Rôle des acides humiques dans le transfert du pyrène entre les minéraux argileux et l'eau

Les substances humiques se fixent en surface des minéraux argileux et modifient les sites d'adsorption des polluants organiques hydrophobes (POH). Parallèlement, les substances humiques dissoutes complexent les POH non ioniques selon des mécanismes de liaison réversible généralement évalués par le coefficient de partage Koc. Les solutés humiques seraient ainsi responsables du transport des POH dans les écosystèmes aquatiques par solubilisation de la fraction adsorbée sur le sédiment. Notre étude a pour objectif la quantification et la modélisation de ces phénomènes pour des composés modèles disponibles commercialement : kaolinite, pyrène et acide humique Aldrich purifié.L'isotherme d'adsorption de l'acide humique (AH) sur la kaolinite à pH 6,5 et à force ionique 10-2 M suit une loi de Freundlich, dont les valeurs du modèle sont KF =0,79 et nF =1,90. Dans les mêmes conditions expérimentales, le pyrène, composé modèle à quatre noyaux du groupe des hydrocarbures aromatiques polycycliques (HAP), semble s'adsorber en formant des microcristaux à la surface de l'argile. La présence d'acide humique fixé sur la kaolinite modifie l'adsorption du pyrène, qui se modélise par une isotherme de Freundlich de paramètres K'F =0,30 et n'F =2,00.Les interactions entre le pyrène et l'acide humique dissous ont été quantifiées par spectroscopie d'extinction de fluorescence et relation de Stern-Volmer. La fraction humique dissoute non adsorbée sur le minéral argileux se caractérise par de plus fortes valeurs de Koc que l'acide humique initial (2,95.105 L.kg-1 contre 1,86.105 L.kg-1). L'hypothèse de fractionnement des substances humiques lors de l'adsorption sur l'argile est confirmée par les variations du poids moléculaire moyen des AH, déterminé par chromatographie d'exclusion stérique, et des variations des intensités de fluorescence des fractions chromatographiées.Les résultats obtenus pour la quantification du pyrène désorbé du solide argileux dans l'eau pure et dans une solution d'AH (50 mg.L-1) tendent à minimiser le rôle de la matière organique naturelle dissoute dans le transfert des polluants hydrophobes du milieu solide au milieu liquide.Humic substances become fixed to the surface of clay minerals and modify the adsorption sites of hydrophobic organic pollutants (HOP). The dissolved humic substances complex the HOP according to reversible binding mechanisms normally assessed by the Koc distribution coefficient. The humic solutes could thus be responsible of transporting HOP in aquatic ecosystems by solubilising the adsorbed fraction on sediment. Our study aims to quantify and model these phenomena using commercially available compounds:- pyrene, a polycyclic aromatic hydrocarbon (PAH) generally used as fluorescence probe and able to bind strongly to humic acid (AH); - a commercially available humic acid (Aldrich), with a high molecular weight and high aromaticity, which can easily adsorb onto colloidal matter and strongly bind PAH; - kaolinite clay, a ubiquitous mineral in aquatic systems, with a particle size distribution in aqueous solution similar to that observed in lake waters.We also have chosen physico-chemical conditions representative of freshwater: pH (6.5) and ionic strength (10-2 M). The adsorption isotherm of the humic acid (HA) on kaolinite at pH=6.5 and at ionic strength 10-2 M follows a Freundlich isotherm, for which model values are fixed at KF =0.79 and nF =1.90. The carboxylic groups of the dissolved HA, which represented more than half the total acidity, were not protonated under these conditions. Despite the negative surface charge of the particles, kaolinite was able to adsorb about 0.2 mgC.g-1 of HA. A decrease in the solution pH occurred as the adsorbed HA quantity increased, suggesting a chemisorption of HA onto clay. The high-pressure size exclusion chromatogram (HPSEC) of the non-adsorbed HA, isolated after centrifugation of the colloidal solution, reflects the selective adsorption of the HA. The higher the molecular weight of the HA (>70 000 Da), the better the adsorption. The hypothesis of the selective adsorption of the humic substances onto clay was also confirmed by the fluorescence variations of the chromatographed fractions.Using the same experimental conditions, pyrene seemed to adsorb and generate micro-crystals on the surface of the clay. The first part of the isotherm fits the pyrene monomer adsorption onto the hydrophobic siloxane surface of the clay. In the second part, the dramatic increase in the adsorption isotherm could be attributed to the formation of pyrene micro-crystals on the solid surface. For a residual pyrene concentration equal to 40 nmol.L-1, the PAH quantity adsorbed onto kaolinite clay (7 nmol.g-1) was about twenty times lower than the quantity adsorbed onto montmorillonite clay (150 nmol.g-1). This could be explained by the inaccessibility of the interlayer cavity of kaolinite to any solute.Natural colloids are often coated by a humic layer. This coating can thus modify HOP adsorption onto the particles. The presence of humic acid fixed on kaolinite effectively modifies pyrene adsorption. This adsorption can be modelled by a Freundlich isotherm with the parameters K'F =0.30 and n'F =2.00. The adsorbed HA molecules seem to limit the formation of pyrene micro-crystals, even if the pyrene adsorption is not competitive with the HA fixation. Indeed, no HA desorption occurs during pyrene fixation onto the organic coated kaolinite.The interactions between pyrene and dissolved humic acid have been quantified by extinction fluorescence spectroscopy and the Stern-Volmer relationship. The unabsorbed, dissolved humic fraction is characterised by Koc values higher than the initial humic acid (2.95 x 105 L.kg-1 compared to 1.86 x 105 L.kg-1). These two values are of the same magnitude as the published value obtained for the non-purified Aldrich HA (2.3±0.3 x 105). The Koc value obtained for the non-adsorbed fraction of HA is unexpected because of the low molecular weight of these molecules. This Koc value can be related either to a better accessibility of the HA hydrophobic cavity for pyrene, or rather to a more efficient fluorescence quenching of pyrene by the humic solutes.The dissolved humic acid may complex the non-ionic PAH according to reversible bonding mechanisms. Therefore, HA can act as a carrier of hydrophobic contaminants if it is able to desorb HOP from the surface of the particles. The results obtained for the quantification of the desorbed pyrene in pure water and in a HA solution (50 mg.L-1) tend to minimise the role of dissolved natural organic matter in the transport of hydrophobic pollutants from the solid to the liquid medium. The values of pyrene concentration in solution obtained after 24 hours contact with kaolinite clay sorbed pyrene with pure water or with the HA solution were very low (respectively 2.4 nM and 12.9 nM) and below the water solubility of pyrene (802 nM). It has been previously demonstrated that the desorption kinetics of pyrene from quartz material are not influenced by the organic matter content of the solution (SCHMITT, 1999). Our results demonstrate that the HA content of the solution did not greatly modify the quantity of pyrene desorbed from clay minerals

