Made available in DSpace on 2014-06-11T19:28:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-02-18Bitstream added on 2014-06-13T20:37:31Z : No. of bitstreams: 1 camargo_la_me_jabo.pdf: 1106150 bytes, checksum: d8d5b3f2596351c9b11f923ae4b5fc44 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Os atributos mineralógicos e físicos possuem dependência espacial e a distribuição espacial destes atributos possui relação com as formas do relevo. O objeto deste trabalho foi avaliar os atributos mineralógicos da fração argila e os atributos físicos de um argissolo em curvaturas do relevo, assim como avaliar a correlação entre esses atributos. Uma malha de dimensão 100 x 100 m foi delimitada em uma área caracterizada pela forma convexa e outra pela fôrma côncava. As malhas possuem espaçamento regular de 10 x 10 m e os pontos de cruzamento deste espaçamento determinaram os pontos de coleta das amostras, num total de 121 pontos amostrais georreferenciados em cada malha. Os atributos físicos foram avaliados nas profundidades 0,0- 0,2 e 0,2-0,4 m e os atributos mineralógicos na profundidade 0,0- 0,2 m. Os atributos físicos analisados foram diâmetro médio ponderado, diâmetro médio geométrico, agregados maiores que 2 mm, agregados entre 2 e 1 mm , agregados menores que 1 mm, microporos, macroporos, volume total de poros, densidade do solo, resistência do solo à penetração e teor de água no solo, já os atributos mineralógicos da fração argila foram largura a meia altura, diâmetro médio do cristal dos óxidos de ferro, da caulinita e gibbsita, substituição isomórfica e área de superfície específica da hematita e goethita. Os teores da goethita e hematita e razão goethita/(goethita+hematita) e razão caulinita/(caulinita+gibbsita) também foram calculados. Os dados foram submetidos às análises estatísticas e geoestatísticas para avaliação da variabilidade espacial e influência das curvaturas nestes atributos. Para avaliação da relação entre os atributos da mineralogia e físicos realizaram-se as análises de correlação simples e espacial. Os atributos físicos e mineralógicos apresentaram-se dependentes das curvaturas do relevo... / The mineralogicals and physical attributes have spatial dependence and the distribution of these attributes has relation with the forms of relief. The object of this study was to evaluate the attributes of clay mineralogy and the physical attributes of an argissol in curvatures of relief, as well as assess the correlation between these attributes. A grid size of 100 x 100 meters was defined in an area characterized by the convex shape and another in an area characterized by the concave shape. The grids have regular spacing of 10 x 10 m and the spacing of the points of intersection determine the points of collection of samples, a total of 121 georeferenced sample points in each grid. The physical attributes were evaluated in depth from 0.0 - 0.2 and 0.2 -0.4 m and the mineralogical attributes in depth 0,00-0,20 m. The physical attributes were analyzed: mean weight diameter, mean geometric diameter, aggregates larger than 2 mm, aggregates between 2 and 1 mm, aggregates smaller than 1 mm, microporosity, macroporosity, total porosity, bulk density, penetration resistance and water content in soil. The attributes of minerals were: width at half height, average diameter of crystals of iron oxides and kaolinite and gibbsite and isomorphic substitution and specific surface area of hematite and goethite. The contents of goethite and hematite and ratio goethite / (goethite + hematite) [Gt / (Gt + Hm)] and ratio kaolinite / (kaolinite + gibbsite) [Ct / (Ct + Gb)] were also calculated. Data were subjected to statistical and geostatistical analysis to evaluate the spatial variability and influence of these curvatures on these attributes. To assess the relation between mineralogy and physical attributes simple and spation correlation analysis where made. The physical and mineralogical attributes and depend on the curvature of the relief. There was also the influence of crystallinity of goethite and gibbsite in soil physical.

