The Virginia Tech Equilibrium Chemistry (VTEC) code is a keyboard interactive, user friendly, chemical equilibrium solver for use on a personal computer. The code is particularly suitable for a teaching / learning environment. For a set of reactants at a defined thermodynamic state given by a user, the program will select all species in the JANAF thermochemical database which could exist in the products. The program will then calculate equilibrium composition, flame temperature, and other thermodynamic properties for many common cases. Examples in this thesis show VTEC's ability to predict chemical equilibrium compositions and flame temperature for selected reactions, and demonstrate how VTEC can substitute for and aid in the design of lab experiments, and identify trends in parametric studies. The 1976 NASA Lewis Chemical Equilibrium Code (CEC76) from which VTEC has been adapted uses Lagrangian multipliers to minimize free energy. CEC76 was written for mainframe computer use. Later versions of CEC76, adapted for personal computer use are available for a fee and have a very minimal user interface. / Master of Science

Several misconceptions show up when learners answer questions on Chemical Equilibrium during examinations. Literature from other researchers shows similar trend of misconceptions (Johnstone, 2000; Morais, Paiva and Barros, 2007; Adesoji and Babatunde, 2008) for example, ‘apply pressure to the reactants’ (Johnstone, 2000). This shows that Chemistry has no meaning to these learners and they end up with misconceptions as they try to memorise facts in order to pass examinations. Learners are taught before writing these examinations, but how are they taught the concepts of Chemical Equilibrium? A descriptive approach was used on an exploratory survey conducted in Thohoyandou Cluster among Physical Science (Chemistry) FET band Educators. Cluster sampling of 40 educators from 18 randomly sampled schools responded to questionnaires. Five ‘well experienced’ educators who have been producing ‘good’ results at Grade 12 NSC examinations and two Physical Sciences subject advisors were interviewed. Using Spearman Brown Split-Half statistical method a 0,891 reliability coefficient was obtained. Research results show lack or under utilisation of laboratory equipment, teaching strategies which promote rote learning. Lack of confidence of educators due to deficiency in topic content knowledge and pedagogical skills which promote conceptual understanding were identified. Problem of English language leading to communication breakdown between educator-learners and between learner-subject leading to emergency of knowledge gaps in learners. Educators consider professional development through re-training and workshops on subject content matter and teaching strategies as the way forward to improve the quality of teaching. Topic specific PCK focusing on problem-solving strategy was recommended as a means to increasing educators’ efficiency in teaching and enhance learners’ comprehension and achievement in Physical Science. / Science and Technology Education / M. Sc. (Mathematics, Science and Technology Education (Chemistry Education))

Several misconceptions show up when learners answer questions on Chemical Equilibrium during examinations. Literature from other researchers shows similar trend of misconceptions (Johnstone, 2000; Morais, Paiva and Barros, 2007; Adesoji and Babatunde, 2008) for example, ‘apply pressure to the reactants’ (Johnstone, 2000). This shows that Chemistry has no meaning to these learners and they end up with misconceptions as they try to memorise facts in order to pass examinations. Learners are taught before writing these examinations, but how are they taught the concepts of Chemical Equilibrium? A descriptive approach was used on an exploratory survey conducted in Thohoyandou Cluster among Physical Science (Chemistry) FET band Educators. Cluster sampling of 40 educators from 18 randomly sampled schools responded to questionnaires. Five ‘well experienced’ educators who have been producing ‘good’ results at Grade 12 NSC examinations and two Physical Sciences subject advisors were interviewed. Using Spearman Brown Split-Half