Um grande passivo ambiental da atualidade refere-se à contaminação dos recursos hídricos por hidrocarbonetos. Os atuais sistemas de remediação buscam a utilização de adsorventes alternativos para remoção destes poluentes. O objetivo desta tese de doutorado foi avaliar o uso da cinza de casca de arroz (CCA) e de carvão ativado (CA) na adsorção de BTEX – benzeno, tolueno, etilbenzeno e xileno em soluções aquosas. A CCA foi gerada a partir do processo de queima de casca de arroz para aproveitamento energético e o CA obtido comercialmente. As propriedades físicas, químicas e microestruturais da CCA e do CA foram caracterizadas através de análises de distribuição granulométrica, área superficial, porosidade, massa específica, capacidade de hidratação, pH, ponto de carga zero, perda ao fogo, carbono total, composição química elementar, determinação de fases cristalinas, determinação de grupos funcionais e análise de imagem. Estudos de adsorção cinéticos e de equilíbrio (isotermas) foram efetuados com soluções padrões de benzeno, tolueno, xileno e etilbenzeno em sistemas monocompostos e em misturas BTEX. A quantificação foi realizada por por cromatografia gasosa com detector de ionização de chama. Na cinética de adsorção, foram avaliadas as variáveis: tempo de contato adsorvente-adsorbato (15, 30, 60, 120 e 240 minutos); concentração inicial do adsorbato (1, 5, 10 e 20 mg/L) e dosagem do adsorvente (10 e 20 g/L). Os modelos cinéticos de Pseudo-primeira ordem, Pseudo-segunda ordem e Difusão intrapartícula foram ajustados aos dados experimentais. Isotermas experimentais foram obtidas para cada composto e para a mistura BTEX. Os modelos de Langmuir, Freundlich e Sips foram ajustados aos resultados experimentais para os sistemas com monocompostos. A caracterização das amostras indicou que o CA apresenta microestrutura uniforme com grande área superficial formada por micro e mesoporos e alto teor de carbono. Já a CCA apresenta uma microestrutura heterogênea formada por macroporos e com alto teor de sílica. Os estudos cinéticos demonstraram que a CCA e o CA apresentam capacidades de adsorção altas e semelhantes no tempo de equilíbrio de 120 minutos. De forma geral, a remoção de cada composto na mistura foi menor que a remoção obtida quando em sistemas de monocompostos, onde a capacidade de adsorção se deu na seguinte ordem (em massa de adsorbato por massa de adsorvente): etilbenzeno > xileno > tolueno > benzeno. O modelo cinético de Pseudo-segunda ordem apresentou a melhor correlação para todos os ensaios. As isotermas experimentais obtidas para os monocompostos caracterizam a adsorção em superfícies porosas com formação de monocamada. Os ajustes aos modelos teóricos não apresentaram unanimidade, observando em algumas situações uma correlação adequada para Langmuir e Freundlich. Nas misturas BTEX, as isotermas experimentais para a CCA indicam uma competição pelos sítios ativos do adsorvente entre benzeno/tolueno e entre etilbenzeno/xileno. Os resultados obtidos sugerem que a adsorção de BTEX ocorre preferencialmente através de efeito hidrofóbico já que o CA é um material carbonoso e a CCA configura-se como uma matriz de sílica com fração carbonosa. Os valores de remoção ficaram entre 78,8 e 100%, demonstrando que a CCA apresenta-se como um material alternativo para a adsorção de benzeno, tolueno, etilbenzeno e xileno presente em solução aquosas. / The contamination of water resources by hydrocarbons is considered a significant environmental impact. The remediation systems currently search alternative adsorbents to remove this pollutants. The aim of this work was to investigate the use of rice husk ash (RHA) and activated carbon (AC) in the removal of BTEX (benzene, toluene, ethylbenzene, and xylene) from aqueous solutions. The RHA used was generated as a byproduct of the combustion of rice husk for energy generation, while AC was purchased from the market. Samples of both materials were characterized based on physical, chemical, and microstructural standards (grain size distribution, surface area, porosity, specific weight, hydration capacity, pH, zero load test, loss on ignition, total carbon, chemical composition, crystalline phases, functional groups, and image analysis). The adsorption assays were carried out using standard benzene, toluene, xylene, and ethylbenzene individually and mixed. Quantification of compounds was conducted by gas chromatography with Flame Ionization Detector. Adsorption kinetics was evaluated based on the variables contact time between adsorbent and adsorbate (15, 30, 60, 120, and 240 min), initial adsorbate concentration (1, 5, 10, and 20 mg/L), and adsorbent dose (10 and 20 g/L). The kinetic