Precipitation and purification of uranium from rock phosphate

This study was carried-out to leach uranium from rock phosphate using sulphuric acid in the presence of potassium chlorate as an oxidant and to investigate the relative purity of different forms of yellow cakes produced with ammonia, magnesia and sodium hydroxide as precipitants, as well as purification of the products with TBP and matching its impurity levels with specifications of the commercial products. Alpha-particle spectrometry was used for determination of activity concentration of uranium isotopes in rock phosphate, resulting phosphoric acid, and in different forms of the yellow cake. Likewise, atomic absorption spectroscopy was used for determination of impurities. On the average, the equivalent mass concentration of uranium was 119.38 ± 79.66 ppm (rock phosphate) and 57.85 ± 20.46 ppm (phosphoric acid) with corresponding low percent of dissolution (48 %) which is considered low. The isotopic ratio (²³⁴U:²³⁸U) in all stages of hydrometallurgical process was not much different from unity indicating lack of fractionation. Upon comparing the levels of impurities in different form of crude yellow cakes, it was found that the lowest levels were measured in hydrated trioxide (UO₃·xH₂O). This implies that saturated magnesia is least aggressive relative to other precipitants and gives relatively pure crude cake. Therefore, it was used as an index to judge the relative purity of other forms of yellow cakes by taking the respective elemental ratios. The levels of impurities (Fe, Zn, Mn, Cu, Ni, Cd and Pb) in the purified yellow cake were found comparable with those specified for commercial products.     

Substoichiometric determination of phosphorus

Phosphorus in orchard leaves (NBS SRM-1571) and spinach (SRM-1570) was determined by various substoichiometric analytical methods such as the direct method, GRASHCHENKO's method and the method of carrier amount variation. All samples were labelled with³²P radioisotope. The data obtained by the method of carrier amount variation were also treated by the method of least squares instead of De VOE's method. Phosphorus concentration in orchard leaves was 0.206±0.011% by the direct method, 0.219±0.011% by GRASHCHENKO's method, 0.211±0.011% by the method of carrier amount variation and 0.207±0.007% by the method of least squares, respectively. These values agree with the value reported by NBS (0.21±0.01%). Furthermore, these concentrations obtained by various substoichiometric methods were compared with those by radioactivation reported in a prevoius paper.     

Substoichiometric determination of chromium

The present work deals with the determination of Cr/III/ by means of the substoichiometric isotope dilution method, using PAN, 1-/2-pyridylazo/-2-naphthol as a complexing agent. Chromium forms a 12 complex with PAN. Heating to 90°C for 3 min was necessary for complete complexation. The complex was extracted into chloroform at pH 3.5 /acetate buffer/. Tens of micrograms of chromium could be determined. Effect of diverse metal ions was also studied.     

A simplified determination of uranium in phosphate rock and phosphogypsum by alpha-spectroscopy after its separation by liquid-extraction

A relatively rapid, economic and robust procedure is described for the radiometric analysis of uranium in phosphate rock and phosphogypsum. The analysis is performed by alpha spectroscopy after pre-concentration and separation of uranium by liquid-extraction using tributyl-phosphate (30% TBP in dodecan) and finally its electrodeposition on stainless steel discs. The method has been successfully applied to 0.1 g samples of phosphate rock and phosphogypsum resulting in high-quality spectra for measurement times ≥15 h. The main advantage of the procedure is the use of tracer solution (²³²U) that allows reliable measurements and evaluation of the separation procedure. The separation efficiency of the proposed method has been estimated to be (75 ± 20)%.     

Extraction and spectrophotometric determination of uranium in phosphate fertilizers

An extraction and spectrophotometric method for determination of trace amounts of uranium in phosphate fertilizers is described. It is based on the extraction of uranium with trioctylphosphine oxide in benzene and the spectrophotometric determination of uranium with Arsenazo III in buffer-alcoholic medium. The maximum absorbance occurs at 655 nm with a molar absorptivity of 1.2·10⁴ l·mol^–1·cm^–1. Beer's law is obeyed over the range 0.6–15.0 g·ml^–1 of uranium(VI). The proposed method has been applied successfully to the analysis of phosphate fertilizers with phosphate concentrations of 45% P₂O₅.     

Substoichiometric determination of cobalt in crud

A substoichiometric extraction method with nitroso-R salt (NRS) has been studied for the determination of trace Co in crud. The Co-NRS complex is extracted substoichiometrically into Capriquat-CHCl3 at pH 6.5-9.0 in 20 min of shaking time. The analytical results obtained by the method are within 3% of relative error in the determination range of 5 to 50 micrograms. The proposed method is simple and has sensitivity of 0.5 micrograms, though Fe(II), Ni(II) and Cu(II) seriously interfere. The results applied for the determination of trace Co in crud are described.     

