Arsenic represents a threat to all living organisms due to its toxicity which depends on its speciation. This element is carcinogenic, teratogenic and is certainly one of the most important contaminants affecting millions of people around the world. Abiotic and biotic processes control its speciation and distribution in the environment. We have previously shown that a new bacterial strain named ULPAs1 performed oxidation of As(III) (1.33 mM) to As(V) in batch cultures. In order to develop new methods to remove arsenic from contaminated effluents or waste, by bacterial oxidation of As(III) to As(V) followed by its sorption, the conservation of oxidative properties of ULPAs1 was investigated when cultivated in batch reactors in the presence of two solid phases, chabazite and kutnahorite, already used as microorganisms immobilizing materials in biological remediation processes. In parallel, the retention efficiency of these solid phases toward arsenic ions and particularly arsenate was studied. Pure quartz sand was used as a reference material. Kutnahorite efficiently sorbed As(V), chabazite alone performed As(III) oxidation and pure quartz sand did not sorb arsenic at all. The arsenite oxidative properties of ULPAs1 were conserved when cultivated in the presence of quartz or chabazite.

The aim of this study is to understand the sorption of tributyltin (TBT) onto natural quartz sand by classical batch experiments and spectroscopic surface analyses. At pH < 6, the major species of TBT is the cation TBT+. Due to the presence of both the cationic part and the butyl chains, TBT should present amphiphilic properties. For concentrations lower than 40 muM, TBT sorption occurs as a homovalent 1: 1 cation exchange between either H+ or Na+ and TBT+. The increasing affinity of TBT with respect to the different materials follows the series kaolinite much less than natural sand < treated sand < pure quartz. From XPS analyses, where the chemical environment of Sn did not change, indicating possible complete reversibility of the TBT sorption, it seems that inner-sphere surface complexes could be formed due to the increase in the 3d-level binding energy. At TBT concentrations higher than 100 muM, we showed by flotation experiments and XPS analysis that the surface becomes hydrophobic. After one monolayer was formed, the TBT sorption could thus be due to hydrophobic interaction between the butyl chains of the sorbed TBT and those of the TBT still available from the bulk solution. This mechanism is consistent with surface condensation and the shape of the sorption isotherm. (C) 2003 Elsevier Science (USA). All rights reserved.

The influence of ligands (halogens, sulphur-containing ligands and organic ligands) on the determination of Hg by cold vapour atomic absorption spectrometry (CVAAS) was studied. The principle of the cold vapour technique is to break the Hg-ligand structure under oxidative and pH stress to generate Hg(II) as Hg2+ cation which is then reduced to atomic Hg(0) by Sn(II). The presence of chemical species, which can strongly complex Hg2+ or Sn2+, can partially or totally inhibit the Hg reduction. The aim of this study was to evaluate the effect of ligands (Cl-, I-, S2-, SO32-, S2O32-, cysteine, EDTA) on the Hg detection by CVAAS for different ligand concentration ([L]) and pH. The conditional constants, K', taking into account both complex formation and redox equilibrium were calculated. The log K' decreases strongly in the presence of strong ligands (I-, S2- and S2O32-) due to the formation of very stable complexes even at low pH (pH < 1). These assumptions were verified experimentally. In fact the presence of strong ligands strongly decreased the Hg signal. The decrease depended on L and Sn(II) concentrations and pH. The reduction kinetics decreases as the ligand concentration increases, the Sn(II) concentration decreases and the pH decreases for F and increases for S2- and S2O32-.

Natural organic matter (NOM), derived from degradation of living organism matter, can significantly control the fate and transport of chemical components, particularly metal ions, by forming organometallic complexes in aquatic systems. Column experiments were performed to study the mobility of humic acids (HA) and Hg. Single component (HA or Hg) and multicomponent (Hg and HA) experiments were conducted to assess transport behaviour of Hg in the presence of HA. A natural quartz sand was used as porous sorbing medium. HA breakthrough curves (BTCs) showed a first step with a sharp front followed by an important tailing over a long period of time. The tailing of HA BTCs is assumed to be due to slow sorption kinetics of HA onto the quartz sand and the non linear nature of the sorption isotherms. The time required to get steady-state concentration for organic C depended on the inlet HA concentration. HA sorption depends also on pH, the highest HA sorption being observed at pH<pH(pzc) due to electrostatic attractions. The Hg transport is strongly enhanced in the presence of HA and the Hg BTCs are quite similar to the HA BTCs. These results suggest strong aqueous complexation between Hg and HA and the formation of ternary surface complexes of type B.

