The Round Top laccolith is considered to be one of the youngest laccoliths in a series of five known as the Sierra Blanca peaks, located in Hudspeth county, Texas. The laccolith is anomalous within the region in that it is peraluminous and enriched in HREEs, F, and U, and is comprised of intermingled discrete packages of various rhyolite types. The laccolith rhyolite varies in color from gray, purple, red, and tan, which combine locally to form distinct geometric mottled textures. The general composition of the rhyolite is 48-52% potassium feldspar, 28-30% quartz, 8-14% plagioclase feldspar, 4-5% annite biotite, 2-3% magnetite-hematite, 1% zircon, and 1% trace phases. The morphology of the trace phases suggests quenching of a late-stage volatile-rich vapor phase at the time of the laccolith formation. The rhyolite displays a wide array of unique mineralogical characteristics indicative to rapid emplacement and metastable crystallization conditions, including three-part quartz phenocrysts, hourglass sector-zoned potassium feldspars, and late-stage anhedral zircons. Unique accessory and trace phases include cassiterite, cerianite-(Ce), changbaiite, columbite, cryolite, tantalite, thorite, yttrofluorite, yttrocerite, and two unidentified minerals named (W) and (X). Initial alteration of the laccolith by high temperature volatile-rich vapor during the late stages of crystallization caused the partial dissolution of the feldspars and quartz. Subsequent quenching of this high temperature vapor phase produced the abundant interstitial, and pore filling REE-fluorides common to the laccolith. The variation in rhyolite color and the presence of the mottled textures are a direct result of partial oxidation of the laccolith by secondary fluids. The oxidizing fluids migrated within the laccolith along an extensive fracture network, altering the adjacent wallrock by oxidizing magnetite phenocrysts to hematite. The gray, purple, and red rhyolite types reflect an increase in turbidity caused by hematitic inclusions primarily within the pore spaces of the potassium feldspar portions of the groundmass. The tan rhyolite is locally restricted to the base of the laccolith and has been subjected to an intense degree of alteration independent of the other rhyolite types, primarily indicated by the conversion of feldspars to clay. Petrographic, microbeam, and geochemical studies have determined little variation in REE concentration between the three rhyolites of similar alteration intensity, but have indicated a depletion in LREEs within the more altered tan rhyolite. The average REE+Y content for the rhyolites sampled (n=11) ranges between 249 ppm and 518 ppm. The REE+Y concentrations between rhyolite samples of the same type show some variation, possibly indicating a correlation between alteration and REE+Y abundance and/or innate heterogeneity in the vapor phase during the initial laccolith formation. The magma emplaced at Round Top underwent a prolonged evolutionary process of fractionation/differentiation as evident by the unusual mineral assemblage and geochemical enrichment associated with the laccolith (e.g. extremely negative europium anomaly, and the positive La/Yb correlation). Future exploration for Round Top style REE-deposits should center within long-lived, tectonically active and complex regions where laccoliths are likely to exist. Specifically, exploration should focus on identifying the youngest laccolith in a felsic series, as this is the most likely to contain the greatest abundance of incompatible elements within the laccolithic group. The early alteration of feldspars by the high temperature vapor phase was crucial in the development of the REE+Y enrichment at Round Top. The feldspar dissolution provided abundant open pore space that was subsequently filled by the REE-fluorides. Thus, exploration should additionally seek laccoliths that have undergone a similar early alteration process, and expand to potential laccolith groups not yet exposed by erosional processes. / text

Ce travail porte sur la compréhension du phénomène d'instabilité qui se produit dans le procédé d'hydroconversion des résidus sous vide (RSV). Au delà de 60% de conversion du RSV, l'instabilité se manifeste par un dépôt solide d'hydrocarbures lourds dans les unités industrielles de conversion des résidus, ce qui empêche d'atteindre un niveau de conversion du RSV plus élevé. L'objectif de cette thèse consiste à mieux comprendre l'influence du catalyseur utilisé dans le procédé d'hydroconversion sur l'apparition du phénomène d'instabilité. Des catalyseurs dopés au fluor et sodium ont été préparés par ajout de dopants à la surface d'un catalyseur NiMo/Al2O3 de référence. Après leur caractérisation, les catalyseurs ont été testés sur charge réelle RSV en réacteur autoclave. Les tests catalytiques ont été réalisés à haute température dans