Experimental studies on zeolite formation conditions
Barth-Wirsching, Ulrike; Holler, Helmut
European Journal of Mineralogy Volume 1 Number 4 (1989), p. 489 - 506
published: Aug 31, 1989
manuscript accepted: Nov 20, 1988
manuscript received: Oct 30, 1988
ArtNo. ESP147050104002, Price: 29.00 €
Abstract Natural zeolite formation, which commonly takes place by reaction of a solution with a source rock, was simulated in experiments using both natural basaltic and rhyolitic glass, nepheline and oligoclase as starting materials. The reacting solutions were Na-, K-, Ca-solutions of different concentrations. The intention was to find out (1) how and to what degree zeolite formation is controlled by starting material, solution chemistry, temperature, reaction time, and closed vs. open system; and (2) how each factor influences the effect of the other factors. The following zeolites have been synthesized so far: gismondine and thomsonite from nepheline only; faujasite-type zeolite X, levyne, and scolecite from basaltic glass only; clinoptilolite, epistilbite, and mordenite from rhyolitic glass only; garronite from both oligoclase and basaltic glass; heulandite from both oligoclase and rhyolitic glass; merlinoite from both basaltic and rhyolitic glass; phillipsite from nepheline, basaltic as well as rhyolitic glass; analcime and wairakite from all the starting materials investigated. Synthetic zeolites Na-P and HS formed from both basaltic and rhyolitic glass. Experiments show that solution pH primarily controls zeolite Si/Al ratio, although the influence of starting material Si/Al ratio and dissolution behaviour is never entirely eliminated. In an open system, the zeolite Si/Al ratio is affected profoundly by Si-removal or by Si-addition (through the migrating solution). The concentration and distribution of alkali and alkaline earth cations in the zeolite being formed are determined by their amounts and concentrations both in the starting material and in the initial solution. Material transport in the open system is also an important factor and is a function of chemical gradient, percolation velocity and reaction time. Zeolite water content appears to be affected by temperature as well as reaction time. In closed-system reactions, starting material, pH in the reacting system, temperature and reaction time are factors of equal significance in controlling zeolite formation, whereas the chemistry of the reacting solution is of minor importance were (1) a dilute solution (0.01 N) is involved and (2) the starting material is rich in sodium or potassium. In the open systems pH and temperature are of equal importance as in a closed system. The effect of solution chemistry and reaction time is greater in open systems, whereas the influence of the starting material may entirely be eliminated by material transport possible in an open system.