For the safety assessment of high-level nuclear waste repositories, it is mandatory to know the transportation paths of contaminants, e.g. actinyl ions, in the geological barrier. The most attention needs to be focused on the transport in aquifers, because water contamination, depending on retention and migration processes of radionuclides in the geosphere, is of primary environmental concern. The migration behavior of actinides in ground water is mainly controlled by aquatic speciations and sorption processes at water-mineral interfaces. Hence, the investigation of complexspecies in aqueous solutions and at mineral surfaces becomes essential for the safety assessment in the near and far field of nuclear repositories. For deep ground repositories, clay and clay minerals are considered as possible host rocks, because they show a low permeability and are expected to have a high retention capacity towards actinyl ions. But the complexity of naturally occurring minerals in particular their surface often hampers the unequivocal interpretation of results obtained from sorption experiments. The use of model phases only showing one particular functional group at the surfaces with a well defined surface topology is an appropriate approach for the understanding of the basic sorption processes. Aluminum oxide and hydroxides are of special interest because they represent main components in clays and clay minerals. In particular, gibbsite is widely used as a model system because it represents not only the most common crystalline aluminum hydroxide but also a ubiquitous weathering product of alumosilicates. Furthermore, the elemental structural unit of gibbsite, that is the Al(OH)6 octahedron, occurs ubiquitously as part of the structure of common clay minerals like kaolinite. In the present study, the sorption processes of U(VI) and Np(V) on gibbsite were studied under consideration of the aqueous speciation.

Several recent studies that have proposed MUSIC models for gibbsite surfaces have purported to achieve a very good fit with potentiometric titration data. However, in order to achieve such results, several significant parameters, such as the number of surface sites, site densities, and pKa values were sometimes re-introduced in the model as fitted parameters, and physically unrealistic modeling assumptions were sometimes used. In addition, recent evidence supports the idea that some of the gibbsite potentiometric titration data from these studies may be unreliable. In order to re-interpret the potentiometric titration data, we used several recently published methods. In order to detect possible problems with estimates of gibbsite basal and edge surface area, we synthesized two gibbsite samples with different aspect ratios and characterized their surface areas using BET, AFM, and computerized image analysis routines. We also estimated pKa values for acid/base reactions at gibbsite surfaces by applying a new bond-valence method to gibbsite (001)-type and (100)-type surface structures based on ab initio calculations. The resulting pKa estimates are not to be taken as precise values due to difficulties and assumptions associated with calculating reasonable ab initio surface structures. Instead, we believe they represent a more reasonable range than has been previously estimated. Using these estimates, we propose an improved MUSIC model for gibbsite, which seems to predict surface adsorption, not perfectly, but within a reasonable range for a number of titration data sets without re-introducing any of our estimated parameters as adjustable parameters. Discrepancies that exist between model predictions and various potentiometric titration data sets are likely due to error associated with potentiometric titrations and pKa predictions.

