Dissertations / Theses on the topic 'Calcium carbonate (CaCO3) cycle'

L’alcalinité de l’océan (Alk) est essentielle dans l’absorption de carbone atmosphérique et offre une capacité tampon contre l’acidification. Dans le cadre des prévisions de l’absorption de carbone par les océans et des impacts potentiels sur les écosystèmes, la représentation de l’Alk et du principal facteur de sa distribution dans l’océan profond, le cycle du carbonate de calcium (CaCO3), ont souvent été négligés. Cette thèse aborde le manque de considération accordé à l’Alk et au cycle du CaCO3 dans les modèles du système terrestre (ESM) et explore les implications pour le cycle du carbone dans un océan pré-industriel ainsi que dans des scénarios de changement climatique. À travers une intercomparaison des ESMs, une réduction des biais simulés de l’Alk dans la 6ème phase du Projet d’Intercomparaison de Modèles Couplés (CMIP6) est rapportée. Cette réduction peut s’expliquer partiellement par une calcification pélagique accrue, redistribuant l’Alk en surface et renforçant son gradient vertical dans la colonne d’eau. Une revue des modèles de biogéochimie marine utilisés dans les ESMs actuels révèle une représentation diverse du cycle du CaCO3 et des processus affectant l’Alk. Les schémas de paramétrisation de la production, de l’exportation, de la dissolution et de l’enfouissement du CaCO3 varient considérablement, avec une prise en compte généralement limitée à la seule calcite, et sans calcification benthique. Cette diversité entraîne des projections contrastées de l’export de carbone associé au CaCO3 depuis l’océan de surface vers l’océan profond dans les scénarios futurs. Cependant, des simulations de sensibilité effectuées avec le modèle de biogéochimie marine NEMO-PISCES indiquent que la rétroaction associée sur le flux de carbone anthropique et l’acidification des océans reste limitée. À travers un ensemble de simulations NEMO-PISCES, il est démontré qu’une attention particulière au bilan d’Alk est cruciale pour estimer le dégazage de carbone océanique pré-industriel dû aux apports fluviaux ainsi qu’à l’enfouissement de matière organique et de CaCO3. De telles estimations sont fondamentales pour évaluer le flux de carbone air-mer anthropique en utilisant des données d’observation, et mettent en évidence la nécessité de mieux contraindre le bilan d’Alk de l’océan. Enfin, fidèle au message qu’elle véhicule sur le changement climatique, cette thèse offre une perspective nouvelle et radicale sur les sciences du climat et le système de la recherche actuel
Ocean alkalinity (Alk) is critical for the uptake of atmospheric carbon and provides buffering capacity against acidification. Within the context of projections of ocean carbon uptake and potential ecosystem impacts, the representation of Alk and the main driver of its distribution in the ocean interior, the calcium carbonate (CaCO3) cycle, have often been overlooked. This thesis addresses the lack of consideration given to Alk and the CaCO3 cycle in Earth system models (ESMs) and explores the implications for the carbon cycle in a pre-industrial ocean as well as under climate change scenarios. Through an ESM intercomparison, a reduction in simulated Alk biases in the 6th phase of the Coupled Model Intercomparison Project (CMIP6) is reported. This reduction can be partially explained by increased pelagic calcification, redistributing Alk at the surface and strengthening its vertical gradient in the water column. A review of the ocean biogeochemical models used in current ESMs reveals a diverse representation of the CaCO3 cycle and processes affecting Alk. Parameterization schemes for CaCO3 production, export, dissolution, and burial vary substantially, with no benthic calcification and generally only calcite considered. This diversity leads to contrasting projections of carbon export associated with CaCO3 from the surface ocean to the ocean interior in future scenarios. However, sensitivity simulations performed with the NEMO-PISCES ocean biogeochemical model indicate that the feedback of this on anthropogenic carbon fluxes and ocean acidification remains limited. Through an ensemble of NEMO-PISCES simulations, careful consideration of the Alk budget is shown to be critical to estimating pre-industrial ocean carbon outgassing due to riverine discharge and the burial of organic matter and CaCO3. Such estimates are fundamental to assessing anthropogenic air-sea carbon fluxes using observational data and highlight the need for greater constraints on the ocean Alk budget

The hydrolysis of urea by the widely distributed enzyme urease is special in that it is one of the few biologically occurring reactions that can generate carbonate ions without an associated production of protons. When this hydrolysis occurs in a calcium-rich environment, calcite (calcium carbonate) precipitates from solution forming a solid-crystalline material. The binding strength of the precipitated crystals is highly dependent on the rate of carbonate formation and under suitable conditions it is possible to control the reaction to generate hard binding calcite cement (or Biocement). The objective of this thesis was to develop an industrially suitable cost-effective microbial process for the production of urease active cells and investigate the potential for urease active cells to act as a catalyst for the production of Biocement. The biocementation capability of two suitable strains was compared. Sporosarcina pasteurii (formally Bacillus pasteurii) produced significantly higher levels of urease activity compared to Proteus vulgaris, however the level of urease activity was variable with respect to biomass suggesting that the enzyme was not constitutive as indicated by the literature, but subject to regulation. The environmental and physiological conditions for maximum urease activity in S. pasteurii were investigated and it was found that the potential urease capacity of the organism was very high (29 mM urea.min-1.OD-1) and sufficient for biocementation without additional processing (e.g. concentration, cell lysis). The regulation mechanism for S. pasteurii urease was not fully elucidated in this study, however it was shown that low specific urease activity was not due to depletion of urea nor due to the high concentrations of the main reaction product, ammonium. pH conditions were shown to have a regulatory effect on urease but it was evident that another co-regulating mechanism existed. Despite not fully exploiting the urease capability of S. pasteurii, sufficient urease activity to allow direct application of the enzyme without additional processing could still be achieved and the organism was considered suitable for biocementation. Urease was the most expensive component of the cementation process and cost-efficient production was desired, thus an economic growth procedure was developed for large-scale cultivation of S. pasteurii. The organism is a moderate alkaliphile (growth optimum pH 9.25) and it was shown that sufficient activity for biocementation could be cultivated in non-sterile conditions with a minimum of upstream and downstream processing. The cultivation medium was economised and expensive components were replace with a food-grade protein source and acetate, which lowered production costs by 95%. A high level of urease activity (21 mM urea hydrolysed.min-1) was produced in the new medium at a low cost ($0.20 (AUD) per L). The performance of urease in whole S. pasteurii cells was evaluated under biocementation conditions (i.e. presence of high concentrations of urea, Ca2+, NH4 +/NH3, NO3 - and Cl- ions). It was established that the rate of urea hydrolysis was not constant during cementation, but largely controlled by the external concentrations of urea and calcium, which constantly changed during cementation due to precipitation of solid calcium carbonate from the system. A simple model was generated that predicted the change in urea hydrolysis rate over the course of cementation. It was shown that whole cell S. pasteurii urease was tolerant to concentrations of up to 3 M urea and 2 M calcium, and the rate of urea hydrolysis was unaffected up to by 3 M ammonium. This allowed the controlled precipitation of up to 1.5 M CaCO3 within one treatment, and indicated that the enzyme was very stable inspite of extreme chemical conditions. A cost-efficient cementation procedure for the production of high cementation strength was developed. Several biocementation trials were conducted into order to optimise the imparted cementation strength by determining the effect of urea hydrolysis rate on the development of strength. It was shown that high cementation strength was produced at low urea hydrolysis rates and that the development of cementation strength was not linear over the course of the reaction but mostly occurred in the first few hours of the reaction. In addition, the whole cell bacterial enzyme had capacity to be immobilised in the cementation material and re-used to subsequent applications, offering a significant cost-saving to the process. An industry-sponsored trial was undertaken to investigate the effectiveness of Biocement for increasing in-situ strength and stiffness of two different sandy soils; (a) Koolschijn sand and (b) 90% Koolschijn sand mixed with 10% peat (Holland Veen). After biocementation treatment, Koolschijn sand indicated a shear strength of 1.8 MPa and a stiffness of 250 MPa, which represents an 8-fold and 3-fold respective improvement in strength compared to unconsolidated sand. Significantly lower strength improvements were observed in sand mixed with peat. In combination, trials of producing bacteria under economically acceptable conditions and cementation trials support the possibility of on-site production and in-situ application of large field applications.

