M+/H+ ion exchange behavior of the phosphoantimonic acids HnSbnP2O3n+5 center dot xH(2)O (n = 1,3) for M = Cs and other alkali metal ions

International audienceThe sorptions of cesium and of other alkali metal ions have been studied by batch techniques; the data are well fitted using the Langmuir equation. The values of the various thermodynamic parameters associated to the ion exchange are reported (free energies, enthalpies, entropies, distribution coefficients Kd, selectivity coefficients Kc) and discussed; the ion selectivity, at infinite exchange on HSbP2O8 (called H-1) and on H3Sb3P2O14 (called H-3) varies according to the sequence Cs > Rb > K > Na. The very negative values of Delta G(Cs/H)degrees, and Delta G(Rb/H)degrees are indicative of a preferential adsorption of Cs+ and Rb+ higher in H-3 than in H, by about one order of magnitude at low concentration level. The selectivity coefficients for Cs+, Rb+ on H-1 vary linearly with the fractional exchange (x) over bar(M) in solid (Kielland plot) suggesting a unique site of exchange. The Kielland plot for H-3 can be described in terms of a multisite ion exchange model (two sites) in agreement with the number of sites in the crystalline structure of K-3 (homologous compound). Radiotracers have been used to estimate the parameters Kd at low concentration levels. The results are discussed on the basis of the thermodynamic data together with the structures. (C) 1998 Elsevier Science B.V. All rights reserved

Study of the ion exchange selectivity of layered titanosilicate Na-3(Na,H)Ti2O2[Si2O6](2) center dot 2H(2)O, AM-4, for strontium

International audienceThis paper describes for the first time the sorption behaviour of a titanosilicate, AM-4, that exhibits an extremely high affinity for strontium in neutral and alkaline media. The ion exchange selectivity of this layered titanosilicate is explained in relation to the crystalline structure. The simple approach which consists in studying carefully the distribution of formal charges of oxygens in the anionic framework and calculating a normalized bond length in order to measure the ion stability in its site has enabled us to account for the AM-4 performances for the strontium remediation in competition with alkali and alkaline earth metal ions, The Sr uptake amounts as a function of the pH were determined, they can be correlated to the formal charges of Si-O-nbo. The effect of sodium, potassium, calcium and magnesium on the Sr2+ ions sorption was also studied in binary solutions Sr2+/Na+, Sr2+/K+, Sr2+/Ca2+, Sr2+/Mg2+. The determination of the equilibrium constant Sr2+/2Na(+) and of the ion competitive effects with adsorption data have shown that Ca2+ is the most efficient to reduce the uptake of Sr2+. The preliminary Kd values provide an indication that this exchanger may act as a sorber for groundwater and nuclear remediation applications

Study of the ion exchange selectivity of layered titanosilicate Na-3(Na,H)Ti2O2[Si2O6](2) center dot 2H(2)O, AM-4, for strontium

International audienceThis paper describes for the first time the sorption behaviour of a titanosilicate, AM-4, that exhibits an extremely high affinity for strontium in neutral and alkaline media. The ion exchange selectivity of this layered titanosilicate is explained in relation to the crystalline structure. The simple approach which consists in studying carefully the distribution of formal charges of oxygens in the anionic framework and calculating a normalized bond length in order to measure the ion stability in its site has enabled us to account for the AM-4 performances for the strontium remediation in competition with alkali and alkaline earth metal ions, The Sr uptake amounts as a function of the pH were determined, they can be correlated to the formal charges of Si-O-nbo. The effect of sodium, potassium, calcium and magnesium on the Sr2+ ions sorption was also studied in binary solutions Sr2+/Na+, Sr2+/K+, Sr2+/Ca2+, Sr2+/Mg2+. The determination of the equilibrium constant Sr2+/2Na(+) and of the ion competitive effects with adsorption data have shown that Ca2+ is the most efficient to reduce the uptake of Sr2+. The preliminary Kd values provide an indication that this exchanger may act as a sorber for groundwater and nuclear remediation applications