Centenas de compostos orgânicos são emitidos para a atmosfera por uma variedade de fontes biogênicas e antrópicas. Essa mistura complexa causa preocupação devido ao impacto que esses compostos podem provocar na saúde e no ambiente. Apesar de constituírem 10-70% da massa do aerossol atmosférico, a caracterização dos compostos orgânicos particulados permanece ainda deficitária. A contribuição das principais fontes de emissão para a poluição a nível regional pode ser diagnosticada através da utilização de marcadores moleculares específicos. De acordo com esta necessidade, o objetivo do presente trabalho é a caracterização de compostos orgânicos do aerossol atmosférico coletado em sítios de cidades da América do Sul. As amostragens do material particulado (MP10) foram realizadas em duas áreas em Bogotá na Colômbia, uma de influência industrial (BOI) e outra veicular (BOV) em 2007, e em áreas urbanas em São Paulo no Brasil em 2007 (SPA 07) e 2008 (SPA 08), e em Buenos Aires (BAI) na Argentina em 2008. Diferentes classes de compostos orgânicos foram determinadas: n-alcanos e hidrocarbonetos policíclicos aromáticos (HPA) por cromatografia a gás com detecção por ionização em chama (CG-DIC), n-alcanais e n-alcanonas por cromatografia a gás com detecção por espectrometria de massas (CG/EM). A composição e concentração do aerossol atmosférico foram afetadas substancialmente pelo transporte de massas provenientes de regiões com queima de biomassa e pelas condições meteorológicas locais. Em SPA 08, BOI e BAI foram encontradas as maiores concentrações de MP10 onde as amostragens foram realizadas em época de seca, favorecendo a acumulação dos poluentes. A constituição orgânica do MP10 nos sítios estudados reflete a incorporação nas amostras de marcadores moleculares biogênicos como n-alcanos com número ímpar de carbonos. Dentre os traçadores antrópicos, foram identificadas a presença de pristano e fitano, a mistura complexa não-resolvida (MCNR) e HPA de queima de combustíveis fósseis. Em SPA 08 foi identificada a presença do reteno, um traçador da queima de biomassa. As maiores concentrações de n-alcanais e n-alcanonas foram observadas no sítio BOV. Os n-alcanais (< C20) identificados nos sítios deste trabalho podem ser originados a partir da oxidação de alcanos e alcenos, e as n-alcanonas (< C20) podem ter como origem atividades antrópicas, processos oxidativos na atmosfera ou atuação microbiana sobre outros compostos. / Hundreds of organic compounds are emitted to the atmosphere by biogenic and anthropogenic sources. This complex mixture generates concern due to the impact of these compounds on health and environment. In spite of accounting for 10-70% of the atmospheric aerosol mass, particulate-phase organic compounds are not yet well characterized. The contribution of the major emission sources to regional particulate pollution can be diagnosed by using specific molecular markers. According to this necessity, the present work has as objective the characterization of organic compounds from atmospheric aerosol collected in sites of South American cities. The particulate matter (PM10) sampling were accomplished in two areas in Bogota (Colombia), one with industrial (BOI) and other with vehicular (BOV) influence in 2007, and in urban areas in Sao Paulo (Brazil) in 2007 (SPA 07) and 2008 (SPA 08), and in Buenos Aires (BAI), Argentina, in 2008. Different organic classes were determined: n-alkanes and polycyclic aromatic hydrocarbons (PAH) by gas chromatograph with flame ionization detection (GC-FID), n-alkanals and n-alkanones by gas chromatograph with mass spectrometer detection (CG/MS). The aerosol atmospheric composition and concentration were substantially affected by mass transport from biomass burning regions and by the local meteorological conditions. In SPA 08, BOI and BAI were found the highest PM10 concentrations where the samplings were accomplished in dry period, contributing for the pollutants accumulation. The PM10 organic composition at studied sites reflects the incorporation from biogenic molecular markers in the samples like n-alkanes with odd carbon number. Among the anthropogenic tracers, were identified the presence of pristane and phytane, the unresolved complex mixture (UCM) and PAH from fossil fuel combustion. In SPA 08 was observed the presence of retene, a biomass burning tracer. Higher concentration from n-alkanals and n-alkanones were observed at the BOV site. The n-alkanals (< C20) identified at sites from this work may be originated from oxidation of alkanes and alkenes, and n-alkanones (< C20) are derived from anthropogenic activity, atmospheric oxidative processes or microbial action over other compounds.

