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Orientador: Ines Joeks / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-10T13:30:49Z (GMT). No. of bitstreams: 1 Cardoso_AtiliodeOliveira_D.pdf: 4999395 bytes, checksum: 7096b1378702c52ba1881ec1b2449019 (MD5) Previous issue date: 2007 / Resumo: Crisotila é um silicato de magnésio de hábito fibroso, com fórmula ideal Mg6Si4O10(OH)8 e estrutura 1:1, intercalando camada tetraédrica de tridimita (sílica) com camada octaédrica de hidróxido de magnésio (brucita). Para haver coordenação entre os planos de tridimita e brucita as bicamadas se curvam e se enrolam sobre si mesmas, formando fibrilas cilíndricas com superfície constituída de brucita. As fibrilas se agregam dando origem a fibras que em meio aquoso, sob extensa faixa de pH, possuem potencial zeta positivo, em razão de haver cátions magnésio na superfície, originados por dissociação de ânions hidroxila, o que ocasiona pH de equilíbrio igual a 8,5. Apesar do potencial zeta essencialmente positivo, crisotila é um material sobre o qual aderem, espontaneamente, e em grande quantidade, materiais particulados de natureza negativa ou positiva. Visando compreender as causas do fenômeno, partículas de látex de poliestireno, com superfície negativa, PS-, e positiva, PS+, foram sintetizadas em meio aquoso, na ausência de surfactantes, e utilizadas em experimentos de heterocoagulação com crisotila, variando: i) o grau de desfibrilamento da crisotila, em meio aquoso, através de ação mecânica e através de hidrofobicidade causada por metilação da superfície das fibras usando Si(CH3)2Cl2; ii) o potencial zeta de crisotila através de lavagem com HCl, variação do pH do meio de dispersão usando NaOH e lavagem com solução aquosa de silicato de sódio; iii) a quantidade adicionada de partículas de poliestireno por mg de crisotila; iv) o potencial zeta das partículas de poliestireno através da adsorção de surfactante catiônico brometo de cetil-trimetil-amônio (CTAB). Resultados de análise microscópica via MEV mostraram que a formação de heterocoágulos ocorre preferencialmente sobre fibras de crisotila mais finas e portanto flexíveis, havendo expressiva formação de homocoágulos de látex a partir de aproximadamente 10 partículas por mg de crisotila. De acordo com resultados de medidas de densidade óptica residual de sobrenadantes, os procedimentos que diminuem o grau de desfibrilamento e o potencial zeta de crisotila diminuem a velocidade inicial de formação de heterocoágulos com partículas de PS-. A adsorção de CTAB inibe a adesão de partículas PS- e não interfere na adesão de partículas PS+ sobre crisotila. A heterocoagulação de látex PS- é completamente revertida com a adição de silicato de sódio ao meio de dispersão. Em meio aquoso, silicato de sódio extrai impurezas da crisotila, detectadas por aumento da densidade óptica do meio de dispersão. Partículas de látex PS+ praticamente não aderem sobre crisotila lavada com silicato de sódio. Os resultados indicam que a adesão de partículas negativas sobre crisotila ocorre preferencialmente sobre sítios positivos oriundos de magnésio dissociado de hidroxila, enquanto a adesão de partículas positivas ocorre sobre sítios negativos, ocasionados pela pré-adesão de impurezas durante a etapa de lavagem da crisotila com água. A densidade superficial de sítios positivos é significativa em fibras mais finas e flexíveis, sobre as quais a heterocoagulação ocorre preferencialmente. Sugerese que a homocoagulação seja dependente principalmente da mobilidade de heterocoágulos préformados, que sob agitação do sistema colidem entre si com energia mecânica suficiente para causar a adesão entre as partículas de látex / Abstract: Chrysotile is a magnesium silicate with fibrous habit and ideal formula Mg6Si4O10(OH)8, having 1:1 layered structure of tetrahedral tridimite (silicate) with octahedral brucite (magnesium hydroxide). The layers are curved and rolled, resulting in cylindrical fibrils with brucite in the external surface and tridimite in the hollow internal surface. The fibrils aggregate giving rise to bundles, or fibers, which have a positive zeta-potential in aqueous medium. This results from the Mg occurrence after dissociation of the surface hydroxyl groups. Despite its positive zeta potential, the surface of chrysotile attaches colloidal particles of negative or positive nature. Aiming to understand this phenomenon, polystyrene latex particles, with negative (PS-) and positive (PS+) surface charge, were synthesized in aqueous solution, in the absence of