Solid state multinuclear NMR study of iron species in natural and modified clinoptilolite from Tasajera deposit (Cuba)

The present study has been conducted to elucidate the Fe-sites in natural clinoptilolite, and the possibility to produce a reversible replacement of these atoms in the zeolite framework. In order to achieve these results we have tried to introduce iron in clinoptilolite structure after the almost total extraction of the natural iron species. A sample of the purified natural clinoptilolite from Tasajeras deposit, Central region of Cuba, was modified by a hydrothermal treatment with orthophosphoric acid. Iron exchange forms of the orthophosphoric zeolite were obtained using FeSO4 and Fe2(SO4)3 solutions. The modified zeolites were studied by multinuclear magnetic resonance (27Al, 29Si, 31P MAS NMR and 129Xe NMR). Other analytical techniques as Electron Paramagnetic Resonance, X-ray diffraction, Mössbauer and Infrared spectrometry, volumetric measurements and chemical analysis by Induced Plasma Coupled spectroscopy were used to support the results of NMR studies. The presence of iron species with tetrahedral and octahedral coordination in the structure of a natural clinoptilolite has been confirmed. The influence of iron in tetrahedral coordination in the thermal stability of the clinoptilolite structure was also confirmed.