Lithium-oxygen batteries, also known as Lithium-air batteries, could possibly revolutionize energy storage as we know. By letting lithium react with ambient oxygen gas very large theoretical energy densities are possible. However, there are several challenges remaining to be solved, such as finding suitable materials and understanding the reaction, before the lithium-oxygen battery could be commercialized. The scope of this thesis is focusing on the latter of these challenges. Efficient ion transport between the electrodes is imperative for all batteries that need high power density and energy efficiency. Here the mass transport properties of lithium ions in several different solvents was evaluated. The results showed that the lithium  mass transport in electrolytes based on the commonly used lithium-oxygen battery solvent dimethyl sulfoxide (DMSO) was very similar to that of conventional lithium-ion battery electrolytes. However, when room temperature ionic liquids were used the performance severely decreased. Addition of Li salt will effect the oxygen concentration in DMSO-based electrolytes. The choice of lithium salt influenced whether the oxygen concentration increased or decreased. At one molar salt concentration the highest oxygen solubility was 68 % larger than the lowest one. Two model systems was used to study the electrochemical reaction: A quartz crystal microbalance and a cylindrical ultramicroelectrode. The combined usage of these systems showed that during discharge soluble lithium superoxide was produced. A consequence of this was that not all discharge product ended up on the electrode surface. During discharge the cylindrical ultramicroelectrodes displayed signs of passivation that previous theory could not adequately describe. Here the passivation was explained in terms of depletion of active sites. A mechanism was also proposed. The O2 and Li+ concentration dependencies of the discharge process were evaluated by determining the reactant reaction order under kinetic and mass transport control. Under kinetic control the system showed non-integer reaction orders with that of oxygen close to 0.5 suggesting that the current determining step involves adsorption of oxygen. At higher overpotentials, at mass transport control, the reaction order of lithium and oxygen was zero and one, respectively. These results suggest that changes in oxygen concentration will influence the current more than that of lithium. During charging not all of the reaction product was removed. This caused an accumulation when several cycles was examined. The charge reaction pathway involved de-lithiation and bulk oxidation, it also showed an oxygen concentration dependence. / Litiumsyrebatteriet, även känt som litiumluftbatteriet, kan potentiellt revolutionera vårt förhållande till energilagring. Genom att låta litium reagera med syrgas från luften kan teoretiskt höga energitätheter uppnås. Dock så behöver många problem lösas, så som att hitta lämpliga elektrod- och elektrolytmaterial samt att få en ökad förståelse för reaktionsmekanismen, innan litiumsyrebatteriet kan kommersialiseras. Den här avhandlingen behandlar de sistnämnda av dessa problem. För att ett batteri ska kunna leverera hög effekttäthet och energieffektivitet krävs en effektiv jontransport mellan elektroderna. Här utvärderades masstransporten hos flera olika elektrolyter. Resultatet visade att masstransporten av litium i en litiumsyrebatterielektrolyt (baserad på dimetylsulfoxid (DMSO)) är likvärdig med en konventionell litiumjonbatterielektrolyt. När elektrolyter baserade på jonvätskor användes uppvisades väldigt stora energiförluster. När litiumsalt tillsattes påverkades lösligheten av syre i DMSO-baserade elektrolyter. Vilken sorts litiumsalt som användes påverkade om lösligheten av syre ökade eller minskade. Vid en saltkoncentration på en molar var den högsta syrelösligheten 68 \% större än den lägsta. Två olika modellsystem används för att studera den elektrokemiska