EXPERIMENTAL-STUDY OF ALKALINE-EARTH ION-EXCHANGE BETWEEN SILICATE GELS AND AQUEOUS-SOLUTIONS

Exchange equilibria of two cations A2+, B2+, where A2+ and B2+ are taken in the alkaline-earth series: Ca2+, Sr2+, Ba2+, between silicate gels SiO2-(A,B)O-nH2O and aqueous solutions (A2+, B2+) were studied. The standard molar Gibbs free energy of the exchange reaction is given by the linear relation: DELTA-G(A-B)0,gel-sol = K.DELTA-G(A-B)0,hydrox-sol, with K = 0.20. This value differs significantly from the value previously obtained for magnesium and divalent transition elements of the first series: 0.72, probably owing to structural differences between the two families of gels.