A new hydrous crystalline silicotitanate (CST), which we call TAM-5, has be synthesized that selectively removes cesium cations from solutions containing up to 5.7 M Na+ and for a pH range of less than 1 to greater than 14. In basic media and at the high concentrations of Na+ the CST also removes strontium cations from the solution. For a solution containing 5.7 M Na+, 0.6 M OH-, 5.1 M NOS-, 100 m g L Cs+, and 20 m e Sr2+, the distribution coefficients for cesium and strontium are 1000 mug and greater than 4,000 mug, respectively. For a solution of 5.7 M NaN03,lOO mg/L Cs+ and 20 mg/L S9+ the distribution coefficient for cesium is greater than 10 000 m u g and for strontium it is equal to 200 m u g . Experimental studies have also been conducted using complex waste simulants, which compare the performance of this CST and up to 60 other potential ion exchangers/absorbents. These studies substantiate the high selectivity of the CST for cesium in acidic and basic solutions. This new CST, labeled TAM-5, has considerable potential for removing cesium and strontium from defense wastes.

A new hydrous crystalline silicotitanate, labeled TAM-5 or CST, was developed for removing radioactive Cs+ from aqueous nuclear waste. This material is stable to radiation, highly selective for cesium relative to sodium, potassium, rubidium, and protons, and performs well in acidic, neutral, and basic solutions. Various experiments were conducted to determine the ion exchange properties of TAM-5. Two kinds of ion exchange sites exist in the solid, and cation exchange in one site affects the ion exchange properties of the other site. These two types of sites have different thermal effects: with increasing temperature the pH of one increases and the pH of the other one decreases. The total ion exchange capacity is 4.6 mequiv/g, but the cesium ion exchange capacity was less, which shows that not all of the ion exchange sites are available for cesium exchange. Step changes were observed in the ion exchange isotherms. The solid phase behaved ideally prior to the step changes. The apparent capacities within the ideal solid region were 0.57 mequiv/g for Cs+, 1.18 mequiv/g for Rb+, and 1.2 mequiv/g for K+. Both direct competition by rubidium and protons and indirect competition by protons and potassium were observed. The rational selectivities, which were measured from binary ion exchange data, can be used in different solutions including the multicomponent ion exchange systems, because they are constant for an ideal solid. Binary ion exchange isotherms were also developed using the rational selectivity as the parameter for the isotherms of cesium, rubidinium, and potassium.

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C. V. Philip and David W. Brooks consistent with the data in Table V. Although the relative constancy of klp does not establish the pathway as being FeOH + HL for all these systems, this fact, plus the other observations, argues for the assignment of the rate constants to ks as indicated in Table V. If fcip is on the order of 101 sec"1 for the kx pathway, then the contributions from this pathway to the measured rate would be quite small for ligands which are mostly protonated in acid solutions.

TAM-5 is a hydrous crystalline sodium silicotitanate inorganic ion exchanger with a high selectivity for Cs + . The kinetics of Cs + -Na + ion exchange using TAM-5 in multicomponent electrolyte solutions were determined using batch experiments. For the powder, which is composed of crystals, a single-phase, homogeneous model fit the data best. For the granules, which were prepared from the powder, a two-phase, heterogeneous model resulted in an excellent fit of the data. Macropore and crystal diffusivities were determined by fitting the model to experimental data collected on the powder and the granules. Intracrystalline diffusivities were concentration dependent and were on the order of 10 -19 m 2 /s. Macropore diffusivities were on the order of 10 -10 m 2 /s. Resistance to diffusion in the macropores was not significant for granules with diameters less than 15 µm. A two-phase, homogeneous model, where liquid within the pores is in equilibrium with the solid, was also evaluated for the granules. Surprisingly, for the granules, an excellent fit of the data was obtained; however, the effective macropore diffusivity was 1.1 × 10 -11 m 2 /s, an order of magnitude smaller than the macropore diffusivity found using the two-phase, heterogeneous model.