Investigation of HEU-type zeolite crystals after interaction with Sr2+ cations in aqueous solution using nuclear and surface analytical techniques |
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Authors: | J Orechovska P Misaelides A Godelitsas P Rajec H Klewe-Nebenius F Noli E Pavlidou |
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Institution: | (1) Department of Nuclear Chemistry, Comenius University, SK-84215 Bratislava, Slovak Republic;(2) Department of General & Inorganic Chemistry, Aristotle University, GR-54006 Thessaloniki, Greece;(3) Institut für Instrumentelle Analytik, Forschungszentrum Karlsruhe, P.O. Box 3640, D-76021 Karlsruhe, Germany;(4) Department of Solid State Physics, Aristotle University, GR-54006 Thessaloniki, Greece;(5) Present address: TVX Hellas S.A.-Mines and Gold Industry/Environmental & Quality Control Division, Stratoni, 63082 Chalkidiki, Greece |
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Abstract: | Pure HEU-type zeolite (heulandite) crystals were allowed to interact with Sr2+ cations in aqueous solution. The powdered solid experimental products obtained from batch-type sorption experiments, using
solutions of Sr2+-concentrations between 10 and 1000 mg/l, were investigated using INAA, RI-XRF and SEM-EDS. The Sr uptake by the mineral which
can adequately be described with a Freundlich-type isotherm, varies from 3.14 to 6.22 mg/g. The distribution coefficients
increase progressively by decreasing the solutions concentration reaching a value of 1800 ml/g. The investigated zeolite interacts
with Sr2+ cations through ion exchange reactions and initial exchangeable Ca2+ cations are replaced into the structural micropores. However, in the best case, only ca. 43% of the theoretical CEC can be
covered because of the limited availability of the extra framework Ca2+ cations that can be removed from the lattice under ambient treatment conditions. The XPS investigation of Sr-loaded single
crystals indicated that adsorption of Sr2+ cations on the outer surface also occurs while surface precipitation phenomena must be excluded. Similar surface analyses
by means of12C-RBS showed that the Sr depth-distribution at near-surface layers is quite homogenous in contrast to a previous relevant
study revealing an intense surface Sr-accumulation on a natural Ca-zeolite of different structural characteristics (scolecite). |
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