A dynamic study of the sorption and the transport processes of cadmium in calcareous sandy soils

The interactions of Cd2+ with silica and calcite were observed through laboratory dynamic experiments. Cd2+ sorption processes were characterised as a function of reaction kinetics in aqueous solutions saturated or not with respect to calcite. Chromatographic column experiments show that Cd2+ sorption on silica can be considered as a reversible equilibrate reaction which depends on water composition and pH. For a porous medium composed by a mixture of silica and calcite, the Cd2+ migration behaviours are predominantly controlled by calcite. The amount and the reversibility of sorbed Cd on calcite are strongly affected by kinetic limitations. Stirred flow through reactor experiments provide an original method to separate and characterise the 'fast' and 'slow' Cd sorption on calcite processes. The 'fast' Cd reversible adsorption isotherms and the rate of Cd subsequent uptake by 'slow' reactions are determined. In addition, the inhibition of calcite dissolution is observed as a function of sorbed Cd in order to provide a complete mechanistic database for coupled transport-geochemistry models.