O objetivo do presente trabalho foi avaliar o impacto de diferentes variáveis no ensaio de dissolução intrínseca de metronidazol. Inicialmente, as amostras, com diferentes graus de micronização, foram submetidas à caracterização físico-química, sendo realizados ensaios de solubilidade, tamanho de partícula, análise térmica (DSC/ TG), infravermelho por transformada de Fourier (FTIR), difratometria de raios X (DRX), análise de área superficial pelo método BET, microscopia óptica, densidade verdadeira e densidade compactada. Na sequência, foram realizados os ensaios de dissolução intrínseca segundo um planejamento experimental do tipo fatorial fracionado, sendo cada fator avaliado em três níveis. Para o delineamento, utilizou-se o programa Statistica 8.0. e os fatores estudados foram: velocidade de rotação, pressão utilizada na formação do compactado do fármaco, meio de dissolução e grau de micronização. Os resultados mostraram alteração nas propriedades reológicas do material conforme o aumento do grau de micronização, enquanto as demais propriedades não foram afetadas. Entre os fatores estudados no delineamento, a velocidade de rotação e o meio de dissolução, foram aqueles que exerceram influência significativa na dissolução intrínseca do metronidazol. Embora a solubilidade do fármaco não sofra influência do tamanho de partícula, valores superiores foram observados em HCl 0,1 M, meio em que também foram obtidas as mais elevadas velocidades de dissolução intrínseca (VDIs). / The purpose of this study is to evaluate the impact of different variables in the intrinsic dissolution test of metronidazol. Initially, the samples, with different levels of micronization, underwent physicochemical characterization, whereby they were tested for solubility, particle size, thermal analysis (DSC/TG), Fourier transform infrared (FTIR) spectroscopy, X-ray diffractometry (DRX), surface area analysis by the BET method, optical microscopy, true density and tapped density. Then, intrinsic dissolution tests were carried out according to fractional factorial experimental planning, with each factor being evaluated on three levels. The Statistica 8.0 software program was used for design, and the factors studied were: rotational velocity, pressure used in the formation of the compressed drug, dissolution medium and level of micronization. The results indicated alterations in the rheological properties of the material, as the level of micronization increased, while the remaining properties were unaffected. Among the factors studied in the design, the rotation speed and the dissolution medium were the factors that exercised the most significant influence on the intrinsic dissolution of metronidazol. Although the solubility of the drug is not influenced by particle size, higher values were observed in HCl 0.1 M, the medium in which the highest intrinsic dissolution rates (IDRs) were also obtained.

A gênese, a química, a macro e micromorfologia dos solos desenvolvidos nos ambientes arenosos da planície costeira do Estado de São Paulo foram investigadas. Nesses ambientes, genericamente denominados de restinga, a podzolização é o processo pedogenético predominante, sendo os Espodossolos e Neossolos Quartzarênicos os solos mais comumente encontrados. Os municípios paulistas de Cananéia, Ilha Comprida e Bertioga foram selecionados para o desenvolvimento desta pesquisa devido à presença de diferentes unidades sedimentares, de vegetação remanescente e de solos, representativos da planície costeira do Estado de São Paulo. Nesses locais foram descritos e amostrados 31 perfis, muitos deles em cronosseqüência. A idade dos sedimentos e da matéria orgânica de horizontes cimentados selecionados (ortstein) também foram investigadas e, juntamente às análises químicas, incluindo procedimentos de dissolução seletiva do Fe e Al (DC, oxalato e pirofosfato para Fe e Al; NaOH, KCl, LaCl3 e CuCl2 para Al) e às micromorfológicas, permitiram concluir que: (a) os Espodossolos mais evoluídos e antigos, dotados de horizontes ortstein, podem ser considerados indicadores dos sedimentos pleistocênicos da Formação Cananéia das planícies costeiras quaternárias estudadas e, possivelmente, são paleossolos; (b) o tempo e o relevo foram os principais fatores de formação, condicionantes da diferenciação dos Espodossolos na paisagem; (c) os solos mais antigos, bem drenados devido às condições de relevo e dinâmica sedimentar (Ilha de Cananéia e Bertioga), apresentam grande variabilidade e diversidade de seus horizontes e atributos morfológicos, diferindo daqueles mais jovens e mal drenados, mais homogêneos, geralmente destituídos de horizonte Bs (Bertioga); (d) a química da maioria dos solos estudados são típicas daqueles já descritos para as áreas sob vegetação de restinga: baixas soma e saturação por bases, extremamente a fortemente