CONG Xin, ZHENG Li, SUN Sikun, MEI Aoxue

（College of Environmental Science and Engineering, Liaoning Technical University, Fuxin 123000, China）

Abstract: In order to study the desorption characteristics of PCBs in polluted soils, two typical soils, red soil and black soil, from South and North China, respectively were selected as the research media, and PCB138 was selected as the target pollutant. The desorption behaviors of PCB138 in red soil and black soil, as well as in humic acid and humin extracted from the two soils were discussed. Relationship between the soil physicochemical properties and the desorption rate and amount is discussed. The results showed that the desorption of PCB138 in two soils and their organic matter components reach a dynamic equilibrium at time of 360min.The fitting results of pseudo first-order, pseudo second-order, Elovich and internal diffusion models showed that the R2 values of pseudo second-order dynamic equation are 0.911-0.998, and with the best fitting effect of this equation. The desorption rate and desorption quantity of PCB138 in black soil are slightly higher than those in red soil. It revealed that the Freundlich model can better describe the desorption process of PCB138 in soil and its organic matter components than other two isotherm models of Langmuir and D-R. The Koc value decreases in humin>nature soil>humic acid. The desorption amount of PCB138 in soil and its components declines with temperature increasing from 25 ℃ to 45 ℃. The calculated thermodynamic data indicates that the values of ΔG°>0, ΔH°and ΔS° are all less than zero, suggesting the desorption of PCB138 in two soils and their components was a non-spontaneous exothermic reaction, and the disorder of solid-liquid interface and the system chaosdecrease during the desorption process. The Pearson correlation analysis shows that there is no significant correlation between the desorption rate, the desorption amount of PCB138 in soil and the proportion of soil organic matter and associated specific surface area.

Key words: soil; hexachlorinated biphenyl; desorption; humic acid; humin

EARTH AND ENVIRONMENT Vol.48, No.6, Tot No.338, 2020, Page 704-710