Analytical evaluation of heavy metal desorption process from contaminated soil under chelator leaching

Analytical solutions elucidating the desorption process of soil flushing aided with chelating agent were established based on advection-domination assumption. The proposed analytical models are feasible for the simulation of eluent leaching tests, which is validated by the numerical analyses as well as column leaching tests of heavy metal contaminated silty soil using ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) chelating agents. Based on the fittings using the proposed model, the desorption mode of heavy metals aided by EDTA-2Na in the column flushing tests more accords with the pseudo-first-order model comparing to the pseudo-second-order model. The desorption rates calibrated from the column tests are 3∼10 times slower than those from batch tests while the equilibrium desorption ratios are consistent. Limited reaction space and insufficient contacting of chelating agents are supposed to be the major cause of this phenomenon. The proposed analytical model aids deeper understanding for the soil flushing assisted with chelating agents, and can help to provide theoretical basis for soil flushing remediations.