Liquid-liquid extraction separation and sequential determination of plutonium and americium in environmental samples by alpha-spectrometry

A procedure is described by which plutonium and americium can be determined in environmental samples. The sample is leached with nitric acid and hydrogen peroxide, and the two elements are co-precipitated with ferric hydroxide and calcium oxalate. The calcium oxalate is incinerated at 450 degrees and the ash is dissolved in nitric acid. Plutonium is extracted with tri-n-octylamine solution in xylene from 4M nitric acid and stripped with ammonium iodide/hydrochloric acid. Americium is extracted with thenoyltrifluoroacetone solution in xylene at pH 4 together with rare-earth elements and stripped with 1M nitric acid. Americium and the rare-earth elements thus separated are sorbed on Dowex 1 x 4 resin from 1M nitric acid in 93% methanol, the rare-earth elements are eluted with 0.1M hydrochloric acid/0.5M ammonium thiocyanate/80% methanol and the americium is finally eluted with 1.5M hydrochloric acid in 86% methanol. Plutonium and americium in each fraction are electro-deposited and determined by alpha-spectrometry. Overall average recoveries are 81% for plutonium and 59% for americium.     

Sorption extraction of lanthanides from phosphoric acid solutions

The possibility of sorption extraction of lanthanides from nitric-phosphoric and phosphoric acid solutions with inorganic sorbents based on hydrated titanyl hydrophosphate was studied. New technological solutions were suggested for lanthanide sorption from the products which are formed in processing of the Khibiny apatite concentrate on mineral fertilizers (frozen nitric-phosphoric acid extract, a product of nitric acid decomposition of apatite, and the production phosphoric acid from the dihydrate process).     

Sulfuric Acid Technology for Processing of Eudialyte Concentrate

Sulfuric acid decomposition of eudialyte was studied, and a technological process including two-stage treatment with sulfuric acid, separation and washing of an insoluble residue, successive hydrolytic precipitation of zirconium and iron-manganese concentrates from solution, and recovery of rare-earth elements from the insoluble residue by leaching, was considered. It was found that zirconium(IV) is recovered from a complex carbonate precipitate in the form of a basic sulfate.     

Preconcentration of lanthanides from natural waters with a lipophilic crown ether carboxylic acid

Lipophilic crown ether carboxylic acids such as 2-(sym-dibenzo-16-crown-5-oxy)stearic acid with a cavity size comparable to the ionic radius of rare-earth elements are selective chelation agents for preconcentration and separation of lanthanides from natural waters for NAA. Interfering matrix elements such as sodium and bromine can be simultaneously eliminated during the extraction. The lanthanides can be back-extracted into a dilute acid solution for NAA, thus providing a large preconcentration factor. This two-step extraction method appears suitable for the determination of lanthanides in natural waters and in biological samples.     

Analysis of the CCRMP Oka-2 rare-earth reference mineral of the britholite-apatite series by electrothermal atomic-absorption and inductively-coupled plasma atomic-emission spectrometry

The lanthanides and yttrium in the Canadian Certified Reference Materials Project (CCRMP) new rare-earth mineral reference material, Oka-2, were determined by electrothermal atomic-absorption and inductively-coupled plasma atomic-emission spectrometry (ICPAES) after sample decomposition with acids and separation of the rare-earth metals from phosphate and other matrix elements by precipitation as fluorides and oxalates. Thorium, yttrium and the common major and minor elements were determined by ICPAES after sample decomposition by fusion with lithium meta- and tetraborates and dissolution of the melt in a mixture of dilute nitric acid and ethylenediaminetetra-acetic acid solution. For comparison purposes, silicon, phosphorus, calcium, magnesium and iron were also determined by other methods. The results obtained are compared with other CCRMP values and with those obtained previously for a similar rare-earth mineral from the same geographical area. Oka-2 is considered to be a thorian intermediate member of the britholite—apatite series.     

