Sorption and desorption of Eu and Yb on alumina: mechanisms and effect of fulvic acid

Sorption of Cs+ and Eu3+ ions onto sedimentary rock in the presence of gamma-irradiated humic acid

The influence of humic acid (HA) and its radiological degradation on the sorption of Cs⁺ and Eu³⁺ by sedimentary rock (obtained from the Horonobe Underground Research Laboratory in Japan) was investigated to understand the sorption process of metal ions and humic substances. Aldrich HA solution was gamma-irradiated assuming a strong radiation from a highly radioactive waste to be disposed of in deep geological formations. Batch sorption experiments were performed to evaluate the effect of gamma-irradiated HA on the sorption of Cs⁺ and Eu³⁺ ions. The addition of non-irradiated HA weakened the Eu sorption because of the lower sorption of the negatively charged Eu-HA complexes compared with free Eu ions. The sorption of Cs ions was barely affected by the presence of HA and its gamma irradiation. The concentration ratio of metal complexed and non-complexed species in the solid and liquid phases was evaluated by sequential filtration and chemical equilibrium calculations. The ratios were low in both phases for Cs and supported the minimal contribution of HA to Cs sorption. However, the concentration ratio for Eu³⁺ in the liquid phase was high, indicating that the complexing ability of HA to Eu³⁺ was higher than that of HA to Cs⁺.

Conditions Affecting the Release of Heavy and Rare Earth Metals from the Mine Tailings Kola Subarctic

In the Kola Subarctic, a mining industry has developed, which is a source of environmental pollution with heavy metals. The objects of study were the tailings of three large mining enterprises in the region: apatite-nepheline, complex and loparite ores. The geotechnical characteristics were studied, and the granulometric composition of the samples was established. The main minerals that make up the material of ore dressing tailings have been determined. Using inductively coupled plasma mass spectrometry, the content of trace elements, in particular heavy metals and rare earth elements, has been established. The enrichment factor, the geoaccumulation indexes, the potential ecological risk index factor and the potential environmental hazard index have been calculated. Priority pollutants characteristics for specific objects have been identified. It is noted that the finely dispersed material of the tailings of loparite and complex ores is 1.5–3 times enriched in heavy and rare earth metals in comparison with the total material of the tailings. In laboratory conditions, experiments were carried out to simulate the process of interaction of dust particles with soil solutions containing different amounts of dissolved organic matter and at average seasonal temperatures. It was found that a decrease in the pH of the solution and an increase in the amount of organic carbon and temperature lead to the mobilization of heavy and rare earth metals from the tailings.

Delineating the influence of picolinic acid on Eu(iii) sorption by γ-alumina

The present study aims at understanding the sorption mechanism of Eu(iii) by γ-alumina in the presence of picolinic acid (PA), a decontaminating agent used in the nuclear industry, through batch sorption studies, spectroscopy and surface complexation modeling. PA is weakly sorbed by γ-alumina, with the sorption increasing with pH up to 4.5 and decreasing with further increase in pH. Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR) measurements indicate that PA forms an inner sphere surface complex on γ-alumina. The presence of PA does not affect Eu(iii) sorption by γ-alumina at low [Eu(iii)], while it drastically reduces Eu(iii) sorption at high [Eu(iii)]. Similar Eu(iii) sorption profiles with different addition sequences of Eu(iii) and PA suggest identical Eu(iii) surface species for Eu(iii) sorption on γ-alumina in the presence of PA which has been validated by time resolved fluorescence spectroscopy (TRFS). TRFS measurements of Eu(iii) sorbed on γ-alumina in the absence (binary systems) and presence of PA (ternary systems) exhibited two components 1 & 2. The lifetime value of component 1 in ternary systems is enhanced compared to that in binary systems signifying the formation of new surface species containing Eu(iii), PA and the γ-alumina surface whereas the similarity of component 2 in both the binary and ternary systems reveals an almost identical coordination environment of Eu(iii) in the two types of system. Using the spectroscopic information obtained from TRFS, Eu(iii) sorption, at high [Eu(iii)], in ternary systems has been successfully modeled by considering Eu(iii) bridged PA surface species at both low and high affinity sites of γ-alumina. At low [Eu(iii)] both PA and Eu(iii) bridged ternary surface complexes only at high affinity sites of γ-alumina could describe the Eu(iii) sorption adequately.