Les chirurgiens sont confrontés à des pertes de substance osseuse qui impliquent l'utilisation de biomatériaux synthétiques de comblement. Leur utilisation permet de limiter les réponses immunitaires et leur disponibilité est quasi illimitée. Notre travail a porté sur des géopolymères (Si/Al=21). Ces aluminosilicates synthétisés ont été associés à des phosphates de calcium. Chauffés à 500ʿC, les géopolymères présentent des pH de 7 et un bon compromis propriétés mécaniques/ porosité. Ces matériaux ont été étudiés in vitro et in vivo pour évaluer leur potentiel pour une utilisation comme biomatériaux. Les cinétiques de minéralisation des géopolymères et du biomatériau CaCO3 ont été étudiées. Les résultats obtenus par PIXE et NAA pour le CaCO3 montrent un comportement in vivo similaire à celui d'un TCP. Les études in vivo réalisées sur les géopolymères ont confirmé l’ostéointégration des implants. Les analyses par PIXE des implants confirment la consolidation de l'interface dès 1 mois.

Le développement considérable réalisé ces dix dernières années dans les techniques de diffraction sur des échantillons sous forme de poudre même très texturés (temps d’enregistrement raisonnable et très bonne résolution) et les progrès fascinants des moyens de calcul sur des machines individuelles rendent possible l’accès à des informations précises et avec des temps de calcul raisonnablement courts. Dans ce travail, nous avons appliqué l’analyse combinée basée sur la méthode de Rietveld pour étudier des échantillons de carbonates de calcium naturels de coquilles de certaines espèces de mollusques (structure, texture, tailles anisotropes…etc. ) et synthétiques par biomimétisme dans le but de comprendre l’influence des différents facteurs intervenants dans la croissance et la forme des grains des différents polymorphes de CaCO3. Dans les échantillons naturels, nous avons clairement mis en évidence l’existence de déformations de mailles cristallines dues à la présence des macromolécules intra-cristallines et extra-cristallines, en complément d’études du même genre réalisées sur des échantillons broyés. Dans les échantillons synthétiques obtenus par une méthode de synthèse simple, nous avons analysé l’effet de l’ajout d’acide polyacrylique, en termes de modulateur de croissance des polymorphes de CaCO3. La simulation des digrammes de diffraction anisotropes réalisée sur ces deux types d’échantillons nous a permis d’accéder aux informations pertinentes de façon précise (tailles anisotropes des cristallites, structure, texture, proportion volumique des polymorphes)
The tremendous development of powder diffraction techniques achieved over the last ten years even operational on strongly textured samples within good resolutions, together with the fascinating development of individual calculating capabilities, make it possible to access precise information in reasonably short times. In this work, we apply the combined analysis based on the Rietveld method to study samples of natural calcium carbonates from two living species of molluscan shells and of synthetic CaCO3 in order to understand the influence of the different parameters in the growth and shape of the crystallites of the different polymorphs of CaCO3. In natural species we clearly put into evidence the existence of distortions of crystalline cells due to the presence of the intra- and extra-crystalline macromolecules, in opposition with similar studies operated on powderised samples. In synthetic samples we studied, using a simple synthesis method and taking as a model the polyacrylic acid, the role of the soluble macromolecules in the growth of the CaCO3 polymorphs. The simulation of the anisotropic diffraction diagrams on both sample types allowed us to reach pertaining information within good precision (anisotropic sizes of the crystallites, structure, texture, volume fraction of the polymorphs

Muitos organismos vivos, tal como seus constituintes, são formados por sistemas químicos complexos que envolvem a interação entre compostos orgânicos e inorgânicos ligados química e/ou fisicamente. Nestes sistemas as matrizes orgânicas são geralmente compostas por macromoléculas como polissacarídeos e proteínas. Essas moléculas têm o papel de direcionar a nucleação e o crescimento da porção inorgânica. O uso de superfícies metálicas adequadas recobertas por este tipo de filme híbrido tem potencial aplicação em implantes de substituição óssea, no qual são requeridas superfícies quimicamente inertes, mas que ao mesmo tempo estimulem processos de calcificação. Nesta tese estudou-se o crescimento de CaCO3 sobre superfícies metálicas de alumínio e aço inox recobertas por matrizes orgânicas compostas por diferentes poliânions e pelo policátion quitosana, na forma de filmes montados camada-a-camada (do inglês LbL), na presença ou não de fosfolipídeos (filmes Langmuir-Blodgett), formando um meio confinado para o crescimento do mineral. Diferentes técnicas foram utilizadas: microscopia eletrônica, microscopia de força atômica, espectroscopias de reflexão nas regiões do Uv-vis, e do infravermelho, Raman, espalhamento e difração de raios-X. Estudou-se a influência de diferentes grupos carregados dos fosfolipídeos e dos poliânions, tal como sua conformação, no crescimento de CaCO3. O tipo de interação entre o poliânion e a quitosana leva ao crescimento de matrizes poliméricas com diferenças em suas espessuras e capacidade de retenção de líquido, modificando as condições de supersaturação local e influenciando no tipo de estrutura de CaCO3. Puderam ser identificados dois polimorfos formados sobre os filmes orgânicos de poli(ácido acrílico) e quitosana, sugerindo que existem dois diferentes sítios onde a nucleação pode ser iniciada: a partir da solução de CaCl2 aprisionada na matriz polimérica e o outro a partir dos íons cálcio ligados como contra-íons aos grupos negativamente carregados do poliânion. Na presença do pré-recobrimento LB, a natureza da cabeça polar do fosfolipídeo direciona o tipo de ligação e crescimento da matriz polimérica, que levam ao crescimento de partículas de CaCO3 com morfologia e tamanho variados, explicados em termos da presença de ambientes com diferenças de concentrações locais de Ca2+. Além disso, verificou-se que a rugosidade superficial dos suportes metálicos pode favorecer a formação do polimorfo de CaCO3 cineticamente mais estável, mostrando que o processo de cristalização sobre estes suportes é um processo governado por difusão. A hidrofilicidade dos suportes é aumentada pela presença da matriz orgânica e pela presença de CaCO3 sobre as matrizes. O crescimento de CaCO3 em meios confinados tridimensionais, formados por membranas de policarbonato modificadas com filme finos de polieletrólitos, também foi estudado. Este tipo de molde leva à formação de estruturas cilíndricas que seguem a morfologia dos poros da membrana. A presença de poli(ácido acrílico) leva a formação de estruturas cilíndricas ocas, enquanto que cilindros completamente preenchidos foram formados nos poros contendo quitosana na última camada. Estes resultados foram explicados com base em diferenças na etapa de nucleação: na presença de PAA a nucleação de CaCO3 deve iniciar-se a partir dos íons Ca2+ ligados ao poliânion que, por sua vez, está ligado diretamente às paredes do molde; já na presença que quitosana, com maior capacidade de retenção de liquido e sem interação específica com Ca2+ a nucleação e seqüente cristalização devem ocorrer por todo o poro da membrana. As estruturas formadas são em sua maioria monocristais de calcita hexagonal orientadas na direção cristalográfica <2 -2 1>.
Some living organisms as well as their constituents are formed by complex chemical systems which involves the interaction among organic and inorganic compounds bounded physically or chemically. In these systems the organic matrices are usually composed by macromolecules like polysaccharides and proteins. These molecules have an important hole in tailoring the nucleation and the sequent growth of the inorganic portion. Metallic surfaces coated with these hybrid films have potential application as implants for bone substitution for which the surfaces must be chemically inert but at the same time they should stimulate calcification processes. In this present thesis we studied the growth of CaCO3 over aluminium and stainless steal surfaces coated with layer-by-layer films composed by different polyanions and chitosan as polycation, in the presence or not of phospholipids (Langmuir-Blodgett films). These organic matrices formed a confined medium within which CaCO3 particles were growth. Different techniques were applied in order to understand these systems: electronic microscopy, atomic force microscopy, UV-Vis and infrared reflection spectroscopy, Raman, and X-ray scattering and diffraction. We studied the influence of the different charged groups of the phospholipids and the polyanion as well as their conformation on CaCO3 growth. The type of interaction between the polycation and the polyanions tailors the growth of the organic matrices, forming films with different thickness and different water retention abilities which change the local supersaturation conditions changing the structure of the CaCO3 formed. Two types of CaCO3 polymorphs were growth over poly(acrylic acid) (PAA) and chitosan films suggesting that there are two sites where the nucleation can be started: the CaCl2 solution retained in the gel-like organic films and the Ca2+ ions bounded to the negative groups of the polyanion. In the presence of the LB pre-coating, the nature of the phospholipid polar head tailors the binding and the growth of the polymeric matrices leading to the formation of CaCO3 particles with difference in their sizes and morphologies. This result was explained in basis of the differences in the Ca2+ local concentrations in each situation. Moreover, it was observed that the surface roughness of the supports can favour the formation of vaterite, the kinetically most stable CaCO3 polymorph, showing that the crystallization may be guided by diffusion processes. The hidrophilicity of the supports was improved by the presence of both organic and hybrid films. The growth of CaCO3 in tridimentional confined mediums was done using LbL modified polycarbonate membranes as template. This template leads to the formation of cylindrical CaCO3 particles following the morphology of the membrane pores. CaCO3 tube-like structures were formed in presence of PAA, while rod-like structures were formed in presence of chitosan in the top LbL layer. These results were explained on basis of the difference in the nucleation stages: in the presence of PAA the nucleation starts on the Ca2+ ions bounded to the polyanion that is linked to the walls of the template; in the presence of chitosan that presents higher water retention ability and has no specific interaction with Ca2+ ions, the nucleation and sequent crystallization should occur through the entire pore of the membrane. The electron diffraction patterns showed that the CaCO3 structures are single crystals of the calcite polymorph oriented in < 2 -2 1> crystallographic direction.

