Geochemical partitioning of actinides, 137Cs and 40K in a Tyrrhenian sea sediment sample: Comparison to stable elements

The knowledge of radioactive and stable elements partitioning to natural sediment systems is essential for modelling their environmental fate. A sequential extraction method consisting of six operationally-defined fractions has been developed for determining the geochemical partitioning of natural (U, Th, ⁴⁰K) and antropogenic (Pu, ²⁴¹Am, ¹³⁷Cs) radionuclides in a 10 cm deep sediment sample collected in the Tyrrhenian sea (Gaeta Gulf, Italy) in front of the Garigliano Nuclear Power Plant. ¹³⁷Cs and ⁴⁰K were measured by gamma-spectrometry. Extraction chromatography with Microthene-TOPO (U, Th), Microthene-TNOA (Pu) and Microthene-HDEHP (Am) was used for the chemical separation of the alpha-emitters: after electrodeposition alpha-spectrometry was carried out. Some stable elements (Fe, Mn, Al, Ca, Pb, Ba, Ti, Sr, Cu, Ni) were also determined in the different fractions to get more information about the chemical association of the radionuclides.     

Effects of supercritical fluid extractions on metal ion partitioning as indicated by sequential extractions

We have studied the partitioning of stable elements and uranium to two sediments using sequential extractions (SE). These matrices were then subjected to supercritical fluid extraction (SFE) to attempt to remove the uranium. SEs were repeated on the material remaining after SFE to determine any changes in partitioning. We have confirmed that under suitable chemical conditions, ligand-assisted SFE can be used to extract many metal ions from such matrices. Under the conditions we used, the "easily leachable" metals were extracted, but the refractory metals were not. In addition, SFE appears to redistibute the remaining metal cations among the remaining geochemical after SFE treatment. Our results are presented and discussed in the context of developing decontamination strategies for contaminated soils and sediments.     

Comparison of the standard SM&T sequential extraction method with small-scale ultrasound-assisted single extractions for metal partitioning in sediments

A single extraction method based on the reagents employed in the SM&T (standards, measurement and testing programme) sequential extraction scheme for partitioning of Cd, Cr, Cu, Ni, and Pb in sediments has been developed. Small-scale extractions adapted to electrothermal atomic absorption spectrometric determinations (i.e. 25 mg mass in 1 mL extractant) have been used for the first time in conjunction with selective reagents using conventional operating conditions (i.e. conductive heating, magnetic stirring) or ultrasound-assisted extraction. Small-scale slurry preparations were implemented for determination of the residual/total metal content. The methodology developed enabled drastic reduction of extraction times, yielding extractable contents in accordance with those obtained by application of the conventional SM&T method, which can be regarded as a standard method. An important saving in the amount of sample and reagents is also achieved with small-scale extractions. Homogeneity of sediments at the mg level proved acceptable - precision was similar for between-batch and within-batch measurements. Method development was performed with CRM BCR 601 lake sediment for which extractable amounts of several metals are known. An application to a "real-world" sediment is also presented.     

Rapid sequential separation of actinides using Eichrom's extraction chromatographic material

The presence of ²²⁶ Ra in an estuary formerly affected by direct discharges of waste from a phosphate fertilizer complex has been investigated. Specific activities ranging from 3.6 to 45.2 mBq/l have been detected. In general, activity levels are lower than those detected when direct discharges were carried out. However, there is still a clear contamination due to the disposal of phosphogypsum in open air piles by the river. Moreover, it seems that ²²⁶ Ra is being redissolved from the contaminated bed sediments, which also contributes to an enhancement in the activity levels of the estuary waters.     

A rapid sequential separation of actinides using Eichrom's extraction chromatographic material

For the past 10 years, Eichrom has provided a variety of innovative products for faster separation of radionuclides to radioanalytical laboratories. However, recently, environmental testing laboratories have been challenged to generate reliable data more quickly. To assist our customers with rapid separations, Eichrom has developed a new configuration for its existing extraction chromatographic material that operates with vacuum assisted flow. After pre-concentration of actinides from a given sample, the actinides are dissolved in a suitable solution. Appropriate Eichrom Resin Cartridges are placed on a vacuum box system. Sample solutions are then passed through the cartridges under optimal vacuum pressure. In this paper, a scheme for separation of actinides in different matrices are discussed using Eichrom Resin Cartridges. Time required for separations, test results and ease of use are the primary discussions of this paper.     

Chromatographic separation of trivalent actinides and rare earth elements by using pyridine type resin

Summary In order to develop the partitioning-transmutation system for the reduction of high-level radioactive wastes, the group and mutual separation of actinides and rare earth elements in spent fuels is required. In the present work, a chromatographic separation of trivalent actinides (Am and Cm) and rare earth elements was examined in hydrochloric acid/methanol mixed solvents by using a pyridine resin embedded in high-porous silica beads. In a 70 vol% hydrochloric acid (11.7 mol HCl/dm³)/30 vol% methanol mixed solvent, the elution curves of the trivalent actinides were separated completely from those of rare earth elements at room temperature. The present paper discusses the separation behavior of trivalent actinides and rare earth elements as a function of flow rate, temperature and solvent compositions.     

