Thorium In Solution Research Articles

Investigations of systems ThO 2–MO 2–P 2O 5 (M=U, Ce, Zr, Pu). Solid solutions of thorium–uranium (IV) and thorium–plutonium (IV) phosphate–diphosphates

In the framework of nuclear waste management aiming at the research of a storage matrix, the chemistry of thorium phosphates has been completely re-examined. In the ThO 2–P 2O 5 system a new compound thorium phosphate–diphosphate Th 4(PO 4) 4P 2O 7 has been synthesized. The replacement of Th 4+ by a smaller cation like U 4+ and Pu 4+ in the thorium phosphate–diphosphate (TPD) lattice has been achieved. Th 4− x U x (PO 4) 4P 2O 7 and Th 4− x Pu x (PO 4) 4P 2O 7 solid solutions have been synthesized through wet and dry processes with 0< x<3.0 for uranium and 0< x<1.0 for plutonium. From the variation of the unit cell parameters, an upper x value equal to 1.67 has been estimated for the thorium–plutonium (IV) phosphate–diphosphate solid solutions. Two other tetravalent cations, Ce 4+ and Zr 4+, cannot be incorporated in the TPD lattice: cerium (IV) because of its reduction into Ce (III) at high temperature, and zirconium probably because of its too small radius compared to thorium.

Spectrophotometric determination of thorium as molybdothoric acid with basic dyes

Color developments based on the ion-association complexes of molybdothoric acid with three basic dyes (BD), rhodamine B(RB), butylrhodamine B(BRB) and nile blue (NB), were investigated in aqueous acidic solution in the presence of poly(vinyl alcohol) (PVA). Their spectrophotometric behavior, such as the conditions suitable for the reactions and the effects of foreign ions, were thoroughly studied. The Th∶Mo∶BD ratio in the complexes was found to be 1∶12∶3. Their absorption maxima were at 570, 570 and 590 nm with apparent molar absorptivities of 3.50 × 10−6, 3.63 × 106 and 4.45 × 106 dm3 mol−1 cm−1, respectively. Beer's law was obeyed up to 0.8, 0.8 and 0.7 μg thorium per 25 ml, respectively. The detection limits (3σ) were 1.1, 1.8 and 3.4 ng ml−1, respectively, and for 0.02 ug ml−1 solution of thorium the relative standard deviations were 3.0, 2.9 and 1.5%, respectively (n = 11). The proposed methods were applied to the determination of trace amounts of thorium in some geological samples.

Extraction of thorium from aqueous nitric acid solution by bis-2-(butoxyethyl ether) (DBC)

The solvent extraction of thorium(IV) (4.3·10−4M) from nitric acid solution by bis-2-(butoxyethyl ether) (butex or DBC) has been studied. It has been investigated as a function of nitric acid, extractant and metal ion concentration. The effect of equilibration time, diverse ions and salting-out agent on the extraction has also been examined. Among anions, fluoride, phosphate, oxalate and perchlorate have reduced the extraction. Cations such as Na(I), K(I), Ca(II), Zn(II), Al(III), Ti(IV), Zr(IV) except Sr(II) and Pb(II) do not interfere in the extraction. The extraction is enhanced upto 97% in three stages at 6M HNO3 having 2.94M NaNO3 as salting-out agent. The extraction is found to be independent of thorium concentration in the range studied (4.3·10−4–4.3·10−2M). The temperature (18–45°C) has an adverse effect on the extraction. A 1% solution of ammonium bifluoride is found to be a good stripping solution and recovery of thorium is >98%.

The removal of thorium from aqueous solutions using zeolites

The ability of zeolites to remove thorium-232 from naturally radioactive thorium nitrate solutions was studied by ion exchange, adsorption and surface phenomena. The best zeolites were a clinoptilolite from Mudhills, California, USA and a mordenite rich tuff from Eastgate, Nevada, USA. As the concentration of thorium in solution was increased the mechanism of thorium removal switches from that of partial ion-exchange to a surface precipitation. This was confirmed by electron probe microanalysis (EPMA) in conjunction with XRD and Energy Dispersive X-ray analysis (EDX). A Langmuir-type of adsorption occurred with the thorium-232 daughter isotopes at the same time as partial exchange/precipitation of the thorium parent which is in regular equilibrium with its natural daughters. Some experiments with234Th were carried out to confirm this hypothesis as well as column experiments to confirm the usefulness of the Th removal.

