Le travail s’inscrit dans un cadre interdisciplinaire, à l’interface de la chimie sol-gel, la biologie et la physique des matériaux. Nous nous sommes intéressés en premier lieu à l’étude d’une matrice de silice obtenue par le procédé sol-gel à partir d’un mélange de silice colloïdale et de silicates de sodium. Le but était de comprendre les interactions entre les précurseurs et d’étudier l'effet des différents paramètres de synthèse sur la structure de la matrice afin de trouver les meilleures propriétés optiques et mécaniques. Ces matrices ont été largement caractérisées au moyen de différentes techniques (absorption UV-Visible, infrarouge, ATG, BET, RMN, MET et MEB). Cette étude nous permet pour la première fois de partir des propriétés finales désirées et de préciser la combinaison nécessaire pour les obtenir en termes de concentrations des précurseurs et de pH. Ensuite, nous avons pu étudier l’effet des propriétés de la matrice sur la survie des cellules photosynthétiques encapsulées et on a pu obtenir des matériaux phyco-compatibles avec une large gamme de propriétés optiques et mécaniques. Après avoir fixé les conditions de synthèse convenables pour la survie des micro-organismes, on a pu passer à l’étude de la fonctionnalité des matériaux en présence des contaminants toxiques (qui sont les métaux lourds Cd (II) et Pb (II) et un hydrocarbure aromatique polycyclique l’anthracène) et on a réussi à obtenir un biocapteur fonctionnel. De façon intéressante, une certaine spécificité de la détection a pu être obtenue en fonction du couple microalgue/matrice choisi / The work is an interdisciplinary framework, at the interface of the sol-gel chemistry, biology and physics of materials. First, we are interested to the study of a silica matrix obtained by sol-gel process from a mixture of colloidal silica and sodium silicate. The goal was to understand the interactions between the precursors and to study the effect of different synthesis parameters on the structure of the matrix in order to find the best optical and mechanical properties. These matrices have been extensively characterized using various techniques (UV-Visible absorption, IR, TGA, BET, NMR, TEM and SEM). This study allows us for the first time to choose final properties and to specify the initial combination to get them in terms of concentrations of precursors and pH. Next, we studied the effect of the matrix properties on the survival of photosynthetic encapsulated cells and we got phyco-compatible materials with a wide range of optical and mechanical properties. After precising the best synthesis conditions for the survival of microorganisms, one could proceed to study the functionality in the presence of toxic contaminants (heavy metals Cd (II) and Pb (II) and a polycyclic aromatic hydrocarbon: anthracene) and we managed to get a functional biosensor. Interestingly, some specificity of detection could be obtained according to the combination of microalga / selected matrix

Lead and lead-tin solder were widely used in premise plumbing in North America until the 1980’s. Although this soldering practice has reduced significantly, lead release from older premise plumbing remains a concern. Utilities often use corrosion inhibitors to protect the piping in the distribution system and reduce lead release in premise plumbing. This study compares sodium silicates and phosphates as corrosion inhibitors for lead release in low alkalinity water. The study was carried out at the J.D. Kline Water Treatment Plant in Halifax, Nova Scotia, Canada. The experimental design compared sodium silicates (concentration of 18mg/L) and zinc orthophosphate (concentration of 0.8mg/L) as corrosion inhibitors at a pH of 7.3 for three disinfectant treatment groups (high chloramines (3mg/L), low chloramines (1mg/L), and chlorine (1mg/L)).

Mondi Ltd. operates a deinking plant at its Merebank mill. The plant recycles 85 000 tons per annum of flat news and magazine to produce a furnish for its newsprint papermachines. A review of the relevant pulping and flotation chemistry literature revealed that the role played by sodium silicate appears to be multi-faceted and in some dispute. Sodium silicate has an undisputed role in pH buffering, hydrogen peroxide stabilisation and the prevention of fibre yellowing. However, its role in deinking is said to be that of an ink collector or alternatively an ink dispersant. The mill's own experience has shown that the sodium silicate plays a vital role in the deinking process. Sodium silicate's ability to disperse ink, both alone and in the presence of calcium ions and fatty acid soaps, was investigated using a model ink system. A representative newsprint ink base was dispersed in the laboratory under conditions similar to those encountered in a deinking pulper. The resultant dispersions were studied using turbidity and particle size analysis. The morphology of the ink particles was determined using a scanning electron microscope. Sodium silicate proved to be a poor disperser of ink particles, but nevertheless appeared to greatly influence the dispersing properties of the soap in the presence of calcium ions. The nature of the interactions between sodium silicate, calcium ions and the collector soap were studied in an attempt to elucidate the role of sodium silicate. A model system consisting of the sodium salt of collector soap, calcium ions and sodium silicate was studied under the conditions that prevail in a typical newsprint deinking pulper. It was found that the soap and the sodium silicate compete for the calcium ions, and sodium silicate showed a measurable chelating e:ffect on calcium ions. Thus, increasing levels of sodium silicate lead to an increase in the concentration of sodium soap in solution. It was hypothesised that this effect would lead to better dispersion of ink particles and improved deinking performance. This chelating effect was evaluated in laboratory deinking studies. Samples of newsprint were pulped in a 251 Lamort laboratory pulper under a variety of conditions, viz. with fresh water, with an excess of soap, with an excess of calcium, with and without sodium silicate. The pulps were floated in a 201 flotation cell. The brightness and colour of the unfloated and floated pulps were measured. The level of the final brightness after flotation was taken as a measure of deinking efficiency. The highest final brightness was achieved when there was an excess of sodium soap and a low Ca hardness in the pulper. Softening the water used in pulping without adding excess sodium soap did not significantly improve pulp brightness. The lowest final brightness occurred in the presence of an excess of calcium in the pulper. Calcium in the pulper in the presence of sodium silicate did not result in a significantly lower final brightness. The results support the hypothesis that sodium silicate sequesters the soluble calcium in a pulping system, thereby increasing the sodium soap concentration and the resultant deinking performance. Apart from sodium silicate's chief role as a peroxide stabiliser, the sequestering action on calcium appears to be its main mechanism of action in a deinking system. An appreciation of this role will facilitate the optimisation of deinking systems with respect to calcium hardness and silicate concentration. To this end it was recommended that the Merebank deinking plant should evaluate the use of water with a low calcium ion concentration and the addition of some soap into the pulper to improve their deinking plant performance. / Thesis (M.Sc.)-University of Natal, Durban, 2003.

