Two cation exchange models for direct and inverse modelling of solution major cation composition in equilibrium with illite surfaces

Abstract

Na/K, Na/Ca and Na/Mg exchange isotherms were performed on the fine fraction (<2 lm) of Imt-2 illite samples at a total normality of about 0.005 mol/L in anionic chloride medium. The derived selectivity coefficients for Na/K, Na/Ca and Na/Mg were found to vary as a function of the exchanger composition and compared well with the data collected in the literature for similar experimental conditions. Two models were built to reproduce the data: the first was a multi(2)-site model with constant Gaines and Thomas selectivity coefficients; the second was a one-site model taking into account surface species activity coefficients. The results of the models were in rather good agreement with both our data and literature data. The multi-site model proved to be efficient in predicting the exchanger composition as a function of the Na/Ca/Mg/K concentrations in solution, whereas the one-site model proved to be a better approach to derive the Na/ Ca/Mg/K concentrations in solution based on the knowledge of the exchanger composition and the total normality of the solution. The interest of this approach is illustrated by the need for major cation solute concentration predictions in compacted clay for the characterization of nuclear deep disposal host rock repositories.

Benchmarks for multicomponent reactive transport across a cement/clay interface

“…The model considers ion exchange on illite and smectite represented by the selectivity exchange coefficients on the two exchangers [42,43].…”

“…The ion exchange composition on the claystone was initially equilibrated with the COx pore water shown in Table 4. The selectivity coefficients available in Table 9 were calculated using exchange models given by Tournassat et al [42,43]. The coefficients are based on the Gaines and Thomas convention [50,51].…”

A robust model for pore-water chemistry of clayrock

“…Analyses of cation exchange populations were performed on whole rock samples using the cobalt hexamine method (Rémy and Orsini, 1976;Ciesielski and Sterckeman, 1997) as previously described by Gaucher et al (2004Gaucher et al ( , 2006 and Tournassat et al (2007Tournassat et al ( , 2008Tournassat et al ( , 2009. Experimental tests showed that carbonate minerals and sulphate minerals (e.g.…”

“…Cation concentrations in the supernatant and in the cobalt hexamine solutions were analysed by liquid ionic chromatography (HPLC, Dionex). Cation exchange selectivity coefficients were calculated from these data (see Tournassat et al, 2007 for method details).…”

Natural Water Treatment Systems for Safe and Sustainable Water Supply in the Indian Context: Saph Pani

“…It is not a thermodynamic constant, but varies with the exchanger composition (e.g. Tournassat et al, 2007after Jensen, 1973. For the exchanger phases of the three sediment types (sand, sand with kankar, kankar), equilibrium equations for Na/K, Na/Mg, Na/Ca, Na/NH 4 were set up using the Gaines Thomas convention (Gaines & Thomas, 1953) and measurements of the cation compositions on the exchanger as well as the corresponding activities in groundwater samples.…”