Uranium retention in a Callovo-Oxfordian clay rock formation: From laboratory-based models to in natura conditions

For the performance assessment of radioactive waste disposal, it is critical to predict the mobility of radionuclides in the geological barrier that hosts it. A key challenge consists of assessing the transferability of current knowledge on the retention properties deduced from model systems to in natura situations. The case of the redox-sensitive element uranium in the Callovo-Oxfordian clay formation (COx) is presented herein. Extensive experimental work was carried out with respect to parameters affecting uranium speciation (pH, P_CO2, [Ca] and redox potential) with illite, COx clay fraction and raw COx claystone. The "bottom-up" approach implemented, with illite and montmorillonite as reactive phases, quantitatively explains the adsorption results of U(VI) and U(IV) on COx. While retention is high for U(IV) (Rd∼10⁴ L kg^-1), it remains very low for U(VI) (Rd∼4 L kg^-1) due to the formation of soluble ternary Ca(Mg)-U(VI)-carbonate complexes. The applicability of the sorption model was then assessed by comparing predictive analyses with data characterizing the behavior of naturally-occurring U (<3 mg kg^-1). The COx clay phase is the largest reservoir of naturally-occurring U (∼65%) but only a small fraction appears to be adsorbed (∼1%). Under representative site conditions (especially with respect to reducing conditions), we have concluded that ternary U(VI) complexes control U speciation in solution while U(IV) surface species dominate U adsorption, with Rd values > 70 L kg^-1.

An integrated approach combining soil profile, records and tree ring analysis to identify the origin of environmental contamination in a former uranium mine (Rophin, France)

Uranium mining and milling activities raise environmental concerns due to the release of radioactive and other toxic elements. Their long-term management thus requires a knowledge of past events coupled with a good understanding of the geochemical mechanisms regulating the mobility of residual radionuclides. This article presents the results on the traces of anthropic activity linked to previous uranium (U) mining activities in the vicinity of the Rophin tailings storage site (Puy de Dôme, France). Several complementary approaches were developed based on a study of the site's history and records, as well as on a radiological and chemical characterization of soil cores and a dendrochronology. Gamma survey measurements of the wetland downstream of the Rophin site revealed a level of 1050 nSv.h^-1. Soil cores extracted in the wetland showed U concentrations of up to 1855 mg.kg^-1, which appears to be associated with the presence of a whitish silt loam (WSL) soil layer located below an organic topsoil layer. Records, corroborated by prior aerial photographs and analyses of ¹³⁷Cs and ¹⁴C activities, suggest the discharge of U mineral particles while the site was being operated. Moreover, lead isotope ratios indicate that contamination in the WSL layer can be discriminated by a larger contribution of radiogenic lead to total lead. The dendroanalysis correlate U emissions from Rophin with the site's history. Oak tree rings located downstream of the site contain uranium concentrations ten times higher than values measured on unaffected trees. Moreover, the highest U concentrations were recorded not only for the operating period, but more surprisingly for the recent site renovations as well. This integrated approach corroborates that U mineral particles were initially transported as mineral particles in Rophin's watershed and that a majority of the deposited uranium appears to have been trapped in the topsoil layer, with high organic matter content.

Natural organic matter contained in clay rock pore water: Direct quantification at the molecular level using electrospray ionization mass spectrometry

RATIONALE

Natural organic matter (NOM) is present in the environment and could influence the migration of heavy metals/radionuclides. The dissolved fraction of NOM (DOM) is usually quantified using total organic carbon analysis or UV-visible spectrometry. Nonetheless, analysis using pattern recognition cannot provide the full spectrum of organic molecules contained in waters, especially low-molecular-weight compounds. In the context of nuclear performance assessment studies, ground waters may contain DOM and a key aspect is to quantify different categories of NOM types in order to further evaluate the transport and fate of radionuclides in the environment.

