[Show abstract][Hide abstract] ABSTRACT: We studied tracer (Tritiated Water (HTO); Tritium replaces one of the stable hydrogen atoms in the H(2)O molecule) and nanoparticle (quantum dots (QD)) transport by means of column migration experiments and comparison to 3D CFD modeling. Concerning the modeling approach, a natural single fracture was scanned using micro computed tomography (μCT) serving as direct input for the model generation. The 3D simulation does not incorporate any chemical processes besides the molecular diffusion coefficient solely reflecting the impact of fracture heterogeneity on mass (solute and nanoparticles) transport. Complex fluid velocity distributions (flow channeling and flowpath heterogeneity) evolve as direct function of fracture geometry. Both experimental and simulated solute and colloidal breakthrough curves show heavy tailing (non-Fickian transport behavior), respectively. Regarding the type of quantum dots and geochemical conditions prevailing (Grimsel ground water chemistry, QD and diorite surface charge, respectively and porosity of the Äspö diorite drill core) experimental breakthrough of the quantum dots always arrives faster than the solute tracer in line with the modeling results. Besides retardation processes like sorption, filtration, straining or matrix diffusion, the results show that natural 3D fracture heterogeneity represents an important additional retardation mechanism for solutes and colloidal phases. This is clearly verified by the numerical simulations, where the 3D real natural fracture geometry and the resulting complex flow velocity distribution is the only possible process causing solute/nanoparticle retardation. Differences between the experimental results and the simulations are discussed with respect to uncertainties in the μCT measurements and experimental and simulation boundary conditions, respectively.
Journal of contaminant hydrology 03/2012; 133:40-52. · 2.01 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The capabilities of the asymmetrical flow field-flow fractionation (AsFlFFF) technique coupled with inductively coupled plasma mass spectrometry and UV–Vis spectrophotometry in the characterization of synthetic and natural colloidal samples are demonstrated in two different systems. The first system is a sol of hectorite which was co-precipitated in the presence of Lu. The results show that hectorite nanoparticles can be mobilized from a bulk sample and that they still contain the dopant Lu, which is homogeneously incorporated into the hectorite crystal structure. The second system is a natural groundwater from the Gorleben site on the northern German plain, which is being tentatively explored to assess its suitability as a nuclear waste repository. Colloidal matter heterogeneity is evident in this system. Alkaline-earth elements are mainly found as ionic species. Rare earth elements (REEs) and actinides are distributed in two main colloidal fractions: the heavier REEs and U are concentrated in the REEs and Th are concentrated in colloidal particles between 4 and 18 nm in size that are both organic and inorganic in nature. Similar results are reported for another sample from the same site, collected ∼2 km from the first one, demonstrating the homogeneity of the aquifer system and/or a possible colloid migration pathway. The extent of the reversibility of colloid–radionuclide interactions remains to be evaluated.
[Show abstract][Hide abstract] ABSTRACT: Hectorite was synthesized from a Eu(III)-bearing brucite precursor in a multistep procedure. In a separate experiment, Eu(III) ions were adsorbed onto hectorite in suspension. Colloids were extracted from both samples. The size distributions in the colloidal fractions were characterized by application of the asymmetrical flow field-flow fractionation (AsFlFFF) method and the corresponding elemental compositions were obtained by ICP-MS. Extended X-ray absorption fine structure (EXAFS) spectroscopy was used to characterize the local chemical environment surrounding Eu in the bulk samples and in the colloidal fractions. The EXAFS results show that Eu is associated with hectorite upon co-precipitation or adsorption. Results from AsFlFFF suggest that Eu is structurally associated with the colloidal fraction extracted from bulk Eu-bearing co-precipitated hectorite. The AsFlFFF data are different for the colloidal fraction containing Eu(III) adsorbed on hectorite; in this sample they are consistent with a surface retention mechanism. These small but significant differences enable surface sorbed Eu to be distinguished from co-precipitated Eu. Eu is very likely located in a clay-like environment in the co-precipitation experiment, and it forms inner-sphere surface complexes in the adsorption experiment. The results obtained using the different experimental techniques agree, and show the benefits of using multiple methods of analysis. Trivalent europium was used as non-radioactive chemical homologue for trivalent actinides. Similar retention mechanisms are expected for the trivalent actinides if they are co-precipitating with or adsorbing onto sheet silicates. The present study provides information which can be usefully added to the safety assessments required for deeply buried nuclear waste disposal sites.