statistical method a 0,891 reliability coefficient was obtained. Research results show lack or under utilisation of laboratory equipment, teaching strategies which promote rote learning. Lack of confidence of educators due to deficiency in topic content knowledge and pedagogical skills which promote conceptual understanding were identified. Problem of English language leading to communication breakdown between educator-learners and between learner-subject leading to emergency of knowledge gaps in learners. Educators consider professional development through re-training and workshops on subject content matter and teaching strategies as the way forward to improve the quality of teaching. Topic specific PCK focusing on problem-solving strategy was recommended as a means to increasing educators’ efficiency in teaching and enhance learners’ comprehension and achievement in Physical Science. / Science and Technology Education / M. Sc. (Mathematics, Science and Technology Education (Chemistry Education))

This thesis investigates sustainability measures for quicklime and cement clinker production. It is the aim of this thesis to contribute to the effort of creating a more sustainable modus of industrial production. The methods used comprises process simulations through multicomponent chemical equilibrium calculations, fuel characterization and raw materials characterization through dynamic rate thermogravimetry. The investigated measures relate to alternative fuels, co-combustion, oxygen enrichment, oxyfuel combustion, mineral carbonation and optimizing raw material mixes based on thermal decomposition characteristics. The predictive multicomponent chemical equilibrium simulation tool developed has been used to investigate new process designs and combustion concepts. The results show that fuel selection and oxygen enrichment influence energy efficiency, and that oxyfuel combustion and mineral carbonation could allow for considerable emission reductions at low energy penalty, as compared to conventional post-combustion carbon dioxide capture technologies. Dynamic rate thermogravimetry, applied to kiln feed limestone, allows for improved feed analysis with a deeper understanding of how mixing of different feed materials will affect the production processes. The predictive simulation tool has proven to be of practical value when planning and executing production and full scale campaigns, reducing costs related to trial and error. The main conclusion of this work is that several measures are available to increase the sustainability of the industry.

Na parte inicial deste trabalho faz-se estudo monográfico sobre o íon azoteto e sua estrutura. Também nesta parte encontram-se reunidas referências sobre o íon uranilo em meio aquoso e os possíveis produtos de hidrólise, propostos na literatura, bem como, em presença de azoteto. Algumas considerações sobre a formação de complexos mistos polinucleares são também apresentadas. Sendo o ácido azotídrico um eletrólito fraco, as mudanças de pH nos tampões N-3/HN3 podem ser acompanhadas após a introdução de íons U2O2+5, potenciometricamente, com eletrodo de vidro. No intuito de obtenção de medidas mais precisas, determinou-se a resposta Nernstiana do eletrodo utilizado. O tratamento de dados aplicado à obtenção das constantes de formação, em meio azoteto, através do numero médio de ligantes e do grau de complexação, a diferentes concentrações de ligante, força iônica 2,00 M e temperatura de (25,0 ± 0,l) ºC, permitiu a avaliação de três constantes de equilíbrio: β1 = 2,136 x 104 (M-1), β2 = 6,090 x 105 (M-2), β3 = 1,421 x 108 (M-3). Tais constantes de formação, nas condições estudadas, bem como o crescimento da estabilidade especialmente do primeiro complexo, sugerem a existência dos seguintes equilíbrios: (Ver arquivo PDF). É proposto um método alternativo , para a determinação de acidez livre das soluções padrões de câtions de metais hidrolisáveis, por medidas de pH condicional, à força iônica constante, por adição de padrão ácido. Correção de pH para respostas não Nernstianas do eletrodo de vidro recomenda o processo para resultados analíticos mais precisos. Estudos espectrofotométricos em meio aquoso