51. Removal of manganese in batch and fluidized bed systems using beads of zeolite a as adsorbentMina Jovanovic, Iztok Arčon, Janez Kovač, Nataša Novak Tušar, Bojana Obradovic, Nevenka Rajić, 2016, izvirni znanstveni članek Opis: In this study the uptake capacity of Mn(II) ions by zeolite A beads was investigated for different initial Mn concentration (100e400 mg Mn dm^-3) in batch mode at 25e55 C. The obtained adsorption capacity varying from 30 to 50 mg Mn g^-1 demonstrated a high affinity of zeolite A towards Mn(II) present in solutions. Kinetic studies indicated the intra-particle diffusion as the rate limiting step up to 45 C with apparent diffusivities in the range (1.2e2.0) x 10^-13 m2 s^-1 and the activation energy of 21.9 kJ mol^-1, which implies strong interactions between the zeolite A and Mn ions. At 55 C ion-exchange became the rate limiting step. The adsorption isotherms were studied at 25 C showing that the Mn adsorption is the best described by the Langmuir model suggesting a homogenous zeolite surface. XPS analysis of the Mnloaded beads showed that there is no surface accumulation of Mn but an almost uniform Mn distribution inside zeolite A, whereas XANES and EXAFS suggested that the adsorption of Mn(II) was followed by the Mn(II) oxidation and oxide formation. Regeneration of the spent zeolite was examined in 8 adsorption/desorption cycles by a chelating Na2EDTA in a fluidized column. It has been found that zeolite A beads could be reused for at least 4 cycles with satisfactory Mn(II) adsorption efficiencies of about 70%.
Ključne besede: Zeolite A
Manganese
Adsorption kinetics
EXAFS/XANES
XPS
Objavljeno v RUNG: 01.04.2016; Ogledov: 6701; Prenosov: 0
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53. High-resolution X-ray absorption spectrometry of atomic vaporsIztok Arčon, Jana Padežnik Gomilšek, Alojz Kodre, Andrej Mihelič, 2004, izvirni znanstveni članek Opis: A measurement of an x-ray absorption spectrum of a monatomic sample yields pure atomic absorption essential for the EXAFS (Extended X-ray Absorption FineStructure) analysis in cases of a weak structural signal. A construction of an absorption cell to contain vapor sample takes into account specific properties of the investigated element. Metal-vapor absorption cells for the elements K, zn, Rb, Cd, Cs, and Hg are presented and comments are made on the use of materials and the operating mechanisms of the cells.
Ključne besede: X-žarki, absorpcija, EXAFS, absorpcijske celice
Objavljeno v RUNG: 10.07.2015; Ogledov: 6097; Prenosov: 29
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54. X-ray absorption spectroscopy and related techniquesIztok Arčon, Alojz Kodre, Jana Padežnik Gomilšek, 2004, izvirni znanstveni članek Opis: In the extensive field of X-ray diagnostic techniques, nowadays mostly implemented on synchrotron X-ray sources, the X-ray absorption methods offer a relatively simple tool for structural analysis of materials. The advantage of the methods is the sensitivity to chemical species and the insensitivity to the long-range order. An overview of various detection techniques is given together with the discussion of accuracy of the method with regard to the spatial resolution and the possible contamination by intra-atomic contributions, the multielectron photoexcitations.
Ključne besede: X-žarki, absorpcija, EXAFS, XANES
Objavljeno v RUNG: 10.07.2015; Ogledov: 5804; Prenosov: 28
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