ácidos, capacidade de troca de cátions dependente da matéria orgânica e saturada com Al trocável, aumento do carbono orgânico em profundidade; (e) o Al é o principal cátion envolvido na podzolização, sendo que suas formas ativas são: complexos de Alhúmus e compostos inorgânicos pouco cristalinos. Os primeiros predominam nos horizontes superficiais e horizontes espódicos hidromórficos; as formas inorgânicas se relacionam a alguns horizontes espódicos (Bs, Bh, Bhs e Bsm) situados na base de perfis bem drenados; (f) Al inorgânico pouco cristalino também foi extraído pelos reagentes pirofosfato e CuCl2, geralmente utilizados para avaliar Al unido à matéria orgânica; ao contrário, LaCl3 extraiu apenas as formas ativas da interação Al-húmus, sendo que KCl não incluiu todas essas formas reativas; (g) a decomposição de raízes in situ e, sobretudo, os processos de formação e transporte de complexos Al-húmus foram observados em alguns (decomposição de raízes) ou em todos os perfis estudados (complexos Al-húmus), originando os horizontes espódicos às expensas dos eluviais; (h) a imobilização desses complexos se dá por diferentes mecanismos: filtragem físicomecânica dos poros do solo, aumento do pH em profundidade, incorporação adicional de Al durante seu transporte e o efeito da absorção seletiva das raízes. Neste último processo, as raízes absorvem seletivamente água e nutrientes, segregando e precipitando ao seu redor os complexos Al-húmus da solução do solo, mobilizados dos horizontes superiores ou presentes nas águas de drenagem. / The genesis, chemistry and macro and micromorphology of soils developed on the sandy coastal plain of the São Paulo State were investigated. In these environments, often designated restinga, podzolization is the main pedogenetic process, being Spodosols and Quartzipsamments the soils most commonly found. Cananéia, Ilha Comprida and Bertioga cities were selected for the development of this research due to the representativeness of this environmental condition in the São Paulo State. In these environments 31 soil profiles were described and sampled, mainly in chronosequences. Age of sediments and of organic matter of cemented horizons (ortstein) were investigated as well. These data associated to the chemical analysis, including Fe and Al selective dissolution procedures (dithionite-citrate, oxalate and pyrophosphate for Fe and Al; NaOH, KCl, LaCl3 and CuCl2 for Al) and micromorphological analysis allowed the following conclusions: (a) the most developed Spodosols have ortstein horizons and can be considered indicators of sediments of Pleistocene age from the Cananéia Formation of the studied quaternary coastal plain and possibly are paleosols; (b) time and relief were the main soil formation factors responsible for differentiation of Spodosols on the landscape; (c) the oldest and well drained soils due to relief conditions and sedimentary dynamics (Cananéia and Bertioga) showed great variability and diversity of their horizons and morphological properties, differing from the youngest, poorly drained and more homogeneous Spodosols usually without Bs horizon (Bertioga). The youngest and well drained Spodosols (Ilha Comprida) showed an advanced degree of degradation; (d) the chemical properties of the studied soils are similar to other soils already described in the restinga: low in exchangeable bases, low in base saturation, strongly acidic, organic-matter dependent and Al-saturated CEC, increase in organic carbon with depth; (e) Al is main metal related to the podzolization process. The reactive forms of this element are Al-humus complexes and inorganic poorly crystalline compounds. Alhumus complexes predominate in the superficial and spodic, poorly drained horizons; the Alinorganic forms occur in some well drained spodic horizons (Bs, Bh, Bhs and Bsm) situated at the bottom of the well-drained soil profiles; (f) Al inorganic, poorly crystalline forms were extracted by pyrophosphate and CuCl2 reagents, usually used to determinate Al bound to organic matter; unlike, LaCl3 only extracted the reactive forms of Al-humus interaction, whereas KCl did not include these reactive forms; (g) Al-humus formation and mobilization were the main pedogenetic processes, but roots decomposition were observed in some horizons; (h) different mechanisms are related to Al-humus complexes immobilization: physical-mechanical filtering effect on soil pores, precipitation as pH increases with depth, precipitation with the decrease of C-to-metal ratio during organic matter complexation and roots selective absorption effect. In the latter, there is selective absorption of water and nutrients with segregation and precipitation of Al-humus complexes around roots. These Al-humus complexes are either mobilized from the superficial horizons or already dissolved in the draining water.