complementam os estudos de hidrólise para o íon uranilo. Estudos das características espectrais dos sistemas U(VI), Fe(III) e Cu(II) em meio azotídrico, sugerem apresentação de um método analítico, para a determinação simultânea destes íons, baseado nas altas absortividades molares dos complexos formados: (Ver arquivo PDF). Em decorrência do estudo de interferentes, após extenso estudo sobre a oxidação e estabilidade dos sistemas cobalto (II) e níquel(II), em meio azotídrico, baseado nas trocas espectrais de cobalto(II) à cobalto(III), é apresentado um método alternativo para a detecção de traços de cobalto em diferentes sais de níquel (perclorato, nitrato, sulfato e cloreto), após estudo monográfico apresentando os clássicos para tal finalidade. Em meio 2,9 M de ‌N-3‌ e 0,10 M ‌HN3‌ pela ação de 10 mM de H2O2 à 365 - 353 nm marcantes diferenças espectrais devidas à oxidação de íons de cobalto recomendam o método da adição de padrão para limites entre 0,59 - 1,7 mg de Co(II) com interferências de níquel(II) em concentrações superiores à 250 mg . Medidas potenciométricas permitiram uma estimativa da constante global de formação da espécie ‌Co(N3)6‌3- por oxidação anódica de íons de cobalto(II) em meio não complexante, a baixas temperaturas e pela ação de oxidante químico, PbO2, em meio complexante, como sendo da ordem de 1016 (M-6) em força iônica 2,00 M (NaClO4) à (25,0 ± 0,1) °C. / The study starts with a monographic study about the azide ion and its structure. In this part we can also meet bibliographic references about the uranyl ion, in aqueous medium, and its possible hydrolysis products is proposed in the literature. Some considerations of the mixed polinuclear complex formation are also presented. Being hydrazoic acida weak electrolyte, the change of pH in N-3/HN3 buffers can be followed after introduction of U2O2+5 ions, potentiometrically, with glass electrode. In order to obtain accurate measurements the Nernstian response of this electrode was determined. Data treatment was applied to obtain the hydrolysis formation constants , in azide medium, through the average ligand number and complexity function, at several ligand concentrations, ionic strenght 2.00 M and temperature of (25.0 ± 0.l) ºC. The following constants are avaliable: β1 = 2,136 x 104 (M-1), β2 = 6,090 x 105 (M-2), β3 = 1,421 x 108 (M-3). Referred to the equilibria (3) - (5): (See file PDF). It has been proposed an alternative method for the determination of free strong acid in standard solutions of hydrolysable cations, can be achieved by measurements of the conditional pH, at constant ionic strenght, with standard acid addition. Corrections of the measured pH for non Nernstian response of the glass electrode is a recomended procedure for more accurate analytical results. Spectrophotometric studies, in aqueous medium, are completing the hydrolysis studies of uranyl ion. Spectral studies of the U(VI), Cu(II) and Fe(III) systems, in azide medium, to render possible a new analytical method, for simultaneous determination of these ions, based in high molar absortivities of the complex formed (See file PDF). Running allway of the foreign ins study, after the great study about the oxidation and stability of cobalt(II) and nickel(II) systems, in azide medium, based in spectral changes of cobalt(II) to cobalt(III), it has been formed an alternative method for determination of traces of cobalt in different nickel salts (perchlorate, nitrate, sulphate, and chloride). A monographic study, giving the different methods of the literature, has been completed. In 2.9 M ‌N-3‌ and 0.10 M ‌HN3‌ by the action of 10 mM of H2O2 at 365 - 353 nm a marked spectral differences arosen from oxidation of cobalt(II). A standard addition method leved to determination of 0.59 - 1.7 mg Co of nickel interferes when in concentrations higher than 250 mg, i.e., higher than 0.010 M. Potentiometric measurements lead to an estimation of overall formation constant of ‌Co(N3)6‌3- specie by anodic oxidation of cobalt(II) ions, in non complexing medium, at low temperatures and by chemical oxidant action, PbO2, in complexing medium, as being 1016 (M-6) order in ionic strenght 2.00 M (NaClO4) at (25.0 ± 0.1) ºC.

