Removal of actinides and fission products activity from intermediate alkaline waste using inorganic exchangers

Hydrated iron oxide or amorphous-Fe₂O₃·3.5 H₂O (HFeO), hydrated titanium oxide (HTiO) and hydrated thorium oxide (HThO) were synthesized and their applicability for the decontamination of intermediate level liquid wastes (ILLW) was tested. The sorption of a few actinides like plutonium and americium on HFeO, ¹³⁷Cs and ¹⁰⁶Ru on HTiO and ⁹⁰Sr on HThO was investigated as a function of pH, time and loading capacity of the hydrous oxide with metal ions. The influence of the total dissolved salt content was also monitored. Some of these parameters influenced the sorption behavior significantly. The radiation stability of these inorganic sorbents were studied by irradiating them up to 48 Mrad. Adsorbed actinides and fission products were successfully eluted from HFeO and from the mix-bed of HTiO and HThO by 0.5M nitric acid.The authors wish to thank Shri R. D. Changarani, Chief Superintendent NRG Facilities and Shri P. K. Dey, Head FRD for their valuable advice and constant support.     

Extraction and coordination behavior of diphenyl hydrogen phosphine oxide towards actinides

Extraction behavior of some selected actinides like U(VI), Th(IV), and Am(III) was investigated with three different H-phosphine oxides, viz. diphenyl hydrogen phosphine oxide (DPhPO), dihexyl hydrogen phosphine oxide (DHePO) and diphenyl phosphite (DPP). The H-phosphine oxides exhibited a dual nature towards the extraction of actinides where the ligand not only extracts the metals by cation exchange but also by coordination with the phosphoryl group at lower and higher acidic concentrations, respectively. Among all ligands employed, DPhPO showed highest extraction with actinides with a substituent dependent trend as follows: DPhPO > DHePO > DPP. This trend emphasizes the importance of substituents around the phosphine oxide towards their extraction of actinides. The coordination behavior of DPhPO was studied by investigating its corresponding complexes with Th(NO₃)₄ and UO₂(NO₃)₂. The metal complexes of these actinides were characterized using FT-IR, ¹H and ³¹P NMR spectroscopic techniques. Density Functional Theory (DFT) calculations were also performed to understand the electronic and geometric structure of the ligand and the corresponding metal complexes.     

Sorption of144Ce(III) and147Pm(III) on hydrated iron sesquioxide

The sorption of¹⁴⁴Ce(III) and of¹⁴⁷Pm(III) on hydrated iron sesquioxide suspension and the sorption of¹⁴⁴Ce(III) on hydrated iron sesquioxide in a laboratory column were studied. The dependence of the sorption on pH and time, the sorption isotherm, the temperature-dependence of sorption, and the effects of ionic strength on sorption and desorption were determined under static conditions. The maximum sorptions of¹⁴⁴Ce(III) and¹⁴⁷Pm(III) were reached at pH=7.4 (K_d=8.9·10⁵) and pH=9.1 (K_d=6.2·10⁵), respectively.     

Neptunium, plutonium and 137Cs sorption by bentonite clays and their speciation in pore waters

Summary The properties of bentonite to remove radionuclides from aqueous solutions were studied as a function of pH and ionic strength. The sorption of cesium is due to ion-exchange while in the case of actinides, sorption is defined by surface complexation at neutral and slightly alkaline conditions and by both mechanisms at acidic pH. Due to the presence of Fe(II), actinides are reduced to low valence states that defines their strong retention onto bentonite and low solubilities. The solubility of both neptunium and plutonium were in the order of 2 ^. 10^-8-4 ^. 10^-8M with amorphous An(IV)O₂ as solubility limiting phases.     

