Water involved in transformation of soil organo-mineral fractions during catalytic thermal desorption of dioxins-like polychlorinated biphenyls

Abstract

To turn a disadvantage into an advantage for clay soils with strong water retention, it necessitates water-activation-facilitated reductive thermal desorption (TD) of dioxins-like polychlorinated biphenyls (dl-PCBs). The acidic clay soil with abundant clay minerals (CH) and basic clay soil with unique K₂O (CL) were supplemented with CaO-based additives, against nano-Fe⁰ (NZVI) and plasmonic nano-TiN with good hydride ion conductivities. As regards to molecular configurations of dl-PCBs, the high-efficiently removed heptachlorobiphenyl and instead refractory tetrachlorobiphenyl were identified by TD pilot study without water activation, which was further certificated via calculated dechlorination pathways. The TD results and theoretical calculations revealed that naturally occurring K₂O induced water activation in CL rather than water-suppressed TD in CH. And water was involved in electron transfer of deoxygenation-aromatization process at the soil organo-mineral interface during catalyst-enhanced TD with removal efficiencies increment of 59.1% in CH, which was firstly characterized by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analyses. Interestingly, the NZVI and the plasmonic nano-TiN facilitated selective aromatization of epoxide and C-heteroatom groups in CH, as opposed to selective esterification and epoxidation of aliphatic C-O groups in CL, and detailed transformation mechanisms of soil organic carbon were revealed by X-ray photoelectron spectroscopy (XPS).