A leucemia mielóide crônica (LMC) é uma doença cujo marcador molecular é o rearranjo gênico BCR/ABL, original da translocação t(9;22), conhecida como cromossomo Philadelphia. Recentemente, os inibidores da enzima tirosina-quinase têm sido estudados e utilizados para o tratamento da LMC. Nesta classe, está o Mesilato de Imatinibe, uma pequena molécula que inibe competitivamente a BCR/ABL tirosina quinase, impedindo sua atividade. Por não possuir monografia publicada em compêndios oficiais, o objetivo deste trabalho foi avaliar o perfil in vitro de dissolução de comprimidos de mesilato em diferentes condições. A quantificação do fármaco foi feita utilizando a cromatografia líquida de alta eficiência em fase reversa (CLAE-FR) e as análises foram realizadas em uma coluna C18 Gemini Phenomenex®, utilizando como fase móvel tampão acetato de sódio 10,7 mmol/L, pH 3,0:metanol (40:60 v/v). O método foi validado e apresentou-se linear no intervalo de concentração de 10-150 µg/mL (r=0,9993). Os coeficientes de variação obtidos foram inferiores a 2,0 % e a exatidão próxima de 100 %. Também foram avaliados os parâmetros seletividade, robustez, estabilidade e limite de quantificação (10 µg/mL). A avaliação do perfil in vitro de dissolução foi realizada em três diferentes meios de dissolução (HCl 0,1 N, tampão acetato de sódio pH 4,5 e tampão fosfato de potássio monobásico pH 6,8), três velocidades de agitação (50, 75 e 100 rpm) e dois tipos de aparatos (pá e cesta). Os resultados obtidos neste teste indicaram que a forma farmacêutica em estudo é de liberação imediata, uma vez que foi verificada liberação de grande quantidade do fármaco em um curto período de tempo. A comparação dos perfis de dissolução, realizada através do cálculo da eficiência de dissolução, apresentou diferenças em relação à porcentagem do fármaco liberado. a condição mais adequada para avaliar o perfil in vitro de dissolução é o meio de dissolução HCl 0,1 N, aparato da pá e velocidade de agitação de 75 ou 100 rpm. / Chronic myeloid leukemia (CML) is a disease whose molecular marker is the BCR/ABL, original of the translocation t (9; 22), known as the Philadelphia chromosome. Recently, inhibitors of the enzyme tyrosine kinase have been studied and used for the treatment of CML. In this class, is the Imatinib mesylate, a small molecule that competitively inhibits BCR/ABL tyrosine kinase, preventing its activity. To do not have a monograph published in official compendia, the objective of this study was to evaluate the in vitro dissolution of tablets mesylate in different conditions. The quantification of the drug was made using high performance liquid chromatography on reversed phase (RP-HPLC) and analysis was performed on a Phenomenex® Gemini C18 column using a mobile phase of sodium acetate buffer 10.7 mmol/L pH 3.0:methanol (40:60 v/v). The method was validated and presented in a linear concentration range of 10-150 µg/mL (r=0.9993). The coefficients of variation obtained were below 2.0% and accuracy near 100%. We also evaluated the parameters selectivity, robustness, stability and limit of quantification (10 µg/mL). The evaluation of in vitro dissolution was conducted in three different dissolution media (0.1 N HCl, sodium acetate buffer pH 4.5 and potassium phosphate monobasic buffer pH 6.8), three agitation speeds (50, 75 and 100 rpm) and two types of devices (paddle and basket). The results of this tests indicated that the pharmaceutical form in question is immediate release, since it was observed release of large amounts of the drug in a short period of time. The comparison of dissolution profiles, conducted by calculating the dissolution efficiency, showed differences compared to the percentage of drug released. The best conditions to evaluate the in vitro profile of dissolution is the dissolution medium 0.1 N HCl, paddle apparatus and stirring speed of 75 or 100 rpm.