Contribution to the study of the sorption of radionuclides on hydrated oxides

The mechanism of¹⁰⁶Ru(III),¹⁰⁶RuNO(II),¹⁴⁴Ce(III),¹⁴⁷Pm(III),⁸⁵Sr(II),¹³¹I⁻,³⁵SO ₄ ²⁻ , and H₂ ³²PO ₄ ²⁻ radionuclide sorption on hydrated ferrous, ferric, aluminium and chromic hydrated oxides was studied. The dependence of sorption on the pH has shown that in a certain range of pH values it is the ion exchange of the radionuclide for a proton or a hydroxyl group of the oxide that probably plays a decisive role in the sorption process. The sorption depends considerably on the pH in the whole range of studied, but its decrease with cations in alkaline media and its increase with I⁻ ion in acidic media does not agree with the above sorption mechanism. Similarly, the course of the dependence of sorption on the sorbent concentration does not indicate ion exchange to be the only mechanis, but it indicates a more complicated sorption process. Probably the sorption of colloidal forms of the radionuclides proceeds, too.     

Actinide speciation in the environment

Nuclear test explosions and nuclear reactor wastes and accidents have released large amounts of radioactivity into the environment. Actinideions in waters often are not in a state of thermodynamic equilibrium and their solubility and migration behavior is related to the form in which the nuclides are introduced into the aquatic system. Chemical speciation, oxidation state, redox reactions, and sorption characteristics are necessary in predicting solubility of the different actinides, their migration behaviors and their potential effects on marine biota. The most significant of these variables is the oxidation state of the metal ion as the simultaneous presence of more than one oxidation state for some actinides in a solution complicates actinide environmental behavior. Both Np(V)O₂ ⁺ and Pu(V)O₂ ⁺, the most significant soluble states in natural oxic waters, are relatively noncomplexing and resistant to hydrolysis and subsequent precipitation. The solubility of NpO₂ ⁺ can be as high as 10⁻⁴M while that of PuO₂ ⁺ is much more limited by reduction to the insoluble tetravalent species, Pu(OH)₄, (pK_sp≥56) but which can be present in the pentavalent form in aqautic phases as colloidal material. The solubility of hexavalent UO₂ ²⁺ in sea water is relatively high due to formation of carbonate complexes. The insoluble trivalent americium hydroxocarbonate, Am(OH)(CO₃) is the limiting species for the solubility of Am(III) in sea water. Thorium(IV) is present as Th(OH)₄, in colloidal form. The chemistry of actinide ions in the environment is reviewed to show the spectrum of reactions that can occur in natural waters which must be considered in assessing the environmental behavior of actinides. Much is understood about sorption of actinides on surfaces, the mode of migration of actinides in such waters and the potential effects of these radioactive species on marine biota, but much more understanding of the behavior of the actinides in the environment is needed to allow proper and reliable modeling needed for disposition of nuclear waste over many thousands of years. This paper has been presented as a Hevesy Medal Award Lecture by the medalist author at the 1st International Nuclear Chemistry Congress (1st-INCC), 22–29 May 2005, Kusadasi, Turkey     

Sorption of europium and actinides by means of octyl(phenyl)-N,N-diisobutyl carbamoylmethyl phosphine oxide (CMPO) loaded on silica

The octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO), loaded as stationary phase on silica, has been used for the sorption of Eu and actinides from acidic aqueous solution. Different commerical solid support were investigated and, finally SiO₂ was chosen. Experiments were performed to obtain basic data on actinide removal. Distribution coefficients, kinetics, sorption isotherms (three adsorption model correlations were tested) and the acidic concentration effect were studied.     

Sorption Characteristics of Radioeuropium on Bentonite and Kaolinite

The factors affecting the sorption of radioeuropium(III) by bentonite and kaolinite were studied with the aim to assess the important factors which should be included in modeling of radioeuropium(III) migration in soils and sediments. Europium(III) is an analogue of trivalent actinides. The distribution coefficients of radioeuropium for sorption on bentonite and kaolinite from aqueous solutions were determined by using the batch method, and it was found that they were sensitive to the loading, the pH, the humic substance and the sorption direction. Thus, these sorption characteristics of radioeuropium on bentonite and kaolinite were found to be different from those of radiocobalt¹, and the mathematical modeling of trivalent lanthanides and actinides migration will be more complicated than that of radiocobalt. It is improbable that the migration modeling with a constant distribution coefficient will be successful in the case of trivalent lanthanides and actinides.     

