Sorption of uranyl ions on hydrous titanium dioxide

Summary The mechanism of the sorption of U on TiO₂ · x H₂O is investigated in absence and in presence of carbonate as function of pH. Speciation of U in solution and the state of the surface of TiO₂ · x H₂O are taken into account. In the experiments the mole fractions of the U species in presence of carbonate are the same as in seawater. Below pH 5 the sorption of U can be described in absence and in presence of carbonate by ion exchange of UO ₂ ²⁺ or alternatively by sorption of UO₂OH⁺, because hydrolysis and sorption are occurring simultaneously. Above pH 5 in absence of carbonate, first pH-independent sorption of (UO₂)₃(OH) ₇ ^– and then (above the isoelectric point of TiO₂ · x H₂O) pH-dependent sorption of (UO₂)₃(OH) ₇ ^– are observed. In the same pH range, but in presence of carbonate, two species of U are dominating in solution, first UO₂CO₃OH^– and then UO₂(CO₃) ₃ ^4– · UO₂CO₃OH^– is not sorbed in measurable amounts which causes a drastic decrease of the sorption ratio. UO₂(CO₃) ₃ ^4– , which begins to dominate above pH 6 (depending on the carbonate concentration), is sorbed either by formation of TiOUO₂ bonds or (at carbonate concentrations >10^–2 mol/l) via carbonate bridges.

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Sorption von Uranylionen an wasserhaltigem Titandioxid

     

Sorption of uranium on freshly prepared hydrous titanium oxide and its utilization in determination of 236U using accelerator mass spectrometry

Journal of Radioanalytical and Nuclear Chemistry - The determination of 236U with accelerator mass spectrometry (AMS) requires efficient separation methods with high concentration factors. The...     

Sorption of radioactive strontium on a silica-titania mixed hydrous oxide gel

A silica-titania (Si–Ti) mixed hydroxide gel with Ti to Si mole ratio of 11 was prepared. Studies on the sorption of radiostrontium from alkaline solutions having various concentrations of sodium were carried out with Si–Ti. The distribution coefficient (K _d) of strontium decreased with increasing concentrations of sodium from 0.1 to 4.0 mol·dm^–3. The plot of logK _d versus log [Na⁺] gave a slope of –0.55 as against the theoretical value of –2.0. This suggests that some other paths in addition to the simple stoichiometric ion exchange is also existing for sorption. From pH titrations the pH_pzc of Si–Ti was found to be 4.22 coinciding nearly with the pH sorption edge. An attempt was made to correlate the sorption results with the surface characteristics of the sorbent. It was found that sorption is favored when the surface of the sorbent transforms into an anionic form. Sharp increase in the sorption of strontium was observed when the equilibrium pH was between 7 and 10. This behavior could be attributed to the abrupt increase in net negative charge on the surface of the sorbent.     

Sorption of cesium and strontium ions on hydrous titanium dioxide from chloride medium

Epiboron instrumental neutron activation analysis (EINAA) using flexible boron as thermal neutron filter, has been used to analyze several salt samples obtained from various markets in Ghana for iodine. The method involves the irradiation of samples in boron carbide-lined polyethylene vials at the outer irradiation site of the Ghana Research Reactor-1 (GHARR-1). The samples were then counted directly without any pre-treatment on a Canberra N-type HPGe detector. The qualitative and quantitative analyses were done using the 443 keV photopeak of ¹²⁸I. The precision and accuracy of the method have been evaluated and the detection limits of the various samples were calculated. The values of iodine determined in the iodized salt range between 10.0 and 210 ppm. For non-iodinated salts, iodine levels were below 500 ppb. The values obtained show great variations among the salt samples, sample collection time and from market to market. This results show that the method can be successfully applied in the determination of trace amount of iodine in salt samples without any chemical separation.     

Sorption of uranyl ions on titanium oxide studied by ATR-IR spectroscopy

ATR-IR spectroscopy was used to study the sorption of uranyl ions (10(-4) M) onto titanium oxide (mixture of rutile and anatase). A circulation setup, filled with a solution in D(2)O, allowed recording of the evolution of the antisymmetric O=U=O stretching of uranyl species onto titanium oxide particles deposited on the ATR crystal. The band centered at 915 cm(-1) has been decomposed in two Gaussian peaks at 920 and 905 cm(-1). From these values, and the observation that the ratio of the areas of the two peaks vs pH was constant, we have proposed that uranyl sorption on titanium oxide in the pH range 4-7 leads to the formation of one surface complex where uranium atoms have two different chemical environments. A trimer surface complex linked by two uranium atoms to the titanium oxide surface would be consistent with this interpretation.     

