A novel metastable layered titanium phosphate has been synthesized by the treatment of layered titanates (Na2Ti3O7 and Na4Ti9O20) with 1–2 M phosphoric acid solution at 120–150 °C. Based on the data of 31P MAS NMR and IR spectroscopy, x-ray powder diffraction, and thermal and elemental analysis, the formula Ti2O3(H2PO4)2 · 2H2O was assigned to the novel compound. The layered nature of the compound was confirmed from n-alkylamine intercalation and the ion exchange behavior toward alkali, alkaline earth, and some transition metal ions.

A zirconium trisilicate compound, with composition K(2)ZrSi(3)O(9).H(2)O (1), was prepared under mild hydrothermal conditions and was structurally characterized by using its X-ray powder diffraction data. The compound crystallizes in the space group P2(1)2(1)2(1) with a = 10.2977(2) Å, b = 13.3207(3) Å, c = 7.1956(1) Å, and Z = 4. The asymmetric unit consists of a metal atom, a trisilicate group, and three lattice positions corresponding to two cations and a water oxygen atom. In the structure, the Zr atom is octahedrally coordinated by the six terminal oxygens of the trisilicate group. The trisilicate groups exist as linear chain polymers connected to each other through the Zr atoms. This arrangement leads to channels and cavities in the structure that are occupied by the cations and water molecules. The K(+) ions in compound 1 were exchanged for Cs(+) ions in two steps. In the first case about 50% of the K(+) ions were exchanged to give a compound with composition K(0.9)Cs(1.1)ZrSi(3)O(9).H(2)O (2). Compound 2 was then loaded with additional Cs(+) ions which resulted in a phase K(0.5)Cs(1.5)ZrSi(3)O(9).H(2)O (3). These exchanged phases retain the crystal symmetry of compound 1, but their unit cell dimensions have expanded as a result of large Cs(+) ions replacing the smaller K(+) ions. Structure analyses of the exchanged phases show that the cations found in the cavities of compound 1 are highly selective for Cs(+) ions. A small amount of Cs ions also go to a site in the large channel that is very close to that occupied by the water oxygen in compound 1. In the absence of Cs, this site is filled with water molecules. The second cation found in the channel of 1 is partially occupied by water and K(+) ions. The K(+) ions in compound 1 were completely exchanged for Na(+) ions, and the compound thus obtained, Na(2)ZrSi(3)O(9).H(2)O (4), was treated with Cs(+) ions in a manner similar to that carried out for compound 1. The low Cs(+) ion phase, Na(0.98)Cs(1.02)ZrSi(3)O(9).H(2)O (5), and the high Cs(+) ion phase, Na(0.6)Cs(1.4)ZrSi(3)O(9).H(2)O (6), show ion distributions very similar to compounds 2 and 3 except for the fact that in the Na phases a small amount Cs(+) ion also goes to the second cation site. Compound 1 on heating releases the lattice water and transforms into a hexagonal phase, K(2)ZrSi(3)O(9), corresponding to the mineral wadeite. In the high-temperature phase the silicate group exists as a condensed cyclic group and the K(+) ions are sandwiched between trisilicate groups. A possible pathway for this conversion is also discussed.

New crystalline phases of fibrous titanium(IV) oxophosphates were prepared hydrothermally from titanium(IV) chloride in phosphoric acid solutions. The influence of several factors (concentration of reagents, molar ratio P:Ti in the reaction mixture, and reaction times) was studied. A phase diagram of the system is given. On the basis of elemental and thermal analysis, X-ray powder diffraction, 31 P MAS NMR, and IR spectroscopy, the formula Ti 2 O-(PO 4 ) 2 ‚2H 2 O was assigned to the novel compounds. The new phases (π-TiP and F-TiP) have different structures. The crystal structure of F-TiP was solved from X-ray powder data and was shown to be of the framework type with tunnels parallel to the c-axis direction. The absence of n-alkylamine intercalation processes for both compounds and other physical and behavioral similarities suggests a framework type structure for π-TiP also. The ion-exchange behavior toward alkali and alkaline earth ions was studied.

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The ion exchange testing of 30 synthetic adsorbents including layered and framework polyvalent metal silicates and phosphates, as well as amorphous exchangers was carried out. Their selectivity to alkali and alkaline earth metal cations in individual and complex solutions was determined. Several exchangers were found to have high selectivity for cesium and strontium. These exchangers are sodium phlogopite, layered sodium titanium silicate Na,TiSi,Oi2H,O, framework niobium (Na,Nb,Si,O,,'4H,O, tentative formula), zirconium (Na,ZrSi,O,H,O) and titanium (Na,Ti,SiO,'2H,o) silicates, and a layered o-tin phosphate (Sn(HPO,),2H,O). For all these materials cesiumand strontium ionexchange capacities as a function of pH were determined. The effect of sodium. magnesium and calcium on Cs and Sr" ions sorption was also studied over the concentration range 0.005 M -1.0 M and the explanations for the phenomena observed were proposed based on the knowledge of the crystal structure of the exchangers. Testing of the most promising exchangers for selective cesium and strontium recovery from ground water simulant in batchregime was carried out.

A framework potassium titanium silicate K 2 TiSi 3 O 9 ‚H 2 O, compound I, was synthesized by the reaction of a titanium-hydrogen peroxide complex and SiO 2 in alkaline media under mild hydrothermal conditions (180 °C). This compound was converted to the corresponding sodium phase, Na 2 TiSi 3 O 9 ‚H 2 O (IV) and two proton-containing phases, K 1.26 H 0.74 TiSi 3 O 9 ‚ 1.8H 2 O (II) and K 0.3 H 1.7 TiSi 3 O 9 ‚2.4H 2 O (III) by ion exchange. These products were characterized by elemental analysis, TGA, FT-IR, MAS 29 Si NMR, and X-ray diffraction. The ion exchange behavior of K 2 TiSi 3 O 9 ‚H 2 O and K 0.3 H 1.7 TiSi 3 O 9 ‚2H 2 O toward alkali, alkaline earth, and some transition metal ions solutions was studied. A high affinity of the protonic form of titanium trisilicate exchanger for cesium and potassium makes it promising for radionuclide-contaminated groundwater treatment and certain analytical separations. The crystal structure of K 2 TiSi 3 O 9 ‚H 2 O was found to be isomorphous with that of the zirconium analogue and contains a framework enclosing two types of tunnels. The exchange properties were interpreted on the basis of this structure and selectivity of the Zr and Ti phases rationalized on the basis of the tunnel sizes. The structure of II was solved on the basis of a monoclinic cell, whereas the K 2 TiSi 3 O 9 ‚H 2 O phase is orthorhombic. The relationship of structure II, monoclinic, to the parent orthorhombic structure is described. Phase III yielded a complex X-ray pattern with evidence of disorder and a highly complex 29 Si NMR spectrum. On reexchanging with K + , the original crystal lattice was restored.

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