Facile preparation of potassium 32P-phosphonate

Simple and easy to operate experimental assemblies were for the first time designed for the successful preparation of potassium ³²P-phosphonate from ³²P-orthophosphate. Phosphate was first converted to phosphoryl chloride by reacting with phosphorus pentachloride. Then the phosphoryl chloride formed was reduced to phosphorus trichloride by heating with charcoal at 650 °C. The latter was absorbed in aqueous potassium hydroxide to obtain potassium ³²P-phosphonate at a yield of about 75%. The chemical purity of ³²P-phosphonate was assayed using ion-chromatography and the radiochemical purity was also determined.The authors thank Shri. J. K. Ghosh, Chief Executive, BRIT and Dr. N. Sivaprasad, General Manager, RPh & ILCJ, BRIT for their support and encouragement throughout this work.     

Facile preparation of potassium 32P-phosphonate

Simple and easy to operate experimental assemblies were for the first time designed for the successful preparation of potassium ³²P-phosphonate from ³²P-orthophosphate. Phosphate was first converted to phosphoryl chloride by reacting with phosphorus pentachloride. Then the phosphoryl chloride formed was reduced to phosphorus trichloride by heating with charcoal at 650 °C. The latter was absorbed in aqueous potassium hydroxide to obtain potassium ³²P-phosphonate at a yield of about 75%. The chemical purity of ³²P-phosphonate was assayed using ion-chromatography and the radiochemical purity was also determined.The authors thank Shri. J. K. Ghosh, Chief Executive, BRIT and Dr. N. Sivaprasad, General Manager, RPh & ILCJ, BRIT for their support and encouragement throughout this work.     

Sorbents based on calix[4]arenes for extraction of technetium(vii) from acidic and alkaline media

Sorption of Tc^VII from solutions of various compositions with new sorbents prepared by the noncovalent immobilization of (thia)calix[4]arenes on the Amberlite XAD-7™ support was studied. The sorbents studied efficiently extract technetium(vii) from both acidic and alkaline media. The sorption capacity of the sorbent with thiacalix[4]arene groups is superior to that of the sorbents with calix[4]arene groups and several times higher than that of the sorbents previously proposed for the sorption of Tc^VII. Technetium(vii) is sorbed by this sorbent as 1: 1 and 1: 2 thiacalix[4]arene—NH₄TcO₄ and 1: 1 and 1: 2 thiacalix[4]arene—NaTcO₄ complexes.     

Colloidal forms of radionuclides and their separation from water solution

Colloidal properties of¹⁴⁴Ce(III),¹⁴⁷Pm(III),⁹¹Y(III), and other, radionuclides were determined from the course of their self-diffusion. A reduced self-diffusion indicated the formation of colloidal radionuclides. The decrease in the self-diffusion coefficient began from a certain value of pH, and a pH region of slowest self-diffusion existed for each of the radionuclides studies. The maximum formation of colloidal radionuclides may be assumed to lie in the range of these pH values. An increase in the rate of self-diffusion was observed with radionuclides in colloidal forms under the effect of gamma-radiation. The possibility of mutual interaction between radionuclides was also inferred from the course their self-diffusion. High effective sorption of¹⁴⁷Pm(III) was attained on hydrated ferric oxide in the pH range were hydrolytic products and colloidal forms of¹⁴⁷Pm(III) were formad to a large extent.     

Sorption von Jod an hydratisiertem Mangandioxyd

The distribution coefficients for iodine have been determined in the system “hydrated manganese dioxide—nitric acid” (K _D∼10⁴). Some factors affecting the kinetics and yield of sorption are discussed, and the possibilities of practical application indicated. A mechanism is outlined to explain the sorption of iodine on hydrated manganese dioxide.      

Modelling of the Sorption of Sr(II) on Hydrous Zirconium Oxide

The amphoteric acid-base behavior of hydrous zirconium oxide (HZO) was investigated by titrating HZO with 0.05M HNO₃ and NaOH at constant ionic strength. The sorption of strontium from 0.05M NaNO₃ solution was measured as a function of pH. Abrupt increase in sorption was observed at the equilibrium pH of 9. The experimental titration and strontium sorption data on HZO were evaluated using the constant capacitance model (CCM) and diffuse double layer model (DLM). Various model parameters of Surface Complexation Models (SCM) were estimated, numerically, by non-linear regression. Modeling the sorption and speciation of Sr²⁺ on HZO indicated that the hydrolysis of Sr²⁺ to lower charged SrOH⁺ is the pre-requisite for the abrupt sorption behavior at pH 9.     

