Este estudo apresenta um modelo matemático fenomenológico para um sistema convencional de Eletrodiálise (ED) para dessalinização de água, com operação contínua em estágios. O modelo, elaborado a partir de balanços materiais em cada compartimento de um estágio genérico, foi aplicado para separação dos seguintes sais em solução aquosa: NaCl, KCl, Na2SO4 e MgCl2. A restrição operacional de sistemas de ED devida à densidade de corrente limite é particular para cada sistema e depende da configuração geométrica do equipamento, características das membranas seletivas e das propriedades do soluto. Para sua determinação, foram realizados experimentos em uma unidade de ED em escala laboratório, construída no Departamento de Engenharia Química da EPUSP. Essa unidade experimental foi utilizada para validação do modelo. A sensibilidade do modelo foi analisada para diferentes solutos em relação às seguintes variáveis: resistência elétrica da membrana, temperatura, vazão do fluido na célula, espessura da célula e concentração da alimentação, visando estabelecer seu efeito nos custos totais do sistema. O modelo foi aplicado em simulações para sistemas de ED operando em diferentes configurações: em contracorrente, com reciclo e em batelada. A partir de um caso base, foi elaborado um algoritmo de otimização pelo método de busca direta para determinar a configuração geométrica e potencial elétrico ótimo que minimizem os custos operacionais e de investimento do processo. A melhor configuração do ponto de vista econômico corresponde a um sistema em concorrente com reciclo. Os estudos de sensibilidade indicaram que o custo de remoção de Na2SO4 foi maior do que o custo de remoção de NaCl e KCl, aparentemente devido ao fato de se tratar de íons divalentes. Finalmente, apesar de haver diminuição do custo com o aumento da velocidade do fluido através das membranas, esse custo passa a aumentar para altas velocidades, devido ao maior efeito do custo de bombeamento. / This study presents a phenomenological mathematical model for an electrodialysis system (ED) for water desalination, operating continuously in stages. The model is based on material balances for the species in each compartment of a generic stage, and was applied to the separation of the following salts from water solutions: NaCl, KCl, Na2SO4, and MgCl2. One major operational restriction in ED systems is the limiting current density, which is specific for each system and depends on the equipment configuration, membrane characteristics, and solute properties. The limiting current density was determined by means of a series of laboratory scale experiments in an ED unit designed and assembled in the Chemical Engineering Department, University of São Paulo. This same experimental unit was used to validate the model. A sensitivity analysis was carried out for solutions containing different solutes, with relation to the following variables: membrane electrical resistance, temperature, fluid flow rate in the cell, cell thickness, and feed concentration, aiming at evaluating their effect on the total cost. The model was applied to simulate ED systems with different configurations: countercurrent, with recycle stream, or operating in batch mode. Based on a reference configuration, a direct search algorithm was used to estimate optimal values of design variables and electrical potential that minimize the investment and operational costs of an ED plant. The most feasible process configuration from the economic point of view corresponds to a co-current system with recycle, which has minimum membrane area. No effect of the temperature on the processing cost was detected. The desalination cost is larger for Na2SO4 than for NaCl or KCl, possibly due to the fact that these are monovalent ions. The increase in the velocity of the solution in the cell compartments causes a decrease in the processing cost due to the increase in the transfer rates, but large velocities result in high pumping costs, which contribute to the increase in processing costs.