surfactants, and used in experiments of heterocoagulation with chrysotile. The aggregation of the fibers was controled through mechanical action or improved hidrofobicity by metilation of the surface using Si(CH3)2Cl2. The zeta potential of chrysotile was modified by washing with HCl or adding NaOH or sodium silicate aqueous solution. The amount of polystyrene particles was varied and its surface charge adjusted adding cetyl trimethylammonium bromide cationic surfactant (CTAB). Results of microscopic analysis (MEV) showed that the formation of heteroaggregates occurs preferentially on disaggregated fibers, or fibrils, which are the most flexible. Also, an expressive quantity of homoaggregates of latex with approximately 10 particles/mg of chrysotile are formed. According with the results of optical density of the supernatants, procedures that reduce the disaggregation and the zeta-potential of chrysotile decrease the initial rate of formation of heteroaggregates with particles of PS-. The adsorption of CTAB inhibits the adhesion of PS- particles and does not interfere in the adhesion of PS+ particles on chrysotile. The heterocoagulation of PS- latex is completely reverted with the addition of sodium silicate to the dispersion. In aqueous suspension, sodium silicate removes impurities of the chrysotile surface, as detected by the increase in the optical density of the dispersion. Particles of PS+ latex practically will not attach on chrysotile washed with sodium silicate. The results indicate that the adhesion of negative particles on chrysotile occurs preferentially at positive surface sites, while the adhesion of positive particles occurs at the negative surface sites, probably caused by the pre-adhesion of impurities on the chrysotile when washing with water. The surface density of positive sites is more significant in flexible and disaggregated fibers, on which the heterocoagulation occurs preferentially. The homoaggregation of the latex particles seems to be dependent mainly on the mobility of the preformed heteroaggregates, which, under stirring, collide among themselves with enough mechanical energy to cause the adhesion between the latex particles / Doutorado / Físico-Química / Doutor em Ciências

The extended DLVO theory was used to develop a flotation model by considering both hydrodynamic and surface forces involved in the process. A stream function was used to estimate the kinetic energies for thinning the water films between bubbles and particles, which were compared with the energy barriers, created by surface forces, to determine the probability of adhesion. A general expression for the probability of detachment was derived from similar mechanism for chemical reaction, and the kinetic energy for detachment was estimated with French and Wilson's model. The hydrophobic force parameter (K132) calculated from the rate constants of single bubble flotation tests showed that, K132 for bubble-particle interaction were close to the geometric means of K131 for particle-particle interactions and K232 for bubble-bubble interaction, indicating that the combining rules developed for dispersion forces may be useful for hydrophobic forces. The model was used to predict flotation results as functions of several important parameters such as contact angle, double-layer potentials, particle size, bubble size, etc. The predictions were consistent with experience, and could be explained in view of the various subprocesses considered in the model development. Furthermore, the model suggested optimum conditions for achieving the maximum separation efficiency. The extended DLVO theory was also used to determine the hydrophobic force between two oil/solution interfaces from the equilibrium film thicknesses of dodecylammonium chloride (RNH3Cl) solutions obtained using Thin Film Balance (TFB) technique. The results showed that, the oil droplets were inherently hydrophobic, and the hydrophobic force played an important role in the stability of emulsions. This force decreased with increasing surfactant concentration, and also changed with pH and the addition of electrolyte. The interfacial area occupied by molecules indicated that, the dodecane molecules might present between two surfactant ions at interface, thus the hydrophobicity of oil/solution interface was less sensitive to the addition of the surfactant than that of air/solution interface. Thermodynamic analysis suggested that, there might exist a relationship between the interfacial hydrophobicity and the interfacial tension. / Ph. D.

