Characterisation of potentially toxic natural fibrous zeolites by means of electron paramagnetic resonance spectroscopy and morphological-mineralogical studies

This study explored the morphological, mineralogical, and physico-chemical features of carcinogenic erionite and other possibly hazardous zeolites, such as mesolite and thomsonite, while also investigating the interacting capability of the mineral surface at the liquid/solid interface. Extremely fibrous erionite is K+ and Ca2+-rich and shows the highest Si/Al ratio (3.38) and specific surface area (8.14 m2/g). Fibrous mesolite is Na+ and Ca2+-rich and displays both a lower Si/Al ratio (1.56) and a smaller specific surface area (1.56 m2/g). The thomsonite composition shows the lowest values of Si/Al ratio (1.23) and specific surface area (0.38 m2/g). Electron paramagnetic resonance data from selected spin probes reveal that erionite has a homogeneous site distribution and interacts well with all spin probes. The surfaces of mesolite and thomsonite are less homogeneous and closer polar sites were found through consequent interaction with the probes. The mesolite surface can also clearly interact but with a lower strength and may represent a potential health hazard for humans, though with a lower degree if compared to erionite. The thomsonite surface is not inert and interacts with the probes with a low-grade capability. We can expect small fragments of thomsonite to interact with the biological environment, though with a low-grade intensity.