Study of solute transport by recycled soil column leaching experiments

Desorption and leaching of solutes in soil were studied by means of laboratory experiments, consisting of leaching soil columns with a desorption solution and recycling the leachate through the column. In order to accurately evaluate desorption and leaching characteristics of the soil, radioactive tracers were added and monitored in the leachate. Parallel experiments were conducted with chloride and calcium such that transport and desorption parameters can be determined independently. The experimental data was analysed with a transport model, taking into account mobile and immobile soil water fractions, and in case of calcium an equilibrium Langmuir adsorption isotherm. It is shown that the transport is highly dependent upon the mobility of the soil water, and in particular upon the fraction of the soil water to which the chemical is confined, due to its ionic properties. In case of chloride an exclusion soil water phase has to be taken into account in order to fit the experimental results. It also appears that, immobile or mobile water and solute transfer and transport properties are of primary concern to explain the leaching and desorption processes.