Chemistry of thorium : Volumetric determination of thorium

Thorium has been determined volumetrically. It has been precipitated with m-nitrobenzoic acid according to the method of Neish. Thorium m-nitrobenzoate has been then dissolved in sulphuric acid and titrated with titanous chloride to determine the NO₂-group which gives the amount of thorium directly.     

Conductometric estimation of thorium in dilute thorium chloride

Summary Conductometric titrations of thorium chloride against oxalic acid, ammonium oxalate and silver nitrate have been carried out at high dilutions (0.001, 0.0005 and 0.00033 M) of the chloride. Oxalic acid is found to be a suitable titrant for rapid estimation of thorium, the minimum error being +0.5%. The other titrants do not give good results. The titrations with ammonium oxalate indicate the step-wise ionisation of ThCl₄ into ThCl₂ ²⁺, ThCl³⁺ and Th⁴⁺. For mixtures of thorium chloride and cerous chloride, only the equivalence point corresponding to complete precipitation of both thorium and cerium is indicated.The authors express their sincere thanks to Prof. S. S.Joshi for his keen interest in this work and to Dr. G. S.Deshmukh for his advice and help in so many ways during the progress of these studies.     

Radiochemical separation of thorium acetylacetonate from other thorium species

A solvent extraction technique to separate different chemical species of thorium is presented. The products formed by the chemical effects of the /n,/ reaction on the Th/acac/₄ were separated by this method and the retention value was measured.     

Simultaneous determination of uranium and thorium in high grade thorium ores

A routine procedure has been developed for the simultaneous determination of uranium and thorium in high concentration thorium ores. INAA is used to determine the uranium and thorium concentration. However, for very low concentrations of uranium a radiochemical procedure based on the use of NPy/benzene as an extractant has to be employed. The precision and accuracy of the method has been determined by analyzing IAEA and NBL standard thorium/uranium ores.     

Complexometric estimation of thorium

Summary Thorium has been determined by titration with EDTA (disodium salt) solution as complexometric reagent at p_H 3–4.5 using a drop of 0.01 M iron(III) solution mixed with thiocyanate-p-anisidine as indicator. Calcium, barium, strontium, magnesium or manganese ions do not interfere, but zinc, zirconium, lead, silver, aluminium, bismuth, phosphate, fluoride or oxalate ions interfere in this estimation. In these complexometric titrations the quantitative results obtained by using a drop of iron(III) solution mixed with thiocyanate-p-anisidine as indicator are comparable with those obtained with pyrocatechol violet indicator.

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Zusammenfassung Thorium wird bei p_H 4–4,5 mit ÄDTA titriert, wobei ein Gemisch eines Tropfens Eisen(III)-lösung mit Thiocyanat-p-Anisidinlösung als Indicator dient. Calcium, Barium, Strontium, Magnesium oder Mangan verursachen keine Störung, wogegen folgende Ionen stören: Zink, Zirkonium, Blei, Silber, Aluminium, Wismut, Phosphat, Fluorid oder Oxalat. Der erwähnte Mischindicator liefert ähnlich genaue Titrationsergebnisse wie bei Verwendung von Brenzcatechinviolett als Indicator.

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The authors take this opportunity to thank the Council of Scientific and Industrial Research (India) for the award of Junior Fellowship to one of them (junior author). This has enabled us to pursue the study of complexometric titrations.     

Isotopic compositions of terrestrial thorium: A search in terrestrial thorium for the unidentified excess 4.6 meV alpha-activity of lunar thorium

Since thorium in lunar crystalline rocks was reported to be excessive in 4.6 MeV alpha-activity up to 80%, which was attributed to a long-lived isomer of²³²Th with an origin different from normal thorium, we have measured alpha-spectra of various terrestrial thorium in order to see if terrestrial thorium also contains some excess 4.6 MeV alpha-activity. The results showed that the content of the excess 4.6 MeV alpha-activity in terrestrial thorium, if any, is much less than 3%. An approach to set an upper limit for the excess alpha-activity in terrestrial thorium is proposed. The origin of the excess alpha-activity is discussed.     

Interpretation of thorium bioassay data

This study is a comparison between bioassay data of thorium-exposed workers from two different facilities. The first of these facilities is a monazite sand extraction plant. Isotopic equilibrium between²³²Th and²²⁸Th was not observed in excreta samples of these workers. The second facility is a gas mantle factory. An isotopic equilibrium between²³²Th and²²⁸Th was observed in excreta samples. Whole body counter measurements have indicated a very low intake of thorium through inhalation. As the concentration of thorium in feces was very high we concluded that the main pathway of entrance of the nuclide was ingestion, mainly via contamination through dirty hands.The comparison between the bioassay results of workers from the two facilities shows that the lack of Th isotopic equilibrium observed in the excretion from the workers at the monazite sand plant possibly occurred due to an additional Th intake by ingestion of contaminated fresh food. This is presumably because²²⁸Ra is more efficiently taken up from the soil by plants, in comparison to²²⁸Th or²³²Th, and subsequently,²²⁸Th grows in from its immediate parent,²²⁸Ra.     

