Ce travail de thèse s’inscrit dans un projet de grande envergure piloté par l’IRT M2P, intitulé « Hard Chrome by Trivalent Chromium » qui regroupe 15 partenaires industriels et 2 partenaires académiques. L’objectif principal est de substituer les composés du chrome hexavalent par des électrolytes à base de chrome trivalent dans les procédés de chromage « dur », en réponse à l’application du règlement européen REACH en septembre 2017, même si des demandes d’autorisations temporaires sont en cours. Dans le cadre de cette thèse, des études électrochimiques ont été réalisées sur des bains commercial et synthétique. Celles-ci ont conduit au choix d’un matériau jouant le rôle d’anode, à une meilleure compréhension des mécanismes mis en jeu et de ce fait à une optimisation des conditions d’utilisation du bain commercial. D’autre part, une étude approfondie des courbes transitoires permet de mieux appréhender le comportement des électrolytes de chrome trivalent vis-à-vis des courants pulsés. Ainsi, un plan d’expérience sur les paramètres des pulses avec pour sortie de multiples caractérisations des dépôts de chrome montre que les courants pulsés influent sur plusieurs propriétés telles que : la teneur en carbone, la structure cristalline, la microdureté, la morphologie de surface et la microfissuration. Grâce au traitement des données issues du plan d’expériences, l’optimisation des paramètres de polarisation aboutit à l’élaboration de séquences de pulses optimisées. L’utilisation de celles-ci, employées seules ou en combinaison avec d’autres séquences de pulses issues également du plan d’expériences, aboutit à l’obtention de dépôts de chrome trivalent dont les propriétés sont modulables en fonction des paramètres procédés. Dans l’optique de la mise en place d’une nouvelle stratégie de choix des paramètres de l’impulsion anodique, un dispositif permettant la mesure du pH local en fonction des séquences et à proximité immédiate de la surface a été élaboré. Les premières tendances confirment les modes d’action des courants pulsés, et les choix qui ont été faits pour l’optimisation. / This thesis work is part of an ambitious project handled by IRT M2P, named “Hard Chrome by Trivalent Chromium” which gathers 15 industrials partners but also 2 academic partners. The main objective is to substitute the hexavalent chromium compounds in hard chromium electroplating process before there ban by European instances (REACH, ECHA) in September 2017, excepted for those authorized. As part of this thesis, electrochemical studies were realized on commercial and synthetic baths. Thanks to this studies, a material has been chosen to act as an anode for the making of the trivalent chromium coatings ; furthermore, the utilization conditions of the commercial bath has been optimized. Moreover, another study based on transient curves allows a better comprehension of the behaviour of the trivalent chromium electrolytes regarding pulsed current. This work permitted the elaboration of pulse sequences in the form of an experimental design. The realization and characterization of trivalent chromium coatings as a part of the experimental design show that pulsed current have an effect on several properties of the coatings such as carbon content, crystalline structure, microhardness, surface morphologies an microcracking. Thanks to the analyses of the results from the experimental design, an optimization of pulsed current has been made to obtain optimized pulse sequences. The utilization of those pulse sequences, used alone or combine with some pulse sequences of the experimental design lead to the elaboration of trivalent chromium coatings which properties are adjustables depending on the set parameters of the process. To further optimize the properties of the coatings, the basis of an analysis tool based on local pH measurements are developed; this analysis tool must make it possible to select the most interesting pulse sequences for the realization of trivalent chromium coatings.

Research efforts in aquatic toxicology have historically centered on the chemical analyses and toxic effects of waters to aquatic organisms. More recently, sediment-source toxicity has been explored, with efforts concentrated on establishing sensitive and accurate methodologies. This study focused on the toxicity of trivalent chromium, hexavalent chromium, and fluoranthene to Pimephales promelas, Ictalurus punctatus, and Lepomis macrochirus. Test fish were exposed to both water-borne and sediment-source toxicants for 96 hours (h) and 30 days (d). A 96-h and 30-d LC50 (mg/L Cr, ug/L Fluoranthene) was determined for each fish species exposed to aqueous toxicants. In addition, 96-h and 30-d LC50s were determined for each fish species from sediment chromium concentrations (mg/kg) and sediment fluoranthene concentrations (ug/kg). Although lethality endpoints were used throughout this research, acute effects other than mortality were determined for Lepomis macrochirus exposed to hexavalent chromium. Lethal toxicity values (96-h and 30-d LC50 and their 95% confidence limits) for trivalent chromium could not be determined since trivalent chromium concentations above 6.0 mg/L could not be obtained at water pHs compatible with these fish species. Trivalent chromium addition to test waters at pHs compatible with fish survival resulted in a chromium precipitate that was not lethal to test fish. In contrast, fathead minnows, channel catfish, and bluegill sunfish exposed to hexavalent chromium in water and sediments experienced mortality. Fathead minnows exposed to fluoranthene in water for 96h demonstrated a maximum mortality of 69%, while 100% mortality was achieved with channel catfish in similar tests. Sediment tests with fluoranthene resulted in 100% mortality with both fathead minnows and channel catfish.

