Determination of thorium isotopes in gas lantern mantles by alpha-spectrometry

A procedure for the determination of the three main isotopes of thorium in gas lantern mantles by alpha-spectrometry has been developed. The samples examined were dissolved in concentrated nitric acid and thorium was precipitated as hydroxide. Thorium was then dissolved in hydrochloric acid to be extracted into a TOPO solution, back-extracted with sulfuric acid, electrodeposited onto a steel disc and finally counted alpha-spectrometrically. The radiochemical recovery for thorium was 94% with a counting efficiency of 37%.     

Determination of uranium and thorium in solar salts by neutron activation analysis

Uranium and thorium contents of solar salts were measured by neutron activation analysis. In advance of neutron irradiation, U and Th were concentrated and separated from some interfering elements by neutralization in which they were precipitated with aluminium hydroxide from solutions obtained by dissolving the salts in water or dilute nitric acid solution. The uranium and thorium concentrations determined were from several hundred ppt to 10 ppb. It was strongly indicated that uranium tends to remain in the solution (brine from seawater) phase in the process of solar salt production while thorium tends to transfer to the solid (solar salt) phase.     

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.     

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.     

Separation of rare-earth elements and thorium in sorption conversion of phosphate rare-earth concentrate produced in nitric acid processing of Khibiny apatite concentrate

It is shown that REEs and thorium can be separated directly in the course of a sorption conversion of the phosphate rare-earth concentrate precipitated in nitric acid processing of the Khibiny apatite concentrate by introduction of compounds containing fluoride ions into the nitric acid solution used in the process. Under the optimal conditions, REEs are quantitatively adsorbed by the sulfo cation exchanger, whereas thorium mostly remains together with phosphorus and fluorine in the mother pulp. The influence exerted by the composition of compounds containing fluoride ions and process conditions on the separation efficiency of REEs and thorium. The suggested approach rules out formation of burial-requiring radioactive wastes with increased content of thorium.     

Procedures for isolation and determination of thorium

The cation-exchange behaviour of micro and trace quantities of thorium on Dowex 50-X8 in the presence of carbonate and phosphate has been studied. Carbonate causes loss of thorium to the column effluent at pH 10.In the presence of phosphate, thorium is incompletely sorbed in the pH range 2-4.5, the loss being maximum at pH 3.8. Outside this range, thorium is quantitatively sorbed and recovered. A method that does not employ ion-exchange has been developed for the microdetermination of thorium in phosphate solution. The phosphate is precipitated as bismuth phosphate and thorium is leached from the precipitate with ammonium carbonate solution and determined with Arsenazo III. Uranium, molybdenum and vanadium are removed with Alamine 336. The results obtained for a standard ore are in excellent agreement with the certified value.     

Rapid determination of thorium in ores : Separation as iodate in presence of oxalic acid

It has been shown that thorium could be precipitated quantitatively in 40% nitric acid solution as iodate, in presence of oxalic acid which complexes all those elements that interfere seriously in the usual iodate procedure. Thorium is thus freed from all the cations in a single operation from solutions containing sulphate and phosphate radicals. The method is very quick and thorium oxide in a sample of monazitc could be estimated with precision in 8–9 hours.     

Rapid determination of thorium in ores : Estimation of trace amounts of thorium in complex minerals and ores

A very rapid method for the estimation, of trace amounts of thorium up to 0.01 per cent. or thereabouts even in complex minerals like ilmenite and columbitetantalite has been described. Thorium is collected in an acid solution with phosphates of zirconium and titanium without prior separation of silica, after decomposition of the mineral with sodium peroxide. Thorium is next collected as fluoride with lanthanum as a carrier, precipitated as thorium iodate in potassium iodate-oxalic acid mixture and finally titrated against 0.01N sodium thiosulphate. Accurate results are obtained within a short time of two working days.     