reaktionen: En elektrokemisk kvartskristallmikrovåg och en cylindrisk ultramikroelektrod. Vid kombinerad användning av dessa system påvisades att löslig litiumsuperoxid bildades vid urladdningen. Följden av detta blev att endast delar av urladdningsprodukten hamnade på elektroden. Vid urladdning visade ultramikroelektroderna tecken på passivering som inte kunde beskrivas av tidigare teori. Här föreslås att passiveringen uppstår på grund av en blockering av de aktiva säten där reaktionen fortskrider. För denna process föreslås även en detaljerad mekanism. Urladdningsprocessens koncentrationsberoende utvärderades genom att bestämma reaktionsordningen för syre och litium under kinetisk- och masstransport kontroll. Under kinetisk kontroll fanns inga heltalsreaktionsordningar, för syre var reaktionsordningen nära 0.5 vilket föreslår att det reaktionssteg som bestämmer strömstorleken innefattar en adsorption av syre. Vid högre överpotentialer, då systemet var under masstransportkontroll, var reaktionsordningarna för litium och syre noll respektive ett. Detta föreslår att ändringar i syrekoncentration påverkar strömmen betydligt mer än vad det gör för litium. Under uppladdning kunde inte all reaktionsprodukt avlägsnas från elektroden. Detta ledde till en ackumulation då flera cykler studerades. Uppladdningens delsteg innefattade en delitiering följt av en oxidation av reaktionsproduktbulken. Denna process uppvisade även ett syrekoncentrationsberoende. / <p>QC 20171114</p>

Abstract Volatile Organic Compounds (VOCs) in wastewaters from the chemical industry are of major concern because of their environmental and health impacts. The reclamation of VOCs from wastewaters would not only reduce the hazard to the environment but also contribute to an efficient use of resources. The thesis explores the reclamation of n-butanol and dichloromethane from sodium chloride containing mixtures by pervaporation. Another aim was to gain understanding of mass transport phenomena during the pervaporation of multicomponent systems, and the effect of sodium chloride on the pervaporation performance. In this work, the reclamation of n-butanol and dichloromethane was conducted as a sequence of pervaporation stages which utilised first hydrophobic and then hydrophilic membranes. The objective was to segregate the mixture of n-butanol/dichloromethane/sodium chloride/water into three different streams: a re-use quality concentrate of VOCs, brine, and discharge quality purified water. The effect of the experimental variables, VOCs feed concentration, feed temperature and sodium chloride content on the performance of the pervaporation stages was studied. A statistical design, response surface methodology, was used to further resource efficiency. The results indicate the potential of pervaporation for the reclamation of n-butanol and dichloromethane from aqueous mixtures. A single step of pervaporation of n-butanol/dichloromethane/sodium chloride/water systems using the CMX-GF-010-D (Celfa) and PERTHESE® 500-1 (P 500-1) membranes does not sufficiently concentrate the VOCs for direct re-use. It is also demonstrated that the electrolyte does not permeate through the membranes and does not affect their separation effectiveness significantly. The pervaporation of the water/dichloromethane/n-butanol system using the hydrophilic poly(vinyl alcohol)-titanium dioxide/polyacrylonitrile/polyphenylene sulfide (PVA-TiO2/PAN/PPS) membrane is effective for dewatering purposes. The membrane shows impermeable features towards dichloromethane in the studied conditions. The analysis of the mass transport phenomena demonstrates that, under the experimental conditions studied, the resistance towards the mass transport of the compounds through the membrane is mainly exhibited by the membrane itself. This study also shows the advantage of analysing the effect of temperature on membrane permeation by the permeation activation energy instead of by the apparent activation energy.

