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Dense CsAlSi 5 O 12 was successfully obtained by hot pressing of Cs-exchanged clinoptilolite at 900 °C. Simultaneous application of high temperature and mechanical pressure allowed formation of CsAlSi 5 O 12 at temperature considerably lower than 1150 °C which was the lowest reported temperature of CsAlSi 5 O 12 formation in pressureless sintered Cs-exchanged clinoptilolite. CsAlSi 5 O 12 formation was preceded by complete amorphisation of Cs-exchanged clinoptilolite in temperature range between 700 and 900 °C. Bearing in mind that clinoptilolite possesses high affinity for Cs cation it is believed that hot pressing of Cs-exchanged clinoptilolite might be an efficient way to immobilize radioactive Cs by its incorporation into crystal lattice of stable CsAlSi 5 O 12 . The samples sintered at 950 °C had relative density about 84% of theoretical density and open porosity of only 6% which is expected to result in low Cs leaching rate. [ABSTRACT FROM AUTHOR]

A simple one-step method with direct thermal conversion at lower temperatures for preparing a stabile Cs-aluminsilicate phase, known as pollucite, is presented. Cs-exchanged form of Na, Ca-LTA type of zeolite (Cs-LTA) was pressureless sintered and hot pressed at certain temperatures in order to obtain pollucite. XRD and FTIR analysis were used to study structural changes of Cs-LTA before and after thermal treatments. Pressureless sintered sample recrystallized into pollucite phase after heat treatment at 1000 °C (3 h) (PLS1000) and hot pressed sample at 750 °C (3 h) using pressure of 35 MPa (HP750), indicating reduced temperature of 250°. SEM micrographs confirmed that HP750 has higher density than PLS1000 which leads to higher value of compressive strength. The HP750 showed better resistance to Cs leaching than the PLS1000. Base on these results one can conclude that hot pressing is the promising method for the permanent disposal of Cs radionuclides. [ABSTRACT FROM AUTHOR]