Bai Bing

Title : Cotransport of heavy metals and suspended particles at different temperatures by seepage in porous materials

Abstract:

The transport of heavy metals (HMs) in groundwater and the resulting interactions between HMs and the soil medium are vital topics in environmental geotechnology. The cotransport of HMs and shell powders (SPs) in a porous medium (SiO₂ particles) at different temperatures was investigated by one-dimensional laboratory column experiments. Considering the significant differences in particle size and dielectric property between HMs and SPs, a theoretical model describing their cotransport was developed. For the transport of HMs in porous media, we propose a nonlinear attachment-detachment model. The test results show that temperature and Darcy velocity have a negligible effect on the transport of individual HMs and that the recovery ratio of Cd²⁺ is higher than that of Pb²⁺, which can be attributed to the lower adsorption of Cd²⁺ on the solid matrix. The presence of SPs can facilitate the transport of HMs due to the strong adsorption of positively charged HMs on negatively charged SPs. However, this effect tends to decrease with the size of the SiO₂ particles. An increase in temperature results in a decrease in the recovery ratio of HMs because more HMs adsorbed on SPs can be deposited at high temperatures. The adsorption of HMs on SPs can also change the dielectric properties of the SPs, thus causing a reduction in the repulsion between the SPs and the solid matrix and a consequent decrease in the recovery ratio of HMs. In addition, the results show that the developed model fits well with the experimental results. The proposed nonlinear attachment-detachment model uses an adsorption function and scanning desorption isotherms to model the deposition process of HMs. By distinguishing the differences in particle size and dielectric property between the HMs and SPs, the proposed theoretical model is capable of describing the cotransport processes of HMs and SPs.