Rare earth elements (REY) sorption on soils of contrasting mineralogy and texture

Rare earth elements (REY) are the lanthanide elements (Z = 57-71), which have an ever-growing occurrence in present-day industries, agriculture, and modern life. Consequently, environmental concentrations are expected to increase accordingly as a result of intensified utilization. Soils are an important sink for REY, yet little research has been conducted concerning activity, inputs, and lability in soil systems. This study evaluated the REY (lanthanides + yttrium) sorption and partition coefficients (K_d) in two broadly representative natural soils (A horizon), with contrasting mineralogy and organic character, formed under distinct environmental conditions: an Oxisol from Brazil and a Mollisol from the USA. Batch reactions of soils suspended in a background electrolyte solution of 5 μmoles kg^-1 of Ca(NO₃)₂ at 1:100 solid to solution were reacted with 80 μmoles kg^-1 REY added individually and in multi-REY competitive systems to evaluated adsorption after 3 h and 72 h over a wide pH range (from ca. 2 to 8). Results showed sorption was similar for all REY within each soil type when examined at the natural measured soil pH; Mollisol pH 6.85, Oxisol pH 4.35. However, REY sorption (by K_d) was nearly two-fold greater in the Mollisol compared to the Oxisol for the single REY experiments. Multi-REY competitive sorption reactions showed a decrease in K_d for both soils at 3 and 72 h, and to a greater extent for the Mollisol, indicating soil type had a strong effect on the sorption affinity of each REY. It was also observed that REY sorption increased from low to high pH (pH 2-8) in the Oxisol, and increased with pH from 2 up to the point zero charge (PZC) in the Mollisol, then stabilized. The varying REY K_d values from these two distinct and abundant soils, with and without REY competition, and over a range of pH are explained in terms of soil mineralogy (i.e., 2:1 clays in the Mollisol; oxides in the Oxisol) and organic matter content. Our findings show that soil characteristic controls sorption, precipitation, and cation exchange capacity, which are the key mechanisms for predicting REY fate and transport in the environment.

Dependence of samarium-soil interaction on samarium concentration: Implications for environmental risk assessment

The sorption and desorption behaviour of samarium (Sm), an emerging contaminant, was examined in soil samples at varying Sm concentrations. The obtained sorption and desorption parameters revealed that soil possessed a high Sm retention capacity (sorption was higher than 99% and desorption lower than 2%) at low Sm concentrations, whereas at high Sm concentrations, the sorption-desorption behaviour varied among the soil samples tested. The fractionation of the Sm sorbed in soils, obtained by sequential extractions, allowed to suggest the soil properties (pH and organic matter solubility) and phases (organic matter, carbonates and clay minerals) governing the Sm-soil interaction. The sorption models constructed in the present work along with the sorption behaviour of Sm explained in terms of soil main characteristics will allow properly assessing the Sm-soil interaction depending on the contamination scenario under study. Moreover, the sorption and desorption K_d values of radiosamarium in soils were strongly correlated with those of stable Sm at low concentrations (r = 0.98); indicating that the mobility of Sm radioisotopes and, thus, the risk of radioactive Sm contamination can be predicted using data from low concentrations of stable Sm.

Sequestration and speciation of Eu(iii) on gamma alumina: role of temperature and contact order

The speciation, migration and transport of radionuclides in the environment are significantly influenced by their interactions with the natural minerals and humic substances therein. In view of this, the effect of temperature and contact order on the sorption behaviors of trivalent Eu(iii) in the γ-Al2O3/Eu(iii) and γ-Al2O3/HA/Eu(iii) systems was studied using batch experiments and the extended X-ray absorption fine structure spectroscopy (EXAFS) technique. The endothermic sorption behavior of Eu(iii) in the γ-Al2O3/Eu(iii) systems was induced by the hydrolysis reaction of Eu(iii) in solution and the complexation of Eu(iii) with the γ-Al2O3 surface sites. The endothermic sorption of Eu(iii) in the γ-Al2O3/HA/Eu(iii) systems was attributed to the endothermic binding of HA on γ-Al2O3 and the endothermic complexation between Eu(iii) and HA. EXAFS analysis suggested the formation of type B ternary complexes and their thermodynamic stability improves with rising temperature. The different sorption percentages under various contact orders were closely related to the binding mode of Eu(iii) on the exposed γ-Al2O3 surfaces or the γ-Al2O3/HA colloids. The findings obtained herein are important to evaluate the security of the radioactive waste repository and predict the fate of trivalent actinides (e.g., Am(iii), Cm(iii), Pu(iii), etc.) near the geological repository.