[Show abstract][Hide abstract] ABSTRACT: The interaction of Cs(I), Eu(III), Th(IV) and U(VI) with montmorillonite colloids was investigated in natural Grimsel Test Site groundwater over a 3 years period. The asymmetric flow field-flow fractionation combined with various detectors was applied to study size variations of colloids and to monitor colloid association of trace metals. The colloids suspended directly in the low ionic strength (I), slightly alkaline granitic groundwater (I = 10-3 mol/L, pH 9.6) showed a gradual agglomeration with a size distribution shift from initially 10-200 nm to 50-400 nm within over 3 years. The Ca2+ concentration of 2.1 × 10-4 mol/L in the ground water is believed to be responsible for the slow agglomeration due to Ca2+ ion exchange against Li+ and Na+ at the permanently charged basal clay planes. Furthermore, the Ca2+ concentration lies close to the critical coagulation concentration (CCC) of 10-3 mol L-1 for clay colloids. Slow destabilization may delimit clay colloid migration in this specific groundwater over long time scales. Eu(III) and Th(IV) are found predominantly bound to clay colloids, while U(VI) prevails as the UO2(OH)3- complex and Cs(I) remains mainly as aquo ion under our experimental conditions. Speciation calculations qualitatively represent the experimental data. A focus was set on the reversibility of metal ion-colloid binding. Addition of humic acid as a competing ligand induces rapid metal ion dissociation from clay colloids in the case of Eu(III) even after previous aging for about 3 years. Interestingly only partial dissociation occurs in the case of Th(IV). Experiments and calculations prove that the humate complexes dominate the speciation of all metal ions under given conditions. The partial irreversibility of clay bound Th(IV) is presently not understood but might play an important role for the colloid-mediated transport of polyvalent actinides over wide distances in natural groundwater.
Geochimica et Cosmochimica Acta 01/2011; 75:3866-3880. · 3.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In the present study, the sorption of europium and lutetium onto titanium dioxide from aqueous solutions is presented, as a function of pH, ionic strength and concentration. An acid base model for the titanium dioxide surface was determined from potentiometric titrations and zeta-potential measurements. The common intersection point of potentiometric titrations coincided with the isoelectric point from electrokinetic experiments, resulting in a pristine point of zero charge of about 6.1. The experimental data were in agreement with previously published results and a previously published MUSIC-type model was used as the basis to model the acid-base behavior. Comparison of europium and lutetium showed no difference in the adsorption behavior. Furthermore, no difference was observed both in uptake and spectroscopic studies whether carbonate was absent or present. The absence of a noticeable effect of the ionic strength on the adsorption behavior was indicative of strong binding. EXAFS revealed rough conservation of the coordination with 9-8 water and surface hydroxyl groups upon sorption. EXAFS results suggested the existence of different metal-oxygen distances, more varied than that observed for the respective aquo complex and thus indicative for inner-sphere surface complexation. A clear differentiation of surface complexation denticity was not possible based on spectroscopic data. A multisite surface complexation model approach was applied by assuming monodentate and multidentate binding to describe the trivalent metal uptake data. It is conceivable that mono- and multidentate species contribute to lanthanide sorption to titanium dioxide. In other words a distribution of states occurs in cation surface complexation reactions.
Journal of Colloid and Interface Science 10/2010; 350(2):551-61. · 3.17 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A straightforward quantification method is presented for the application of asymmetric flow field-flow fractionation (AsFlFFF) combined with inductively coupled plasma mass spectrometry (ICPMS) to the characterization of colloid-borne metal ions and nanoparticles. Reproducibility of the size calibration and recovery of elements are examined. Channel flow fluctuations are observed notably after initiation of the fractionation procedure. Their impact on quantification is considered by using (103)Rh as internal reference. Intensity ratios measured for various elements and Rh are calculated for each data point. These ratios turned out to be independent of the metal concentration and total sample solution flow introduced into the nebulizer within a range of 0.4-1.2 mL min(-1). The method is applied to study the interaction of Eu, U(VI) and Th with a mixture of humic acid and clay colloids and to the characterization of synthetic nanoparticles, namely CdSe/ZnS-MAA (mercaptoacetic acid) core/shell-coated quantum dots (QDs). Information is given not only on inorganic element composition but also on the effective hydrodynamic size under relevant conditions. Detection limits (DLs) are estimated for Ca, Al, Fe, the lanthanide Ce and the natural actinides Th and U in colloid-containing groundwater. For standard crossflow nebulizer, estimated values are 7 x 10(3), 20, 3 x 10(2), 0.1, 0.1 and 7 x 10(-2) microg L(-1), respectively. DLs for Zn and Cd in QD characterization are 28 and 11 microg L(-1), respectively.
