ion-exchange properties of Terskite. II. experimental study in mixed solutions

Grigorieva A.A.*, Pekov I.V.*^,**, Bryzgalov I.A.*

*Lomonosov Moscow State University, Moscow, Russia;

**Institute of Geochemistry and Analytical Chemistry RAS, Moscow, Russia

Terskite, Na₄ZrSi₆O₁₆·2H₂O, is a zeolite-like zirconosilicate. The base of its crystal structure is a framework consisting of branched chains of Si tetrahedra linked by isolated Zr-octahedra. Na atoms and H₂O molecules are located in the cavities of the framework (Pyatenko et al., 1999).

It was experimentally found that terskite has strong cation-exchange properties. Na can be easily exchanged to K, Rb, Cs, Ca, Sr, Ba or Pb in solutions of their salts even under room conditions (Grigorieva et al., 2008).

Cation exchange properties of terskite can occur in nature. We can assume that cation composition of natural solutions is heterogeneous. Basing of this assumption, we made a series of the ion-exchange experiments with mixed (polycationic) solutions to study a character of selectivity of terskite. In the experiments, samples of terskite from the Shkatulka pegmatite (Mt. Alluaiv, Lovozero alkaline massif, Kola Peninsula, Russia) were used. Several series of experiments were performed: for twenty-four hours under room temperature and for three hours under 90 and 120њC. Equivoluminous mixtures of 1M solutions of: (I) KCl and ВаCl₂; (II) KCl, RbNO₃, CsNO₃, CaCl₂, SrCl₂ and BaCl₂; (III) KCl and CsNO₃; (IV) CsNO₃ and BaCl₂ (last – only under 90њC and 120њC) were used.

Terskite demonstrates cation-exchange properties in all experiments. In the solution I (K+Ba), Na was the most strongly replaced by Ba. As the temperature increases then the ability of the mineral to exchange Na to K decreases, while for Ba, we observe significant increase of the exchange degree.

In the solution II (K+Rb+Cs+Ca+Sr+Ba) under the room temperature, monovalent cations enter to the mineral the most strongly. Under 90ºC, Na replaced by both monovalent and bivalent cations. Under 120ºC, the degree of exchange of Na by bivalent cations increases greatly. It is more strongly replaced by Ca (up to 3.2 wt. % CaO: recorded in the samples tested under 120º while after the experiments under the room temperature, only up to 0.7% CaO was found). At the same time, K content decreases: up to 0.5 % K₂O after the experiment under 120ºC while up to 1.3 % - under room conditions. Degree of exchange of Na to Cs decreases twice with the temperature increase: 4.1% Cs₂O was recorded in the samples after experiments under 120ºC while up to 9.8 % - under the room temperature.

The series of experiments with the solution III (K+Cs) did not show considerable changes with temperature increase. The replacement of Na by Cs is the strongest in all cases.

In the solution IV (Cs+Ba), increase of content of a monovalent cation (Cs), but not bivalent cation (Ba), is observed with temperature increase: up to 8% BaO was recorded in the samples after experiments under the 90ºC and up to 15 % BaO – under the 120ºC. љ

Thus, Na in terskite can be replaced by all cations used in the experiments. The strongest cation exchange was recorded for Cs and Ba. The experiments showed that in the solutions with the most diversity of cations (solution II), a role of reactions with bivalent cations rises with temperature increase. Under room conditions, the strong preference of replacement of Na by other monovalent cations is observed. The only exception is the case of the solution IV (Cs+Ba): temperature increase gives rising of degree of replacement of Na by Cs but not Ba.

This study was supported by grants of President of Russain Federation Nos. 863.2008.5 and 2192.2008.5 and grant of Russian Science Support Foundation (I.V.P.).

References:

Grigorieva A.A., Pekov I.V., Bryzgalov I.A. Ion-exchange properties of natural zirconosilicate terskite // Minerals as Advanced Materials I. Springer Verlag, Berlin – Heidelberg, 2008, 87-89.

љPyatenko Yu.A., Kurova T.A., Chernitsova N.M., Pudovkina Z.V., Blinov V.A., Maksimova N.V. Niobium, Tantalum and Zirconium in the Minerals. M., IMGRE, 1999. 212 p.