Made available in DSpace on 2017-07-10T17:31:12Z (GMT). No. of bitstreams: 1 Wellington_Barbosa_da_Silva.pdf: 4552878 bytes, checksum: cced6a1f2d0a0c2426792ba3f3f8ce33 (MD5) Previous issue date: 2011-07-08 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / On the Guarapuava Plateau/Palmas, in a low slope hillside of superficial covering from basaltic origins, on the right bank of the Rio das Pombas, Paraná state, processes of tunnel erosion (pipes) were identified. These are subsuperficial erosion processes with typical features, such as subsidence of the tunnel roof and rebate structures, which tend to evolve to superficial features. The emerging of this erosive process depends on a set of factors, being the main one, the properties of the superficial covering, such as: texture, macroporosity, granulometric composition (chemical matter make-up), density, porosity e chemical elements that make up the matter, those concerning the hydrological conditions and the topography of the hillside. In order to recognize and characterize the superficial covering in the sector of low hillside, sieve analysis was used, as well as real and apparent density, total porosity verified; toposequences were made and X-ray scattering techniques performed. The results showed that the matter which covers the low hillside sector, where the tunnels are, have a sandy texture due to the properties of microagregation generated by clay mineral, gibbsite; leaving the matter with a high porosity level, thus favoring the flowing of water through subsurfaces. The generated flows tend to be exfiltrated to a ditch wall-like surface, which causes the removal of small particles of matter (seepage). With the opening of small gullies through subsurface, the flow tend to become concentrated (tunnel scour) and consequently enlarge the subsuperficial channels by the mechanical action of the water. In a sequence of factors that can be used for the analysis of the process generation, which causes: alteration in basalt rocks, microaggregation of the matter, macroporosity and increase of water flow through subsurface. Therefore, the hydrology conditions in the hillside contributed for erosion mechanisms to emerge in subsurface, development of erosion process, formation of subsuperficial erosion and, ultimately, superficial erosion process development. These both chemical and physical features found in such field of study, show that the superficial covering is a determining factor for the subsuperficial tunnel erosion to originate in the hillside. / No Planalto de Guarapuava/Palmas, em encosta de baixa declividade e cobertura superficial de origem basáltica, à margem direita do Rio das Pombas em Guarapuava (Paraná), foram identificados processos de erosão em túneis (pipes). Trata-se de processos subsuperficiais de erosão que apresentam feições típicas, tais como, subsidência do teto do túnel e estruturas de abatimento, que tendem a evoluir para feições superficiais. A instalação desse processo erosivo depende de um conjunto de fatores, destacando-se como condicionantes, as propriedades da cobertura superficial como: textura, macroporosidade, composição granulométrica, densidade, porosidade e constituintes químicos dos materiais, e aqueles relativos às condições hidrológicas e à topografia da encosta. Buscando-se reconhecer e caracterizar a cobertura superficial do setor de baixa encosta, foram realizadas análises granulométricas, de densidade aparente, real e porosidade total, construção de topossequências e análises químicas de difração de raios-X. Os resultados indicaram que o material que recobre o setor de baixa encosta, onde aparecem os túneis, apresenta textura arenosa devido às propriedades de microagregação gerada pelo argilomineral gibbsita, deixando o material com porosidade alta, favorecendo assim a circulação de água em subsuperficie. Os fluxos gerados tendem a ser exfiltrados para uma superfície de exposição, o que provoca a remoção de pequenas partículas de material (seepage). Com a abertura de pequenos canais em subsuperfície, os fluxos tendem a se concentrar (tunnel scour) e consequentemente ampliar os canais subsuperficiais pela ação mecânica da água. Numa sequência de fatores que possam ser postos para análise da geração do processo, têm-se: alteração da rocha basáltica, microagregação do material, macroporosidade e aumento da circulação de água em subsuperfície. Assume-se que as condições hidrológicas da encosta propiciaram a instalação de mecanismos de erosão em subsuperfície, evolução do processo erosivo, formação de feições erosivas subsuperficiais e, por fim, instalação de feições erosivas superficiais. Essas características físicas e químicas encontradas na área de estudo, demonstram que a cobertura superficial é determinante para a instalação da erosão subsuperficial em túneis na encosta.