models pseudo 1st order, pseudo 2nd order, and intra-particle diffusion were adjusted to experimental data. Experimental isotherms were obtained for each compound and for the BTEX mixture. The Langmuir, Freundlich, and Sips models were adjusted to the experimental results for the systems that used one compound at a time. Sample characterization revealed the differences in composition, microstructure, surface area, and pore size between RHA and AC. Kinetic studies showed that RHA and AC have high and similar adsorption capacities at the equilibrium time of 120 min. Generally, the amount of each hydrocarbon removed from the mixture was lower than the removal achieved in the single-compound systems, for which removal rate followed the sequence (adsorbate mass/ adsorbent mass) ethylbenzene > xylene > toluene > benzene. The pseudo 2nd order kinetics model presented the best correlation for all assays. The experimental isotherms obtained for single-compound systems characterized the adsorption on porous surfaces, forming monolayers. No overall concordance was observed in the adjustment of the theoretical models, and in some situations the Langmiur and Freundlich models presented appropriate correlation coefficients. Considering the BTEX mixtures, the experimental isotherms constructed for RHA indicated the existence of competition for active sites of the adsorbent material between benzene and toluene and between ethylbenzene and xylene. The results obtained suggest that BTEX adsorption occurs preferentially through the hydrophobic effect, since AC is a carbonaceous material, while RHA is composed mainly of silica, with a carbonaceous fraction. Removal rates were between 78.8% and 100%, indicating that RHA is an interesting alternative in the removal of benzene, toluene, ethylbenzene, and xylene from aqueous solutions.

White cement has currently received increasing attention due to potential for use in sustainable concrete structures. Based on the U.S. Green Building Council certification practice, the LEED Green Building Rating System for New Construction and Major Renovation (LEED-NC) considers that the reflective quality of white surfaces may help to improve lighting efficiency and reduce temperature fluctuations, resulting in lower heating and cooling with reduction of related energy costs. In addition to the environmental impact, white concrete represents a valuable tool for the aesthetic acceptability of a structure, and can also offer important practical benefits in terms of safety (i.e., light reflection in the dark). In this thesis white concrete was combined with off-white rice husk ash and with a glass fibers reinforced polymer to obtain an innovative composite system able to: a) reduce the energy used for the production of the primary materials, b) decrease the temperature fluctuation in the building resulting in less energy needed for heating and cooling, and c) increase the life of the structure and thereby reduce energy usage for material disposal. It is evident that in applications where aesthetics is the driver, a great deal of attention needs to be devoted to the concrete mixture, but also to durability properties. To further improve the durability of white concrete, novel methodologies were introduced to study the corrosion mechanism of steel embedded in concrete and its effect on the color degradation of white surface. This study demonstrates the validity of the sustainable system made by white cement, OWRHA, and GFRP, and of the methodology introduce to evaluate corrosion and color degradation of reinforced concrete.

Η φέτα είναι είδος τυριού στην άλμη, τις ρίζες της οποίας τις βρίσκουμε χιλιάδες χρόνια πριν στην Αρχαία Ελλάδα. Παρασκευάζεται αποκλειστικά από γάλα προβάτου ή αιγοπρόβειο, δηλαδή μείγμα με έως 30% γάλα κατσίκας. Με βάση την παραδοσιακή μέθοδο παρασκευής της φέτας παρασκευάστηκε ένα νέο τυρί τύπου φέτας με την προσθήκη φλοιού σιταριού ο οποίος χρησιμοποιήθηκε για την ακινητοποίηση των κυττάρων του προβιοτικού μικροοργανισμού L.casei ATCC 393. O ακινητοποιημένος βιοκαταλύτης προστέθηκε ξεχωριστά κατά τη διάρκεια παρασκευής του τυριού τύπου φέτα στος 37 oC Στόχος του πειράματος ήταν η δημιουργία ενός νέου τυριού άλμης στο οποίο θα προσδίδονταν νέες προβιοτικές αλλά και πριβιοτικές ιδιότητες. Πέρα του τυριού με τον ακινητοποιημένο βιοκαταλύτη (L.casei και φλοιός σιταριού) για λόγους σύγκρισης παρασκευάστηκαν 3 ακόμη διαφορετικά τυριά άλμης, μια παραδοσιακή φέτα, ένα τυρί τύπου φέτας με ελέυθερο τον προβιοτικό μικροοργανισμό L.casei και ένα τυρί τύπου φέτας με προσθήκη φλοιού σιταριού. Στα παραγόμενα προϊόντα μελετήθηκε η επίδραση του ακινητοποιημένου βιοκαταλύτη στα φυσικοχημικά