Dechlorination of hexachlorobenzene using ultrafine Ca–Fe composite oxides

Abstract

Ca–Fe composite oxides with different Ca/Fe atomic ratios were synthesized by co-precipitation method and characterized by X-ray diffraction (XRD), scanning electron microscopy with elemental X-ray analysis (SEM-EDX) and inductively coupled plasma optical emission spectrometer (ICP-OES). Their dechlorination activities were evaluated using hexachlorobenzene (HCB) as a model compound. The results indicate that the dechlorination activity is related to the composition of metal oxides. Different compositions lead to the formation of different phases of Ca–Fe composite oxides. When Ca/Fe atomic ratio was 3.4, the dechlorination activity reached 97%, which was the highest in the dechlorination of HCB at 300 °C for 0.5 h. This may be related to the formation of Ca 2Fe 2O 5 phase and small agglomerate size of oxide crystal of about 1 μm. The effect of reaction time on HCB dechlorination and the pathway of dechlorination were investigated using the Ca–Fe composite oxide with the highest activity. It was found that hydrodechlorination took place in the destruction of HCB, the dechlorination efficiency is almost 100% after 2 h reaction. After reaction, quantitative measurement of chloride ion and qualitative analysis of CaCO 3 indicate besides hydrodechlorination, other degradation routes may be present. The mechanism of synergic dechlorination using Ca–Fe composite oxides was discussed.