les conditions industrielles (430°C) et à plus basse température (390°C), afin de favoriser les réactions catalytiques par rapport aux réactions thermiques. Les tests catalytiques réalisés à 390 et 430°C montrent une teneur en sédiments deux fois moins importante avec le catalyseur F-NiMo, ce qui est expliqué par une amélioration de la conversion des asphaltènes. Celle-ci est expliquée par l'amélioration des réactions d'hydrogénation et de l'acidité, et par une meilleure résistance au cokage à 390°C. L'effet de la température sur la stabilité a également été étudié. Les résultats démontrent que la teneur en sédiments des effluents est deux fois supérieure pour les tests réalisés à 430°C par rapport aux tests réalisés à 390°C. Cet accroissement de l'instabilité est attribué à un caractère plus aromatique et condensé des molécules qui précipitent (asphaltènes), qui ont en conséquence une tendance accrue à s'agréger, et par la désalkylation des molécules qui stabilisent (résines). / This work focuses on the instability phenomena occurring during vacuum residue hydroconversion. At high level of residue conversion, carbonaceous sediments (sediments) are formed and have detrimental effects on the industrial units during the hydroprocessing operations. The aim of this work is investigate the influence of the catalyst used inhydroconversion process on the sediments formation. Modified catalysts have been prepared by sodium and fluorine deposition on a NiMo/Al2O3 reference catalyst. After having been characterized, the catalysts have been tested in a perfectly stirred batch reactor. Catalytic tests have been performed at high temperature (430°C) in industrial conditions and at lower temperature (390°C) in order to favor catalytic reactions rather thermic reactions. The catalytic tests at the two temperatures show that the amount of sediments is two times lower with F-NiMo catalyst. This is explained by the improvement of asphaltenes conversion due to an increase of catalyst acidity and hydrogenation reactions. At 390°C, coking with F-NiMo catalyst is reduced so that porous volume is higher. The temperature effect on effluents stability has also been studied. Results show that the amount of sediments is twice lower at 390°C for a same catalyst. The increase of instability at 430°C is attributed to more condensed and aromatic asphaltenes and resins dealkylation which increase selfaggregation tendency of asphaltenes.

The aim of this thesis is to determine the sources, controls and risk aspects of fluoride in surface water and groundwater in a region of southeastern Sweden where the fluorine-rich 1.45 Ga circular Götemar granite (5 km in diameter) crops out in the surrounding 1.8 Ga granites and quartz monzodiorites (TIB rocks). The materials of this thesis include both primary data, collected for the purpose of this thesis, and a large set of secondary data, retrieved from the Swedish Nuclear Fuel and Waste Management Co., the Swedish Geological Survey and the Kalmar County Council. A characteristic feature of the area is high fluoride concentrations in all kinds of natural waters, including surface waters (such as streams) and groundwater in both the Quaternary deposits (regolith groundwater) and bedrock fractures (fracture groundwater). A number of potential sources and controls of the high fluoride concentrations were investigated, including a variety of geological, mineralogical, mineral-chemical and hydrological features and processes. For the stream waters and regolith groundwater, high fluoride concentrations were correlated with the location of the Götemar granite. This finding is explained by the discharge of fluoride-rich groundwater from fractures in the bedrock and/or the release of fluoride due to the weathering of fluorine-bearing minerals in the Quaternary deposits; however, the Quaternary deposits had considerably lower fluoride concentrations than the underlying bedrock. The high fluoride concentrations in the fresh fracture groundwater (up to 7.4 mg/L) in the TIB-rocks are proposed to be the result of long residence times and the alteration/dissolution of fluorine-bearing primary and secondary minerals along the fracture walls. In terms of risk aspects, this thesis shows that fluoride can add to the transport and inorganic complexation of aluminium in humic-rich, acidic streams. Additionally, 24 % of the children in households with private wells in Kalmar County were assessed to be at risk of excess fluoride intake based on the WHO drinking water guideline value (1.5 mg/L). However, the risk increased significantly when instead the US EPA reference dose (0.06 mg/kg-day) was used, both when all relevant exposure pathways were taken into account as well as water consumption alone. Hence, it is shown that the risk of an excess intake of fluoride is strongly dependent on the basis for evaluation.