τους χαρακτηριστικά, καθώς και στο μικροβιολογικό και οργανοληπτικό τους προφίλ κατά τη διάρκεια αποθήκευσής τους για διάστημα 65 ημερών. Η βιοσιμότητα του L. casei εξετάστηκε επίσης. / Feta is a kind of cheese in brine, which was first found in ancient Greece thousands of years ago. It is made from sheep’s milk or mixture of sheep’s and goat’s milk which conclude up to 30% goat’s milk.According to the traditional method which is used in feta manufacture a new kind of feta cheese was produced. In this kind of feta cheese wheat bran was used for the immobilization of L. casei ATCC 393 cells. The immobilized biocatalysts were separately added as adjuncts during cheese type “Feta” production at 37oC.Τhe main purpose of conducting this experiment was producing a new type of cheese in brine in which new probiotic and pribiotic characteristics would be transfused. For comparison reasons cheeses with and without free L. casei cells were prepared as well as a traditional feta cheese. The effect of the immobilized biocatalysts as adjuncts at cheeses on physicochemical parameters, microbiological and organoleptic characteristics were studied for 60 storage days. The viability of L. casei during storage was also studied

In this study, the pore structures and surface areas of activated carbons produced from hazelnut shell and hazelnut husk by chemical activation technique using phosphoric acid (H3PO4), at relatively low temperatures (300, 400 and 500oC), were investigated. Raw materials were impregnated with different H3PO4 solutions of 30%, 40%, 50% and 60% by weight. To produce activated carbon, acid impregnated samples were heated / at a heating rate of 20 oC/min to the final carbonization temperature and held at that temperature for 2 hours. The volume and surface areas of mesopores (2-50 nm) and BET surface areas of the samples were determined by N2 gas adsorption technique at -195.6oC. The pore volume and the area of the micropores with diameters less than 2 nm were determined by CO2 adsorption measurements at 0oC by the application of Dubinin Radushkevich equation. N2 (BET) surface areas of the hazelnut shell and hazelnut husk based activated carbons were in the range of 242-596 m2/g and 705-1565 m2/g, respectively. CO2 (D-R) surface areas of the hazelnut shell and hazelnut husk based activated carbons were in the range of 433-576 m2/g and 376-724 m2/g, respectively. The highest BET surface area was obtained as 596 m2/g among hazelnut shell based samples (HS 60.4 / shell impregnated with 60 wt.% H3PO4, carbonized at 400 &ordm / C) and as 1565 m2/g among hazelnut husk based samples (HH 40.4 / husk impregnated with 40 wt.% H3PO4, carbonized at 400 &ordm / C). Hazelnut shell based activated carbons were mainly microporous while hazelnut husk based ones were mesoporous.

Η Τέφρα Φλοιού Ρυζιού (ΤΦΡ) είναι ένα από τα κυριότερα γεωργικά απόβλητα και προέρχεται από την καύση του φλοιού ρυζιού (ΦΡ) στις ορυζοβιομηχανίες για παραγωγή ενέργειας ή και μείωσης του όγκου των αποβλήτων. Η τέφρα φλοιού ρυζιού αποτελεί περίπου το 18-20% του φλοιού του ρυζιού, ο οποίος αποτελεί περίπου το 20% του ακατέργαστου ρυζιού ενώ συνήθως είναι κρυσταλλική. Καθώς ο παγκόσμιος όγκος της ετήσιας παραγωγής σε ρύζι και κατ’ επέκταση σε τέφρα φλοιού ρυζιού αυξάνεται διαρκώς, εγείροντας περιβαλλοντικά και οικονομικά ζητήματα, η ανεύρεση ενός αποδοτικού και οικολογικού τρόπου εκμετάλλευσης της είναι θέμα μείζονος σημασίας. Παράλληλα, τα υψηλά ποσοστά της ΤΦΡ σε διοξείδιο του πυριτίου την καθιστούν πιθανή πηγή πυριτίου για πολλές εφαρμογές, μία από τις οποίες είναι και οι σύνθεση ζεόλιθων. Στην παρούσα εργασία μελετήθηκε η αξιοποίηση κρυσταλλικής ΤΦΡ στην σύνθεση τεσσάρων τύπων ζεόλιθων και συγκεκριμένα των MFI, FAU, BEA και LTA. Για τον σκοπό αυτό αρχικά χαρακτηρίστηκε η πρώτη ύλη, δηλαδή η ΤΦΡ, τόσο ως προς την χημική της σύσταση και περιεκτικότητα σε άκαυτο άνθρακα όσο και ως προς την κρυσταλλική δομή της. Στη συνέχεια εξακριβώθηκαν οι συνθήκες καύσης του ΦΡ οι οποίες οδηγούν στην μετατροπή από την άμορφη στην κρυσταλλική δομή του διοξειδίου του πυριτίου, η οποία ονομάζεται χριστοβαλίτης. Εφόσον αυτή η κρυσταλλική δομή είναι ακατάλληλη για την παραγωγή ζεόλιθων, μελετήθηκε η δυνατότητα διαλυτοποίησης της ΤΦΡ σε υδατικό διάλυμα καυστικού νατρίου ώστε να καταστραφούν οι κρύσταλλοι και να παραληφθεί άμορφο διοξείδιο του πυριτίου. Για το σκοπό αυτό, επιλέχθηκαν οι μοριακές αναλογίες των πρώτων υλών που οδηγούν στη σύνθεση καθενός από τους τέσσερεις τύπους ζεόλιθων και η ΤΦΡ επεξεργάστηκε με την κατάλληλη αναλογία καυστικού νατρίου σε υδατικό διάλυμα σε διάφορες θερμοκρασίες και συνθήκες. Παρατηρήθηκε κρυστάλλωση του επιθυμητού τύπου ζεόλιθου σε κάθε