Silver is a heavy metal which is present at different oxidation states in the environment and which can be released into aquatic systems from agricultural activities or industries (mines, metallurgy, pharmaceutical and electronic activities, electrochemistry, photography, nuclear industry and power plants...). The aim of this work was to understand the Ag(I) sorption at low concentrations in aquatic systems, specially natural porous media such as soils, sediments and ground waters. Kinetic and thermodynamic experiments were performed in batch reactors at room temperature in the dark. A pure silica sand and a natural aquifer quartz sand were used. Silver concentration and pH (2, 4, 6 and 8) play an important role, while the ionic strength (NaNO3) does not affect neither sorption kinetics nor sorption thermodynamics. For each point, more than four days were necessary to observe equilibrium state. Ag sorption rate law does not appear to be simple, with a change in the reaction order depending on experimental conditions. Sorption isotherms were modelled with Langmuir type relationship for a Ag-range concentration from nanomolar to millimolar. In both kinetic and thermodynamic experiments, one to three sites were necessary to take into account the surface heterogeneity of the natural quartz sand depending on experimental conditions.

Contaminated groundwater typically contains different metal contaminants which may compete with each other for the same adsorption sites. Understanding the fate of these micro-pollutants is of primary importance for the assessment of the risk associated with their dispersion in the environment and for the evaluation of the most appropriate remediation technology. In this regard, column techniques can be considered as useful tools both to perform transport experiments and to obtain equilibrium adsorption data without any perturbation of the actual solid/liquid interface. Cd and Pb monocomponent step column experiments were used to obtain adsorption isotherms on a natural aquifer material. A General Composite approach was used to define the equilibrium adsorption model characterized by two types of sites (ion-exchange and surface complexation sites). Coupling the adsorption model with the Advection-Dispersion equation (by IMPACT code) allowed us to well represent the monocomponent step experiments. The model was successfully used to predict the competitive Cd and Pb transport behaviour. Cd peaks of concentration due to Pb competition were experimentally observed and simulated by the model. This behaviour can be described only by an accurate modelling of the interaction and cannot be predicted by simple isotherms (such as Langmuir or Freundlich type).

The aim of this work is to study the As retention capacity of two natural sand, a quartz sand and a volcanic red sand. Sorption experiments were performed in batch reactors at a constant ionic strength (0.010 M NaNO 3 ). pH was controlled by acid or base microadditions. As, Fe, Al and Si were analysed in the aqueous phase to control their fate. Kinetic experiments of arsenic sorption showed that a fast step followed by a slow one could be observed depending on the sand. In the most rapid step, the formation of monodentate complexes could be the main phenomenon while in the slowest one bidendate and binuclear complexes could predominate. During As(V) sorption, the analyses of Al, Fe and Si showed that the dissolution of the different minerals present in the sands as Al, Si and Fe (hydr)oxides was not affected by As(V) sorption. From the point of view of the surface reactivity, the quartz sand has more available sites for arsenic sorption than the volcanic sand. However, the red soil shows a better retention capacity as expressed in amount of As per solid mass unit: 666 nmol/g and 9.4 nmol/g for the red soil and the quartz sand, respectively, for a contact time of 288 h.

Modeling thermodynamic equilibrium of complex nonlinear chemical systems with the most used Newton-Raphson method can lead to nonconvergence. From the mathematical properties of the set of equations, a chemically permitted interval is defined. By, imposing this interval, the robustness of the Newton-Raphson method is increased at a low computing time cost. The new method, the positive continuous fraction, does not depend on the first derivative of the objective function to find the solution. A new algorithm is thus built by the association of this very robust method with the fast Newton-Raphson method and the definition of the chemically allowed interval. This combined algorithm is very impressive in terms of reliability robustness, and speed.

The adsorption of copper, cadmium, and nickel on goethite was examined in natural groundwater samples from an infiltration site of the river Glatt at Glattfelden (Switzerland). Unfractionated dissolved organic matter was used at its natural concentrations. Metal concentrations were close to environmental conditions. Cu, Cd, and Ni presented the typical pH adsorption edge of cations. The major influence on metal adsorption was due to a strong organic ligand L(I), which inhibited adsorption of Cu, Cd, and Ni in the alkaline pH region. Complexation of Cu, Cd, and Ni by the natural organic ligands was described with a model defining a minimum number of discrete ligands: a strong ligand L(I) at low concentration and additional weaker ligands with higher concentrations. The adsorption of Cu, Cd, and Ni on the goethite surface in the presence of the natural organic ligands was adequately described by considering only surface complexation and complexation in solution by organic ligands. No ternary complexes had to be invoked in the model. The major effect was complexation by the strongest ligand, whereas interactions with other cations and anions had only a minor influence. Competition reactions between Cu and Ni for complexation with the same strong ligand L(I) were observed.