MSc dissertation - Faculty of Engineering and the Built Environment / Waste electrolyte from fluorine cells is a major waste problem for the fluorine chemical industry. Processes have to be developed to reduce, recycle and re-use the spent electrolyte that has up to now been stockpiled. This dissertation is a compilation of the research work that has been done to derive a process to treat waste electrolyte for re-use. Different conversion processes were investigated to develop a Waste Management plan for the fluorine generating facility in respect of the electrolyte. Gravity settling, centrifuging, filtration, the addition of KF.HF to the to the electrolyte to decrease the HF concentration in the electrolyte and consequently decrease the solubility of Fe, Cu and Ni and addition of NaOH to the electrolyte to convert soluble Fe to the insoluble triple salt were tested. Gravity settling and centrifuging were shown to produce the best solution. However, significant sedimentation of the insoluble metal impurities in the electrolyte is timeously. The implementation of sedimentation as an industrial separation process to purify waste electrolyte of excess metal impurities is therefore impractical. The results indicated that sparging molten electrolyte with N2 gas to remove HF (thus precipitating soluble Fe, Cu and Ni, and removing moisture to reduce corrosion of metal components), followed by sediment centrifuging, appears to be a practical basis for an industrial waste electrolyte treatment process. During an assessment carried out by the Economics Trends Research Group (ETRG) (3) at the University of Cape Town a strong argument was made for the need to direct companies in South Africa to address environmental concerns with high priority. In South Africa there is very little awareness of the concept of Clean Technology. Not only must the level of contamination be reduced before waste is released into the environment, but natural resources like water must be conserved, and energy consumption must be reduced. Public concern over degradation of the environment can no longer be ignored. Globally, the chemical industries are considered to be the main culprits in the degradation of the environment. The assessment carried out by the ETRG showed that the chemical industries are classed among the top 5 generators of toxic and hazardous waste in every country. The metallurgical sector (mining) is in most cases classed as the top waste generator. Development and implementation of technologies that are more efficient are not a matter of choice any more. Each new facility that is developed should meet the challenge of generating as little waste as possible. Unfortunately, many old industries and facilities did not focus on increasing efficiency and minimising waste. These old facilities experience a challenge now to develop technology to make them part of this Cleaner Production and Technology era. Cleaner Production implies generating less effluent or waste and recycling waste to be used as raw material in the same or another facility. Cleaner Production also concentrates on the increase of efficiency but this is often limited by the chemical properties of substances. This research was based on the ideas for implementation of Cleaner Production in the fluorine generation facility at Necsa. Waste reduction almost always implies investment in equipment and development of new technologies. However there is ample evidence to show that the cost of rehabilitation of contaminated environment is exceedingly high in comparison with the precautionary steps taken to prevent contamination. Waste/Effluent Management have become new buzz words in the industrial environment.

In the Introduction part of this thesis, the chemistry of organofluorine compounds is discussed, particularly the methods for the preparation of organofluorine compounds mainly by fluoroalkylation methods. Furthermore, the chemistry of fluorinated phosphonates, methods of their preparation, reactivity and biological activity is discussed. Additionally, the reactivity of fluoromethane derivatives is briefly mentioned and especially, the reactivity of diethyl fluoromalonate and fluorobisfenylsulfonylmethane is described. The Results and discussion part is devoted to the reactivity of three fluorinated phosphonates: tetraethyl fluoromethylenbisphosphonate, diethyl fluorophenylsulfonylphosphonate and previously not described diethyl fluoronitromethylphosphonate. These fluorinated phosphonates belong to the family of nucleophilic monofluoroalkylation reagents, meaning that these compounds are convenient starting materials for the synthesis of complex organic molecules containing the fluorine atom. The results deal with the reactivity of above mentioned fluorinated phosphonates, mainly with alkylation reactions, Horner-Wadsworth-Emmons reactions and conjugated additions. Also, other synthetic methods such as the Mitsunobu reaction or the palladium catalyzed allylation reaction were investigated; however,...