μία από τις περιπτώσεις που εξετάστηκαν, ενώ το ποσοστό της διάλυσης του χριστοβαλίτη βρέθηκε ότι είχε την σημαντικότερη επίδραση στην απόδοση της διεργασίας και την καθαρότητα του προϊόντος. Ταυτόχρονα διαπιστώθηκε ότι το ποσοστό της διάλυσης του χριστοβαλίτη εξαρτάται κυρίως από την αναλογία μαζών RHA/NaOH και βρέθηκαν οι κατάλληλες τιμές. Καθώς το μεγαλύτερο ποσοστό διαλυμένου χριστοβαλίτη παρατηρήθηκε στην περίπτωση της σύνθεσης του ζεόλιθου LTA, η οποία επιπλέον δεν χρειάζεται οργανικό παράγοντα δομής ούτε υψηλές θερμοκρασίες, επιλέχθηκε να χρησιμοποιηθεί για την μελέτη και την βελτιστοποίηση της διεργασίας. Συγκεκριμένα, εξετάστηκαν διαφορετικές μέθοδοι επεξεργασίας της ΤΦΡ με καυστικό νάτριο, σε μεγάλο θερμοκρασιακό και χρονικό εύρος, ώστε να μελετηθεί η κινητική της διάλυσης του χριστοβαλίτη και να βρεθεί η ενέργεια ενεργοποίησης της. Στη συνέχεια μελετήθηκε η επίδραση της θερμοκρασίας και της διάρκειας στην κρυστάλλωση του ζεόλιθου LTA ώστε να μελετηθεί η κινητική της αντίδρασης και να βρεθεί η ενέργεια ενεργοποίησης της καθώς και οι βέλτιστες συνθήκες απόδοσης της διεργασίας και καθαρότητας του τελικού προϊόντος. Τέλος, εξετάστηκε η επίδραση δύο σημαντικών παραμέτρων, της θερμοκρασίας σύνθεσης και της ταχύτητας ανάδευσης στην ποιότητα του τελικού προϊόντος και βρέθηκαν οι βέλτιστες τιμές τους. Τα αποτελέσματα και τα συμπεράσματα από την παρούσα εργασία, έχουν κατατεθεί στον Οργανισμό Βιομηχανικής Ιδιοκτησίας (Ο.Β.Ι.), για την χορήγηση Διπλώματος Ευρεσιτεχνίας (Δ.Ε.), με αριθμό αίτησης: 20120100391. / Rice husk ash (RHA) is one of the major agricultural wastes and results from the combustion of rice husk (RH) at rice in milling facilities for energy production or waste volumes reduction. Rice husk ash is about 18-20% of the cortex of the rice, which is approximately 20% of raw rice and is usually in its crystalline form. As the global volume of annual production in rice and hence rice husk ash is increasing, raising environmental and economic issues, finding an efficient and ecological way of RHA exploitation is a major issue. In addition, the high rates of RHA on silica render possible silicon source for many applications, one of which is the synthesis of zeolites. In this study, the use of crystalline RHA in the synthesis of four zeolite types, namely MFI, FAU, BEA and LTA was investigated. For this purpose, the raw material, i.e. RHA, was characterized both in terms of its chemical composition and unburned carbon content as well as its crystalline structure. Afterwards, the combustion conditions of RH which lead to the conversion from the amorphous to the crystalline structure of silica, called cristobalite, were determined. Since this crystalline structure is unsuitable for the production of zeolites, the possibility of solubilizing RHA in aqueous sodium hydroxide solution was investigated, in order to destroy the crystals and receive amorphous silica. For this purpose, the molar ratios of the raw materials which would result in the synthesis of each of the four types of zeolites were selected and RHA was treated with the appropriate amount of sodium hydroxide in aqueous solution at various temperatures and conditions. The crystallization of the desired zeolite type in each of the cases examined was verified, while the rate of dissolution of cristobalite was found to have the most significant effect on the process efficiency and the product purity. Simultaneously, it was found that the rate of dissolution of cristobalite mainly depends on the mass ratio of RHA / NaOH and the most suitable values were determined. As the majority of dissolved cristobalite was observed in the case of LTA synthesis, which moreover does not require organic structure directing agent nor high temperatures, it was chosen to be used for the study of design and optimization process. Specifically, several methods of RHA treatment with sodium hydroxide at high temperature and time range were examined, in order to study the kinetics of dissolution of cristobalite and to find the activation energy. Then, the influence of temperature and duration on the crystallization of LTA was examined in order to study the kinetics of the reaction and to determine the activation energy as well as the optimum conditions of the process in terms of efficiency and final product purity. Finally, the effect of two important parameters, the temperature of the synthesis and the stirring speed, on the final product quality was investigated and the optimal values were found. The results and the conclusions of this study, have been submitted to the Hellenic Industrial Property Organization for the grant of Patent with application number: 20120100391.