Tributyltin (TBT) is the most important organotin compound that has been introduced into aquatic ecosystems. A better understanding of its interactions with solid surfaces is essential to estimate the possibilities of TBT migration through subsurface environments. For this purpose, TBT sorption onto a porous matrix of natural origin, a quartz sand as an aquifer material, was studied at low concentration levels with a monodirectional model of column type allowing sequential investigation of sorption and desorption processes. Different treatments of the solid phase were performed by injecting alkaline solutions, NaOH at pH 10.8 or NaClO-NaCl at pH 11.5, by decreasing the ionic strength or by adding kaolinite to change the surface composition and properties. The removal of iron and aluminum (hydr)oxides from the sand surface did not affect so much the sorption (decrease in 14% as compared to sorption on the raw sand). The original use of X-ray photoelectron spectroscopy to control treatment efficiency and to characterize sand surface modifications permitted to relate TBT sorption onto the aquifer material to quartz, the main component of the sand, and clay minerals (mainly kaolinite) present at trace levels at the sand surface. A first attempt of transport modeling with these two surface sites showed the consistency of our assumption. Moreover, estimation of Langmuir-type constants showed that TBT sorption affinity for the quartz surface (KL = 26.7 L micromol(-1)) was much greater than for kaolinite (KL = 6.3 L micromol(-1)).

Sorption of mercury(II) onto well-characterized samples of pyrite was studied between DH 2 and 12 using X-ray photoelectron spectroscopy for surface analysis and extended X-ray absorption fine structure fur surface speciation. In the presence of Hg, the surface oxidation of pyrite was strongly decreased. Even if the sorption capacity of pyrite for Hg was high, the sorption reversibility was possible by adding some strong ligands, such as I-, S2O32-, and CN-, to the aqueous phase. Spectroscopic studies showed the absence of Hg(0) and S(-II) and evidenced the formation of a surface complex between S(-I) and Hg(II). At low pH, ternary surface complexes =S-1-Hg-OH or =S-1-Hg-Cl were formed with the following distances: R=S-Hg = 2.40 Angstrom, RHg-OH = 2.25 Angstrom, and RHg-Cl = 2.33 Angstrom if Cl- was present. At high pH, the spectroscopic signals of Hg, S, or Fe decreased, possibly because of the presence at the surface of a solid solution constituted of Fe (hydr)oxides and surface complexes between Hg and both oxides and pyritic sulfur.

In this study, the sorption of Hg(II) onto pyrite was investigated as a function of the aqueous solution pH, X-ray photoelectron spectroscopy (XPS) was used to characterize the surfaces, and to identify the adsorbed species when possible. After 12 h of equilibration at a given initial pH (between 6 and 10,5), slabs of pyrite were in contact with Hg(II) solution (210 mu M, constant ionic strength fixed with 0.01 M NaNO3) for 24 h, The final pH ranged between 4.1 and 3.6, The solid samples were then dried and transferred into the XPS machine for surface analyses (Hg 4f, S 2p, O 1s and Fe 2p levels).Taking advantage of the differential charge effect when the surface was partly covered with Fe(III) oxyhydroxides, it was shown that Hg could be sorbed onto both pyritic zones and oxidized patches. On pyritic zones where no charge effect was observed, the Hg 4f(7/2) level was pointed out at 100.7 eV, ruling the presence of Hg(O) at the surface out. The S 2p level analyses clearly showed that the main component was S-2(2-), with some traces of polysulphur, Neither S(II) nor S(VI) were detected in any experiment, excluding the formation of HgS, sulphate and thiosulphate, Most observations were understood as the formation of two surface complexes between mercury and either the pyritic functional groups or the oxyhydroxide sites. Copyright (C) 2000 John Wiley & Sons, Ltd.

A set of complex chemical, biological, geological and physical mechanisms controls the hydrogeochemical cycles of many elements and chemical compounds in natural systems. The chemical composition of oceans, fresh waters and the atmosphere is also controlled by these processes in which living organisms play a key role. It is thus necessary to consider all the interactions between the different compartments (waters, biosphere, atmosphere, soils and rocks) in order to understand the composition of natural waters. Moreover, it is important to take into account the change It? fluxes of matter due to human activities which can strongly disturb the cycles and thus the chemical composition of natural waters of large reservoirs.

