Peculiarities of U(VI) sorption on composites containing hydrated titanium dioxide and potassium-cobalt hexacyanoferrate(II)

As opposed to polymer sorbents, inorganic materials are stable against ionizing radiation. This gives a possibility to use them for the removal of radionuclides from water. As a rule, highly selective inorganic sorbents are obtained in a form of finely dispersive powder. This makes it difficult to use them in practice. Here the composites based on hydrated titanium dioxide containing K2Co[Fe(CN)6] have been developed. The modifier was inserted into partially (hydrogel) and fully (xerogel) formed oxide matrices. Modifying of hydrogel followed its transformation to xerogel provides the formation of potassium-cobalt hexacyanoferrate(II) nanoparticles (up to 10 nm), which are not washed out in aqueous media due to encapsulation in hydrated oxide. A number of the methods for sample characterization were used in this work: transmission electronic microscopy for vizualization of embedded nanoparticles, optical microscopy to measure granule size, FT-IR spectroscopy, X-ray fluorescence spectroscopy for chemical analysis of the samples, potentiometric titration to estimate ion exchange properties, and spectrophotometric analysis of the solution to determine U(VI) concentration. The features of U(VI) sorption from nitrate and sulfate solutions are considered: the effect of the sorbent dosage and solution composition was in a focus of attention. The influence of the modifier is the most pronounced at pH ³ 4, when U(VI) is in a form of one-charged cations (UO2OH+): the removal degree of U(VI) is close to 100 %. This positive effect of the selective constituent is expressed in a presence of an excess of NO3–, SO42– and Na+ ions. The model of chemical reaction of pseudo second order has been applied to sorption. Both pristine sorbent and composite are most completely regenerated with a 0.1 M KOH solution - the regeneration degree is 92 and 96 % respectively. In this case, the half-exchange time is minimal and equal to » 23 min (initial hydrated titanium dioxide) and 47 min (composite). Desorption obeys the model of particle diffusion: the diffusion coefficients for ions being exchanged are (1.7–7.6)´10–13 m2s–1.

Electrorheological Properties of Polydimethylsiloxane/TiO2-Based Composite Elastomers

Electrorheological elastomers based on polydimethylsiloxane filled with hydrated titanium dioxide with a particle size of 100–200 nm were obtained by polymerization of the elastomeric matrix, either in the presence, or in the absence, of an external electric field. The viscoelastic and dielectric properties of the obtained elastomers were compared. Analysis of the storage modulus and loss modulus of the filled elastomers made it possible to reveal the influence of the electric field on the Payne effect in electrorheological elastomers. The elastomer vulcanized in the electric field showed high values of electrorheological sensitivity, 250% for storage modulus and 1100% for loss modulus. It was shown, for the first time, that vulcanization of filled elastomers in the electric field leads to a significant decrease in the degree of crosslinking in the elastomer. This effect should be taken into account in the design of electroactive elastomeric materials.

Interaction of titanium oxide with sodium hydroxide at hydrothermal conditions

Sodium titanates were obtained by hydrothermal treatment using titanium tetrabutoxide (ТBT), titanium tetroisopropoxide (TIPT), hydrated titanium dioxide (prepared by hydrolysis of titanium alkoxide) or air-dried TiO2 sol with a molar ratio of TBT/TIPT/TiO2: NaOH equal to 1:10–80, at the temperature 130–180 °C and treatment time 24–72 h. Samples were characterized by the adsorption method, X-ray phase analysis, scanning electron microscopy. The photocatalytic properties of nanostructured titanate in the H-form in the process of Rhodamine FL–BM photodegradation under UV-irradiation (K = 0.03–0.05 min–1), as well as the electrorheological properties, were evaluated. Partially hydrated sodium titanates as a filler of the electrorheological dispersion (the filler content of dispersion was 5 %) exhibited the shear stress of 50–60 Pa and the leakage current density of 1.0–1.5 μA/cm2 at an electric field strength of E = 4 kV/cm at a shear rate of 17.1 s–1.

Justification of the prospects of using phosphatotitanium ion exchangers for extracting rare earth metals from solutions of radionuclides

The results of a study of the sorption properties of ion-exchange materials based on hydrated titanium (IV) oxohydroxophosphates with respect to rare-earth metal cations are presented in this paper. A high affinity of the latters for the sorption matrix in nitrate media was established, which is determined by the ion radius of the sorbate and increases in the series Y3+  Gd3+  Eu3+ Sm3+ Nd3+ Ce3+ at pH=4 and La3+  Ce3+  Y3+  Yb3+ at pH=1.5 for all the studied sample compositions. It was experimentally shown that the doping of sorbents based on titanium (IV) oxyhydroxophosphates with zirconium (IV) cations, which differs from titanium (IV) in acid-base properties, leads to an increase in the sorption properties of ion exchangers, which allows the use of modified compositions for sorption of rare-earth metal cations from solutions with high acidity. It was established that partial dehydration of the sorption matrix and increase in temperature increase the sorption ability of ion-exchange materials. Sorption extraction of rare-earth element cations by sorbents of various compositions was carried out from solutions simulating real technological objects generated during the processing of nuclear fuel waste. It is shown that sorption materials based on hydrated titanium (IV) oxohydroxophosphates are promising ion exchangers for the extraction of rare-earth element cations from technological solutions with complex chemical composition. It was established that unmodified sorbent compositions are promising for the selective extraction of rare-earth element cations, while modified compositions are of interest for group sorption. The thermal treatment of a sorbent saturated with radioisotopes leads to the formation of crystalline insoluble mineral-like compounds, which ensures reliable immobilization of the sorbed components during long-term storage of the spent product.

Seawater purification from cesium and strontium radionuclides

The article deals with the study of sorption (under batch conditions) of cesium and strontium radionuclides from sea water with ferrocyanidic sorbents based on hydrated titanium and zirconium dioxides (Т-35, NPF-HTD), glauconite and clinoptilolite natural aluminum silicates (NPF-G, NPF-C), zirconium phosphate (Т-3А), modified hydrated zirconium dioxide (Т-3К), and manganese dioxide based on hydrated titanium dioxide (MD-HTD). We have obtained the sorption isotherms, defined the cesium and strontium distribution coefficients. Dependences of the cesium distribution coefficient by the sorbents in seawater saline content have been obtained. The authors recommend NPF-G and NPF-HTD sorbents for treatment of liquid radioactive waste based on seawater with various salt content. Coefficients of the cesium distribution between solid and liquid phases were 1,0∙105 and 1,0∙104 mg/l, respectively, even at solutions with the salt content of 100 g/l. In the process of strontium sorption from seawater, the strontium distribution coefficients do not exceed 1,9·102 ml/g, this is connected with big proportion (34±7 %) of stable colloidal forms of strontium in the simulated seawater.