Speciation of Am(III)/Eu(III) sorbed on γ-alumina: effect of metal ion concentration

The present paper describes the speciation of Am(III)/Eu(III) sorbed on γ-alumina, and its evolution with changing metal ion concentration, studied using batch sorption experiment, time resolved fluorescence spectroscopy (TRFS), extended X-ray absorption fine structure (EXAFS) and surface Complexation modeling (SCM). Though numerous studies exist in the literature on the speciation of trivalent actinides and lanthanides on alumina surface, the mechanism of sorption at high metal ion concentrations is not yet fully understood. Batch sorption experiments of Am(III) on γ-alumina under varying condition of pH (3–10), ionic strength (0.005–0.1 M NaClO4) and metal ion concentration (10−7–10−4 M) were performed. Higher metal ion concentration was achieved by the addition of Eu(III) considering it as an analogue of Am(III). Time resolved fluorescence spectroscopy (TRFS) study of Eu(III) sorbed on γ-alumina at the metal ion concentration of 5.0 × 10−5 M was carried out over pH 4 to 7. TRFS showed the presence of two surface species, with distinctly different fluorescence decay life times. The shorter lifetime value and its changing pattern with pH indicate the surface species corresponding to this component to be monodentate species >AlOAm2+ and its hydrolyzed forms. The sorbed Eu3+ species corresponding to the longer lifetime value has 2–3 water molecules in its first coordination sphere and is multidentate in its binding on alumina surface. Extended X-ray absorption fine structure (EXAFS) measurement of Eu:γ-Al2O3 sorption systems at pH 6.18 and 7.15 corroborate the existence of two surface complexes. Further it suggests the edge sharing bidentate binding of Eu on AlO6 octahedra as the co-ordination mode of the higher lifetime component. Surface Complexation Modeling (SCM) of Am(III)/Eu(III) sorption onto γ-alumina at pH ≤ 7 has been carried out using these two surface species. 2-pK surface complexation modeling coupled with constant capacitance model for surface charge, revealed monodentate surface speciation as the predominant species at 10−7–10−6 M, while at 10−5 M, above pH 5.5, bidentate surface species starts to compete with monodentate speciation, and becomes the predominant surface species of Am(III)/Eu(III) on alumina surface at 10−4 M.

The influence of temperature and small organic ligands on the sorption of Eu(III) on Opalinus Clay

The influence of temperature up to 50 ºC and small organic ligands (citrate, tartrate) on the sorption of Eu(III) on the natural clay rock Opalinus Clay (OPA) under aerobic (p CO2 = 10−3.5 atm) synthetic OPA pore water conditions (pH 7.6, I = 0.4 mol L−1) was investigated. Batch sorption experiments and time-resolved laser-induced fluorescence spectroscopy (TRLFS) were used to study these influencing factors on the Eu(III) sorption.

Sorption isotherms and distribution coefficients R d (15 ºC: log R d = 4.50 ± 0.05...50 ºC: log R d = 5.54 ± 0.06) at 2 × 10−9 mol L−1 Eu(III) as a function of the solid-to-liquid ratio (up to 3 g L−1) and temperature were determined. A significant temperature dependency of the Eu(III) sorption was observed. With rising temperature the Eu(III) sorption increases. The surface reaction is endothermic (Δ H sorb ∼ 50 kJ mol−1). Using TRLFS, a surface species with a luminescence emission lifetime of 201 ± 9 μs was identified.

In the presence of tartrate or citrate the Eu(III) sorption decreases with increasing ligand concentration due to a complex formation of Eu(III) in solution, with citrate having a more pronounced influence on the sorption than tartrate. With the batch sorption experiments it can be shown that at a citrate concentration larger than 10−5 mol L−1 and at a tartrate concentration larger than 10−4 mol L−1 an increasing Eu(III) desorption occurs. This result is supported by TRLFS measurements, which show the correlation between the complexation of Eu(III) by citrate or tartrate in solution and the Eu(III) desorption process. Possible Eu(III) citrate or Eu(III) tartrate surface species on OPA could not be detected using TRLFS.