En industrie chimique, on cherche continuellement des molécules biologiquement actives essentiellement pour les domaines pharmaceutique et agrochimique. De plus en plus les exigences à ces produits deviennent dures. Elles concernent, par exemple, les activités secondaires ou l'écotoxicité. En conséquence, un grand nombre de structures doit être testé pour trouver des composés actifs remplissant les propriétés imposées. En parallèle, les capacités dans l'industrie pour tester un grand nombre de composés différents en peu de temps ont considérablement augmentées. En conséquence, l'industrie cherche des nouvelles méthodes de synthèse pour accéder rapidement à une plus grande variété des structures moléculaires.Dans ce contexte, l'industrie chimique et pharmaceutique s'intéresse fortement aux réactions photochimiques appliquées en synthèse organique. Ces réactions permettent de synthétiser des composés en grande variété structurale inaccessibles par la synthèse organique conventionnelle. Les produits des réactions photochimiques sont une partie de l’espace chimique qui n’a pas encore été complètement exploré pour la recherche des structures avec de l’activité biologique.Dans les travaux de thèse presentés nous nous sommes interessés d’abord à la photocycloaddition [2+2] entre un groupement carbonyl et un alcène, la réaction de Paternò-Büchi. Nous avons utilisé cette reáction pour obtenir des oxétanes qui possèdent des groupements intéressants en agrochimie et au même temps des sites clés qui permettront d’autres transformations lors des étapes ultérieures. Par la suite nous avons exploré la réaction de Paternò-Büchi avec des alcènes fluorés. Les résultats ont été très encourageants. Nous avons découvert une nouvelle famille d’oxétanes fluorés très stables. Au vu de ses propriétés, ces produits peuvent être utilisés comme des <chassis moléculaires> pour l’obtention des composés biologiquement actifs. D’autre côté, une nouvelle reactivité photochimique a été découverte : il s’agit d’une réaction Photo-Wittig analogue. Cette reactivité chimique dépend des substituants sur le carbonyl. Nous pensons que cette réactivité chimique est directement liée à l’état excité du carbonyl. / In life sciences, there is a continuos research for new biological active molecules, this is true for both pharmaceultical industry and agrochemical industry. In the last years regulations have become more and more severe. In recent years, the technology for the test of new chemical compounds in industry has considerably evolved. Nowdays it is possible to test a vast number of compounds for the screening of biological activity in a short time. This means that industry is searching for new methodologies that allow the obtention of diverse chemical structures that can present biological activity.In this context, chemical industry, in particular, pharmaceutical and agrochemical industry are interested in the use of photochemical reactions in organic synthesis. Photochemical reactions allow the obtention of a variety of complex structures that are not easily obtained by classical methods. This chemical space has not been completly explored in the search of biological active compounds.In the works presented in this PhD research we first explored the [2+2] photocycloadtion of a carbonyl compound to an olefin, the called Paternò-Büchi reaction. We succesfully applied this reaction to obtain oxetanes wich posses agro-like substituents and key sites for further functionalization, a requirement demanded in industry. We also explored the use of fluorinated olefins in this photoreaction. The results are very promising: we discovered a new family of stable fluorinated oxetanes. These compounds can be used cas molecular scaffolds for the obtention of biological active compounds. At the same time, we discovered a new photochemical reactivity: a Photo-Wittig like reaction. This new reactivity depends on the substitution pattern of the carbonyl group. We hypothesize that the new reactivity depends on the excited state of the carbonyl compound.