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The morphology and physicochemical properties of bacterial cells at the molecular level influence their adhesion to surfaces and interfaces. In this study, atomic force microscopy (AFM) was used to explore the morphology of soft, living cells in aqueous buffer, to map bacterial surface heterogeneities, to directly correlate the results in the AFM force distance curves to the macroscopic properties of the microbial surfaces, and to model the experimental AFM force curves using classical Derjaguin-Landau-Verweij-Overbeek (DLVO) theory of colloidal stability. The surfaces of two bacterial species exhibiting different macroscopic surface hydrophobicity, measured as the oil/water contact angle (Ө): Acinetobacter venetianus RAG-1 (Ө =56.4°) and Rhodococcus erythropolis 20SE1c (Ө =152.9°) were probed with chemically functionalized AFM tips, terminated in hydrophobic and hydrophilic groups. All force measurements were obtained in contact mode and made on a location of the bacterium selected from the tapping mode image. AFM imaging revealed morphological details of the microbial-surface ultrastructures with about 20 nm resolution. The heterogeneity in surface morphology was directly correlated with differences in adhesion forces as emphasized by retraction force curves and also with the presence of external structures, either pili or capsules, as confirmed by transmission electron microscopy. The AFM retraction force curves for A. venetianus RAG-1 and R. erythropolis 20S-E1-c showed differences in the interactions of the external structures with hydrophilic and hydrophobic tips. A. venetianus RAG-1 exhibited an asymmetrical pattern with multiple adhesion peaks suggesting the existence of biopolymers with different lengths on its surface. R. erythropolis 20S-E1-c showed long-range attraction forces accompanied by single rupture events indicating a more hydrophobic and smoother surface. The magnitude of the adhesion forces was proportional to the water contact angle on the two bacterial lawns. The experimental force curves between the two microbial cells and functionalized AFM probes presented discrepancies when compared to the classical DLVO theory. Therefore, an extended DLVO model incorporating an acid–base component to account for attractive hydrophobic interactions and repulsive hydration effects was used to assess the additional interactions. Extended DLVO predictions agreed well with AFM experimental data for both A. venetianus RAG-1, whose surface consists of an exopolymeric capsule and pili, and R. erythropolis 20S-E1-c, whose surface is covered by mycolic acids as well as an exopolymeric capsule. The extended model for the bacteria-AFM tip interactions was consistent with the effects of acid base and steric forces, in addition to classical DLVO theory. / Chemical Engineering

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Titanium dioxide nanoparticles are widely used in a variety of products, such as pigments, paints, paper, plastics, cosmetics, nano-fibers, food coloring and photovoltaic cells, and the industry is growing at anexponential rate. It is believed that by 2025, 2.5 million tons of nano-TiO2 will be manufactured annually. Thus far, there has been very little research in the environmental impact of nano-TiO2. There is a need to understand the fate and transport of nanoTiO2 to mitigate their effect on human health, the ecosystems and the environment in general. The aim of this study was to investigate the impact of pH, flow rate and ionic strength on the deposition of nano-TiO2 in a saturated porous media (sand). Nano-TiO2 formed aggregates in solutions that had a pH near the point of zero charge for TiO2, which is at approximately pH 6.2 for TiO2. The formed aggregates showed very little mobility due to site blocking in the pores of the sandy medium, whereas at pH 7.5, the solutions’ concentration was more stable than at pH 6.3 and more mobile up to 10 mM. Above 10 mM, a decrease in mobility, due to reduction in repulsive energy interaction between the medium and the nanoparticles could be observed. Flow rate had also a marked effect on the deposition, i.e., the slower the flow rate, the higher on deposition, because of an increase in attachment efficiency. To verify the experimental results, a finite element solution of the reactive transport equation in one dimension was used to compare the fit between observed and simulated results. The model was run in inverse mode, to determine unknown parameter values such as dispersivity and detachment rate. In general, it was possible to obtain a good fit to theexperimental BTCs. / Nanopartiklar av titaniumdioxid används allmänt i en mängd olika produkter, såsom pigment, färger,papper, plast, kosmetika, nanofibrer, matfärgläggning, och solceller. Branschen växer explosionsartat.Man tror att år 2025 kommer 2,5 miljoner ton nano-TiO2 tillverkas årligen. Hittills har väldigt lite forskning gjorts på området nano-TiO2. Det finns ett behov av att förstå transportprocesser och vad som händer med nanoTiO2 i miljön