CLINOPTILOLITE AND HEULANDITE STRUCTURAL DIFFERENCES AS REVEALED BY MULTINUCLEAR NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY

Wide-line proton NMR has revealed differences in the water environment in two zeolitic isomorphs: clinoptilolite and heulandite. The proton spectrum of clinoptilolite is Gaussian in shape, while that of heuland ite is a (reduced splitting) Fake doublet. Studies of clinoptilolite f rom five different locations and heulandite from nine different sites agree with this observation. These results suggest a simple nondestruc tive NMR method for distinguishing heulandite from clinoptilolite. Deh ydration experiments are particularly informative. Proton line widths of clinoptilolite as a function of the dehydration temperature reveal three types of water binding, none being absorbed water. Similar studi es with heulandite reveal a change from the Fake doublet to a Gaussian , which is probably associated with the heulandite to heulandite B tra nsformation; Al-27 and Si-29 NMR studies of clinoptilolite indicate a change in framework structure and/or cation binding with dehydration. Al-27 NMR of heulandite exhibits an increase in line width with dehydr ation temperature to 175 degrees C. At this temperature the increase s tops and the line width remains constant to 215 degrees C, the maximum temperature studied. This agrees with the proton studies and is attri buted to the heulandite to heulandite B transformation. Si-29 NMR of h eulandite reveals a framework structural change and/or cation binding with dehydration. All of these observations are reversible upon rehydr ation.