Sorption of curium by silica colloids: effect of humic acid

Sorption of curium by silica colloids has been studied as a function of pH and ionic strength using (244)Cm as a tracer. The sorption was found to increase with increasing pH and reach a saturation value of ∼95% at pH beyond 5.3. The effect of humic acid on the sorption of (244)Cm onto silica was studied by changing the order of addition of the metal ion and humic acid. In general, in the presence of humic acid (2 mg/L), the sorption increased at lower pH (<5) while it decreased in the pH range 6.5-8 and above pH 8, the sorption was found to increase again. As curium forms strong complex with humic acid, its presence results in the enhancement of curium sorption at lower pH. At higher pH the humic acid present in the solution competes with the surface sites for curium thus decreasing the sorption. The decrease in the Cm sorption in presence of humic acid was found to be less when humic acid was added after the addition of curium. Linear additive model qualitatively reproduced the profile of the Cm(III) sorption by silica in presence of humic acid at least in the lower pH region, however it failed to yield quantitative agreement with the experimental results. The results of the present study evidenced the incorporation of Cm into the silica matrix.

Effect of humic acid on the sorption of Cm(III) ontoγ-Al2O3studied by the time-resolved laser fluorescence spectroscopy

Sorption of Cm(III) ontoγ-alumina coated with humic acid (HA) is studied by the Time Resolved Laser Fluorescence Spectroscopy (TRLFS). The experiments are performed at 0.1 M NaClO4, 0.44 g/Lγ-Al2O3, 10 mg/L HA and at a metal ion concentration of 2×10-7mol/L. At the investigated pH range (4 to 10) HA is completely sorbed to γ-Al2O3. The excitation spectrum of Cm(III) bound to HA/γ-Al2O3in the wavelength range 370-400 nm exhibits broad flat bands very different from those obtained for the Cm(III) aquo ion and the Cm(III)-γ-Al2O3surface complex, respectively. The spectrum, lacking distinctive structure due to intramolecular energy transfer processes, points to the predominant binding of the Cm(III) to surface-bound HA. TRLFS experiments performed at two different excitation wavelengths (λex=355 and 396.6 nm) allow for a differentiation of humic-bound and non-humic-bound Cm(III). Differences in fluorescence spectra obtained at the different excitation wavelengths are found at pH<6.9. They are due to the presence of the non-complexed Cm(III) aquo ion which is not detected in the indirect excitation mode (λex=355 nm). At pH≥7, the fluorescence spectra obtained by indirect and direct excitation become congruent and again point to the existence of only humic-bound Cm(III) species. Comparison of peak maxima and fluorescence lifetimes for Cm(III)-HA and Cm(III)-HA/γ-Al2O3, however, reveal differences. The results clearly indicate a contribution of theγ-Al2O3surface to the Cm(III) binding and, thus, suggest the formation of ternary complexes such as >Al-O-Cm(III)(HA).

Sorption of Eu(III) on humic acid or fulvic acid bound to hydrous alumina studied by SEM-EDS, XPS, TRLFS, and batch techniques

To identify the effect of humic acid (HA) and fulvic acid (FA) on the sorption mechanism of Eu(III) on organic--inorganic colloids in the environment at a molecular level, surface adsorbed/ complexed Eu(III) on hydrous alumina, HA-, and FA-hydrous alumina hybrids were characterized by using X-ray photoelectron spectroscopy (XPS) and time-resolved laser fluorescence spectroscopy (TRLFS). The experiments were performed in 0.1 mol/L KNO3 or 0.1 mol/L NaClO4 under ambient conditions. The pH values were varied between 2 and 11 at a fixed Eu(III) concentration of 6.0 x 10(-7) mol/L and 4.3 x 10(-5) mol/L. The different Eu(III)/FA(HA)/hydrous alumina complexes were characterized by their fluorescence emission spectra ((5D0-F1)/ (5D0 --> 7F2)) and binding energy of Eu(III). Inner-sphere surface complexation may contribute mainly to Eu(III) sorption on hydrous alumina, and a ternary surface complex is formed at the HA/ FA-hydrous alumina hybrid surfaces. The sorption and species of Eu(III) in ternary Eu-HA/FA-hydrous alumina systems are not dominated by either HA/FA or hydrous alumina, but are dominated by both HA/FA and hydrous alumina. The results are important for understanding the sorption mechanisms and the nature of surface adsorbed Eu(III) species and trivalent chemical homologues of Eu(III) in the natural environment.