Partindo do princípio de que a aprendizagem conceitual envolve o estabelecimento de relações significativas entre os diversos conceitos que compõem um tema de ensino e, considerando também que o professor, ao preparar suas aulas, faz uso de um livro didático, e este pode ser utilizado como fonte de pesquisa por seus alunos, desejou-se compreender a inter-relação entre aprendizado, conhecimento estabelecido, e processo de ensino, norteada pelo modelo triádico de Gowin. Para este fim, foram elaboradas estruturas como redes e mapas conceituais referentes a todos os dados coletados. De maneira bastante simplificada, redes de conceitos são representações gráficas constituídas por nós (conceitos) que são ligados entre si formando uma rede que tem como intuito expressar de maneira objetiva uma determinada estrutura de conhecimento. Já mapas conceituais são diagramas de significados, ou seja, conceitos organizados de tal forma que aqueles que possuem relação entre si (dentro do entendimento de quem os constrói) são ligados por uma linha. Frases de ligação curtas e simples são escritas sobre essa linha, explicando qual o significado da relação conceitual. Os dados a partir dos quais foram elaboradas tais estruturas são, para os alunos (aprendizado), uma questão versando sobre os aspectos macroscópicos e submicroscópicos do equilíbrio químico; para o livro didático (conhecimento estabelecido), o texto introdutório do capítulo que faz referência ao tema citado e; para o professor (processo de ensino), um fragmento da primeira aula, onde os conceitos inicias e primordiais relacionados ao equilíbrio foram apresentados e discutidos com os alunos. A análise das redes e mapas conceituais revelou que, no decorrer do curso, os alunos aprimoraram seu conhecimento referente aos principais conceitos acerca do tema. Além disso, foi possível perceber que de fato os elementos da tríade de Gowin encontram-se bastante interligados, ora se complementando, ora se reforçando, mas nunca se contradizendo. Em relação aos aspectos macroscópicos e submicroscópicos do equilíbrio químico, percebeu-se que ambos são pouco aprofundados na discussão do livro didático e durante as aulas, o que consequentemente refletiu numa abordagem superficial feita pelos alunos. / Assuming that conceptual learning involves the establishment of meaningful relationships between the various concepts that make up a teaching theme, and also considering that the teacher, when preparing his classes, makes use of a textbook, and this one can be used as a research source by his students, we wanted to understand the relationships between learning, established knowledge, and teaching process, guided by Gowin\'s triadic model. For this purpose, structures such as networks and concep maps were elaborated for all the collected data. In a very simplified way, concept networks are graphic representations constituted by nodes (concepts) that are linked to one another, forming a network with the clear intention of expressing a given knowledge structure. Concept maps are diagrams of meanings, that is, concepts organized in such a way that those who have relations with each other (within the understanding of who builds them) are linked by a line. Short and simple propositions are written on this line, explaining the meaning of the concept relation. The data from which these structures were elaborated are, for students (learning), an issue dealing with macroscopic and submicroscopic aspects of chemical equilibrium; for the textbook (established knowledge), the introductory text of the chapter that refers to the subject cited and; for the teacher (teaching process), a fragment of the first class, where the initial and primordial concepts related to the equilibruim were presented and discussed with the students. The analysis of the networks and concept maps revealed that, during the course, the students improved their knowledge regarding the main concepts about the theme. In addition, it was possible to see that in fact the elements of Gowin\'s triad are very intertwined, sometimes complemented, sometimes strengthened, but never contradicted. In relation to the macroscopic and submicroscopic aspects of the chemical equilibrium, it was noticed that both are not deepened in the discussion of the textbook and during the classes, which consequently reflected in a superficial approach made by the students.