Ce mémoire décrit des essais de la micro et l'ultrafiltration dynamique effectués avec trois pilotes de laboratoire, un pilote MSD à disque membranaire rotatif sur deux arbres, un pilote à disque rotatif avec une membrane organique fixe, et un pilote à cylindre tournant avec une membrane concentrique. Le module MSD a été testé en microfiltration de suspensions de CaCO3 où nous avons comparé des membranes céramiques et organiques. Les essais ont confirmé l'importance du recouvrement des disques. Ensuite, nous avons appliqué le système de MSD aux traitements des effluents modèles de surfactants anioniques (solutions de SDBS et SDS), avec une comparaison au système à disque rotatif, qui permettait une pression plus élevée de fonctionnement. En terme de flux de perméat et de taux de rétention, ces deux systèmes possèdent des avantages par rapport aux systèmes de filtration tangentielle classique. Puis, les modules à disque rotatif et à cylindre tournant ont été employés à l'ultrafiltration des solutions d'albumine bovine (BSA) pour simuler l'hémofiltration (traitement de l'insuffisance rénale aiguë)
This thesis focuses on dynamic micro and ultrafiltration conducted on three laboratory pilots, one with rotating membrane disks mounted on two shafts (MSD), one with a disk rotating close to a static organic membrane, and one with a cylinder rotating inside a concentric membrane. The MSD module was first used for ultrafiltration of CaCO3 suspensions, and in these tests ceramic and organic membranes were compared. The results confirmed the importance of disk overlapping in this module. Then, the MSD system was applied to the treatment of model wastewater containing anionic surfactants (SDBS and SDS solutions), and compared with the rotating disk system, which permitted a higher operating pressure. These two dynamic filtration systems present advantages compared to crossflow filtration systems, in terms of the permeate flux and membrane retention. In addition, the rotating disk and the rotating cylinder modules were used for ultrafiltration of bovine serum albumin (BSA) solutions to simulate hemofiltration in the treatment of acute renal failure

A indústria da construção civil é conhecida como umas das atividades econômicas que causam os maiores impactos ambientais desde o processo de extração da matéria prima até a produção dos produtos, incluindo o transporte e manutenção do ambiente construído. A produção de um dos seus principais componentes, o cimento, é o maior contribuinte para a emissão de gases de efeito estufa, principalmente devido a queima de combustíveis fósseis. Por este motivo, pesquisas na área de biotecnologia sustentável são conduzidas para diminuir e até mitigar os efeitos danosos provocados pelos fatores que compõem a construção civil. Dentre estas pesquisas destacam-se as que se baseiam na Biomimética, que é uma ciência que busca na Natureza as soluções tecnológicas para os problemas que os desenvolvimentos humanos geralmente apresentam: a geração de resíduos poluentes, uso de produtos químicos tóxicos e processos que operam com energia e pressão elevadas. Com base nos conceitos biomiméticos, este trabalho se propôs a estudar a biomineralização, que é um processo que ocorre na Natureza a milhares de anos e é responsável pela formação de muitas estruturas biomineralizadas tanto no ambiente terrestre como aquático. A biomineralização é um fenômeno provocado pela ação de diversas espécies de microrganismos que durante o processo de obtenção de energia reciclam minerais presentes no solo e na água e os precipitam na forma de sais inorgânicos. Este material precipitado age como agente ligante de partículas como no caso de formações geológicas (estromatólitos) ou exoesqueletos de animais marinhos, por exemplo. Neste estudo foi avaliado a biomineralização por biodeposição de carbonato de cálcio precipitado na presença da espécie de bactéria ureolítica (Bacillus subtilis) em ensaios em escala laboratorial utilizando corpos de prova de areia, argamassa e concreto. Os corpos de prova em areia e argamassa foram observados em MEV e EDS permitindo a identificação de células de microrganismos, formação de biofilme e provável formação de cristais de carbonato de cálcio na região de biofilme. Os corpos de prova de concreto foram utilizados para avaliar as consequências da biodeposição na absorção de água por capilaridade do material. Resultados indicam redução de 20% na absorção de água por capilaridade. Com os resultados obtidos é possível concluir que a técnica de biodeposição pode ser uma alternativa ao tratamento superficial de estruturas de concreto, contudo requer estudos posteriores de aplicação técnica e viabilidade econômica.
The construction industry has been known as one of the economic activities that cause the major environment impacts since the process of raw material extraction until the products manufacturing including transport and maintenance of the built environment. The production of one of the main compounds, the cement, is the largest contributor to the greenhouse gas emissions, mainly due to burn fossil fuels. For this reason, researches in sustainable biotechnological area are conducted to minimize and even mitigate the damaging effects either promoted by construction industry factors. Among these ones, it stands out researches based on Biomimetic, which is a science that seeks in Nature the technological solutions for problems that human’s development usually presents: the generation of pollutant residues, the use of toxic chemicals and process that operates in high pressure and energy. Based on biomimetic concepts this research proposes to study the biomineralization, which is a process that has occurred in the Nature for thousands of years and it is responsible for the formation of many structures either in soil and water environments. The biomineralization is a phenomenon caused by several specimens of microorganisms that during the process of obtaining energy, they recycle minerals presents at soil and water inducing precipitation as inorganic salts. This precipitated material works as a binder of particles similar to geologic formations (stromatolites) or exoskeleton of sea animal for example. In this study the biomineralization was evaluated through biodeposition of precipitated calcium carbonate by specimen of ureolytic bacteria (Bacillus subtilis). Essays were held using samples made by sand, mortar and concrete. The samples made by sand and mortar were observed at MEV and EDS, allowing the identification of microorganism cells, biofilm formation and probable formation of calcium carbonate crystals at biofilm region. The concrete samples were used to evaluate the consequences of biodeposition on water absorption by capillarity of the material. The results show reduction of 20% on water absorption by capillarity. According the results achieved it possible to conclude that the biodeposition technique can be an alternative to superficial treatment for concrete structures. However, it will be required more studies to evaluate technical application and economical availability.

Thesis (PhD (Chemistry and Polymer Science))--Stellenbosch University, 2008.
Polysaccharides were modified with selected polymers via the grafting technique. Both anionic and cationic polysaccharides were prepared. Random and crosslinked graft copolymers were also prepared. The percentage grafting was determined by gravimetric analysis and results were confirmed by cross-polarization magic angle spinning carbon-13 nuclear magnetic resonance microscopy (CP/MAS 13C NMR). These modified biodegradable polymers were then used to flocculate precipitated calcium carbonate (PCC). The effects of pH, percentage grafting, crosslinker concentration and polysaccharide concentration on PCC flocculation were evaluated. Furthermore, the effects of anionic and cationic starch, either added to PCC sequentially or simultaneously, on PCC flocculation were also investigated. Generally, anionically modified starch showed excellent flocculation properties, which are desirable for the end application of PCC retention. The effect of polyacrylic acid (PAA) and polyacrylamide (PAM) modified cellulose fibers on calcium carbonate crystal nucleation and growth modification was investigated. When the heterogeneous crystallization of CaCO3 was carried out in the presence of modified cellulose fibers the CaCO3 crystals were found to be residing on the surface of the fibers. The morphologies of the crystallized CaCO3, polymorph and fiber surface coverage were different for cellulose materials grafted with polymers of different functionalities, meaning that there is interaction between the crystal growth modifier and the growing nuclei. The effect of the modified starch on the crystallization of calcium carbonate gave useful insight into designing CaCO3 filler morphologies. It was found that the filler size, morphology and surface properties of fillers can be tailor-made by choosing suitable CaCO3 crystallization conditions as well as a suitable crystal growth modifier. The crystallized CaCO3 had a negatively charged surface. Results of fluorescence studies showed that the PAA modified starch (polymeric additive used) resided on the surface of the crystals. Thus the presence of the polysaccharide on the surface of a filler could be advantageous for strengthening fiber–filler bonding in paper applications. Anionic starch materials were also used to prepare anionic-starch-coated starch particles. Both the anionic starch and anionic-starch-coated starch particles were evaluated for PCC retention and other properties of hand sheets. When anionic-starch-coated starch particles were used there was generally an improvement in the PCC retention, while the other paper properties remained desirable. The success achieved with the use of anionic-starch-coated starch particles now opens the way for the further preparation and testing of various modified starch particles, for optimization of filler retention.