Extraction of Rare-Earth Elements in Hydrofluoride Decomposition of Loparite Concentrate

Distribution and existence forms of rare-earth elements in decomposition of the loparite concentrate with ammonium hydrofluoride were studied. It was found that, in the course of the aqueous leaching of the fluorinated concentrate, rare-earth elements fully remain in the insoluble residue as complex salts of general formula NaLnF₄. The process of pyrohydrolysis of the insoluble residue was examined. It was shown that varying the process conditions always results in that a NaLnF4-containing product is obtained. It was found that rare-earth elements can be extracted from the insoluble residue and separated from calcium and thorium, and the conditions for this extraction were determined.     

Preparation,properties and analytical application of silica with chemically grafted hydroxamic acid groups

The synthesis of silica chemically modified with propanohydroxamic acid groups and salicylhydroxamic acid is described. Sorption of 13 metal ions is studied as a function of pH. The composition of the sorbed complexes is determined and the apparent stability constants of the complexes in the sorbent phase are calculated. A correlation between the stabilities of the complexes in the sorbent phase and in aqueous solution is observed in some cases. Some analytical applications of the sorbents are demonstrated: trace amounts of elements can be concentrated from large volumes; molybdenum(VI) and zirconium(IV) can be separated from 10⁴-fold amounts of accompanying elements, and vanadium(V) can be determined in the sorbent phase by using diffuse reflection and photoacoustic spectrometric techniques.     

A combined method of sample preparation for the determination of the total element composition of oils

A comprehensive approach to the determination of the elemental composition of oils (including those with a viscosity of 5000 mm²/s) is proposed. It ensures the determination of the most elements present in oils using two versions of sample preparation, autoclave decomposition of oil samples and extraction preconcentration of elements from oil into an aqueous solution on rotating coiled columns (RCCs). The application of RCCs in the elemental analysis of oil ensures the preconcentration of a number of trace elements from oil (including rare-earth elements) and the determination of their concentrations at a level of ng/kg. The preconcentration factor of trace elements from oil using an RCC depends on the volume of oil sample pumped through a constant volume of the stationary phase (acid solution) retained in the column and on the speciation of elements in the oil.     

The separation of tellurium and selenium by polyurethane foam sorbents

Tellurium and selenium can be sorbed from hydrochloric acid and hydrobromic acid solution by both polyether and polyester-based polyurethane foam. Although some acid is needed, the substitution of sodium chloride or sodium bromide increases the extraction significantly. Tellurium is extracted rapidly with > 99% sorbed in 2 min from 1.0/5.0M and 2.0/4.0M hydrochloric acid/sodium bromide. Selenium can also be sorbed quantitatively but much more slowly so that a separation is possible based on the relative rates of extraction. The capacity of polyether foam is 3% by weight of tellurium.     

Chelating ion-exchangers containing n-substituted hydroxylamine functional groups: Part 6. Sorption and separation of gold and silver by a polyhydroxamic acid

The sorption and desorption characteristics of gold and silver on a polyhydroxamic acid chelating resin are described. Gold is quantitatively sorbed from 0.5 M nitric acid or neutral solutions, and readily eluted with 0.5% ($\text{w}\text{v}$) potassium cyanide solution. Silver is removed from 0.05 M nitric acid or neutral solutions, and can be eluted with the cyanide solution or with 0.5 M nitric acid. Gold can be quantitatively separated from copper, iron and silver; gold and silver are sorbed from dilute cyanide solutions. Tests with river water and other eluting systems are reported.     

Separation and preconcentration of the rare-earth elements and yttrium from geological materials by ion-exchange and sequential acid elution

The abundance of rare-earth elements (REE) and yttrium in geological materials is generally low, and most samples contain elements that interfere in the determination of the REE and Y, so a separation and/or preconcentration step is often necessary. This is often achieved by ion-exchange chromatography with either nitric or hydrochloric acid. It is advantageous, however, to use both acids sequentially. The final solution thus obtained contains only the REE and Y, with minor amounts of Al, Ba, Ca, Sc, Sr and Ti. Elements that potentially interfere, such as Be, Co, Cr, Fe, Mn, Th, U, V and Zr, are virtually eliminated. Inductively-coupled argon plasma atomic-emission spectroscopy can then be used for a final precise and accurate measurement. The method can also be used with other instrumental methods of analysis.     