Precipitation of copper 8-hydroxyquinaldate from homogeneous solution

Copper can be precipitated quantitatively, over a wide range of pH, by 8-hydroxyquinaldine produced from the hydrolysis of 8-acetoxyquinaldine. The copper 8-hydroxyquinaldate can be weighed as either the monohydrate or the anhydrous dichelate. Differences in the appropriate pH conditions, between the PFHS and conventional precipitation methods, and between thorium and copper precipitations from homogeneous solution, are accounted for.     

Thermogravimetric investigation of manganese(ii), silver and thorium diliturates

Thermolysis curves for manganese(II), silver and thorium diliturates were obtained. Manganese diliturate precipitated as the octahydrate and dehydrated in two steps. Silver diliturate formed as a monohydrate from aqueous solutions. Thorium diliturate formed as a hydrate containing 20 moles of water and dehydrated in two steps.Methods for the thermogravimetric determination of manganese(II) and thorium by precipitation as the diliturates are suggested.     

Diphenic acid as an analytical reagent

Summary Diphenic acid can separate thorium completely from moderate amounts of ferrous iron and titanium in almost neutral solutions. As the reagent forms quantitative precipitates with ferric iron and zirconium, workable methods for their separation from thorium and their co-determinations in a mixture with the help of this reagent have also been developed. The reagent can separate thorium from zirconium by precipitating the latter below p_h2, and the same from iron(ic) can be accomplished by the use of ascorbic acid as a masking agent. Ferric iron can be precipitated from solution containing ascorbic acid, by the ammonium salt of the reagent. A convenient process for the estimation and separation of zirconium, thorium, iron(ic) and titanium, when present in a mixture, has also been described, which involves the proper control ofph and the use of ascorbic acid as a complexing agent for ferric iron.My sincere thanks are due to Dr. A.K. Mukherjee of the Indian Association for the Cultivation of Science, Calcutta for his valuable suggestions and to Dr. A. K. Ghosal, Principal, Darjeeling Government College for providing laboratory facilities.     

Method of separating uranium from iron and thorium

Acid leaching of uranium deposits is not a selective process. Sulfuric acid solubilizes iron(III) and half or more of the thorium depending on the mineralog of this element. In uranium recovery by solvent extraction process, uranium is separated from iron by an organic phase consisting of 10 vol% tributylphosphate(TBP) in kerosine diluent. Provided that the aqueous phase is saturated with ammonium nitrate or made 4–5 M in nitric acid prior to extraction. Nitric acid or ammonium nitrate is added to the leach solution in order to obtain a uranyl nitrate product. Leach solutions containing thorium(IV) besides iron are treated in an analogous fashion. Uranium can be extracted away from thorium using 10 vol% TBP in kerosine diluent. The aqueous phase should be saturated with ammonium nitrate and the pH of the solution lowered to 0.5 with sufficient amount of sulfuric acid. In other words, the separation of uranium and thorium depends on the way the relative distributions of the two materials between aqueous solutions and TBP vary with sulfuric acid concentration. Thorium is later recovered from the waste leach liquor, after removal of sulfate ions. Uranium can be stripped from the organic phase by distilled water, and precipitated as ammonium diuranate.     

Gravimetric determination of uranium(VI) with pyridine-2,6-dicarboxylic acid

Uranium(VI) can be quantitatively precipitated from aqueous solution in the pH range 2.1-6.9 with pyridine-2,6-dicarboxylic acid in the presence of tetraphenylarsonium chloride. This provides a new rapid gravimetric method for uranyl ion as an organic chelate complex of high molecular weight. Sodium, aluminium, copper and nickel as well as nitrate, chloride, sulphate and acetate ions, do not interfere, but iron(III) and thorium(IV) do.     

Determination of thorium in magnesium alloys that contain zirconium

Summary An indirect polarographic method for the determination of thorium in magnesium alloys that contain zirconium, zinc, and rare-earth elements is described. The method depends on the precipitation of thorium as the tetra (m-nitrobenzoate) and the polarographic determination of the m-nitrobenzoic acid that is equivalent to the amount of thorium that was so precipitated. The only interference, that of zirconium, is forestalled by the prior removal of the zirconium on an anion-exchange resin. The zirconium can easily be eluted quantitatively from the resin, for subsequent determination.The method avoids tedious separational procedures, and yields accurate and precise values for thorium in the alloys for which it was devised. It is also applicable to simpler substances.The authors gratefully acknowledge the grant from the Defence Research Board of Canada that made possible this investigation (Project D44-75-10-04).     