Revegetation of bauxite residue is hampered by a lack of understanding of the limitations imposed on plant growth in highly saline and alkaline growth mediums. In this study, several of these growth limiting factors were investigated. The toxicity of the hydroxyl ion (OH-) was examined using a solution culture system developed to allow studies at high pH without nutritional limitations. Also using this solution culture system, the effect of the high Na and Mg concentrations of bauxite residue on the Ca nutrition of plants was investigated. As the toxicity of Al at high pH is not known, a study was conducted to examine the rhizotoxicity of aluminate (Al(OH)4-) and polycationic Al at high pH. The ability of plant roots to reduce rhizosphere pH in bauxite residue was also considered. A novel gypsum application method was assessed for its efficiency at improving the Ca status of bauxite residue. Manual adjustment, ion exchange resins and automated titration were examined for their suitability for nutrient solution pH control in alkaline conditions. For short-term studies, it was found that a solution without supply of Cu, Fe, Mn and Zn, and aerated with CO2 depleted air, greatly reduced nutrient precipitation at high pH, thus eliminating nutritional differences between treatments. Manual pH adjustment and the use of ion exchange resins as pH buffers were unsuitable methods of pH control. In contrast, pH control by automated titration had little effect on solution composition while maintaining constant pH. The solution culture system was used to examine OH- toxicity in mungbeans (Vigna radiata (L.) Wilczek cv. Emerald), with root length reduced at a bulk solution pH of 8.5 and greater. The effect of Ca activity ratio (CAR) and pH on Ca uptake by mungbeans and Rhodes grass (Chloris gayana cv. Pioneer) in Na dominated solution cultures and in soil was investigated. Changes in pH in the alkaline range were shown to have no effect on the critical CAR of 0.024 (corresponding to 90 % relative root length) for mungbeans grown in solution culture. Results from soil grown mungbeans confirmed those from solution culture, with a critical CAR of 0.025. A critical CAR of 0.034 was also established for soil grown Rhodes grass. However, using dilute nutrient solutions dominated by Mg at pH 9.0, root growth was found to be more limited than had been observed for Na solutions, with growth reduced beneath a critical CAR of 0.050. Using a CAR equation modified with plasma membrane binding constants (to incorporate the differing antagonistic effects of Mg and Na), new critical CAR values were calculated for Na (0.56) and Mg (0.44) dominated solutions. This modified CAR equation permits the calculation of CAR irrespective of the dominant salt present. Solubilities of various gypsum sources and size fractions in seawater were studied to investigate the effectiveness of gypsum addition to the residue sand pipeline, rather than as a direct field application. The dissolution rate constant varied with gypsum source (analytical grade (AR) > phosphogypsum (PG) > mined gypsum (MG)) due to reactivity and surface area differences, generally reaching saturation within 15 s (AR) to 30 min (MG > 2.0). The ability of bauxite residue to remove Ca from solution (due to cation exchange and precipitation) was also examined; the quantity of the total solution Ca adsorbed was found to be small (5 %). These low rates of solution Ca adsorption, comparatively rapid dissolution rates, and long pumping times (20 min), preclude the application of gypsum to the residue sand/seawater slurry as a method for residue amelioration. Dilute, alkaline (pH 9.5) nutrient solutions were used to investigate the effects of aluminate (Al(OH)4-) on mungbean root growth. Although root growth in Al(OH)4- solutions was slightly limited, the symptoms associated with this growth reduction were observed to be similar to those caused by the Al13 polycation at concentrations lower than that which can be detected. Also, when roots displaying these symptoms were transferred to fresh Al(OH)4- solutions, no root tip lesions were observed, and root hair growth on the lateral roots improved. Thus, Al(OH)4- is considered to be non-toxic, with the observed reduction in root growth in solutions containing Al(OH)4- due to the gradual formation of toxic Al13 in the bulk nutrient solution resulting from the acidification of the alkaline nutrient solution by the plant roots. The effect of Mn deficiency in Rhodes grass and of legume inoculation in lucerne (Medicago sativa L. cv. Hunter River), on the rhizosphere pH of plants grown in highly alkaline bauxite residue was investigated. In response to Mn deficiency in residue sand, Rhodes grass was observed to increase acidification of its rhizosphere (being up to 1.22 pH units lower than the bulk soil). Due to its ability to fix atmospheric N2 rather than relying on soil N (NO3-) reserves, inoculated lucerne (1.75 pH unit decrease) was also found to acidify its rhizosphere to a greater extent than non-inoculated lucerne (1.16 pH unit decrease).

