Sodium Titanates

As described in Section 2.6.3.2, sodium titanates are built from three-Ti06-octahedra-sharing edges, which are mutually connected through their corners to other similar chains of octahedra, forming, layers where the sodium ions are placed in the middle of the layers [3], 

The ion-exchange properties of this material are usually controlled by the interplanar distance, which can be modified to be large enough to permit the diffusion of cations in their hydrated forms into the structure [91], 

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Anatase and mtile are produced commercially, whereas brookite has been produced by heating amorphous titanium dioxide, which is prepared from an alkyl titanate or sodium titanate [12034-34-3] with sodium or potassium hydroxide in. an autoclave at 200—600°C for several days. Only mtile has been synthesized from melts in the form of large single crystals. More recentiy (57), a new polymorph of titanium dioxide, Ti02(B), has been demonstrated, which is formed by hydrolysis of K Ti O to form 20, followed by subsequent calcination/dehydration at 500°C. The relatively open stmcture... 

Sodium thiosulfate, 23 674 use in selenium analysis, 22 94-95 Sodium titanate, 25 100 Sodium toluenesulfonate... 

Figure 2. Generator, A = water reservoir sodium titanate column containing Th-228 C = cation exchange column and Pb-212.

The overall yield is essentially 100 by any of the preparation methods, but the physical characteristics of the ion exchangers are dependent on preparation conditions. For example, sodium titanate prepared by Eqs. la and lb with hydrolysis in one liter of water per mole of Ti(OC3H7)4 has a bulk density of 0.U5 g/cm3 and a specific surface area of lO-UO m /g. The same material prepared by Eqs. la and lb and hydrolyzed in a solution of 100 ml of water in 1000 ml of acetone for each mole of Ti(OC2H7)4 has a bulk density of 0.35 g/cm3 and a specific surface area of 200-UOO m /g. In all cases, the materials consist of agglomerates of 50-100 A particles with the degree of aggregation of the particles determining both the bulk density and surface area. 

A program to characterize the sodium titanate material has verified that the chemical and physical properties are reproducible from batch to batch for any of the preparation methods. 

This reaction is significant for sodium titanate (Keq — 10 moles /l ) and sodium zirconate, but is negligible for sodium niobate and some other "titanates" such as Mg(Ti205H)2. Gelatinous hydroxide precipitates which would appear likely based on Eq. 3 were not observed in the reaction of sodium titanate with aqueous waste, and stoichiometric loading was achieved with polyvalent cations which form insoluble hydroxides as well as for those forming soluble hydroxides. 

Figure 1. Elemental distribution of fission waste nuclides on a sodium titanate column. The distribution shown on the left was determined from qualitative analyses of the numbered column segments. The Cs and Na distributions on the right were obtained by quantitative analyses of each numbered segment. (O), Cs ( ), Na.

The waste nuclides were fractionated on the column into several hands as shown in Fig. 1 for a sodium titanate column. 

More efficient use of the titanate material was achieved by passing the column effluent through a synthetic zeolite bed (Zeolon 900 Na from the Norton Co., Akron, Ohio) to sorb Cs which "leaked" from the column. A zeolite bed equal to 20% by weight of the titanate was sufficient to produce a Cs DF>10° in the effluent from a titanate column loaded to slightly more than 100% of the calculated capacity. The use of the zeolite does not effect the overall process conditions since it can be incorporated directly into the sodium titanate during preparation. A Dowex 1-X8 resin bed was used to remove the from the effluent and also served... 

Wide variations in Cs and Na leaching observed in some of the first samples produced were found to result from the formation of the corresponding molybdate compounds which are highly water soluble. This problem was eliminated by the addition of 1-2% by weight of elemental silicon which served as a reducing agent and prevented molybdate formation. The silicon was added during the preparation of the sodium titanate material. 

Sodium titanate has been found to be very effective in removing Sr from defense waste typified by a 6m NaNO - 0.6m NaOH solution also containing the sodium salts of aluminate, nitrite, phosphate, carbonate, sulfate, and chromate in the range of O.lU to 0.007 N and Sr in the analytical concentration range of O.OU to O.U ppm ( ). Sodium titanate columns have provided a Sr decontamination factor of greater than io3 for 2500 column volumes of the waste at flow rates of 2 to 6 column volumes per hour. The material has also been shown to remove residual actinide contamination from the same and similar waste streams ( ). 