La biominéralisation des carbonates de calcium est un processus répandu chez les bactéries. Cependant les mécanismes moléculaires sous-jacents restent mal compris. Récemment, la biominéralisation intracellulaire de phases amorphes de carbonate de calcium (iACC) a été découverte chez des cyanobactéries répandues environnementalement et phylogénétiquement. Un gène orphelin de fonction inconnue, nommé ccyA et codant pour une protéine nommée Calcyanine, a été identifié uniquement chez ces cyanobactéries. Ainsi mon travail de thèse a consisté à développer une approche génétique pour analyser la fonction in vivo du gène ccyA et déterminer si la protéine qu’il code est impliquée ou non dans la formation des iACC. L’échec des tentatives de délétion de ccyA chez Cyanothece sp. PCC 7425 et Synechococcus sp. PCC 6312 suggère que ce gène leur est essentiel. Nous avons donc construit une expression hétérologue de ccyA dans des cyanobactéries modèles ne formant pas naturellement des iACC. L’expression constitutive de diverses séquences du gène ccyA a montré que la croissance de Synechococcus elongatus PCC 7942 est ralentie par rapport à celle de la souche sauvage. En accord, les mutants exprimant le ccyA présentent plus de cellules mortes que la souche sauvage. Enfin, ces mutants possèdent plus de calcium intracellulaire que la souche sauvage, suggérant une modification de l’homéostasie du calcium. Enfin, j’ai introduit des plasmides par conjugaison chez Cyanothece sp. PCC 7425 et Synechococcus sp. PCC 6312 leur permettant de surproduire ccyA. La Calcyanine fusionnée avec la eGFP se localise à la membrane et aux pôles des cellules chez la souche Synechococcus sp. PCC 6312
The biomineralization of calcium carbonates is a common process in bacteria, however, the underlying molecular mechanisms remain poorly understood. Recently, intracellular biomineralization of amorphous calcium carbonate phases (iACC) has been discovered in environmentally and phylogenetically widespread cyanobacteria. An orphan gene of unknown function, named ccyA and coding for a protein named Calcyanin, has been identified only in these cyanobacteria. My thesis work consisted in developing a genetic approach to analyze the in vivo function of the ccyA gene and determine whether or not the encoded protein is involved in the formation of iACCs. The failure of ccyA deletion attempts in Cyanothece sp. PCC 7425 and Synechococcus sp. PCC 6312 suggests that this gene could be essential to cells viability. We have therefore introduced a plasmid allowing heterologous expression of ccyA in model cyanobacteria that do not naturally form iACC. The constitutive expression of various ccyA sequences in Synechococcus elongatus PCC 7942 is slowed down compared to that of the wild strain. In agreement, ccyA-expressing mutants have more dead cells than the wild-type strain. Finally, these mutants have more intracellular calcium than the wild strain, suggesting a modification of calcium homeostasis. Finally, I introduced plasmids by conjugation in Cyanothece sp. PCC 7425 and Synechococcus sp. PCC 6312 allowing them to overproduce ccyA. Calcyanin fused with eGFP is localized to the membrane and poles of cells in Synechococcus sp. PCC 6312

Le développement considérable réalisé ces dix dernières années dans les techniques de
diffraction sur des échantillons sous forme de poudre même très texturés (temps
d'enregistrement raisonnable et très bonne résolution) et les progrès fascinants des moyens de
calcul sur des machines individuelles rendent possible l'accès à des informations précises et
avec des temps de calcul raisonnablement courts. Dans ce travail, nous avons appliqué
l'analyse combinée basée sur la méthode de Rietveld pour étudier des échantillons de
carbonates de calcium naturels de coquilles de certaines espèces de mollusques (structure,
texture, tailles anisotropes...etc.) et synthétiques par biomimétisme dans le but de comprendre
l'influence des différents facteurs intervenants dans la croissance et la forme des grains des
différents polymorphes de CaCO3. Dans les échantillons naturels, nous avons clairement mis
en évidence l'existence de déformations de mailles cristallines dues à la présence des
macromolécules intra-cristallines et extra-cristallines, en complément d'études du même
genre réalisées sur des échantillons broyés. Dans les échantillons synthétiques obtenus par une
méthode de synthèse simple, nous avons analysé l'effet de l'ajout d'acide polyacrylique, en
termes de modulateur de croissance des polymorphes de CaCO3. La simulation des
digrammes de diffraction anisotropes réalisée sur ces deux types d'échantillons nous a permis
d'accéder aux informations pertinentes de façon précise (tailles anisotropes des cristallites,
structure, texture, proportion volumique des polymorphes).

L'objectif de l'etude est d'ameliorer la resistance au choc et la rigidite d'un melange polyethylene/polystyrene. Nous avons envisage d'ameliorer la rigidite par l'incorporation d'une charge minerale (carbonate de calcium). Pour compenser l'effet fragilisant d'une telle charge, nous avons incorpore ensuite des copolymeres elastomeres susceptibles d'agir aux interfaces du systeme et ameliorer ainsi la resistance au choc. Le materiau final etant complexe, nous avons decompose l'etude pour mieux comprendre les effets apportes par chaque constituant. Nous avons d'abord etudie les comportements des deux phases dispersees polystyrene et carbonate de calcium dans la matrice pehd. Nous avons pu ainsi compare les effets apportes par une phase rigide d'origine organique (ps) et une phase rigide d'origine minerale (caco#3) en relation avec leur morphologie. Nous avons ensuite etudie le comportement des copolymeres elastomeres dans les systemes pehd/ps (75/25) et pehd/caco#3 (60/40) en liaison avec leur localisation (a l'interface ou dans la matrice) et leur action adhesive. A partir de ces etudes preliminaires, nous avons pu mieux comprendre le systeme pehd/ps/caco#3 resultant de l'incorporation de caco#3 dans le melange pehd/ps. Nous avons pu aussi relier l'effet des copolymeres elastomeres dans le systeme pehd/ps/caco#3 a leur mode d'action au niveau des differentes interfaces du systeme. Au bilan, nous arrivons a ameliorer a la fois la resistance au choc et la rigidite d'un melange pehd/ps (75/25) en incorporant 40% en masse de caco#3 et 4% de copolymere elastomere sebs. Cette demarche a ete appliquee avec succes sur des melanges industriels de produits recycles pehd et ps.

