Experimental Study on the Formation of Zeolites from Obsidian by Interaction with NaOH and KOH Solutions at 150 and 200 °C

Motoharu Kawano1 and Katsutoshi Tomita2
1 Department of Environmental Sciences and Technology, Faculty of Agriculture, Kagoshima University, 1-21-24 Korimoto, Kagoshima 890, Japan
2 Institute of Earth Sciences, Faculty of Science, Kagoshima University, 1-21-35 Korimoto, Kagoshima 890, Japan

Abstract: Experimental alteration of obsidian was performed in 0.001 to 0.5 N NaOH and KOH solutions at 150 and 200 °C for 1 to 30 d. The products were examined by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray analysis (EDX). Changes in chemical composition and pH value of solutions during the reactions were also measured. As the pH of reacting solutions was increased, smectite, phillipsite and rhodesite crystallized progressively in NaOH solutions, while smectite, merlinoite and sanidine grew successively in KOH solutions. In addition, a small amount of less-soluble, poorly ordered boehmite was present as products of all the experiments. Smectite mainly appeared at slightly high pH, Si/Al and Na/K conditions, whereas rhodesite should be produced in extremely high pH, Na/K and Si/Al conditions. Sanidine was also formed in conditions of very high pH and Si/Al and very low Na/K. In intermediate conditions of pH and Si/Al, crystallization of phillipsite was stimulated in solutions of Na/K > 10, while formation of merlinoite was favored in conditions of Na/K < 1.

Key Words: KOH solution • Merlinoite • NaOH Solution • Obsidian • Phillipsite • Rhodesite • Sanidine • Smectite

Clays and Clay Minerals; June 1997 v. 45; no. 3; p. 365-377; DOI: 10.1346/CCMN.1997.0450307
© 1997, The Clay Minerals Society
Clay Minerals Society (www.clays.org)