The primary evaluation and characterization of obsolete DDT pesticide from a precalciner of a cement kiln

1,1,1-Trichloro-2,2-bi(4-chlorophenyl)ethane (DDT) pesticide that has been extensively used in agriculture in China in the last century, and even now, has been banned from all purposes. The disposal of obsolete DDT pesticide has been an urgent task for the Chinese government. In order to evaluate the feasibility of co-processing DDT in the current new style dry-process rotary kiln with a precalciner as the feeding point, the destruction efficiency (DE) of DDTs (including <i>p,p</i>^′-DDT, <i>o,p</i>^′-DDT, <i>p,p</i>^′-DDE and <i>p,p</i>^′-DDD), proportion of DDTs in the combustion residue and exhaust gas, and the release of chlorine were studied under different operating conditions of temperature, oxygen content and gas retention time in the laboratory. The DE of DDTs exceeded 99% when the temperature was over 800 °C with enough oxygen. As the temperature increased from 600 °C to 1200 °C, the proportion of <i>p,p</i>^′-DDD increased and <i>p,p</i>^′-DDT decreased but still the main effective component remained in the combustion residue. In the exhaust gas, the most dominant phenomenon was the rapid increase in <i>p,p</i>^′-DDE concentration as the temperature increased. The release of chlorine reached a peak between 800 °C and 900 °C. It was found that the oxygen content had a positive correlation with the process of dechlorination. The proportion of <i>p,p</i>^′-DDE increased as the oxygen content was increased in the exhaust gas. The gas retention time had almost no influenced on the DE of DDTs, but affected the degradation extent of DDTs in the gas phase. These experiments showed that co-processing of obsolete DDT pesticide in cement kiln precalciners is feasible.

1,1,1-三氯-2,2-双(4-氯苯基)乙烷（1,1,1-Trichloro-2,2-bi(4-chlorophenyl)ethane，简称DDT）类农药曾于上个世纪在我国农业领域被大规模施用，即便时至今日，仍被全面禁止用于所有用途。老旧DDT农药的处置工作已成为我国政府亟待解决的重要任务。为评估以分解炉为投料点的新型干法预分解回转窑协同处置DDT的可行性，本研究在实验室条件下，考察了温度、氧含量及气体停留时间等不同运行参数下，滴滴涕类物质（包括p,p′-滴滴涕（p,p′-DDT）、o,p′-滴滴涕（o,p′-DDT）、p,p′-滴滴依（p,p′-DDE）及p,p′-滴滴滴（p,p′-DDD））的销毁效率（destruction efficiency，简称DE）、燃烧残渣与废气中滴滴涕类物质的占比，以及氯元素的释放量。当温度高于800℃且氧含量充足时，滴滴涕类物质的销毁效率可超过99%。当温度从600℃升至1200℃时，p,p′-滴滴滴的占比逐渐升高，p,p′-滴滴涕的占比则逐步下降，但燃烧残渣中仍以p,p′-滴滴涕为主要残留组分。在废气中，最显著的现象是随着温度升高，p,p′-滴滴依的浓度快速上升。氯元素的释放量在800℃至900℃区间达到峰值。研究发现，氧含量与脱氯过程呈正相关关系；废气中p,p′-滴滴依的占比随氧含量升高而增加。气体停留时间对滴滴涕类物质的销毁效率几乎无影响，但会影响气相中滴滴涕类物质的降解程度。本实验结果表明，在水泥窑分解炉中协同处置老旧DDT农药具备可行性。