A gaseificação é um processo de conversão termoquímica que compreende a oxidação parcial de um combustível para convertê-lo em uma mistura gasosa (“syngas”). Geralmente a modelagem desses processos utiliza uma descrição cinética detalhada ou os aproximam ao equilíbrio químico. Ambas as abordagens têm vantagens e desvantagens, bem como limitações. O objetivo deste trabalho foi o desenvolvimento de uma nova modelagem fenomenológica de processos de gaseificação através de um modelo “híbrido” aqui chamado de modelo híbrido adaptativo por zonas (HAZ). Este modelo assumiu que o gaseificador é representado por zonas de dois tipos: uma dominada pela cinética química, representada por um modelo cinético, e outra onde a cinética química é rápida e as espécies químicas estão em equilíbrio químico, representada por um modelo de equilíbrio. Um critério de transição entre as zonas foi proposto através de um número de Damköhler (Da) que relaciona tempos de residência e de reação química. Desta forma, o modelo adapta-se conforme os processos dominantes em cada zona. Em um primeiro momento, um modelo de equilíbrio multifásico (EM) foi desenvolvido e aplicado para um estudo da cogaseificação de carvão mineral e biomassas disponíveis no Brasil. A seguir, o modelo HAZ foi construído através da técnica de rede equivalente de reatores químicos (ERN) a partir do modelo EM e de um modelo cinético, também desenvolvido neste trabalho. Uma metodologia de aplicação do modelo HAZ foi proposta, aplicada e validada para duas configurações de gaseificadores: dois casos de gaseificadores de biomassa em leito fluidizado borbulhante e um caso de gaseificador de carvão mineral em leito de arraste. Para os dois primeiros casos foi estimada que a transição ocorra para Da ≥ 10+5 e para o último caso; chegou-se a Da ≥ 10+3. A aplicação do modelo HAZ se mostrou satisfatória sendo que foi possível a redução do tempo computacional em pelo menos 40% com relação a uma abordagem puramente cinética. Cabe ressaltar ainda que o modelo HAZ possibilitou um maior entendimento físico e químico ao identificar os processos dominantes locais. / Gasification is a thermochemical conversion process consisting of partial oxidation of a fuel to convert it to a gas mixture (“syngas”). Generally, the gasification process modeling uses a kinetic detailed description, or approach it to a chemical equilibrium state. Both approaches have advantages and disadvantages, as well as limitations. The objective of this work was to develop a new phenomenological modeling of gasification processes through a “hybrid” model here called hybrid adaptive zone model (HAZ). This proposed modeling assumed the gasifier is represented by two types of zones: one dominated by chemical kinetics, represented by a kinetic model, and another where chemical kinetics is fast so chemical species are assumed in chemical equilibrium states, represented by an equilibrium model. A transition criterion between zones was defined by a Damköhler number (Da) which relates residence time and chemical reaction time. Therefore, the HAZ model can adapted according to the dominant processes in each zone. Firstly, a multi-phase equilibrium model (ME) was developed and applied to study the coal-biomass co-gasification of Brazilian sources. Hereafter, the HAZ model was built using the technique of equivalent reactor network (ERN) with the ME model and a kinetic model developed in this work. A methodology of use of the HAZ model was proposed, applied and validated for two configurations of gasifiers: two cases of biomass bubbling fluidized-bed gasifiers and one case of coal entrained-flow gasifier. In the first two cases the transition was estimated to occur on Da ≥ 10+5 and in the last case; we estimated on Da ≥ 10+3. The application of the HAZ model proved to be satisfactory since it could reduce the computation time by at least 40% compared to a pure kinetic approach. It should already be emphasized that the HAZ model allowed a better physical and chemical understanding of gasification by identifying the dominant local processes.

Partindo do princípio de que a aprendizagem conceitual envolve o estabelecimento de relações significativas entre os diversos conceitos que compõem um tema de ensino e, considerando também que o professor, ao preparar suas aulas, faz uso de um livro didático, e este pode ser utilizado como fonte de pesquisa por seus alunos, desejou-se compreender a inter-relação entre aprendizado, conhecimento estabelecido, e processo de ensino, norteada pelo modelo triádico de Gowin. Para este fim, foram elaboradas estruturas como redes e mapas conceituais referentes a todos os dados coletados. De maneira bastante simplificada, redes de conceitos são representações gráficas constituídas por nós (conceitos) que são ligados entre si formando uma rede que tem como intuito expressar de maneira objetiva uma determinada estrutura de conhecimento. Já mapas conceituais são diagramas de significados, ou seja, conceitos organizados de tal forma que aqueles que possuem relação entre si (dentro do entendimento de quem os constrói) são ligados por uma linha. Frases de ligação curtas e simples são escritas sobre essa linha, explicando qual o significado da relação conceitual. Os dados a partir dos quais foram elaboradas tais estruturas são, para os alunos (aprendizado), uma questão versando sobre os aspectos macroscópicos e submicroscópicos do equilíbrio químico; para o livro didático (conhecimento estabelecido), o texto introdutório do capítulo que faz referência ao tema citado e; para o professor (processo de ensino), um fragmento da primeira aula, onde os conceitos inicias e primordiais relacionados ao equilíbrio foram apresentados e discutidos com os alunos. A análise das redes e mapas conceituais revelou que, no decorrer do curso, os alunos aprimoraram seu conhecimento referente aos principais conceitos acerca do tema. Além disso, foi possível perceber que de fato os elementos da tríade de Gowin encontram-se bastante interligados, ora se complementando, ora se reforçando, mas nunca se contradizendo. Em relação aos aspectos macroscópicos e submicroscópicos do equilíbrio químico, percebeu-se que ambos são pouco aprofundados na discussão do livro didático e durante as aulas, o que consequentemente refletiu numa abordagem superficial feita pelos alunos. / Assuming that conceptual learning involves the establishment of meaningful relationships between the various concepts that make up a teaching theme, and also considering that the teacher, when preparing his classes, makes use of a textbook, and this one can be used as a research source by his students, we wanted to understand the relationships between learning, established knowledge, and teaching process, guided by Gowin\'s triadic model. For this purpose, structures such as networks and concep maps were elaborated for all the collected data. In a very simplified way, concept networks are graphic representations constituted by nodes (concepts) that are linked to one another, forming a network with the clear intention of expressing a given knowledge structure. Concept maps are diagrams of meanings, that is, concepts organized in such a way that those who have relations with each other (within the understanding of who builds them) are linked by a line. Short and simple propositions are written on this line, explaining the meaning of the concept relation. The data from which these structures were elaborated are, for students (learning), an issue dealing with macroscopic and submicroscopic aspects of chemical equilibrium; for the textbook (established knowledge), the introductory text of the chapter that refers to the subject cited and; for the teacher (teaching process), a fragment of the first class, where the initial and primordial concepts related to the equilibruim were presented and discussed with the students. The analysis of the networks and concept maps revealed that, during the course, the students improved their knowledge regarding the main concepts about the theme. In addition, it was possible to see that in fact the elements of Gowin\'s triad are very intertwined, sometimes complemented, sometimes strengthened, but never contradicted. In relation to the macroscopic and submicroscopic aspects of the chemical equilibrium, it was noticed that both are not deepened in the discussion of the textbook and during the classes, which consequently reflected in a superficial approach made by the students.

<p>The increased use of biomass and recovered waste fuels in favor of fossil fuels for heat and power production is an important step towards a sustainable future. Combustion of waste fuels also offers several advantages over traditional landfilling, such as substantial volume reduction, detoxification of pathological wastes, and reduction of toxic leaches and greenhouse gas (methane) formation from landfills. However, combustion of recovered waste fuels emits more harmful trace elements than combustion of other fuels. These elements are distributed between bottom ash, fly ash and flue gas, depending on the elements partitioning and enrichment behavior. Volatilized harmful trace elements are mainly enriched in the submicron fly ash fraction. If emitted to the atmosphere, submicron particles can penetrate deep into the alveoli of the lungs, causing severe impacts on human health. Consequently, to reduce ash related problems and to control the emissions to the atmosphere, there is an increased need for understanding the physicochemical processes involved in ash transformation, including particle formation.</p><p>The objective of this thesis was to carefully and systematically study the fate of trace elements during combustion, i.e. the chemical form of the elements and the partitioning behavior, by means of chemical equilibrium model calculations, X-ray diffraction, microscopy techniques and various spectroscopy methods. The influence of some fuel additives was also analyzed. Primarily, the elements copper, chromium and arsenic were studied.