för att bla kunna mildra effekter av dessa partiklar på människors hälsa, ekologi och miljö. Syftet med denna studie var att undersöka effekten av pH, flöde och jonstyrka (IS) på transporten av nano - TiO2 i vattenmättade porösa medier (sand). Nano - TiO2 bildade aggregat i lösningar som hade ett pH nära pH(PZC), pH(PZC) är pH-värdet vid vilket laddningen är noll, ungefär pH 6,2 för TiO2. Vid pH 6,3 visade nano partiklarna mycket liten rörlighet på grund av fysisk igentäppning i porerna av sandmediet, medan vid pH 7,5 var lösningens koncentration mer stabil och partiklarna mer mobila upp till en jonstyrka på 10 mM. Över 10 mM, observerades en minskning i rörlighet, på grund av minskad repellerande energi mellan mediet och nano partiklarna.Flödeshastighet hade också en markant inverkan på retentionen av partiklar i kolonnen, ju långsammare flöde, desto större retention, på grund av mer gynnsamma förhållande för fastläggning av partiklar till mediet. För att verifiera de experimentella resultaten och jämföra observerade och simulerade resultat användes en lösning med finita-elementmetoden av den reaktiva transportekvationen i en dimension. Inversmodellering gjordes för att ta reda på okända parametervärden såsom dispersivitet och fastläggning. Det var i allmänhet möjligt att uppnå god överensstämmelse mellan observerade ochexperimentella genombrottskurvor.

A first-principle flotation model was derived at Virginia Tech from the basic mechanisms involved in the bubble-particle and bubble-bubble interactions occurring in a flotation cell (Yoon and Mao, 1996; Sherrell and Yoon, 2005; Do, H, 2010). The model consists of a series of analytical equations for bubble generation, bubble-particle collision, attachment, detachment, and froth phase recovery. The process of bubble-particle attachment has been modelled on the premise that bubble-particle attachment occurs when the disjoining pressure of the thin liquid in a wetting films formed between particle and bubble is negative, as was first suggested by Laskowski and Kitchener (1969). These provisions allow for the flotation model to incorporate various chemistry parameters such as zeta-potentials, contact angles, surface tension in addition to the physical and hydrodynamic parameters such as particle size, bubble size, and energy dissipation rate. In the present work, the effects of both hydrodynamic and chemistry parameters have been studied using the model-based computer simulator. A series of laboratory batch flotation experiments carried out on mono-sized glass beads validated the simulation results. The flotation feeds were characterized in terms of particle size, contact angle, and Hamaker constant, and the flotation experiments were conducted at different energy dissipation rates, gas rates, froth heights. The flotation tests were also carried out on mixtures of hydrophobic silica and hydrophilic magnetite particles, so that the grades of the flotation products can be readily determined by magnetic separation. The experimental results are in good agreement with the model predictions both in terms of grade and recovery. / Master of Science

<p>A series of experiments were carried out to gain a better understanding of the mechanisms governing the transport of biological and non-biological particles through single, saturated dolomite fractures at the laboratory scale. Fracture apertures and general roughness were characterized using hydraulic and conservative solute tracer experiments.</p> <p>The effects of particle size, surface characteristics and ionic strength of carrying solution were all evaluated. Particulate material studied included MS2, <em>E. coli</em> and two sizes of carboxylated microspheres. To elucidate the effect of ionic strength on particulate transport, the ionic strength of the carrying solution was altered during each experiment. All particulate experiments were completed at a specific discharge of 15 m/day to facilitate comparisons.</p> <p>Recovery of biological particulate material was found to be much less relative to the carboxylated microspheres, even though the energy profiles predicted similar interactions with the fracture surface. This suggests that the biological surface has a significant impact on retention within the fracture. Further, altering the ionic strength of the carrying solution did not spur significant elution of additional particulate material, regardless of surface characteristics. Therefore, it was determined that retention within the secondary energy minimum was negligible under these operating conditions.</p> <p>With respect to carboxylated microspheres, increased retention was observed within the less variable fracture. This suggests that increased variability within a fracture results in increased eddying within the aperture field. This eddying effectively reduces the aperture region available for particle transport, lessening the particle/fracture interaction. Overall, while mean residence times were similar, recovery of biological particles was poorly replicated by microspheres.</p> / Master of Applied Science (MASc)