Ph. D. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology. / Driven by the need of sustainably sourced catalysts and the use of reaction systems that generate environmentally benign by-products, the present study aimed to deposit stable, dispersed palladium (Pd) nanoparticles on the modified surfaces of granular macadamia nutshell (MNS) biomass for catalytic reduction of hexavalent chromium [Cr(VI)] to trivalent chromium [Cr(III)]. Through wet impregnation with Pd(II) ions and subsequent hydrazine-mediated reduction to Pd(0), Pd nanoparticles were embedded in a scaffold of polyethyleneimine grafted on bleached MNS previously coated with a chemically bound layer of polyglycidyl methacrylate. Visualization and imagery from scanning electron microscopy showed the formation of different layers of the polymeric coating and dispersed palladium resulting from surface modification and palladium nanoparticle synthesis, respectively. X-ray diffraction, energy-dispersive X-ray spectroscopic analysis confirmed the formation of Pd on the modified MNS surface. An estimate of 5.0 nm for crystallite size was calculated by application of the Scherrer equation. The composite material, denoted Pd@PEI-MNS, exhibited catalytic activity in formic acid-mediated Cr(VI) reduction. Through a one-factor-at-a-time experimental design, the activity of the Pd@PEI-MNS was illustrated to be dependent on solution pH; initial Cr(VI) concentration, initial formic acid concentration, and presence of competing anions; Pd@PEI-MNS dose; and temperature. Subsequent modeling of the Cr(VI) removal process by response surface methodology revealed that the most influential factor was Pd@PEI-MNS dose followed by temperature and formic acid concentration. The influence of initial Cr(VI) concentration, was surpassed by the dose-temperature and dose-formic acid concentration interactive effects. Elucidation of the Cr(VI) removal mechanism by XPS and FTIR demonstrated the active participation of surface -CH2OH functional groups, the bulk of which originated from the reduction of esters of the grafted ligands. Replacement of formic acid to carbon dioxide, the -CH2OH groups were converted to -COO- groups.

Made available in DSpace on 2017-07-10T18:08:10Z (GMT). No. of bitstreams: 1 Neiva Martin.pdf: 2565426 bytes, checksum: 9ed40e36b9798ff30f3a52b416d705e9 (MD5) Previous issue date: 2008-10-08 / In this work, the chromium ions bioaccumulation experiment was carried out using three species of aquatic macrophytes: Salvinia auriculata, Pistia stratiotes and Eicchornia crassipes, in order to confirm the hexavalent chromium detoxification during the biosorption process. Previously, a chromium speciation test based on chemical extraction of trivalent chromium from hexavalent chromium-doped hydroponic solutions was also performed at different pH, in order to verify if the nutritive solution pH could be responsible by the natural reduction of oxidation state on chromium before the biosorption process by the plants. No reduction from Cr(VI) to Cr(III) was observed at all solution pH. Based on the peculiar characteristics of High Resolution X-ray Fluorescence technique (HR-XRF), which allows to measure the X-ray Kß spectral line energy with good energy resolution (around 2,0 eV) for the transition metal region, the change on oxidation state of hexavalent chromium was possible to study through the Kß1,3, Kß2,5 and Kß spectral lines, which bring up information on chromium oxidation state and chemical environment. The HR-XRF measurements were performed at the XRD1 vacuum chamber available in the National Laboratory of Synchrotron Light, located near Campinas city. After collection, dry roots and chromium compound standard were prepared in compact disk by pressing. Each sample disk, spherical curved analyzer, and radiation detector were placed in a circle of Rowland within an arrangement of Johann. Another radiation detector was also used to monitoring of monochromatic X-ray beam intensity during the measurements. All the samples were irradiated by a 6.1 keV monochromatic X-ray beam. All the emission spectra were normalized to the monitor counts, and subtracted the organic matrix contribution