METHODS

Thus, a method for the quantification of DOM at the molecular level was developed, based on electrospray ionization mass spectrometry (ESI-MS). This method simultaneously gives structural information on DOM and the individual concentrations of these low-molecular-weight compounds without pretreatment and/or preconcentration of the samples.

RESULTS

Several methods of quantification (internal calibration, calibrated addition of external standard, sequential tandem mass spectrometry) have been optimized and successfully applied to real natural samples. They are discussed in this paper with a focus on acidic compounds, which are the compounds that most probably could influence the migration of heavy metals and radionuclides in the clay rock pore water from the French Callovo-Oxfordian (COx) nuclear repository site.

CONCLUSIONS

Quantification of in situ dissolved NOM from the COx has been performed using ESI-MS. For the first time to our knowledge, it was possible to give a quite exhaustive and quantitative inventory of the small organic compounds present without proceeding to any chemical treatment or sample crushing and for naturally occurring concentrations.

State of Fukushima nuclear fuel debris tracked by Cs137 in cooling water

It is still difficult to assess the risk originating from the radioactivity inventory remaining in the damaged Fukushima nuclear reactors. Here we show that cooling water analyses provide a means to assess source terms for potential future releases. Until now already about 34% of the inventories of (137)Cs of three reactors has been released into water. We found that the release rate of (137)Cs has been constant for 2 years at about 1.8% of the inventory per year indicating ongoing dissolution of the fuel debris. Compared to laboratory studies on spent nuclear fuel behavior in water, (137)Cs release rates are on the higher end, caused by the strong radiation field and oxidant production by water radiolysis and by impacts of accessible grain boundaries. It is concluded that radionuclide analyses in cooling water allow tracking of the conditions of the damaged fuel and the associated risks.

Coupling of Chemical Processes in the Near Field

Coupled modelling has been performed using geochemical/transport codes and radiolysis models to describe the chemical evolution of the waste forms “high-level waste glass” and “spent nuclear fuel” together with its waste package and engineered barrier surroundings. Near field processes considered include container corrosion, hydrogen generation, mass transfer for radionuclides and other waste matrix components in corrosion products and buffer materials, geochemistry of near field solution chemistry, sorption of radionuclides on surface sites in the nano-sized pore space of near field materials and the radiolytic decomposition of pore water. The rate limiting steps in waste form dissolution and secondary phase formation mechanism and the associated radionuclide mobilisation chemistry (solubility, solid solution formation, speciation, redox stability) are strongly influenced by the near field constraints.

Modeling of the Effect of Iron Corrosion Products on Nuclear Waste Glass Performance

Experiments [1], performed in the frame of the JSS-project (joint Japanese [CRIEPI], Swiss [NAGRA], Swedish [SKB] project), demonstrated that the effect of iron corrosion products on the long-term stability of HLW-glass depends on the effective surface area of the corrosion products. The experimental results were described quantitatively by thermodynamic and kinetic modeling with the computer codes GLASSOL and PHREEQE. The model interprets the effect in terms of surface sorption of a monolayer of silica molecules from solution. Silica saturation occurs in solution only, when all surface sites are occupied. The effect of bentonite is also considered. The agreement between calculations and experiment is about as good as in the case of modeling the glass-water reaction only.

A Comparison of the Performance of Nuclear Waste Glasses by Modeling

The reprocessing of spent fuel from nuclear reactors and processing of fuels for defense purposes have generated large volumes of high-level liquid waste that need to be immobilized prior to final storage. For immobilization, the wastes must be converted to a less soluble solid, and, although other waste forms exist, glass currently appears to be the choice for the transuranic-containing portion of the reprocessed waste. Once produced, this glass will be sent in canisters to a geologic repository located some 200 to 500 m below the surface of the earth.