Le monoxyde de carbone déshydrogénase (CODH) catalyse la réduction réversible du dioxyde de carbone par son site actif. En utilisant une méthode électrochimique appelée voltammétrie de film protéique, nous étudions le mécanisme enzymatique de CODH en immobilisant l'enzyme à une surface d'électrode de graphite où le transfert direct d'électrons est possible. Traditionnellement, pour empêcher la déplétion du substrat à l'électrode, les électrochimistes utilisent des électrodes tournantes (RDE). Cependant, comme la CODH est très active, même la RDE ne peut pas empêcher l'épuisement, ce qui masque les caractéristiques cinétiques importantes de l’enzyme. Nous ne pouvons pas résoudre le problème avec RDE, puisque nous l’utilisons déjà à la vitesse maximum. Par conséquent, nous devons concevoir une nouvelle cellule électrochimique. Pour cela, nous avons utilisé des simulations de dynamique des fluides computationnelles pour explorer diverses géométries afin d'en trouver une appropriée. Nous avons commencé par valider notre méthode numérique avec la solution théorique bien définie de la cellule réelle de RDE. Après la bonne validation, nous avons déterminé les vitesses de transport de masse au sein de plusieurs géométries et à basé sur l'optimisation des paramètres géométriques, nous avons atteint notre conception appropriée. Ce nouveau prototype a une électrode graphite uniformément accessible avec un taux de transport trois fois plus rapide que le RDE à des vitesses de solution acceptables. Nous avons construit, mis en place avec succès le système pour caractériser ses performances de transport, et trouvé un excellent accord entre les résultats numériques et expérimentaux / Carbon monoxide dehydrogenase (CODH) catalyzes the reversible reduction of carbon dioxide by its active site. Thus, CODH participates in the first step of fuel production. Using an electrochemical method called protein film voltammetry, we study the enzymatic mechanism of CODH by immobilizing the enzyme at a graphite electrode surface where direct electron transfer is possible. Traditionally, to prevent depletion of the substrate at the electrode, electrochemists use rotating electrodes (RDE). However, since CODH is very active, even RDE cannot prevent depletion, which masks the important kinetic characteristics of the enzyme and complicates the analysis of the enzymatic response.We cannot solve the problem with RDE, since we already use it at maximum speed. Therefore, we must completely change our approach and design a new electrochemical cell. For this, we used computational fluid dynamics (CFD) simulations to explore various geometries to find a suitable one. We began by validating our numerical method with the well-defined theoretical solution of the real cell of RDE. After good validation, we determined the mass transport velocities within several proposed geometries of the flow cell of hydrodynamic channel and jet electrodes. Based on the optimization of geometric parameters, we have achieved our proper design of jet electrode. This new prototype has a uniformly accessible graphite electrode with a transport rate three times faster than the RDE at acceptable solution speeds. We have successfully built and implemented the system to characterize its transport performance. We found an excellent agreement between the numerical and experimental results

<p>   </p> <p>Subcutaneous injection is a biotherapeutic drug delivery method that is currently growing due to low cost, better patient compliance, minimally invasive, and the convenience that it can be done at home. Common injection sites for subcutaneous injection include the upper outer arms, abdomen, buttocks, and upper outer thigh. Heterogeneity of the tissue exists between and within each of these locations. The subcutaneous tissue space is made up of adipose tissue, proteins, collagen, and blood vessels and each of these components has an impact on the mass transport of the injected biotherapeutics and how they are absorbed into the vascular system and then distributed to the body. The current methods used to model the subcutaneous tissue space are either very expensive and not feasible for multiple repetitions, cannot incorporate fibrillar proteins or cellular components, or model a more homogeneous tissue space. These limitations do not allow for these models to accurately represent the subcutaneous tissue space. The engineering objective for this project was to develop a platform with tunable matrix architecture and biochemical composition for evaluating mass transport. This project utilizes collagen and the primary matrix due to the large abundance of collagen in the body.  