L'altération des lithologies himalayennes a potentiellement impacté le cycle global du carbone. Pour pouvoir contraindre et comprendre les processus qui se sont produits dans l'Himalaya et qui ont affecté ces cycles, nous devons être distinguer les signatures de l'altération du silicate et du carbonate dans la charge dissoute des fleuves de l'Himalaya. Des études antérieures ont tenté de le faire en utilisant diverses méthodes mais il n’existe toujours pas de consensus clair sur l’ampleur et le flux de l’altération du silicate dans l’Himalaya. Cette thèse propose l'utilisation du 40Ca comme traceur pouvant améliorer la quantification du flux d'altération du silicate et du carbonate dans la charge dissoute des rivières himalayennes. Des travaux antérieurs ont montré que le budget de l'eau de mer 40Ca est dominé par une source de manteau, de sorte que les carbonates marins ont une signature homogène de 40Ca indiscernable par rapport à la valeur du manteau. En revanche, la croûte supérieure de silicate devrait avoir développé une composition radiogénique. La différence entre la signature en Ca radiogénique des lithologies de carbonate et de silicate peut donc être utilisée pour différencier l’altération du carbonate et du silicate dans la charge dissoute des rivières. Nous présentons ici une étude géochimique comprenant des analyses de Ca radiogénique des rivières drainant les principales unités lithologiques de l'Himalaya, ainsi que des résultats provenant de sédiments, de substrat rocheux, de sol et de gravier. Nos résultats montrent que les carbonates de l’Himalaya ne présentent pas d’excès de 40Ca radiogénique malgré des signatures très variables 87Sr/86Sr, alors que les sédiments sont radiogènes (+0.9 à +4). Ceci suggère que pour Ca, contrairement à Sr, l'échange isotopique entre les lithologies silicate et carbonate a été minime. La composition en Ca radiogène de l'eau des rivières va de +0.1 dans les captages à prédominance carbonatée à +11 dans les rivières drainant des bassins versants silicatés. Pour les grandes rivières, les estimations du budget relatives à l’altération du silicate et du carbonate sur la base des éléments principaux et la composition en Ca radiogénique tendent à concorder. Cependant, pour certaines rivières plus petites, en particulier celles drainant des bassins à dominance silicatée dans les formations cristallines de HHC et du LH, certaines divergences sont observées. Celles-ci ne peuvent pas être attribuées à une définition imprécise de la composition chimique ou radiogénique en Ca des pôles de mélange utilisés pour la modélisation budgétaire, car les valeurs requises pour résoudre le modèle ne sont pas raisonnables. Ils ne peuvent pas non plus être expliqués par la précipitation de carbonates secondaires dans les rivières car la composition non radiogénique de carbonates suggère que ce processus n'est que mineur. Au contraire, ces différences peuvent être dues à la dissolution des traces de calcite radiogénique contenues dans les lithologies de silicate HHC et LH. Le vieillissement de ce matériau, qui ne représente qu'une infime partie de la surface du captage du silicate, pourrait produire une proportion substantielle du Ca radiogénique et pourrait ainsi avoir une influence significative sur le calcul des budgets de ces bassins à partir des données isotopiques. Néanmoins, comme cet effet est observé principalement dans les bassins à faible taux d’érosion des silicates, son influence sur les estimations du flux global de vieillissement du silicate sera mineure. Plus généralement, les résultats de cette thèse impliquent que le système 40Ca permet une résolution de problématiques qui ne peuvent pas être approfondies avec succès à l'aide d'isotopes Sr dans l'Himalaya. Des travaux supplémentaires sont nécessaires pour définir la gamme complète des compositions de Ca radiogénique dans l’Himalaya afin de répondre clairement aux questions concernant les flux d’altération des silicates
Weathering of Himalayan lithologies has had a potential impact on the global carbon cycle. To be able to constrain and understand the processes that occurred in the Himalayas that affected these cycles, we must be able to distinguish the signatures of silicate and carbonate weathering in the dissolved load of Himalayan rivers. Previous studies have attempted to do this using a variety of methods but there is still not a clear consensus on the magnitude and flux of silicate weathering in the Himalaya. This thesis proposes the use of 40Ca as a tracer that could improve the quantification of the silicate and carbonate weathering flux in the dissolved load of Himalayan rivers. Previous work has shown that the 40Ca budget of seawater is dominated by a mantle source, such that marine carbonates have a homogeneous 40Ca signature indistinguishable from the mantle value. In contrast, the upper silicate crust is expected to have developed a radiogenic composition. The difference between the radiogenic Ca signature of carbonate and silicate lithologies can be therefore used to differentiate between carbonate and silicate weathering in the dissolved load of rivers. Here, we present a geochemical survey, including radiogenic Ca analyses, of rivers draining the main lithological units of the Himalaya, as well as results from sediments, bedrock, soil and gravel. Our results show that Himalayan carbonates exhibit no radiogenic 40Ca excesses despite highly variable 87Sr/86Sr signatures, whereas sediments are variably radiogenic (+0.9 to +4). This suggests that for Ca, unlike for Sr, isotopic exchange between the silicate and carbonate lithologies has been minimal. The radiogenic Ca composition of river water ranges from +0.1 in carbonate dominated catchments to +11 in rivers draining silicate catchments. For large rivers, silicate and carbonate weathering budget estimates based on major elements and radiogenic Ca compositions tend to agree. However, for some smaller rivers, especially those draining silicate dominated basins in the HHC and LH formations, some discrepancies are observed. These cannot be attributed to poor definition of the chemical or radiogenic Ca composition of the endmembers used for budget modeling, as the values required to bring the estimates into agreement are unreasonable. They also cannot be explained by precipitation of secondary carbonates in the rivers as the non-radiogenic composition of the carbonate fraction of sediments suggests that this process is only minor. Rather, these discrepancies may be due to the dissolution/weathering of trace amounts of radiogenic calcite contained within HHC and LH silicate lithologies. The weathering of such material, which represents only a tiny fraction of the area of the silicate catchment, could yield a substantial proportion of the radiogenic Ca and may thus have a significant influence on the isotopically based weathering budgets of these basins. Nevertheless, as this effect is observed primarily in basins with low silicate erosion rates, its influence on estimates of the overall silicate weathering flux will be minor. More generally, the results of this thesis imply that the 40K–40Ca system can resolve issues that cannot be successfully addressed using Sr isotopes in the Himalaya. Further work is needed to define the full range of radiogenic Ca compositions in the Himalaya in order to clearly answer questions regarding silicate weathering fluxes

Este trabalho consiste na sÃntese de sÃlica mesoporosa de grande Ãrea superficial e seu uso para fins de tratamento de efluentes na remoÃÃo de metais tÃxicos e compostos orgÃnicos, alÃm do seu uso conjunto com CaCO3 e o extrato aquoso das folhas da planta Musa spp (Bananeira) que provavelmente contem taninos. Existem diversos trabalhos sobre a utilizaÃÃo de sÃlica mesoporosa, de taninos vegetais e do carbonato de cÃlcio, que possuem eficiÃncia na remoÃÃo de metais tÃxicos e de compostos orgÃnicos de corpos hÃdricos e efluentes. A sÃlica à um polÃmero inorgÃnico de formula mÃnima SiO2, onde muitos estudos utilizando sÃlica mostram sua eficiÃncia na remoÃÃo da grande maioria dos contaminantes das Ãguas por adsorÃÃo e/ou precipitaÃÃo, sendo esses contaminantes orgÃnicos ou inorgÃnicos e a sÃlica ainda podendo ser utilizada diversas vezes apÃs sua purificaÃÃo. Os taninos sÃo polihidroxifenois de origem vegetal (com massa entre 500 e 3000 g/mol) e os CaCO3 à um minÃrio com os mais diversos usos. Assim como os taninos, a utilizaÃÃo de carbonato de cÃlcio para o tratamento de efluentes jà se mostrou ser um mÃtodo simples e eficiente. Como amostragem para os testes de remoÃÃo de metais utilizando os compostos isoladamente e depois em conjunto foi utilizada uma soluÃÃo padrÃo dos sais de metais tÃxicos do 1 e do 3 grupos analÃticos, contendo aos metais de transiÃÃo da tabela periÃdica e o Al3+, que sÃo os grupos analÃticos de concentraÃÃo conhecida (1 grupo: Ag+, Pb2+, Hg22+; 3 grupos: Al3+, Cr2+, Fe2+, Mn2+, Zn2+, Co2+ e Ni2+); onde foram feitos os testes de eficiÃncia e as adiÃÃes dos compostos para retirada dos contaminantes. Ambos os testes de eficiÃncia e de adiÃÃo mostraram retirar boa parte de micro poluentes orgÃnicos e inorgÃnicos, sendo a concentraÃÃo de compostos orgÃnicos medidos pela DQO diminuÃdos a nÃveis abaixo de 5 mg/L e metais como Al3+, Fe2+ e Pb2+ foram removidos da soluÃÃo com eficiÃncia de 95% em relaÃÃo a concentraÃÃo inicial.
This work consists in the synthesis of mesoporous silica of high surface area and its use for wastewater treatment in the removal of toxic metals and organic compounds, and their use together with CaCO3 and aqueous extract of the leaves of the plant Musa spp (Banana) that probably contains tannins. There are several studies on the use of mesoporous silica, vegetable tannin and calcium carbonate, which have efficiency in the removal of toxic metals and organic compounds of bodies of water and wastewater. Silica is an inorganic polymer of formula minimum SiO2, with many studies using silica show its efficiency in removing the majority of contaminants from water by adsorption and / or precipitation with organic or inorganic contaminants such and the silica may still be used several times after its purification. The tannins are polihidroxifenois of plant origin (with mass between 500 and 3000 g / mol) and CaCO3 is a mineral with many uses. As tannins, the use of calcium carbonate to sewage treatment has proved to be a simple and efficient method. As a sample for testing for metal removal using the compounds separately and then together we used a standard solution of the salts of toxic metals of the 1st and 3rd groups analytical containing the transition metals of the periodic table and Al3+, which groups are Analytical known concentration (1st group: Ag+, Pb2+ HG22+; 3rd group: Al3+, Cr2+, Fe2+, Mn2+, Zn2+, Co2+ and Ni2+), where the tests were done and efficiency additions of compounds to remove the contaminants. Both tests of efficiency and plus shown remove much of micro organic and inorganic pollutants, and the concentration of organic compounds measured by COD reduced to levels below 5 mg / l and metals such as Al3+, Fe2+ and Pb2+ were removed from the solution 95% efficiency compared to the initial concentration.