Extraction of rare-earth elements with solutions of di-(2-ethylhexyl)phosphoric acid in flow-through system under local vibrational treatment

Results obtained in a study of the influence exerted by the vibrational treatment in the dynamic interfacial layer on the extraction of rare-earth elements with solutions of di-(2-ethylhexyl)phosphoric acid in a diluent in a flow-through system are presented. It was shown that the coefficient of extraction acceleration under a local vibrational treatment of the dynamic interfacial layer is smaller than that in the static system and is determined by the nature of an element being extracted and a solvent, frequency and amplitude of oscillations of the vibration element, and fluid flow rate. The degree of extraction of rare-earth elements in a certain time is noticeably higher and can reach a double excess if there is a local vibrational treatment of the dynamic interfacial layer. In this case, the accumulation of a lanthanide in the dynamic interfacial layer is substantially lower, and it does not exceed 10% of the total amount of rare-earth elements in the system.     

Ion-exchange chromatography with an oxalic acid-α-hydroxyisobutyric acid eluent for the separation and quantitation of rare-earth elements in monazite and xenotime

Summary An oxalic acid-α-hydroxyisobutyric acid eluent has been used for the separation and determination of rare-earth elements by high-performance ion-exchange chromatography. Fifteen rare-earth elements were separated within less than 25 min on a 150×4.6 mm i.d. column packed with 5-μm sulfonic acid-bonded silica particles by elution with a combined gradient of 0.60–9.0 mM oxalic acid and 19.0–5.0 mM α-hydroxyisobutyric acid at pH 4.6. Detection and quantitation of the separated rare-earth elements was accomplished by visible-absorbance measurements at 600 nm after postcolumn reaction with arsenazo I. The gradient of the two complexing agents was optimized to enable the separation of yttrium(III) without interference from other elements, especially dysprosium(III) and terbium(III). Mass detection limits of the elements were in the range of 2–4 ng. Finally, the chromatographic system was applied to the quantitative analysis of rare-earth elements in monazite and xenotime.     

Separation of transplutonium and rare-earth elements by extraction with HDEHP from DTPA solutions

The extraction behaviour of Am, Cm, Bk, Cf, Es, La, Ce, Pr, Pm, Sm, Eu, Gd, Ho, Yb and Lu in the system HDEHP—DTPA in lactic acid has been studied from the point of view of group separation of the transplutonium and rare-earth elements. Optimum separation conditions have been found on the basis of the results obtained. Some test separations of transplutonium elements from rare-earth fission products have been carried out in real solutions by extraction chromatography. It has been shown that this method can be used successfully for the analytical determination of transplutonium elements as well as for recovery of the latter from irradiated samples.     

Extraction of Nitric Acid from Chloride-Nitrate Solutions

The extraction of nitric acid from chloride-nitrate solutions simulating solutions that result from eudialyte breakdown with hydrochloric acid after extractive recovery of rare-earth elements was studied. A general flowsheet was suggested for the extraction of rare-earth elements from chloride solutions and utilization of nitrate ions as concentrated solutions of nitrates used in recycling.     

