Small organic ‘collector’ ligands play an important role in the recovery of platinum group minerals (PGMs) from the industrial platinum mining process via the froth flotation process, which separates finely ground minerals on the basis of relative hydrophobicity. Design of novel ligands to improve PGM recovery is an ongoing industrial interest. This thesis involves the application of computational chemistry techniques to gain a first-principles understanding of simple mineral-collector ligand interactions, with a view to applying this understanding to the design of novel collector ligands. Experimental techniques are also used, where appropriate, to validate computational modelling in order to gauge the applicability of computational chemistry to this field. Sperrylite (PtAs2), the world’s most common PGM, was used as a model for a typical platinum group sulfide mineral. Pentlandite ((Fe,Ni)9S8) and pyrite (FeS2), two base metal sulfide minerals commonly associated with PGMs, were used as competitor surfaces to gauge collector selectivity. α-quartz (SiO2) was used as to model silicaceous waste material, and pure platinum (Pt) as an internal standard to gauge Pt-collector interactions. Chapter 1 provides an overview of PGM mining with particular focus on the froth flotation process. A brief overview of the computational methods applied in this work is provided in Chapter 2. Chapter 3 presents modelling work based on assessing the various mineral and metal surfaces upon which ligands adsorption is modelled. Stable ‘working surfaces’ are defined by calculating surface energies for various low Miller index cleavages of the bulk unit cells of these solids. Surface stability with respect to slab depth is also assessed. A number of methods, including application of the virtual crystal approximation, a pairwise cluster expansion and explicit site modelling, are used to resolve the issue of positional disorder of the metal sites in pentlandite. This leads to the observation that pentlandite slabs with a higher concentration of Ni atoms at the mineral/vacuum interface are more stable. A global minimum energy bulk unit cell of pentlandite is described. Chapters 4 and 5 deal with the adsorption of collector and aqua ligands onto these surfaces, with Chapter 5 also reporting attempts at rational in-silico ligand design. A novel method for calculating the binding energy of anionic species in periodic systems via a work-function based correction is described and tested for both mono- and dianionic species. Modelling of ethyl xanthate (H5C2OCS2-) and xanthate-based analogues (H5C2XCS2-, where X=N, NH, NC2H5, S, CH, CH2) shows a trend of increased binding strength upon formation of dianionic species. Whilst this observation was supported (to a lesser degree) by geometrical parameters, the extension of the work-function based correction to deal with dianionic species tended to significantly overbind these ligands and so the work function correction was found to be inappropriate for use in models with a charge state greater than -1. Modelling of heterocyclic ligands on selected surfaces shows weaker adsorption than non-heterocyclic species due to unfavourable electronic effects of the delocalised heterocycle on the R-CS2- head group. Efforts in ligand design focussed on optimising the electronic properties of the tail group in the xanthate structure to provide maximum electron density to the CS2- system. The output from this process was p-methoxyphenyl dithiocarbamate (H2CO-C6H4-N=CS2²-), which performed well in computational models. Synthesis of this ligand, as well as protonated Nethyl dithiocarbamate (H5C2NHCS2-) failed, however, due to the intrinsic instability of monosubstituted dithiocarbamates. Attempts to validate modelling results using two experimental techniques are reported in Chapter 6. Firstly, cyclic voltammetry experiments using sperrylite, pentlandite and platinum working electrodes suspended in collector solutions of concentration 1x10-3 M are reported, which show some correlation between the order of calculated binding energies and the relative position of the oxidation potential for the formation of disulfide oxidation products, a process which is affected by surface adsorption. Correlation is best for ethyl xanthate and diisobutyl dithiophospinate, but poor for N,N-diethyl dithiocarbamate ((H5C2)2NCS2-). Secondly, microflotation experiments for the recovery of sperrylite, pentlandite and pyrite using various collector ligands were conducted. Results broadly agree with prior microflotation literature, but show no simple correlation between ligand binding energies and flotation recovery, suggesting that more complex factors than simple ligand/mineral adsorption are involved.

No description available.