Effect of soil humic and fulvic acids, pH and ionic strength on Th(IV) sorption to TiO2 nanoparticles

Thorium is considered as a chemical analog of other tetravalent actinides. Herein, the sorption of Th(IV) on TiO(2) in the presence or absence of soil fulvic acid (FA)/humic acid (HA) as a function of pH, ionic strength and FA/HA concentration has been studied by a batch method. The morphology was characterized by scanning electron microscopy (SEM). The results indicate that sorption of Th(IV) on TiO(2) increases from 0% to approximately 94% at pH 1 approximately 4, and then maintains level with increasing pH values. Both FA and HA have a positive effect on Th(IV) sorption at low pH values and the contribution of FA on Th(IV) sorption is rather higher than that of HA at pH<4. The sorption is weakly dependent on the concentration of KNO(3) in solution, but the cations K(+), Na(+) and Li(+) influence Th(IV) sorption more obviously. The batch results indicate that the inner sphere complex formation is formed at bare surfaces or FA/HA-bound TiO(2) particle surfaces. Results of SEM analysis show that the particle sizes of TiO(2), Th-TiO(2) and Th-HA-TiO(2) colloids are quite different. Surface complexation may be considered as the main sorption mechanism.

Sorption of Th (IV) to silica as a function of pH, humic/fulvic acid, ionic strength, electrolyte type

The removal behavior of thorium (Th(IV)) has been investigated in multicomponent systems containing silica (SiO2) as the model of inorganic particles because of its widespread presence in the earth's crust and soil humic acid (HA)/fulvic acid (FA) by batch experiments. The influence of pH from 2 to 12, ionic strength from 0.02 to 0.2 M KNO3, soil HA/FA concentration from 8.3 to 22.5 mg/L, and foreign cations (Li+, Na+, K+) and anions (NO3(-), Cl-) on the sorption of Th(IV) onto SiO2 was also tested. The sorption isotherms of Th(IV) at approximately constant pH (3.50+/-0.02) were determined and analyzed regressively with three kinds of sorption isotherm models, i.e., linear, Langmuir, and Freundlich models. The results demonstrated that the sorption of Th(IV) onto SiO2 increased steeply with increasing pH from 2 to 4. Generally, humic substances (HSs) were shown to enhance Th(IV) sorption at low pH, but to reduce Th(IV) sorption at intermediate and high pH. It was a hypothesis that the significantly positive influence of HA/FA at pH from 2 to 4 on the sorption of Th(IV) onto SiO2 was attributed to strong surface binding of HA/FA on SiO2 and subsequently the formation of ternary surface complexes such as [triple bond]MO-O-HA-Th or [triple bond]MO-O-FA-Th. The results also demonstrated that the sorption was strongly dependent on the concentration of HA/FA, and independent of ionic strength and foreign ions under our experimental conditions.

Effect of pH, ionic strength and fulvic acid on the sorption and desorption of cobalt to bentonite

Humic substances and bentonite have attracted great interest in radioactive waste management. Here the sorption of cobalt on bentonite in the presence and absence of fulvic acid (FA) under ambient conditions was studied. The effects of pH, ionic strength, FA and solution concentrations on cobalt sorption to bentonite were also investigated using batch techniques. The results indicate that the sorption of cobalt is strongly dependent on pH and is independent of ionic strength under our experimental conditions. Surface complexation is considered the main mechanism of cobalt sorption to bentonite. In the presence of FA, little effect of FA on cobalt sorption was found at pH<6; a positive effect of FA on cobalt sorption was found for pH 6-8; and a negative effect of FA on cobalt sorption was found at pH>8. The addition sequences of FA/Co(2+) to the bentonite suspension on the sorption of cobalt to FA-coated bentonite were also studied. The results indicated that the sorption is not influenced by the addition sequences. Some possible mechanisms are discussed.