Made available in DSpace on 2017-05-12T14:42:43Z (GMT). No. of bitstreams: 1 Wellington_Barbosa_da_Silva.pdf: 4552878 bytes, checksum: cced6a1f2d0a0c2426792ba3f3f8ce33 (MD5) Previous issue date: 2011-07-08 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / On the Guarapuava Plateau/Palmas, in a low slope hillside of superficial covering from basaltic origins, on the right bank of the Rio das Pombas, Paraná state, processes of tunnel erosion (pipes) were identified. These are subsuperficial erosion processes with typical features, such as subsidence of the tunnel roof and rebate structures, which tend to evolve to superficial features. The emerging of this erosive process depends on a set of factors, being the main one, the properties of the superficial covering, such as: texture, macroporosity, granulometric composition (chemical matter make-up), density, porosity e chemical elements that make up the matter, those concerning the hydrological conditions and the topography of the hillside. In order to recognize and characterize the superficial covering in the sector of low hillside, sieve analysis was used, as well as real and apparent density, total porosity verified; toposequences were made and X-ray scattering techniques performed. The results showed that the matter which covers the low hillside sector, where the tunnels are, have a sandy texture due to the properties of microagregation generated by clay mineral, gibbsite; leaving the matter with a high porosity level, thus favoring the flowing of water through subsurfaces. The generated flows tend to be exfiltrated to a ditch wall-like surface, which causes the removal of small particles of matter (seepage). With the opening of small gullies through subsurface, the flow tend to become concentrated (tunnel scour) and consequently enlarge the subsuperficial channels by the mechanical action of the water. In a sequence of factors that can be used for the analysis of the process generation, which causes: alteration in basalt rocks, microaggregation of the matter, macroporosity and increase of water flow through subsurface. Therefore, the hydrology conditions in the hillside contributed for erosion mechanisms to emerge in subsurface, development of erosion process, formation of subsuperficial erosion and, ultimately, superficial erosion process development. These both chemical and physical features found in such field of study, show that the superficial covering is a determining factor for the subsuperficial tunnel erosion to originate in the hillside. / No Planalto de Guarapuava/Palmas, em encosta de baixa declividade e cobertura superficial de origem basáltica, à margem direita do Rio das Pombas em Guarapuava (Paraná), foram identificados processos de erosão em túneis (pipes). Trata-se de processos subsuperficiais de erosão que apresentam feições típicas, tais como, subsidência do teto do túnel e estruturas de abatimento, que tendem a evoluir para feições superficiais. A instalação desse processo erosivo depende de um conjunto de fatores, destacando-se como condicionantes, as propriedades da cobertura superficial como: textura, macroporosidade, composição granulométrica, densidade, porosidade e constituintes químicos dos materiais, e aqueles relativos às condições hidrológicas e à topografia da encosta. Buscando-se reconhecer e caracterizar a cobertura superficial do setor de baixa encosta, foram realizadas análises granulométricas, de densidade aparente, real e porosidade total, construção de topossequências e análises químicas de difração de raios-X. Os resultados indicaram que o material que recobre o setor de baixa encosta, onde aparecem os túneis, apresenta textura arenosa devido às propriedades de microagregação gerada pelo argilomineral gibbsita, deixando o material com porosidade alta, favorecendo assim a circulação de água em subsuperficie. Os fluxos gerados tendem a ser exfiltrados para uma superfície de exposição, o que provoca a remoção de pequenas partículas de material (seepage). Com a abertura de pequenos canais em subsuperfície, os fluxos tendem a se concentrar (tunnel scour) e consequentemente ampliar os canais subsuperficiais pela ação mecânica da água. Numa sequência de fatores que possam ser postos para análise da geração do processo, têm-se: alteração da rocha basáltica, microagregação do material, macroporosidade e aumento da circulação de água em subsuperfície. Assume-se que as condições hidrológicas da encosta propiciaram a instalação de mecanismos de erosão em subsuperfície, evolução do processo erosivo, formação de feições erosivas subsuperficiais e, por fim, instalação de feições erosivas superficiais. Essas características físicas e químicas encontradas na área de estudo, demonstram que a cobertura superficial é determinante para a instalação da erosão subsuperficial em túneis na encosta.