We explored the effects that a change in polymerization temperature of the collagen and collagen concentration had on the fiber architecture and pore diameter. The results showed that higher polymerization temperatures of the collagen gels resulted in smaller fiber and pore diameters and an increase in concentration resulted in an increase in fiber volume fraction and a decrease in pore diameter. Fibronectin (FN) and hyaluronic acid (HA) were added to the collagen gels to analyze the impact on the structure of collagen gels with a change in polymerization temperature and collagen concentration. The addition of FN did not strongly alter the collagen fiber architecture between polymerization temperatures and collagen concentrations. Through staining and imaging, we saw an aggregation of FN around the collagen fibrils due to their opposing charges causing them to bind. The addition of HA had moderate impact on collagen fiber architecture across all polymerization temperatures and between collagen concentrations. The collagen + FN gels were used for the mass transport study. The results showed that there was little to no difference between the recovery rates of macromolecules of different charges and size between the collagen and collagen + FN gels, indicating that the transport of molecules through both of the collagen gels was impacted by a steric effect rather than an effect in charge.</p> <p>  </p>

Vid produktion av biodiesel produceras även råglycerol (10 vikt%) som biprodukt och utbudet av råglycerol har ökat över de senaste åren till följd av att biodieselproduktionen ökat. Marknadsvärdet för råglycerol är lågt, men det är en utmärkt föregångare till att producera mervärdesprodukter för exempelvis läkemedelsindustrin, kemikalieindustrin eller kosmetika. Genom att reformera glycerol till mervärdesprodukter ökar konkurrenskraftigheten för biodiesel och värdekedjans ekonomiska hållbarhet. Elektrokemisk reformering av glycerol är en lovande metod för att producera dess mervärdesprodukter, eftersom processen är justerbar och miljövänlig. En ytterligare fördel är att vätgas kan samproduceras med mervärdesprodukterna genom denna metod och energikonsumtionen för att producera vätgas genom denna metod är ungefär hälften av vad som krävs vid vattenelektrolys. Denna studie utvärderar hur masstransport påverkar selektiviteten och prestandan för elektrokemisk oxidation av glycerol, genom att utföra elektrokemiska experiment, karaktärisera processens katalysator och analysera produkter som produceras.  Den experimentella uppställningen innefattar en roterande diskelektrod med ett elektrodepositerat lager av Pd, på ett Ni-substrat, i varierande tjocklek. Elektroden undersöks i elektrolyter bestående av varierande koncentration av NaOH (1, 0.5 och 0.25 M) och 0.5 M glycerol vid 25 oC. Systemet konstrueras även som modell i Comsol Multiphysics 6.0 för att simulera experiment. Resultaten visar att masstransport av glycerol begränsar systemet genom att orsaka deaktiveringen av katalysatorn. Vid de lägre NaOH koncentrationerna begränsar även masstransport av OH- reaktionshastigheten genom att miljön omgärdande elektroden blir mindre oxidativ. Slutligen visas att reaktionsmekanismen vid alla tjocklekar av katalysatorn utgörs av två parallella reaktionsvägar. En ökande tjocklek hos katalysatorn ökar selektiviteten mot den ena reaktionsvägen framför den andra, samt ökar antal oxidationssteg som åstadkoms vid reaktionen. / Biodiesel production gives rise to 10 wt% crude glycerol as a byproduct, which is becoming increasingly available on the market owing to the increased biodiesel production over the last few years. Crude glycerol has a low market value, but it is an excellent precursor to producing value added products for the pharmaceutical industry, chemical industry or cosmetics to mention a few. By producing value added products with biodiesel derived glycerol, the ability of biodiesel to compete with fossil fuels is improved and its economical sustainability is promoted. One of the most promising methods to convert glycerol into its value added products is electrochemical reforming, as it poses high tunability and is an environmentally friendly process. Additionally, the process produces hydrogen concurrently and halves the energy consumption compared to producing hydrogen from water electrolysis. This study evaluates the impact of mass transport in the glycerol electrooxidation reaction (GEOR), as a parameter that can be used to finetune product selectivity and optimise the system performance. To do so, the study employs electrochemical experiments, catalyst characterisation and product analysis. The experimental setup consists of a rotating disk electrode (RDE) cell with electrodeposited Pd on Ni substrate at varying thicknesses, operating in 1, 0.5, 0.25 M NaOH and 0.5 M glycerol electrolyte at 25 oC. Additionally, the system is modelled in Comsol Multiphysics 6.0 which is used to perform simulations. It is found that mass transport of glycerol is limiting the system by causing the deactivation of the catalyst. At lower NaOH bulk concentrations for the thicker electrodes, the mass transport of OH- also limits the reaction rate by causing the formation of a locally less oxidative environment. Finally, it is found that all electrodes pose dual reaction mechanisms. Increasing the electrode thickness promotes one reaction mechanism over the other as well as it increases the number of oxidation steps achieved in the reaction.