A set of complex chemical, biological, geological and physical mechanisms controls the hydrogeochemical cycles of many elements and chemical compounds in natural systems. The chemical composition of oceans, fresh waters and the atmosphere is also controlled by these processes in which living organisms play a key role. It is thus necessary to consider all the interactions between the different compartments (waters, biosphere, atmosphere, soils and rocks) in order to understand the composition of natural waters. Moreover, it is important to take into account the change in fluxes of matter due to human activities which can strongly disturb the cycles and thus the chemical composition of natural waters of large reservoirs.

The surface complexation model is used to describe sorption experiments of inorganic mercury(II) in the presence of an amorphous silica, Aerosil 200, or an iron (hydr)oxide, the goethite α-FeOOH (Bayferrox 910). In the simulations, one assumes the formation of a monodentate surface complex SOHg+ and of ternary surface complexes with OH− surface groups, SOHgOH and SOHgCl, when chlorides are present in solution. Participation of the complex SOHgCl has been especially evidenced. The mercury(II) surface complexation on oxides can be described by the following equilibria (298.15 K, I = 0): with log = 5.8 and 8.0 for amorphous silica and goethite, respectively. Comparisons with other data from the literature have been made to investigate the influence of the nature of the oxide on the mechanism of mercury(II) adsorption. X-ray photoelectron spectroscopy was used to characterize the surface of the (hydr)oxides prior to adsorption and to observe when possible the mercury surface compounds.

Reversed-phase ion-pair liquid chromatography is often used to analyse traces of EDTA in natural water samples. Some perturbations due to the presence of major anions in samples, which can compete for ion pair formation with the Fe-EDTA complex used for the detection, have been observed but never estimated and quantified. A new operational method for determining EDTA in natural water samples is proposed by taking into account anion interactions. Qualitative and quantitative analyses of EDTA were performed with a synthetic water at various ionic strengths. From the effect of the ionic strength controlled by CaCl2, the concentration of the counter-ion tetrabutylammonium bromide (TBA+Br–) and the methanol of the mobile phase, optimal analytical conditions were proposed for a better determination of EDTA concentration. The limit of detection without preconcentration and the reproducibility defined as relative standard deviation were 5 μg/L and 3.6% (n = 12), respectively. This method was applied to natural samples.

The highly toxic organotin compounds which have been used as biocides in ship antifouling paints have been introduced into aquatic ecosystems. Among them, tributyltin (TBT) is the most important organotin compound which has been produced on the largest scale. Understanding its fate in the environment is therefore of primary importance to prevent its migration. TBT sorption from aqueous solutions was studied at much lower concentrations (10 nM to 2 mu M)than those used in previous studies. Experiments were performed using column reactors filled with a quartz sand. The influence of physicochemical parameters on TBT partitioning, i.e. ionic strength, pH, and nature of electrolyte cation was investigated. Equilibrium times were short as TBT retention appeared to be independent of the mean pore velocity. TBT sorption was affected strongly by the pH and slightly by the ionic strength of the solution. Competitions with monovalent alkaline cations showed a small influence of Li+, Na+, K+, Rb+, with respect to Cs+ on TBT retardation. Moreover, the injection of two different TBT concentrations accounted for the nonlinearity of TBT sorption. The theory of nonlinear chromatography was used for the calculation of convex adsorption isotherms. Retardation factors and distribution coefficients were estimated.

Pyrite, the most abundant metal sulfide at the surface of Earth, plays a key role in many processes such as acid mine drainage, redox cycling of metals at oxic-anoxic boundaries of lake bottom, and degradation of pollutants. The oxidation of pyrite was studied in batch experiments over a large range of pH (2.5−12), with trace oxygen. Surface analysis of the samples was performed using X-ray photoelectron spectroscopy (XPS). Speciation of the aqueous species was investigated by inductively coupled plasma atomic emission spectrometry (ICP-AES), ionic chromatography, and UV−vis spectrophotometry. The pyrite surface can drastically change with the pH, which was never at steady state and tended to reach an acidic value whatever the initial pH. For pH <4, Fe(II) and SO42- were released into solution; from XPS analyses, the pyrite surface presented O−H groups, an Fe-deficient composition Fe1-xS2, and iron(III) (hydr)oxide traces. Whatever the pH, the sulfur of the FeS2 surface was mainly under the (−I) state oxi...