Polymer tracer detection systems with UV fluorescence spectrometry to improve product reyclability

The recycling of materials originating from end-of life products is essential to preserve our raw material resources, which are increasingly expensive and whose extraction is increasingly impactful for the environment.However, certain materials are still not recycled today. In the case of plastics, their recycling includes grinding, which generates complex mixtures. It is not possible to sort these mixtures and reach a high degree of purity with the existing physico-chemical processes. Automated sorting processes using near infrared spectroscopy are limited to dark-colored materials. One option is to add tracers to virgin materials to allow identification and rapid sorting of end-of-life products, using UV fluorescence spectrometry as the identification technique. The optimization of the polymer/tracer/detection system is based on several criteria: the reliability and speed of detection of UV fluorescence tracers added to a polymer matrix with carbon black, the relevance of the environmental impact of the tracers, and the preservation of the mechanical properties of the polymer with the tracers added.International audienceThe recycling of materials originating from end-of life products is essential to preserve our raw material resources, which are increasingly expensive and whose extraction is increasingly impactful for the environment.However, certain materials are still not recycled today. In the case of plastics, their recycling includes grinding, which generates complex mixtures. It is not possible to sort these mixtures and reach a high degree of purity with the existing physico-chemical processes. Automated sorting processes using near infrared spectroscopy are limited to dark-colored materials. One option is to add tracers to virgin materials to allow identification and rapid sorting of end-of-life products, using UV fluorescence spectrometry as the identification technique. The optimization of the polymer/tracer/detection system is based on several criteria: the reliability and speed of detection of UV fluorescence tracers added to a polymer matrix with carbon black, the relevance of the environmental impact of the tracers, and the preservation of the mechanical properties of the polymer with the tracers added

Polymer tracer detection systems with UV fluorescence spectrometry to improve product reyclability

