The Release Characteristics of Cr(VI) in Contaminated Soil by Dynamic Simulation of Acid Rain

The release characteristics of Cr(Ⅵ) from contaminated soil, spiked with inorganic salts of Cr(Ⅵ),were investigated by dynamic leaching experiment in soil column with simulated acid rain. The soil samples were divided into five groups (i.e., A, B, C, D, E). Respectively, the contents of Cr(Ⅵ) were 100mg, 135mg, 170mg, 205mg, 240mg in per kilogram soil. In general, with the leaching time extension, the Cr(Ⅵ) concentration of leachate was declined obviously, repectively, A was from 0.55 to 0mg/L, B was from 1.12 to 0.12mg/L, C was from 2.65 to 0.62mg/L, D was from 1.84 to 2.27mg/L, E was from 1.87 to 0.12mg/L. The release rate of Cr(Ⅵ) was initially rapid and gradually declined after the fourth leaching. Cr(Ⅵ) loss percentage of leachate from soil was as high as 2.11%, 5.36%, 11.06%, 9.24%, 10.94% after leaching experiment. The results show that The release processes of Cr(Ⅵ) from soil were fitted with mathematical equations. The amended Elovich equation could better describe the release processes of Cr(Ⅵ).It implies that The release process of Cr(Ⅵ) is affected by a diffusion factor and reaction rate but not simply conformed to the first order kinetics. The pH values of leachate under simulated acid rain, whose pH value was 3.8, was in the range of 8.0 to 8.4. It implies that the pH values of leachate have nothing to do with Cr(Ⅵ) concentration in soil, and the soil has buffer capacity for H+. With this study and its results, the release of Cr(Ⅵ) in soil to ground water can be Predicted and the theoretical and technical support can be provided for ecological environment restoration.