A escassez de água nos grandes centros urbanos deve se agravar nos próximos anos. Novas fontes de água são necessárias para suprir a demanda. Nas cidades não há disponibilidade de terrenos para construção de estações de tratamento de águas e esgotos convencionais. Por isso, são necessários novos processos de tratamento. Processos de separação por membranas como osmose reversa e eletrodiálise são usados na dessalinização de águas e efluentes. Para a realização do estudo foi montada unidade de eletrodiálise em escala de laboratório. Na montagem selecionaram-se equipamentos que fossem resistentes à salinidade das soluções. As bombas magnéticas deveriam, ainda, superar a perda de cargas causada pelas membranas. As membranas foram adquiridas no exterior; os equipamentos, no mercado local. Os experimentos foram realizados em duas etapas: exploratória e comparativa. Eles seguiram os planejamentos de fatorial e do tipo Doehlert, respectivamente. Estudou-se a dessalinização de soluções aquosas unitárias (NaCl, Na2SO4, MgCl2 e KCl), com salinidade similar à água marinha (3,5%). Obtiveram-se como respostas os fluxos de sal, de água e consumo de energia em função dos fatores envolvidos no processo. Análises estatísticas propiciaram relacionar os fatores estudados com os resultados empíricos. Os fluxos salinos são proporcionais às densidade de corrente aplicadas e não apresentaram diferenças significativas entre si. Observou-se que o fluxo de água é relevante pelo mecanismo de solvatação de íons removidos e pela osmose. O consumo de energia é proporcional à densidade de corrente e maior para os sais bivalentes. / Water shortage in urban centers is expected to get worse in the next years. New water sources are necessary to meet demand. At urban area there are no available lands to build conventional water and sewage treatment plants. Therefore, new treatment processes are needed. Membrane processes like reverse osmosis and electrodialysis are used in water and wastewater desalination. A lab-scale electrodialysis unit was assembled for the study, based on a stack of electrodialysis membranes and support components that are capable of resisting solution salinity. The membrane stack was imported; the other equipment, obtained locally. The experiments were divided in two phases: exploratory and comparative. The experiments followed factorial and Doehlert designs, respectively. The desalination of aqueous solutions containing different inorganic salts (NaCl, Na2SO4, MgCl2 e KCl) in seawater salinity (3.5% mass) was studied. The responses were the salt and water fluxes and energy consumption in function of the processes variables selected. By means of a statistical analysis, it was possible to obtain the correlations for the studied factors based on the experimental results. The salt fluxes are proportional to the applied current density and they are not significantly different for the salts included in the study. It was observed that the water fluxes are relevant due to solvation of removed ions and osmosis. The energy consumption is proportional to current density and is larger for bivalent salts.

Atualmente, a preocupação com a redução da poluição industrial tem motivado os pesquisadores na busca de novas tecnologias para o tratamento de resíduos industriais. Tecnologias limpas, como a eletrodiálise, são capazes de tratar alguns destes resíduos, como por exemplo o efluente da indústria de galvanoplastia, minimizando os impactos que ocorreriam caso eles fossem descartados diretamente no meio ambiente. O componente principal desta técnica é a membrana na qual ocorre a etapa de retirada dos íons da solução. Atualmente estas membranas são importadas e caras, o que justifica o desenvolvimento de membranas eficientes e acessíveis. Neste sentido, no presente trabalho membranas de poliestireno sulfonado/ poliestireno de alto impacto (SPS/HIPS), polianilina dopada com ácido canforsulfônico/ poliestireno sulfonado/ poliestireno de alto impacto (PAniCSA/SPS/HIPS), polianilina sulfonada/ poliestireno sulfonado/ poliestireno de alto impacto (SPAN/SPS/HIPS), e polianilina dopada com ácido p-tolueno sulfônico/ poliestireno sulfonado/ poliestireno de alto impacto (PAniTSA/SPS/HIPS) foram desenvolvidas usando o método de mistura química. As membranas foram caracterizadas utilizando as técnicas Análise termogravimétrica (TGA), Análise dinâmico Mecânica (DMA), e Microscopia Eletrônica de Varredura (MEV). Membranas foram submetidas a curvas corrente-potencial e ensaios de eletrodiálise em soluções de NaCl e KCl, a fim de determinar o transporte iônico através das mesmas. Os resultados foram comparados com uma membrana comercial Selemion CMT. A extração percentual média para íons de Na+ obtidos pelas membranas desenvolvidas foi superior a 20%. / Nowadays the concern with the reduction of industrial pollution has motivated researchers to found out new technologies for treatment of industrial waste. The clean technologies, as electrodialysis, are capable of treating some these residues, as for example the galvanoplasty’s waste, minimizing the impacts that would happen to them if they were discarded directly on the environment. The main component of this technique is the membrane on which occurs the ions removal stage of the solution. The membranes are imported and expensive what justifies the development of efficient and accessible membranes. In this sense, in the present work membranes of sulfonated polystyrene / high impact polystyrene (SPS/HIPS), polyaniline doped with camphorsulfonic acid / sulfonated polystyrene / high impact polystyrene (PAniCSA/SPS/HIPS), sulfonated polyaniline/ sulfonated polystyrene / high impact polystyrene (SPAN/SPS/HIPS), and polyaniline doped with p-toluenesulfonic acid / sulfonated polystyrene / high impact polystyrene (PAniTSA/SPS/HIPS) were developed using chemical mixture method. Membranes were characterized by Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Dynamic Mechanical Analysis (DMA) and Scanning Electronic Microscopy (SEM). Membranes were submitted to current-voltage curves and electrodialysis experiments with NaCl and KCl solutions, in order to determine ionic transport through them. Results were compared with a commercial membrane, Selemion CMT. The average percent extraction for Na+ ions obtained by membranes developed were beyond 20%.

