Solid-state transformations of Zn-clinoptilolite through heating

Zn-clinoptilolite was heated and analyzed ex-situ. Breakdown occurred between 400-700 degrees C. After 2 h at 850 degrees C gahnite and Zn-beta-quartz nucleated. Exolution of zinc and aluminum from Zn-beta-quartz determined Zn-alpha-quartz formation after 8 h. An increase in temperature and/or heating time determined exolution also in Zn-alpha-quartz, that progressively turned into cristobalite. Zn-beta-quartz decreased over time at 1000 degrees C and disappeared after 100 h, whereas at 900 degrees C the quantitative ratio beta-quartz/alpha-quartz asymptotically stabilized at approximate to 2.5. Rietveld refinements evidenced that at 900 degrees C the decrease of zinc occupancy followed an almost asymptotic path in both quartz phases. Considering the formula ZnxAl2xSi3-2xO6, if x < 0.173 +/- 0.008 Zn-beta-quartz is not stable at room temperature. Treatments of 2 h at 1100 and 1200 degrees C produced the same quantities of gahnite (approximate to 20.6%) and glass (approximate to 11.6%), and slight differences for cristobalite (56 vs. 63%) and quartz (8.4 vs. 1.5%). Basically, gahnite incorporated all Zn2+ contained in clinoptilolite.