Biosorption of radionuclides by fungal biomass.

Four kinds of bioreactor were evaluated for thorium removal by fungal biomass. Static-bed or stirred-bed bioreactors did not give satisfactory thorium removal probably because of poor mixing. An air-lift bioreactor removed approximately 90-95% of the thorium supplied over extended time periods and exhibited a well-defined breakthrough point after biosorbent saturation. The air-lift bioreactor promoted efficient circulation and effective contact between the thorium solution and the mycelial pellets. Of several fungal species tested, Rhizopus arrhizus and Aspergillus niger were the most effective biosorbents with loading capacities of 0.5 and 0.6 mmol g-1 respectively (116 and 138 mg g-1) at an inflow thorium concentration of 3 mmol dm-3. The efficiency of thorium biosorption by A. niger was markedly reduced in the presence of other inorganic solutes while thorium biosorption by R. arrhizus was relatively unaffected. Air-lift bioreactors containing R. arrhizus biomass could effectively remove thorium from acidic solution (1 mol dm-3 HNO3) over a wide range of initial thorium concentrations (0.1-3 mmol dm-3). The biotechnological application and significance of these results are discussed in the wider context of fungal biosorption of radionuclides.

Determination of nitrate in thorium, uranium and plutonium solutions

A potentiometric titration method and a conductometric titration method were standardized for the determination of nitrate in thorium, uranium and plutonium solutions in the range of 2–10 mg, and 15–30 mg, respectively, with a precision and accuracy of 2% in both cases. The results were compared with those of other methods like Devarda's alloy reduction method and volumetric titration method. The procedures standardized have been recommended for the determination of nitrate in heavy element solutions used for the preparation of oxide and mixed oxide microspheres by the sol-gel technique.

Neutron activation analysis of thorium after separation of233Th by isotopic ion exchange

The procedure for thorium determination in ammonium diuranate (ADU) and rocks, by neutron activation analysis after chemical separation of233Th, is presented. The separation of233Th from the interfering radioisotopes is based on the retention of233Th by a resin saturated with thorium (isotopic exchange) and on the elution of the interfering radioisotopes by a dilute solution of thorium in 0.5M HCl (ion exchange). The determination limit of thorium in rocks and ADU was found to be 0.56 and 9.3 μg, respectively, when a 20% relative standard deviation was assumed as acceptable. The highest value obtained for the determination limit of thorium in uranium compounds, on account of the234Th activity present, is discussed.

The direct electrochemical synthesis of some thorium(IV) nitrate complexes

The electrochemical oxidation of thorium in either nitric acid/tri-n-butyl phosphate (TBP) or dinitrogen tetroxide/ethyl acetate/acetonitrile media gives rise to non-aqueous solutions of thorium(IV) nitrate species. The only neutral adduct which could be obtained from HNO3/TBP solution was Th(NO3)4•8dmso (dmso = dimethylsulphoxide). Salts of [Th(NO3)6]2− with Et4N+, [(bpyH)3NO3]2+, and [(phenH)3NO3]2+ (bpy = 2,2′-bipyridine; phen = 1,10-phenanthroline) were also prepared by this route. Solutions in N2O4/EtOAc/CH3CN yield Th(NO3)4, and neutral adducts with dmso, bpy, phen, Ph3PO, and pyridine-N-oxide.

A new method for determination of thorium in solution by X-ray fluorescence technique

A method of thorium determination in aqueous solutions is described using X-ray fluorescence technique. Experimental and theoretical saturation values have been calculated for thorium analysis. The109Cd∶Ge(Li) system was used in the study. Effects of escape peak of Ge(Li) detector have been corrected by using the Compton peak of blank spectra. Therefore, X-ray spectra have been normalized in order to evaluate the net thorium spectrum and to increase the sensitivity of analysis.