Neste trabalho é desenvolvido um novo método para a análise de flúor em água, na região de concentrações de décimos de ppm, baseado na técnica PIGE (Particle-Induced Gamma-ray Emission). Mostra-se que a determinação de concentrações dessa ordem de grandeza pela técnica PIGE exige o uso de um método de pré-concentração. Algumas tentativas de pré-concentração do flúor por meio de sua adsorção em sólidos em pó (carvão ativado, sílica e óxido de zircônio, entre outros) são descritas. A não-uniformidade da distribuição de flúor observada nestes materiais, após a adsorção, constituiu um problema crítico para a análise PIGE, que inviabilizou a extração de informações quantitativas a respeito das concentrações. Assim, o método utilizado para pré-concentrar o flúor nas amostras de água foi a redução de volume por evaporação. As amostras pré-concentradas foram irradiadas por um feixe de prótons de 4 MeV, em ar. Para testar a validade da metodologia de análise desenvolvida, cinco amostras de água fuoretada da cidade de São Paulo foram coletadas para a realização de um exame intercomparativo com outros cinco laboratórios. A análise nestes laboratórios foi realizada por meio das técnicas do eletrodo íon-seletivo e de cromatografia iônica. Os resultados da intercomparação demonstram claramente que a metodologia proposta neste trabalho é adequada para a análise de água fluoretada. Não foram observados indícios de erros sistemáticos e a precisão final nos valores de concentração foi de 5 a 10%. Algumas perspectivas de tornar a análise mais precisa são apontadas e discutidas. / This work presents a new method for the analysis of fluorine in water, at the tenth of ppm concentration level, based on the PIGE (Particle-Induced Gamma-ray Emission) technique. It is shown that determination of concentrations of this order of magnitude by PIGE requires the use of a preconcentration method. Some attempts of preconcentration of fluorine by adsorption in powdered solids (activated carbon, silica and zirconium oxide, among others) are described. The non-uniformity of the fluorine distribution in these materials, after adsorption, was a critical problem for the PIGE analysis, hinding the extraction of quantitative information about fluorine concentrations. This, volume reduction by evaporation was used to preconcentrate fluorine in water. The preconcentrated samples were irradiated by a 4 MeV proton beam, in air. In order to test the validity of the analytical method developed in this work, five samples of fluoridated water of the city of São Paulo were collected for an intercomparative exam with ve other laboratories. Analysis in these laboratories was performed by the ion-selective electrode and ion cromatography techniques. The intercomparison results show with confidence that the methodology proposed in this work is adequate for the analysis of fluoridated water. No significant systematic errors were observed and the precision was at the 5-10% level. Possibilities for the improvement of precision are pointed and discussed.

Nenhuma / 3-Desoxi-3-[18F]Fluor-Timidina (18FLT) é um análogo radioativo do nucleosídeo timidina usado desde 1998 em exames de tomografia por emissão de pósitrons (PET) para diagnóstico de vários tipos de tumores, como de mama, pulmonar, colorretal, cerebral, entre outros. Seu uso amplia a cobertura dos exames PET em diagnóstico de câncer, já que existem limitações da [18F]Fludesoxiglicose (18FDG), o radiofármaco PET mais usado no mundo atualmente. Para implementação da produção de 18FLT, na Unidade de Pesquisa e Produção de Radiofármacos do Centro de Desenvolvimento da Tecnologia Nuclear (UPPR/CDTN), o módulo de síntese de 18FDG foi adaptado usando-se 3 protocolos nos quais se variou a concentração de etanol (0; 8 e 10% V/V). Também foram desenvolvidos testes de Controle de Qualidade, como pH, determinação de catalisador, determinação de etanol e acetonitrila, pureza química e radioquímica, entre outros. A formulação foi avaliada in vitro quanto a sua segurança, pelos ensaios de viabilidade metabólica (MTT) e toxicidade clonogênica, e quanto a sua eficácia para a detecção de tumores pelo ensaio de interação (Binding). Os rendimentos corrigidos obtidos da síntese de 18FLT foram 6,52%; 253% e 233% para o 1, o 2 e o 3 protocolo, respectivamente. O produto do protocolo 3 (Etanol 8%) apresentou menor citotoxicidade no teste in vitro MTT do que o do segundo (Etanol 10%). Além disso, a formulação de 18FLT e as impurezas químicas presentes na mesma não afetaram a clonogenicidade das células testadas. Com base nestes resultados o