Biomineralization refers to the production of mineralized tissues by organisms. The fine control which organisms can exert over this process produces crystals with morphologies and properties contrasting to that of non-biogenic crystals and specifically altered to suit the required functional need. A key model system of biomineralization are a unicellular marine algae, coccolithophores, which produce calcium carbonate scales known as coccoliths. These coccoliths are comprised of arrangements of single crystals of calcite interlocked to form a plate-shaped structure. Coccoliths are developed intracellularly in a specialised compartment called the coccolith vesicle, before being extruded to the cell surface. In this work, two vital components of the coccolith biomineralization process are investigated - a soluble polysaccharide thought to act as a habit modifier and an insoluble organic scaffold known as a baseplate that provides the surface for nucleation and growth of the crystals. Whilst both these elements are thought to play a key part in the biomineralization process, the role of each is not fully understood. To investigate the effect of coccolith-associated polysaccharides (CAPs) on nucleation and polymorph selection, two systems that promote different polymorphs of calcium carbonate were utilised. In both systems, the intracrystalline polysaccharide fraction extracted from one species, Gephyrocapsa oceanica, was able to promote calcite nucleation in vitro, even under conditions favouring the kinetically-privileged polymorphs of calcium carbonate: vaterite and aragonite. As this property is not observed with CAPs extracted from its 'sister species', Emiliania huxleyi, the in vivo function of CAPs may differ between the two species. Both cryo-transmission electron microscopy (cryoTEM) and scanning electron microscopy (SEM) were used to determine the mechanism of calcite growth in the presence of G. oceanica CAPs, showing its impact on the forming amorphous calcium carbonate (ACC), decreasing the size of the particles and producing irregular, angular particles. Using cryo-electron tomography (cryoET), it was possible to create a 3D representation of the structure of the baseplate from the coccolithophore Pleurochrysis carterae, revealing its two-sided organisation. Examination of several stages of the coccolith growth process demonstrated the interlocking nature of the calcite crystals that make up the coccolith and the progression of the crystal morphologies over time, and the interaction of these crystals with the baseplate rim. Additionally, the effect of inhibiting carbonic anhydrase (CA), an enzyme involved in the regulation of carbonate species, revealed that inhibition of CA can affect coccolithogenesis as well as cell proliferation.

L’objectif principal de cette thèse est de mieux comprendre les différents facteurs contrôlant la pompe biologique de carbone en Atlantique Nord et dans l’Océan Austral, à proximité des îles Kerguelen, en utilisant notamment deux approches: le Thorium-234 (234Th) et le baryum biogénique (Baxs).En Atlantique Nord, les flux d’export de carbone organique particulaire (POC) augmentent lorsqu’ils sont associés à des minéraux biogéniques (silice biogénique et carbonate de calcium) et lithogènes, capable de lester les particules. L’efficacité d’export, généralement plus faible que précédemment supposé (< 10%), est inversement corrélée à la production, soulignant un décalage temporel entre production et export. La plus forte efficacité de transfert, i.e. la fraction de POC atteignant 400m, est reliée à des particules lestées par du carbonate de calcium ou des minéraux lithogènes.Les flux de reminéralisation mésopélagique sont similaires ou parfois supérieurs aux flux d’exports et dépendent de l’intensité du développement phytoplanctonique, de la structure en taille, des communautés phytoplanctoniques et des processus physiques (advection verticale).Comme observé pour le POC, l’export des éléments traces est influencé par les particules lithogènes provenant des marges océaniques, mais aussi des différentes espèces phytoplanctoniques.Dans l’Océan Austral, la zone à proximité de l’île de Kerguelen est naturellement fertilisée en fer, augmentant les flux d’export de fer, d’azote et de silice biogénique. Il a été démontré que la variabilité des flux dépendait des communautés phytoplanctoniques dans la zone fertilisée
The main objective of this thesis is to improve our understanding of the different controls that affect the oceanic biological carbon pump. Particulate export and remineralization fluxes were investigated using the thorium-234 (234Th) and biogenic barium (Baxs) proxies.In the North Atlantic, the highest particulate organic carbon (POC) export fluxes were associated to biogenic (biogenic silica or calcium carbonate) and lithogenic minerals, ballasting the particles.Export efficiency was generally low (< 10%) and inversely related to primary production, highlighting a phase lag between production and export. The highest transfer efficiencies, i.e. the fraction of POC that reached 400m, were driven by sinking particles ballasted by calcite or lithogenic minerals.The regional variation of mesopelagic remineralization was attributed to changes in bloom intensity, phytoplankton cell size, community structure and physical forcing (downwelling). Carbon remineralization balanced, or even exceeded, POC export, highlighting the impact of mesopelagic remineralization on the biological pump with a near-zero, deep carbon sequestration for spring 2014.Export of trace metals appeared strongly influenced by lithogenic material advected from the margins. However, at open ocean stations not influenced by lithogenic matter, trace metal export rather depended on phytoplankton activity and biomass.A last part of this work focused on export of biogenic silica, particulate nitrogen and iron near the Kerguelen Island. This area is characterized by a natural iron-fertilization that increases export fluxes. Inside the fertilized area, flux variability is related to phytoplankton community composition

The rapid increase in the demand on fresh water due the increase in the world population and scarcity of natural water puts more stress on the desalination industrial sector to install more desalination plants around the world. Among these desalination plants, multistage flash desalination process (MSF) is considered to be the most reliable technique of producing potable water from saline water. In recent years, however, the MSF process is confronting many problems to cut off the cost and increase its performance. Among these problems are the non-condensable gases (NCGs) and the accumulation of fouling which they work as heat insulation materials. As a result, the MSF pumps and the heat transfer equipment are overdesigned and consequently increase the capital cost and decrease the performance of the plants. Moreover, improved process control is a cost effective approach to energy conservation and increased process profitability. Thus, this study is motivated by the real absence of detailed kinetic fouling model and implementation of advance process control (APC). To accomplish the above tasks, commercial modelling tools can be utilized to model and simulate MSF process taking into account the NCGs and fouling effect, and optimum control strategy. In this research, gPROMS (general PROcess Modeling System) model builder has been used to develop the MSF process model. First, a dynamic mathematical model of MSF is developed based on the basic laws of mass balance, energy balance and heat transfer. Physical and thermodynamic properties of brine, distillate and water vapour are included to support the model. The model simulation results are validated against actual plant data published in the literature and good agreement with these data is obtained. Second, the design of venting system in MSF plant and the effect of NCGs on the overall heat transfer coefficient (OHTC) are studied. The release rate of NCGs is studied using Henry’s law and the locations of venting points are optimised. The results reveal that high concentration of NCGs heavily affects the OHTC. Furthermore, advance control strategy namely: generic model control (GMC) is designed and introduced to the MSF process to control and track the set points of the two most important variables in the MSF plant; namely the Top Brine Temperature (TBT) which is the output temperature of the brine heater and the Brine Level (BL) in the last stage. The results are compared to conventional Proportional Integral Derivative Controller (PID) and show that GMC controller provides better performance over conventional PID controller to handle a nonlinear system. In addition, a new control strategy called hybrid Fuzzy-GMC is developed and implemented to control the same aforementioned loops. Its results reveal that the new control outperforms the pure GMC in some areas. Finally, a dynamic fouling model is developed and incorporated into the MSF dynamic process model to predict fouling at high temperature and high velocity. The proposed dynamic model considers the attachment and removal mechanisms of calcium carbonate and magnesium hydroxide with more relaxation of the assumptions. Since the MSF plant stages work as a series of heat exchangers, there is a continuous change of temperature, heat flux and salinity of the seawater. The proposed model predicts the behaviour of fouling based on the physical and thermal conditions of every single stage of the plant.