Weathered Basalt Glass: A Natural Analogue for the Effects of REACTION Progress on Nuclear Waste Glass Alteration

Laboratory experiments alone cannot be used to verify models for the long-term release of radionuclides from nuclear waste glasses. Basalt glasses have been proposed as an appropriate natural analogue for the long-term validation of release models [1]. Their analogous behavior has been demonstrated in laboratory experiments in which both types of glasses display similar reaction rates, alteration products and surface layer morphologies [2,3]. This paper illustrates how empirical data from natural occurrences of basalt glass can be interpreted by a model which is developed to describe the reaction progress of the corrosion of nuclear waste form borosilicate glass [4,5].

The Long-Term Corrosion and Modelling of Two Simulated Belgian Reference High-Level Waste Glasses

The corrosion behaviour in distilled water of two simulated candidate high level waste borosilicate glasses (SAN602519L3C2 and SM58LW11) his been investigated at 90°C for different SA/V condition's 10, 100, 7800 m−1). The experimental data were modelled using the PHREEQE and GLASSOL computer codes. The model is quite successful for describing the corrosion behaviour, using experimentally derived values for the forward rate, silica saturation and the final rate. GWss SAN60 is more stable than glass SM58 at SA/V values of 10 and 100 m−1, but in the long term the relative performance is inverse. Indeed, the high Al content of SAN60 induces the creation of analcime crystals after SiO2 has reached its saturation concentration in solution, which cause an enhancement of the final rate of dissolution of the glass; for SM58 on the contrary the SiO2 solution is a stable condition.

Dissolution of Basaltic Glass in Seawater : Experiments and Thermodynamic Modelling

The reaction of basalt glasses with natural waters were proposed as analog systems to the long-term alteration of nuclear waste glasses in the geosphere [1].

A General Rate Equation for Nuclear Waste Glass Corrosion

A general rate equation was developed to describe the reaction of nuclear waste glasses with aqueous solutions as a function of pH, the ratio of sample surface area to solution volume, temperature, time, glass- and solution composition. Thermodynamic and kinetic models have been combined in a new model. Glass network dissolution, pH variation, precipitation of stable or metastable solid reaction products, silica saturation at the glass and solution interface (reaction zone) and a residual affinity for the long term reaction under near saturation conditions have been addressed. The model has been successfully used to interpret a great number of experimental data reported in literature.

Corrosion Behaviour of British Magnox Waste Glass in Pure Water

The corrosion behaviour of Magnox Waste (MW) glass in deionized water has been investigated under the aegis of the Japanese-Swedish-Swiss (JSS) project. The studies carried out at PSI and BNFL included static leaching and corrosion layer characterization. The results were used by HMI to derive the modelling parameters for the MW glass with the PHREEQE/GLASSOL codes. The silica concentration was found to strongly influence the corrosion rate of the glass. The MW glass selectively retains Cs due to the formation of a Cs-Mg-Al-Si-O-rich layer on its surface.

Chemistry of Glass Corrosion in High Saline Brines

Experimental data were obtained for conventional pH values corrected for liquid junction, amorphous silica solubility and glass corrosion in concentrated salt brines. The data were interpreted with a geochemical model. The brine chemistry was described with the Pitzer formalism [1] using a data base which allows calculation of brine compositions in equilibrium with salt minerals at temperatures up to 200°C.

In MgCl2 dominated brines Mg silicates form and due to the consumption of Mg the pH decreases with proceeding reaction. A constant pH (about 4) and composition of alteration products is achieved, when the alkali release from the glass balances the Mg consumption. The low pH results in high release of rare earth elements REE and U from the glass. In the NaCl dominated brine MgCl2 becomes exhausted by Mg silicate formation. As long as there is still Mg left in solution the pH decreases. After exhaustion of Mg the pH rises with the alkali release from the glass and analcime is formed.

The Role of Metal Ion Solubility in Leaching of Nuclear Waste Glasses

The leachability of solid nuclear waste forms has been studied by many investigators to evaluate the short-term kinetics of elemental release or to determine the effects of leachant composition or other system parameters. Some general observations from these studies have included: incongruent leaching; formation of reaction layers that contain rare-earth, alkaline-earth, or transition metal elements; and apparent saturation of some elements in solution while others continue to be leached. Before these observations can be used to predict long-term performance of waste glasses under repository conditions, the mechanisms controlling the release of elements from the solid must be understood.