protocolo 3 foi escolhido como a síntese padrão de 18FLT. A interação da 18FLT com as linhagens celulares foi saturável, com ligação específica maior que 90%, atestando a eficácia do radiofármaco na detecção de tumores. A afinidade do radiofármaco 18FLT por células de glioblastoma humano (U87MG) foi da ordem de 0,24 &#956;mol/L (Kd). Por fim, constatou-se que quantidades adicionais de timidina e clorotimidina, duas impurezas presentes na formulação, reduziram significativamente a interação de 18FLT (IC50 ~ 1 - 34 &#956;mol/L) com as células tumorais, o que pode reduzir sua eficácia para o diagnóstico. Assim, sugere-se que um valor máximo seja estabelecido para a concentração destas impurezas como um dos critérios de Pureza Química de 18FLT, baseando-se no ensaio de eficácia de interação. Portanto, a UPPR/CDTN está apta a fornecer rotineiramente o radiofármaco 18FLT para estudos não clínicos e clínicos, de acordo com os requisitos de Boas Práticas de Fabricação de Medicamentos exigidos pela ANVISA. / 3-Deoxy-3-[18F]Fluorothymidine (18FLT) is a Thymidine radioactive analog that is being used since 1998 for cancer diagnostics by Positron Emission Tomography (PET) for several types of cancer, as breast, lung, colorectal, brain, among others. Its use extends coverage of PET scans in diagnosis of cancers in certain organs and tissues, since there are limitations of [18F] Fludeoxyglucose (18FDG), which is the most used PET radiopharmaceutical in the world today. An 18FDG synthesis module was adapted to implement 18FLT production in Research and Production Unit of Radiopharmaceuticals from Center of Nuclear Technology Development (UPPR/CDTN). Three protocols were used varying the concentration of ethanol (0%, 8% and 10%). Quality control tests were also developed, as pH, catalyst determination, ethanol and acetonitrile determination, chemical and radiochemical purity, amongst others. The formulation was evaluated in vitro for its safety, using the metabolic viability (MTTs assay) and clonogenic toxicity assays, and for its effectiveness in tumors, using the binding test. The corrected yields were 6.52%; 253%; and 233% for the first, second and third synthesis protocols, respectively. The third protocol (Ethanol 8%) was found to be less cytotoxicity comparing to the second one (Ethanol 10%). Furthermore, 18FLT chemical impurities and the entire formulation did not affect the clonogenicity of the cells in Clonogenic Assay. Based on these results the protocol 3 was chosen as the standard 18FLT synthesis. The interaction of 18FLT with the cell lines was saturable, with specific binding higher than 81%, confirming the effectiveness of the radiopharmaceutical in tumor detection. The affinity between 18FLT and human glioblastoma cells (U87MG) was found to be 0.24 &#956;mol/L (Kd). Finally, it was found that additional quantities of thymidine and chlorothymidine reduced significantly 18FLT interaction (IC50 ~ 1 - 34 &#956;mol/L) with tumor cells, which can reduce its effectiveness in PET diagnosis. For this reason it is suggested that a maximum value must be set for the concentration of these impurities in the 18FLT Chemical Purity quality control test based in efficacy binding assays. Therefore, CDTN is able to routinely provide 18FLT radiopharmaceutical for clinical and non clinical studies, according to the Brazilian Good Manufacturing Practices for Radiopharmaceuticals required by ANVISA.

Nenhuma / O processo sol-gel foi usado para nanoestruturar partículas de oxihidróxido de ferro e aprisiona-las na estrutura de micro-, meso- e macroporos + macroburacos (poros de dimensões micrométricas) da rede polimérica do PVA (álcool polivinílico). Esferas hidrogel de oxihidróxido de Fe-PVA com (3433 63 &#956;m) e sem (2833 69 &#956;m) macroburacos foram obtidas. Espectroscopia Mössbauer mostra que as esferas obtidas têm nanopartículas (majoritariamente &#8804;20 nm) de &#945;-Fe2O3, &#61543;-Fe2O3, &#945;-FeOOH e fases ainda superparamagnéticas a 20 K. As esferas hidrogel obtidas possuem elevada estabilidade química e boa rigidez mecânica. Capacidade adsortiva: 77,9 e 204,9 mgF/g, respectivamente para as esferas hidrogel sem (bom ajuste aos modelos de Langmuir e Freundlich) e com (bom ajuste ao modelo de Freundlich) macroburacos. Nos dois tipos de esferas, o mecanismo de quimissorção é predominante, mas o modelo de difusão intrapartícula sugere que o mecanismo de adsorção é mais complexo. Quatro ciclos de adsorção no modo coluna mostram uma pequena queda da eficiência de captura do F de 61,8 para 56,2%; neles, dessorção com solução NH3 min. 25% em