A Novel Natural Iron-Rich Tourmaline Activated Bisulfite System for the Efficient Degradation of Aqueous Imidacloprid

Advanced oxidation processes (AOPs) based on bisulfite (BS) have been promising for wastewater treatment in recent years. Natural tourmaline (TML) has the advantages of economic competitiveness and environmental friendliness. In this study, natural TML was innovatively applied to activate BS for the removal of imidacloprid (IMI) from an aqueous solution. The TML/BS system achieved 87.34% IMI removal within 60 min under the optimized conditions: TML dosage, 0.6 g/L; BS, 0.8 mM; IMI concentration, 5 mg/L; and pH 4.2. The toxicity of the IMI solution was notably reduced after the TML/BS treatment. Free radical scavenging experiments and electron paramagnetic resonance characterization confirmed that SO₄^•- was the dominant radical in the TML/BS system, and ^•OH also contributed to IMI degradation. Three degradation pathways were identified, of which the bond cleavage of the five- and six-membered heterocycles of IMI was responsible for the majority of contaminant decomposition. This study could provide a novel and efficient approach for further wastewater purification application.