The determination of lanthanum,cerium and thorium without separations: The determination of lanthanum and cerium in thorium

A method is proposed for the spectrophotometric determination of small quantities of lanthanum, cerium and thorium in the presence of one another without separations. Cerium is estimated from its absorption peak in the ultraviolet region, thorium with thorin, and the 3 elements together with arsenazo. The lanthanum is calculated after subtraction of the combined absorbances of the arsenazo complexes of the thorium and cerium. The procedure can be readily applied to the determination of microgram amounts of the 2 rare earths in thorium. In this case the majority of the thorium is removed from the solution by solvent extraction with TTA before the estimation of the rare earths. The interference of iron is considered and proposals made for its removal.     

The oxinates of thorium and some cerite earths

The pH of precipitation of oxinates of thorium, cerium and lanthanum has been studied. By controlling the pH of precipitation, thorium has been separated as the oxinate.From a spectrochemical study of the 4 and 5 oxinates of thorium in dilute hydrochloric acid, acetone, carbontetrachloride, chloroform, and toluene, it has been suggested that the 5 complex is a definite compound, but not an addition body of the 4 compound.A colorimetric estimation of thorium has been suggested by measuring absorption at 320 mμ in hydrochloric acid and 330 mμ in acetone. 2 p.p.m. of the oxide has thus been estimated.     

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 degrees 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.     

Separation and spectrophotometric determination of thorium contained in uranium concentrate

A method for the determination of thorium in uranium concentrate by spectrophotometry with Arsenazo III has been developed. Preliminary solvent extraction procedures were used to eliminate interfering species. Samples were dissolved in nitric, perchloric and sulfuric acid and the uranium extracted from the solution using tri-octylamine. The aqueous layer was evaporated to dryness and the residue re-dissolved with hydrochloric acid, thorium was extracted by tri-n-octyl phosphine oxide and stripped with oxalic acid. For a typical uranium concentrate produced from the phosphate rock of Itataia, Brazil, concentrations of thorium as low as 5 g·g^-1 can be determined.     

The precise determination of 239Np for the evaluation of 238U capture cross-sections at varying neutron energies in a zero-energy fast reactor

A method is described for the determination of ²³⁹Np in natural uranium metal foils irradiated in a zero-energy reactor. The foils are dissolved in nitric acid in the presence of ²³⁷Np used for the determination of the yield of ²³⁹Np. Neptunium is co-precipitated with lanthanum fluoride; lanthanum and thorium are removed by anion exchange in hydrochloric acid solution, and the neptunium is further purified by anion exchange in nitric acid solution. Sources for counting are prepared by direct evaporation of an aqueous solution onto a stainless steel disc. No corrections are necessary to the ²³⁷Np α-count for absorption in the source. The method does not necessitate prior separation of daughter ²³³Pa from the ²³⁷Np tracer and gives sources of high purity in good yield.     

Determination of traces of rare earths in high-purity thorium dioxide by neutron activation analysis

The use of thorium dioxide as a nuclear fuel requires the determination of individual rare earth impurities at 0.08–1 mg kg^?1 levels. Neutron activation is sufficiently sensitive but separation from the matrix is essential. In the proposed method, thorium dioxide (5–20 g) is dissolved in concentrated nitric acid with a little hydrofluoric acid; after evaporation, thorium is complexed with ammonium carbonate and the solution is passed through a small column of Chelex-100 resin which retains the rare earths quantitatively without retaining thorium. The rare earth elements are eluted with dilute nitric acid, concentrated, and irradiated with standards; after irradiation the rare earth are collected on a lanthanum carrier and measured by γ-ray spectrometry. The recoveries of rare earths were checked with tracers and by standard addition to thorium dioxide matrices. The reproducibility for La, Eu and Dy was satisfactory at 0.01, 0.003 and 0.002 mg kg^?1, respectively; as was the reproducibility for all rare earths added to thorium dioxide (1–4 μg/5 g). Limits of detection are adequate for certification of nuclear-grade material.     

A comparative study of some lanthanon chelates of alizarin complexan as reagents for fluoride

A study has been made of the comparative suitability of the cerium^III, lanthanum and praseodymium chelates of alizarin complexan as reagents for the spectrophotometric determination of microgram amounts of fluoride. The cerium^III reagent is most sensitive at pH < 4.5 and the lanthanum reagent at pH 5.0. An enhancement of sensitivity may be obtained for both reagents at pH 4.3 by addition of acetone to 25 % v/v, but the most sensitive means of determination is to use the lanthanum reagent in aqueous solution at pH 5.2 with measurement at 281 mμ. This procedure is 200% more sensitive than the standard method at 620 mμ.     