Le colmatage à la surface et dans la masse d’une membrane échangeuse d’ions est un obstacle majeur à son utilisation en électrodialyse. En bloquant les voies conductrices d’ions à travers la membrane, le dépôt réduit la surface active de la membrane et conduit à une résistance au transfert de matière supplémentaire.Trois membranes échangeuses de cations ont été utilisées lors de ce travail: une membrane commerciale hétérogène MK-40 et deux de ses modifications (une membrane MK-40/Nafion obtenue par revêtement de la surface de MK-40 avec un film de Nafion® homogène conducteur d’ions, et une membrane MK-40/PANI obtenue par synthèse de polyaniline sur la surface de la MK-40). Les solutions utilisées sont des solutions de CaCl2 et MgCl2 aux concentrations 0,02 et 0,04 mol/L, ainsi qu’une solution modélisant la composition minérale du lait, concentrée 3 fois. La visualisation de la surface de la membrane est réalisée par microscopie optique et microscopie électronique à balayage. L’analyse élémentaire des dépôts sur la surface de la membrane est réalisée par l’analyse aux rayons X. Le caractère hydrophobe-hydrophile de la surface de la membrane est estimé par la mesure de l’angle de contact. La chronopotentiométrie et la voltamétrie ont été utilisées pour caractériser la vitesse de transport des cations à travers les membranes et la dissociation d’eau à la surface ; la mesure du pH de la solution dessalée a été effectuée en parallèle.Il est démontré que l’hydrophobicité relativement élevée de la surface de la membrane, son hétérogénéité électrique et géométrique créent les conditions favorables au développement de l’électroconvection. L’intensité de l’électroconvection par rapport à la membrane non modifiée est significativement plus élevée dans le cas de la MK-40/Nafion mais plus faible dans le cas de la MK-40/PANI. L’électroconvection provoque le mélange de la solution à la surface de la membrane dans une couche d’environ 10 µm d’épaisseur. Cet effet augmente de manière significative le transfert de matière en mode de courant intensif, empêche ou réduit le colmatage et réduit aussi le taux de dissociation de l’eau sur la surface de la membrane. L’intensité de l’électroconvection dépend essentiellement du degré d’hydratation du contre-ion ; elle augmente avec son rayon de Stokes. Le taux de croissance des dépôts minéraux Mg(OH)2, Ca(OH)2 et CaCO3 sur la surface de la membrane échangeuse d’ions est déterminé par la pente du chronopotentiogramme. On établit expérimentalement que, par rapport à la vitesse de colmatage sur la membrane MK-40 non modifiée, celle sur la surface de MK-40/Nafion devient plus petite mais celle sur la surface de la MK-40/PANI, devient plus grande.Le taux du colmatage est considérablement réduit lorsqu’un mode de courant électrique pulsé est appliqué. Un tel mode permet de réduire de moitié la différence de potentiel et d’atteindre un état quasi-stable du fait que le précipité devient instable / Scaling on the surface and in the bulk of ion-exchange membranes is a considerable locker for electrodialysis. The scale reduces the effective surface area of the membrane and leads to additional resistance to the mass transfer and solution flow.Three cation-exchange membranes are used in this study: a heterogeneous commercial MK-40 membrane and two of its modifications. The MK-40/Nafion membrane is obtained by mechanical coating the MK-40 