HCH REMOVAL EFFICIENCY RELATED TO TEMPERATURE AND PARTICLE SIZE OF SOIL IN AN EX-SITU THERMAL DESORPTION PROCESS

摘要

Soil samples contaminated by hexachlorocyclohexanes (HCHs) were collected from a pesticide-contaminated site in Beijing, and treated with thermal desorption to investigate the behavior of HCHs removal at different temperatures and soil particle sizes (four different particle sizes were : < 0.18, 0.18-0.45, 0.45-2, and > 2 mm). The test results show that removal efficiencies were significantly affected by temperature. High removal efficiency (> 99%) was obtained at temperatures higher than 340℃, and residual concentration of HCHs at this temperature (0.347 mg/kg) met the Environmental Quality Standard for Soils of the Chinese National Standard, suggesting 340℃ was an optimum for this type of soil. Soils with particle sizes larger than 2 mm possessed lower removal efficiency than those with smaller particle size, which may result from the internal diffusion phenomenon of contaminants in larger particles. Kinetics of thermal desorption were well described by a second-order kinetic model, and the desorption rate of HCHs of larger particle sizes was lower than those of smaller ones.