Jacques Dumonceau

Sorption of selenium anionic species on apatites and iron oxides from aqueous solutions.

The sorption of selenite and selenate ions from aqueous solutions was investigated on hydroxyapatite, fluorapatite, goethite and hematite, in order to simulate the behavior of radioactive selenium in natural or artificial sorbing media. Correlation studies with acido-basic properties and solubility of the solids were also performed. The sorption is pH dependant, but these solids are very efficient for retaining selenite at pH values generally encountered in natural waters, with however higher K(d) values for oxides than apatites. Selenate ions are much less sorbed than selenite. Several methods such as electron microscopy and spectroscopic techniques were used to identify the sorption mechanisms. In the case of hydroxyapatite, sorption proceeds by substitution of phosphate groups in the lattice of the apatite crystal in the superficial layers of the solid. In the case of goethite and hematite, sorption can be interpreted and modeled by a surface complexation process, but there is a discrepancy between sorption site densities for selenite and for protons.

Combination of X-ray photoelectron and solid-state 13C nuclear magnetic resonance spectroscopy in the structural characterisation of humic acids

Leonardite humic acid (LHA) and soil humic acid (SHA), purchased from the IHSS, as well as purified humic acid from Aldrich (HA) are characterised by cross-polarisation magic angle spinning (CP-MAS) and Bloch decay 13C NMR spectroscopy and X-ray photoelectron spectroscopy (XPS). For the 13C CP-MAS NMR experiments, the effects of both the sample spinning sidebands and the influence of the cross-polarisation contact time are investigated. The functional groups distribution obtained by CP-MAS NMR is compared to the one resulting from chemical analyses. It is found that CP-MAS NMR overestimates the concentration of CO2H groups for certain humic compounds, whereas the concentration of phenolic groups is in reasonable agreement with the values determined by chemical methods. XPS was used as a complementary technique to understand the overestimation of carboxylic groups by NMR. The results from XPS, a surface characterisation technique, are in good agreement with those measured by elemental analyses of the bulk structure. High resolution C 1s and N 1s spectra show that the overestimation of the CO2H content by NMR is due to the presence of amide groups which give overlapping signals in the CO2H region of the NMR spectra.

Acid/base and Cu(II) binding properties of natural organic matter extracted from wheat bran: modeling by the surface complexation model.

A simple surface complexation model, the double-layer model (DLM), was used to describe the sorption of Cu(II) on a lignocellulosic substrate extracted from wheat bran. The solid was first characterized by IR and 13C-NMR and the binding of protons was studied by potentiometric titrations. The organic solid was represented by two acid sites. From the acid–base titration data, total concentrations of these sites and H+ binding constants (SiOH⇔SiO−+H+) were obtained by using the computer program FITEQL 3.2. The binding of Cu(II) was then investigated. The thermodynamic approach was completed by two spectroscopic studies. A laser microspectrofluorimetry study was used to specify the adsorption phenomena. The square planar geometry of the solid/Cu complexes and the formation of inner-sphere complexes were suggested by an ESR study. After identifying the stoichiometry of the surface complexes by potentiometric titrations of the Cu2+/solid system, the surface complexation model was applied to describe Cu(II) binding by the lignocellulosic substrate. A single set of data was used; the model fit was good and covered a wide range of pH. The surface complexation constants derived from this single metal data set were then used to predict the sorption for increasing metal loading, different solid to solution ratios or different ionic strength. The predictions agreed well with the experimental data showing the capability for the DLM surface complexation model to describe Cu binding to natural organic matter with a minimum number of adjustable parameters (only five parameters were necessary to describe the data).

Sorption of cesium, barium and europium on magnetite

Laboratory experiments have been performed on magnetite according to the batch method. The sorption of three cations of three different oxidation states has been investigated under various pH: Cs (I) and Ba (II) which have long lived isotopes, and Eu (III) which can be considered as a chemical analogue of Am (III). Results showed that magnetite has a high capacity of retention for Ba2+ and Eu3+, especially under pH conditions expected in a deep geological disposal. Cs+ is not sorbed on a pure magnetite but it can be sorbed if magnetite contents some impurities such as silica. In this case the sorption was strongly dependent on the presence of other alkaline metal ions such as sodium. A good fitting of these experimental results has been obtained by using the surface complexation theory (fiteql 3.2 code) with the diffuse layer model (DLM) (leading to the species ≡XOHBa2+, ≡XOBaOH, ≡XOHEu3+, ≡XOEu(OH)2 with log K respectively equal to 4.05–11.50 6.43 and −14.87).

Metal ions binding onto a lignocellulosic substrate extracted from wheat bran: a NICA-Donnan approach

In this study ion binding to solid organic matter was investigated. We used the NICA-Donnan model to describe the interaction between Cu(II), Pb(II), and Cd(II) ions and a lignocellulosic substrate extracted from wheat bran. Such a material represents a very cheap and flexible substrate, which can be used as a natural filter to remove toxic metal ions from industrial effluents or applied in the decontamination and rehabilitation of abandoned industrial sites. Moreover, such a material also represents a very simple model of natural organic matter derived from lignin and cellulose, for which there is now a lack of thermodynamic data as far as their interaction with toxic metal ions is concerned. Experimental results were obtained in various conditions of pH and ionic strength. In our modeling, we used the acidity constants and the concentration of sites that were determined in a previous work. The parameters deduced from the NICA-Donnan model were also compared to thermodynamic data available for other cases of natural organic matter, mainly humic substances.

Characterisation of a wheat straw cell wall residue by various techniques: A comparative study with a synthetic and an extracted lignin

Comparative studies using various analytical and spectroscopic techniques have been carried out on three samples of lignin: two samples of natural lignin that have been extracted using different processes, and one sample of synthetic lignin. This paper discusses the general features common to all three kinds of lignin, as well as the differences between, on one hand, the two natural lignins coming from different extraction processes, and, on the other hand, the natural lignins and the synthetic one. The advantages of each technique in explaining the structure of these three different lignins are emphasised.

Sorption of the Herbicide Terbumeton and its Metabolites onto Soils. Influence of Copper(II)

Environmental Context.Agrochemicals have contributed greatly to modern agriculture, allowing better yields and lower costs. However, their extensive use has led to frequent contamination of underground and surface water. A better knowledge of the fate of pesticides from the sprayer to the water that would take into account the diversity of the physical and chemical properties of the various molecules and environmental conditions should help in the challenge of protecting and restoring natural water quality. Abstract.The intensive use of terbumeton (N-(1,1-dimethyl)-N′-ethyl-6-methoxy-1,3,5-triazine-2,4-diamine) has resulted in its widespread presence, together with its main metabolites, in surface- and groundwater. To estimate the fate of these compounds, their adsorption and desorption properties were studied in vineyard soils. The values of the organic carbon normalized adsorption coefficient (KOC) for terbumeton (34.6 and 39.2 L g−1) were significantly higher than those of its metabolites (between 6.8 and 21.1 L g−1). Terbumeton exhibited a higher adsorption capacity and a lower desorption potential as compared with the metabolites. An important hysteresis was observed in all cases. The Freundlich isotherms exhibited a linear shape, which was interpreted as non-specific interaction. The influence of copper(II), a ubiquitous metal cation in vineyard soils, on pesticide sorption was also studied. Copper significantly decreased the amount of adsorbed terbumeton when present in a high concentration (2 ×10−4 M).