Influence of Alkali Cations (Me = Li, Na, K, Rb, Cs) on Physico-chemical Properties of the Liquid and Solid Phases of Me-aluminosilicate Hydrogels

Josip Bronić,a,* Tatjana Antonić Jelić,a Ivan Krznarić,a Jasmina Kontrec,a Boris Subotića and Gregor Malib

a Ruđer Bošković Institute, Bijenička 54, P.O.Box 180, 10002 Zagreb, Croatia
b National Institute of Chemistry, Hajdrihova 19, 1001 Ljubljana, Slovenia
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Me-alumosilicate hydrogels having the batch molar oxide composition xMe2O × Al2O3 × ySiO2 × zH2O (Me = Li, Na, K, Rb and Cs); x = 4.24–4.66, y = 2.49 and z = 334.53–344.48 of the hydrogels (series a), and x = 9.52–10.30, y = 7.91–7.95 and z = 1073.38–1097.29 of the hydrogels (series b), were prepared by mixing of the appropriate Me-silicate and Me-aluminate solutions at room temperature. After ageing for 48 h at 25 °C and solid-liquid separation, the chemical compositions (contents of Me2O, Al2O3 and SiO2) of the liquid and solid phases were determined by AAS. Solid samples were additionally analyzed by XRD, FTIR and DTG. Specific equilibrium distributions of Me2O, Al2O3 and SiO2 between the solid and liquid phases were discussed in the terms of: (a) influence of Me ions on distribution of different silicate species and their degrees of hydroxylation in the starting Me-silicate solutions and (b) influence of the degrees of hydroxylation of silicate species in the starting Me-silicate solutions on the polycondensation reactions with monomeric [Al(OH)4] anions during the formation of the gel. The presence/absence of the formation of zeolite-like structures (“quasi-crystalline”) in the gel matrix was discussed in the terms of the “structure-forming” nature of Li+ and Na+ ions and the “structure-breaking” character of K+, Rb+ and Cs+ cations.

Keywords: Zeolite A, nucleation, hydrogels, “structure-breaking” cations, ageing