Sorption and complexation of Eu(III) on alumina: Effects of pH, ionic strength, humic acid and chelating resin on kinetic dissociation study

The effects of pH (pH=2-12), ionic strength (0.01-2 mol/l NaNO(3)) and humic acid on the sorption and complexation of Eu(III) on alumina were investigated by using batch techniques. The experiments were carried out at room temperature and under ambient conditions. The results indicate that the sorption of Eu(III) on alumina is strongly influenced by humic acid. The sorption of Eu(III) on alumina is significantly dependent on pH values and independent of ionic strength. The sorption of Eu(III) on alumina may be attributed to surface complexation. The species of Eu(III) on HA-alumina colloids is dominated by both HA and alumina, and the addition sequences of HA or Eu(III) to the ternary system do not influence the sorption of Eu(III) to HA-coated alumina. Kinetic dissociation of Eu(III) from bare and HA-coated alumina was also studied by using the chelating resin. The result was discussed by a pseudo-first-order kinetics model.

Th(IV) adsorption on alumina: Effects of contact time, pH, ionic strength and phosphate

Adsorption of Th(IV) (total concentration, 10(-5)-10(-4) mol/L) was studied by a batch technique. The effects of pH, ionic strength, contact time, and phosphate on the adsorption of Th(IV) onto alumina were investigated. Adsorption isotherms of Th(IV) on alumina at approximately constant pH and three ionic strengths (0.05, 0.1, 0.5 mol/L KNO3) were determined. It was found that the pH values of aqueous solutions of both the Th(IV)-alumina and phosphate-alumina adsorption systems increase with increasing contact time, respectively. Adsorption of Th(IV) on alumina steeply increases with increasing pH from 1 to 4.5 and the adsorption edge consists of three regions. The phosphate added clearly enhances Th(IV) adsorption in the pH range 1-4. From the adsorption isotherms at approximately constant pH and three different ionic strengths, a reduced ionic strength effect was observed and is contradictory to the insensitive effect obtained from the adsorption edges on three oxides of Fe, Al, and Si at different ionic strengths. Compared with the adsorption edges at different ionic strengths, the adsorption isotherms at approximately constant pH and different ionic strengths are more advantageous in the investigation of ionic strength effect. The significantly positive effect of phosphate on Th(IV) adsorption onto alumina was attributed to strong surface binding of phosphate on alumina and the subsequent formation of ternary surface complexes involving Th(IV) and phosphate.

Simulation of radionuclides 99Tc and 243Am migration in compacted bentonite

The distribution coefficients of radionuclides derived from batch experiments are used to evaluate the migration behavior of radionuclides (99)Tc and (243)Am in compacted bentonite after different times. The effects of times, dispersion coefficient, distribution coefficient and pore water velocity on the concentration distribution of (99)Tc and (243)Am in the environment are also calculated from the theoretical migration equation. (99)Tc is poorly sorbed to bentonite and moves quickly into the environment. Migration of radionuclide increases with increasing dispersion coefficient and decreasing distribution coefficient. The effects of water velocity on the migration of Tc and Am are obvious. Most (243)Am is retained in the first several meters, and 20 m of the backfill-compacted bentonites are sufficient to prevent the migration of radionuclide Am from the repository to the environment.

Characterization of adsorption sites on aggregate soil samples using synchrotron X-ray computerized microtomography

Synchrotron-source X-ray computerized microtomography (CMT) was used to evaluate the adsorptive properties of aggregate soil samples. A linear relationship between measured mean mass attenuation coefficient (sigma) and mass fraction iron was generated by imaging mineral standards with known iron contents. On the basis of reported stoichiometries of the clay minerals and identifications of iron oxyhydroxides (1), we calculated the mass fraction iron and iron oxyhydroxide in the intergranular material. The mass fractions of iron were estimated to range from 0.17 to 0.22 for measurements made at 18 keV and from 0.18 to 0.21 for measurements made at 26 keV. One aggregate sample also contained regions within the intergranular material with mass fraction iron ranging from 0.29 to 0.31 and from 0.33 to 0.36 for the 18 and 26 keV measurements, respectively. The mass fraction iron oxyhydroxide ranged from 0.18 to 0.35 for the low-iron intergranular material and from 0.40 to 0.59 for the high-iron intergranular material. Using absorption edge difference imaging with CMT, we visualized cesium on the intergranular material, presumably because of adsorption and possible exchange reactions. By characterizing the mass fraction iron, the mass fraction iron oxyhydroxide, and the adsorptive capacity of these soil mineral aggregates, we provide information useful for conceptualization, development, and parametrization of transport models.