This work treats the thermal and mechanical performances of gas-filled, flat plate solar collectors in order to achieve a better performance than that of air filled collectors. The gases examined are argon, krypton and xenon which all have lower thermal conductivity than air. The absorber is formed as a tray connected to the glass. The pressure of the gas inside is near to the ambient and since the gas volume will vary as the temperature changes, there are potential risks for fatigue in the material. One heat transfer model and one mechanical model were built. The mechanical model gave stresses and information on the movements. The factors of safety were calculated from the stresses, and the movements were used as input for the heat transfer model where the thermal performance was calculated. It is shown that gas-filled, flat plate solar collectors can be designed to achieve good thermal performance at a competitive cost. The best yield is achieved with a xenon gas filling together with a normal thick absorber, where normal thick means a 0.25 mm copper absorber. However, a great deal of energy is needed to produce the xenon gas, and if this aspect is taken into account, the krypton filling is better. Good thermal performance can also be achieved using less material; a collector with a 0.1 mm thick copper absorber and the third best gas, which is argon, still gives a better operating performance than a common, commercially produced, air filled collector with a 0.25 mm absorber. When manufacturing gas-filled flat plate solar collectors, one way of decreasing the total material costs significantly, is by changing absorber material from copper to aluminium. Best yield per monetary outlay is given by a thin (0.3 mm) alu-minium absorber with an argon filling. A high factor of safety is achieved with thin absorbers, large absorber areas, rectangular constructions with long tubes and short distances between glass and absorber. The latter will also give a thin layer of gas which gives good thermal performance. The only doubtii ful construction is an argon filled collector with a normal thick (> 0.50 mm) aluminium absorber. In general, an assessment of the stresses for the proposed construction together with appropriate tests are recommended before manufacturing, since it is hard to predict the factor of safety; if one part is reinforced, some other parts can experience more stress and the factor of safety actually drops.

Froth flotation is the most efficient method for phosphate separation, which is a physic-chemical separation process based on the difference of surface properties between the valuable minerals and unwanted gangue minerals. However, the presence of clay slimes in the slurry after grinding consumes a large amount of reagents, decreases the collision probability between bubbles and minerals, prevents phosphate particle attachment to air bubbles, and thus considerably reduces flotation recovery and concentrate grade. Georgia Pacific Chemical, LLC has recently developed novel depressants, i.e., clay binders, which are a series of low molecular weight specialty polymers to help improve phosphate flotation performance by selectively agglomerating and depressing clay particles, thus lowering their surface area and reducing the adsorption of surfactants. This thesis addresses the effects of clay binders on phosphate flotation performance and their adsorption behavior on different minerals in a sedimentary phosphate ore. Quartz Crystal Microbalance with Dissipation technique (QCM-D) was used to study adsorption characteristics of clay binders and batch flotation tests were performed under different conditions to investigate phosphate flotation performance. The experimental results have shown that clay binders significantly improved phosphate flotation selectivity and reduced the dosages of collector and sodium silicate used as dispersant in the industry.

Flotation models describe the separability of mineral particles using a loosely defined term known as floatability or probability of collection, a response of particles in the pulp zone of a flotation vessel, unrelated to events in the froth phase. The Bubble Load measurement samples the particles that have attached to bubbles in the pulp zone and, thus, should give an indication of floatability. This thesis investigates the role of floatability in flotation models, and assesses the Bubble Load measurement as a direct estimate of floatability. Towards these ends, continuous pilot-scale flotation tests were carried out in which collector addition rate was varied. This allowed the floatability of mineral particles to be back-calculated on a size-by-liberation basis and be compared to the measured Bubble Load. Contrary to expectations it was found that, with increasing collector addition rate, the “floatability” of a majority of galena particle classes did not increase after 5 mg/kg of collector, while the measured Bubble Load actually decreased. This was found to be due to the stability of the froth increasing with collector addition rate, causing more galena to reach the concentrate, and less to drop-back to the pulp phase to be reattached. Conversely, there were other particle classes (such as sphalerite and coarse galena) where the expected trends were found, namely increasing floatability and Bubble Load with collector addition rate. These results indicate a high level of interdependence between the pulp and froth zones of the studied flotation cell through the flow of material between them (internal reflux). In the case of galena, the flow of material returning via drop-back from the froth had a greater impact on the Bubble Load than the galena in the feed made sufficiently hydrophobic to attach to bubbles. This means that, for the system studied here, the Bubble Load measurement does not provide a direct estimate of mineral particle floatability, defined as a sole consequence of pulp phase events. Moreover, for the current case, it appears that this definition of floatability is not sufficient to capture the interactions between the pulp and the froth. It is recommended that pulp and froth zone flotation models be developed in concert, recognising the interaction between the two zones, and that flotation models be formulated with due allowance for the material transport paths within a flotation vessel. It should be recognised that “floatability” is an aid for the imagination; a term for a process, rather than a particle “property” to be measured. An extension of the kinetic chemical reaction analogue, incorporating flotation sub-processes, is suggested/revived, to give some phenomenological basis to kinetic flotation models.