The recycling of materials originating from end-of life products is essential to preserve our raw material resources, which are increasingly expensive and whose extraction is increasingly impactful for the environment. However, certain materials are still not recycled today. In the case of plastics, their recycling includes grinding, which generates complex mixtures. It is not possible to sort these mixtures and reach a high degree of purity with the existing physico-chemical processes. Automated sorting processes using near infrared spectroscopy are limited to dark-colored materials. One option is to add tracers to virgin materials to allow identification and rapid sorting of end-of-life products, using UV fluorescence spectrometry as the identification technique. The optimization of the polymer/tracer/detection system is based on several criteria: the reliability and speed of detection of UV fluorescence tracers added to a polymer matrix with carbon black, the relevance of the environmental impact of the tracers, and the preservation of the mechanical properties of the polymer with the tracers added.ANR TRIPTIC + RECOR

Etude de la dégradation photocatalytique de polluants organiques en présence de dioxyde de titane, en suspension aqueuse et en lit fixe.

La première partie de ce travail est consacrée à l évaluation de l efficacité photocatalytique de plusieurs semiconducteurs commerciaux. La comparaison est basée sur la détermination de leurs propriétés physiques: diamètre des particules, taille des cristallites, structure cristallographique, propriétés électroniques, composition chimique ainsi que capacité d adsorption. L efficacité photocatalytique est testée sur le phénol, un polluant modèle. Alors que ZnO présente une activité photocatalytique légèrement supérieure à celle des différents TiO2 étudiés, c est pour le TiO2 P25 que la plus faible résistivité a été observée. C est donc au sein de ce dernier que la circulation électronique est la meilleure. L existence de différentes formes cristallographiques pour le TiO2 est démontrée être également un autre paramètre fondamental gouvernant la réactivité. Si la partition anatase/rutile (80/20%) est donc importante, le fait que le TiO2-P25 soit formé d'un seul cristallite le semble tout autant, car c est tout le grain qui peut être considéré comme actif.Une seconde partie est dédiée à l étude de la dégradation photocatalytique d un colorant, le Vert Cibacron (RG12) utilisé dans l industrie textile. Le travail est réalisé en suspension aqueuse en présence de dioxyde de titane TiO2-P25. La décoloration de la suspension est effective après 90min de traitement et s accompagne d une minéralisation partielle de 60% pour une gamme de concentration initiale en RG12 entre 10-40 mgL-1. Pour déterminer le mécanisme général de la photocatalyse, des investigations thermodynamiques et cinétiques ont été menées sur l adsorption du colorant sur TiO2-P25. La chimisorption s est avérée être le processus spontané endothermique majoritaire se déroulant à la surface du photocatalyseur. La cinétique d adsorption suit globalement une loi de pseudo-ordre deux accompagnée d un mécanisme de diffusion intraparticulaire observé aux fortes concentrations (80-120 mgL-1) mettant en avant les mésopores du matériau. Un modèle faisant intervenir une adsorption compétitive des espèces à la surface du photocatalyseur a été élaboré. Les molécules de colorant, de sous-produits de dégradation, les molécules d eau et ions hydroxydes, ainsi que le dioxygène présent en solution et à la surface du TiO2 sont supposés entrer en compétition vis à vis des mêmes sites d adsorption. Il est alors observé que l inverse de la constante de dégradation photocatalytique du colorant dépend d un polynôme du second degré de la concentration initiale du colorant de départ.Afin de contrecarrer le problème récurrent de la filtration des suspensions aqueuses de TiO2, la fixation de TiO2 par la méthode PMTP sur des plaques de verre a été étudiée. La caractérisation des dépôts par MEB et DRX a permis de montrer que ceux-ci étaient homogènes. Les performances du TiO2 supporté ont été comparées au procédé photocatalytique classique en suspension aqueuse sur le colorant Vert Cibacron dans un réacteur à recirculation de 500 mL dont les conditions optimales de fonctionnement ont été déterminées. Le modèle précédent de compétition d adsorption des espèces à la surface du photocatalyseur, s est montré adapté à décrire les résultats expérimentaux comparativement au modèle de Langmuir-Hinshelwood.Enfin, le couplage photocatalyse/sonolyse a été examiné pour la dégradation du vert Cibacron. Le dosage des espèces actives générées par chaque technique a été réalisé. Une synergie est apparue lors du couplage de la photocatalyse sous irradiation solaire en présence d ultrasons 500 kHz.The first part of this work is dedicated to the evaluation of the photocatalytic efficiency of semiconductors ZnO, TiO2 P25, and two other titanium dioxides (anatase 100%). The comparison was based on determining the physical properties of photocatalysts, mainly: the particle diameter, crystallite size, crystallographic structure, electronic properties, chemical composition and the adsorption capacity. The photocatalytic efficiency was tested with phenol as target molecule. While comparable photocatalytic activity was found with ZnO and TiO2 P25, the lowest resistivity was observed with TiO2 P25, which means that a better electronic circulation occurs in this last photocatalyst compared to ZnO, but also that there is another fundamental parameter governing the reactivity. Under the same crystallographic form, 100% anatase, the photoreactivity of TiO2 is slightly higher with the photocatalyst having the lowest grain's diameter. The highest photoreactivity of TiO2 P25 can be explained by the partition anatase/rutile (80/20%), a higher electronic circulation and by the fact that TiO2 P25 is formed from a single crystallite, where any grains are considered as photoactive. Second part concerns the photocatalytic degradation of dye Cibacron Green (RG12) used by textile industry, in aqueous suspension in the presence of titanium dioxide TiO2 P25. Discoloration of the suspension was effective after 90min treatment with a partial mineralization 60% of the initial dye (10-40 mgL-1). To determine the general mechanism of the photocatalytic process, especially if the surface of the material is involved or not, thermodynamic and kinetic investigations were investiagted on adsorption. Chemisorption was found to be the majority endothermic spontaneous process occurring on the surface of the photocatalyst. Moreover, the adsorption kinetics follows a pseudo-second order law with a intraparticle diffusion mechanism which was observed at higher concentrations (80-120 mgL-1) highlighting the mesopores of TiO2. As the Langmuir-Hinshelwood, Ollis and Direct Indirect models were enable to fully describe our experimental results, a new model involving a competitive adsorption of species on the surface of the photocatalyst was developed. Dye molecules, byproducts of degradation, water molecules, hydroxide ions and the oxygen present in solution are assumed to compete with respect to the same sites of adsorption at the TiO2 surface. The model showed that the inverse of the constant of the dye photocatalytic degradation depended on a second degree polynomial of the initial concentration of initial dye. Binding experiments of TiO2 on glass plates by the method PMTP were carried out in order to work with supported TiO2 in a dedicated reactor having a recirculation of 0.5 L and where optimum operating conditions were determined. Characterization of deposits by SEM and XRD showed that they were homogeneous with a density of 0.26 mg TiO2/cm . Performances of the supported TiO2 were compared to the conventional photocatalytic process in aqueous suspension by studying the discoloration of the previous dye Cibacron green. The competitive adsorption model elaborated well described experimental results. Final examination was done by coupling photocatalysis and sonolysis for the degradation of Cibacron Green. The determination of the active species generated by each technique was performed. A synergy was observed under solar irradiation of TiO2 in the presence of 500 kHz ultrasound which could provide from an extensive mass transfer of the dye on the photocatalyst induced by ultrasounds.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Natural archives of long-range transported contamination at the remote lake Letšeng-la Letsie, Maloti Mountains, Lesotho