Kinetochromic spectrophotometry-III Determination of fluoride by catalysis of the zirconimn-Methylthymol blue reaction

The determination of 0.5-4.75 mug of fluoride ion by its catalytic action upon the slow reaction between Methylthymol Blue and zirconium(IV) in aqueous solution is described. Calibration curves obtained after 60 min under optimal conditions are smooth, and yield an effective molar absorptivity of 3.23 x 10(4) 1.mole(-1)mm(-1) at 586 nm. There is considerably less cationic interference than in the alizarin complexan-cerium(III) or lanthanum procedure, but more serious anionic interference is encountered when phosphate, arsenate and, to a lesser extent, sulphate ions are present in the sample solution.     

Amperometry with Two Polarizable Electrodes. Chelometric Determination of Rare Earths

Abstract

The method of determining rare earths by chelometric EDTA titration with biamperometric end-point indication using two stationary platinum electrodes was studied. The convenient pH range for the determination of lanthanum is 5.0 – 8.0, for yttrium 3.5 – 8.0 and for ytterbium 3.0 – 8.0. Rare earths have been determined in the presence of iron and thorium. Iron and thorium can be titrated at pH 1.5 – 2.0 and rare earths of the lanthanum group can be determined by successive titration at pH 5.0. Large amounts of rare earths of the yttrium group interfere with the determination of iron and thorium.     

Determination of metals in phospholipids by atomic-absorption spectrophotometry

A procedure is described for the determination of sodium, potassium, calcium, magnesium and manganese in phospholipids by atomic-absorption spectrophotometry. The method uses a solution of phospholipid in isopentyl acetate; phosphate interference is controlled by the addition of aqueous lanthanum chloride solution homogenized with ethanol. Standards are prepared in a similar solvent mixture. A comparison between the described method and that of standard additions show it to be free of phospholipid matrix effects.     

Polarographic determination of trace amounts of thorium

A sensitive linear-sweep polarographic method for the determination of thorium is described. It is based on the thorium complex with Xylidyl Blue I (XBI) in a medium containing ethylenediamine, 1,10-phenanthroline, oxalic acid and ninhydrin, at pH 10.5-11.5. The complex has been proved to be Th(XBI)(2), with log beta' = 9.6. The method can be used to determine trace amounts of thorium over the range 3.5 x 10(-8)-3 x 10(-6)M. The detection limit is 1 x 10(-8)M. A solvent extraction procedure is necessary to eliminate interference from several cations. The method has been applied to determination of traces of thorium in minerals, with good results.     

Precipitation of metal 8-hydroxyquinolates from homogeneous solution—II Thorium

A comparison has been made of the precipitation of thorium with 8-hydroxyquinoline by the direct method of addition of reagent and by precipitation from homogeneous solution by generation of the reagent from 8-acetoxyquinoline. The latter reagent produces a thorium precipitate with superior physical characteristics. Separation studies using cerium^III as a diverse ion also indicate the superiority of the method using 8-acetoxyquinoline. Further studies of thorium 8-hydroxyquinolate, precipitated by either method, indicate that ignition to thorium oxide is a reliable way to conclude the determination. Methods involving weighing or brominating the 8-hydroxyquinolate generally furnish erroneous results.     

Spectrophotometric Determination of Thorium with Disodium Salt of Arsenazo-III in Perchloric Acid

A rapid and sensitive spectrophotometric method has been developed for the determination of thorium using 0.04% Arsenazo-III in a 2M perchloric acid solution. Absorbance was measured in 1 cm cell and the complex has a sensitive absorption peak at 654 nm. The complex is formed instantly in perchloric acid and remains stable for 45 minutes with constant absorbance. Beer's law is obeyed in the range 1–60 g·g^–1 of thorium concentration with a molar absorptivity at 654 nm = 3.07·10⁵ M^–1·cm^–1 at 24±2°C. The foreign ions interference in thorium determination have been checked. The cations were tested at >60-fold excess of thorium, Mn(II), Fe(III), Co(II) and Ni(II) interfere negatively, whereas only Ce(III) has increased the absorbance. Among the anions, cyanide, phosphate, thiocyanate and acetate at 150-fold excess of thorium cause significant interference. However, thorium can bedetermined in the presence of nitrate, chloride, oxalate, tartrate, ascorbate, thiosulphate and citrate. The method has been applied on certified reference material for thorium determination after extractive separation and the result was found in good agreement with the certified value. The method has been also applied successfully to determine thorium at g·g^–1 level in local ore samples with a precision of ±0.04%.     