Na primeira etapa deste trabalho foi avaliada a potencialidade do uso da cinza de casca de arroz como carga em polipropileno (PP) comparando-a com o talco que é a carga mineral mais utilizada em polímeros. Esta comparação foi feita utilizando os compósitos formados por polipropileno com 20% da cinza de casca de arroz assim como, os formados por polipropileno com 20% de talco, determinando as suas propriedades. Apesar das propriedades do compósito de PP com a carga de 20% de cinza de casca de arroz apresentarem resultados inferiores em relação àqueles quando se utilizou o talco como carga, pode-se dizer que a cinza de casca de arroz pode ser usada como carga para outros usos menos nobres do PP. Desta forma se está dando um destino para esse resíduo que hoje é descartado no meio ambiente contribuindo assim, para a preservação do mesmo, além de reduzir o custo do produto. Este trabalho também teve como objetivo estudar o efeito da radiação ionizante nas propriedades destes compósitos de PP com 20% de cinza de casca de arroz. Utilizou-se o agente de acoplagem, anidrido maleico, para verificar se houve melhora na homogeneização das amostras. Em virtude do PP ser um polímero semicristalino, quando exposto ao processo de irradiação, tem sua morfologia modificada devido aos mecanismos de cisão das cadeias poliméricas. Este fato é atribuído aos mecanismos de cisão das cadeias poliméricas, que está de acordo com a literatura. / In the first step of this work, it was evaluated the possibility of using rice husk ash as a filler in polypropylene (PP) making a comparison with talc which is the most used mineral filler in polymers. This comparison was made by using polypropylene with 20% rice husk ash as well as polypropylene with 20% talc measuring their properties. Despite the properties of the PP with 20% rice husk ash decreased compared with the composite of polypropylene with 20% talc it can be said that the rice husk ash can be used as filler for or other utilization less noble of PP . This way it is being given a destination for this residue that it is disposable in the environment contributing to its preservation, moreover reducing the product cost. This work had also as an aim to study the ionizing radiation effect in the properties of these composites. It was used the coupling agent, maleic anhydride , to verify a best sample homogenization. According to the results it can be said that PP is a semicrystalline polymer, and so it has its morphology modified when exposed to the irradiation process. This fact is due to the scission mechanisms of the polymeric chains which it is in compliance to the literature.

Apesar do avanço tecnológico crescente na construção civil, a falta de durabilidade das estruturas de concreto, tanto em edificações como pavimentação, tem sido constatada com acentuada assiduidade e proporção. O compósito cimentício de elevada deformação, também conhecido como Engineered Cementitious Composites (ECC), foi difundido a partir do conceito de concretos de alto desempenho reforçado com fibras, visando suprir o comportamento frágil do concreto convencional e problemas relacionados à falta de durabilidade gerada, principalmente, devido à propagação de fissuras. Neste contexto, o Laboratório de Ensaio de Modelos Estruturais (LEME) da Universidade Federal do Rio Grande do Sul (UFRGS) consolidou, nos últimos cinco anos, um grupo de pesquisa voltado ao estudo do ECC aliado a utilização de materiais nacionais. A concepção tem sido baseada na aplicação de materiais que proporcionem custos mais baixos e fomentem questões de sustentabilidade ambiental. Assim, foram incorporados ao material, fibra de polipropileno (2% em volume) e substituição parcial do cimento por 30% (em volume) de cinza de casca de arroz residual. O presente trabalho visa analisar questões de durabilidade destes compósitos (com e sem a incorporação de cinza), e compará-los a concretos convencionais, através de ensaios relacionados ao estudo da estrutura de poros (absortividade, absorção e índice de vazios, absorção e água por capilaridade, absorção de água pelo método do cachimbo e microscopia eletrônica de varredura), penetração e difusão de íons cloretos, retração livre e restringida, e, por fim, resistência à abrasão. Os resultados obtidos indicam que a incorporação de cinza de casca de arroz melhorou significativamente as propriedades do compósito relacionadas à conexão e solução dos poros, dificultando a passagem de cloretos, além de apresentar resistência à abrasão semelhante ao compósito de referência. Sua desvantagem está relacionada às maiores aberturas de fissuras ocasionadas devido à retração restringida. Entretanto, o trabalho evidencia a viabilidade e vantagem do uso de cinza de casca de arroz na produção do compósito, em termos de durabilidade. / Despite the increasing technological advances in construction, the lack of concrete structures durability, both in buildings and pavement, have been found with severe attendance and proportion. The high strain cementitious composite, also known as Engineered Cementitious Composites (ECC), was widespread from the concept of high performance fiber reinforced concrete, in order to supply the fragile behavior of conventional concrete and