A desorption-dissolution model for metal release from polluted soil under reductive conditions

Various natural or provoked situations can cause significant variations in redox conditions that can induce reductive dissolution of soil components. When this happens, heavy metals that may be bound to solid phases are released. A surface desorption-dissolution model, which takes into account the effect of reductive conditions on surface site density, was established. This model is based on conventional reactions of surface hydroxyl groups, surface complexation reactions with cations and double-layer theory. The solid dissolution rate was taken into account, by following changes in total surface site number (i.e., cation exchange capacity [CEC]) under reductive conditions. This term was introduced in an electrostatic desorption model. Curves obtained by this calculation provided a good fit of experimental data as shown by statistical parameters. Experimental data corresponded to Pb and Cd released from a cultivated soil under reductive conditions induced by sodium ascorbate.