[en] The use of in-situ X-ray and neutron diffraction has elucidated the differences in the mechanism of ion exchange between a titanium silicate and a phase in which Nb is substituted for Ti at the 25% level both with the sitinakite structure. The area of interest is the very high level of selectivity required of the exchangers for use in nuclear waste systems.

[en] The exchange of Cs⁺ into H_1.22K_0.84ZrSi₃O₉ · 2.16H₂O (umbite-(HK)) was followed in situ using time-resolved X-ray diffraction at the National Synchrotron Light Source. The umbite framework (space group P2₁/c with cell dimensions of a = 7.2814(3) (angstrom), b = 10.4201(4) (angstrom), c = 13.4529(7) (angstrom), and β = 90.53(1)^o) consists of wollastonite-like silicate chains linked by isolated zirconia octahedra. Within umbite-(HK) there are two unique ion exchange sites in the tunnels running parallel to the a-axis. Exchange Site 1 is marked by 8 member-ring (MR) windows in the bc-plane and contains K⁺ cations. Exchange Site 2 is marked by a larger 8-MR channel parallel to [100], and contains H₂O molecules. The occupancy of the Cs⁺ cations through these channels was modeled by Rietveld structure refinements of the diffraction data and demonstrated that there is a two-step exchange process. The incoming Cs⁺ ions populated the larger 8-MR channel (Exchange Site 2) first and then migrated into the smaller 8-MR channel. During the exchange process a structural change occurs, transforming the exchanger from monoclinic P2₁/c to orthorhombic P2₁2₁2₁. This structural change occurs when Cs⁺ occupancy in the small cavity becomes greater than 0.50. The final in situ ion exchange diffraction pattern was refined to yield umbite-(CsK) with the molecular formula H_0.18K_0.45Cs_1.37ZrSi₃O₉ · 0.98H₂O and possessing an orthorhombic unit cell with dimensions a = 10.6668(8) (angstrom), b = 13.5821(11) (angstrom), c = 7.3946(6) (angstrom). Solid state ¹³³Cs MAS NMR showed there is only a slight difference between the two cavities electronically. Valence bond sums for the completely occupied Exchange Site 1 demonstrate that Cs-O bonds of up to 3.8 (angstrom) contribute to the coordination of the Cs⁺ cation.

[en] 'In this research program, Oak Ridge National Laboratory (ORNL) is collaborating with Texas A and M University in the development of highly selective inorganic ion exchangers for the removal of cesium and strontium from nuclear tank-waste and from groundwater. Inorganic ion exchangers are developed and characterized at Texas A and M University; ORNL is involved in preparing the powders in engineered forms and testing the performance of the sorbents in actual nuclear waste solutions. The Texas A and M studies are divided into two main categories: (1) exchangers for tank wastes and (2) exchangers for groundwater remediation. These are subdivided into exchangers for use in acid and alkaline solutions for tank wastes and those that can be recycled for use in groundwater remediation. The exchangers will also be considered for in situ immobilization of radionuclides. The approach will involve a combination of exchanger synthesis, structural characterization, and ion exchange behavior. ORNL has developed a technique for preparing inorganic ion exchangers in the form of spherules by a gel-sphere internal gelation process. This technology, which was developed and used for making nuclear fuels, has the potential of greatly enhancing the usability of many other special inorganic materials because of the improved flow dynamics of the spherules. Also, pure inorganic spherules can be made without the use of binders. ORNL also has access to actual nuclear waste in the form of waste tank supernatant solutions for testing the capabilities of the sorbents for removing the cesium and strontium radionuclides from actual waste solutions. The ORNL collaboration will involve the preparation of the powdered ion exchangers, developed and synthesized at Texas A and M, in the form of spherules, and evaluating the performance of the exchangers in real nuclear waste solutions. Selected sorbents will be provided by Texas A and M for potential incorporation into microspheres, and the performance of the sorbents and microspheres will be examined using actual waste supernatant solutions. This collaborative program could potentially take an exchanger from concept, synthesis, structure determination, and elucidation of exchange mechanism, to engineered product and testing on real waste streams.'

[en] The ion exchange behaviour of zirconium phosphates possessing different degrees of crystallinity was examined for the NH₄⁺/H⁺ system. In the most crystalline exchangers ammonium ion is initially taken into solid-solution without phase change. This initial uptake is followed by conversion of the solid solution to a fully exchanged ammonium ion phase Zr(NH₄PO₄)₂ .H₂O. The composition range of the solid solution increases with decreasing crystallinity until, in the amorphous exchanger it covers the entire range of ammonium ion uptake. The exchange process is reversible for the amorphous exchanger with K = 7.4 x 10^-5. However, with the more crystalline exchangers a half-exchanged phase, Zr(NH₄)H(PO₄)₂.0.33H₂O, is obtained when H⁺ replaces NH₄⁺. These results differ significantly from other published data. (author)

