Process And Mechanism Study On The Mechanochemical Treatment Of DDT With Iron-Zinc Bimetal

DDT was one of the most widely-applied organochlorine pesticides in China.At present,there is still a large number of stocks and contaminated sites within the country,which threats the environmental safty and human health.Because of the risk of secondary pollution,the traditional incineration technology has been questioned and worried,and thus non-incineration technologies have become more promising to the remediation industry.Mechanochemical technology,as a new type of POPs non-incineration treatment technology,has a very broad space for development and application prospects.Based on the previous research of mechanochemical technology in the treatment of DDTs contaminated soil,this paper aims to study the effect and mechanism of iron and zinc in the remediation of DDT contaminated soil.This paper took DDT chemicals as the treatment object and aimed to explore the mechanism of iron-zinc bimetal in the mechanochemical reaction.By Discrete Element Method simulation,the influencing factors of DDT mechanochemical degradation reaction rate were quantified to inquiry reaction kinetics principles.By comprehensive application of various chemical analysis and material characterization means,intermediate products and final products could be identified and changes of groups and components during the reaction process could be indicated.And thus the process and mechanism of mechanochemical reaction between iron-zinc bimetal and DDT could be clarified.Main conclusion of this study were expressed as follows:（1）Fe-Zn bimetal was confirmed to be highly efficient in degradation of DDTs chemicals,after grinding for 4 h DDT removal rate can reach 98%,far better than the traditional treatment with CaO（61%）.Increasing revolution speed and charge ratio of ball to material would help to speed up the removal of DDT.The mathematical model equation between the reaction rate constant,revolution speed and charge ratio was established:k=3.3592-0.0173×v-0.1786×R+0.001×v×R.And prediction could be made that the reaction is difficult to occur when the speed is less than 180 rpm according to the equation.（2）Discrete element simulation software EDEM was used to establish the ball mill model for simulating the motion of milling medium.Simulation under different parameters of the milling process was performed and different motion forms of thegrinding medium was revealed.And the data of impact frequency and impact speed of the balls could be obtained.By analyzing the relationship between the normal impact energy,the revolution speed and charge ratio,the mathematical equation for normal impact energy was obtained:k=3.3592-0.0173×v-0.1786×R+0.001×v×R.The normal impact energy obtained by simulation can be linearly related to the reaction rate constant fitted from the experimental data,and the fitting degree is0.8950.The difference of the single collision energy of grinding ball has caused the difference in the reaction effect.Only the high energy collisions could make the mechanochemical reactions between Fe-Zn and DDT happen,and a lot of low energy collisions could not activate the reaction.（3）Through a variety of characterization and analysis methods,mechanochemical reaction process and mechanism of Fe-Zn bimetal and DDT was observed.Fe and Zn respectively reacted with DDT in mechanochemical reaction,producing the ZnCl₂,FeCl₃ and graphite and amorphous carbon.