Zeolite 2010 – 8th International Conference of the Occurrence, Properties, and Utilization of Natural Zeolites Sofia, Bulgaria, 10–18 July 2010 Zn-exchanged clinoptilolite from Beli plast deposit, Eastern Rhodopes, Bulgaria L. Terziyska1, G. Kirov2, O. Petrov1, and N. Lihareva1 1 Central Laboratory of Mineralogy and Crystallography; Sofia, Bulgaria; Email: anien@abv.bg 2 Sofia University “St. Kl. Ohridski”, Faculty of Geology and Geography; Sofia, Bulgaria Introduction Ion exchange properties of clinoptilolite are utilized in practice and the study of these processes is progressing. Clinoptilolite displays selectivity towards the metals of the first and second group as well as for Al3+, Fe2+, and NH +
4 . Ames (1960) found the following selectivity decreasing order: Rb+, K+, NH4 , Ba+,
Sr2+, Na+, Ca2+, Fe2+, Al3+, Mg2+, Li+. The big monovalent cations like Cs are preferred by the microporous structure of zeolites (Petrov et al., 1991). For small bi-valent cations the selectivity is low. For Cd, Cu, and Zn it has been established to be in the order Cd2+>Cu2+>Zn2+ (Langella et al., 1999). The antibacterial properties of zinc are used in cosmetics and medicine in various preparations for local therapy of skin deceases caused by Propionibacterium acnes or injuries. The system erythromycin – zinc is more effective when during the contact with skin the useful components are released gradually. Clinoptilolite is a suitable for such an effect as it ensures gradual release of zinc in a medium of erythromycin.
The purpose of the present paper is to study in detail the structural changes that take place in
clinoptilolite, when undergoing greater Zn+2 exchange at higher temperatures and durations.
Experimental Methods Enriched clinoptilolite fraction was obtained from rock (Beli plast deposit, East Rhodopes, Bilgaria), which was crushed, ground, and fractioned by sedimentation giving fractions 0.160–0.032 mm (sample С1), 0.032– 0.016 mm (С2), and 0.016–0.002 mm (С3). The fractions were enriched in clinoptilolite by separation with heavy liquid. Zn2+ exchanged clinoptilolite was obtained for fractions С1, С2, and С3 in the way: The material was placed in teflon-lined autoclaves with 1M solution of ZnCl2 at 100°C for 6 days duration. The
solution was renewed on two days intervals with separating material for study. After the 6-th day the samples were decanted, washed with distilled water, and dried at room temperature. The powder XRD experiments were done in the range 8–50° 2q (DRON 3M diffractometer, Fe-filtered CoKα radiation). The chemical analyses were done with AAS for the Zn exchanged modifications and with wet chemical analysis of the light fractions after separation.
Results and Discussion The light fraction is proved by XRD phase analysis to contain mainly clinoptilolite and always traces of opal- C, which is difficult to be removed. Ion exchange degree with heavy cations can be followed by the intensity changes of the basal reflections 0k0 (Petrov, 1995). Zn2+ ions after significant exchange also cause intensity variance of the peaks in the clinoptilolite XRD pattern that allows evaluation of the Zn2+ exchange following the intensity changes of some peaks (Figure 1). It is seen from the figure that when comparing the diffraction patterns of the initial and the exchanged samples there are apparent changes in some of the peaks. Namely, slight lowering of I020 and more expressed lowering of I200. Also, the peaks –201 and 111 decrease in
intensity with the exchange while peaks 001 and – 311 increase. Interestingly, the small peak 220 fully disappears even at the 2nd day of Zn exchange of clinoptilolite. The shown intensity changes in the powder XRD patterns of Zn exchanged clinoptilolite are undoubtedly due to changes in the cationic sub-lattice in the structure of this zeolite. Additionally, the refinement of the unit cell parameters showed constant increase of the values with the content of exchanged Zn. For the initial clinoptilolite sample we obtained a=17.694 Å, b=18.045 Å, c=7.408 Å, b=116.28°, and V=2120 Å3, while the exchanged sample for 30 days has the following parameters: a=17.709 Å; b=18.114 Å; c=7.412 Å; b=116.09°; and V=2135 Å3 (0.7% increase).
AAS confirms the XRD data for Zn content in clinoptilolite after ion exchange (Table 1). From the
theoretically possible 7.1% Zn2+ ions for the studied clinoptilolite (K1.8Ca1.7Na0.5Mg.0.2)6.1Al5.8Fe0.22
Si29.94O72x20H2O) we reached exchange level of 6.8%. Best exchanged is fraction 0.032–0.016 mm (sample
С2). Possible explanation for these results is that this fraction contains less opal-C than C3 (higher clinoptilolite content) and it is finer than C1 (greater exchange surface).
Zeolite 2010 – 8th International Conference of the Occurrence, Properties, and Utilization of Natural Zeolites Sofia, Bulgaria, 10–18 July 2010 Figure 1. Powder XRD patterns of clinoptilolite sample (fraction 0.032–0.016 mm) from Beli plast deposit (initial) and its Zn2+ exchanged forms for duration of 2, 4, and 6 days
Table 1. Content of Zn (wt.%) after ion exchange determined by AAS in different clinoptilolite fractions
The performed studies reveal some crystal chemical peculiarities of Zn-exchanged sedimentary
clinoptilolite, which are needed background for future more detailed structural investigations to explain the localization of Zn2+ ions in the channels of clinoptilolite and predict the possible desorption processes connected with biological contacts.
References Ames, L.L. (1960) The cation sieve properties of clinoptilolite. American Mineralogist, 45, 689–700. Langella, A., Pansini, M., Cappelleti, P., de Gennaro, B., de Gennaro, M. and Collela, C. (2000) NH +
Zn2+, Cd2+ and Pb2+ exchange for Na+ in a sedimentary clinoptilolite, North Sardinia, Italy. Microporous and Mesoporous Materials, 37, 337–343.
Petrov, O. (1995) Cation exchange in clinoptilolite: an x-ray powder diffraction analysis. Pp. 271–279 in:
Natural Zeolites’93 (D.W. Ming, and F.A. Mumton, editors). Int. Comm. Natural Zeolites, Brockport, New York.
Petrov, O., Filizova, L., Kirov, G. (1991) Cation distribution in clinoptilolite structure: Cs-exchanged sample.
Comptes Rendus de L’Academie Bulgare des Sciences, 44, 12, 77–80.
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Zeolite 2010 – 8th International Conference of the Occurrence, Properties, and Utilization of Natural Zeolites Sofia, Bulgaria, 10–18 July 2010
Figure 1. Powder XRD patterns of clinoptilolite sample (fraction 0.032–0.016 mm) from