Improvements to arapid method for separating strontium from liquid milk by treatment with a chelating resin and crown ethers

In an attempt to improve on a previously reported method¹ for rapidly isolating Sr from liquid milk, the following investigations have been carried out: (1) elution of strontium from a chelating resin with dilute nitric acid, (2) separation of strontium from calcium by extracting from this eluate into chloroform solutions of dicyclohexyl-18-crown-6 (DC18C6), (3) transfer of the strontium into aqueous solution, and (4) removal of barium from this solution by extracting into dichloromethane solutions of 21-crown-7 (21C7). Based on the findings of these studies, a separation scheme was proposed and tested by participating in an interlaboratory comparison on the analysis of⁸⁹Sr and⁹⁰Sr in skimmed milk. The separation scheme requires about 3 hours, provides strontium recoveries greater than 90%, and ensures adequate decontamination factors for the nuclides that occur in milk.     

Isotope exchange of strontium and molybdate ions in strontium polymolybdates

The heterogeneous isotopic exchange reactions in strontium polymolybdates of Sr²⁺ and MoO₄ ^2- ions in the strontium nitrate and sodium molybdate solutions have been studied using ⁹⁰Sr and ⁹⁹Mo as tracers. Electrometric methods have been used to study the compositions of strontium molybdates obtained by adding strontium chloride to a progressively acidified solution of sodium molybdate. It has been found that the exchange fraction increases with increasing chain length of strontium polymolybdate. The exchange equilibrium constant (K _ex) has been calculated between 298 and 348 K as well as DG°, DH° and DS°. The results indicate that Sr²⁺ cations have a much higher affinity for exchangers than MoO₄ ^2- anions. By fitting the data to the Dubinin-Radushkevich (D-R) isotherm it has been shown that the exchange capacity (X _m ) for both ions is affected by the ion adsorption process at low temperatures and by the ion exchange process at high temperatures. At high concentrations, the recrystallization process contributes to on the cation exchange but is ineffective on the anion exchange mechanism.     

Determination of radiostrontium in environmental objects by extraction chromatography using tvex-DCH18C6

A new method for the rapid isolation of strontium radionuclides from environmental objects is described. The method is based on the selective extraction of strontium with a solution of dicyclohexyl-18-crown-6 in tetrachloroethane from nitric acid solution. The usage of this process in extraction chromatography permits to isolate strontium radionuclides with contamination coefficients not less than 10²–10³. A highly porous matrix of a copolymer of styrene and divinylbenzene is used as support. The method includes the following steps: nitric acid leaching of the sample calcined at 500–600°C with final adjustment to 1.5–2.0M HNO₃; elution of nitric acid extract through the extraction chromatographic column; washing of the column with 1.5–2.0M HNO₃; desorption of strontium with hot water, precipitation of strontium carbonate and measurement of -activity of the precipitate.     

Extraction behavior of strontium from nitric acid solution with N,N,N′,N′-Tetraisobutyl diglycolamide

The extraction behaviors of strontium from nitric acid solution were investigated with N,N,N′,N′-tetraisobutyl diglycolamide (TiBDGA). Effects of acidity, diluents, concentration of extractant and temperature on the distribution ratio of strontium (D _Sr) were examined. The stoichiometry of the extracted molecule was Sr²⁺:TiBDGA of 1:3. The apparent extraction equilibrium concentration constant logK _ex was 3.25. The enthalpy change ΔH and entropy change ΔS were ?55.6 kJ mol^-1 and ?124 J mol^-1 K^-1, respectively. The extraction is an exothermic process. Through two strip stages, strontium could be stripped effectively by 0.01 M nitric acid solution.     

Stability of Ultradisperse Copper in a Sulfo Cation Exchanger Matrix

The recrystallization of ultradisperse copper chemically deposited onto a sulfo cation exchanger matrix was studied by the potentiometric method. The stationary value of the electrode potential of the copper-sulfo cation exchanger composite was established during a long period of time, which depended on the ionic form of the composite (H⁺, Cu²⁺, or Na⁺), solution composition (CuSO₄, H₂SO₄, and Na₂SO₄), and solution concentration. Recrystallization was favored by copper(II) counterions, which entered the composite as a result of ion exchange, nonexchange absorption of copper sulfate, or preliminary composite transformation into the Cu²⁺ form. In the quasi-equilibrium state, the concentration of copper(II) counterions was maintained at a high level by the Donnan interfacial potential. At all the copper(II) sulfate concentrations used, the potential of the Cu²⁺/Cu ion—metal pair in the ion-exchange matrix remained at virtually the same level, which was indicative of the stable state of copper particles. In the absence of an external source of copper ions, recrystallization was significantly hindered; therefore, the potential exhibited only a slight drift. Copper ions formed in the solution of small crystals were localized in the vicinity of ionogenic matrix centers, which decreased the mobility of these particles as counterions; therefore, the dispersity of particles remained unchanged.     