[pt] Este trabalho apresenta a pesquisa relativa ao tema resíduos sólidos urbanos, mais especificamente a coleta seletiva, no município de Armação dos Búzios (RJ), um dos mais conhecidos e visitados balneários turísticos do Brasil, onde o segmento turístico é o principal pilar econômico. Para essa pesquisa, levantou-se o histórico de implantação do hoje abandonado aterro sanitário do município. Foi feito o acompanhamento in loco, em duas pousadas, de toda a operação de coleta, incluindo pesagem dos resíduos, carregamento destes no caminhão e itinerário diário percorrido.Uma das principais conclusões é a de que todo esse processo de implantação do sistema de gestão da sustentabilidade nas pousadas, com foco na coleta seletiva de seus resíduos, é um processo em que vários setores da sociedade se beneficiam. Ganham os colaboradores internos quando repartem entre si o dinheiro da venda desses resíduos; ganha o empresário, pois pode divulgar com convicção sua postura ambiental e ganha o município, que aumenta o dinheiro circulante na economia local e diminui o volume coletado por seus caminhões. / [en] One of the key issues regarding social policies in Brazil is the one related to universal access to basic sanitation with quality, equity and continuity. The universalization of basic sanitation has been assumed as a commitment of the whole Brazilian society and it is an institutional reform effort involving governments, service providers, industry, financial agents and society through their organizations and channels of participation. By basic sanitation, it is meant the set of services, infrastructure and operational facilities regarding drinking water supply, sewage, solid waste management and urban sanitation, management of urban stormwater and drainage. This issue gains more prominence each day, due to its social impact and the growing concern about quality of life, health, and the environment. The theme and the steps involved in solid waste management are included and defined in Law nº 11.455/07, which established the national guidelines for the basic sanitation federal policy. This law also brought an essential instrument for the implementation of the National Sanitation Plan policy [Plano Nacional de Saneamento Básico], with the preparation of the respective Municipal and/or Regional Plans for Basic Sanitation. It also considers solid waste management as a set of activities, infrastructure and operating facilities for collection, transportation, transfer, treatment and final disposal of household refuse and garbage originated from the sweeping and cleaning of public areas and public roads. The irresponsible treatment and disposal of such waste pave the way for the deteriorating quality of life and health of the population. Among the various alternatives for solid waste treatments, recycling is the most friendly and more attractive to the public and media in general, especially for its strong environmental and educational appeals.