Determination of uranium and radium in phosphate rock and technical phosphoric acid

Summary Uranium in phosphate rock can be determined radiometrically using gamma-counting and spectrophotometrically using arsenazo I. In the latter case the rock is dissolved in HNO₃, then uranium is extracted with tributyl phosphate, stripped with hot water and determined. For the determination of uranium in technical phosphoric acid, the fluorosilicate ion present as impurity must first be precipitated, the uranium separated on Amberlite IRA-400 in the sulfate form, then determined in the eluate spectrophotometrically by arsenazo I. Radium can be determined in leach solutions by the emanation method.

---

Bestimmung von Uran und Radium in Phosphatgestein und technischer Phosphorsäure

Zusammenfassung Uran kann in Phosphatgestein radiometrisch mit -Zählung und spektralphotometrisch mit Arsenazo I bestimmt werden. Zur spektralphotometrischen Bestimmung wird die Probe in Salpetersäure gelöst, dann das Uran mit Tributylphosphat extrahiert, in heißes Wasser überführt und bestimmt. Zur Uranbestimmung in technischer Phosphorsäure muß zuerst das als Verunreinigung vorhandene Fluorosilicat gefällt und dann das Uran mit Hilfe von Amberlit IRA-400 in der Sulfatform abgetrennt werden, bevor es im Eluat mit Arsenazo I bestimmt werden kann. Radium kann in Auslaugungslösungen mit Hilfe der Emanationsmethode bestimmt werden.

     

Substoichiometric determination of cadmium in biological samples

A method is suggested for the determination of submicrogram Cd in quantities by isotope dilution, using substoichiometric extraction into dithizone in chloroform. The applicability of the method was tested in biological samples. Extraction was carried out from a sodium acetate buffer betweenpH 9.7 and 12.0. With amounts of 0.2 μg of Cd, the S.E. was not greater than 0.01 μg. This method is suitable for large scale analysis of trace amounts of Cd in biological materials.     

Dry-column chromatography of uranium. Application to chemical analysis of monazite and phosphate rock for uranium

Summary A dry-column Chromatographic technique has been applied to the separation of uranium from complicated matrices. It has been demonstrated that operating parameters of thin-layer chromatography on silanized silica gel in isopropyl ether-tetrahydrofuran-nitric acid (65203) can be transferred to this technique. Chromatograms are thus easily developed on dry packed column with the solvent system of the type used in the TLC. Uranium is eluted off the column and determined with Arsenazo III spectrophotometrically. The technique is successfully applied to the determination of uranium in monazite and phosphate rock samples with good precision and accuracy.

---

Trockensäulenchromatographie des Urans. Anwendung zur chemischen Analyse von Monazit und Phosphorit

Zusammenfassung Zur Abtrennung des Urans aus komplizierten Matrices wurde die Trockensäulenchromatographie verwendet. Wie gezeigt werden konnte, lassen sich die Bedingungen der Dünnschichtchromatographie (DSC) auf silanisiertem Silikagel mit Isopropylether-Tetrahydrofuran-Salpetersäure (65203) auf das genannte Verfahren übertragen. Chromatogramme sind daher auf trocken geschichteten Säulen mit Lösungsmittelsystemen der DSC herstellbar. Uran wird eluiert und mit Arsenazo III spektrophotometrisch bestimmt. Das Verfahren wurde zur Uranbestimmung in Monazit und Phosphorit erfolgreich angewendet.

     

Substoichiometric neutron activation determination of gold

A highly precise and selective method is described for the determination of traces of gold by substoichiometric extraction from hydrochloric acid with tri-n-octylphosphine sulfide in cyclohexane following thermal neutron activation. Fundamental aspects of the extraction system are discussed and results are reported for the determination of gold in an effluent from a recovery process.     

Substoichiometric determination of micro-amounts of silver in platinum

Selectivity of the isotope dilution analysis with substoichiometric separation for silver determination in platinum has been investigated. From dilute sulfuric acid in the presence of hydroxylamine sulfate silver can be extracted with substoichiometric amount of dithizone in chloroform.     

Substoichiometric isotope dilution analysis for uranium by synergic extraction

Substoichiometric extraction of uranyl ion in a synergic system of a chelating reagent and a neutral ligand is described. The system is based on a substoichiometric amount of 2-thenoyltrifluoroacetone (TTA) and an excess of tributylphosphate (TBP); this is compared with a system involving a substoichiometric amount of trioctylphosphine oxide and an excess of TTA. The reproducibility of the substoichiometric extraction is 0.46 or 0.62%, respectively. The former method is superior because extraction of uranyl ion with TBP alone is negligible. The method is applicable to > ca. 10 μg of uranium.     

