2+ release and reactivity. UV-spectrophotometry and visual assessment of pollutant discoloration indicated successful disruption of RB5's chromophore (NN) structure and naphthalene ring, achieving effective removal. The findings of this research offer valuable insights for the practical application of pyrite/PS systems in the treatment of printing and dyeing wastewaters. •Self-regulating pH of pyrite extends the pH application range of advanced oxidation.•The surface of pyrite and dissolved Fe2+ can effectively catalyze PS.•Pyrite can slowly and persistently release Fe2+, promoting a good Fe2+/Fe3+ cycle.•The degradation of RB5 can be enhanced under light and stirring with Teflon stirrer.•Hydroxyl radicals and sulfate radicals are the main reactive species.