Diffusion of Eu(III) in compacted bentonite—effect of pH, solution concentration and humic acid

The effect of pH, Eu(III) solution concentration and humic acid on the diffusion of Eu(III) in compacted bentonite (rho(b) = 1000 +/- 30 kg/m(3)) was studied with "in-diffusion" method at an ionic strength of 0.1M NaClO(4). The results (K(d) values from the first slice and theoretical calculation, apparent and effective diffusion coefficients) derived from the new capillary method are in good agreement with the literature data under similar conditions, and fit the Fick's second law very well. The results suggest that the diffusion of Eu(III) is dependent on pH values and independent on solution concentration in our experimental conditions. Humic acid forms precipitation/complexation with Eu(III) at the surface of compacted bentonite and thus deduces the diffusion/transport of Eu(III) in compacted bentonite. The K(d) values in compacted bentonite are in most cases lower than those in powdered bentonite obtained from batch experiments. The difference between the K(d) values from powdered and compacted bentonite is a strong function of the bulk density of the bentonite. The results suggest that the content of interlaminary space plays a very important role to the diffusion, sorption and migration of Eu(III) in compacted bentonite.

Am(III) adsorption on oxides of aluminium and silicon: effects of humic substances, pH, and ionic strength

The adsorption of Am(III) (total concentration 10(-9) mol/l) on alumina, silica, and hematite was studied by a batch technique. The effects of pH, ionic strength, and humic substances on the adsorption of Am(III) on alumina and silica were investigated, and the adsorption isotherms of Am(III) on alumina and silica at different pH values were determined. It was found that compared with the adsorption of Am(III) on alumina, the adsorbability of silica on the basis of mass is less, the relative adsorption rate on silica is slower, the sensitivity of adsorption on silica to ionic strength is less, the dependence of adsorption on silica on pH is gentler, and consequently that the adsorption characteristics of Am(III) on alumina and silica are distinctly different. The negative effect of fulvic acid on the adsorption on silica and the positive effect of humic acid on the adsorption on alumina were found. In contrast to the Am(III) adsorption on alumina and silica, a tremendously high adsorbability of Am(III) on hematite was found. The sequence of adsorbabilities of Am(III) on the basis of mass is Fe2O3 > Al2O3 > SiO2.

Sorption behavior of nonylphenol in terrestrial soils

Nonylphenol (NP) as an intermediate from anaerobic degradation of widely used nonionic surfactants occurs widespread in the environment. Partition behavior of this toxic and endocrine-disrupting chemical between soil and water was not examined until yet. The objective of this investigation was to quantify sorption and desorption behavior of 4-nonyl[14C]phenol in a set of 51 soils using the batch equilibrium approach. Kinetic studies indicated apparent equilibrium within 20 h. Sorption was influenced by sorbate structure as could be shown with branched 4-nonyl[14C]phenol and the linear 4-n-NP, respectively. Linear 4-n-NP behaves differently from the branched isomers of 4-NP. Sorption of 4-nonyl[14C]phenol tested with five different initial concentrations resulted in linearly fitted isotherms that provided calculation of sorption partition coefficients (KP). Desorption partition coefficients (KP-des) revealed hysteresis independent of soil properties but decreasing with decreasing initial NP concentrations. KP values were correlated with organic carbon content of the soils yielding a log KOC of 3.97.

Sorption and desorption of Co(II) on alumina: mechanisms and effect of humic substances

The effects of pH, ionic strength and humic substances on the sorption and desorption of Co(II) on alumina and silica were, respectively investigated by using radiotracer 60Co. The distribution coefficients, the breakthrough curves and the displacement curves were experimentally determined in the batch and the column experiments. The pH and the humic substances influenced the sorption of Co(II) on alumina greatly as compared with the sorption of Co(II) on silica. It was found that the sorption characteristics of Co(II) onto alumina and silica are distinctly different, that the strong chemical bonds are formed between the bare alumina surface and Co(II) and between the coated alumina surface and Co(II), and that a transition from the adsorption to the surface-induced precipitation of Co(II) on the bare alumina surface takes place.

