Process And Mechanisim Study Of Mechanochemical Treatment Of DDTs In Soil Using CaO

As one of the firstly controlled 12 POPs of Stockholm convention, DDT was ever widely producted and used worldwide in last century. Due to abide by Stockholm convention, China had closed a large number of manufacturing factories with organochlorine pesticides such as DDT, resulting in a large amount of industrial pollution sites.The traditional incineration method produced large amounts of dioxins and other toxic secondary pollutants, so there was urgent need to develop a kind of noncombustion technology. Mechanochemical technology has become one of the most commercially applicable technologies for treatment of persistent organic pollutants(POPs), because of its simple process, mild conditions and high processing efficiency. Considering actual contaminated-DDTs soil in our country, this study adopted actual high concentrations of contaminated-DDTs soil taken from a retired production site as test objective. Different reagents of calcium series were applied to compare the effectiveness for mechanochemical treatment of DDT and its derivatives in contaminated soil. After that, the single factor test and Box-Behnken test were carried out that mechanochemical treatment of DDTs in soil with CaO. Through these experiments, milling parameters(ball size distribution, rotational speed, charge ratio and material ratio) were optimized, which provided technical reference for mechanochemical treatment of high concentrations of contaminated-DDT soil.In this paper, by comparing the effectiveness for mechanochemical treatment of DDTs in contaminated soil with alkaline earth metal oxide, CaO, MgO and other class material Ca(OH)2, CaO2, CaSx and MnO2, we found that residual DDTs with CaO treatment remained minimum.The addition of SiO2 did not promote the effectiveness for mechanochemical treatment of DDTs in soil.In mechanochemical treatment of DDTs in soil with CaO, the effectiveness of grinding balls with full of big balls are better than other treatment with full of small balls. As the increase of material ratio, rotational speed and charge ratio, the residual DDTs gradually decreased. Through Box-Behnken test, we found that the influential sequence of factors(material ratio, rotational speed and charge ratio) for mechanochemical treatment of DDTs-contaminated soil is charge ratio, rotational speed and material ratio. The interaction of charge ratio and rotational speed had the greatest influence for residual DDTs in the samples. The best technology parameters for mechanochemical treatment of DDTs in soil is material ratio 0.5, the charge ratio 35:1 and rotational speed 500 rpm.To understand DDT removal process and its mechanism, mechanochemical treatment of DDT chemical with CaO was carried out. The results demonstrated that addition of SiO2 has a significantly promoting effect for DDT degradation.Through the comparison of GC/MS chromatogram of DDT and DDE in different milling time, it can be seen that while residual DDT decrease, the concentration of DDE appear to rise firstly and reduce finally. Intermediate products of 2,4’-Dichlorobenzophenone and 2,2’-Dichlorostilbene etc. emerged in milling reaction.