Long term catalytic activity of pyrite in Heterogeneous Fenton-like oxidation for the tertiary treatment of dyeing wastewater

The long term catalytic activity of pyrite in advanced oxidation for wastewater treatment is vital for the practical application. In this work, the efficacy of pyrite catalyzed Fenton-like oxidation for tertiary treatment of dyeing wastewater was investigated for a period of two years. The influence of pyrite oxidation and dissolution on the catalytic activity was studied based on surface characterizations and chemistry studies. Experimental results demonstrated that pyrite can effectively catalyze H2O2 to oxidize recalcitrant pollutants in the biological effluent of dyeing wastewater. At initial pH 3-6, H2O2 of 10 mM and pyrite of 24 g L-1. COD and color removals reached 76.67% and 97.09% in 180 min of reaction time. The higher treatment efficacy of pyrite catalyzed Fenton-like oxidation was due to appropriate conversion rate of H2O2 to hydroxyl radicals compared with the classic Fenton oxidation. Heterogeneous catalysis by Fe(II) on the pyrite surface was much more significant than Homogeneous catalysis by dissolved iron ions of pyrite. The latter contributed only 28.25% abatement of COD at pH 3 and can be negligible at wastewater initial pH > 5. The oxidation of pyrite resulted in acidic pH environment for recalcitrant organic compound destruction even if the initial pH of wastewater was 6.5. It was found that the catalytic activity of pyrite can maintain at least two years, as the surface regeneration of pyrite in that period of time occurred spontaneously due to the slow dissolution of oxidation products.