The ion-exchange properties of the Tournemire argillite: I. Study of the H, Na, K, Cs, Ca and Mg behaviour

The main goal of this study is to understand the mechanisms of adsorption of major cations occurring in groundwater on the Tournemire argillite. The Tournemire argillite contains illite, kaolinite, montmorillonite, quartz and calcite and some traces of pyrite. After calcite removal the mineralogical composition is kaolinite 47%, illite 26%, mixed-layer illite/montmorillonite 6%, montmorillonite 4%, chlorite 4% and quartz 13% with some traces of pyrite. The material was conditioned under homoionic form using Na, K, Cs, Ca and Mg. H was taken into account as a competitor ion for each case. For each cation-exchanged argillite, sorption edges were obtained as a function of pH. The “intrinsic” ion-exchange properties of this material, i.e. the concentrations of the different types of sites and the associated selectivity coefficients for H, Na, K, Cs, Ca and Mg were determined. The Tournemire argillite displays four kinds of sorption sites with respective concentrations of 0.04, 0.043, 0.046 and 0.078 mmol g−1. Besides, some sites in very low concentration (∼5×10−4 mmol g−1) have been revealed by performing adsorption isotherms of Cs.