</p><p>An initial review and evaluation of the content of thermodynamical data in commercial thermochemical databases used for chemical equilibrium model calculations showed that there was a significant difference in number of included phases and species between databases. Thermodynamical data also differed between databases, although in general less for condensed phases than for gaseous species. A state-of-the-art database for Cu, Cr and As was compiled and used for further chemical equilibrium model calculations. The fate of Cu, Cr and As was determined in combustion experiments on wood impregnated with copper, chromium and arsenic (CCA) in a bench scale reactor (15 kW). The results showed that global chemical equilibrium model calculations predicted the overall fate of Cu, Cr and As in bottom ash and ash particles quite well. However, compared to the experimental results the global model overpredicted the formation of refractory calcium arsenates, thus the arsenic volatilization was found to be higher then the predicted volatilization. In terms of chromium volatility, copper was found to be an important refractory element forming stable CuCrO₂(s) and CuCr₂O₄(s) that suppressed the formation of CrO₂(OH)₂(g). The retention and speciation of Cu, Cr and As in bottom ash was further determined from combustion experiments of CCA wood fuel particles in a single particle reactor. Local chemical equilibrium model calculations were performed to simulate the combustion stages of a burning CCA treated wood fuel particle: drying, devolatilization, char burning and post-combustion. The results from the work showed that a mix of global and local chemical equilibrium model calculations is needed to describe the reality and that the combustion stages are partially overlapping. The fate of harmful trace elements, including Cu, Cr and As, was finally studied in full scale (65 MW) combustion experiments. Particles from the raw flue gas emissions were sampled and analyzed. The comparison with chemical equilibrium model calculations showed that the model explained the results well, but due to lack of thermodynamic data for K₂ZnCl₄(s), the formation of this phase could not be predicted.</p>

The increased use of biomass and recovered waste fuels in favor of fossil fuels for heat and power production is an important step towards a sustainable future. Combustion of waste fuels also offers several advantages over traditional landfilling, such as substantial volume reduction, detoxification of pathological wastes, and reduction of toxic leaches and greenhouse gas (methane) formation from landfills. However, combustion of recovered waste fuels emits more harmful trace elements than combustion of other fuels. These elements are distributed between bottom ash, fly ash and flue gas, depending on the elements partitioning and enrichment behavior. Volatilized harmful trace elements are mainly enriched in the submicron fly ash fraction. If emitted to the atmosphere, submicron particles can penetrate deep into the alveoli of the lungs, causing severe impacts on human health. Consequently, to reduce ash related problems and to control the emissions to the atmosphere, there is an increased need for understanding the physicochemical processes involved in ash transformation, including particle formation. The objective of this thesis was to carefully and systematically study the fate of trace elements during combustion, i.e. the chemical form of the elements and the partitioning behavior, by means of chemical equilibrium model calculations, X-ray diffraction, microscopy techniques and various spectroscopy methods. The influence of some fuel additives was also analyzed. Primarily, the elements copper, chromium and arsenic were studied. An initial review and evaluation of the content of thermodynamical data in commercial thermochemical databases used for chemical equilibrium model calculations showed that there was a significant difference in number of included phases and species between databases. Thermodynamical data also differed between databases, although in general less for condensed phases than for gaseous species. A state-of-the-art database for Cu, Cr and As was compiled and used for further chemical equilibrium model calculations. The fate of Cu, Cr and As was determined in combustion experiments on wood impregnated with copper, chromium and arsenic (CCA) in a bench scale reactor (15 kW). The results showed that global chemical equilibrium model calculations predicted the overall fate of Cu, Cr and As in bottom ash and ash particles quite well. However, compared to the experimental results the global model overpredicted the formation of refractory calcium arsenates, thus the arsenic volatilization was found to be higher then the predicted volatilization. In terms of chromium volatility, copper was found to be an important refractory element forming stable CuCrO2(s) and CuCr2O4(s) that suppressed the formation of CrO2(OH)2(g). The retention and speciation of Cu, Cr and As in bottom ash was further determined from combustion experiments of CCA wood fuel particles in a single particle reactor. Local chemical equilibrium model calculations were performed to simulate the combustion stages of a burning CCA treated wood fuel particle: drying, devolatilization, char burning and post-combustion. The results from the work showed that a mix of global and local chemical equilibrium model calculations is needed to describe the reality and that the combustion stages are partially overlapping. The fate of harmful trace elements, including Cu, Cr and As, was finally studied in full scale (65 MW) combustion experiments. Particles from the raw flue gas emissions were sampled and analyzed. The comparison with chemical equilibrium model calculations showed that the model explained the results well, but due to lack of thermodynamic data for K2ZnCl4(s), the formation of this phase could not be predicted.