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Thermal treatment and Radon-radioactivity content of zeolite

Assessment of potential to "foam" zeolite in industrial environment (NTUA and IGME)

A pilot scale expansion furnace (scale-down of industrial facility) appropriate for dynamic thermal treatment of minerals has been used and commissioned for the purposes of the project. NTUA performed experiments to investigate the possibility of thermal treatment of zeolites (foaming) based on similar results found in open literature. Four different types of Italian zeolites and eight types of Greek zeolites have been exposed to abrupt heating up to 11000C. Experiments were performed at heating temperatures of 6000C, 9000C and 11000C, and for two particle size distributions of the raw material, corresponding to 0 - 0.3mm and 0.3 - 0.9mm. Size distribution and dry density (specific weight) of all the treated samples have been measured before and after treatment. Results indicated that, for the conditions under which the experiments were performed, direct heating of zeolite particles up to 11000C does not result to apparent foaming of the material.

Selected thermally treated samples were analysed by IGME using XRD. Results indicate:
- Smectite, is destroyed during thermal expansion process
- Heulandite-2 lattice appears in almost complete destruction
- Some of clinoptilolite and mordenite seems to remain during thermal expansion procedure
- Kaolinite and calcite, if present, they are entirely destroyed by the thermal process.
- Possibly new phases are formed not clearly detected by XRD

From the LOI analytical results it is concluded that in the samples containing heulandite-2 lose over 80% of LOI during the procedure of expansion due mainly to the destruction of the zeolite lattice. In the samples containing clinoptilolite and mordenite that are more stable in high temperatures than heulandite-2 (clinoptilolite, mordenite) a greater percentage of LOI remain after thermal expansion. Representative samples of Greek and Italian zeolites were analysed for their natural radionuclide content using gamma spectroscopy and for radon exhalation rate (ìBqkg-1s-1). The 226Ra content of the Zeolites examined (40-160BqKg-1) lies within the 226 Ra content of European building materials, i.e. 4 - 4000BqKg-1. The Radon exhalation rate of the zeolites examined (80 - 115ìBqKg-1s-1) lies within the range of Greek black cement or fly ashes, i.e. 10 - 110ìBqKg-1s-1, but it is much lower than that of internationally reported values. Measured radon exhalation rate from gypsum boards containing up to 10% zeolite was very low.

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