Modified Zeolite Synergistic Thermal Desorption Repair Research On DDTs Polluted Soil And Its Tail Gas Disposal

DDTs,as one of organochlorine pesticides,have been extensively produced and used.In recent years,with the relocation of organochlorine pesticide chemical plants,the remediation of high concentration DDTs contaminated soil has become a major research hotspot.The application of thermal desorption technology in the remediation of organic matter contaminated sites has the advantages of high disposal efficiency and short remediation cycle,but there are problems such as high energy consumption and secondary pollution of exhaust gas.This article took simulated DDTs contaminated soil as the research object and explored different zeolite modification methods.The synergetic thermal desorption technology with modified zeolite was used to remediate DDTs contaminated soil.Based on the thermal desorption characteristics of DDTs contaminated soil,the synergetic thermal desorption with modified zeolites was conducted,and the treatment of tail gas from thermal desorption by modified zeolites was studied,in order to improve the thermal desorption efficiency and reduce secondary pollution.The main research findings are as follows:(1)The results of thermal desorption research on DDD contaminated soil indicate that temperature and time are key factors affecting thermal desorption efficiency.When the heating time is 60 min,the thermal desorption efficiency is 94.92%at 150℃.When the temperature rises to 200℃and 250℃,the DDD removal efficiency reaches 99.99%under the same time treatment.The thermal desorption treatment of DDTs contaminated soil has a removal efficiency that is proportional to the treatment time and heating temperature,and a degradation efficiency that is inversely proportional to the treatment time.Under the conditions of 150℃ and 60 min,the removal efficiency of DDTs is 48.23%,and the degradation efficiency is 31.45%.When the temperature rises to 250℃,the removal efficiency increases to 51.54%,and the degradation efficiency decreases to 28.86%.When the treatment temperature is 150℃,the removal efficiency increases from 45.28%for 20 minutes to 48.23%for 60 minutes,and the degradation efficiency decreases from 34.87%to 31.45%.After thermal desorption,the concentration of residual p,p’-DDT,o,p’-DDT in soil decreases,while the concentration of DDD and DDE increases.Increasing temperature and prolonging time promote the evaporation desorption and dechlorination degradation of pollutants.(2)After successively modifying natural zeolite with hydrochloric acid,high-temperature,and MgCl2 loading,it was found that the pore structure of the modified zeolite increased,and spherical particles existed on the surface.The highest removal efficiency of DDD contaminated soil was 96.22%when modified zeolite was used for thermal desorption at 150℃ for 60 min.After the synergetic thermal desorption with modified zeolite,the removal efficiency and degradation efficiency of DDTs increased by 8.27%and 12.45%respectively at 150℃ and 60 min.p,p’-DDT was dechlorinated to DDD and DDE,and the proportion of DDD in soil increased from 5.31%to 10.11%.Through the first order kinetics,it was found that the rate constant improved and the synergy factor increased,indicating that modified zeolite promoted thermal desorption process,enhanced the removal,degradation,and dechlorination of DDTs,and contributed to the synergetic thermal desorption of DDTs contaminated soil.The reason is that the modified zeolite had a porous structure,promoting the diffusion of pollutants from the interior to the surface of the soil,and catalyzing the dechlorination and degradation of pentachloro p,p’-DDT to tetrachloro DDE and DDD.(3)The modified zeolite is used to dispose the tail gas after thermal desorption.It was found that natural zeolite was better for adsorption,with the adsorption efficiency of DDTs reaching 55.17%,but the catalytic degradation performance of DDTs is not significant.After modification,the catalytic degradation of zeolite was improved.The zeolite modified at 600℃ and 1.0 mol/L MgCl2 was the best,with a degradation efficiency of 53.30%for gaseous DDTs,much higher than 35.14%without tail gas treatment.The main reason was that modified zeolites provided more active sites and interface contacts for gaseous pollutants and achieved catalytic degradation of pollutants under the action of Mg2+.The random forest model is used to analyze the weight of the influencing factors under the condition of thermal desorption.As far as the removal efficiency of DDTs is concerned,zeolite has a greater impact on the disposal effect.