Revegetation of bauxite residue is hampered by a lack of understanding of the limitations imposed on plant growth in highly saline and alkaline growth mediums. In this study, several of these growth limiting factors were investigated. The toxicity of the hydroxyl ion (OH-) was examined using a solution culture system developed to allow studies at high pH without nutritional limitations. Also using this solution culture system, the effect of the high Na and Mg concentrations of bauxite residue on the Ca nutrition of plants was investigated. As the toxicity of Al at high pH is not known, a study was conducted to examine the rhizotoxicity of aluminate (Al(OH)4-) and polycationic Al at high pH. The ability of plant roots to reduce rhizosphere pH in bauxite residue was also considered. A novel gypsum application method was assessed for its efficiency at improving the Ca status of bauxite residue. Manual adjustment, ion exchange resins and automated titration were examined for their suitability for nutrient solution pH control in alkaline conditions. For short-term studies, it was found that a solution without supply of Cu, Fe, Mn and Zn, and aerated with CO2 depleted air, greatly reduced nutrient precipitation at high pH, thus eliminating nutritional differences between treatments. Manual pH adjustment and the use of ion exchange resins as pH buffers were unsuitable methods of pH control. In contrast, pH control by automated titration had little effect on solution composition while maintaining constant pH. The solution culture system was used to examine OH- toxicity in mungbeans (Vigna radiata (L.) Wilczek cv. Emerald), with root length reduced at a bulk solution pH of 8.5 and greater. The effect of Ca activity ratio (CAR) and pH on Ca uptake by mungbeans and Rhodes grass (Chloris gayana cv. Pioneer) in Na dominated solution cultures and in soil was investigated. Changes in pH in the alkaline range were shown to have no effect on the critical CAR of 0.024 (corresponding to 90 % relative root length) for mungbeans grown in solution culture. Results from soil grown mungbeans confirmed those from solution culture, with a critical CAR of 0.025. A critical CAR of 0.034 was also established for soil grown Rhodes grass. However, using dilute nutrient solutions dominated by Mg at pH 9.0, root growth was found to be more limited than had been observed for Na solutions, with growth reduced beneath a critical CAR of 0.050. Using a CAR equation modified with plasma membrane binding constants (to incorporate the differing antagonistic effects of Mg and Na), new critical CAR values were calculated for Na (0.56) and Mg (0.44) dominated solutions. This modified CAR equation permits the calculation of CAR irrespective of the dominant salt present. Solubilities of various gypsum sources and size fractions in seawater were studied to investigate the effectiveness of gypsum addition to the residue sand pipeline, rather than as a direct field application. The dissolution rate constant varied with gypsum source (analytical grade (AR) > phosphogypsum (PG) > mined gypsum (MG)) due to reactivity and surface area differences, generally reaching saturation within 15 s (AR) to 30 min (MG > 2.0). The ability of bauxite residue to remove Ca