Evalution of sequential extractions on dry and wet sediments

A five-step sequential extraction procedure was applied on dried and wet Ballastplaat Scheldt estuary sediments. When wet (fresh) sediments were used, all sample handling up to the 3rd extraction step, inclusive, was carried out under inert atmosphere. The repeatability of the procedure was very good on dry samples. For Fe as for Mn, RSD values are lower than 4%, except for Mn in the fifth extraction step where a spread of 10% is observed. The observed RSDs for Pb are of the same order of magnitude as those for Mn. On wet samples the spread of the results is higher than on dried ones. The highest RSDs observed for Fe amount to 20%, for Mn to 15% but for Pb an RSD of up to 44% was found. Better homogenization of the solid sediment part of lyophilized sediments and different porosities of wet sediment sub-samples may be the explanation. These results also indicated that drying/oxidizing of the sediment sample causes a shift from less available/mobile metal fractions to more available/mobile fractions. The Mn and Fe oxyhydroxide spikes added to a wet sediment sample were recovered between 100±10%. The results obtained after changing the sequence of the extraction steps (multiple rotations and inversions were tested) corroborated the progressive increase in the aggressive nature of the extraction solutions in our standard scheme. Although there is also no need to change the ratio volume of extractant to amount of sediment, increasing the number of extraction repetitions in steps 1 to 3 resulted, for some of those extraction steps, in a partially modified analyte distribution. Finally the method was applied to sandy and muddy sediment cores of the Scheldt estuary and revealed clear differences between metal distributions in both types of sediment.     

Evaluation of heavy metal bioavailability in soil amended with poultry manure using single and BCR sequential extractions

In the present study, three-step Community Bureau of Reference sequential extraction scheme (BCR-SES) and single extraction methods were performed to assess the mobility and availability of heavy metals (Cd, Cu, Pb, Fe and Zn) in an agricultural soil before and after amendment with poultry waste (PW).The PW samples were collected from poultry farms, situated in Hyderabad Sindh, Pakistan. The extractable heavy metals were measured by flame and electrothermal atomic absorption spectrometry. The validation of the method was carried out by analysis of a certified reference material of soil amended with sewage sludge (BCR-483). The single extractions using calcium chloride and EDTA, separately, while BCR-SESs were developed to evaluate the available heavy metals to plants and their environmental accessibility for control soil (CS), PW and soil amended with PW (SPW).The pH of the PW and SPW were found to be < 6.0, which may enhance the leaching of heavy metals to agricultural soil. The results from the partitioning study indicated that easily mobilised forms (acid exchangeable) of Cd were higher than other heavy metals. The oxidisable fractions of all heavy metals were dominant in PW and SPW as compared to found in CS samples. The EDTA- and CaCl₂-extractable heavy metals correspond to 5.0 to 10 and 0.5 to 3.0%, respectively of total contents in all three solid samples. Contamination factors revealed that the retention of Pb and Zn were higher compared with Cu, Cd and Fe in CS, PW and SPW samples.     

Studies on evaluation of modified TRUEX solvent for the partitioning of minor actinides

An attempt to modify the TRUEX solvent has been initiated by replacing TBP with long-chain alcohols such as isodecanol. Solvent extraction experiments have been carried out determining distribution ratios for Am(III) as a function of concentrations of nitric acid and isodecanol. Acid uptake constant for the combined organic phase has also been arrived at which strongly suggests the interaction of CMPO and isodecanol. The suitability of the organic phase was tested for simulated high-level waste solutions.     

Scaling-up experience of actinides partitioning from intermediate level high salted alkaline waste streams of Purex process using Versatic-10 extractant

Partitioning of minor alpha-emitting actinides, especially U, Pu and Am from medium active alkaline waste is possible from intermediate level liquid wastes (ILLW) produced during spent fuel reprocessing following Purex process. This paper deals with the efficient removal of alpha-activity from ILLW by solvent extraction process. Counter current batch extraction with O/A ratio 2:1 as well as multistage mixer settler has demonstrated that most of the alpha-activity was removed from the alkaline effluents using 20% Versatic-10 (V-10) in dodecane after giving 3 to 4 contacts, thus converting alkaline waste as non-alpha waste. Under the optimum conditions (pH 9.0-9.5 and VA-10), both Pu(IV) and Am(III) are highly extractable whereas U(VI) is relatively poorly extracted. To assess the applicability of this process for regular treatment of the waste, a feasibility study on pilot plant scale using six stage mixer settler was operated to treat the ILLW. The results indicated that almost >99.90% alpha-emitting actinides are removed. Dilute nitric acid (0.5M HNO₃) served as the most efficient strippant for all these actinides. This facilitate an easy regeneration of the extractant which can be recycled. This method is useful in obtaining alpha-free wastes and had positive impact on ease and safety aspects during subsequent waste treatment and long term storage.     