Separation of strontium from calcium by means of anion exchanger and alcoholic solution of nitric acid

A possibility of mutual separation of calcium and strontium on an anion-exchange column has been studied and then used in working out methods of separation of radioactive strontium from natural samples. All examinations, carried out on model systems, showed that calcium could be completely separated from strontium on the column with the anion exchanger Amberlite CG-400 using 0.25M HNO₃ in methanol as eluent. The flow velocity of this eluent in the range between 1 ml/min and 5 ml/min did not influence the efficiency of separation of calcium from strontium. The increase of the concentration of nitric acid in methanol reduced the efficiency of their mutual separation and the increase of exchanger column height neutralized the influence of the increase of acid concentration. Calcium was separated from strontium in the mass concentration ratio (Ca²⁺)/(Sr²⁺) in the range between 11 to 1001. This separation procedure may be used for the isolation of radioactive strontium from real samples instead of using fuming nitric acid.     

A novel Np–Pu separation procedure based on extraction with di-(chlorophenyl)-dithiophosphinic acid in nitric solution

The extraction behavior of Pu(III), Pu(IV), Np(IV) and Np(V) with di(chlorophenyl)-dithiophosphinic acid (DCPDTPA) in toluene from nitric acid solutions was studied systematically. In aqueous solution with high nitric acid concentration, the extraction capability (represented by distribution ratio D) for Pu and Np in different valences with DCPDTPA comes as D _Np(IV) > D _Pu(IV) > D _Np(V) > D _Pu(III). A new radiochemical procedure for Np/Pu separation based on DCPDTPA extraction was proposed and tested with simulated samples. The recoveries of Np and Pu are as high as 80 % after the whole separation procedure, with the decontamination factor of trivalent lanthanide fission product element (e.g. Eu) greater than 1.5 × 10⁴. The decontamination factor of Pu–Np is 2.0 × 10³, while the decontamination factor of Np–Pu is greater than 4.8 × 10³ after additional purification.     

Determination of 90Sr in radioactive concentrate from Nuclear Power Plant Mochovce

This paper describes the use of molecular recognition technology product AnaLig^®Sr-01 gel from IBC Advanced Technologies, Inc. to effectively and selectively pre-concentrate, separate and recover strontium from evaporator concentrate samples from Nuclear Power Plant Mochovce which belongs to the most difficult matrices to analyze. The method is suitable for analyzing highly contaminated samples of radioactive waste in a relatively short time and with high decontamination factors. Activity of ⁹⁰Sr was measured using Cherenkov counting on TRI CARB 2900 TR liquid scintillation counter.     

Investigation on the extraction of strontium ions from aqueous phase using crown ether-ionic liquid systems

The extraction of strontium ions using DCH18C6 as the extractant and various ionic liquids (ILs) as solvents has been investigated. The distribution ratio of Sr²⁺ can reach as high as 10³ under certain conditions, much larger than that in DCH18C6/n-octanol system. The extraction capacity depends greatly on the structure of ionic liquids. In IIs-based extraction systems, the extraction efficiency of strontium ions is reduced by increasing the concentration of nitric acid and can also be influenced directly by the presence of Na⁺ and K⁺ in the aqueous phase. It is confirmed that the extraction proceeds mainly via a cation-exchange mechanism.     

Removal of cesium and strontium from acid solution using a composite of zirconium molybdate and zirconium tungstate

A composite mixture of zirconium molybdate and zirconium tungstate was prepared and studied for the sorption of cesium and strontium as a function of nitric acid, metal ion concentration, time and temperature. The distribution coefficient (K_d) of 7000 ml/g (~90% sorption) and 70 ml/g (~20% sorption) was obtained for the sorption of cesium and strontium in 0.1M nitric acid, respectively. Experimental sorption capacity, b for cesium was found to be 50 mg/g from 0.1M HNO₃ and 30 mg/g for strontium from 0.001M nitric acid. The sorption of strontium on the sorbent was accompanied by the absorption of heat but the sorption of Cs⁺ results in the liberation of heat. Column studies were conducted by following a breakthrough (BT) curve of cesium and strontium up to C/C₀=1 and the results are reported.     

