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
Résumé
This 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.