from solution (due to cation exchange and precipitation) was also examined; the quantity of the total solution Ca adsorbed was found to be small (5 %). These low rates of solution Ca adsorption, comparatively rapid dissolution rates, and long pumping times (20 min), preclude the application of gypsum to the residue sand/seawater slurry as a method for residue amelioration. Dilute, alkaline (pH 9.5) nutrient solutions were used to investigate the effects of aluminate (Al(OH)4-) on mungbean root growth. Although root growth in Al(OH)4- solutions was slightly limited, the symptoms associated with this growth reduction were observed to be similar to those caused by the Al13 polycation at concentrations lower than that which can be detected. Also, when roots displaying these symptoms were transferred to fresh Al(OH)4- solutions, no root tip lesions were observed, and root hair growth on the lateral roots improved. Thus, Al(OH)4- is considered to be non-toxic, with the observed reduction in root growth in solutions containing Al(OH)4- due to the gradual formation of toxic Al13 in the bulk nutrient solution resulting from the acidification of the alkaline nutrient solution by the plant roots. The effect of Mn deficiency in Rhodes grass and of legume inoculation in lucerne (Medicago sativa L. cv. Hunter River), on the rhizosphere pH of plants grown in highly alkaline bauxite residue was investigated. In response to Mn deficiency in residue sand, Rhodes grass was observed to increase acidification of its rhizosphere (being up to 1.22 pH units lower than the bulk soil). Due to its ability to fix atmospheric N2 rather than relying on soil N (NO3-) reserves, inoculated lucerne (1.75 pH unit decrease) was also found to acidify its rhizosphere to a greater extent than non-inoculated lucerne (1.16 pH unit decrease).

L'objectif de cette étude est d'évaluer la réactivité abiotique de l'hydrogène dans un site de stockage géologique de déchets radioactifs en formation argileuse. Nous montrons que l'hydrogène est un agent réducteur pouvant être impliqué dans des réactions d'oxydoréductions sous contrôle cinétique avec certaines espèces oxydées de la formation hôte du stockage. Le système soufre apparait tout particulièrement réactif vis-à-vis de la perturbation redox induite par la présence d'hydrogène, sa déstabilisation se traduit notamment par une importante production de sulfure. Notre étude expérimentale sur la réduction des sulfates par l'hydrogène montre que cette réaction ne peut pas être à l'origine de cette production de sulfure. En effet les temps de demi-vie pour les sulfates sont de l'ordre de 200.000 ans à 90°C et l'énergie d'activation de la réaction est très élevée (131 kJ/mol). Par contre, la pyrite est un oxydant potentiel pour l'hydrogène. Nous montrons que cette dernière réaction est possible sur de courtes périodes de temps dés 90°C. A des pH légèrement alcalins tels que ceux de l'eau porale d'une formation argileuse formation et des températures comprises entre 90 et 180°C, cette réaction conduit à la précipitation de pyrrhotite et à la production d'H2S. Nous proposons une loi de vitesse pour cette réaction pouvant être intégrée dans des simulations numériques évaluant la sûreté du stockage à long terme.