Lithium chloride sorption by zinc hexacyanoferrate(II) from a nonaqueous medium

Mechanisms of lithium chloride sorption by zinc hexacyanoferrate(II) Zn₂Fe(CN)₆ · 2.5H₂O in a nonaqueous medium (ethanol) were studied by chemical analysis, X-ray powder diffraction, wide-line ⁷Li and ¹H NMR, vibrational spectroscopy, and impedance spectroscopy. The physicochemical properties of sorption products are reported. Lithium ions in the sorption products were found to be in a hydrated form. The accommodation of molecularly sorbed Li⁺ aq · Cl^? ion pairs in the bores of channels in the crystal structure results in the formation of a continuous network of hydrogen bonds and changes the proton transport mechanism. As the lithium chloride concentration increases in the temperature range 22–150°C, the conductivity (σ) of sorption products increases three to four orders of magnitude to reach 10^?3 S cm^?1.     

Sorption of Eu(III) by amorphous titania, anatase and rutile

Sorption of Eu(III), an analogue of trivalent actinides (Am, Cm), by amorphous titania as well as different crystalline phases of titania, namely anatase and rutile, have been studied as a function of pH, using ¹⁵⁴Eu (half life?=?8.8 yrs, E_???=?123,247?keV) as a radiotracer. The objective of this study was to investigate the effect of the crystalline phase of the titania on their sorption behaviour towards the metal ion. Amorphous titania was prepared by organic route and was converted into anatase and rutile by heating at elevated temperatures based on the differential thermal analysis studies. Eu(III) sorption by all forms of titania rises sharply with the pH of the suspension, with the sorption edge shifting to higher value in the order; amorphous?<?anatase?<?rutile. However, the normalization of the sorption data to the surface area of the sorbents resulted in the overlapping of the sorption curves for amorphous and anatase phases, with the data being higher for rutle in the lower pH region, indicating the effect of the crystal phase on sorption behaviour of Eu(III).     

Adsorption of uranyl species onto the rutile (110) surface: a periodic DFT study

To model the structures of dissolved uranium contaminants adsorbed on mineral surfaces and further understand their interaction with geological surfaces in nature, we have performed periodic density funtional theory (DFT) calculations on the sorption of uranyl species onto the TiO₂ rutile (110) surface. Two kinds of surfaces, an ideal dry surface and a partially hydrated surface, were considered in this study. The uranyl dication was simulated as penta‐ or hexa‐coordinated in the equatorial plane. Two bonds are contributed by surface bridging oxygen atoms and the remaining equatorial coordination is satisfied by H₂O, OH^?, and CO₃^2? ligands; this is known to be the most stable sorption structure. Experimental structural parameters of the surface–[UO₂(H₂O)₃]²⁺ system were well reproduced by our calculations. With respect to adsorbates, [UO₂(L1)_x(L2)_y(L3)_z]ⁿ (L1=H₂O, L2=OH^?, L3=CO₃^2?, x≤3, y≤3, z≤2, x+y+2z≤4), on the ideal surface, the variation of ligands from H₂O to OH^? and CO₃^2? lengthens the U? O_surf and U? Ti distances. As a result, the uranyl–surface interaction decreases, as is evident from the calculated sorption energies. Our calculations support the experimental observation that the sorptive capacity of TiO₂ decreases in the presence of carbonate ions. The stronger equatorial hydroxide and carbonate ligands around uranyl also result in U?O distances that are longer than those of aquouranyl species by 0.1–0.3 Å. Compared with the ideal surface, the hydrated surface introduces greater hydrogen bonding. This results in longer U?O bond lengths, shorter uranyl–surface separations in most cases, and stronger sorption interactions.     