Nanofibrillated cellulose originated from birch sawdust after sequential extractions: a promising polymeric material from waste to films

The residual cellulose of wood processing waste, sawdust, which was leftover after sequential hot-water extraction processes to isolate hemicelluloses and lignin in a novel forest biorefinery concept, was explored as the starting material for preparation of a highly value-added polymeric material, nanofibrillated cellulose (NFC) also widely termed as cellulose nanofiber, which has provided an alternative efficient way to upgrade sawdust waste. The residual cellulose in sawdust was converted to a transparent NFC suspension in water through the 2,2,6,6-tetramethylpiperidine-1-oxyl radical/NaClO/NaBr oxidization approach. The resultant NFC with a dimension of ca. 5 nm in width and hundreds of nanometers in length were further processed into NFC films. The morphological features of the NFC suspension and its films were assessed by transmission electron microscopy and scanning electron microscopy. Highly even dispersion of NFC fibrils in the films originated from sawdust feasibly contributes to the outstanding mechanical performance of the films. NFC suspension with higher carboxylate content and its resultant NFC films were found to show higher transmission of light.     

Thermodynamic investigations of aqueous-molten paraffin wax liquid-liquid extractions and synergistic extractions of some trivalent rare earth elements

In this paper, liquid-liquid extraction behaviour of RE(III) (RE = La, Sm, E, Yb) by the use of 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5 (PMBP) in liquid paraffin with cersin has been investigated at 343.2 K. Under some conditions, the synergistic extraction behaviour with PMBP and Phen has also been studied. The slope analysis method shows that the compositions of the extracted species are REA(3) and REA(3)B. pH(1 2 ) values were also obtained. Equilibrium extraction constants and thermodynamic parameters were calculated. The results showed that increasing temperature is favourable to extraction of heavy rare earth ions with PMBP and more favourable to synergistic extraction with PMBP and Phen. Synergistic extraction can be carried out at lower pH.     

Kinetic analysis of actinides using differential spectrophotometry

The kinetic method developed allowed us to analyse of two-component actinide mixtures without separation. The concentration changes in the system where complex dissociation reaction takes place were determined by spectrophotometry.     

Fractionation of 137Cs and 60Co in soils by sequential extractions

Comparison of six sequential extraction schemes either widely used or specifically developed for speciation of ¹³⁷Cs and ⁶⁰Co in two types of soil (Chromic Luvisol and Eutric Fluvisol) is presented. The results from the comparison show that extractable radiocesium in Chromic Luvisol (14%) is about three times lower than in Eutric Fluvisol (39%). For Chromic Luvisol the total extractable radiocobalt varies from 42 to 78% while the variation for Eutric Fluvisol is not so substantial (55–83%). The results show that BCR and NIST schemes developed for heavy metals are not efficient for radiocesium fractionation, but give very good results in the case of radiocobalt. The efficiency of a scheme is dependant not only on the type of radionuclide but on the type of soil as well. The best reagent for evaluation of bioavailable cesium is NH₄NO₃ or other NH⁺ ₄-salt. Practically most of the radiocobalt is in extractable form in both soils (about 83%) and major part of radiocesium (more than 60% depending on the soil type) is strongly bound in the soils and not extractable.     

Separation of enzymes by sequential macroaffinity ligand-facilitated three-phase partitioning

Pectinase and cellulase were separated from a commercial enzyme preparation called Pectinex Ultra SP-L. This was carried out using a process called macroaffinity ligand-facilitated three-phase partitioning (MLFTPP). In this method, a water-soluble polymer is floated as an interfacial precipitate by adding ammonium sulfate and tert.-butanol. The polymer (appropriately chosen) in the presence of an enzyme for which it shows affinity, selectively binds to the enzyme and floats as a polymer-enzyme complex. In the first step, pectinase was purified (with alginate as the polymer) 13-fold with 96% activity recovery. In the second MLFTPP step, using chitosan, cellulase was purified 16-fold with 92% activity recovery. Both preparations showed a single band on sodium dodecylsulfate-polyacrylamide gel electrophoresis. This illustrative example shows that the strategy of sequential MLFTPP can be used to separate important biological activities from a crude broth.     

Addition of stable nitroxide radical to stable divalent compounds of heavier group 14 elements

The reactions of stable cyclic dialkylgermylene 2 and dialkylstannylene 3 with 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) radical (2 equiv) gave the corresponding 1:2 adducts 4 and 5, respectively, which were characterized by NMR, MS, and X-ray analyses. The kinetics of the stepwise addition of two TEMPO molecules to germylene 2 revealed that the initial addition of TEMPO to 2 was 1010 times slower than the second TEMPO addition to the resulting germyl radical. The origin of the rate difference was discussed on the basis of the qualitative perturbation theory. In contrast to the reactions of 2 and 3, the reaction of dialkylsilylene 1 with TEMPO gave an interesting 1,3-dioxadisiletane derivative.