Liquid metal electrochemical cells are electrochemical device with at least one liquid metal electrode. They were adopted in electro-metallurgical processing, heat-to-power conversion, and energy storage applications. The electrode's liquid state ensures high current density, resulting in batteries with high power densities and electro-metallurgical reactors with high conversion yields. Mass transport is critical in all liquid metal electrochemical cells, but especially in concentration cells like liquid metal batteries. These are fully liquid three-layer cells where the two electrodes are separated by a thin molten salt electrolyte. There, the positive electrode alloying and de-alloying processes store energy in the cell. Inhomogeneities in the liquid metal electrode reduce cell efficiency and material use. In this work, we are interested in understanding mass transport within this electrode. From a first study of diffusive heat and mass transport, we established that solutal effects are predominant in liquid metal electrodes. Any thermally driven convection can not significantly affect a compositionally stable stratification. A solutal flow will efficiently mix the electrode regardless of the temperature distribution. Following that, we developed a consistent explanation for the differences in the cell resistance between charge and discharge, as observed multiple times in the literature. The latter was based on quantitative analysis of a new experimental result. The voltage evolution was measured during the cycling of a liquid metal battery. During discharge, light elements are electro-deposited at the positive electrode's top interface, forming a gravitationally stable stratification. As only diffusion transports the light element away from the interface, the concentration difference and the mass transport overvoltage increase with time. During charging, the opposite phenomenon (electro-refining) takes place. The flux at the active interface builds up an unstable, asymmetric, and time-dependent buoyancy distribution in the layer. That leads first to a diffusive transient and then to a convective flow in the layer. This solutal convection was studied numerically with finite-volume and spectral-element-method solvers. The two-dimensional axisymmetric simulations performed covered Schmidt numbers from 1.125 to 288 and five orders of magnitude of flux Rayleigh numbers, starting from 10000. Two regimes were identified as a function of the flux Rayleigh number. At low Rayleigh numbers, diffusion affects the full layer height before the onset of convection. This results in a global flow. Instead, convection originates in the thin concentration boundary layer with characteristic plume structures in the high Rayleigh number regime. In this regime, onset time and concentration difference are independent with respect to the layer height. Thanks to the extensive parametric study, we retrieved robust scaling for velocity and concentration differences as a function of the current density and material properties of the layer. These results can be used in the design and operation of liquid metal electrodes. For example, they allow estimating the mass transport overvoltage during charge. Furthermore, we studied numerically solutal convection in three-dimensional cylindrical electrodes. We showed that the two-dimensional approximation captures quite remarkably the evolution of integral quantities observed in fully three-dimensional simulations. This is not due to the axisymmetric nature of the flow. On the contrary, we observed a rich dynamic, with polygonal-shaped cells forming and evolving in the active interface concentration distribution. Finally, the influence of non-uniform current distribution on mass transport in a liquid metal electrode was investigated. Differences with respect to the homogenous configuration are present in pure diffusion and at the onset of convection. The solutal flow is able to reduce the inhomogeneities in the electrode. / Elektrochemische Flüssigmetallzellen sind Zellen mit mindestens einer Flüssigmetall Elektrode. Sie werden in der Elektrometallurgie, bei der Wandlung von Wärme in Elektrizität, sowie zur Energiespeicherung