Source Trends for Performance Assessment of HLW Glass and Spent Fuel as Waste Forms

with respect to the state of validation for source term development. Consequences of the various mechanism on mass half lives of the waste forms are calculated with analytical equations. For glass the largest uncertainty stems from the yet unclear dissolution mechanism under silica saturated conditions. Source terms based on silica solubility coupled to Si-mass transfer are probably neither conservative nor realistic. For spent fuel the largest uncertainty is in the extrapolation of radiolytic fuel oxidation for long periods of time. Considering the uncertainties involved, reaction rates cannot yet be extrapolated reliably to values much lower than the lowest reliable experimental measurements.

Effect of Alpha Radiolysis on UO2Dissolution under Reducing Conditions

Effects of water radiolysis on the dissolution rate of UO2were studied by irradiating UO2colloids with an alpha particle beam of a cyclotron. The solution was kept under reducing conditions by applying a current of -10 or -50 nA and an ultrahigh purity argon bubbling. The solution pH was fixed at 6 during experiment. The particle flux was 1.1×1011α.cm−2.s−1entering in solution with an energy of 5 – 6 MeV. Despite initial reducing conditions water radiolysis increased the dissolution rate of uranium dioxide due to reaction with oxidizing radiolytic species such as H2O2, O2, OH•, HO2•, ClO3−. The monitoring of the redox potential showed that the solutions became rapidly oxidizing. The dissolution rate values were between 0.01 and 26 mg·m−2·d−1depending on the ratio of the irradiated UO2mass to the solution volume. This dependency is caused by hydrogen peroxide consumption at the UO2surface. The rate of hydrogen peroxide consumption by reaction with colloids corresponds to an equivalent rate of UO2oxidation/dissolution between 2 and 60 mg.m−2.d−1indicating that only a small fraction of produced H2O2is consumed by the dissolution reaction.

Minimization of absorption contrast for accurate amorphous phase quantification: application to ZrO2nanoparticles

Monoclinic and tetragonal zirconia samples were characterized by X-ray diffraction, pycnometry, thermogravimetric analysis (TGA), Fourier transform (FT) IR and mass (MS) spectroscopies, and scanning and transmission electron (TEM) microscopies. The results show, for the particular case of a tetragonal zirconia sample, an X-ray-undetected subproduct identified as an amorphous organic phase by FTIR–ATR (attenuated total reflection) and TGA–MS. The observations by TEM allowed this amorphous phase to be localized on the surface as a shell coating the nanoparticles. Moreover, this amorphous phase was quantified by Rietveld refinementviathe addition of an internal silicon standard. Because zirconia and silicon have different linear absorption coefficients, the microabsorption effect was minimized by using small particle sizes. The amorphous phase was calculated to constitute 11.4 (30)% of the initial mass before Brindley correction and 10.6 (30)% of the initial mass after Brindley correction. The closeness of these values shows that the contribution of the Brindley correction can be neglected if precautions are taken on the microabsorption effect. This work has also highlighted the importance of thoroughly characterizing commercial products, which are not necessarily pure. Indeed, the presence of impurities could become a non-negligible parameter for physical and chemical properties studies related to commercial materials.

Speciation of technetium(IV) chloride under gamma irradiation

Speciation of Tc in aqueous solution is a complex phenomenon because several parameters intervene simultaneously. We show under gamma radiations, it is completely modified. At pH 8.5 TcO2is oxidized to Tc(VII) with a yield of 1.38×10−7mol J−1. At pH 1.5, it was demonstrated that Tc is present as hydroxylated species TcnOy(4n-2y)+(L. Vichot, M. Fattahi, M. Musikas: Radiochim. Acta 91, 263 (2003)). Its oxidation leads also to Tc(VII) with an experimental yield of 1.45×10−7mol J−1. In more acidic solutions, results are consistent with hydrolysis and oxidation of Tc(IV) to Tc(V). As for colloidal solutions of Tc(IV) or TcO2, they give Tc(VII) whereas solutions of TcCl62-at pH 0.5 and 1.5 do not lead directly to Tc(VII). Reduced states of Tc are very sensitive to radiation. Hydrolysis as well as polymerisation of Tc are accelerated. Furthermore the radiolytic processes are pH dependent.