Organic ligand complexation reactions at the mineral-water interface play an important role in several environmental and geochemical processes such as adsorption, dissolution, precipitation, pollutant transport, nutrient cycling, and colloidal stability. Although organic ligand surface complexation reactions have been extensively studied, a molecular level understanding regarding the mechanisms underlying the adsorption of such compounds is still limited. The purpose of the current study was to investigate the interactions between some common naturally occurring organic ligands and a common aluminosilicate clay mineral, kaolinite, using a combination of macroscopic and microscopic experimental methods. Molecular level information regarding the structure and binding mode of adsorbed species was obtained using in situ MIR-FTIR spectroscopy. Other experimental techniques including adsorption experiments, surface titrations, and surface complexation modelling were also employed in order to quantify and describe the macroscopic adsorption properties of the organic ligands examined. Three low molecular weight organic acids (oxalic, salicylic, and phthalic acid) and humic acid were chosen as representative organic ligands. Spectroscopic evidence revealed that low molecular weight organic acids are able to form both inner and outer sphere complexes on kaolinite, and the relative concentrations of these surface complexes varies with solution chemistry. Inner sphere coordination modes inferred are a mononuclear bidentate for oxalate (five-membered chelate ring) and phthalate (seven-membered chelate ring); and a mononuclear monodenate (six-membered pseudochelate ring) for salicylic acid. Similar coordination modes were shown to form on simpler mineral (hyrd)oxides. Elucidation of the coordination chemistry of these ligands can provide insights into the dissolution mechanisms of silicate minerals In contrast to low molecular weight organic acids, there was no evidence of inner sphere complexation by humic acid acids on kaolinite or gibbsite. The combined spectroscopic and macroscopic adsorption results suggest that cation bridging and van der Waals interactions are the two most probable mechanisms for the adsorption of humic acid by these mineral substrates. This finding casts doubts over the use of low molecular weight organic acids as humic acid analogs.

In der vorgelegten Arbeit werden sowohl effiziente als auch einfache Modifikationsansätze zur funktionalen Polymerumhüllung von Gibbsit-Plättchen präsentiert. Die plättchen-förmige Morphologie bleibt dabei nach der Polymerumhüllung erhalten. Im ersten Teil wird ein einfacher Ansatz zur Synthese von anisotropen, plättchen-förmigen Gibbsit-Polydopamin (G-PDA) Partikeln vorgestellt. Au NPs von kontrollierbarer Größe wurden auf der G-PDA Partikeloberfläche gebildet. Diese zeigten katalytische Aktivität zur Reduktion von 4-Nitrophenol und Rhodamin B (RhB) mittels Borhydrid. Die Partikel können durch ihre große, plättchen-förmige Kontaktfläche und der stark adhäsiven Eigenschaften der PDA Hülle einfach mittels Spin-Coating auf Siliziumsubstrate aufgebracht werden. Der so präparierte Nanokatalysator kann nun einfach wiederaufbereitet werden und zeigt hervorragende Wiederverwendbarkeit. Im zweiten Teil wurden anisotrope, hybride Kern-Schale Mikrogele mit wohldefinierter Struktur synthetisiert. Dabei bilden die Gibbsit Nanoplättchen den Kern und vernetztes, thermosensitives Poly(N-isopropylacylamid) die Hülle. Depolarisierte dynamische Lichtstreuung zeigte, dass die hybriden Mikrogele im kollabierten Zustand durch die plättchen-förmigen Kerne eine anisotrope Form annehmen. Der dritte Teil der Arbeit befasst sich mit der Herstellung von hochdispergierbaren, mesoporösen und stickstoffhaltighohle Kohlenstoff-Nanoplättchen. Diese neuartige Kohlenstoff-Nanostruktur wurde mittels sogenannter Silika-Nanocasting Technik unter Veswendung von hexagonalen Gibbsit-Templat und Dopamin als Kohlenstoffquelle synthetisiert. Solche hohlen Kohlenstoff-Nanostrukturen weisen exzellente, kolloidale Stabilität in wässrigen Medien vor und können direkt als Elektrodenmaterial für Superkondensatoren verwendet werden. Außerdem können sie in polyionischen Flüssigkeiten hohe Kapazitäten erzielen, wobei gleichzeitig eine hervorragende elektrochemische Stabilität gewährleistet wird. / In the present thesis, efficient and simple modification approaches have been developed to coat gibbsite platelets with a controllable thickness of functional polymer shell, which preserves the plate-like morphology after the polymer coating. In the first part, a facile approach has been presented for the synthesis of anisotropic plate-like gibbsite-polydopamine (G-PDA) particles. Au NPs with tunable size have been formed on the G-PDA particle surface, which show efficient catalytic activity for the reduction of 4-nitrophenol and Rodamine B (RhB) in the presence of borohydride. Such nanocatalysts can be easily deposited on silicon substrate by spin coating due to the large contact area of the plate-like G-PDA particles and the strong adhesive behavior of the PDA layer. The substrate-deposited nanocatalyst can be easily recycled, which shows excellent reusability. Secondly, anisotropic hybrid core-shell microgels with well-defined structures have been synthesized using gibbsite nanoplate as core and crosslinked thermosensitive poly(N-isopropylacrylamide) as shell. The analysis by depolarized dynamic light scattering shows that the hybrid microgels have an anisotropic shape in the collapsed state, caused by the anisotropy of the plate-like core. In the third part, highly dispersible mesoporous nitrogen-doped hollow carbon nanoplates have been synthesized as a new carbon nanostructure via silica nanocasting technique using dopamine as carbon precursor and hexagonal-shaped gibbsite as template. Such hollow carbon nanoplates show excellent colloidal stability in aqueous media and can be directly applied as electrode materials in supercapacitors, which offer high capacitance and excellent electrochemical stability when using poly(ionic liquid) nanoparticles as binder.