membrane surface with a homogeneous ion-conductive Nafion® film. Modification of the MK-40/PANI membrane is carried out by polyaniline synthesis on the membrane surface. The solutions used in the study are 0.02 and 0.04 mol/L CaCl2 and MgCl2 solutions, as well as the solution, imitating the mineral composition of milk, concentrated 3 times. The visualization of the membrane surface is made using optical and scanning electron microscopy. The elemental analysis of the scale on the membrane surface is made by X-ray analysis. The hydrophobic-hydrophilic balance of the membrane surface is estimated by the contact angle measurements. To characterize the cation transport through and the water splitting rate, chronopotentiometry and voltammetry methods are used, pH measurement of the diluate solution is conducted at the same time.It is shown that the relatively high hydrophobicity of the membrane surface, its electrical and geometric heterogeneity, create conditions for the development of electroconvection. The electroconvection intensity in the case of MK-40/Nafion is significantly higher, and in the case of MK-40/PANI is lower in comparison with that of the unmodified membrane. Electroconvection vortexes cause the mixing of the solution at the membrane surface in a 10 µm thick layer. This effect significantly increases mass transfer in intensive current modes and prevents or reduces the scaling process, as well as reduces the water splitting rate at the membrane surface. The rate of electroconvection essentially depends on the counterion hydration degree, it increases with increasing the counterion Stokes radius. The rate of the scale formation on the membrane surface is determined by the slope of the chronopotentiogramme. The formation of Mg(OH)2, Ca(OH)2 and CaCO3 scales is observed. It is experimentally established that the scaling rate on the surface of MK-40/Nafion is smaller, and on the surface of the MK-40/PANI is larger in comparison with the MK-40 membrane. The scaling rate is significantly reduced when the pulsed electric current mode is applied. Such mode allows the reduction of the potential drop more than twice and achievement of a quasi steady-state because an unstable periodically crumbling scale occurs

Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Vor dem Hintergrund des steigenden Lithiumbedarfs und der Ungleichverteilung der weltweiten Lithiumvorkommen gilt es auch, kleinere, heimische Vorkommen, wie die Zinnwalditlagerstätte bei Zinnwald/Cínovec, für eine mögliche Lithiumgewinnung zu untersuchen. Hierfür wurden zur Darstellung von Lithiumcarbonat zwei Verfahren entwickelt, optimiert und ökonomisch bewertet. Dabei konnte gezeigt werden, dass insbesondere das Direktcarbonatisierungsverfahren mit überkritischem CO2 aufgrund des geringen Chemikalienverbrauchs, der hohen Selektivität für Lithium, als auch dem breiten Anwendungsspektrum für weitere primäre und sekundäre Lithiumressourcen ein vielversprechender Ansatz für eine technische Umsetzung darstellt. Des Weiteren wurde die elektrodialytische Darstellung von Lithiumhydroxid untersucht und optimiert. Mittels einer erstellten Simulation wurden hierfür nicht nur Anforderungen an prozessierbare Ausgangslösungen definiert, sondern auch ein Aufbau zur Erhöhung der Prozessstabilität entwickelt, der eine kontinuierliche Filtration eines oder mehrerer Kreisläufe der Elektrodialyse erlaubt.

