Pyrite-activated persulfate to degrade 3,5,6-trichloro-2-pyridyl in water: Degradation and Fe release mechanism.

TCP (3,5,6-trichloro-2-pyridinol), the main recalcitrant degradation product of chlorpyrifos, poses a high risk to human health and ecological systems. This study provided a comprehensive exploration of the pyrite-activated persulfate (PS) system for the removal of TCP in water and placed particular emphasis on the pyrite oxidation process that releases Fe. The results showed that the pyrite-activated PS system can completely degrade TCP within 300 min at 5.0 mmol/L PS and 1000 mg/L pyrite at 25 °C, wherein small amounts of PS (1 mmol/L) can effectively facilitate TCP removal and the oxidation of pyrite elements, while excessive PS (>20 mmol/L) can lead to competitive inhibitory effects, especially in the Fe release process. Aimed at the dual effects, the evident positive correlation (R > 0.90) between TCP degradation (k) and Fe element release (k), but the value of k (0.00237) in the pyrite addition variable experiment was less than that in the PS experiment (k = 0.00729), further indicating that the inhibition effect of excessive addition consists of PS but not notably pyrite. Moreover, the predominant free radicals and non-free radicals produced in the pyrite/PS system were tested, with the order of significance being •OH < Fe (Ⅳ) < SO < •O < O, wherein O emerged as the principal player in both TCP degradation and Fe release from the pyrite oxidation process. Additionally, CO can finitely activate PS but generally slows TCP degradation and inhibit pyrite oxidation releasing Fe process. This study provides a theoretical basis for the degradation of TCP using pyrite-activated PS.