Modeling the complexation properties of mineral-bound organic polyelectrolyte: An attempt at comprehension using the model system alumina/polyacrylic acid/M (M=Eu, Cm, Gd)

This paper contributes to the comprehension of kinetic and equilibrium phenomena governing metal ion sorption on organic-matter-coated mineral particles. Sorption and desorption experiments were carried out with Eu ion and polyacrylic acid (PAA)-coated alumina colloids at pH 5 in 0.1 M NaClO(4) as a function of the metal ion loading. Under these conditions, M interaction with the solid is governed by sorbed PAA (PAA(ads)). The results were compared with spectroscopic data obtained by time-resolved laser-induced fluorescence spectroscopy (TRLFS) with Cm and Gd. The interaction between M and PAA(ads) was characterized by a kinetically controlled process: after rapid metal adsorption within less than 1 min, the speciation of complexed M changed at the particle surface till an equilibrium was reached after about 4 days. At equilibrium, one part of complexed M was shown to be not exchangeable. This process was strongly dependent on the ligand-to-metal ratio. Two models were tested to explain the data. In model 1, the kinetically controlled process was described through successive kinetically controlled reactions that follow the rapid metal ion adsorption. In model 2, the organic layer was considered as a porous medium: the kinetic process was explained by the diffusion of M from the surface into the organic layer. Model 1 allowed a very good description of equilibrium and kinetic experimental data. Model 2 could describe the data at equilibrium but could not explain the kinetic data accurately. In spite of this disagreement, model 2 appeared more realistic considering the results of the TRLFS measurements.

Study of the interaction of Ni2+ and Cs+ on MX-80 bentonite; effect of compaction using the "capillary method"

The goal of the paper is to assess the applicability of sorption models to describe the retention of contaminants on clay materials, both in dispersed and compacted states. A batch method is used to characterize the sorption equilibria between Cs, Ni, and MX-80 bentonite for solid-to-liquid ratios varying from 0.5 to 4200 kg/m3. For compacted bentonite (dry density of 1100 kg/m3), a new method is presented where the material compaction is performed in PEEK capillaries. Sorption edges and isotherms were measured in the presence of a synthetic groundwater. A model considering cation exchange reactions with interlayer cations and surface complexation reactions with edge sites was used for the dispersed state. Montmorillonite was shown to be the dominant interacting phase in MX-80 bentonite. The applicability of the model to compacted bentonite was tested. The results indicate that under conditions where the cation exchange mechanism is dominant, there is no difference between the dispersed and compacted states. For the degree of compaction studied, all exchange sites are available for sorption. For Ni, when surface complexation is the dominant sorption mechanism, a decrease of the Kd values by a factor of about 3 was observed (pH 7-8, trace concentrations). This could be explained quantitatively by a diminution of the conditional interaction constant between Ni and the edge surface site in the compacted state. One consequence of this decrease is that the contribution of the organic matter content of MX-80 bentonite to the total sorption becomes significant.