Analytical and Bioanalytical Chemistry 11/2008; 392(7-8):1447-57. · 3.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The trivalent metal ion (M(III)=Cm, Eu)/polyacrylic acid (PAA) system was studied in the pH range between 3 and 5.5 for a molar PAA-to-metal ratio above 1. The interaction was studied for a wide range of PAA (0.05 mg L(-1)-50 g L(-1)) and metal ion concentrations (2x10(-9)-10(-3) M). This work aimed at 3 goals (i) to determine the stoichiometry of M(III)-PAA complexes, (ii) to determine the number of complexed species and the local environment of the metal ion, and (iii) to quantify the reaction processes. Asymmetric flow-field-flow fractionation (AsFlFFF) coupled to ICP-MS evidenced that size distributions of Eu-PAA complexes and PAA were identical, suggesting that Eu bound to only one PAA chain. Time-resolved laser fluorescence spectroscopy (TRLFS) measurements performed with Eu and Cm showed a continuous shift of the spectra with increasing pH. The environment of complexed metal ions obviously changes with pH. Most probably, spectral variations arose from conformational changes within the M(III)-PAA complex due to pH variation. Complexation data describing the distribution of complexed and free metal ion were measured with Cm by TRLFS. They could be quantitatively described in the whole pH-range studied by considering the existence of only a single complexed species. This indicates that the slight changes in M(III) speciation with pH observed at the molecular level do not significantly affect the intrinsic binding constant. The interaction constant obtained from the modelling must be considered as a mean interaction constant.
Journal of Colloid and Interface Science 09/2008; 327(2):324-32. · 3.17 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study investigated the characteristics of natural groundwater colloids by a laser-induced breakdown detection (LIBD)
and inductively-coupled plasma mass spectrometry (ICP-MS) in a combination with an asymmetrical flow field-flow fractionation
(AsymFFFF). The groundwater was sampled from a borehole in the Yuseong area of Daejeon, Korea at different geological depths
from 30 to 460 m and its geochemical parameters were measured. The combination of AsymFFFF and LIBD revealed a heterogeneous
size fraction with a relatively broad size distribution of the groundwater colloids. One of the size fractions of the groundwater
colloids was about 20 nm up to smaller than 100 nm, and the other fractions were larger than 100 nm. The elemental composition
of the groundwater colloids was also analyzed by the AsymFFFF coupled with an ICP-MS. Results from the ICP-MS coupled with
the AsymFFFF provided us with information about the size-specific elemental composition. The smaller sized fractions mainly
consisted of calcite colloids with strontium, whereas the larger fractions were comprised of colloids such as aluminosilicates
and iron oxides. The observations of all the groundwater samples indicate a similar pattern for the colloid fractions in size
and in element composition except in the concentration.
Korean Journal of Chemical Engineering 08/2007; 24(5):723-729. · 1.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Laser-induced breakdown detection was performed to monitor the nanoparticles in an aqueous solution by means of a two-dimensional
optical imaging method. To verify the relationship between the particle size and the optical image of a laser-induced plasma,
we investigated the characteristics of its spatial distribution corresponding to the number of breakdown events plotted on
the laser beam propagating axis. It was found that, for particles smaller than 50nm in diameter, the spatial distribution
follows a single Gaussian curve. For particles in the diameter range from 100 to 1000nm, however, the spatial distribution
follows a sum of the multiple Gaussian curves with different peak positions and peak heights. We demonstrated that particles
smaller than 20nm in trace concentrations, which are mixed with larger particles in the diameter range of a few hundred nm,
can be measured by a peak deconvolution of the spatial distribution of a laser-induced plasma.
