Chemical speciation of radionuclides migrating in groundwaters

In order to more accurately predict the rates and mechanisms of radionuclide migration from lowlevel waste disposal facilities via groundwater transport, ongoing studies are being conducted at field sites at Chalk River Laboratories to identify and characterize the chemical speciation of mobile, long-lived radionuclides migrating in groundwaters. Large-volume water sampling techniques are being utilized to separate and concentrate radionuclides into particulate, cationic, anionic, and nonionic chemical forms. Most radionuclides are migrating as soluble, anionic species which appear to be predominately organoradionuclide complexes. Laboratory studies utilizing anion exchange chromatography have separated several anionically complexed radionuclides, e.g.,⁶⁰Co and¹⁰⁶Ru, into a number of specific compounds or groups of compounds. Large-volume ultra-filtration experiments have shown that significant fractions of the radionuclides are being transported in these groundwaters in the form of macromolecules having molecular weights ranging from less than 3,000 to 100,000.     

Colloid transport of radionuclides in soils

Radionuclides undergo redistribution and change existence forms (and, therefore, migration dynamics) not only immediately after they enter into the environment, but also during migration. The latter can be associated with changes in the delivery medium (for example, as strongly contaminated wastewaters is diluted by natural), decrease in the concentration of radionuclides (during their sorption and coprecipitation on soil or host rock microparticles), or change in carrier forms (dissolution of fuel matrices). In view of the multifactor nature and complexity of these processes, we set ourselves the task to summarize results obtained at the GEOKHI RAS on the forms of existence and migration dynamics of radionuclides in radioactively contaminated soils. As objects for study we used soils typical of the forest-steppe zone of the Eastern Ural Radioactive Trace (EURT) and taken at a distance of 2 through 8 km from the Trace axis and 2–4 km from the accident place, as well as samples of the high-water bed soils and sediments of the Enisey River, taken 60 km downstream from the Mining Chemical Combine (MCC).     

Arsenic speciation in contaminated soils

A method for arsenic speciation in soils is developed, based on extraction with a mixture of 1 mol l(-1) of phosphoric acid and 0.1 mol l(-1) of ascorbic acid, and further measurement with the coupling liquid chromatography (LC)-ultraviolet (UV) irradiation-hydride generation (HG)-inductively coupled plasma mass spectrometry (ICP/MS). The stability of the arsenic species in the extracts is also studied. The speciation method applied to several Spanish agricultural contaminated soils from the Aznalcollar zone shows that arsenate is the main species in all the soils analysed and that in some samples arsenite and methylated species could also be detected. The determination of the "pseudototal" arsenic in these soils, obtained by applying extraction with aqua regia (ISO Standard 11466), is also carried out. Both the speciation method and the aqua regia method are applied to several certified reference materials (CRMs) in which total arsenic content is certified. Finally, the same LC-UV-HG coupling with atomic fluorescence spectrometry (AFS) detection reveals to be a valid coupling system to perform arsenic speciation in the soils according to its fair quality parameters and easy utilisation.     

Chemical speciation of heavy metals in soils by use of XAFS spectroscopy and electron microscopical techniques

Pb-contaminated soil samples were investigated using XAFS spectroscopy and SEM/EDX as tools for the analysis of chemical binding forms. The soils originated from the vicinity of a battery factory in Hannover (Germany) and had Pb-contents between 50 g/kg and 140 g/kg. PbCO₃, PbSO₄, PbO and basic PbCO₃ could be identified as the main constituents in the samples by XAFS spectroscopy (EXAFS as well as XANES). This result is consistent with the results of the SEM/EDX investigations on the same soil samples, which showed, that almost all of the lead contained in the soils appears in the form of discrete particles of lead compounds. The EDX analysis of these particles consistently shows the presence of Pb, C, O and S.     

Chemical speciation of heavy metals in soils by use of XAFS spectroscopy and electron microscopical techniques

Pb-contaminated soil samples were investigated using XAFS spectroscopy and SEM/EDX as tools for the analysis of chemical binding forms. The soils originated from the vicinity of a battery factory in Hannover (Germany) and had Pb-contents between 50 g/kg and 140 g/kg. PbCO₃, PbSO₄, PbO and basic PbCO₃ could be identified as the main constituents in the samples by XAFS spectroscopy (EXAFS as well as XANES). This result is consistent with the results of the SEM/EDX investigations on the same soil samples, which showed, that almost all of the lead contained in the soils appears in the form of discrete particles of lead compounds. The EDX analysis of these particles consistently shows the presence of Pb, C, O and S. Rececived: 1 September 1998 / Revised: 15 December 1998 / Accepted: 18 December 1998     

Study of the diffusion of trace elements and radionuclides in soils

Thin layer method of measuring diffusion processes was modified to shorten time and to increase efficiency of experiments. For this purpose small and fine glass capillaries of 20 mm length and inner diameter of several millimeters were used as diffusion cells. The diffusion of trace amounts of¹³⁷Cs, its dependence on soil moisture and interaction with the soil have been studied. Experimental technique. evaluation of records and the basic interpretation of the migration process are described.     