problems related to lack of durability generated mainly due to crack propagation. In this context, the Laboratório de Ensaios e Modelos Estruturais (LEME) of the Federal University of Rio Grande do Sul (UFRGS) consolidated over the last five years, a research group focused on the ECC study allied with the use of national materials. The design has been based on the application materials that provide lower costs and promote environmental sustainability issues. Thus, they were incorporated into the material polypropylene fibers (2% by volume) and partial cement replacement of 30% (by volume) of residual rice husk ash. This study aims to examine durability issues of these composites (with and without rice husk ash), and compare them to conventional concretes, through tests related to the study of pore structure (absorptivity, absorption and void ratio, water absorption by capillarity, water absorption by the pipe method and scanning electron microscopy), penetration and diffusion of chloride ions, free and restrained shrinkage, and, finally, abrasion resistance. The results indicate that the incorporation of rice husk ash significantly improved material properties related to connection and pores solution, hindering the chloride ingress, and presents abrasion resistance similar to the reference composite. Its disadvantage is related to the larger cracks due to restrained shrinkage. However, the work demonstrates the viability and advantage of use rice husk ash in the composite production in terms of durability.

A pesquisa relatada nesta dissertação teve por objetivo analisar a viabilidade técnica de estabilizar-se um solo sedimentar arenoso do Uruguai com cinza de casca de arroz (CCA) e cal. O solo utilizado apresenta baixo poder suporte, sendo pouco adequado para camadas de sub-base e base de pavimento rodoviário. Também não é adequado para ser estabilizado com cal e sua estabilização com cimento é muito custosa. Dois tipos básicos de CCA foram utilizados: uma cinza residual do processo de queima de casca de arroz em um forno sem controle de temperatura, e cinzas produzidas em laboratório por incineração de casca de arroz a diferentes temperaturas controladas. Foram realizados ensaios de difratogramas de raios-X, compactação, capacidade de suporte (ISC), compressão simples, tração por compressão diametral e durabilidade do solo, das CCA e das misturas solo-CCA-cal. Determinaram-se as influências do tempo de cura, dos teores de CCA e cal e dos tipos de CCA nos parâmetros de compactação, no ISC, no comportamento tensão-deformação e nas resistências à compressão simples e à tração por compressão diametral. Analisaram-se os efeitos da demora entre mistura e compactação no comportamento tensão-deformação e na resistência à compressão simples nas misturas com CCA residual e cal, além da sua durabilidade a ciclos de molhagem e secagem. As CCA produzidas a temperatura controlada entre 650°C e 800°C mostraram uma maior atividade pozolânica devido a sua estrutura amorfa. Os valores máximos de módulo de deformabilidade e resistência à compressão simples foram obtidos para as misturas com CCA a temperatura controlada. As misturas solo- CCA residual-cal desenvolveram resistência à tração demonstrando a ocorrência de reações pozolânicas. A estabilização do solo sedimentar arenoso com CCA e cal mostrou-se eficaz, permitindo o uso destes materiais em camadas de sub-base de pavimentos. / This MSc thesis was carried out with the purpose of analysing the technical feasibility of stabilizing a Uruguayan sandy soil with rice husk ash (RHA) and lime. The soil utilized present low bearing capacity and is not suitable for road pavement bases and sub-bases. It does not react to lime by itself and its stabilization with Portland cement is prohibitively expensive. Two kinds of RHA were used: a residual ash produced in the process of incinerating rice husk in an oven without temperature control, and ashes produced in laboratory by incineration of rice husk at different controlled temperatures. X-ray diffraction, compaction and bearing capacity (CBR), unconfined compression, split tensile and durability tests were carried out in the soil and in RHA samples and also in soil-RHA- lime mixtures. The influence of curing time, RHA and lime contents and RHA types in compaction parameters, CBR, strain-stress behaviour and unconfined compressive and split tensile strength were evaluated. The effects of the compaction delay on the stress-strain behaviour and the unconfined compression strength of the mixtures with residual RHA and lime were analysed. In order to investigate the mixtures durability, compacted specimens were submitted to wetting and drying cycles. Due to this amorphous structure, the RHA produced at controlled temperatures (650°C to 800°C) showed to be a more reactive concerning pozzolanic activity. The highest strain modulus and unconfined compression strength values were obtained for the mixtures with controlled temperature RHA. The soil-residual RHA-lime mixtures also developed tensile strength proving that pozzolanic took place. The stabilization of the sandy sedimentary soil with RHA and lime proved to be efficient, allowing the use of these materials in pavement sub-base layers.

