LABORATORY-SCALE STUDY ON REACTIVE CONTAMINANT TRANSPORT IN SOIL BY MEANS OF ONE-DIMENSIONAL ADVECTIVE DISPERSIVE MODELS

We measured adsorption and transport of cadmium (Cd) in the presence of Ca²⁺ and Na⁺ salts of varying ionic strengths and pH by using batch and miscible displacement experiments, carried out on undisturbed and homogenized soil columns. A fluvent-vertic soil was used in this study. In the column experiment a clear effect of ionic strength on breakthrough curves (BTCs) of Cd²⁺ was observed when the Na⁺ concentration was increased from 0.02 to 0.2 M. The effect of increasing the Ca²⁺ concentration on Cd²⁺ absorption and transport was relatively less pronounced than that recorded for the Na+ solution. At low pH values, H+ ions competed strongly with Cd²⁺ ions and, at a high pH, precipitation was the main process taking place for Cd²⁺ sorption. The reliability of the advection- dispersion equation (ADE) was tested. When implemented within the least-squares method, the model produced a sufficiently precise space-time distribution of Cd²⁺ ion concentrations. The results of this study demonstrated also, that laboratory leaching experiments, when performed on homogenized soil columns, can greatly underestimate Cd²⁺ ions transport in the field and that preferential flow can increase the mobility and velocity of cadmium movement to the groundwater.