L'altération chimique des roches primaires et des minéraux dans les systèmes naturels a un impact majeur sur la formation des sols et leur composition. L'altération chimique est largement pilotée par la dissolution des minéraux. Les éléments chimiques libérés dans les eaux souterraines par la dissolution des minéraux réagissent facilement pour former des minéraux secondaires comme les argiles, zéolites et carbonates. Les carbonates se forment par réaction des cations divalents (Ca, Fe et Mg) avec CO2 dissous tandis que la formation des kaolins et de la gibbsite est attribuée à l'altération des minéraux riches en aluminium, le plus souvent les feldspaths. Le projet Carbfix à Hellisheiði (sud-ouest de l'Islande) a pour but d'utiliser les processus d'altération naturelle pour former des minéraux carbonatés par réinjection dans les roches basaltiques environnantes de CO2 provenant d'une centrale géothermique. Ce processus trouve son origine dans la dissolution des roches basaltiques riches en cations divalents (Ca, Fe et Mg) qui se combinent au CO2 injecté pour former des minéraux carbonatés. Cette thèse est centrée sur la dissolution du basalte cristallin de Stapafell qui est composé essentiellement de trois phases minérales (plagioclase, pyroxène et olivine) et qui est riche en cations divalents. La vitesse de libération des éléments du basalte à l'état stationnaire et loin de l'équilibre a été mesurée dans des réacteurs à circulation à des pH de 2 à 12 et des températures de 5 à 75°C. Les vitesses de libération de Si et Ca à l'état stationnaire présentent une variation en fonction du pH en forme de U avec une diminution des vitesses lorsque le pH augmente en conditions acides et une augmentation avec le pH en conditions alcalines. Les vitesses de libération du silicium par le basalte cristallin sont comparables à celles par le verre basaltique de même composition chimique aux faibles pH et aux températures ≥ 25°C mais elles sont plus lentes aux pH alcalins et aux températures ≥ 50°C. Par contre, les vitesses de libération de Mg et Fe diminuent de manière monotone avec l'accroissement du pH à toutes les températures. Ce comportement a pour cause les variations contrastées, en fonction du pH, des vitesses de dissolution des trois minéraux constitutifs du basalte: plagioclase, olivine et pyroxène. Les vitesses de libération des éléments déduites de la somme des vitesses de dissolution du plagioclase, pyroxène et olivine normalisées à la fraction volumique de ces minéraux sont, à un ordre de grandeur près, les mêmes que celles mesurées dans cette étude. En outre, les résultats expérimentaux montrent que, durant l'injection d'eaux chargées en CO2 de pH proche de 3.6, le basalte cristallin libère préférentiellement Mg et Fe en solution par rapport à Ca. L'injection de fluides acides chargés en CO2 dans des roches cristallines basaltiques peut donc favoriser la formation de carbonates de Mg et Fe aux dépends de la calcite aux conditions de pH acides à neutres. Le plagioclase, qui est la phase la plus abondante du basalte, influence fortement la réactivité de ce dernier. La vitesse de dissolution du plagioclase, basée sur la libération de la silice, présente une variation en forme de U en fonction du pH, diminuant lorsque le pH augmente aux conditions acides mais augmentant avec le pH aux conditions alcalines. En accord avec les données de la littérature, la vitesse de dissolution du plagioclase à pH constant, en conditions acides, augmente avec sa teneur en anorthite. L'interprétation et le fit des données obtenues suggèrent que la vitesse de dissolution du plagioclase est contrôlée par la décomposition d'un complexe activé riche en silice, formé par le départ de Al de la structure du minéral. Le