Improved method for the separation of radioactive strontium from various samples by mixed solvent anion exchange

Procedures for the separation and determination of⁹⁰Sr in liquid samples, with cation and anion exchangers have been described. Strontium, yttrium and other cations bind to the cation exchanger and are eluted from the column by means of nitric acid. Separation of yttrium and strontium from other cations is carried out on columns filled with strong base anion exchangers in nitrate form with alcoholic solutions of nitric acid. This separation method enables the determination of⁹⁰Sr through yttrium on a low-level gas flow α, β-counter, as well as through strontium on a lowlevel liquid scintillation counter by means of Cherenkov counting. Such procedures have been tested by the determination of⁹⁰Sr in water, wine, medium radioactive liquid waste samples, milk and clover samples. For comparison, the determination has also been carried out by the standard method. It has been showed that the developed procedures might produce a high efficiency in strontium separation and a satisfactory accuracy of determination.     

Adsorption kinetic, isotherm and thermodynamic studies of Sr2+ onto hexagonal tungsten oxide

Hexagonal tungsten oxide (hex-WO₃) with exchangeable sodium and ammonium cations located in hexagonal channel was synthesized by a facile hydrothermal treatment of sodium tungstate dihydrate in concentrated HCl solution in the presence of ammonium sulfate. An attempt was made to assess the potential of hex-WO₃ for the adsorption of Sr²⁺ ions from acidic radioactive waste solutions. Adsorption of Sr²⁺ reached equilibrium very quickly in 2 h in acidic aqueous solution. Maximum removal of Sr²⁺ ions occurred at pH 4. Equilibrium studies showed that the extent of Sr²⁺ ions uptake by hex-WO₃ was better described by the Freundlich isotherm in comparison with the Langmuir model. The thermodynamic parameters showed that the adsorption of Sr²⁺ ions onto hex-WO₃ was spontaneous and exothermic under the studied conditions.     

A rapid separation of radioactive cesium by nitrobenzene extraction using the chromium complex [Cr(aniline)2(NCS)4]−

A rapid separation of radioactive cesium by the solvent extraction method was investigated. Cesium ions are quantitatively extracted with [Cr(NH₂C₆H₅)₂(NCS)₄]⁻ into nitrobenzene. EDTA is an effective masking agent for other polyvalent cations. The extracted cesium can be back-extracted into the aqueous phase by shaking with 6N HCl. The method was applied to samples of a natural mixture of fission products and a reactor coolant. The decontamination factors for other predominant isotopes in fission products were 10²∼10⁴. The separation of^137m Ba from a mixture of¹³⁷Cs and^137m Ba is also described.     

Treatment of an aqueous radioactive waste solution with elevated levels of226Ra and228Ra

Treatment of an aqueous radioactive waste solution to remove radium prior to discharge was conducted at a laboratory scale. The actual solution is mainly composed of combined radium (²²⁶Ra and²²⁸Ra) with high concentrations of manganese, iron and calcium, which are present as chlorides in dilute hydrochloric acid. Direct precipitation by sulfate anions was selected to be the more viable treatment technique. Sulfate anion concentration, free acidity, temperature and aging of the sulfate precipitate in the supernate prior to filtration are factors that were investigated for their effect on the separation efficiency. The data obtained are discussed in detail.     

Treatment of ferric sulfate waste solutions for the production of ammonium ferric sulfate dodecahydrate

The process of precipitation of ammonium ferric sulfate dodecahydrate (NH₄Fe(SO₄)₂·12H₂O) from waste solutions, obtained during autoclave oxidation of pyrite concentrate has been studied. A special feature of these solutions is the high concentration of Fe(III) ions (>60 g L^–1) and sulfuric acid (> 61 g L^–1). Based on comprehensive laboratory tests, the study determined the optimal conditions for the precipitation process of ammonium ferric sulfate dodecahydrate (AFS) by salting out with ammonium sulfate: reagent excess (100% over stoichiometric, temperature 276 K, time 1 h). The process should be conducted under continuous slow stirring which would not allow forming of large crystals that are difficult to remove from the reactor. The test work confirmed that high quality crystals can be produced by prior oxidation of Fe(II) to Fe(III) ions using hydrogen peroxide and copper removal from the solution.     

Unusual structure of new dimethylmalonate coordination polymer with strontium atoms and VO2+ fragments

A reaction of vanadyl sulfate VOSO₄·3H₂O with dimethylmalonic acid strontium salt led to the coordination polymer {Sr(H₂O)₈[VO(Me₂mal)₂]} _n (1, Me₂mal is the dimethylmalonic acid dianion), in which the carboxylate dianions did not form chelate metallocycles with the vanadyl ions. The complex was studied by ESR spectroscopy. The compound 1 exhibited weak spin-spin exchange interactions of ferromagnetic type between the V^IV atoms.     

