Sorption of technetium and rhenium on natural sorbents under aerobic conditions

The uptake of technetium on bentonite materials has been studied from the point of view of the characterization of long-term radioactive elements behavior in nuclear waste repository. It is generally known that bentonite materials show an excellent cation-exchange capacity and on the other hand a poor uptake of anions. The aim of our research has been to find out the conditions suitable for technetium sorption on selected bentonite under oxidizing conditions. The influence of the addition of different materials (e.g., activated carbon, graphite, Fe²⁺, Fe) with bentonite, the effect of solid:aqueous phase ratio and a pH value on the percentage of technetium uptake and on the K _d values were tested.This revised version was published online in November 2005 with corrections to the Cover Date.     

Sorption of radioactive cobalt in natural Mexican clinoptilolite

The ability of a natural Mexican clinoptilolite to sorb radioactive cobalt from aqueous solution was studied. The zeolite was stabilized partially with sodium and the content of Na⁺ in the samples was determined by neutron activation analysis. Ion exchange experiments were performed with solution labeled with radioactive⁶⁰Co at pH 6.5. XRD patterns were used to verify if the crystallinity of the aluminosilicate was affected by ionic exchange. A fast sorption uptake was observed and it was found that 0.408 meq/g of zeolite of Na⁺ ions were replaced by cobalt ions, followed by a desorption process where the uptake decrease to 0.314 meq/g of zeolite. This behavior is a consequence of the partial dehydration of the zeolite.     

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 and desorption of technetium by humic substances under oxic and anoxic conditions

The distribution coefficients K_d for the sorption of^95mTc by peat as well as the corresponding rates of sorption and desorption were determined as a function of the concentration of the supporting electrolyte (CaCl₂), the amount of dissolved oxygen and the pH of the solution. The results show that the K_d-values of Tc (added as Tc(VII)-pertechnetate) increase, if the concentration of CaCl₂ or the amount of dissolved oxygen is decreased. The sorption was reversible with respect to the replacement of Tc by a CaCl₂ solution. The half-times for the rates of sorption and desorption depend on the concentration of CaCl₂ and dissolved oxygen and were in the range of 20–60 minutes and 500–900 minutes for the sorption and desorption processes, respectively.     

Sorption of phenol and radioactive cesium onto surfactant modified insolubilized humic acid

In this study, the sorption behavior of two important contaminants, phenol and radioactive cesium (¹³⁷Cs), onto surfactant modified insolubilized humic acid (SMIA) were investigated as a function of time, sorbate concentration utilizing the radiotracer method and UV–Vis spectroscopy. Phenol sorption process was well described by both Freundlich and Tempkin type isotherms, and cesium sorption was described by Freundlich and Dubinin–Radushkevich isotherms. It was found that SMIA adsorbs both cations and phenolic substances. Kinetic studies indicated that adsorption behavior of phenol obey the pseudo second order rate law. FTIR spectroscopic technique was used to understand the structural changes during modification process with surfactants.     

Sorption of heavy-metal ions and radioactive cesium by “Ultrasorb” composite sorbent

Data are given on the sorption of heavy-metal ions (Fe³⁺, Co²⁺, Cd²⁺, Pb²⁺, Zn²⁺, Cu²⁺ and Ni²⁺) and radioactive isotope¹³⁷Cs from Ringer salt solution by Ultrasorb composite sorbent, which has two components: the modified clay mineral palygorskite (palygorskite-M) and a modified fibrous carbon sorbent of AUT-M type (UVM-Ts). Selectivity series have been determined for the sorption of these toxic metals on the basis of the calculated distribution coefficients K_d under standard conditions. It is shown that the properties of the components combine well in the material, and it is proposed for use as a treatment agent (enterosorbent) having a selective action in the treatment of diseases due to the accumulation of heavy metals and radionuclides in the body. Institute for Sorption and Endoecological Problems, National Academy of Sciences of Ukraine, 13 ul. Generala Naumova, Kiev 03164, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 36, No. 1, pp. 53–57, January–February, 2000.     

Treatment of radioactive wastes: an X-ray absorption spectroscopy study of the reaction of technetium with green rust

Technetium is a long-lived product of nuclear fission that readily forms the soluble pertechnetate anion [TcO(4)](-). Green rusts (layered hydrous oxides containing both Fe(II) and Fe(III) and with interlayer sulfate or carbonate anions) concentrate >99.8% of 99Tc, present as [TcO(4)](-), from aqueous solution, even in the presence of high concentrations of NaNO(3), a common constituent of radioactive waste streams. The mechanism of removal from solution is apparently reduction and formation of strong Tc(IV) surface complexes. X-ray absorption spectroscopy shows that [TcO(4)](-) is indeed reduced by reaction with both sulfate- and carbonate-form green rusts and is found in a TcO(2)-like environment. On contact with air, the green rusts oxidize to poorly crystalline goethite but the Tc environment is unchanged. There is no increase in Tc solubility associated with oxidation of the host green rust. This behavior suggests that green rusts may be useful in the treatment of Tc-containing waste streams, in groundwater cleanup, and in restricting Tc migration from repositories.     