The preparation, composition, structure and leaching characteristics of a crystalline, ceramic radioactive waste form have been discussed, and where applicable, compared with vitrified waste forms. The inorganic ion exchange materials used such as sodium titanate were prepared from the corresponding metal alkoxide. The alkoxides were reacted in methanol with a base containing the desired exchangeable cation and the final powder form was produced by hydrolysis in an acetone-water mixture followed by vacuum drying the precipitate at ambient temperature. 

The baseline process, including the pressure sintering step, was demonstrated with both simulated high level waste and under hot cell conditions using a waste solution prepared from typical spent light water reactor fuel. A batch contacting method using sodium titanate was also evaluated, but the overall decontamination factor was much lower than obtained in the column process. 

Nuclei are produced by converting the purified titanium oxide hydrate to sodium titanate, which is washed free of sulfate and then treated with hydrochloric acid to produce the rutile nuclei. Rutile nuclei can also be prepared by precipitation from titanium tetrachloride solutions with sodium hydroxide solution. 

Hydrous metal oxide powders, such as sodium titanate, NaT O, can be prepared by treating TYZOR TPT with sodium hydroxide in methanol solvent to form a soluble intermediate, which is hydrolyzed in acetone—water to form an ion-exchange material useful in treating radioactive waste (158). Exchange of the sodium ion with an active metal such as Ni, Pt, or Pd gives heterogeneous catalysts useful in olefin polymerization, coal liquification, and hydrotreating. 

Hydrous Sodium Titanate Ion-Exchange Materials for Use as Catalyst Supports... 

To optimize the use of the amorphous sodium titanate powders as catalyst substrates, it is important to fully characterize the ion-exchange properties of the material. Further, the solution properties of the active metal to be loaded onto the support will be an important parameter in the control of the adsorption process. For example, exposure of sodium titanate to a nickel salt solution does not guarantee that nickel will be loaded onto the sodium titanate, or that the nickel, if loaded, will be dispersed on an atomic level. Sodium titanate only behaves as a cation exchange material under certain pH conditions. The solution pH also influences the hydrolysis and speciation of dissolved nickel ions (3), which can form large polymeric clusters or colloidal particles which are not adsorbed by the sodium titanate via a simple ion-exchange process. 

This paper describes some of our initial studies of the solution properties of sodium titanate powders in order to understand and control the metal-loading process in the preparation of a heterogeneous catalyst from the materials. The purposes of this study are 1) to define the pH and concentration regimes in which nickel is loaded onto sodium titanate as monomeric ions via ion exchange, as polymeric clusters via hydrolysis, or as discrete particles of colloidal nickel hydroxide, and 2) to characterize the catalysts with respect to the dispersion of the active metal under reaction conditions by measuring the activity and selectivity of the catalysts for a known "structure-sensitive" reaction, the hydrogenolysis of n-butane. 

Hydrous sodium titanate was prepared by the method of Dosch and Stephens (1). Titanium isopropoxide was slowly added to a 15 wt% solution of sodium hydroxide in methanol. The resulting solution was hydrolyzed by addition to 10 vol% water in acetone. The hydrolysis product is an amorphous hydrous oxide with a Na Ti ratio of 0.5 which contains, after vacuum drying at room temperature, approximately 13.5 wt% water and 2.5 wt% residual alcohol. The ion-exchange characteristics of the sodium titanate and the hydrolysis behavior of the nickel nitrate solutions were characterized using a combination of potentiometric titrations, inductively coupled plasma atomic emission (ICP) analysis of filtrates, and surface charge measurements obtained using a Matec electrosonic amplitude device. 

Three different nickel-loaded sodium titanates were prepared by exposing 5 gm of the sodium titanate powder to aqueous solutions of nickel nitrate containing sufficient nickel to incorporate one mole of nickel for every two moles of sodium on the support (corresponding to the stoichiometry associated with complete ion exchange). Each sample was prepared using different pH conditions (and thus, different Ni(II) concentrations) to vary the mechanism of... 

In order to control the mechanism by which nickel is loaded onto sodium titanate and to control the degree of nickel dispersion, we need to understand the ion-exchange properties of the sodium titanate support, the hydrolysis chemistry of the dissolved nickel, and how the different nickel species are expected to interact with the titanate support. 

Ion-Exchange Behavior of Sodium Titanate. The ion-exchange characteristics of sodium titanate supports are summarized in Fig. 1 (2). In the figure, proton consumption is plotted by the solid line as the Nao.sTi is titrated from a basic pH ( 12) with HC1. Na+ (+) loss from and Cl" (-) adsorption onto the support are followed by... 

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