Rapid titrimetric determination of thorium with fluoride using SPADNS

Summary A rapid titrimetric method for the estimation of thorium in the range from 5 to 88 mg. in a 50 ml. of final volume has been developed which involves the adjustment of P_h at 3.0, addition of 2 ml. of 0.02% SPADNS indicator, dilution to volume and titration with standard NaF until the colour obtained matches a blank containing the buffered solution of the indicator alone. The method has been standardised against known amounts of thorium and a calibration curve relating the titre of the fluoride solution to thorium content has been prepared. Interferences of various cations and anions have also been studied. From the results, the quantitative nature of zirconium interference has been confirmed. The method for the determination of thorium is very rapid and the colour change being sharp from blue-violet to scarlet-red, the detection of endpoint is not at all difficult.The author wishes to thank Dr. A. K. Ghosal, Principal, Darjeeling Government College, for providing Laboratory facilities and Prof. P. Ray and Dr. A. K. Mukherjee of the Indian Association for the Cultivation of Science, Calcutta for their encouragement in the research work.     

Solid phase extraction of uranium and thorium on octadecyl bonded silica modified with Cyanex 302 from aqueous solutions

A simple and reliable method for rapid extraction and determination of uranium and thorium using octadecyl-bonded silica modified with Cyanex 302 is presented. Extraction efficiency and the influence of various parameters such as aqueous phase pH, flow rate of sample solution and amount of extractant has been investigated. The study showed that the extraction of uranium and thorium increase with increasing pH value and was found to be quantitative at pH 6; and the retention of ions was not affected significantly by the flow rate of sample solution. The extraction percent were found to be 89.55 and 86.27 % for uranium and thorium, respectively. The maximal capacity of the cartridges modified by 30 mg of Cyanex 302 was found to be 20 mg of uranium and thorium. The method was successfully applied to the extraction and determination of uranium and thorium in aqueous solutions. The percentage recovery of uranium and thorium in a number of natural as well as seawater samples of Iran were also investigated and found to be in the range of 85–95 %.     

A titrimetric method for the sequential determination of thorium and plutonium

A method for the sequential determination of thorium and plutonium has been developed. In the sample solution containing thorium and plutonium, thorium is first determined by complexometric titration with EDTA and then in the same solution plutonium is determined by redox titration employing potentiometry. Prior to the determination of plutonium, EDTA is destroyed by fuming with concentrated HClO₄. Thorium is determined at 10 mg level and plutonium at 1 mg level with precision and accuracy of better than ±0.5%.     

Determination of phosphorus in steel with a stabilized-temperature graphite furnace and zeeman-corrected atomic absorption spectrometry

The determination of phosphorus in steel by graphite furnace a.a.s. is plagued by a spectral interference from the iron matrix which results in overcompensation when a continuum-source background corrector is used. Zeeman background correction using an alternating transverse magnetic field at the furnace eliminates this problem and allows a routine determination of phosphorus down to 0.002% in steel. Lanthanum is an effective matrix modifier for the phosphorus determination, but its enhancing effect depends largely upon the tube material used and the sample matrix. A 0.2% lanthanum solution was found to be optimum. The stabilized-temperature platform furnace concept allows an interference-free determination of phosphorus in steel, down to 0.002%, directly against aqueous standards. Atomizing the sample from a pyrolytic graphite platform in an uncoated graphite tube provides the optimum environment for a phosphorus determination.     

Extraction studies of thorium(IV) with triphenylphosphine oxide

A simple method is described for the solvent extraction of thorium. Thorium is extracted quantitatively from 5·10^–3M sodium salicylate solution at pH 2.5–3.25 using 2.16·10^–2M triphenylphosphine oxide as an extractant dissolved in toluene. The extracted metal ion is stripped with hydrochloric acid (0.1M) and determined spectrophotometrically with Thoron-1 at 540 nm. The method permits separation of thorium from lanthanum, cerium, neodymium, samarium and uranium from binary mixtures and is applicable to the analysis of monazite sand. The method is precise, accurate and selective.     

The use of lanthanum chloride to prevent interferences in the flame photometric determination of exchangeable calcium in soils

An examination of the interferences of aluminium, bicarbonate, phosphate, sulphate and silicate in the flame photometric determination of calcium in ammonium chloride solutions has shown that, with the exception of bicarbonate, all cause serious interference. Addition of lanthanum to the solution can satisfactorily prevent each of these interferences Provided the lanthanum to aluminium ratio is at least 12.5 I by weight all interference from aluminium can be prevented The use of lanthanum chloride to prevent such interferences in the determination of calcium in ammonium chloride lcachates of soils is discussed and a simple flame photometric method for the determination of exchangeable calcium in soils is proposed.     

Synergistic extraction and separation studies of uranium(VI)

A method is described for the extractive separation and spectrophotometric determination of uranium(VI) from an aqueous solution of pH 5.0–7.0 using benzoylacetone (bzac) and pyridine (py) dissolved in toluene as extractants. The extracted species are UO₂(bzac(₂·2py. The method provides separation of uranium(VI) from lanthanum(III), samarium(III), neodymium(III), cerium(III) and thorium(IV). The method is precise, accurate, fast and selective.