The analysis of zirconium-thorium binary alloys

Thorium-zirconium binary alloys are analysed by complexometric procedures. For alloys containing more than 20% thorium or 5% zirconium by weight, the sum of the constituents is obtained by a back titration procedure at pH 2.6–2.8 with bismuth nitrate using xylenol orange as indicator. Thorium is then masked with sulphate and the liberated EDTA is titrated with bismuth at pH 1.2–1.3. For alloys containing less than 20% of thorium, thorium fluoride is precipitated on lanthanum fluoride to effect its separation before titration. For alloys containing less than 5% of zirconium, the zirconium is separated by precipitation with p-bromo-mandelic acid.     

Determination of thorium isotopes in bastnaesite ores

A procedure for the determination of alpha-emitting thorium isotopes in bastnaesite ores has been developed. The refractory sample was completely decomposed by potassium fluoride fusion in a platinum crucible followed by transposition to a pyrosulfate fusion. The pyrosulfate cake was dissolved in HCl and the resulting precipitate dissolved in DTPA solution; thorium was coprecipitated as hydroxide using cerium present in bastnaesite as natural carrier. Thorium was then extracted into a TOPO solution, separated by using Dowex 1-X8 for anionic exchange, electrodeposited and finally analyzed by alpha-spectrometry. Thorium was also determined spectrophotometrically using Arsenazo as a colorimetric reagent. The thorium yield of the above discussed chemical procedure is more than 85%.     

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 %.     

The determination, in forensic toxicology, of metallic poisons by paper chromatography

Summary Precipitation of ThFe(CN)₆ from a solution of thorium nitrate with potassium ferrocyanide at varius concentrations has been carried out for the estimation of thorium. The precipitate was filtered and the excess of ferrocyanide was titrated with standard ceric sulphate solution. The amount of potassium ferrocyanide thus used was obtained and the amount of thorium calculated.Having established by the physico-chemical methods that the formula for thorium ferrocyanide is ThFe(CN)₆, under all conditions, it has now become possible to estimate thorium volumetrically by the ferrocyanide method.     

Development of selective separation method for thorium and rare earth elements from monazite liquor

The present work succeeded to develop new optional procedures to enhance the separation process of thorium and REEs. Selective precipitation of thorium with pyrophosphate was successfully attained for the upscale level in which, complete and efficient thorium separation (99%) was achieved with relatively low co-precipitation of REEs (average 15%) and Fe(III) (2.6%). On the other hand, promising and costless method has been developed to optimize the selective precipitation of REEs by adjusting the ratio of the free acids H₂SO₄ to H₃PO₄ at 5:1. It could be obviously demonstrated that about 65.3% of LREEs could be precipitated with a minor amount of thorium 11.9%. Finally, this proposed method could be successfully applied for production of Th and REEs with relatively high yield and purity in addition to low-cost–benefit.     

Use of organic reagents in inorganic analysis

Summary Thorium and zirconium have been determined gravimetrically with phenylglycine-p-carboxylic acid and zirconium alone with phenylglycine-o-carboxylic acid, almost within the same pH range. Better results are obtained when zirconium is precipitated in acetic acid solution in presence of a little ammonium acetate. A number of foreign ions may be separated from thorium and zirconium with these reagents. Iron and titanium cause heavy interference. The interference caused by iron, may however, be eliminated by adding a little ascorbic acid, before precipitation of the metals. The para acid can also extract thorium from a mixture of cerite earths and from monazite sands.Part V: See Z. anal. Chem. 158, 347 (1957).The author likes to thank Dr. B. N. Bose, Principal of the College and Dr. S. K. Sinha, the Head of the Department of Chemistry for their kind advice and encouragements.