Cinzas de casca de arroz são resíduos de comprovada eficiência como material pozolânico. No entanto, a variabilidades do material, decorrente das diferentes condições de geração impedem que o mesmo seja comercializado. Assim o presente trabalho tem como objetivo verificar a influência da variação do índice de amorfismo (IA) de cinzas de casca de arroz, sobre a atividade pozolânica deste material. As cinzas foram utilizadas em substituição parcial ao cimento. A metodologia de pesquisa foi dividida nas seguintes fases: (1) Coleta das cascas de arroz; (2) produção das cinzas de casca de arroz através da queima em diferentes temperaturas (500, 650, 800, 950 e 1100ºC) realizada em forno de laboratório. Fixou-se o tempo de residência do material (3 horas), a taxa de aquecimento (5°C/min), e resfriamento lento. Posteriormente utilizou-se a moagem das cinzas em diferentes tempos para que os diâmetros atendessem a finura apropriada para uma pozolana. (3) Em seguida o material gerado foi caracterizado através de ensaios químicos, físicos e mineralógicos; os demais materiais, tais como cimento e areia, também foram caracterizados, de forma que atendam as especificações normativas. (4) Com base nas análises dos resultados, foram moldados 6 corpos-de-provas de argamassas para realização do ensaio de índice de atividade pozolânica com o cimento. (5) A etapa final foi a quantificação do índice de amorfismo por meio de refinamento de Rietveld. Os resultados demonstraram que o índice de amorfismo pode ser utilizado como parâmetro de controle de cinzas residuais. O índice de amorfismo está diretamente relacionado à temperatura de queima e ao tempo de moagem e a atividade pozolânica, sofre influência dessa variável bem como de outras tais como diâmetro médio dos grãos e relação água/aglomerante / The rice husk ash is a waste of proved performance as pozzolanic material. However, the variability of the material, as a result of different generation conditions, restricts its use. Thus, this study aims to determine the influence of variation of the amorphous index (AI) of rice husk ash on the pozzolanic activity of this material. The ash was used as partial replacement of cement. The methodology of research was divided into the following steps: (1) Collection of rice hulls, (2) production of rice husk ash at different temperatures (500, 650, 800, 950 and 1100 °C) made in a small lab furnace. The time into the furnace was fixed (3 hours), as well as the rate of heating (5 ° C / min) and the slow cooling adopted. Thus, the ashes had been grinded at different times until appropriate diameters. (3) Then, chemical, physical and mineralogical characterization had been carried through, as well as other materials such as cement and fine aggregate according standard specifications. (4) According previous analysis of results, 6 mortar samples were molded to perform testing of pozzolanic activity index with Portland cement. (5) The final step was to quantify the amorphous content by the Rietveld refinement. The results showed that the index of amorphous can be used as a control parameter for rice husk ashes. The amorphous index is directly related with the burning temperature and the grinding time, The pozzolanic activity was also influenced by these variables as well as medium diameter of grains and its water/binding ratio.

