Determination of diffusion coefficient and analysis of diffusion factors of Cr(VI) ion in clay soil

Abstract

Some laboratory diffusion tests were conducted with diffusion device to determine the diffusion coefficient of Cr(VI) ion passing through Dalian red clay samples. The concentrations of Cr(VI) at different places of the samples were then measured spectrophotometrically after a standing time of 1 000 d. A one-dimensional solute transport equation was used to simulate the transport of Cr(VI) through clay samples. Back-calculation of diffusion coefficient of Cr(VI) was made with finite difference method. Parametric analysis was conducted to simulate variations in soil dry density, temperature, pH and standing time. The results show that the method used in this paper is simple and effective. The diffusion coefficient of Cr(VI) in Dalian red clay varies from 1.50×10−7 cm2/s to 2.08×10−7 cm2/s. After 1 000 d diffusion, the concentration of the source solution drops down to 1.27 mg/L from 62.5 mg/L, and the diffusion distance is only 3.5 cm. Under the assumption that diffusion coefficient is constant, the diffusion effect becomes more obvious with lower density, lower temperature, higher pH value, and much more time.