Chemical speciation of plutonium in seawater

Concentrations of particulate and dissolved plutonium in seawater were determined together with strong organic ligands (SOL) in particulate matter (PM). The concentration of particulate 239,240Pu in surface waters of the Western North Pacific ranged from 0.03 to 0.3 mBq m(-3) during the period from 1987 to 1997. The percentage of particulate Pu to total Pu in seawater was less than 10% in surface waters, whereas its portions were less than 1% in deep waters. In order to characterize particulate Pu in seawater, the relationships between particulate Pu, dissolved Pu and SOL concentrations in surface PM were examined. The result reveals that particulate Pu was linearly related to the SOL concentration independent of dissolved Pu concentration. Mass balance analysis suggests that a dominant chemical form of Pu in surface PM, which may exist as Pu(IV), is a complex with strong organic ligands in PM.     

Effect of gleysation on remobilization of radionuclides in waterlogged soils

Joint leaching of iron and other macro- and microelements including radionuclides from radioactively contaminated floodplain soil of the Yenisei River is studied on miniecosystems. In developing anaerobic conditions, the redox potential E_h decreased to +140 mV, causing partial reduction of iron and solubilisation of iron hydrous oxide and organomineral films of the soil. Leaching of stable elements and radionuclides with water proceeds parallel to that of iron. To accelerate reductive mobilization of iron, 0.4% aqueous ascorbic acid was used instead of water as the leaching liquid phase. In this case, E_h approached –60 mV, and the leaching of stable and radioactive elements considerably increased, the effect being most pronounced for plutonium. To cite this article: E.K. Legin et al., C. R. Chimie 7 (2004).

Résumé

Effet du passage en milieu anaérobie sur la mobilisation des radionucléides dans les sols humides. La lixiviation simultanée du fer et d’autres éléments de sols contaminés de la vallée de la rivière Yénései a été étudiée. En imposant des conditions anaérobies, le potentiel redox chute à 140 mV, causant une réduction partielle du fer trivalent et la solubilisation de l’hydroxyde de fer et du film organominéral du sol. Les lixiviations du fer, des autres éléments et, par conséquent, des radionucléides contaminant le sol vont de pair. Pour accélérer la mobilisation réductive du fer, une solution d’acide ascorbique à 0,4% a été utilisée à la place de l’eau. Dans ces conditions, la valeur de E_h approche –60 mV et la lixiviation des éléments augmente considérablement, cet effet étant plus prononcé pour le plutonium. Pour citer cet article : E.K. Legin et al., C. R. Chimie 7 (2004).     

A review of the studies on environmental transport and speciation analysis of radionuclides in India

Department of Atomic Energy, India, has a systematic environmental monitoring program to ensure that the impact of radionuclides on human and environment is well within the limits, stipulated by the regulatory body. Concentrations of radionuclides are estimated in air, water, soil, sediment and biota in the environment around the power plant site on a regular basis. The environmental migration pattern and impact of radionuclides in the environment depends upon not only on the total concentration but the physico-chemical nature of radionuclide also. This paper presents a brief review of the studies of environmental transportation of radionuclides and influence of speciation with special reference to Indian conditions. A fairly good amount of results are available on the influence of speciation of radionuclides on the wet and dry deposition and preliminary results are available on the speciation analysis in dietary items, in soil and in ground water. Initial studies are concentrated on tritium, ¹³⁷Cs, Uranium, ⁹⁰Sr and their chemical analogues.     

Bentonite stability,speciation and migration behaviour of some critical radionuclides

The contribution is focused on chemical, geochemical and mineralogical research of bentonite stability with the aim to determine the effect of saturation medium composition and loading by heat on bentonite stability. The main part of the research is directed to the experimental results of bentonite and bentonite leachate samples obtained for the bentonite interaction under laboratory experiments. Computer-modeling methods were used to calculate equilibrium thermodynamic principles, the distributions of predominant aqueous species, and potential solubility controls for the environmentally important oxidation states of each investigated radioactive contaminants. The Eh–pH diagrams of individual chemical species of the tested radionuclides were calculated by the geochemical software tool Geochemist’s Workbench that included the actual chemical compositions of the solid–liquid systems under the given experimental conditions. It was confirmed that smectites are transformed to more stable silicate phases, such as illite/smectite mixed layers, illite. The data obtained from the model calculations conform with experimental results. The effect of the variable aqueous phase composition on bentonite stability using Ca–Mg and Na–Ca bentonites for the experiments was studied. The synthetic granitic waters with the higher concentration of the K⁺ and Mg²⁺ cations were applied for the study of bentonite stability.     

