Coupling the dechlorination of aqueous 4-CP with the mechanochemical destruction of solid PCNB using Fe-Ni-SiO2

A novel combined process was developed for mechanochemical destruction of pentachloronitrobenzene (PCNB) in solid waste, coupled with the dechlorination of aqueous 4-chlorophenol (4-CP) using the nonhazardous residue from the solid-phase destruction step. Using the mixture of iron powder, nickel powder and quartz sand as the additives in a planetary ball mill under the room temperature, the mechanochemical reaction was induced and a complete destruction of PCNB was realized. The resulting solid residue was characterized by various measures including X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDS), which suggested that main components were carbon, chloride besides excess additives. Such nonhazardous residue was then used to effectively dechlorinate aqueous 4-CP. The residue achieving over 93% dechlorination rate was selected as the optimized content. With a series of verification experiments, a possible dechlorination mechanism was proposed, involving the reactions occurred on three interfaces (i.e. Fe/Ni, Fe/C and Fe/C/Ni).