and chromium absorption edge. Based on the spectral Kß2,5 peak intensity of roots and standard samples, the total chromium uptake concentration in plant was calculated, indicating that there is approximately 1.0 % of chromium per dry biomass after 27 days of experiment. When both Cr-Kß spectra of macrophytes roots with Cr(III) and Cr(VI) treatment were compared, their spectral Kß2,5 peak were identical in energy and width for the three aquatic plants, suggesting that the chromium reduction from hexavalent to trivalent form have occurred in all cases studied. The peak width at half maximum for Kß2,5 in all root samples were slightly larger than the chromium compound samples, which can be explained by the fact that there is the possibility to have different ligands to chromium ions inside the biological structure of roots. Based on these results, the chromium detoxification from hexavalent to trivalent form have actually happened during the biosorption of chromium into the macrophytes roots. Finally, these aquatic macrophytes have a great potential to detoxificate and accumulate of chromium ions that can be very useful to the metal removal from industrial effluents. / Neste trabalho foi feito o experimento de bioacumulação do cromo trivalente e hexavalente por três espécies de macrófitas aquáticas: Salvinia auriculata, Pistia stratiotes e Eicchornia crassipes, visando verificar a ocorrência do processo de redução do Cr(VI) durante a biossorção. Previamente, um teste de especiação de cromo baseado em extração química do cromo trivalente a partir de uma solução hidropônica dopada com cromo hexavalente, foi realizado em diferentes pHs, para verificar se o pH da solução nutritiva pode ser o responsável pela redução natural do estado de oxidação do cromo antes do processo de biossorção pelas plantas. Não foi observada a redução do Cr(VI) para Cr(III) no pH da solução de cultivo. Pelas características da técnica de Fluorescência de Raios-X de Alta Resolução em Energia (HR-XRF), que permite medir a energia das linhas espectrais de raios X Kß com alta resolução em energia (em torno de 2,0 eV) para a região dos metais de transição, foi possível estudar a mudança do estado de oxidação do cromo hexavalente através das linhas espectrais Kß1,3, Kß2,5 e Kß , que traz informação sobre o estado de oxidação do metal e seu ambiente químico. As medidas de HR-XRF foram realizadas na câmara de vácuo XRD1, no Laboratório Nacional de Luz Síncrotron, em Campinas. Após a coleta, discos compactados de raízes secas e padrões de compostos de cromo foram preparados. Cada disco de amostra, o analisador esférico, e o detector de radiação foram acomodados em um círculo de Rowland com arranjo de Johann. Durante as medidas, um detector foi usado para monitorar a intensidade do feixe de raios X monocromáticos incidentes. Todas as amostras foram irradiadas com feixe monocromático de 6,1 keV. Os espectros de emissão foram normalizados pelas contagens do monitor, e subtraída as contribuições da matriz orgânica e da borda de absorção do cromo. Baseado na intensidade da linha espectral Kβ2,5 das amostras de raízes e padrões, a concentração de cromo total nas plantas foi calculada, indicando que esta é de aproximadamente 1,0% por biomassa seca após 27 dias de experimento. Os espectros de emissão Cr-Kß das raízes das macrófitas tratadas com Cr(III) ou Cr(VI) foram comparados, e as suas linhas espectrais Kβ2,5 mostraram-se idênticas em energia e largura para as três plantas aquáticas, sugerindo que a redução do cromo, de hexavalente para trivalente, ocorreu em todos os casos estudados. A largura do pico para a linha espectral Kß2,5 em todas as amostras de raízes mostrou-se maior que nas amostras de compostos de cromo, o que pode ser explicado pelo fato de que é possível haver diferentes ligantes para o íon cromo na estrutura orgânica das raízes. Baseado nesses resultados, a redução do Cr(VI) para Cr(III) ocorreu durante o processo de biossorção do cromo pelas raízes das macrófitas aquáticas. Desta forma, verifica-se que estas macrófitas têm um grande potencial para detoxificar e acumular íons cromo, podendo ser utilizada com eficiência na remoção de metais em efluentes industriais.