Many of the habitats occupied by fish are highly dynamic, naturally demonstrating substantial abiotic fluctuations over diurnal, tidal or seasonal cycles. It is also the case that throughout their 545 million year evolutionary history, fish have existed in aquatic environments very different to those of the present day. However, the past several decades have seen unprecedented rates of environmental change, at local and global scales, arising from human activities. The two major themes of the present thesis are: 1) Respiratory responses of fish to changes in environmental oxygen and temperature in the context of exploring intra- and inter-specific trait variation and its ecological implications 2) The effects of environmental factors (oxygen, carbon dioxide, temperature and seawater chemistry) on the intestinal precipitation and excretion of calcium carbonate by marine teleosts. In the first study (chapter two) a comprehensive database of fish critical PO2 (Pcrit) data compiled from the published literature is presented. The systematic review of this literature provided the opportunity to critically examine methodologies for determining Pcrit as well as its usefulness as an indicator of hypoxia tolerance in fish. The second study (chapter three) examines whether inter- and intra-specific variation in thermal and hypoxia tolerance in two reef snapper species (Lutjanus carponotatus and Lutjanus adetii) reflects their distributions across the contrasting biophysical environments of the reef flat and reef slope surrounding Heron Island on the Great Barrier Reef. L. carponotatus was clearly the most thermally and hypoxia tolerant of the two species, demonstrating a ~3.5 °C wider thermal tolerance zone (higher CTmax, lower CTmin) and ~26% lower Pcrit than L. adetii. These results suggest that the contrasting distribution of these species between flat and slope reef zones is reflected in their physiological tolerances. However, there was no evidence of intra-species variation in tolerance between flat and slope caught L. carponotatus individuals, indicating that this species does not form physiologically distinct subpopulations between these reef zones. The third study (chapter four) experimentally quantified the effect of hypercarbia (3000 μatm) and hypoxia (50% air saturation) on gut carbonate production by the European flounder (Platichthys flesus). Both hypercarbia and hypoxia resulted in a significant increase in carbonate excretion rate (1.5-fold and 2.4-fold, respectively) and acted synergistically when combined. In the final study (chapter five), gut carbonate production was measured in the European flounder undergoing conditions simulating the ‘calcite seas’ of the Cretaceous. The results of this study support the hypothesis that ocean conditions prevalent during the Cretaceous period resulted in piscine carbonate production rates substantially higher (~14-fold) than the present day. Ultimately, this thesis directly links the environmental physiology of fish at the individual level to wider scale implications (past, present and future), ranging from local ecological patterns all the way up to global carbon cycles.

abstract: Many species e.g. sea urchin form amorphous calcium carbonate (ACC) precursor phases that subsequently transform into crystalline CaCO3. It is certainly possible that the biogenic ACC might have more than 10 wt% Mg and ∼ 3 wt% of water. The structure of ACC and the mechanisms by which it transforms to crystalline phase are still poorly understood. In this dissertation our goal is to determine an atomic structure model that is consistent with diffraction and IR measurements of ACC. For this purpose a calcite supercell with 24 formula units, containing 120 atoms, was constructed. Various configurations with substitution of Ca by 6 Mg ions (6 wt.%) and insertion of 3-5 H2O molecules (2.25-3.75 wt.%) in the interstitial positions of the supercell, were relaxed using a robust density function code VASP. The most noticeable effects were the tilts of CO3 groups and the distortion of Ca sub-lattice, especially in the hydrated case. The distributions of Ca-Ca nearest neighbor distance and CO3 tilts were extracted from various configurations. The same methods were also applied to aragonite. Sampling from the calculated distortion distributions, we built models for amorphous calcite/aragonite of size ∼ 1700 nm3 based on a multi-scale modeling scheme. We used these models to generate diffraction patterns and profiles with our diffraction code. We found that the induced distortions were not enough to generate a diffraction profile typical of an amorphous material. We then studied the diffraction profiles from several nano-crystallites as recent studies suggest that ACC might be a random array of nanocryatallites. It was found that the generated diffraction profile from a nano-crystallite of size ∼ 2 nm3 is similar to that from the ACC.
Dissertation/Thesis
Ph.D. Physics 2012

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Chemistry. University of the Witwatersrand, Johannesburg. May 2016
In this research project, the morphogenesis and polymorphism of calcium carbonate (CaCO3) and its subsequent use as a template in the fabrication of hollow carbon spheres (HCS) is reported. A series of ratios (i.e. 5:0, 5:1, 5:2, 5:3, 5:4, 5:5, and 0:5) of binary solvent mixtures consisting of polar aprotic (dimethylformamide and dimethyl sulfoxide) and polar protic (methanol, ethanol, isopropanol, and 2-butanol) solvents, with 10% PEG200 as a crystal modifier, were used to influence the morphogenesis and polymorphism of precipitated CaCO3 (PCC). The PCC products were characterised using scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), and laser Raman spectroscopy. An increase in the ratio of the polar protic solvent (methanol, ethanol, isopropanol, and 2-butanol) relative to the polar aprotic solvent (DMF & DMSO) within the binary solvent mixture favored the formation of vaterite particles of different morphologies, while an increase in the ratio of polar aprotic solvent (DMF & DMSO) within the binary solvent mixture favored the precipitation of rhombohedral calcite crystals. Time-resolved ex situ PXRD and SEM measurements revealed that the nucleation and phase transformation of the CaCO3 under polar protic and aprotic solvents followed the dissolution-reprecipitation mechanism. The major phase transformation occurred within 3 hours after mixing the precursor solutions. The effect of poly (4-styrenesulfonic acid) (PSSA) as an additive in the crystallisation of CaCO3 at different temperatures (i.e. 30, 40, 75, and 100 °C) and different crystallisation times (3, 6, 12, and 24 hrs) was investigated. The as-synthesised CaCO3 products were subjected to: SEM, laser Raman spectroscopy, PXRD, thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). The crystallisation of CaCO3 in the presence of PSSA resulted in the self-assembly of vaterite particles into spherical bulk crystals. Varying the crystallisation temperature led to different particle attachment (CPA) pathways, which in turn resulted in bulk crystal morphologies that varied. Changes in the crystallisation temperature were found to not have changed the polymorphism of the precipitated CaCO3 due to the kinetic stabilisation effects of PSSA, instead hollow vaterite spheres formed at 75 and 100 °C. The possibility to synthesise HCS using CaCO3 as a template under chemical vapour deposition (CVD) at different temperatures (i.e. 600, 700 and 800 °C) was, for the first time, demonstrated. The evolution of CO2(g) from the decomposition of the template during CVD resulted in the formation of a rough surface topography on the carbon shell of the HCS. This surface roughness increased with the increase in the reaction temperature due to the increased rate of CaCO3 decomposition. The structural integrity of the spherical template was not affected by the CO2(g) evolution during carbonisation at all the reaction temperatures. The as-synthesised HCS at 600, 700, and 800 °C gave specific BET surface areas of: 193, 55, and 51 m2/g, respectively.
MT2016

Calcium carbonate biomineralization is a self-assembly process that has been studied to be applied in the biomedical field to encapsulate biomolecules. Advantages of engineering mineral capsules include improved drug loading efficiencies and protection against external environment. However, common production methods result in heterogeneous capsules and subject biomolecules to heat and vibration which cause irreversible damage. To overcome these issues, a microfluidic device was designed, manufactured and tested in terms of selectivity for water and oil to produce a W/O/W emulsion. During the development of this work there was one critical challenge: the selective functionalization in closed microfluidic channels. Wet chemical oxidation of PDMS with 1M NaOH, confirmed by FTIR, followed by adsorption of polyelectrolytes - PDADMAC/PSS - confirmed by UV-Vis and AFM results, render the surface of PDMS hydrophilic. UV-Vis spectroscopy also confirmed that this modification did not affect PDMS optical properties, making possible to monitor fluids and droplets. More important, with this approach PDMS remains hydrophilic over time. However, due to equipment constrains selectivity in microchannels was not achieved. Therefore, emulsion studies took place with conventional methods. Several systems were tried, with promising results achieved with CaCO3 in-situ precipitation, without the use of polymers or magnesium. This mineral stabilizes oil droplets in water, but not in air due to incomplete capsule formation.