Compleximetric titration of thorium with potentiometric end-point indication

In this redox-based direct potentiometric method, thorium is titrated with ethylenediaminetetraacetic acid (EDTA) in the presence of the Cu(II)—EDTA complex and ammonium thiocyanate. The indicator electrode is platinum. Solutions of irradiated thorium fuel, with less than 25 μmol in a sample aliquot, can be titrated. Solutions used to dissolve thorium samples contain aluminum, which can be masked kinetically, by pH adjustment, or with oxalate. Metal ions forming EDTA complexes with stability constants similar to or greater than that of copper(II) interfere.

Selective non-destructive determination of sub-pCi levels of thorium in solutions

A non-destructive method has been developed for the determination of sub-pCi levels of thorium in solutions by β-α coincidence measurement of daughter activity from purged thoron ( 220Rn).

The isolation of thorium from monazite by solvent extraction. Part I

An investigation was carried out into the isolation of thorium from the beach-sand mineral monazite by extraction with the secondary amine Adogen 283. The mineral concentrate was decomposed by the sodium hydroxide method, thereby ensuring that phosphate was separated from thorium and the lanthanons at an early stage, which allowed dissolution of their hydrous oxides in dilute sulphuric acid. Solubility of the hydrous oxides in sulphuric acid reached a maximum at an acid concentration of one molar. A 0.1 M solution of Adogen 283 in kerosene effectively extracted thorium from this monazite sulphate solution, a maximum thoria loading of 4.15 g/l being achieved. Co-extraction of the lanthanons decreased markedly with increased thoria loading. The loaded amine was effectively stripped of thorium with 1 M ammonium carbonate in the pH range 9–10. A small-scale counter-current solvent extraction system with the monazite sulphate solution as feed and 0.1 M Adogen 283 as extractant was set up. It consisted of four extraction stages, four scrub stages (0.1 M sulphuric acid) and three strip stages (1 M ammonium carbonate, pH 9–10). Raffinate from the scrub section was cycled to the extraction section. A thoria product in the strip solution was obtained in yield exceeding 99.5% and purity 99.86% based on lanthanon contamination. A flowsheet incorporating known technology for pre-extraction of uranium from the monazite sulphate solution and removal of thorium from the strip solution is proposed.

Preparation, properties and analytical application of thorium n-phenyl- o-nitrobenzohydroxamate

A new complex of thorium(IV) with N-phenyl- o-nitrobenzohydroxamic acid (PNHA) has been prepared by reacting an aqueous solution of thorium with an alcoholic solution of PNHA at 60°C and adjusting the pH to 4–4·5. The infrared spectra and thermal analysis of the complex are discussed. The use of PNHA for gravimetric determination of thorium is described.

The precision and accuracy of some current methods for potentiometric end-point determination with reference to a computer-calculated titration curve

Accurately calculated titration curves make it possible to select the optimal method for evaluating the end-point of a particular potentiometric titration, with respect to systematic error, precision and time required. The potentiometric titration of fluoride with thorium(IV) solution is used as an example. Decreasing systematic error is obtained by the different methods in the following order: methods based on sigmoid curves > differential methods based on Δ E/Δ v plots > differential methods based on Δ v/Δ E plots > methods based on mass-balance and equilibrium equations. Increasing precision is obtained in approximately the same order. The conclusions appear to be generally applicable and are useful in the construction of automatic titrators.

Photochemical precipitation of thorium and cerium and their separation from other ions in aqueous solution

Thorium was precipitated from homogeneous solution by exposing solutions of thorium and periodate in dilute perchloric acid to 253.7 nm radiation from a low-pressure mercury lamp. Periodate is reduced photochemically to iodate which causes the formation of a dense precipitate of the basic iodate of thorium(IV). The precipitate was redissolved, the iodate reduced, the thorium precipitated first as the hydroxide, then as the oxalate and ignited to the dioxide for weighing. Thorium(IV) solutions containing 8–200 mg of ThO 2 gave quantitative results with a standard deviation ( s) of 0.2 mg. Separations from 25 mg each of iron, calcium, magnesium, 50 mg of yttrium and up to 500 mg of uranium(VI) were quantitative ( s = 0.25 mg). Separations from rare earths, except cerium, were accomplished by using hexamethylenetetramine rather than ammonia for the precipitation of the hydroxide. Cerium(III) was similarly precipitated and converted into CeO 2 for weighing. Quantitative results were obtained for 13–150 mg of CeO 2 with a standard deviation of 0.2 mg. Separations from 200 mg of uranium were quantitative. Other rare earths and yttrium interfered seriously. The precipitates of the basic cerium(IV) and thorium iodates obtained are more compact than those obtained by direct precipitation and can be handled easily. Attempts to duplicate Suzuki's method for separating cerium from neodymium and yttrium were not successful.