Please read the abstract in the section 00front of this document. / Thesis (DPhil)--University of Pretoria, 2010. / Chemistry / unrestricted

Flow injection analysis (FIA) is a continuous flow technique developed in the early 1970's. FIA is based on reproducible sample injection, accurate timing and controlled dispersion. This technique is very versatile due to the control of the variables and can easily be automated. This technique is very suitable for routine laboratory analysis. By introducing various sample modifying techniques in tandem with the FIA system, samples can easily be modified. Some modifying techniques are analyte pre-concentration, sample dilution and sample cleanup. Passive dialysis can be used very successfully for sample dilution and cleanup. Problems arise when samples with low analyte concentration have to be analysed. For this reason an electrodialyser unit, equipped with a passive membrane, was developed. The history, development and theory of membranes and membrane processes are discussed. A study of the movement of ions, in solution and across a passive membrane, under the influence of an applied d.c. electrical potential is given. Passive membranes were evaluated for use in the proposed system. The following factors influencing the efficiency of electrodialysis in the F1 system were studies. The flow rate of the donor and acceptor channels; the applied d.c. electrical potential; injection loop volumes; flow direction in the electrodialyser unit. An investigation was done into on-line analyte pre-concentration and regulated dilution probabilities of the electrodialysis system. Systems that were evaluated are the following: The determination of chloride in water effluents; the determination of copper and zinc in pharmaceuticals; the direct and indirect determination of phosphate in fertilizers. A comparative study between the advantages and disadvantages of the passive dialysis and electrodialysis system is given. / Thesis (PhD (Chemistry))--University of Pretoria, 2006. / Chemistry / unrestricted

Los dos baños de cobre más utilizados comercialmente son el baño ácido a base de sulfato y el baño alcalino a base de cianuro. Los baños alcalinos son utilizados principalmente para producir recubrimientos en piezas con geometría compleja y para evitar la deposición galvánica cuando se deposita un metal en un sustrato menos noble. Debido a la toxicidad de los compuestos de cianuro, se han desarrollado baños alternativos usando diferentes agentes complejantes. El punto de partida de la presente investigación es un baño primario sin cianuros para deposición de cobre en sustratos de Zamak desarrollado en el Instituto de Investigaciones Tecnológicas del Estado de Sao Paulo / Brasil. La sustitución de materias primas como el cianuro debe ser económicamente ventajosa y técnicamente viable. De esta manera, la investigación presentada pretendió proponer una alternativa para el tratamiento de residuos líquidos del baño ya mencionado con la finalidad de recuperar de manera simultánea el agua y las materias primas en un sistema cerrado. Se ha estudiado el proceso de separación por membranas de intercambio iónico, la electrodiálisis, usando un sistema en escala de laboratorio y una disolución sintética que simulaba las aguas residuales del baño a base de HEDP. Se ha evaluado la viabilidad del sistema por medio del análisis de los parámetros de operación, como la extracción de iones, la tasa de desmineralización, el porcentaje de concentración, la eficiencia de la intensidad calculada para cada especie y el consumo medio de energía. Debido a que el ácido HEDP es un agente quelante, se ha evaluado el transporte de los quelatos Cu(II) HEDP a través de membranas de intercambio de aniones por medio de métodos electroquímicos. Se han construido curvas cronopotenciométricas y curvas intensidad-potencial para diferentes disoluciones sintéticas que contenían los mismos compuestos que el baño original. Se ha establecido la relación entre la presencia de los quelatos en las disoluciones y los grupos fijos de intercambio de aniones. Por fin, se han realizado las pruebas de deposición usando electrólitos conteniendo los compuestos reciclados y se han evaluado las características de los depósitos obtenidos. Los resultados indicaron que el sistema de electrodiálisis usando membranas de intercambio de aniones con grupos de intercambio de base fuerte ha podido producir disoluciones tratadas y un concentrado conteniendo los iones del baño. Se ha podido añadir el concentrado al baño original para compensar eventuales perdidas del arrastre sin afectar la calidad de los depósitos. Por lo tanto, la aplicación de la electrodiálisis demostró ser una alternativa viable para la recuperación del agua y de las materias primas de la disolución evaluada, reduciendo la generación de residuos líquidos y ahorrando los recursos naturales. / The two most common commercial copper baths are the acid sulfate copper bath and the alkaline cyanide copper bath. Alkaline copper baths are mostly used to coat parts with complex geometry and to avoid galvanic deposition when depositing a metal on a less noble substrate. Because of the toxicity of cyanide compounds, alternative baths have been developed using different complexing agents. The starting point of the present study is a cyanide free strike bath developed for copper plating on Zamak substrates developed by the Institute for Technological Research of the State of São Paulo/ Brazil. The replacement of a raw material such as cyanide must be economically advantageous and technically