Fluorescence and FT-IR spectroscopic studies of Suwannee River fulvic acid complexation with aluminum, terbium and calcium

In this study fluorescence emission and IR spectroscopy have been used to investigate the interaction of the class A (oxygen seeking "hard acid") metal Al(3+), with Suwannee River fulvic acid. Addition of Al(3+) ion results in a significant enhancement in fulvic acid fluorescence emission (at lambda(em)=424 nm) and significant red shift of the excitation wavelength (from lambda(ex)=324 nm to lambda(ex)=344 nm) at low pH values (pH approximately 4.0-5.0). At pH 4.0 (0.1 M ionic strength), where the predominant aluminum ion species is the "free" (aquo) ion, the fulvic acid fluorescence reaches 142% of the value in the absence of added metal ion. Analysis of the pH 4.0 and pH 5.0 fluorescence enhancement data with the nonlinear (single site) model of Ryan and Weber indicated binding constants in the range of 4.67.10(4)-2.87.10(6) M(-1) and concentrations of ligand sites in the range of 18.6.10(-6)-24.0.10(-6) M, both consistent with previous studies performed on both aquatic and soil fulvic acids. Companion fluorescence experiments performed on two other class A metal ions, Ca(2+) and Tb(3+), indicated no significant enhancement or quenching with Ca(2+) and only slight quenching with Tb(3+). Comparison of FT-IR spectra collected on fulvic acid alone and fulvic acid in the presence of the three class A metals (Al(3+), Ca(2+) and Tb(3+)) provides strong evidence for the involvement of carboxyl carbonyl functions in the binding of all three metal ions, which is not unexpected. The spectra also reveal, however, a very pronounced difference in the 4000-2000 cm(-1) IR spectral region between the Al(3+) spectrum and the Ca(2+) and Tb(3+) spectra. The -OH stretch spectral region in the Al(3+) spectrum has a major component shifted to higher energy (compared to fulvic acid alone or to fulvic acid in the presence of Ca(2+) or Tb(3+)). Even more striking is the emergence of a pronounced IR band at 2407 cm(-1), which is present only in the Al(3+) spectrum. The results of fluorescence and IR experiments with the model compounds salicylic acid and phthalic acid further confirm that both salicylic acid-like sites and phthalic acid-like sites are likely complexation sites for Al(3+) in fulvic acid and are major contributors to the observed spectroscopic changes associated with Al(3+) ion complexation. From a comparison of both the fluorescence and IR spectral results for all three class A metals, differing most strongly in the value of their ionic index, it seems clear that major sources of the deviation in spectral properties between Al(3+) and Ca(2+)/Tb(3+) is the unusually high value of its charge density and relatively low propensity for involvement in covalent bonding interactions (very high ionic index and relatively low covalent index in the Nieboer and Richardson classification of environmental metals), as well as affinity for certain functional groups.

Comparative study on sorption/desorption of radioeuropium on alumina, bentonite and red earth: effects of pH, ionic strength, fulvic acid, and iron oxides in red earth

The sorption and desorption of Eu(III) as a representative of trivalent lanthanides and actinides on bentonite, alumina, red earth and red earth treated to remove free iron oxides were comparatively investigated by using batch technique and radiotracer 152 + 154Eu. The effects of pH, ionic strength, fulvic acid, iron oxides in red earth and the sorption mechanism were also discussed. As compared to alumina and red earth, Eu(III) presents a considerable distribution coefficient (Kd) onto bentonite. It was found that the pH and the presence of clay minerals are the main factors dominating the sorption/desorption characteristic of Eu3+ in the soil, and that a sorption-desorption hysteresis on bentonite and red earth actually occurs. Furthermore, the main sorption mechanism of lanthanides onto bentonite, alumina and red earth is the formation of bridged hydroxo complexes with the surface, and there are negative effects of fulvic acid and free iron oxides in red earth on the sorption of Eu(III). The results of this paper indicate that the additivity rule on the sorption characteristic of a soil from the individual component's characteristics is not general.