Adsorption Laws And Mechanisms Of Chlorpyrifos And Triazophos On Humus And Bentonite

Chlorpyrifos and triazophos were the main pesticides for controlling rice stem borers in Yangtze River basin. With the five high-toxic organic phosphorus pesticides banned from 2007, like methamidophos, methyl parathion and so on, high-efficient, low toxic and residual pesticides, chlorpyrifos, triazophos and acephate had become the leading products. But their half lives were longer, slather using them might cause the destruction to eco-environment, pollution to the soil and water, and effected the health of mankind.So, to control and predict the environmental behavior of pesticides, propose the evaluation standards and treatment countermeasures of their environmental quality had been the important problem in environmental science. The pesticides'physical behaviors were restricted by their adsorption and desorption capacity in soil. The pesticides adsorbed in soil not only effected their mobility and volatility, but also effected their physical and chemical degradation characteristics. Grasping the regularities of pesticides'migration and transformation in soil, could provided scientific basis for correctly evaluating effectively treating pesticide-contaminated soils.Humus and bentonite were very important parts in soil. They can adsorb pesticides intensively because of their complicated structures and many functional groups. The adsorption of chlorpyrifos and triazophos on humus and bentonite were studied by gas chromatography, using the equilibrium oscillometric method. The relationship and mechanism between single adsorbent and pesticides under different pH and temperature were investigated. In order to find the optimum adsorption conditions and mixture ratio of mixed adsorbents the adsorption kinetics and thermodynamics of the two pesticides on mixed adsorbents were further researched. The results showed that:(1) Adsorption capacity of humus and bentonite increased gradually with the increase of pesticides equilibrium concentration, but adsorption rate decreased. Humus has the great adsorption capacity than bentonite, and adsorption strength both triazophos more than chlorpyrifos. The adsorption of chlorpyrifos and triazophos on humus fitted well with both Freundlich equation and Langmuir equation, fitted well with the Langmuir equation on bentonite.(2) The effects of pH to adsorption on humus were great, the adsorption rate decreased with the pH increased between test ranges; the pH was little influence to adsorpt them on bentonite. The effects of temperature on humus and bentonite were complex.(3) Contrasted pre-and-post infrared spectrum of adsorption the two pesticides, non-ion polar pesticides chlorpyrifos and triazophos were adsorped on adsorbents by hydrogen bond and van der waals forces.(4) With the proportion increased of humus in mixed adsorbents, adsorption rate increased gradually, but increasing rate decreased. In order to control cost, 1.0g mixed adsorbents should be selected to adsorpt the two pesticides. When the mass ratio of humus in mixed adsorbents respectively was 12% and 14%, the adsorption of chlorpyrifos and triazophos reached saturation. Comprehensively considered pesticides hydrolysis factor, pH 5.0, 25℃were the best adsorption conditions.(5) The equilibrium time of chlorpyrifos and triazophos on mixed adsorbent was 12h and 6h, respectively. Adsorption dynamics fitted well with first-order kinetics equation. Calculated thermodynamic parametersΔG,ΔH andΔS, it was a heat releasing, entropy increasing and physical adsorption process, and it proceed spontaneously.