plus remarquable, par comparaison aux hypothèses antérieures, est que la vitesse de dissolution du plagioclase en conditions alcalines est indépendante de sa teneur en anorthite - e.g. les vitesses de dissolution des plagioclases riches en anorthite augmentent avec le pH aux conditions alcalines. A ces conditions, il est probable que la vitesse de dissolution rapide du plagioclase domine, en raison de sa forte teneur en Ca, la libération vers la phase fluide des cations divalents du basalte cristallin. La gibbsite est généralement le premier minéral qui précipite lors de la dissolution du plagioclase. C'est un hydroxyde d'aluminium que l'on trouve dans divers sols et qui est aussi la phase principale des minerais de bauxite. Les vitesses de précipitation de la gibbsite ont été mesurées dans des réacteurs fermés, en conditions alcalines à 25 et 80°C, en fonction de l'état de saturation du fluide. Les analyses des solides après réaction ont démontré que la précipitation de gibbsite s'est produite dans toutes les expériences. L'interprétation de l'évolution dans le temps de la chimie du fluide réactif fournit des vitesses de précipitation de la gibbsite qui sont près des vitesses de dissolution du plagioclase. En plus, des vitesses de précipitation de la gibbsite diminuent plus rapidement que des vitesses de dissolution du plagioclase quand le pH descende. Ceci suggère que l'étape limitant de l'altération du plagioclase sur la surface de la terre est plutôt la consommation d'Al par formation de la gibbsite que la dissolution même du plagioclase. La kaolinite est en général le second minéral formé après la gibbsite lors de la dissolution du plagioclase à basse température. Les vitesses de précipitation de la kaolinite ont été mesurées dans des réacteurs à circulation à pH = 4 et t = 25°C, en fonction de l'état de saturation du fluide. Au total, 8 expériences de précipitation de longues durées ont été réalisées dans des fluides légèrement supersaturés par rapport à la kaolinite, en utilisant comme germes pour la précipitation une quantité connue de de kaolinite de Géorgie (KGa-1b) contenant peu de défauts et préalablement nettoyée. Les vitesses de précipitation de kaolinite mesurées sont relativement lentes comparées aux vitesses de dissolution du plagioclase. Cette observation suggère que la formation de kaolinite lors de l'altération est limitée par sa vitesse de précipitation plutôt que par que la disponibilité en Al et Si issus de la dissolution du plagioclase. L'ensemble des résultats de cette étude fournit un certain nombre de principes scientifiques de base nécessaires à la prédiction des vitesses et des conséquences de la dissolution du basalte cristallin et du plagioclase à la surface de la Terre et lors de l'injection du CO2 à proximité de la surface dans le cadre des efforts de stockage du carbone. Les résultats obtenus indiquent, bien que les vitesses de précipitation de la gibbsite soient relativement rapides, que la vitesse de précipitation relativement lente de la kaolinite peut être le processus contrôlant la formation de ce minéral à la surface de la Terre. Cette observation souligne la nécessité de poursuivre la quantification de la précipitation de ce minéral secondaire aux conditions typiques de la surface de la Terre. En outre, comme les proportions des différents métaux divalents libérés par les basaltes cristallins varient sensiblement avec le pH, la carbonatation des basaltes doit produire un changement systématique de l'identité des minéraux carbonatés et des zéolites précipités en fonction de la distance au puits d'injection. Cette dernière conclusion pourra être directement testée dans le cadre du projet CarbFix actuellement conduit à Hellisheiði en Islande.