Copper (II) as an Amperometric Indicator: Determination of Thorium

Abstract It has been demonstrated that copper (II) is an attractive amperometric indicator for the titration of small amounts of thorium in solution. EDTA was used as the titrant. Best results are obtained in the titration when the mole ratio of thorium to copper is high. The method should be applicable to several other metal ions that form more stable EDTA complexes than does copper.

Adsorption indicators in the titrations of hexacyanoferrate(II) and oxalate with thorium ions

Alizarin Red S, Pyrocatechol Violet and Xylenol Orange are shown to be effective adsorption indicators for the titrations of hexacyanoferrate(II) and oxalate with Thorium(IV) solution. The action of the indicators can be explained by the theory of surface compound formation.

Synergism in the solvent extraction of di, tri and tetravalent metal ions—IV: Absorption spectral studies of the synergistic complexes

In previous work with radioactive tracers in this series, formulae have been assigned to the metal complexes synergistically extracted from aqueous solution by an organic phase containing thenoyl trifluoracetone (HTTA) and neutral organophosphorous compounds. Stable solid complexes have now been isolated and are shown to have the same formulae. These formulae have been confirmed by ultra-violet and visible absorption spectrophotometric measurements of dilute solutions of uranyl, thorium and neodymium complexes.

A dermal lesion from implanted plutoniu.

Introduction Alpha particle dermatitis is rare following exposure to externally emitted α-radiation, since most of such particles are stopped easily by the horny layer of the epidermis of man. Even the mild effects produced by the therapeutic use of solutions of thorium X and ointments of radon are not ascribable to α-particles alone. Larkin 1 described an erythema produced by accidental exposure to a 32 mev cyclotron beam consisting almost entirely of α-particles. This reaction failed to develop into a radiation ulcer such as that seen after x-ray or β-particle exposure of similar magnitude (estimated 70,000 r), although desquamation occurred and thickening of the epidermis persisted for more than 4 months. Witten et al. 2,3 showed that a surface dose greater than 55 kilorad of α-radiation from polonium was required to produce detectable erythema. Slight pigmentation was the only sequela to the transitory erythema in human skin exposed externally to

The electronic state of cerium in thorium-cerium alloys

In spite of the fact that the atomic diameter of normal γ-cerium exceeds that of thorium, the lattice spacing/composition curve for the thorium-cerium system contains a minimum at approximately 26 at. % cerium. Possible reasons for this behaviour are discussed, and it is concluded that it is justifiable to regard the contraction of the cerium atom in thorium-rich alloys as due to the promotion of the single 4f electron to the conduction levels, brought about by a tendency to minimise the strain energy of solid solution. The process corresponds to abnormal contraction of γ-cerium caused by the application of hydrostatic pressure. An analogous effect to that observed in thorium-cerium alloys occurs in the thorium-plutonium system, where the solution in thorium of plutonium in an expanded four-valent form, as compared with the normal five-valent form, again leads to a lowered strain energy. Cerium is also contracted in cerium-rich thorium-cerium alloys. Analysis suggests that the magnitude of the contraction does not depend on specific thorium-cerium interactions, but is related to the lattice contraction which would be expected from the solution of thorium in normal γ-cerium. The contraction at any atomic percentage C of thorium between 0 and 50 may be represented by the expression KC (0.0759) 100 kX , where K = 0.69 + 9· 10 −4 C 5 3 . The mechanism of the contraction in this composition region is not fully understood, but may be related to the formation of an abnormally contracted form of cerium when normal γ-cerium is cooled to low temperatures. The general implications of valency changes of the solute in solid solution are briefly discussed.