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Ion exchange of zeolite Na-P(c) with Pb2+, Zn2+, and Ni2+ ions

Christidis Georgios, Ioannis Paspaliaris , Aggeliki Moirou

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Summary

This paper examines the ion-exchange properties of synthetic zeolite Na-P0, which was pro- duced from perlite-waste fines and has a SiO2:A1203 ratio of 4.45:1 and a cation-exchange capacity (CEC) of 3.95 meq g ~. Although equilibrium is attained rapidly for all three metals, exchange is incomplete, with At(max) (maximum equilibrium fraction of the metal in the zeolite) being 0.95 for Pb, 0.76 for Zn, and 0.27 for Ni. In both Na ~ ␣89 and Na --* ␣89 exchange, the normalized selectivity coefficient is virtually constant for :~A~(normalized equilibrium fraction of the metal in the zeolite) values of --<0.6, suggesting a pronounced homogeneity of the available exchange sites. The Gibbs standard free energy, AG~ of the Na ---)␣89 exchange calculated from the normalized selectivity coefficient is -3.11 kJ eq and, for the Na ~ 1/2Znexchange, it is 2.75 kJ eq ~.Examination of the solid exchange products with X-ray diffraction (XRD) revealed a possible decrease in crystallinity of zeolite Pb-Pc as suggested by the significant broadening and disappearance of diffraction lines. This decrease is associated with a reduction of pore opening, as indicated from Fourier-transform infrared analysis (FTIR), which in turn results in a decrease of the amount of zeolitic water. Thermogra- vimetric-differential thermogravimetric (TG-DTG) analysis showed that water loss occurs in three steps, the relative significance of which depends on the type of exchangeable cation and subsequently on the type of complex formed with the cation and/or the zeolite channels. Zeolite Na-Pc might be utilized in environmental applications, such as the treatment of acid-mine drainage and electroplating effluents.

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