eingesetzt. Der flüssige Zustand der Elektroden erlaubt hohe Stromdichten, was Batterien mit guter Ratenfähigkeit und elektrometallurgischen Reaktoren mit hoher Raum-Zeit-Ausbeute ermöglicht. Stofftransport ist ein für alle elektrochemischen Flüssigmetallzellen wesentliches Phänomen, insbesonders für Konzentrationszellen wie Flüssigmetallbatterien. Das sind Dreischichtzellen mit komplett flüssigem Inventar, bei denen die beiden Elektroden durch eine Salzschmelze getrennt sind. Die Legierungs- und Entlegierungsprozesse in der positiven Elektroden sind maßgeblich für die Energiespeicherfähigkeit der Zelle. Inhomogenitäten in der Legierungselektrode verringern den Gesamtwirkungsgrad der Zelle und den Nutzungsgrad der Aktivmaterialien. Diese Arbeit widmet sich dem Verständnis des Stofftransports in der positiven Elektrode. Ein Vergleich typischer Kenngrößen für den Wärme-und Stofftransport zeigt auf, dass solutale Effekte die Transportverhältnisse in Flüssigmetallelektroden dominieren. Thermische Konvektion kann eine stabile solutale Schichtung nicht wesentlich beeinflussen. Eine von Konzentrationsgradienten hervorgerufene Strömung durchmischt die Elektrode jedoch unabhängig von der Temperaturverteilung. Darauf aufbauend wird dargelegt, was die Ursache für die wiederholt in der Literatur berichteten Unterschiede im Zellwiderstand zwischen Ladung und Entladung ist. Die Erklärung stützt sich auf eine quantitative Analyse neuer experimenteller Ergebnisse zum Zyklenverhalten von Flüssigmetallbatterien. Während der Entladung werden leichte Elemente am oberen Rand der positiven Elektrode abgeschieden und bilden eine stabile Dichteschichtung. Da das eingelagerte Element geringer Dichte nur durch Diffusion von der Grenzfläche abtransportiert wird, steigen der Konzentrationsgradient und mit ihm die Stofftransportüberspannung mit der Zeit an. Während der Aufladung findet das entgegengesetzte Phänomen (Elektroraffination) statt. Die Extraktion der leichten Komponente an der aktiven Grenzfläche führt zu einer instabilen Dichteschichtung. Dadurch kommt es zunächst zu einer kurzen Phase instationärer Diffusion, die rasch von einer solutal getriebene Konvektion abgelöst wird. Die solutale Konvektion wurde numerisch mit Finite-Volumen- und Spektral-Element-Methoden untersucht. Dazu durchgeführte axialsymmetrische Simulationen umfassten Schmidt-Zahlen von 1,125 bis 288 und fünf Größenordnungen von Rayleigh-Zahlen, beginnend bei 10000. In Abhängigkeit von der Rayleigh-Zahl wurden zwei Regime identifiziert. Bei niedrigen Rayleigh-Zahlen findet Diffusion über die gesamte Schichthöhe statt, bevor es zum Einsetzen der Konvektion kommt. Daraus resultiert eine globale Strömung. Im Bereich hoher Rayleigh-Zahlen entsteht die Konvektion stattdessen bereits in einer dünnen Konzentrationsgrenzschicht an der Phasengrenze und zeigt die charakteristischen Konzentrationsschlieren (plumes). In diesem Regime sind die Eintrittszeit und die zugehörige Konzentrationsdifferenz von der Schichthöhe unabhängig. Die umfassende Parameterstudie bildet die Grundlage zur Herleitung fundierter Skalengesetze für Geschwindigkeit und Konzentration in Abhängigkeit der Stromdichte und der Materialeigenschaften der Fluide. Diese Ergebnisse können zur Auslegung und zum Betrieb von Flüssigmetall-Elektroden verwendet werden. Sie ermöglichen beispielsweise die Bestimmung der Stofftransportüberspannung während des Ladens. Für ausgewählte Konfigurationen wurden dreidimensionalen Simulationen in zylindrischen Elektroden durchgeführt. Die Ergebnisse der zweidimensionalen Simulationen bezüglich der integralen Größen wurden bestätigt. Die dreidimensionalen Simulationen offenbarten eine reichhaltige Dynamik polygonaler Zellen, die sich aufgrund der absinkenden Schlieren in Grenzflächennähe bilden. Abschließend wurde der Einfluss einer ungleichmäßigen Stromverteilung an der Phasengrenze auf den Stofftransport untersucht. Unterschiede zur homogenen Verteilung ergeben sich lediglich bezüglich der rein diffusiven Ausbreitung und des Einsetzens der Konvektion. Die ausgebildete solutale Konvektion durchmischt die Elektrode in beiden Fällen sehr intensiv, so dass in diesem Stadium keine Differenzen feststellbar sind.