D.Phil. (Chemistry)
The formation ofcalcium carbonate scale is a major problem in industry as well as in households. The scale that forms acts as an insulator, decreasing the effectiveness ofheat exchangers, be it a water cooling systems or a water heating system This raises the energy costs ofthat company and the costs of cleaning are expensive. Physical water treatment has been used for at least 50 years in the treatment ofwater with scale forming potential to reduce the formation ofthis scale. In thisthesis, tests were made on a magnetic and constantelectric field antiscaling device on the effect they have, ifany, on CaC03 scale formation. An attempt will be made to give a mechanism for any effect found. It is hoped that a contribution is made by this research in clearing up the misconceptions that abound in this controversial field ofphysical water treatment. Water with a high calcium bicarbonate content was exposed to the antiscaling devices and then calcium carbonate was forced to precipitate out ofsolution. This precipitation was followed by meauring the pH and the crystal structure ofthe precipitated calcium carbonate was studied. The most important results were that by exposing the calcium bicarbonate solution to an antiscalingdevice, the start ofprecipitation ofthe calcium carbonate was significantly delayed and the crystal structure of the calcium carbonate that formed was predominantly aragonite as opposed to calcite that usually formed.

Recently, there has been increased effort in researching methods for producing hollow nanostructures because of their potential impact in the fields of catalysis, separation processes, drug delivery, and energy storage and conversion devices. The purpose of this thesis is to describe a method for forming hollow inorganic-organic hybrid nanoboxes and nanoframes. This approach relies upon ionic liquid (1-butyl-3-methyl-imidazolium chloride) mediated auto-templating assembly of CaCO3 and chitosan to form nanoframes (two open faces) and nanoboxes (one open face). The average dimension of the nanostructures formed was 339 ± 95 x 299 ± 89 nm. Detailed structure of nanoboxes and nanoframes were obtained by 3-D electron tomography and X-ray diffraction. Chemical bonding was determined by FTIR, and the ratio of organics to inorganics in the nanostructures was determined by thermal gravimetric analysis. The chitosan to CaCO3 weigh ratio, mixing strength, temperature, and dialysis time were varied to further elucidate the method of formation. It was found that increasing the mixing power caused the equilibrium nanostructure dimension to decrease. On the other hand, varying the experimental temperature in the range of 80 to 160˚C did not affect the nanostructure dimension. The dialysis study showed that during dialysis the nanostructure core was increasingly removed. Nanoframes were observed after 72 hours of dialysis. With further dialysis, there was continued erosion of nanoframes. Results indicate that the concentration gradient and the solubility difference between the mixture components were responsible for this transformation.

Scaling in green liquor handling systems is a persistent problem in many kraft mills. Scaling is commonly believed to be the result of pirssonite (Na2Ca(CO3)2∙2H2O) deposition. In this work, scale characterization was performed by analyzing 12 scale samples obtained from 10 kraft mills. Only 4 samples were identified as pirssonite while the remaining consisted of CaCO3. The predominant presence of CaCO3 in the scale samples was found to be the result of selective dissolution of Na2CO3 from pirssonite scale, leaving CaCO3 behind. Experimental studies were also conducted to study pirssonite solubility under green liquor conditions. Results obtained from these studies were used to create and validate a database for pirssonite in the OLI Systems® software to predict its formation. This database was used to generate a family of pirssonite solubility curves that can be used by the kraft mills as operational guidelines to prevent pirssonite precipitation.

The extensive growth of nanotechnology has necessitated the development of economical and robust methods for large scale production of nanomaterials. It requires detailed quantitative understanding of lab-scale processes to enable effective scale-up and development of new contacting strategies for their controlled synthesis. In this thesis, attempts are made in both the directions using experimental and modelling approaches for synthesis of different nanoparticles. The two-phase Brust--Schiffrin protocol for the synthesis of gold nanoparticles was investigated first. The mechanism of transfer of reactants from aqueous to organic phase using phase transfer catalyst (PTC) was investigated using the measurement of interfacial tension, viscosity, SLS, SAXS, 1H NMR, DOSY-NMR, and Karl-Fischer titration. The study shows that the reactants are transferred to organic phase through the formation of hydrated complexes between reactants and PTC rather than through the solubilization of reactants in water core of inverse micelles of PTC, proposed recently in the literature. The particle synthesis reactions thus occur in the bulk organic phase. The extensive body of seemingly disparate experimental findings on Brust--Schiffrin protocol were put together next. The emerging picture ruled out both thermodynamic considerations and kinetics based arguments as exemplified by the classical LaMer's mechanism with sequential nucleation growth capping for size control in Brust--Schiffrin protocol. A new model for particle synthesis was developed. The model brought out continued nucleation--growth--capping based size control, an hitherto unknown mechanistic route for the synthesis of monodisperse particles, as the main mechanism. The model not only captured the reported features of the synthesis but also helped to improve the uniformity of the synthesized particles, validated experimentally. The two-step mechanism of Finke--Watzky---first order nucleation from precursor and autocatalytic growth of particles---proposed as an alternative to LaMer model to explain an induction period followed by a sigmoidal decrease in precursor concentration for the synthesis of iridium nanoparticles was investigated next. The mechanism is tested using an equivalent population balance model for its ability to explain the experimentally observed near constant breadth of the evolving size distribution as well. The predictions show that while it captures precursor conversion well, it fails to explain particle synthesis on account of its inability to suppress nucleation. A minimal four-step mechanism with additional steps for nucleation from reduced iridium atoms and their scavenging using particle surface is proposed. The new mechanism when combined with the first or second order nucleation, or classical nucleation with no scavenging of reduced atoms also fails to suppress nucleation. A burst like onset of nuclei formation with homogeneous nucleation and the scavenging of reduced atoms by particles are simultaneously required to explain all the reported features of the synthesis of iridium nanoparticles. A new reactor is proposed for continuous production of CaCO3 nanoparticles in gas-liquid reaction route. The key feature of the new reactor is the control of flow pattern to ensure efficient mixing of reactants. A liquidliquid reaction route for production of CaCO3 nanoparticles is also optimized to produce nanoparticles at high loading. Optimum supersaturation combined with efficient breakup of initial gel-like structure by mechanical agitation and charge control played a crucial role in producing nano sized CaCO3 particles.

The extensive growth of nanotechnology has necessitated the development of economical and robust methods for large scale production of nanomaterials. It requires detailed quantitative understanding of lab-scale processes to enable effective scale-up and development of new contacting strategies for their controlled synthesis. In this thesis, attempts are made in both the directions using experimental and modelling approaches for synthesis of different nanoparticles. The two-phase Brust--Schiffrin protocol for the synthesis of gold nanoparticles was investigated first. The mechanism of transfer of reactants from aqueous to organic phase using phase transfer catalyst (PTC) was investigated using the measurement of interfacial tension, viscosity, SLS, SAXS, 1H NMR, DOSY-NMR, and Karl-Fischer titration. The study shows that the reactants are transferred to organic phase through the formation of hydrated complexes between reactants and PTC rather than through the solubilization of reactants in water core of inverse micelles of PTC, proposed recently in the literature. The particle synthesis reactions thus occur in the bulk organic phase. The extensive body of seemingly disparate experimental findings on Brust--Schiffrin protocol were put together next. The emerging picture ruled out both thermodynamic considerations and kinetics based arguments as exemplified by the classical LaMer's mechanism with sequential nucleation growth capping for size control in Brust--Schiffrin protocol. A new model for particle synthesis was developed. The model brought out continued nucleation--growth--capping based size control, an hitherto unknown mechanistic route for the synthesis of monodisperse particles, as the main mechanism. The model not only captured the reported features of the synthesis but also helped to improve the uniformity of the synthesized particles, validated experimentally. The two-step mechanism of Finke--Watzky---first order nucleation from precursor and autocatalytic growth of particles---proposed as an alternative to LaMer model to explain an induction period followed by a sigmoidal decrease in precursor concentration for the synthesis of iridium nanoparticles was investigated next. The mechanism is tested using an equivalent population balance model for its ability to explain the experimentally observed near constant breadth of the evolving size distribution as well. The predictions show that while it captures precursor conversion well, it fails to explain particle synthesis on account of its inability to suppress nucleation. A minimal four-step mechanism with additional steps for nucleation from reduced iridium atoms and their scavenging using particle surface is proposed. The new mechanism when combined with the first or second order nucleation, or classical nucleation with no scavenging of reduced atoms also fails to suppress nucleation. A burst like onset of nuclei formation with homogeneous nucleation and the scavenging of reduced atoms by particles are simultaneously required to explain all the reported features of the synthesis of iridium nanoparticles. A new reactor is proposed for continuous production of CaCO3 nanoparticles in gas-liquid reaction route. The key feature of the new reactor is the control of flow pattern to ensure efficient mixing of reactants. A liquidliquid reaction route for production of CaCO3 nanoparticles is also optimized to produce nanoparticles at high loading. Optimum supersaturation combined with efficient breakup of initial gel-like structure by mechanical agitation and charge control played a crucial role in producing nano sized CaCO3 particles.