Chemical speciation of particulate uranium in seawater

Uranium shows relatively conservative behaviour in seawater because of the formation of stable carbonato complexes, whereas particulate uranium, involved in suspended particles with the particle size of more than 0.45 m, is a minor constituent. It was found that particulate uranium, with a range from 0.24 to 39 Bq·1^–1, varies spatially and temporally. Its highest concentration occurs in the tropical region of the western North Pacific during the winter of 1983, corresponding to the 1983 El Nifio event. A leaching experiment revealed that major species of particulate uranium are labile organic complexes. Mass balance considerations suggest that particulate uranium in open ocean waters correlates with the presence of particulate organic matter (POM). A high peak of particulate uranium in 1983 may indicate that POM, i.e., primary productivity, increased in the western tropical Pacific during the El Niño event.     

Chemical speciation of mercury in natural waters

Improved sensitivity of the cold-vapour atomic absorption method for mercury can be obtained by equilibrating the reduced sample with a small volume of air at 90°C. An automated system has been developed that has a detection limit of 1 ng Hg l^-1. By changing the reducing conditions three species of mercury can be differentiated and determined, inorganic mercury, arylmercury compounds such as phenylmercury(II) chloride, and alkylmercury compounds such as methylmercury(II) chloride. Speciation of mercury in natural waters is possible.     

Selenium speciation analysis at trace level in soils

This paper describes the development of an analytical methodology to determine speciation of selenium present in soils at trace level (μg kg(-1)). The methodology was based on parallel single extractions and high performance liquid chromatography hyphenated to inductively coupled plasma mass spectrometry (HPLC-ICPMS). Two complementary chromatographic separations were used to confirm Se species identity. Different extractants, selected on the basis of sequential extraction schemes, were compared. Ultrapure water, 0.1 molL(-1) phosphate buffer (KH(2)PO(4)/K(2)HPO(4)) at pH 7 and 0.1 molL(-1) sodium hydroxide extractants were finally chosen owing to their efficiency in extracting Se and compatibility with Se species stability. These extractants allow also assessing respectively water-soluble Se (i.e. the most mobile Se fraction), exchangeable Se (i.e. sorbed onto soil component surface) and Se bound to soil organic matter. This methodology gives thus information on Se mobility related to its distribution in soil with preservation of original Se speciation. Detection limits range from 3 to 29ng(Se)L(-1) and from 0.1 to 10 μg(Se)kg(-1), allowing determination of Se species concentrations in extracts from soils containing native Se at trace level. The methodology was applied to three soils with total Se concentrations between 210 and 1560 μg(Se)kg(-1).     

Sequential extraction for the speciation of some heavy metals in soils

The five step sequential extraction for speciation of copper and nickel originally designed for sediments has been applied to soil samples. The extractant solutions were: 1 mol/l ammonium acetate, 1 mol/l hydroxylammonium chloride in 25% acetic acid (1∶1), 0.1 mol/l hydrochlorid acid, 0.5 mol/l sodium hydroxide and 8 mol/l nitric acid. The residue was decomposed by HF and HNO₃. Using this procedure the metal fraction bound to the organic matter can be distinguished. The concentrations of analytes were determined in the soil extracts by FAAS and ETAAS. Accuracy was assessed by comparing the sum of the contents of copper and nickel in soil extracts with the total certified values of CRMs of soils. The overall recovery values for nickel was 84–105% and for copper 105–114%.     

Validation of the methods for heavy metal speciation in soils and sediments

The knowledge of the chemical forms of metals is used to assess their availability and uptake by plants, and in sediments the forms of metals determine their transport and mobility in the aquatic media. This information may be obtained by determining chemical forms of metals (speciation) or different phases in which the metals are bound, obtained by applying extraction schemes. The analytical methods used include different steps and all of them must be validated. We report here the recommendations to minimize the errors in this kind of analysis. For validation the use of Certified Reference Materials (CRMs) and the participation in interlaboratory exercises are highly recommended.     

