Preliminary Study On Mechanochemical Treatment Of Soil Heavily Contaminated With DDT

DDT, an organochlorinated pesticide that listed as POPs by the StockholmConvention, had been widely used around the world. In1983, China banned productionand usage of DDT, and as a result, it brought about large numbers of POPs contaminatedsites that need to be treated urgently. As the traditional high-temperature incinerationtechnology will produce highly toxic by-products, such as dioxins, non-combustiontechnologies have been proposed and developed. Mechanochemical technology hasattracted much attention in the world for potential applications as a non-combustiontechnology. However, there was little reaserch that had been done in China and most ofthe work focused on treatment of pure chemicals or fly ash but little contaminated soils.Therefore, the objectives of this study were to develop the analytical method for thesoil DDT and screen effective mechanochemical ball mill reagents and optimize ballmill parameters. This study will lay the foundation for future studies on mechanism andequipment scale-up.The main results are as follows:(1) The DDTs’ recovery rates of the method developed in this study were between83.52%and90.30%, and the method detection limits of DDTs were between2.0ng g-1and5.4ng g-1. The treatment process is as follows: use20mL mixture solution ofhexane/acetone (V:V=1:1) to extract the soil for3times by ultrasonic method. Thesoil extracts was then purified by a patented four-channel purification chromatogramby using a mixed filling material and elution with dichloromethane/n-hexane(V:V=4:1), and then using the Gas Chromatography with Electron Capture Detector(GC-ECD) to detect the volumn specified extracts.(2) CaO, CaO+S, Fe+Ni, Fe+Zn were fund to be highly effective reagents forDDTs’mechanochemical destruction of soil DDTs and Fe+Zn metalic mixture was themost effective reagents. After4hours operation, DDTs in soil decreased by99.46%、99.46%、99.47%、99.85%respectively, at the conditions of500rpm,ball to meaterialratio(charge ratio)28:1, reagents to soil ratio(material ratio)1:2.(3) The investigation on the operating parameters showed that the longer ballmilling time, the faster rotation speed, the larger charge ratio, material ratio and Zn toFe+Zn ratio, the higher destruction rate will be. And the DDTs destruction rate willincrease at a much slower rate when the rotation speed>350rpm, charge ratio>15material ratio>0.35, Zn to Fe+Zn ratio>30%. The different combination of balls size will affect DDTs’ destruction rate significantly at the same charge ratio. The bestdestruction rate was achived with small balls and the the lowest destruction rate withbig balls.(4) The results of the orthogonal experiment indicated that the rotation speed,charge ratio, material ratio and Zn to Fe+Zn ratio affect DDTs’ destruction ratesignificantly and with the degree of influence decreased in the sorder of charge ratio>rotation speed> Zn to Fe+Zn ratio> material ratio. The best ball mill operatingparameters were charge ratio28:1, rotation speed500rpm, Zn to Fe+Zn ratio1:1,material ratio1:2.