Chlorine migration and transformation mechanism in organochlorine hazardous waste treated with alkaline alcohol system

Abstract

Chlorinated organic hazardous wastes (COWs) are highly toxic, chemically stable, and resistant to natural degradation, their environmental persistence and bioaccumulation pose serious threats to human health and ecosystems. Dechlorination is a key approach to reducing toxicity, lowering environmental pollution risks, and enabling subsequent treatment and resource recovery. In this study, an alkaline alcoholysis system based on sodium hydroxide and anhydrous ethanol was developed to treat chlorinated pesticide waste liquid (CPWL) under ambient conditions. Multiple analytical techniques, including gas chromatography–mass spectrometry (GC–MS) and Fourier transform infrared spectroscopy (FTIR), were used to examine changes in chemical composition, molecular structure, and functional groups in CPWL. Mechanistic analysis indicates that nucleophilic substitution is the dominant reaction pathway. Before treatment, the major pollutants2-chloro-6-(trichloromethyl) pyridine and 1,3,7-trichloronaphthalene accounted for 36.63 % and 38.80 % of the mixture, respectively; after treatment, their contents decreased to 0.12 % and non-detectable levels. The released chlorine was effectively converted into sodium chloride, achieving efficient chlorine immobilization. DFT calculations reveal the initial attack site as -CCl₃, with a total enthalpy change ΔH = −24.7 kcal·mol⁻¹ and an energy barrier of 14.5–38.6 kcal·mol⁻¹. ECOSAR assessment indicates reduced toxicity of CPWL products following reaction. This alkaline alcoholysis system demonstrates significant effectiveness in detoxifying chlorinated organic wastes and provides a feasible route for resource recovery.