La magnésite (MgCO3) est la forme anhydre la plus stable d'une série de carbonates de magnésium qui présentent différents degrés d'hydratation. Malgré sa rareté dans les environnements naturels, elle constitue une phase minérale fondamentale pour le piégeage minéral permanent du CO2. La détermination expérimentale des vitesses de précipitation et de dissolution de la magnésite dans des conditions représentatives de la séquestration géologique est donc fondamentale pour l'estimation du potentiel de séquestration de CO2 par cette phase dans les basaltes et dans les roches ultrabasiques et pour l'optimisation des procédés de stockage du CO2. Nous avons mesuré les vitesses de précipitation de la magnésite en utilisant des réacteurs à circulation et des réacteurs fermés, en fonction de la température (100 ≤ T ≤ 200 °C), de la composition de la solution aqueuse et de la pression partielle de CO2 (de 0 à 30 bar). Les vitesses mésurées sont indépendantes de la force ionique de la solution pour 0.1 M < I < 1.1 M, mais elles diminuent significativement avec l'augmentation de l'activité des ions CO32- pour des pH supérieures à 8. Les vitesses mesurées dans les réacteurs à circulation sont cohérentes avec le modèle de coordination chimique surfacique de Pokrovsky et al. (1999) selon lequel les vitesses de précipitation de la magnésite sont proportionnelles à la concentration des sites surfaciques >MgOH2+. L'étude des vitesses de cristallisation conduite par microscopie à force atomique hydrothermale (HAFM) a montré un bon accord entre les vitesses déduites de mesures microscopiques et les vitesses macroscopiques et a aussi démontré que la précipitation de la magnésite s'effectue selon un mécanisme de croissance spirale. Suivant les observations effectuées par AFM, ce mécanisme contrôle la vitesse de croissance de la magnésite dans un grand intervalle de température et d'indice de saturation (15≤ Ω ≤ 200 pour 80 ≤ T < 120 °C). En raison de l'inhibition de la précipitation de la magnésite par les ions carbonates, il est recommandé d'opérer sous des pressions partielles de CO2 assez élevées, ce qui présente en outre l'avantage d'accélérer la cinétique de dissolution des silicates magnésiens, grâce à l'acidification de la solution par le CO2. La détermination des vitesses de dissolution de la magnésite dans des réacteurs à circulation à 150 et 200 °C et en milieu neutre à alcalin nous a permis d'améliorer le modèle de complexation de surface et d'étendre son application aux températures considérées. La diminution des vitesses de dissolution observée de 150 à 200 °C peut être expliquée par l'augmentation, en fonction de la température, de la carbonatation et de l'hydrolyse des sites >MgOH2+ qui contrôlent la vitesse de dissolution de la magnésite. Des températures supérieures à 100 °C qui entrainent une diminution de la vitesse de dissolution de la magnésite et des autres carbonates sont donc favorables au stockage de CO2 sous forme dissoute dans les aquifères profonds riches en minéraux carbonatés. L'utilisation d'une cellule à électrodes d'hydrogène (HECC) nous a permis de préciser les données cinétiques à proximité de l'équilibre grâce à la détermination précise du produit de solubilité de la magnésite en fonction de la température (50-200 °C). De plus, ces mesures nous ont permis de générer les propriétés thermodynamiques de la magnésite et de les comparer à celles obtenues par mesures calorimétriques et par équilibres de phases. Les résultats de cette étude représentent une importante contribution à la compréhension des cinétiques de réaction des minéraux carbonatés dans les systèmes hydrothermaux et permettent de proposer une base de données essentielle pour la quantification des réactions de dissolution/précipitation des carbonates dans les systèmes complexes. En outre, ce travail fournit des contraintes cinétiques pour la modélisation géochimique des processus de séquestration du CO2 et sera utile à l'évaluation de l'impact et des risques liés au stockage de CO2 à long terme.

One of the key research issues in surface geochemistry is to understand the processes responsible of the surface water compositions to both improve fundamental knowledge of controlling mechanisms and protection of water resources. Processes occurring at solid-solution interface are predominant among the known involved chemical mechanisms. Solids, such as soil colloids, particles, sediments or colloids occurring as suspension in waters, present very large specific surfaces. This latter point gives them strong complexation or sequestration properties for elements such as metals, trace elements...These solids include mineral (oxyhydroxydes Fe and Mn, silicates, carbonates ...), organic colloid (humic substances...) and biological cells (algae, bacteria...) bound or not in between them. Sorption, co-precipitation and surface precipitation are the three major processes at interfaces involving these solid surfaces. They partly control the mobility and dissolved concentrations of metals and trace elements in waters and soil solutions. However, these processes are themselves controlled by physico-chemical parameters such as pH, Eh, T..., the solid nature and the interactions in between. The present work has therefore been focused on assessing the influence of these factors on the reactivity of elements at solid/solution interfaces. To address this issue, a combined approach involving laboratory experiments and modelling to answer to the questions identified in the field, was used. Firstly, the impact of redox condition variations on the mobilization of metals sourced in minerals (natural and synthetic oxyhydroxydes Fe and Mn, and slags from metallurgic industry) was experimentally evaluated. In a second step, this work was focused on the in situ monitoring of the iron cycle in a natural wetland soil. This implied the development of an innovative tool allowing the insertion of synthetic iron oxides directly in soil horizons. This research has been conducted to identify the impact of the iron oxides reductive dissolution and/or mineralogical changes on the mobilization of associated trace elements. Since organic matter release is often linked to iron reductive dissolution in wetland soil solutions, two experimental studies were also conducted: (i) on the redox condition impact on the dynamics of organic matter and trace element mobility and (ii) on the impact of organic complexation on the rare earth element (REE) speciation in solution. This work is ended by a research project dedicated to the rare earth element partitioning at solid-water interface and its impact on REE geochemical behaviour and associated fingerprinting properties.