Sorption of radioactive cobalt onto nano calcium silicate/CuO composite modified by humic acid

The sorption process of Co(II) onto nanoparticles of calcium silicate doped with 5% CuO treated by humic acid was evaluated using batch technique. This process follows the second order kinetic model. Equilibrium isotherm models of Co(II) sorption onto the modified composite was 208.91 mg/g. Negative value of free energy change (ΔG⁰), confirms the spontaneous sorption of Co(II) ions onto the modified composite. The removal efficiency (R%) reached 96.9% using 0.5 g of the modified composite. Therefore, the composite could be used for treatment of radioactive waste containing ⁶⁰Co.

     

Hydrogenation of acetone on technetium catalysts

The catalytic properties of supported mono- and bimetallic catalysts of the Tc/support, M/support, and M-Tc/support types (M=Pt, Pd, Rh, Ru, Ni, Re, Co; supports are γ-Al₂O₃, MgO, SiO₂) were investigated in the acetone hydrogenation. The main products of this reaction are isopropyl alcohol and propane. The catalytic activity in the acetone hydrogenation of the metals studied decreases in the consequence Pt>Tc≈Rh>Pd>Ru >Ni≈Re>Co (with γ-Al₂O₃ as the support). The influence of support nature on the catalytic activity was investigated for the Rh−Tc system as an example. A nonadditive increase in the catalytic activity of Rh−Tc/γ-Al₂O₃ in comparison with monometallic catalysts was found. The state of the surface of the catalysts was characterized by the UV-VIS diffuse reflectance spectra. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 414–417, March, 1998.     

Lipophilic technetium complexes

A series of technetium complexes with different alkyl dithiocarbamates, dithiophosphates and xanthates has been prepared at tracer level (10^–4 molar) starting from hydrazine-reduced pertechnetate and Tc(V) gluconate, respectively. Solution studies show the complexes to be neutral, lipid-soluble tracers. Their in vitro properties can be varied in a wide range by variation of alkyl substitution of the ligands.     

Correction to: Sorption of radioactive cobalt onto nano calcium silicate/CuO composite modified by humic acid

Journal of Radioanalytical and Nuclear Chemistry - In the original publication of the article, Figs. 8, 9 and 10 were published incorrectly as linear regression.     

A simple technetium generator

A systematic study on the extraction of⁹⁹Mo and its daughter^99mTc by pure organic diluents and dinonylnaphthalinesulfonic acid (DNNS) is described. The aqueous phases used are H₂SO₄, HCl, KI and their binary mixture solutions. The effect of alcohols on the distribution coefficient has been investigated. As a result of the study, a simple and rapid generator is built for the production of pure^99mTc from⁹⁹Mo.     

Solvent extraction of heptavalent technetium

An extraction study was performed on technetium in its highest oxidation state as a function of nitric acid concentration at 25, 50 and 70 °C. A long chain amine (tri-n-octylamine TOA) and an organophosphorus solvent (TBP) have been investigated. Addition of NH₄NO₃ has a salting-out effect on the extraction of TBP in the aqueous phase and therefore decreases the distribution coefficient for heptavalent technetium. The mechanism of extraction is discussed in the light of the results obtained.     

Sorption of neptunium on clays

Batch sorption experiments with²³⁷Np using kaolinite and molasse clays were carried out under oxic conditions. The sorption kinetics and the effects of particle size of clay samples, concentration of neptunium in the solutions and the pH below and above the point of zero charge of the clays on the sorption coefficients were studied. The sorption coefficients of neptunium, on kaolinite were between 23 and 1100 ml/g at pH 1.5 and 7.6, respectively, whereas, sorption on the molasse clay was not affected significantly by pH (R_d600 ml/g).     

Sorption of cobalt on bentonite

Sorption of Co on bentonite has been studied by using a batch technique. Distribution coefficients (K _d ) were determined for the bentonite-cobalt solution system as a function of contact time, pH, sorbent and sorbate concentration and temperature. Sorption data have been interpreted in terms of Freundlich, Langmuir and Dubinin-Radushkevich equations. Thermodynamic parameters for the sorption system have been determined at three different temperatures. The positive value of the heat of sorption, H ⁰=22.08 kJ/mol at 298 K shows that the sorption of cobalt on bentonite is endothermic, where as the negative value of the free energy of sorption, G ⁰=–10.75 kJ/mol at 298 K shows the spontaneity of the process. G ⁰ becomes more negative with an increase in temperature which shows that the sorption process is more favourable at higher temperatures. The mean free energyE7.7 kJ/mol for sorption of cobalt on bentonite shows that ion-exchange is the predominant mode of sorption in the concentration range of the metal studied i.e. 0.01 to 0.3 mol/dm³. The presence of some complementary cations depress the sorption of cobalt on bentonite in the order of K⁺>Ca²⁺>Mg²⁺>Na⁺. Some organic complexing agents and natural ligands also affect the sorption of cobalt. The desorption studies with ground water at low cobalt loadings on bentonite show that about 97% metal is irreversibly sorbed.