L. Szirtes

Effect of γ-radiation on various synthetic inorganic ion exchangers

Abstract The structure and some properties of crystalline zirconium and cerium phosphates and cerium arsenate ion exchangers after irradiation have been investigated. The absorbed dose was about 109 rad. No change in the structure of crystalline zirconium phosphate was observed, while cerium arsenate showed changes both in the structure and other properties; cerium phosphate was destroyed during the irradiation.

Exchange of iron ions into layers of α-zirconium phosphate

Abstract Exchange of Fe 3+ and Fe 2+ ions into layers of α-zirconium phosphate is achieved in aqueous media by using monosodium and/or ethanolic forms of the host precursor. The products obtained are characterized by chemical analysis, X-ray powder diffraction and Mossbauer spectroscopy. For site assignments, structural modeling is used by combining the measured and simulated X-ray diffractograms. Fe 3+ ions are incorporated only in part, and a biphasic product is obtained. Exchange of Fe 2+ ions leads to a single phase with 50% iron loading with Fe 2+ ions located in two different coordination states. On a long-term storage in open air, Fe 2+ →Fe 3+ oxidation proceeds without noticeable change in the crystal structure.

On the mechanism of diffusion and ionic transport in crystalline insoluble acid salts of tetravalent metals—II self diffusion of Na+ and K+ on microcrystals of Zr(NaPO4)2·3H2O and Zr(KPO4)2·3H2O

Abstract A modification of the Fick equation solution for diffusion in spherical particles from a well-stirred solution of limited volume that takes into account the non-uniformity of the particle-size has been developed. The equation obtained has been employed in a study of the self-diffusion rate of 24Na+ and 42K+ in Zr(NaPO4)2·3H2O and Zr(KPO4)2·3H2O, respectively. The self diffusion processes have been followed at different temperatures and the Arrhenius plot has been shown to hold. In the range of temperature studied the self-diffusion occurs in a single step and activation energies of 73 and 79 KJ/mole have been found for the sodium and potassium forms, respectively. The mobility data are compared with conductivity data available for the same ionic forms.

Thermoanalytical investigation of layered titanium salts

The investigated materials have similar routes of thermal decomposition; i.e. they lose their crystal water first, then at a higher temperature their structural one. At least the result TiP2O7 goes through a phase change at about 1000 K. The amorphous titanium phosphate lost its crystal and structural water at higher temperature than those of crystalline forms. Both α- and γ-titanium phosphates and also their transition metal containing forms have layered structure. In case of α- and γ-forms after the loss of crystal water a phase change occurs which is followed by the decomposition of the molecule. Various transition metals containing γ-titanium phosphates lose their crystal water at the same temperature, with the exception of Ni containing ones. The process is finished in this case at temperature 90 K higher than that of the others.

INVESTIGATION OF SILICA GEL SUPPORTED INORGANIC ION EXCHANGERS

Microcrystalline zirconium phosphate (α-ZrP), hydrous manganese dioxide (HMnO), ammonium molybdophosphate (AMP) and silica gel supported forms of these materials as well as silica gel (SG) itself were investigated by thermoanalytical, electron microscopic, X-ray diffraction and infrared spectrometric methods. Chemical composition, structure and some related properties of the inorganic ion exchangers mentioned above are reported.

FT-IR studies on intercalates and organic derivatives of crystalline (α- and γ-forms) zirconium phosphate and zirconium phosphate-phosphite

FT-IR studies were carried out for various α- and γ-crystalline intercalates of zirconium phosphate (ZrP) and also for zirconium phosphatephosphite (ZrPP). The characteristic peaks of n-alkanols, n-alkylamines, benzylalcohol and benzylamine, diethyleneglycol and also some amino acid intercalates/derivatives were determined. Based on the data assumptions are made about the type of bonding between the layers and also the variety of intercalates of various crystalline form zirconium phosphates was determined.

Mixed insoluble acidic salts of tetravalent metals IV. Crystalline mixed zirconium — Titanium phosphates

Mixed crystalline alpha zirconium — titanium phosphates with variable zirconium to titanium ratios have been prepared both by the well known gel reflux method and a modified HF method. Chemical analysis, X-ray, i.r. and thermal analysis were used to characterize the materials. Exchange capacities for these ion-exchangers have been evaluated by pH-titration combined with radioisotope tract technique for Na+, K+, Rb+ and Cs+.

Comparative study of layered tetravalent metal phosphates containing various first-row divalent metals. Synthesis, crystalline structure

The transition metal forms of α-zirconium-. titanium-, and hafnium phosphates were prepared by ion exchange method. Their structure was investigated by X-ray powder diffraction (XRPD) method. It was found that the transition metal containing phosphates have the same layered structure as the pristine tetravalent metal phosphates, except for the increase of interlayer distance from 7.6 Å to ∼9.5 Å. As a result of the incorporation of transition metals in the layers, the c-axis is increased from ∼15 Å to ∼20 Å (in the case of titanium phosphate to ∼25 Å). All other parameters (a, b and β °) are practically unchanged.

Effect of gamma-radiation on amorphous mixed zirconium-titanium phosphates

A precipitation method was used to prepare amorphous mixed zirconium-titanium phosphates with various titanium contents. In this way the acidic solutions of ZrOCl2.8H2O and TiCl4 in various ratios were rapidly mixed with a phosphoric acid solution under continuous stirring. The resulting precipitate, characterized as [ZrxTi/1−x//HPO4/2.n H2O] was contacted with water of ethanol, then washed to pH ∼3.0 and dried at room temperature. The samples were irradiated with γ-rays of a60Co source giving a 6.6×107 Gy total dose. The thermal, chemical and ion-exchange properties of irradiated samples were investigated.

Self-diffusion of the sodium ion in the monosodium and disodium forms of α- and γ-zirconium phosphate

Summary α- and γ-zirconium phosphate are layered exchangers that differ both in their structures and the packing sequence of the layers. In γ-zirconium phosphate the structure of the layer is more compact and the interlayer distance is greater than in γ-zirconium phosphate. These compounds are therefore good models for studying the effect of the distance between the fixed charges and of the interlayer distance on the transport properties of layered exchangers. The self-diffusion processes of 24Na+ in the monosodium and disodium forms of α- and γ-zirconium phosphate were therefore investigated. In the first stages of the processes, the rate seems to be controlled by fast interfacial isotopic exchange reactions, whereas in the last stages the rate is particle diffusion controlled. The self-diffusion constants and hence the activation energies were calculated by using an approximate equation valid for long diffusion times. The activation energies for self-diffusion increase in the order γ-Zr(NaPO4)2 5H2O (33 kJ/mole) O− fixed charges lying on the faces of the layers.