@article{3006371,
    title = "Extra-framework cation release from heulandite-type rich tuffs on exchange with NH4+",
    author = "Kantiranis, N. and Sikalidis, K. and Godelitsas, A. and Squires, C. and Papastergios, G. and Filippidis, A.",
    journal = "Australasian Journal of Environmental Management",
    year = "2011",
    volume = "92",
    number = "6",
    pages = "1569-1576",
    issn = "1448-6563, 2159-5356",
    doi = "10.1016/j.jenvman.2011.01.013",
    keywords = "alkali metal;  ammonia;  ammonium acetate;  calcium ion;  heulandite;  magnesium ion;  metal ion;  potassium ion;  sodium ion;  unclassified drug;  zeolite, ammonium;  atomic absorption spectroscopy;  calcium;  cation;  heulandite;  ion exchange;  scanning electron microscopy;  sorption;  tuff;  X-ray diffraction, absorption;  adsorption kinetics;  article;  atomic absorption spectrometry;  calcium transport;  cation transport;  magnesium transport;  potassium transport;  scanning electron microscopy;  sodium transport;  transport kinetics;  X ray powder diffraction, Acetates;  Calcium;  Cations;  Kinetics;  Microscopy, Electron, Scanning;  Sodium;  Spectrophotometry, Atomic;  Time Factors;  Volcanic Eruptions;  X-Ray Diffraction;  Zeolites",
    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 Ca2+ 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, Ca2+ and Mg2+ 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. © 2011 Elsevier Ltd."
}