engleski

Sorption of Cr3+ on clinoptilolite tuff: A structural investigation

A Cr3+-modified natural zeolite sample from the deposit of Donje Jesenje (Croatia) was structurally studied using X-Ray Powder Diffraction (XRPD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDXS), Inductively Coupled Plasma Mass Spectrometry (ICP-MS), X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS). The analyses revealed the presence of up to 0.4 wt. % of chromium in the clinoptilolite crystals. The X-ray Photoelectron Spectroscopy depth analysis suggested a uniform distribution of chromium from the surface of the crystallites to the depth of 50(3) nm. The study of local environment of chromium by XANES (X-ray Absorption Near Edge Structure) showed that chromium cations in the sample were predominantly in the 3+ oxidation state. EXAFS (Extended X-ray Absorption Fine Structure) analysis revealed that Cr3+ cations bond to six oxygen atoms at the distance of 1.97(2) Å and two chromium atoms at the distance of 2.54(2) Å suggesting that Cr3+ cations most probably arrange in the zeolite pores in the form of small clusters of CrO6 octahedra. The chromium could not be completely desorbed from the sample after posttreatment with NaCl or HCl solutions thus indicating mostly irreversible sorption of chromium in the zeolite

clinoptilolite ; zeolite ; chromium-loaded ; Cr3+ ; XANES ; EXAFS ; XPS

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