A contaminação do solo com resíduos tóxicos tornou-se um dos maiores problemas ambientais. Na maioria das vezes, as condições do local incluem a contaminação da água subterrânea. Neste contexto, os metais pesados têm sido motivo de preocupação, destacando-se o cromo hexavalente como poluente de elevada toxicidade e mobilidade. Quando um problema de contaminação no solo é identificado, ações de remediação devem ser aplicadas. Dentre as tecnologias existentes, uma das mais promissoras é o uso de barreiras reativas permeáveis. A barreira é construída com materiais reativos de forma a interceptar a pluma contaminada, atenuando a concentração do contaminante a níveis aceitáveis ou controláveis. É possível converter resíduos agrícolas em carvões ativados, material adsorvente resultante de processo pirolítico. Esses carvões podem apresentar desempenhos diferenciados em aplicações específicas. A presente tese tem como objetivo geral avaliar a aplicação de carvões ativados, oriundos da pirólise de casca de arroz, em barreiras reativas permeáveis. Os objetivos específicos consistem em estudar o desenvolvimento de carvões quimicamente ativados e investigar, por meio de ensaios de laboratório, sua aplicação na remoção de cromo hexavalente de meios aquosos e de meios porosos saturados. Para a preparação dos carvões ativados, foi desenvolvida uma unidade pirolítica rápida a vácuo com características escaláveis e com ênfase no controle e registro das variáveis do processo. Foram preparados carvões por ativação química com K2CO3 e KOH e determinadas suas características físico-químicas, texturais e análise morfológica por microscopia eletrônica de varredura. Ensaios de batelada e um ensaio de coluna com soluções de cromo foram realizados para avaliação da atenuação do contaminante. Os carvões ativados apresentaram baixa densidade aparente, similares valores de pH e de condutividade elétrica e elevado conteúdo de cinzas quando comparados com carvões de outras biomassas. A ativação química com reagentes alcalinos, associada às condições pirolíticas, resultou em superfícies menos ácidas, característica favorável para adsorção de Cr(VI). Resultaram em adsorventes mesoporosos, característica necessária para a adsorção de íons de elevado peso molecular; exibiram baixas áreas superficiais e similaridade morfológica entre si com a predominância da estrutura de sílica. Embora os carvões tenham apresentado baixas áreas superficiais, a adsorção teve a predominância da influência do diâmetro médio dos poros, seguido da área de mesoporos e da carga superficial negativa, indicando o potencial de aplicação dos carvões na remoção de Cr(VI). O ensaio de coluna possibilitou demonstrar o emprego do carvão ativado de casca de arroz em barreiras reativas, indicando suas limitações em pHs próximo à neutralidade e candidatando-o a situações de tratamento em série ou seqüenciais. Os trabalhos realizados estabeleceram base segura para o desenvolvimento de equipamento adequado para a pirólise e domínio do processo de manufatura do carvão ativado. A análise conjunta dos resultados sugere que as condições do processo pirolítico a vácuo adotado, juntamente com a ativação química com baixas concentrações de reagente ativantes, configuram uma rota atrativa para a elaboração de material poroso a partir de casca de arroz, com potencial aplicação na remoção de Cr(VI) em barreiras reativas permeáveis. / Soil contamination with toxic waste has become one of the biggest environmental problems. Site conditions often include groundwater contamination. In this context, heavy metals have been a matter of concern with chromium hexavalent recognized as pollutant of high toxicity and mobility. When a problem of soil contamination is identified, remediation tasks must be applied. Amongst the new technologies, the use of permeable reactive barriers is one of the most promising. This barrier is constructed with reactive materials in order to intercept the contaminated plume, attenuating the contaminant concentration to acceptable or controllable levels. It is possible to convert agricultural waste into activated carbon, an adsorbent material resulting from the pyrolytic process. This carbon can perform differently face to environmental applications. The present thesis has as a major objective to evaluate the application of activated carbons, derived from rice husk pyrolysis, in permeable reactive barriers, with emphasis on the remediation of contaminated soil with heavy metals. The specific objectives consist of studying the development of activated carbon from chemical activation and also investigating, through laboratory tests, its application in chromium removal from watery and saturated porous media. With the purpose of preparing activated carbons, a fast pyrolytic unit of rice husk was developed, with characteristics that can be scaled up and with emphasis on the control and register of process variables. Chemical activated carbons using K2CO3 and KOH have been prepared in different activation conditions and determined their physico-chemical and textural parameters. The morphological analysis was performed by scanning electron microscopy. Batch tests and a column test with solutions of chromium were performed to evaluate the attenuation of the contaminant. The activated carbons showed a low apparent density, similar values of pH and electrical conductivity and high ash content compared to carbons from other biomass. The chemical activation with alkaline reagents, associated with pyrolytic conditions, resulted in less acidic surface, characteristic favorable for Cr(VI) adsorption. The adsorbent manufactured results in mesoporous carbons, a characteristic necessary for the adsorption of ions of high molecular weight, exhibited low surface areas and morphological similarities between them, with the predominance of the structure of silica. Despite the carbons have shown low surfaces areas, the adsorption showed the predominant influence of the average pore diameter, followed by the mesopores area and surface negative charge, indicating the potential application of these carbons in Cr(VI) removal. The column test has demonstrated the use of activated carbon from rice husk in reactive barriers, showing its limitations in pHs close to neutrality and pointing it to cases of serial or sequential processing. The work carried out established safe basis for the development of suitable equipment for the pyrolysis and for the domain of the manufacturing process of activated carbon. The analysis of the results suggests that the conditions of the adopted vacuum pyrolytic process, jointly with the chemical activation with low concentrations of activate reagent, constitute an attractive route for the preparation of porous material from rice husk, with potential application in removing Cr (VI) in permeable reactive barriers.