Effect of thermal treatment conditions on the release and transformation of organic impurities in industrial waste salts

Abstract

Industrial waste salts, laden with toxic organic impurities, pose significant environmental hazards. Thermal treatment has emerged as a promising strategy to reduce these contaminants. However, previous studies have focused on total organic carbon removal. Still, this work utilizes advanced two-dimensional gas chromatography time-of-flight mass spectrometry (GC × GC-TOFMS) and pyrolysis gas chromatography-mass spectrometry (PY-GC/MS) to provide unprecedented detail on the release and transformation pathways of specific organic groups (aromatics, nitrogenous, halogenated, etc.) in pesticide waste salts. This study investigates waste salts under medium-temperature conditions (400–500°C) in inert and oxygen-containing atmospheres. Results indicate that under an oxygen-containing atmosphere, the removal rate surpassed 99% within 20 minutes at 400 and 500°C. Oxygen-containing conditions significantly improve the removal efficiency but leave more complex organic residue in the treated salt, which retains nitrogen-containing compounds, aliphatic hydrocarbons and oxygenates. Organic impurities follow distinct transformation pathways: volatile P-xylene produces styrene, ethylbenzene and benzaldehyde; nitrogen-containing compounds (e.g. amines) form complex nitrogen- and oxygen-containing products; and halogenated compounds cleave into shorter-chain halogenated derivatives. These findings offer crucial insights into the thermal behaviour of organic contaminants in waste salts and guide the further treatment process of waste salts.