Comparison of complexed species of Eu in alumina-bound and free polyacrylic acid: A spectroscopic study

The speciation of Eu complexed with polyacrylic acid (PAA) and alumina-bound PAA (PAA(ads)) was studied at pH 5 in 0.1 M NaClO(4). Structural parameters were obtained from (7)F(0) -->(5)D(0) excitation spectra measured by laser-induced fluorescence spectroscopy as well as from Eu L(III)-edge extended X-ray absorption fine structure (EXAFS) spectra. The coordination mode was also investigated by infrared spectroscopy. To elucidate the nature of the complexed species, Eu-acetate complexes were used as references. The spectroscopic techniques show that two carboxylate groups with 2-3 (EuPAA) and 4-5 (EuPAA(ads)) water molecules are coordinated to Eu in the first coordination sphere. For EuPAA(ads), the coordination between carboxylate groups and Eu appears to be bidendate. A similar coordination is probable for EuPAA but the EXAFS data indicate a slightly distorted coordination. The results show that the degree of freedom of carboxylate groups is not the same for free or adsorbed PAA. For PAA, the degree of freedom is constrained by the flexibility of the methylene chain. When PAA is adsorbed on alumina, the polymer chains cannot any more be treated as independent chains. One may rather assume formation of aggregates that form an organic layer at the mineral surface presenting a complex arrangement of carboxylate groups.

Study of the interaction between europium (III) and Bacillus subtilis: fixation sites, biosorption modeling and reversibility

In order to elucidate the underlying mechanisms involved in the biosorption of metal ions, potentiometric titrations, complexation studies, and time-resolved laser-induced fluorescence spectroscopy (TRLFS) measurements were used to characterize the interaction between Eu(III) and Bacillus subtilis. The reversibility of the interaction between Eu(III) and Bacillus subtilis was studied by a cation-exchange technique using the Chelex resin. For complexation studies in the presence of 0.15 mol/l of NaCl, the metal ion, the biomass, concentrations and the pH were varied. The adsorption data were quantified by a surface complexation model without electrostatic term. The data on the Eu(III)/B.subtilis system at pH 5 were satisfactorily described by one site at which Eu(III) was bound through one carboxylic function of the bacteria. With increasing pH, another site should be considered, involving a phosphate-bound environment. This was partially confirmed by time-resolved laser-induced fluorescence spectroscopy. In addition to this, it was evidenced that the site availability was dependent on the nature of the cation, i.e., a proton or Eu(III). Finally, it was shown that, at pH 5, the Eu(III)/Bacillus subtilis equilibrium was reversible.

Microbial reduction of 99Tc in organic matter-rich soils

For safety assessment purposes, it is necessary to study the mobility of long-lived radionuclides in the geosphere and the biosphere. Within this framework, we studied the behaviour of (99)Tc in biologically active organic matter-rich soils. To simulate the redox conditions in soils, we stimulated the growth of aerobic and facultative denitrifying and anaerobic sulphate-reducing bacteria (SRB). In the presence of either a pure culture of denitrifiers (Pseudomonas aeruginosa) or a consortium of soil denitrifiers, the solubility of TcO(4)(-) was not affected. The nonsorption of TcO(4)(-) onto bacteria was confirmed in biosorption experiments with washed cells of P. aeruginosa regardless of the pH. At the end of denitrification with indigenous denitrifiers in soil/water batch experiments, the redox potential (E(H)) dropped and this was accompanied by an increase of Fe concentration in solution as a result of reduction of less soluble Fe(III) to Fe(II) from the soil particles. It is suggested that this is due to the growth of a consortium of anaerobic bacteria (e.g., Fe-reducing bacteria). The drop in E(H) was accompanied by a strong decrease in Tc concentration as a result of Tc(VII) reduction to Tc(IV). Thermodynamic calculations suggested the precipitation of TcO(2). The stimulation of the growth of indigenous sulphate-reducing bacteria in soil/water systems led to even lower E(H) with final Tc concentration of 10(-8) M. Experiments with glass columns filled with soil reproduced the results obtained with batch cultures. Sequential chemical extraction of precipitated Tc in soils showed that this radionuclide is strongly immobilised within soil particles under anaerobic conditions. More than 90% of Tc is released together with organic matter (60-66%) and Fe-oxyhydroxides (23-31%). The present work shows that ubiquitous indigenous anaerobic bacteria in soils play a major role in Tc immobilisation. In addition, organic matter plays a key role in the stability of the reduced Tc.