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The raw water in some of Umeå's abstraction wells has shown high nickel levels for more than a decade. The cause has not been determined but there is an investigation from 2010 where the results indicate sulphide clay found adjacent to two basins used for artificial infiltration. The previous investigation further declares that the leaching occurs due to oxidation in an unsaturated state when the groundwater is lowered. However, the data points used for the investigation are limited and the source references are few. Today, over 10 years of data have been collected and the number of published scientific articles dealing with sulphide soils has increased, which motivates a follow-up on the subject. This degree project aims to contribute with further knowledge to the issue of high nickel concentrations in raw water with the purpose to strengthen or reject the hypothesis by: performing a literature review on sulphide soil; comparing nickel level with groundwater level; constructing a groundwater model and performing simulations. A large database is available from various investigations performed on the site from the 1940s until today. The literature review shows that the geological conditions exist for sulphide material to be present in the area, as well as several studies and investigations that confirm the suspicion of the presence of sulphide soil. Furthermore, the data points show a correlation between the groundwater level and the nickel concentration in raw water from extraction wells 17 and 20. The most obvious interpretation is the decrease in the nickel content as the groundwater level is raised, although a low groundwater level indicates high nickel levels. The modeling of the groundwater flow and mass transport shows how nickel can move from the area of suspected sulphide material to the extraction wells. An overall assessment of the project strengthens the thesis, however, more investigations are needed to exclude uncertainties inherent in the result. / Råvatten i vissa av Umeås uttagsbrunnar har uppvisat höga nickelhalter i mer än ett decennium. Orsaken är inte fastställd men det finns en tidig utredning från 2010 som misstänker sulfidlera som finns i anslutning till två bassänger som används för konstgjord infiltration. Den tidigare utredningen deklarerar vidare att urlakningen sker på grund av oxidation i omättat tillstånd när grundvattnet sänks. Dock var dataunderlaget till utredningen begränsad samt ett fåtal källhänvisningar. Idag finns över 10 års data samlat och antalet publicerade vetenskapliga artiklar som behandlar sulfidjord har ökat, vilket motiverar en uppföljning i ämnet. Detta examensarbete syftar till att bidra med ytterligare kunskap i syfte att stärka eller förkasta hypotesen genom att: utföra en litteraturstudie om sulfidjord; jämföra nickelnivå med grundvattennivå; konstruera en grundvattenmodell och utföra simuleringar. En stor databas finns tillgänglig från olika undersökningar som har gjorts på platsen från 1940-talet fram till idag.  Litteraturstudien visar att den geologiska förutsättningen finns för att sulfidjord ska finnas i området samt flera studier och undersökningar som stärker misstanken om närvaron av sulfidjord. Vidare visar resultatet av data punkter på en korrelation mellan grundvattennivån och nickelhalten i råvattnet till uttagsbrunn 17 och 20. Tydligast blir minskningen av nickelhalten när grundvattennivån höjs, även om en låg grundvattennivå indikerar höga nickelhalter. Modelleringen av grundvattenflödet och masstransporten visar hur nickel kan röra sig från området med misstänkt sulfidjord till uttagsbrunnarna. En helhetsbedömning av projektet stärker tesen, dock krävs fler undersökningar för att utesluta osäkerheter i resultatet.

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