Applied Physics B 04/2007; 87(3):497-502. · 1.78 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The use of three different separation techniques, ultrafiltration (UF), high performance size exclusion chromatography (HPSEC) and asymmetrical flow field-flow fractionation (AsFlFFF), for the characterization of a compost leachate is described. The possible interaction of about 30 elements with different size fractions of humic substances (HS) has been investigated coupling these separation techniques with UV-vis absorption spectrophotometry and inductively coupled plasma-mass spectrometry (ICP-MS) as detection techniques. The organic matter is constituted by a polydisperse mixture of humic substances ranging from low molecular weights (around 1kDa) to significantly larger entities. Elements can be classified into three main groups with regard to their interaction with HS. The first group is constituted by primarily the monovalent alkaline metal ions and anionic species like B, W, Mo, As existing as oxyanions all being not significantly associated to HS. The second group consists of elements that are at least partly associated to a smaller HS size fraction (such as Ni, Cu, Cr and Co). A third group of mainly tri- and tetravalent metal ions like Al, Fe, the lanthanides, Sn and Th are rather associated to larger-sized HS fractions. The three separation techniques provide a fairly consistent size classification for most of the metal ions, even though slight disagreements were observed. The number-average molecular weight (Mn), the weight-average molecular weight (Mw) and the polydispersity (rho) parameters have been calculated both from AsFlFFF and HPSEC experiments and compared for HS and some metal-HS species. Differences in values can be partly explained by an overloading effect observed in the AsFlFFF experiments induced by electrostatic repulsion effects in the low ionic strength, high pH carrier solution. Size information obtained from ultrafiltration is not as resolved as for the other methods. Molecular weight cut-offs (MWCO) of the individual filter membranes refer to globular proteins and molecular weight information may therefore, deviate from that given by the other methods after calibration with polystyrene sulfonate (PSS) standards.
Journal of Chromatography A 11/2006; 1129(2):236-46. · 4.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The release of metal ions from a coal mining tailing area, Lamphun, Northern Thailand, is studied by leaching tests. Considerable amounts of Mn, Fe, Al, Ni and Co are dissolved in both simulated rain water (pH 4) and 10 mg L(-1) humic acid (HA) solution (Aldrich humic acid, pH 7). Due to the presence of oxidizing pyrite and sulfide minerals, the pH in both leachates decreases down to approximately 3 combined with high sulfate concentrations typical to acid mine drainage (AMD) water composition. Interaction of the acidic leachates upon mixing with ground- and surface water containing natural organic matter is simulated by subsequent dilution (1:100; 1:200; 1:300; 1:500) with a 10 mg L(-1) HA solution (ionic strength: 10(-3) mol L(-1)). Combining asymmetric flow field-flow fractionation (AsFlFFF) with UV/Vis and ICP-MS detection allows for the investigation of metal ion interaction with HA colloid and colloid size evolution. Formation of colloid aggregates is observed by filtration and AsFlFFF depending on the degree of the dilution. While the average HA size is initially found to be 2 nm, metal-HA complexes are always found to be larger. Such observation is attributed to a metal induced HA agglomeration, which is found even at low coverage of HA functional groups with metal ions. Increasing the metal ion to HA ratio, the HA bound metal ions and the HA entities are growing in size from <3 to >450 nm. At high metal ion to HA ratios, precipitation of FeOOH phases and HA agglomeration due to colloid charge neutralization by complete saturation of HA complexing sites are responsible for the fact that most of Fe and Al precipitate and are found in a size fraction >450 nm. In the more diluted solutions, HA is more relevant as a carrier for metal ion mobilization.
Water Research 06/2006; 40(10):2044-54. · 4.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The combination of asymmetrical flow field-flow fractionation (AsFlFFF) with the laser-induced breakdown detection (LIBD) is presented as a powerful tool for the determination of colloid size distribution at trace particle concentrations. Detection limits (D1) of 1, 4, and 20 microg/L have been determined for a mixture of polystyrene reference particles with 20, 50, and 100 nm in size, respectively. This corresponds to injected masses of 1, 4, and 20 pg, which is lower than found in a previous study with the symmetrical FlFFF (SyFlFFF). The improvement is mainly due to the lower colloid background discharged from the AsFlFFF channel. The combined method of AsFlFFF-LIBD is then applied to the analysis of iron oxi/hydroxide colloids being considered as potential carriers for the radionuclide migration from a nuclear waste repository. Our LIBD arrangement is less sensitive for iron colloid detection as compared to reference polystyrene particles which results in a detection limit of approximately 240 microg/L FeOOH for the AsFlFFF-LIBD analysis. This is superior to the detection via UV-Vis absorbance and comparable to ICP-MS detection. Size information (mean size 11-18 nm) for different iron oxi/hydroxide colloids supplied by the present method is comparable to that obtained by sequential ultrafiltration and dynamic light scattering. A combined on-line ICP-MS detection is used to gain insight into the colloid-borne main and trace elements.