Nature of the HCl-soluble sulfate in the sequential extraction for sulfur speciation in soils

Thirty soils collected from different regions of China were used to investigate the nature of HCl-soluble sulfate (HCl-S) and to evaluate the importance of HCl-S for sulfur speciation in soils. The soils were first extracted with NaH₂PO₄ solution to remove water-soluble and adsorbed sulfate, followed by extraction in 1 mol/l HCl at room temperature, minimizing the hydrolysis of organic sulfur into sulfate. Excellent linear correlations (r = 0.986) were found between the HCl-S and the carbonate contents in these soils, indicating HCl-S was mainly the carbonate-occluded inorganic sulfate in calcareous soils, averaging for 39% of total sulfur. However, the traditionally recognized major form of soil sulfate (water-soluble and adsorbed sulfate) only account for 7.5% of total sulfur. The non-calcareous soils were also found to contain some of HCl-S (6.9% of total sulfur). Large errors will occur in the determination of ester sulfur if HCl-S is not subtracted from the HI-reducible sulfur, especially in calcareous soils and soils containing little organic matter, which was the common practice in sulfur speciation studies. The reasonableness of including HCl-S in the subtraction method to determine ester sulfur was further verified by the good correlations between ester sulfur and organic carbon content in the soils Received: 21 February 1996 / Revised: 10 June 1996 / Accepted: 14 June 1996     

Chemical speciation of nanoparticles surrounding metal-on-metal hips

Spectromicroscopy of tissue surrounding failed CoCr metal-on-metal hip replacements detected corroded nanoscale debris in periprosthetic tissue in two chemical states, with concomitant mitochondrial damage. The majority of debris contained Cr(3+), with trace amounts of oxidised cobalt. A minority phase containing a core of metallic chromium and cobalt was also observed.     

Microstructures and speciation of radionuclides in natural environment studied by advanced spectroscopy and theoretical calculation

The environmental behavior of radionuclides is mainly dependent on their speciation and microstructures at solid particles.The speciation and microstructures of radionuclides at molecular level can be achieved from advanced spectroscopy techniques and theoretical calculations.In this perspective,we give a brief introduction of the advanced X-ray absorption fine structure(XAFS) technique and theoretical calculation in the analysis of the speciation and microstructures of radionuclides in the natural environment,which is crucial to evaluate the physicochemical behavior of radionuclides in the environment.     

Chemical modification of waste cooking oil for the biolubricant production through transesterification process

Concerns and restrictions around contamination and environmental pollution are developing. The production of waste cooking oil and the pollution brought on by mineral oils are two important issues. The FSSAI's new standards state that cooking oil that contains more than 25% polar compounds is inappropriate for use and should be discarded. Therefore, both issues can be resolved with the aid of chemical modifications to waste cooking oil. Waste cooking oils are an attractive alternative to mineral oils because they are biodegradable and renewable sources of lubricants. The goal of the current research work is to create an environmentally friendly lubricant through transesterification reaction. Fatty acid methyl esters (FAMEs) of WCO with various alcohols (1-Heptanol, 2-Ethyl-1-Hexanol & Neopentyl Glycol) with diverse branching were used to create bio lubricant. As a heterogeneous catalyst, zinc acetate was used to carry out the reaction. Complex esters, which have been produced, have the potential to be used as biodegradable lubricants in industrial lubricant applications. Using the GC-MS technique, the structure of the generated bio lubricant was examined. The structural modification of waste cooking oil resulted in improvement in both physicochemical and tribological properties. The created bio lubricant had improved flash and fire points as well as a superior viscosity index (>120). The generated bio lubricant possesses friction characteristics that are comparable to those of commercial mineral oil-based lubricants. According to the results of this study, waste cooking oil lubricant has a lot of potential for use as a base stock due to its favorable biodegradability and tribological performance.     

Spectroscopic study on the zinc-contaminated soils for the determination of zinc speciation

The purpose of this paper reported the zinc species in the highly contaminated soils from metallurgical area around Erh-Jen River in the southern of Taiwan. FTIR and XPS were used to investigate the zinc species in the contaminated soils. Through a FTIR analysis, appreciable of zinc bound by organic matter was found and their bonding structure consisted of antisymmetric and symmetric stretchings, Zn-HSsym and Zn-HSasym. With XPS analysis, the Angstrom scale depth scan was surveyed for investigation the zinc speciation. No signal of zinc was detected in the depth of 900A for the larger particle contaminated soils whereas the detectable signal of zinc was determined in the XPS experiment. With further regression and fitting results, the major zinc species presented in the surface of larger and fine particle contaminated soils consisted of reductive and oxidative zinc species. In the deeper depth of contaminated soils, an inverse spinel zinc ferrite was found in the case of larger particle soil. No inverse spinel zinc ferrite was detected in the case of fine particle soil and could be attributed to the relatively small particle size.