Made available in DSpace on 2014-06-11T19:27:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-01-12Bitstream added on 2014-06-13T20:17:00Z : No. of bitstreams: 1 campana_m_me_botfmvz.pdf: 694345 bytes, checksum: 5b95a0f43e56990d64086b8a724378b9 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Universidade Estadual Paulista (UNESP) / Com objetivo de validar o uso no campo do coletor de espuma com ácido e politetrafluoroetileno que capta amônia volatilizada e quantificar essa perda oriunda de fontes e formas de aplicação de nitrogênio (N) em pastagens, realizou-se 2 experimentos. No experimento 1, para avaliação do coletor, utilizou-se fatorial 2 x 2 - doses de N (50 e 100 kg/ha) e coletores de amônia (coletor semi-aberto e absorvedor de espuma com ácido e politretafluoroetileno). O período experimental foi de 22 dias. No experimento 2 utilizou-se delineamento de blocos ao acaso e os tratamentos foram: uréia; Super N®; uréia + 12,5% de zeólita; uréia + 25% de zeólita; uréia + 50% de zeólita; uréia em pulverização foliar; 75% de uréia + 25% de sulfato de amônio; nitrato de amônio e sem N (testemunha). A avaliação das perdas por volatilização de amônia ocorreu em 3 épocas. No verão/07 e inverno/07 utilizou-se dose de 50 kg/ha de N para adubos sólidos e 15 kg/ha de N para pulverização foliar e para o verão/08 as doses foram duplicadas. As perdas diárias de amônia foram avaliadas em onze amostragens a cada dois dias para ambos os experimentos. Para o experimento 1, não houve diferença entre os coletores na perda acumulada e diária de amônia com a dose de 50 kg/ha de N. Entretanto, na dose de 100 kg/ha de N o coletor semi-aberto captou o maior pico de volatilização diária e maior acúmulo de amônia. No experimento 2 as menores perdas por volatilização foram detectadas para nitrato de amônio aplicado a lanço e uréia via pulverização foliar. Dessa forma poderia ocorrer melhor uso do fertilizante pela planta refletindo em aumento na produção e qualidade da forragem. / With the objective of validating the field use of the foam collector with acid and polytetrafluorethylene, which captures volatilized ammonia and quantify this loss when using sources and application forms of nitrogen (N) in pastures, 2 experiments were realized. In the experiment 1, to evaluate the collector a 2 x 2 factorial – N doses (50 and 100 kg/ha) and ammonia collectors (semi-open collector and foam absorber with acid and polytetrafluorethylene). The experimental period was 22 days. In the experiment 2, the experimental design was a randomized block design and the treatments were: urea; Super N®; urea + 12,5% of zeolite; urea + 25% of zeolite; urea + 50% of zeolite; urea leaf spraying, 75% of urea + 25% of ammonium sulfate, ammonium nitrate, and without nitrogen (control). The evaluation of the volatilization losses occurred in 3 periods. On summer/07 and winter/2007 a 50 kg/ha of N dose for solid fertilizers was used and a 15 kg/ha N dose for leaf spraying and on summer/2008 the doses were doubled. The daily losses of ammonia were evaluated in eleven samplings every two days for both experiments. In the experiment 1, there was no difference between the collectors in the accumulated and daily loss in the dose of 50kg/ha of N. However, with the dose of 100 kg/ha of N the semi-open collector showed the highest peak of daily volatilization and accumulated the highest volatilization loss. In the experiment 2, the lowest volatilization losses were detected for ammonium nitrate in soil application and urea in leaf spraying application. So, in this cases might happen the better use of the fertilizer by the plant, reflecting in the increase of the forage production and quality.

Orientador: Vicente Luiz Scalon / Delson Luiz Modolo / João Batista Campos Silva / Resumo: Nas últimas décadas, o crescente aumento do preço dos combustíveis fósseis associado às crescentes preocupações ambientais têm incentivado as pesquisas sobre o uso de fontes de energia renováveis e os aprimoramentos de seus sistemas e equipamentos. Dentre as fontes alternativas existentes, a energia solar merece ser destacada pelo seu grande potencial de exploração. Os dispositivos solares permitem um amplo espectro de uso, podendo ser utilizados desde operações de grande porte, como hotéis e indústrias, até em sistemas menores típicos de residências. Dentre as aplicações possíveis de energia solar, o sistema de aquecimento de água residencial utilizando coletores solares planos ainda é o mais comum. Este tipo de dispositivo capta a radiação solar por meio de seus coletores e aquece a água que escoa no seu interior e a armazena dentro de um reservatório. Este trabalho propõe estudar uma geometria de coletor alternativa para a captação de energia baseada no coletor de absorção direta. Neste tipo de dispositivo, o fluido de trabalho escoa entre uma placa absorvedora negra e uma placa de vidro e é aquecido indiretamente pela placa absorvedora. Para a avaliação da geometria um modelo numérico bidimensional utilizando o OpenFOAM® foi elaborado. As análises realizadas visaram determinar as condições de contorno ideais para as simulações envolvendo escoamentos de vazão constante e devido ao efeito de termossifão. Com o modelo estabelecido, determinou-se a curva de rendimento da geom... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: On last decades, the increasing price of fossil fuels associated with the growing concern with the environmental have encouraged researches about renewable energy sources and improvements to its systems and equipment. Among the available alternative sources, solar energy deserves to be highlighted for its great exploitation potential. Solar devices allow a wide range of use, since large operations, such as hotels and industries, to typical smaller residences systems. Among possible applications for solar power, residential water heating systems using flat solar collectors are the most common ones. This type of devices capture solar radiation through their collectors, heat the inside flowing water and stores it in a reservoir. The present work intends to study an alternative collector geometry for energy harvesting based on the direct absorption collector. In this device, the working fluid flows between a black absorber plate and a glass cover and is heated indirectly by the absorber plate. For the geometry evaluation a two-dimensional numeric model was created using OpenFOAM. The analysis aimed to determine the optimal boundary conditions for simulations involving a constant flow and a thermosiphon effect flow. With the model stablished, it was determined the efficiency curve for the geometry in order to find the optimal fluid thickness that flows inside the collector. After the analysis, it can be concluded that the thickness effect on the thermal efficiency is small and, am... (Complete abstract click electronic access below) / Mestre