Sorption studies of strontium on hydrous zirconium dioxide

Summary Hydrous zirconium dioxide was prepared to study the sorption behavior and the removal of strontium from radioactive waste solutions. The hydrous zirconium dioxide were identified and characterized. The parameters affecting the strontium adsorption were investigated. Sorption data have been interpreted in terms of Langmuir equations. Thermodynamic parameters for the sorption system have been determined at 303, 313, 323 and 333 K temperatures. The values ofDH°=102.30 kJ/mol andDG°=-26.03 kJ/mol at 313 K prove that the sorption of strontium on hydrous zirconium oxide is an endothermic and a spontaneous process.     

Mixing characterization in batch reactors using the radiotracer technique

The infusion rate of a slug of tracer into an anchor agitated 100-liter batch mixer was characterized by a decay rate constant. This constant was then used to define a dimensionless mixing-rate number which was related to the stirrer Reynolds number. This correlationship allows the calculation of time or rotational speed needed to achieve any desired degree of uniformity of the mixture.^99mTc was used as radiotracer and the mixing process was followed by a scintillation Nal(Tl) counter situated on the reactor wall near the injection point.     

Sorption studies of europium(III) on hydrous silica

Summary Sorption behavior of europium, Eu³⁺, on SiO₂ ^. xH₂O (silica gel) has been investigated as a function of time, the amount of silica gel, Eu³⁺ concentration, the ionic strength, and pH (in absence and in presence of carbonate). The sorption data were fitted to Freundlich, Langmuir and Dubinin-Radushkevich (D-R) isotherms. The sorption capacity of silica gel was determined to be in the range of (2.62-8.00) ^. 10^-7 mol/g at pH 5.30±0.05 and 0.20M NaClO₄. The mean energy of sorption was calculated to be 13.50±0.05 kJ/mol from the D-R isotherm, suggesting the involvement of ion-exchange reactions in the sorption process. Sorption of Eu³⁺ decreased with increased ionic strength. A gradual decrease in pH with increased ionic strength supports the involvement of an ion-exchange mechanism in the sorption process. The diffusion coefficient of Eu³⁺ ion on silica gel was calculated as (3.98±0.12) ^. 10^-13 m^{2 .} s^-1 under the particle diffusion-controlled conditions.     

Sorption kinetics of strontium in porous hydrous ferric oxide aggregates I. The Donnan diffusion model

Sorption of ions by hydrous ferric oxide (HFO) often shows a fast initial sorption reaction followed by a much slower sorption process. The second step is diffusion-controlled and can continue for days or months before equilibrium is reached. In this paper, we demonstrate that the diffusion rate may be explained by electrostatic interactions. The internal and external surfaces of HFO are generally positively charged and therefore repel cations. This can result in extremely low cation concentrations in pores, and therefore a significant reduction in pore diffusion rate. The theory is demonstrated here for sorption of Sr(2+) in HFO aggregates. The ion concentrations in the pore space are calculated using a Donnan model and diffusion is calculated from the Donnan concentration and potential gradients. This diffusion model is compared with nonelectrostatic pore diffusion, which does not take electrostatic interactions into account. The Donnan model predicts very low concentrations of Sr(2+) in the pores and diffusion rates that are up to 8000 times lower than predicted with a nonelectrostatic model.     

Thermal transformations of hydrous titanium dioxide

During heating hydrous titanium dioxide with a general empirical formula TiO₂·xH ₂O·ySO ₃ prepared by hydrolysis of titanium sulphate solution drying, dehydration, desulphurization and anatase — rutile transformation proceed. The studies applying the DTA, TG, DTG methods have been carried out. To separate the particular effects damp samples, dried up to constant mass samples as well as samples after removing sulphur compounds have been used.

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Zusammenfassung Während des Erhitzens von wasserhaltigem Titandioxid der allgemeinen Formel TiO₂ ·xH₂O ·ySO₃, hergestellt durch Hydrolyse von Titansulfatlösung, verlaufen Trocknung, Dehydratation, Desulfurisation und eine Anatas — Rutil Umwandlung. Die Untersuchungen wurden unter Anwendung von DTA, TG und DTG durchgeführt. Zur Unterscheidung der einzelnen Effekte wurden feuchte, bis zur Massekonstantheit getrocknete als auch entschwefelte Proben verwendet.

     

Kinetic study of ethylene polymerization with chromium oxide catalysts by a radiotracer technique

The quenching of polymerization with a chromium oxide catalyst by radioactive methanol ¹⁴CH₃OH enables one to determine the concentration of propagation centers and then to calculate the rate constant of the propagation. The dependence of the concentration of propagation centers and the polymerization rate on reaction time, ethylene concentration, and temperature was investigated. The change of the concentration of propagation centers with the duration of polymerization was found to be responsible for the time dependence of the overall polymerization rate. The propagation reaction is of first order on ethylene concentration in the pressure range 2–25 kg/cm². For catalysts of different composition, the temperature dependence of the overall polymerization rate and the propagation rate constant were determined, and the overall activation energy E_ov and activation energy of the propagation state E_p were calculated. The difference between E_ov and E_p is due to the change of the number of propagation centers with temperature. The variation of catalyst composition and preliminary reduction of the catalyst influence the shape of the temperature dependence of the propagation center concentration and change E_ov.     

