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 Fe 2+ , thereby fostering an optimal Fe 2+ /Fe 3+ cycle. In a simulated wastewater environment, the pyrite/PS system exhibited resilience against interference from NH 4 + , NO 3 − , and humic acid (HA), while exhibiting a synergistic catalytic effect with Fe 2+ and enhancing Fe 2+ /Fe 3+ cycling at elevated Cu 2+ concentrations. Electron paramagnetic resonance (EPR) tests and quenching experiments confirmed the generation of both hydroxyl radicals ( OH) and sulfate radicals (SO 4 − ), with SO 4 − serving as the primary radical species. Scanning electron microscopy (SEM) analysis identified rough microparticles as the primary sites for Fe 2+ release and reactivity. UV-spectrophotometry and visual assessment of pollutant discoloration indicated successful disruption of RB5's chromophore ( N N ) 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.