feasible. Therefore, this study intended to propose an alternative to the treatment of liquid wastes from the mentioned bath, aiming at simultaneous water reclamation and chemicals recovery in a closed system. The electrodialysis membrane separation process was studied, using a laboratory-scale system operating with a synthetic solution simulating the rinsing waters from the HEDP-based bath. The feasibility of the technique was evaluated by analyzing operational parameters such as ion extraction, demineralization rate, concentration rate, current efficiency for each anionic specie and average energy consumption. Because HEDP is a chelating agent, the transport of Cu(II) HEDP chelates through anion exchange membranes was also evaluated by means of electrochemical methods. Chronopotentiometric and current-voltage curves were constructed for different model solutions containing the same compounds as the original bath. A relation between the presence of chelates in the solutions and the fixed ion exchange group could be established. Lastly, deposition tests were performed using electrolytes containing the recycled inputs and the characteristics of the coatings were analyzed. The results showed that an electrodialysis stack using strongly basic anion exchange membranes was suitable to produce treated solutions and a concentrate containing the ions from the bath. The concentrate could be added to the copper bath to compensate eventual drag-out losses without affecting the quality of the coatings. Thus, the application of electrodialysis was shown to be a feasible alternative for recovering water and inputs from the evaluated solution, reducing the wastewater generation and saving natural resources. / Els dos banys de coure més utilitzats comercialment són el bany àcid a base de sulfat i el bany alcalí a base de cianur. Els banys alcalins són utilitzats principalment per a produir recobriments en peces amb geometria complexa i per a evitar la deposició galvànica quan es deposita un metall en un substrat menys noble. A causa de la toxicitat dels compostos de cianur, s'han desenrotllat banys alternatius usant diferents agents complexants. El punt de partida de la present investigació és un bany primari sense cianurs per a deposició de coure en substrats de Zamak desenrotllat en l'Institut d'Investigacions Tecnològiques de l'Estat de Sao Paulo / Brasil. La substitució de matèries primeres com el cianur ha de ser econòmicament avantatjosa i tècnicament viable. D'aquesta manera, la investigació presentada va pretendre proposar una alternativa per al tractament de residus líquids del bany ja mencionat amb la finalitat de recuperar de manera simultània l'aigua i les matèries primeres en un sistema tancat. S'ha estudiat el procés de separació per membranes d'intercanvi iònic, electrodiàlisi, usant un sistema en escala de laboratori i una dissolució sintètica que simulava les aigües residuals del bany a base d'HEDP. S'ha avaluat la viabilitat del sistema per mitjà de l'anàlisi dels paràmetres d'operació, com l'extracció d'ions, la taxa de desmineralització, el percentatge de concentració, l'eficiència de la intensitat calculada per a cada espècie i el consum mitjà d'energia. Pel fet que l'àcid HEDP és un agent quelant, s'ha avaluat el transport dels quelats Cu (II)-HEDP a través de membranes d'intercanvi d'anions per mitjà de mètodes electroquímics. S'han construït corbes cronopotenciomètriques i corbes intensitat-potencial per a diferents dissolucions sintètiques que contenien els mateixos compostos que el bany original. S'ha establit la relació entre la presència dels quelats en les dissolucions i els grups fixos d'intercanvi d'anions. Finalment, s'han realitzat les proves de deposició usant electròlits contenint els compostos reciclats i s'han avaluat les característiques dels depòsits obtinguts. Els resultats van indicar que el sistema d'electrodiàlisi usant membranes d'intercanvi d'anions amb grups d'intercanvi de base forta ha pogut produir dissolucions tractades i un concentrat que conté els ions del bany. S'ha pogut afegir el concentrat al bany original per a compensar eventuals perdudes de l'arrossegament sense afectar la qualitat dels depòsits. Per tant, l'aplicació de l'electrodiàlisi va demostrar ser una alternativa viable per a la recuperació de l'aigua i de les matèries primeres de la dissolució avaluada, reduint la generació de residus líquids i estalviant els recursos naturals. / Scarazzato, T. (2017). Treatment of a cyanide-free copper electroplating solution by electrodialysis: study of ion transport and evaluation of water and inputs recovery [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/98502 / TESIS

This diploma thesis deals with the general characteristics of membrane processes and separations. It includes a chapter on the history of development of the technology industry using membranes as a medium for separating chemicals based on their specific properties and also the importance of such processes at present. This work then introduces the basic principles of mass transport by membranes and describes various types of membranes and materials used for their production. It also deals with electromembrane separations, including electrodialysis. The practical part focuses on experimental separation of solutions of four sodium salts by means of electrodialysis. Based on the electrical current and conductivity measurements of these solutions in time during membrane separation are evaluated process parameters such as efficiency, energy consumption, transferred electrical charge, and mass of the sodium salt.