Measurement of discharge rate in a canal using radiotracer dilution technique

Measurement of discharge rates of fluids and solids is an essential requirement in industrial and environmental systems. Radiotracer techniques are widely used for measurement of fluids/solids in situations where conventional techniques cannot be applied. The present paper describes application of radiotracer dilution technique to measure the discharge rate of water in a canal with an objective to validate efficiency of the Concrete Volute Pump used for pumping water in the canal. ¹³¹I radioisotope having activity of 55.5 GBq was used as radiotracer. The discharge rate of water was measured to be 20.6 m³/s.     

Atomic layer deposition of hafnium oxide from hafnium chloride and water

Hafnium oxide (HfO2) is a leading candidate to replace silicon oxide as the gate dielectric for future generation metal-oxide-semiconductor based nanoelectronic devices. Atomic layer deposition (ALD) has recently gained interest because of its suitability for fabrication of conformal films with thicknesses in the nanometer range. This study uses periodic density functional theory (DFT) to investigate the mechanisms of both half-reactions occurring on the growing surface during the ALD of HfO2 using HfCl4 and water as precursors. We find that the adsorption energy and the preferred site of adsorption of the metal precursor are strong functions of the water coverage. As water coverage increases, the metal precursor preferentially interacts with multiple surface adsorption sites. During the water pulse the removal of Cl can be facilitated by either a ligand exchange reaction or the dissociation of Cl upon increase in coordination of the Hf atom of the precursor. Our predicted potential energy surface indicates that a more likely mechanism is hydration of the adsorbed Hf complex up to a coordination number of 7, followed by the dissociation of a chloride ion that is stabilized by solvation. Born-Oppenheimer molecular dynamics (BOMD) simulations of an adsorbed metal precursor in the presence of a multilayer of water shows that Cl dissociation is facile if sufficient water molecules are present to solvate the Cl(-) anions. Hence, solvation plays a crucial role during the water pulse and provides an alternative explanation for why ALD growth rates for this system decrease at high temperatures.     

Sorption properties of oxides VIII: sorption of uranium on hydrous oxides

Sorption of unranium from nitrate solution on four hydrous oxides, namely, hydrous titanium, zirconium, cerium and thorium oxides (TiO₂, ZrO₂, CeO₂, ThO₂) has been studied at pH 3.5 as a function of uranyl concentration and temperature. The sorbed species was uranyl ion in the case of hydrous TiO₂ and CeO₂, while in the case of hydrous ZrO₂ and ThO₂, electrolyte sorption involving uranyl nitrate predominated. Sorption site densities calculated from saturation capacities, evaluated from Langmuir adsorption isotherm and surface areas, bear a direct relationship with the heat of sorption values. Results indicate that, in terms of sorption site density, hydrous CeO₂ seems to be a better sorbent than hydrous TiO₂ for the sorption of uranium.     

Adsorption of selected ions on hydrous cerium oxide

Hydrous cerium oxide was synthesized and laboratory study was conducted to address its applicability for decontamination of barium, strontium, molybdenum, europium, iodine, samarium and cesium ions from radioactive liquid wastes using radiotracer technique. The adsorption of Ba(II), Sr(II), Mo(II), Eu(II), I(I), Sm(III) and Cs(I) on hydrous cerium oxide has been investigated as a function of pH, concentration and temperature of the adsorptive solution and the result obtained show that these parameters affect the extent of adsorption. The ion-exchange capacity decreased at higher temperatures which could be due to decrease of active sites as well as hydrophilic properties of surface adsorbent. Hydrous cerium oxide shows relatively high adsorption in acidic and neutral media towards the radiotracers studied, which can be attributed to large hydrated radius and ion exclusion effect.     

Certain micro-chemical separations using hydrous ferric oxide as a selective sorbent

Traces of cadmium from relatively high amounts of nickel and copper can be separated by the selective sorption of the cadmium ethylenediamine complex on hydrous ferric oxide. A batch chromatographic technique has been elaborated on this basis.     

Determination of hafnium in zirconium oxide using inductively coupled plasma emission spectrometry

Determination of Hf using Inductively Coupled Plasma Spectrometry down to 100 ppm and less in Zr matrix has been studied. Standard additions method has been applied for determination of Hf at different Hf wavelengths. Additionally, Hf was determined after its separation from Zr matrix using AG 1-X8 Biorad anion exchange resin. It has been observed that hf content determined following standard additions method at Hf line 356.166 nm compared well with the results obtained using prior separation method.     

Residence time distribution measurements in an ethyl acetate reactor using radiotracer technique

Journal of Radioanalytical and Nuclear Chemistry - In the present study, residence time distribution measurements were carried out in an industrial-scale ethyl acetate reactors using Bromine-82 as...