Hydrothermal Conversion of Trachytic Glass to Zeolite. 3. Monocationic Model Glasses

Maurizio de' Gennaro1, Alessio Langella2, Piergiulio Cappelletti1 and Carmine Colella3
1 Dipartimento di Scienze della Terra dell'Università Federico II, Via Mezzocannone 8, 80134 Napoli, Italy
2 Università del Sannio, Via Caio Ponzio Telesino, 11, 82100, Benevento, Italy
3 Dipartimento d'Ingegneria dei Materiali e della Produzione dell'Università Federico II, Piazzale V. Tecchio 80, 80125, Napoli, Italy

Abstract: Experiments on zeolitization were conducted on four synthetic monocationic glasses (Na, K, Ca, or Mg-rich glass) with Si/Al molar ratios of 2.67, similar in acidity to many volcanic glasses of partially zeolitized Italian tuffs. The products of the hydrothermal treatment at 100, 150, and 200°C of single glasses or glass mixtures with deionized H2O or monosaline solutions (NaCl, KCl, CaCl2) were characterized by X-ray diffraction, thermal, microscopic and chemical analyses. Chemical analyses of mother liquors were also performed. Mineral assemblages, containing chabazite, phillipsite, analcime, and K-feldspar, very similar to those found in altered, volcaniclastic alkali-trachytic or trachytic glass deposits were produced. Potassium was essential to chabazite and phillipsite crystallization, although phillipsite was obtained also in Ca-Na mixed systems. Sodium was necessary for analcime formation. Calcium plays only a secondary role in zeolitization, and magnesium does not favor zeolite crystallization but promotes the formation of smectite. Glass composition determines the mineral assemblages obtained and hence in those commonly found in nature.

Key Words: Analcime • Chabazite • Glass-to-Zeolite Conversion • Phillipsite • Synthesis • Trachytic Glasses • Zeolite Synthesis

Clays and Clay Minerals; June 1999 v. 47; no. 3; p. 348-357; DOI: 10.1346/CCMN.1999.0470311
© 1999, The Clay Minerals Society
Clay Minerals Society (www.clays.org)