沸石协同热脱附DDTs污染土壤脱氯脱毒机理研究

The thermal desorption of DDTs contaminated soil has become a hot issue in organochlorine pesticide contaminated site remediation. However, the thermal desorption of DDTs contaminated soil with high concentration is of high energy consumption. Also the treatment of gaseous and secondary pollutants is not so effectively. In this work, the synergetic thermal desorption with zeolite is employed to remediate DDTs contaminated soil. It focuses on the enhanced desorption of primary pollutants, inhibition of the secondary pollutants and degradation of gaseous pollutants. Firstly, the specific modification method of zeolite will be studied to optimize the key effect on thermal desorption. Also the mechanisms of DDTs desorption and transformation strengthened by zeolite in soil will be revealed. Secondly, by exploration of pathways and conditions of dioxins formation, the mechanisms of dioxins inhibition and removal by zeolite in soil will be discussed. Thirdly, by investigating the fate of gaseous pollutants, the mechanisms of adsorption and catalytic degradation of DDTs and dioxins by zeolite in gas will be analyzed. Based on desorption, dechlorination and detoxication in synergetic thermal desorption with zeolite, the efficient thermal desorption technique will be constructed with the core of “enhanced desorption in soil by zeolite + adsorption/catalytic degradation in gas by zeolite”, which provides scientific basis and technical support for economical, efficient and safe thermal desorption of organochlorine pesticide contaminated soil.

DDTs污染土壤热脱附是有机氯农药污染场地修复的一大研究热点。针对高浓度DDTs污染土壤热脱附过程能耗高、气态及二次污染物未有效处置等问题，本项目拟采用沸石协同热脱附对DDTs污染土壤进行修复，着力解决强化脱附一次污染物、有效抑制二次污染物、催化降解气态污染物等关键科学问题。通过研究筛选特异性沸石改性方法，优化热脱附关键影响因素，揭示协同作用下沸石强化土壤中DDTs脱附及转化机理；研究抑制二恶英生成的途径和条件，探讨沸石协同土壤中二恶英的抑制及脱除机理；探明气态污染物的归趋，阐明沸石促进气相中DDTs及二恶英的吸附及催化降解机理。基于沸石协同热脱附的污染物脱附、脱氯、脱毒机制，构建以“固相沸石强化脱附+气相沸石吸附/催化降解”为核心的高效热脱附技术，为有机氯农药污染土壤经济、高效、安全热脱附提供科学依据和技术支撑。

热脱附技术修复DDTs污染土壤是一种处置效率高、应用广泛的场地修复方式，但存在能耗高、气态污染物未有效处置等问题。本项目采用沸石协同热脱附DDTs污染土壤，着力解决强化脱附一次污染物、催化降解气态污染物等关键问题，实现土壤修复及尾气净化。土壤中加入改性沸石显著降低了DDTs含量，提高了DDTs去除效率，在250℃、60min下，土壤中DDTs的去除效率由51.5%显著升高至61.5%，同时改性沸石也进一步强化了DDTs分子的脱氯降解，将高氯代DDT脱氯降解为低氯代DDE和DDD。含有DDTs尾气经过改性沸石后，进一步促进了DDTs降解，最佳条件下为53.3%，显著高于不加尾气净化系统的43.9%。尾气净化系统中改性沸石不仅对DDTs有吸附作用，同时强化了气相DDTs的脱氯降解。一级反应动力学模型被用来描述DDTs在沸石协同作用下的去除。在200℃时加速效应非常显著，协同热脱附的加速效应因子达到最大值1.38。改性沸石协同热脱附强化了土壤中DDTs的去除、降解和脱氯，为DDTs的脱附和脱氯提供了丰富的微孔结构和金属活性位点，促进了DDTs在土壤颗粒上的蒸发脱附、表面扩散和脱氯降解。同时，改性沸石有助于尾气中DDTs的吸附和脱氯，强化了DDTs的催化降解。本项目构建了以“固相沸石强化脱附+气相沸石吸附/催化降解”为核心的协同热脱附技术，有效提高热脱附效率，有助于尾气净化，对于有机氯农药污染场地修复具有实际工程应用价值。