Synthetic mixtures of thorium isotopes

A series of synthetic mixtures of thorium isotopes was prepared on a gravimetrical basis. The starting compounds consisted of natural thorium ²³²Th (99.99%) and highly enriched ²³⁰Th (99.8%). These materials were chemically purified and characterized for isotopic composition and chemical purity. Thorium dioxide (ThO₂) was demonstrated to be a suitable compound for gravimetrical blending. The isotope amount ratios in the mixtures ranged from 10⁻² to 3 × 10⁻⁶. These synthetic isotope mixtures are to our knowledge, the first ever prepared for thorium and may serve for calibration purposes.     

Electrodeposition of uranium and thorium

Cathodic depositions of uranium and thorium were carried out from a number of baths containing the metal salts, and complexing agents. A reducing agent was also present to prevent oxidation of the element. The deposition was also carried out at controlled pH. The current density ranged from 50 to 200 mA cm^–2. The purity of the deposited metals was better than 99.7%. The mechanism of formation of uranium and thorium is proposed and discussed.     

Vaporization thermodynamics of thorium tetrafluoride

The thermal decomposition kinetics of Pr₂(SO₄)₃ to Pr₂O₂SO₄ have been studied by isothermal weight change determination. The reaction was found to obey a linear law up to α = 0.5; beyond α = 0.5 it could be described as a phase-boundary controlled process. A dependence of the activation energy upon the sample weight was observed. The changes in surface area and density which occur during the decomposition are also given.     

A colorimetric determination of thorium

A colorimetric method for the determination of thorium is proposed. It is based upon the precipitation of thorium with a standard solution of oxalic acid and the subsequent reaction of the excess oxalic acid with a standard solution of potassium permanganate. The absorbancy of the remaining permanganate solution is directly proportional to the thorium present. The variables affecting this method have been critically studied. Reliable determinations can be made in the range of 3 to 30 mg of thorium in 1 cm cells when the colored solution is diluted to 250 ml. Most interfering substances can be removed by electrolysis in a mercury cathode cell or by the precipitation of thorium with potassium iodate.     

Nuclear forensic analysis of thorium

A comprehensive radiochemical isolation procedure and data analysis/interpretation method for the nuclear forensic investigation of Th has been developed. The protocol includes sample dissolution, chemical separation, nuclear counting techniques, consideration of isotopic parent-daughter equilibria, and data interpretation tactics. Practical application of the technology was demonstrated by analyses of a questioned specimen confiscated at an illegal drug synthesis laboratory by law enforcement authorities.     

Field study on thorium uptake by plants within and around of a thorium ore deposit

Thorium concentration was determined in natural forage materials, thyme and barley (stern and kemel) in underlying substrate soil within, and around the thorium mine in Kizilcaoren-Eskisehir. Plant/soil concentration ratios (CR) for thorium were estimated in details for sixteen places including ore pits, mine tailings and cultivation area. The experiments were carried out by using energy dispersive X-ray fluorescence spectrometry. As a result, no demonstrable differences in thorium concentrations between washed plant groups except thyme, and collection time were found. However, thorium amount and CR values for unwashed plant samples were higher than those for washed ones at all sites due to dust contamination. No thorium was observed in the kemels     

Separation of thorium from uranium ore

Thorium-230 has many research applications, but there is not a commercial source of this isotope. However, since ²³⁰Th is part of the ²³⁸U decay chain, it can be separated from naturally occurring uranium. In this work, a novel procedure was developed to separate thorium from uranium ore, consisting of leaching, liquid–liquid extraction, precipitations and ion exchange chromatography. The final product was 91.32?±?0.77 mg of thorium with a purity of 99.5?±?1.2 wt%. Of that, 7.65?±?0.10 mg was ²³⁰Th and the remainder ²³²Th. The total yield of ²³⁰Th was 71.1?±?5.4%. Ways to improve the yield by further processing the back-extraction solution are suggested.

     

The initial oxidation of polycrystalline thorium

The initial oxidation of clean, polycrystalline α‐Th from background CO/CO₂ and saturation of the Th surface by O₂ has been examined by angle‐resolved Auger electron spectroscopy (ARAES) and time of flight secondary ion mass spectrometry (ToF‐SIMS). Following dissociative adsorption of very low doses of background CO/CO₂ (<1 L), the carbon surface population was dominant and spontaneously formed thorium carbide. The accompanying oxygen population increased at a rate roughly one‐third that of the carbon, suggesting simultaneous oxygen incorporation into the bulk. To further corroborate the surface kinetics of adsorbed oxygen, O₂ was admitted, following heating and sputter cleaning of the Th; some oxygen atoms continued to diffuse into the bulk until formation of stoichiometric ThO₂ at ～37 L. ARAES measurements showed an oxygen concentration gradient in the near‐surface region confirming rapid oxygen incorporation at low doses; however, once the surface is saturated, virtually no variation in the oxygen intensity is observed. AES and ToF‐SIMS depth profiling revealed complete oxide formation to a depth of 2 nm. Copyright © 2010 John Wiley & Sons, Ltd.