[en] This paper describes the structure and principal ion exchange characteristics of acid salts of polyvalent metals and hydrous oxides. The acid salts can be prepared in crystalline (layered) form, as amorphous gels and in intermediate stages of crystallinity. Ion exchange behavior is then related to the crystallinity of the exchanger. Separations of importance to nuclear technology are also described. The acid salts can be classified into five types based upon structure. The hydrous oxides are considered to fall into two main types. Those such as ZrO₂, TiO₂ and SnO₂ consist of small particles of oxide with hydrated surfaces and interparticle water. The nature of the surface is described and related to the ion exchange properties of the hydrous oxide. Other hydrous oxides such as Sb₂O₅ and MnO₂ are described in terms of the pyrochlore and spinel structures, respectively. It is suggested that the properties of these exchangers can be controlled to greater specificities through synthetic procedures. (author)

[en] The basic science goal in this project identifies structure/affinity relationships for selected radionuclides and existing sorbents. The task will apply this knowledge to the design and synthesis of new sorbents that will exhibit increased cesium, strontium and actinide removal. The target problem focuses on the treatment of high-level nuclear wastes. The general approach can likewise be applied to non-radioactive separations

No abstract available

[en] A framework potassium titanium silicate K₂TiSi₃O₉·H₂O, compound I, was synthesized by the reaction of a titanium-hydrogen peroxide complex and SiO₃ in alkaline media under mild hydrothermal conditions (180 C). This compound was converted to the corresponding sodium phase, Na₂TiSi₃O₉·H₂O (IV) and two proton-containing phases, K_1.26H_0.74TiSi₃O₉·1.8H₂O (II) and K_0.3H_1.7TiSi₃O₉·2.4H₂O (III) by ion exchange. These products were characterized by elemental analysis, TGA, FT-IR, MAS ²⁹Si NMR, and X-ray diffraction. The ion exchange behavior of compound I and III 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 compound I 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 compound I 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 ²⁹Si NMR spectrum. On reexchanging with K⁺, the original crystal lattice was restored

[en] This project seeks to determine if inorganic or hybrid inorganic ion-exchange materials can be exploited to provide effective americium and curium separations. Specifically, we seek to understand the fundamental structural and chemical factors responsible for the selectivity of the tested ion-exchange materials for actinide and lanthanide ions. During FY13, experimental work focused in the following areas: (1) investigating methods to oxidize americium in dilute nitric acid with subsequent ion-exchange performance measurements of ion exchangers with the oxidized americium and (2) synthesis, characterization and testing of ion-exchange materials. Ion-exchange materials tested included alkali titanates, alkali titanosilicates, carbon nanotubes and group(IV) metal phosphonates. Americium oxidation testing sought to determine the influence that other redox active components may have on the oxidation of Am(III). Experimental findings indicated that Pu(IV) is oxidized to Pu(VI) by peroxydisulfate, but there are no indications that the presence of plutonium affects the rate or extent of americium oxidation at the concentrations of peroxydisulfate being used. Tests also explored the influence of nitrite on the oxidation of Am(III). Given the formation of Am(V) and Am(VI) in the presence of nitrite, it appears that nitrite is not a strong deterrent to the oxidation of Am(III), but may be limiting Am(VI) by quickly reducing Am(VI) to Am(V). Interestingly, additional absorbance peaks were observed in the UV-Vis spectra at 524 and 544 nm in both nitric acid and perchloric acid solutions when the peroxydisulfate was added as a solution. These peaks have not been previously observed and do not correspond to the expected peak locations for oxidized americium in solution. Additional studies are in progress to identify these unknown peaks. Three titanosilicate ion exchangers were synthesized using a microwave-accelerated reaction system (MARS^®) and determined to have high affinities for lanthanide ions in dilute nitric acid. The K-TSP ion exchanger exhibited the highest affinity for lanthanides in dilute nitric acid solutions. The Ge-TSP ion exchanger shows promise as a material with high affinity, but additional tests are needed to confirm the preliminary results. On the other hand, carbon nanotubes and nitrogen-doped carbon nanotubes exhibited low, but measureable affinities for lanthanide ions in dilute nitric acid solutions (pH 3 and 6). The MWCNT exhibited much lower affinities than the K-TSP in dilute nitric acid solutions. However, the MWCNT are much more chemically stable in concentrated nitric acid solutions and, therefore, may be candidates for ion exchange in more concentrated nitric acid solutions

[en] The exchange of transition metal (M²⁺) ions from manganese through cobalt, nickel, copper to zinc with γ-zirconium phosphate was examined. By using acetate salts the hydrogen ion concentration is kept low enough to achieve high loadings. The fully loaded solids have the composition ZrM(PO₄)₂.4H₂O. Near quantitative uptakes are achieved at 100⁰C. The interlayer spacings change very little with loading indicating that γ-zirconium phosphate is able to accommodate cations and water molecules without appreciable increase in volume. The copper exchanged phase readily forms an acetylacetonate when shaken with 2,4-pentanedione. (author)