Research on a pellet co-precipitation micro-filtration process for the treatment of liquid waste containing strontium

The chemical precipitation method for radioactive wastewater treatment has the advantages of being simple and cost-effective. However, difficulties with the solid–liquid separation and sludge concentration restrict the application of this method. In this paper, a pellet co-precipitation micro-filtration (PCM) process was studied for treating strontium-containing wastewater on a laboratory scale. The seed was prepared by CaCO₃ powders. Sr²⁺ and CO₃ ^2? were constantly crystallised on the seed surface, with Na₂CO₃ as the precipitating agent in the pellet reactor. The following membrane separator with the addition of FeCl₃ enhanced the treatment effect. The average strontium concentrations in the raw water and in the effluent were 12.0 and 0.0220 mg/L, respectively. The strontium decontamination factor (DF) increased with the operation time, with an average value of 577. The precipitate particles formed gradually grew larger, with good sedimentation properties. When the experiment was complete, the formed precipitate was separated easily from the liquid phase and directly discharged. The concentration factor (CF) was 1,958. In the PCM process, crystallisation was the main mechanism for strontium removal, with the influent strontium level playing an important role. Membrane pore blockage and cake layer formation could help to further intercept the strontium crystallites. Furthermore, ferric chloride coagulation in the membrane separator also contributed to strontium removal. The PCM process has potential for wider application in the removal of strontium from wastewater.     

Radiochenical determination of technetium-99 in LLW by chelation with sodium diethyl dithiocarbamate (NaDDC) and extraction with chloroform

A radiochemical method has been developed for the determination of⁹⁹Tc in low-level radioactive, waste from nuclear facilities, using^99mTc as an internal tracer. Radioactive contaminants were removed by carrier hydroxide precipitation and chelating extraction with NaDDC/CHCl₃ system at pH 4. The final technetium was chelated with NaDDC in 3N HCl solution and extracted selectively into chloroform. The average of radiochemical recovery for various types of LLW sample is about 90%. The decontamination factors for most radioactive nuclides are higher than 10⁵. The detection limit for⁹⁹Tc in a sample of about 10 g is 0.17 pCi/g (6.5 Bq·kg^–1) for a 100-minute count.     

Cation-exchange separation of uranium from thorium in nitric acid medium</p> </p>

Summary Sorption behavior of Th and U on cation-exchange resins was investigated from nitric acid medium by both batch and column methods. The cation-exchange studies involved the sorption of UO₂²⁺ and Th⁴⁺ and their cationic complexes onto Dowex 50Wx8 and Dowex 50Wx4 resins (50-100 mesh). The batch data yielded a separation factor (K_d,Th/K_d,U) value of >100 for the cation-exchanger, Dowex 50Wx4 at 1-2M HNO₃. Separation of uranium from thorium was also carried out by column method in nitric acid medium using cation-exchangers, Dowex 50Wx4 as well as Dowex 50Wx8. While uranium elution was possible at 1M HNO₃, Th could be eluted only at higher concentration of nitric acid (>6M). The stripped solution emanating from a mixer settler employing di-2-ethyl hexyl isobutyramide as extractant and feed solution similar to THOREX process comprising 350 mg/l U and 380 mg/l Th in 0.75M HNO₃ was loaded on the column and the decontamination factor value for U in the product was >1000.</p> </p>     

Diffusion with hydrolysis and ion association in aqueous solutions of beryllium sulfate

Taylor dispersion is used to measure mutual diffusion coefficients for aqueous solutions of beryllium sulfate at concentrations from 0.005 to 1 mol-L^–1 at 25°C. Least-squares analysis of the dispersion profiles shows that diffusion of the partially hydrolyzed salt produces a small additional flow of sulfuric acid, about 0.04 mol sulfuric acid per mole of total beryllium sulfate. Ternary diffusion coefficients measured for the aqueous BeSO₄–H₂SO₄ system are qualitatively consistent with Nernst-Planck predictions based on the formation of beryllium sulfate ion pairs, bisulfate ions, and the hydrolysis equilibria 2Be²⁺+H₂O= Be₂OH³⁺+H⁺, 3Be²⁺+2H₂O=Be₃(OH) ₂ ⁴⁺ +2H⁺. Except for very dilute solutions, the predicted flow of sulfuric acid is small compared to the flow of beryllium sulfate because most of the beryllium ions are protected from hydrolysis by the formation of BeSO₄ ion pairs, and most of the hydrogen ions produced by hydrolysis are converted to less-mobile bisulfate ions.