peso mostra uma eficiência variando entre 95,8 e 98,8%. A estratégia de nanoestruturar as partículas de oxihidróxido de ferro e introduzir macroburacos na rede polimérica do PVA foi eficaz e realmente reforçou a captura do F. / The sol-gel process was used to nanostructure iron oxyhydroxide particles and to trap them into the structure of micro-, meso-, and macropores + macroholes (micrometer size pore) of the PVA (polyvinyl alcohol) polymeric network. Iron oxyhydroxide-PVA hydrogel spheres with (3433 63 microns) and without (2833 69 microns) macroholes were obtained. Mössbauer spectroscopy shows that the obtained spheres have nanoparticles (mainly &#8804;20 nm) of &#945;-Fe2O3, &#61543;-Fe2O3, &#945;-FeOOH, and phases still superparamagnetic at 20 K. The obtained hydrogel spheres have high chemical stability and good mechanical rigidity. Adsorptive capacity: 77.9 and 204.9 mgF/g, respectively for the hydrogel spheres without (fit well by the Langmuir and Freundlich models) and with (fit well by the Freundlich model) macroholes. In both types of spheres, the chemisorption mechanism is predominant, but the intraparticle diffusion model suggests that the adsorption mechanism is more complex. Four cycles of adsorption in the column mode show a small decrease of F capture efficiency from 61.8 to 56.2%; therein, desorption with NH3 solution min. 25 wt% shows an efficiency ranging between 95.8 and 98.8%. The strategy to nanostructure particles of iron oxyhydroxide and to introduce macroholes into the PVA polymer network was effective and really reinforced the F capture. Keywords: fluorine;

Foi realizado um estudo, a fim de comparar o efeito na redução do ataque de cárie de uma solução de fluoreto de sódio, na concentração de 0,5 por cento , aplicada sob a forma de bochecho, escovação e escovaçao e bochecho, uma vez por semana, sob supervisão, durante um período escolar de 10 meses, em 424 escolares de 9 e 10 anos de idade matriculados em cinco escolas estaduais da cidade de são Paulo. As crianças foram distribuídas igualmente em três grupos experimentais e um grupo controle, de acordo com a idade dental (número de superfícies de dentes permanentes irrompidas) e experiência anterior de cárie (CPOS). Ao final do estudo, 307 crianças foram examinadas e os resultados mostram que houve uma redução, estatisticamente significante ao nível de 0,05 do ataque de cárie, entre os grupos experimentais e controle da ordem de 30,50 por cento para o grupo de bochecho (grupo I), de 32,68 por cento para o grupo de escovação (grupo II) e de 46,77 por cento para o grupo de escovação e bochecho (grupo IV), para as superfícies presentes no início do estudo. Para as superfícies que irromperam durante o estudo as reduções foram da ordem de 69,19 por cento (grupo I), de 76,23 por cento (grupo II) e de 71,83 por cento (grupo IV). Em relação as superfícies presentes no início e nas que irromperam durante o estudo as diferenças foram da ordem de 35,19 por cento (grupo I), de 37,91 por cento (grupo II) e de 49,77 por cento (grupo IV). Quando comparados os grupos experimentais entre si nao houve diferenças estatisticamente significantes ao nível de 0,05 presentes ou/e no final do estudo. / A study has been accomplished to make a comparison of the anti cariogenic effect of a solution of sodium fluoride, in the concentration of 0,5 per cent , applied weekly and under supervision, as mouthwash and toothbrushing used independently or in combination, during 10 school months, on 424 children of 9 and 10 years of age from five public schools of São Paulo, Brazil. The children were equally distributed in three experimental groups and one control group according to the dental age (number of erupted permanent teeth surfaces) and caries experience (DMFS). At the end of the study 307 children were examined and the results show a statistically significant decrease at the 0,05 level in the caries experience between the experimental and control groups: 30,50 per cent for the mouthwash, (group I); 32,68 per cent toothbrushing,( group II) ;and 46,77 per cent mouthwash and toothbrushing, (group IV) on the surfaces presented at the beginning of the study; of 69,19 per cent (group I), 76,23. per cent (group II) and 71,83 per cent (group IV) on the surfaces that erupted during the study, and of 35,19 per cent (group I), 37,91 per cent (group II) and 49,77 per cent (group IV) on the surfaces present at the beginning and the surfaces that erupted during the study. When the experimental groups were compared there was no significant difference of proportions at the 0,05 level.