Substoichiometric determination of trace impurities in zinc selenide

Determination of trace impurities in zinc selenide was carried out by substoichiometric neutron activation analysis. Trace impurities were separated from matrix elements by suitable procedures and determined by substoichiometric methods, i.e., Au was extracted with rhodamine-B, Ag and Cu with dithizone, Cr with sodium diethyldithiocarbamate, Co with 1-nitroso-2-naphthol, and Sb with cupferron. Two sorts of zinc selenide single crystals were supplied for analysis and the following values were obtained as impurity concentration; Au 0.36, 0.076 ppb, Ag 42, 32 ppb, Cr. 1.8, 0.63 ppm, Co 0.16, 0.0079 ppm, Sb 8.5, 5.9 ppb and Cu 1.4, 0.44 ppm. The behavior of copper by heat-treatment of zinc selenide was also studied by means of substoichiometric isotope dilution analysis.     

Polarographic waves of tri-n-butyl phosphate and polarographic determination of uranium in the presence of tri-n-butyl phosphate

The results of a study on the polarographic behaviour of TBP and its influence on the determination of uranyl ions is presented. The half-wave potential of the adsorption wave of TBP depends on the concentration of TBP, type of supporting elec trolyte and its concentration. In the presence of TBP the polarographic wave of U(VI) ion is changed. Below 7·10^?5 M TBP the polarographic wave of U(VI) is not affected, between 7·10^?5 and 2·10^?4 M TBP the shape, height and half-wave potential of U(VI) waves are changed and above 2·10^?4 M, up to saturated solution of TBP, the waves of U(VI) do, not change further. The bes supporting electrolytes for the determination of U(VI) are KNO₃ or NaClO₄ in concentrations of 0.1 to 0.5 M, pH 1–2 and TBP concentrations from 3·10^?4 to 1.2·10^?3 M.     

Substoichiometric determination of manganese by neutron-activation analysis

A simple and rapid method for the substoichiometric determination of traces of manganese in various materials by neutron-activation analysis has been developed. After dissolution of the irradiated test sample, manganese(II) carrier is added and subsequently oxidised by peroxodisulphate to the heptavalent state. The permanganate thus formed is finally extracted into chloroform as tetraphenylarsonium permanganate using a substoichiometric amount of tetraphenylarsonium chloride. This single separation step isolates radiochemically pure manganese-56 in the analysis of a relatively simple material in which interfering elements (gold, rhenium, etc.) are absent. When this is not true, a preliminary separation of manganese from the irradiated sample, based on the extraction of manganese diethyldithio-carbamate into chloroform and followed by stripping of the manganese with dilute sulphuric acid, must be used. A simultaneously irradiated standard containing manganese must be treated in exactly the same way as a test sample. In the materials analysed by the new method 10(-5) to 10(-3)% of manganese has been determined.     

Substoichiometric determination of inorganic tin in organotin compounds

Inorganic tin(IV) present in organotin compounds is determined substoichiometrically by complexation with salicylideneamino-2-thiophenol in a non-aqueous medium, after isolation of the tin(IV) by iodide extraction. The method is applied to the degradation products in commercial chemicals and those formed by u.v.-irradiation.     

Substoichiometric separation and determination of trace metals

Substoichiometric methods are eminently suitable for the determination of many elements. As a new application of substoichiometry, a substoichiometric speciation of the element in different chemical states is proposed. Substoichiometric speciation of As(III) and As(V) is demonstrated as an example. This is based on a highly selective substoichiometric extraction of As(III) with thionalide and As(V) with tetraphenylarsonium chloride in the presence of an excess amount of pyrogallol. Coexistence of other diverse arsenic species including methylarsenic compounds does not give any interference to the selective determination of As(III) and As(V). For substoichiometric radioactivation, a novel application of the synergistic extraction system in a combination of a substoichiometric amount of thenoyltrifluoroacetone with an excess amount of phenanthroline is demonstrated for Yb as an example. Substoichiometric speciation based on the selective speration and an application of synergistic extraction to substoichiometric separation have additional possibilities in substoichiometry.     

Polarographic determination of uranium(VI) in aqueous tri-n-butyl phosphate solutions

The effect of TBP as well as the organic diluents on the polarographic wave of U(VI) reduction has been investigated in sulphuric and perchloric acids. It was found that the presence of TBP traces in the solution to be analyzed induced another wave which was more prominent in sulphuric acid solutions. This can be eliminated by boiling the solutions for about 5 min before their analysis for uranium. The effect of supporting electrolyte on the polarographic reduction of U(VI) was also studied and the use of 6N HClO₄ was recommended.     

Substoichiometric determination of mercury with cetyltrimethylammonium bromide

A radiometric method based on substoichiometric isotope dilution analysis has been developed for the determination of mercury using cetyltrimethylammonium bromide (CTAB) as the substoichiometric reagent. The method is based on the extraction of mercury as an ionassociation complex of tetraiodomercurate(II) ion with a substoichiometric amount of CTAB in benzene. The calibration graph was found to be linear in the range 0–10 μg Hg (II) in the aqueous phase of 10 ml volume. A detection limit of 0.06 μg·ml⁻¹ could be achieved by the proposed method. The relative standard deviation of the method was found to be 3.0% and the method has been successfully applied to study the determination of mercury in various synthetic mixtures.