Rational Combination of the Dissolution of Some Inorganic Compounds of Rare-Earth Elements with the Determination of Chemical Forms of Major Constituents in These Compounds

It was found that the major constituents (F^– and S^2–) in fluorides, sulfides, and sulfofluorides of rare-earth elements, and europium(II) in europium fluoride, can be determined titrimetrically. Peculiarities of the decomposition and analysis of initial samples of these compounds and samples after high-temperature treatment in vacuum were considered. The analytical procedures are based on the combination of the decomposition of the test materials using solutions of iodine (determination of S^2–), boric acid (determination of F^–), and vanadium(V) salts (determination of europium(II) salts) and the final titration of excess reagents that selectively reacted with a chemical form of the analyte. Potentiometry with an ion-selective electrode was also used in the determination of fluoride ions. The total concentration of rare-earth elements was determined by chelatometry.     

Preconcentration of cobalt with N-(dithiocarboxy)sarcosine and amberlite xad-4 resin

Cobalt reacts with N-(dithiocarboxy)sarcosine (DTCS) to form a 1:3 Co:DTCS complex which is so stable that after its formation no decomposition occurs even in 4M hydrochloric acid. The complex is sorbed on a column of Amberlite XAD-4 copolymer from an acidic solution and eluted with 10 ml of a 1:1:3 v v mixture of 1.0M ammonia solution (pH = 9), 0.1M EDTA and methanol. The absorbance of the eluted chelate is measured at 320 nm against water ( = 2.15 x 10(4) l.mole(-1).cm(-1)). The recovery of cobalt from 1 litre of tap-water or sea-water is quantitative. The effect of diverse ions can be eliminated by the addition of EDTA after chelation of the cobalt. The copper complex with DTCS is partly sorbed on the column because of its slow rate of decomposition by EDTA, but most of the copper chelate sorbed can be eluted with hydrochloric acid and any co-eluted with the cobalt chelate can be completely decomposed by heating the eluate. Cobalt enrichment factors of at least 100 are obtained, so the method is applicable to the determination of cobalt at the ng ml level.     

Selective separation of chromium from other elements by ion-exchange-II Anion- and cation-exchange in oxalic acid solutions

The kinetic inertness of the chromium(III) aquo-ion towards substitution reactions with oxalate has been exploited for selective separation of chromium from other elements. Most transition elements, with the notable exception of chromium, react rapidly with oxalate, and may be sorbed on a strongly basic anion-exchange resin as anionic oxalato complexes. On the other hand chromium sorbed on a cation-exchange resin is not eluted with oxalic acid solutions. This permits separation of chromium from elements which react rapidly with oxalate.     

Method of two reagents on a solid phase for the determination of simultaneously present vanadium(V) and molybdenum(VI)

The possibility of the use of two reagents for the determination of two elements from one sample on one disk of fibrous sorbent was studied. Vanadium(V) and molybdenum(VI) are sorbed on a disk of an anionexchange fibrous material and, next, sequentially detected by diffuse reflection spectrometry with 8-hydroxyquinoline-5-sulfonic acid and phenylfluorone. It was demonstrated that vanadium and molybdenum can be determined when present simultaneously in ratios from 1 : 10 to 10 : 1 in the concentration range 0.01-0.15 ώg/mL (RSD < 15%). The detection limit is 0.005 and 0.003 ώg/mL for vanadium and molybdenum, respectively.     

Use of alcoholic solutions for the isolation and purification of americium and curium with anion-exchangers

The sorption of transplutonium (TPE), rare-earth (RE) and other elements by anion-exchangers (Dowex 1 type) from aqueous alcoholic solutions of nitric acid and ammonium thiocyanate was investigated. This investigation allowed the development of simple and effective methods of americium—curium separation from frradiated plutonium. Plutonium, TPE (in a +3 oxidation state) and RE are firmly sorbed by the anion-exchanger from 1 M HNO₃ in 90% alcohol, Fe, Al and fission products Cs, Sr, Nb, Zr, and Ru pass through the column under these conditions. The RE separation from TPE is achieved by washing the column with 0.5M NH₄SCN in 80% alcohol. The column is then washed with 0.5 M HNO₃ in 85% alcohol, and americium—curium separation proceeds. Use of this method for recovery of an irradiated plutonium target containing 100 mg Pu, Am and Cm is described.