Synthesis of core–shell structured Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@carboxymethyl cellulose magnetic composite for highly efficient removal of Eu(III)

In this work, a carboxymethyl cellulose (CMC)-modified Fe₃O₄ (denoted as Fe₃O₄@CMC) composite was synthesized via a simple co-precipitation approach. Fourier transform infrared spectroscopy, zeta potential and thermogravimetric analysis results indicated that CMC was successfully coated on the Fe₃O₄ surfaces with a weight percent of ~30 % (w/w). The prepared Fe₃O₄@CMC composite was stable in acidic solution and could be easily collected with the aid of an external magnet. A batch technique was adopted to check the ability of the Fe₃O₄@CMC composite to remove Eu(III) as a function of various environmental parameters such as contact time, solution pH, ionic strength, solid content and temperature. The sorption kinetics process achieved equilibrium within a contact time of 7 h. The sorption isotherms were well simulated by the Langmuir model, and the maximum sorption capacity at 293 K was calculated to be 2.78 × 10^?4 mol/g, being higher than the series of adsorbent materials reported to date. The ionic strength-independent sorption behaviors, desorption experiments by using ammonium acetate and disodium ethylenediamine tetraacetate as well as the spectroscopic characterization suggested that Eu(III) was sequestrated on the hydroxyl and carboxyl sites of Fe₃O₄@CMC via inner-sphere complexation. Overall, the Fe₃O₄@CMC composite could be utilized as a cost-effective adsorbent for the removal of trivalent lanthanide/actinides (e.g., ^152+154Eu, ²⁴¹Am and ²⁴⁴Cm) from radioactive wastewater.     

Effect of Temperature on Cd2+ Sorption by Mixed Oxides of Iron and Silicon

The current study focuses on the synthesis and sorption properties of two mixed oxides of iron and silicon prepared by physical mixing (M₁) and sequential precipitation methods (M₂). Both the mixed oxides were synthesized from equimolar ratios of Fe(OH)₃ and SiO₂ and characterized for surface area, EDX, XRD and PZC. The surface area, micropore volume and average pore width of the oxide M₁ were higher as compared to the oxide M₂. However, potentiometric titrations revealed that mixed oxide synthesized by this method had a very high capacity towards Cd²⁺ ions as compared to the mixed oxide M₁. Sorption of Cd²⁺ ions at pH 5 on mixed oxide, M₂ was found to increase with temperature in the range 288 to 318 K. Langmuir equation was found applicable to the sorption data with R²>0.99. Entropy (ΔS^?), enthalpy (ΔH^?) and free energy changes (ΔG^?) were calculated which revealed the process to be endothermic and spontaneous in nature.     

Sorption of hafnium on hydrous titanium oxide using radiotracer technique

The sorption of hafnium on hydrous titanium oxide (TiO₂·1.94 H₂O) has been studied in detail. Maximum sorption of hafnium can be achieved from a pH 7 buffer solution containing boric acid and sodium hydroxide using 50 mg of the oxide after 30 minutes shaking. The value ofk _d, the rate constant of intraparticle transport for hafnium sorption, from 0.01M hydrochloric and perchloric acid and pH 7 buffer solutions has been found to be 17 mmole·g^–1·min^–2. The kinetics of hafnium sorption follows Lagergren equation in 0.01M HCl solution only. The values of the overall rate constantK=6.33·10^–2 min^–1 and of the rate constant for sorptionk ₁=6.32·10^–2 min^–1 and desorptionk ₂=2.28·10^–5 min^–1 have been evaluated using linear regression analysis. The value of correlation factor() is 0.9824. The influence of hafnium concentration on its sorption has been examined from 4.55·10^–5 to 9.01·10^–4 M from pH 7 buffer solution. The sorption data followed only the Langmuir sorption isotherm. The saturation capacity of 9.52 mmole·g^–1 and of a constant related to sorption energy have been estimated to be 2917 dm³·mole^–1. Among all the additional anions and cations tested only citrate ions reduce the sorption significantly. Under optimal experimental conditions selected for hafnium sorption, As(III), Sn(V), Co(II), Se(IV) and Eu(III) have shown higher sorption whereas Mn(II), Ag(I) and Sc(III) are sorbed to a lesser extent. It can be concluded that a titanium oxide bed can be used for the preconcentration and removal of hafnium and other metal ions showing higher sorption from their very dilute solutions. The oxide can also be employed for the decontamination of radioactive liquid waste and for pollution abatement studies.