Naturally accumulating archives, such as lake sediments and wetland peats, in remote areas may be used to identify the scale and rates of atmospherically deposited pollutant inputs to natural ecosystems. Co-located lake sediment and wetland cores were collected from Letšeng-la Letsie, a remote lake in the Maloti Mountains of southern Lesotho. The cores were radiometrically dated and analysed for a suite of contaminants including trace metals and metalloids (Hg, Pb, Cu, Ni, Zn, As), fly-ash particles, stable nitrogen isotopes, polycyclic aromatic hydrocarbons (PAHs) and persistent organic pollutants such as polychlorinated biphenyls (PCBs), polybrominated flame retardants (PBDEs) and hexachlorobenzene (HCB). While most trace metals showed no recent enrichment, mercury, fly-ash particles, high molecular weight PAHs and total PCBs showed low but increasing levels of contamination since c.1970, likely the result of long-range transport from coal combustion and other industrial sources in the Highveld region of South Africa. However, back-trajectory analysis revealed that atmospheric transport from this region to southern Lesotho is infrequent and the scale of contamination is low. To our knowledge, these data represent the first palaeolimnological records and the first trace contaminant data for Lesotho, and one of the first multi-pollutant historical records for southern Africa. They therefore provide a baseline for future regional assessments in the context of continued coal combustion in South Africa through to the mid-21st century

Adsorption kinetics of 4-chlorophenol onto granular activated carbon in the presence of high frequency ultrasound

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Incidence de l’exposition pré- et périnatale aux PCBs sur les capacités intellectuelles des enfants

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Réactivité abiotique des PCB : application aux écosystèmes lacustres

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30 ans de suivi de la qualité physico-chimique et microbiologique de l’eau du Rhône en Savoie GRUTTEE

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