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Sorption processes and XRD analysis of a natural zeolite exchanged with Pb2+, Cd2+ and Zn2+ cations

Castaldi, Paola and Santona, Laura and Enzo, Stefano and Melis, Pietro (2008) Sorption processes and XRD analysis of a natural zeolite exchanged with Pb2+, Cd2+ and Zn2+ cations. Journal of Hazardous Materials, Vol. 156 (1-3), p. 428-434. ISSN 0304-3894. Article.

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DOI: 10.1016/j.jhazmat.2007.12.040

Abstract

In this study the Pb2+, Cd2+ and Zn2+ adsorption capacity of a natural zeolite was evaluated in batch tests at a constant pH of 5.5 by polluting this mineral with solutions containing increasing concentrations of the three cations to obtain adsorption isotherms. In addition X-ray powder diffraction (XRD) was used to investigate the changes of zeolite structure caused by the exchange with cations of different ionic radius. The zeolite adsorption capacity for the three cations was Zn > Pb > Cd. Moreover a sequential extraction procedure [H2O, 0.05 M Ca(NO3)2 and 0.02 M EDTA] was applied to zeolite samples used in the adsorption experiments to determine the chemical form of the cations bound to the sorbent. Using this approach it was shown that low concentrations of Pb2+, Cd2+ and Zn2+ were present as water-soluble and exchangeable fractions (<25% of the Me adsorbed), while EDTA extracted most of the adsorbed cations from the zeolite (>27% of the Me adsorbed). The XRD pattern of zeolite, analysed according to the Rietveld method, showed that the main mineralogical phase involved in the adsorption process was clinoptilolite. Besides structure information showed that the incorporation of Pb2+, Cd2+ and Zn2+, into the zeolite frameworks changed slightly but appreciably the lattice parameters. XRD analysis also showed the occurrence of some isomorphic substitution phenomena where the Al3+ ions of the clinoptilolite framework were replaced by exchanged Pb2+ cations in the course of the ion exchange reaction. This mechanism was instead less evident in the patterns of the samples doped with Cd2+ and Zn2+ cations.

Item Type:Article
ID Code:1471
Status:Published
Refereed:Yes
Uncontrolled Keywords:Natural zeolites, heavy metals, adsorption capacity, XRD investigations
Subjects:Area 03 - Scienze chimiche > CHIM/02 Chimica fisica
Area 07 - Scienze agrarie e veterinarie > AGR/13 Chimica agraria
Divisions:001 Università di Sassari > 01 Dipartimenti > Chimica
001 Università di Sassari > 01 Dipartimenti > Scienze ambientali agrarie e biotecnologie agro-alimentari
Publisher:Elsevier
ISSN:0304-3894
Additional Information:Pubblicato online il 23 dicembre 2007.
Deposited On:18 Aug 2009 10:05

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