Interaction of Eu(III)/Cm(III) with alumina-bound poly(acrylic acid): sorption, desorption, and spectroscopic studies

This paper contributes to the comprehension of kinetic and equilibrium phenomena governing trace metal ion sorption on organic matter coated mineral particles. Sorption and desorption experiments were carried out with trivalent metal ions M(III) (M = Eu, Cm) and poly(acrylic acid) (PAA)-coated alumina colloids at pH 5 in 0.1 M NaClO4. Under these conditions, M(III) interaction with the solid is governed by sorbed PAA. The results were compared with spectroscopic data obtained by time-resolved laser-induced fluorescence spectroscopy (TRLFS). Within less than 30 s, a state of local equilibrium is reached between M(III) and adsorbed poly(acrylic acid). M(II) bound to the organic-mineral surface and to dissolved PAA keeps five water molecules in its first hydration sphere. Interaction of M(III) with alumina-bound PAA appears to be strongerthan with dissolved PAA. With increasing contact time, a change of the metal ion speciation occurs at the organic-mineral surface. This change is explained quantitatively by kinetically controlled reactions, which succeed a rapid local equilibrium. The experimental findings suggest, in agreement with model calculations, that a part of the initially sorbed M(III) is slowly converted to a kinetically stabilized species, thereby losing water molecules from the first coordination sphere as indicated by TRLFS. This species might be assigned as a ternary Al2O3-M(III)-PAA complex. The second part of the initially bound M(II) appears to experience as well kinetically controlled reactions, however, without showing changes in the first coordination sphere. We assume that the kinetic stabilization is the consequence of rearrangement processes of the PAA at the alumina surface.

Transfer of Eu (III) associated with polymaleic acid to Bacillus subtilis

The aim of this study is to contribute to the understanding of the distribution of Eu(III) between dissolved organic matter and microorganisms, and to investigate the effect of competitive ions such as Ca(+2) on adsorption properties. Polymaleic acid (PMA), is used as synthetic organic matter, having similar properties as natural fulvic acid, and Bacillus subtilis is chosen as microorganism. A double labeling method was used: [14C]MPA and 152Eu to quantify the behavior of the various components. Preliminary experiments showed that the adsorption of polymaleic acid onto Bacillus subtilis was negligible at pH=5 in 0.15mol/l of NaCl. In the absence of Ca(+2), the transfer of Eu(III) from PMA to B. subtilis could be described by a simple empirical model based on data obtained from sorption isotherms on the reference systems Eu(III)/PMA and Eu(III)/B. subtilis. In the presence of Ca(+2), the transfer was increased. The hypothesis that Ca(+2) ions acted as a bridging agent between PMA and the bacteria was proposed.

Complexation studies of Eu(III) with alumina-bound polymaleic acid: effect of organic polymer loading and metal ion concentration

To contribute to the comprehension of the metal ion sorption properties in mixed mineral-organic matter systems, interaction studies between Eu(III) and polymaleic acid (PMA)-coated alumina colloids were carried out at pH 5 in 0.1 M NaClO4. The studied parameters were the metal ion concentration (1 x 10(-10) to 1 x 10(-4) M) and PMA loading on alumina (gamma = 10-70 mg/g). The data were described by a surface complexation model. The constant capacitance model was used to account for electrostatic interactions. The results showed thattwo sites were necessary to explain the sorption data. At high Eu loading, Eu is surrounded by one carboxylate group and one aluminol group. The existence of this ternary surface site was in agreement with time-resolved laser-induced fluorescence spectroscopy measurements. At low metal ion concentrations, a surface site corresponding to a 1:1 Eu/COO-stoichiometry was deduced from modeling. Spectroscopic data did not corroborate the existence of this latter site. This discrepancy was explained by postadsorption kinetic phenomenon: a migration of the metal ion within the adsorbed organic layer.