Extra-framework cation release from heulandite-type rich tuffs on exchange with NH(4)(+) |
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Authors: | Kantiranis N Sikalidis K Godelitsas A Squires C Papastergios G Filippidis A |
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Affiliation: | School of Geology, Aristotle University, Thessaloniki, Greece. kantira@geo.auth.gr |
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Abstract: | The outgoing cations of Greek heulandite-rich tuff samples (heulandite type-III, 91wt.%, mica 4wt.%, feldspar 5wt. %, CEC 2.22meq/g) were analysed upon exchange with ammonium acetate using atomic absorption spectrometry (AAS). The kinetic curves of each cation were investigated over a total time of contact of 720h with sampling at frequent intervals. The materials were examined by powder X-ray diffraction, SEM-EDS, and AAS. The sorption ability was measured using the ammonium acetate saturation method. It was found that Ca(2+) presents an unexpected extra-framework release and a surprisingly high degree of exchange (90%). The exchange of Mg (57%) is also worthy of note whereas the behavior of K(+) showed an expected rapid initial release. The behavior of Na(+) must be similar. However, its lower concentration in the zeolitic material minimizes its overall significance somewhat. On the other hand, Ca(2+) and Mg(2+) release is kinetically much slower, compared to that of alkali metal ions, and this phenomenon indicates that different exchange energies are needed till final equilibrium. |
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Keywords: | Ca NH4+ Ion-exchange selectivity HEU-type zeolite |
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