L'objectif de cette étude est d'évaluer le comportement à long terme d'une nouvelle matrice de conditionnement des actinides mineurs à structure apatitique. La résistance à l'altération aqueuse des minéraux à structure apatitique a été étudiée à partir de l'étude combinée d'une fluorapatite naturelle et d'une britholite synthétique contenant un atome de néodyme pour simuler la présence d'actinides trivalents. La surface minérale a été caractérisée à partir d'une approche combinant des mesures électrocinétiques, potentiométriques et spectroscopiques, et les vitesses de dissolution ont été mesurées en réacteurs ouverts et fermés dans différentes conditions d'altération. Les résultats suggèrent que les minéraux apatitiques se dissolvent suivant 1) libération des fluors, 2) libération des cations localisés dans les sites I, et 3) la rupture des liaisons Ca-O permettant la libération des cations II et des phosphates. Une équation cinétique basée sur la TST a été établie pour rendre compte de la dissolution de la fluorapatite naturelle et de la britholite synthétique en fonction des conditions d'altération. La concentration aqueuse de néodyme est contrôlée par la précipitation de rhabdophane.

Les études géophysiques identifient une partition entre segments à comportement sismique et segments à comportement asismique le long des grandes failles actives californiennes. Il a été proposé que la présence des serpentinites le long de certains segments soit une cause potentielle d'un fluage asismique à ces endroits. Afin d'améliorer nos connaissances sur les mécanismes de déformation des serpentinites dans ce type de contexte, nous avons réalisé une étude des structures de déformation naturelles dans ces roches, collectées dans le réseau de failles actives de San Andreas (Californie). Le couplage de plusieurs techniques (microscope pétrographique, MEB, MET, microsonde) a été nécessaire pour préserver les informations au cours des changements d'échelles d'observations. Les serpentinites hors des zones cisaillées offrent des indices de leur histoire, antérieurement à la tectonique actuelle. L'étude détaillée des veines a permis, d'une part, une bonne caractérisation des textures optiques complexes classiquement rencontrées dans ces roches et, d'autre part, une meilleure compréhension des mécanismes de croissance des serpentines dans les interstices et les fractures ouvertes. Des effets capillaires pourraient faciliter la cristallisation dans des interstices de l'ordre du micron en permettant la mise en place d'un transfert de matière par diffusion en phase aqueuse depuis l'encaissant vers la veine. Ce mécanisme a été proposé pour expliquer la formation de veines fibreuses à ouverture lente ou saccadée (crack-seal). En revanche, les fractures ouvertes seraient nourries grâce à un transport advectif des éléments au sein d'un fluide. La précipitation serait alors permise par la chute de la solubilité du soluté au contact d'un encaissant relativement plus froid. La cinétique de croissance apparaît comme un facteur déterminant sur les conditions d'occurrence relative des différents types de serpentines représentés (lizardite et chrysotile), ce qui relativise le rôle des facteurs thermodynamiques classiques (pression et température). La déformation des serpentinites dans les failles naturelles, caractérisées par un taux de déformation lent et la présence de fluides, est très localisée, soit dans une zone de gouge, soit sur un plan de faille brillant. La déformation y est accommodée, respectivement, par un mécanisme de fluage par dissolution-cristallisation (glissement stable) et des épisodes de glissement fragiles instables (magnitudes faibles, M<0). Cela aboutit à un comportement globalement asismique des serpentines à l'échelle des failles actives.