Journal of Chromatography A 07/2004; 1040(1):97-104. · 4.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The application of the flow-field flow fractionation (FFFF) combined with on-line ICP-mass spectrometry (ICP-MS) to the characterization of aquatic colloids is described. The capabilities and drawbacks of the technique are discussed with the aid of two examples. (1) The size distribution of smectitic colloids dispersed from a natural bentonite is determined by FFFF and laser light scattering (LLS) and compared with the size information obtained by ICP-MS detection. Due to the pronounced size dependency of the scatter light intensity, the LLS detection tends to overestimate the larger sized particles. Therefore, the FFFF-ICP-MS fractogram delivers more reliable size information. (2) Groundwater humic/fulvic colloids and the humic matter extracted from the corresponding sediment, both taken from the Gorleben aquifer (Lower Saxony, Northern Germany), are analysed by FFFF-ICP-MS. The location of REE, U, Th and Ca in different colloid size fractions appears to be very similar in both samples. The element specific fractograms suggest in agreement with earlier studies the location of Th and the REE mainly in inorganic colloids>17 nm containing also Fe and/or Al. U and Ca appear to be distributed between larger colloids and the fulvic/humic acid fraction with a size <3 nm. The results demonstrate that even in groundwater/sediment systems with high humic/fulvic content, inorganic colloids may play an important role as carrier for polyvalent metal ions. The consequences of this finding on the applicability of in-situ Kd values for U, Th and REE, taken as naturally abundant representatives of the nuclear waste derived actinides, for the assessment of laboratory sorption data is discussed.
Colloids and Surfaces A Physicochemical and Engineering Aspects 01/2003; · 2.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Thorium(IV) hydroxide / Solubility / Hydrolysis / Colloids / LIBD / EXAFS Summary. The solubility of amorphous Th(IV) hydroxide at pH 3.0–13.5 and the aqueous speciation at pH < 4 are investigated in 0.5 M NaCl and 25 • C. The laser-induced breakdown detection (LIBD) is used to monitor the initial formation of thorium hydroxide colloids during the coulo-metric titration of 1.2 × 10 −2 –1.0 × 10 −5 M thorium solutions in the pH range of 2.7–4.5. The accurate solubility limit determined by this method is comparable with data measured from undersaturation with an X-ray amorphous solid precipi-tated at higher pH and dried at room temperature. Based on hydrolysis constants selected from the literature, the solubility product of Th(OH) 4 (am) in 0.5 M NaCl is calculated to be log K sp = −44.48 ± 0.24 and log K • sp = −47.8 ± 0.3 (converted to I = 0 with the SIT coefficients of the NEA-TDB). In other solubility studies with amorphous Th(IV) hy-droxide or hydrous oxide, considerably higher thorium concentrations are measured at pH 3.5–5. Therefore, solutions of comparable H + and thorium concentrations are prepared by careful coulometric titration and examined by ultrafil-tration, LIBD and X-ray absorption fine structure (XAFS) spectroscopy. These measurements demonstrate the presence of a large amount of small Th(IV) colloids. The Th L 3 edge EXAFS spectra of these colloidal suspensions are similar to that of the amorphous solid.
[Show abstract][Hide abstract] ABSTRACT: Humic colloids in deep groundwater are characterized in order to ascertain how heavy metal ions of chemical homologue to actinides are associated in different size fractions. The colloid size fractionation is made by two different methods: flow field flow fractionation (FFFF) and size exclusion chromatography (SEC), which is followed by analysis of chemical composition using UV spectroscopy for organic components and ICP-MS for inorganic components. Relative number density of humic colloids following the size fractionation is determined by laser-induced breakdown detection (LIBD). For the appraisal of colloid size change upon metal ion complexation, purified Aldrich humic acid is loaded with the Eu3+ ion on increasing the concentration and the size change is then determined by LIBD. Humic colloids are interacted with radioactive tracers, Eu-155(III) and Th-228(IV), to appreciate their sorption behaviour onto different colloid size fractions and thus to compare with natural humic colloid-borne elements