The optical properties of the absorber pipe in a parabolic trough collector isessential for the performance of the solar collector. The desirable propertiesare high absorptance (α) of solar radiation and low emittance (ε) of thermalradiation. A surface with these properties is known as a solar selective surface. There are several techniques used to produce selective surfaces, but one of the most common ones is electroplating. Research done by Vargas, indicates that optical properties of α = 0.98 and ε = 0.03 [1], which is superior to the best commercial alternatives (α = 0.95 and ε = 0.04 [2]), can be achieved by electroplating a Co-Cr coating on a stainless steel substrate. Additionally, Vargas used an electrolyte of trivalent chromium dissolved in a deep eutectic solvent, as opposed to the traditionally used aqueous electrolytes containing hexavalent chromium, which is toxic and carcinogenic. In this project, a coating of Co-Cr was electroplated on a stainless steel substratewith a method similar to that of Vargas in order to obtain a solar selective surface. The electrolyte was composed of ethylene glycol, choline chloride, CrCl3•6H2O and CoCl2•6H2O in a molar ratio of 16:1:0.4:0.2. The plating process was conducted using chronoamperometric electrodeposition with an applied potential of -1.2 V (against an Ag/AgCl reference electrode) for 15 min. The system was investigated using Cyclic Voltammetry (CV). The total absorptance was measured using UV-Vis spectroscopy, while the emittance was measured using an IR-thermometer. The microstructure and chemical composition was investigated using Scanning ElectronMicroscopy (SEM), Focused Ion Beam (FIB), Energy-Dispersive X-ray Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy. The thermal stability of the coating was investigated by exposingit to 400°C in air for 24 h. The electroplated coating is approximately 2.8 μm thick and exhibits a porousstructure with a surface of fine fiber-like flakes. The coating consists largely of Co hydroxides with low concentrations of Cr compounds, Co oxides and metallic Co. Hence, a satisfactory co-deposition was not accomplished, as the Cr concentration is low. The coating is not thermally stable up to 400°C, exhibiting signs of at least partially melting in the annealing process. The compounds in the coating were largely oxidized in the process. The electroplated surface does however exhibits strong selectivity, with a total solar absorptance of α = 0.952 and total emittance of ε = 0.32 at 160°C.

The thesis deals with energy simulation of a solar energy system in a low-energy family house with warm-air heating. The simulations performed resulted in the assessment of the energy contribution of four solar systems with different types of collectors. The profitability and return of investment for the particular system have been evaluated based on investment costs and the savings gained. The theoretical part includes an introduction to the solar energy field, solar panel systems and the passive house concept. The practical part is devoted to description of the simulated object models as used in the TRNSYS environment, the simulation results evaluation along with the assessment of the economic return on investment. The conclusion recommendations regarding a suitable type and size of the solar panel with respect to the economic criteria chosen are given.