Study On Remediation Of Typical POPs-contaminated Soils By Thermal Desorption

POPs (persistent organic pollutants) pesticides are tremendously bad for humanhealth and ecological environment. The threat of such kind of pesticide residue in soilhas been paid more attention at recent years. As a physical process, thermal desorptionis a soil heating method to separated the contaminants from the soil. Because of its highefficiency, thermal desorption has been widely used. The overall goal of this study wasto focus on the analytical methods of DDTs and HCHs in soil samples; to evaluate thedifferent impact factors on removal efficiency of HCHs from soil by thermal desorptionand determine the suitable parameters for POPs-contaminated soil; at the same time,desorption kinetics were investigated to facility the explaination of the removalmechanisms for the thermal desorption process; The article also explored the changes ofphysicochemical properties of the treated soil after thermal desorption process, and thepossibility of reclaiming the soil.Results showed that the trace analytical method for DDTs and HCHs in soilsamples were developed including sample preparation methods of accelerated solventextraction (ASE) combining with Florisil column purification, and the concentrations ofDDTs and HCHs in soil were analyzed by gas chromatography with electron capture(GC-ECD), which could meet the requirement of experiment. Thermal desorptioneliminated DDTs and HCHs in soils effectively, temperature and time were key factors,More than99%of∑HCH and∑DDT were removed from soil at the temperature of340℃and370℃, respectively, and the residue met the Environmental QualityStandards of Chinese National Standard (0.05mg/kg) at the time of15min and20min,respectively. Kinetics of thermal desorption could be described well by a first-orderkinetic model for DDTs and a second-order kinetic model for HCHs. Changes ofphysicochemical properties of the soils after thermal desorption varied depending on thedegree of thermal desorption temperatures, with suitable temperature, acceptable changeof physicochemical properties of the treated soils can be obtained, it was possible torecover soil fertility to farming again.