Mining is an important industry that plays a significant role in the development of human civilization and economies. However, the underground mining process produces a large volume of mine wastes (e.g., tailings) as well as creates large voids that require filling, typically with an engineering backfill material. Filling the voids with mine waste materials provides an environmental-friendly way of disposing mining waste. It is also an effective way of increasing ore recovery and improving the safety of miners. One of the best techniques of mine backfill is called cemented paste backfill (CPB), which is typically a mixture of tailings, binder and water. The most common binder used in the preparation of CPB is Portland cement (PC). PC is not only a costly binder, but its production is highly energy-intensive and also generates a large amount of CO2. The cement consumption can represent up to 75% of the cost of CPB. These above-mentioned factors have compelled mining companies to seek for cement alternatives that enhance the engineering properties of the CPB, decrease the cement content and reduce the carbon footprint of the mining industry. Sodium silicate is the most recent chemical additive that is proposed to reduce the binder content in CPB. Sodium silicate is an alkaline solution that is used to activate a pozzolanic material, such as cement, slag and Fly ash. However, the effect of sodium silicate on the strength and key environmental properties (permeability or saturated hydraulic conductivity, reactivity) of CPB is not well understood. The objective of this thesis is to investigate the possibility of using sodium silicate as an activator in cemented paste backfill and obtain an improvement in the aforementioned engineering properties of CPB. In order to determine the effect of the sodium silicate on backfill properties, some CPB testing methods were developed to fulfill the objectives of this research. Thus, the evolution of hydraulic, mechanical and microstructural properties of CPB samples containing sodium silicate (SS-CPB) have been tested or monitored at different curing ages (1, 3, 7, 28 and 90 days) and different CPB mixtures as well. The results of these studies show that activating CPB with sodium silicate develop CPB strength faster than CPB samples without sodium silicate. In addition, hydraulic conductivity and reactivity results show a positive change in samples containing sodium silicate compared to free sodium silicate CPB samples. Indeed, this activation leads to decreasing permeability and reactivity due to the formation of cement hydration products and acceleration of the binder hydration process. Moreover, binder type and content in the presence of sodium silicate as an alkali activator in the CPB play a significant role in lowering hydraulic conductivity and reactivity of CPB.

abstract: This study evaluates the use of plant-extracted silica solution as a bio-based grout material for improvement of granular soils. Although silicate grout is a very well-established and popular technique in the ground improvement market, efforts have been initiated to replace chemically-synthesized silicate grout with plant-extracted silica grout. This initiative will increase the level of sustainability and consequently improve the existing market acceptability. The silica-rich plant source used for extraction was rice husk, which is an abundantly produced agricultural waste. The extraction method includes acid-leaching, temperature-controlled rice husk ash production and the preparation of an aqueous sodium silicate solution from the ash through an alkaline leachate method. Silica ash was in amorphous form containing 95% of silica content which is suitable for soil treatment. Gelation time was controlled in the absence and presence of sand under different pH values. Bio-based silica grouting showed an improvement of the shear strength of the soil as well as the hydraulic conductivity reduction. / Dissertation/Thesis / Masters Thesis Civil, Environmental and Sustainable Engineering 2019

No description available.

A tentativa de modificar algumas propriedades dos solos é antiga. Alguns autores fazem considerações a tentativas ocorridas a três mil anos atrás. Com o crescimento populacional e o desenvolvimento de novos sistemas de produção ocorridos após a Revolução Industrial no século XVIII, houve uma intensa ocupação territorial exigindo obras de infra-estrutura e obras complementares, tornando cada vez mais comum o melhoramento de solos. Uma técnica in situ passível de aplicação para melhorar as propriedades mecânicas dos solos é a técnica de eletrocinética associada à injeção de soluções químicas. Esta é caracterizada pela aplicação de um baixo gradiente elétrico através de eletrodos num meio poroso inundado com soluções químicas. Nesta pesquisa, foram realizados ensaios associando as soluções de cloreto de cálcio com água carbonatada, cloreto de cálcio com bicarbonato de sódio além de cloreto de cálcio com silicato de sódio. Para verificação da ocorrência da cimentação entre as partículas de areia, após a saturação do corpo de prova com as devidas soluções, mas anterior à aplicação da diferença de potencial elétrico ao solo, foram realizados três ensaios de prospecção com um Miniature Cone, desenvolvido nesta pesquisa. Esses foram comparados a outros três ensaios que foram realizados após o período de aplicação da técnica. Todas as associações resultaram em regiões cimentadas não homogêneas, sendo que os melhores resultados foram obtidos com a associação das soluções de cloreto de cálcio e silicato de sódio. A aplicação da técnica de eletrocinética associada a injeções de soluções químicas mostrou se complexa e difícil de predizer devido ao número de variáveis que podem modificar o seu resultado final. / The attempt to change some soil properties of the soil is not new. Some authors describes attempts occurred three thousand years ago. With population growth and the new production systems development that occurred after the Industrial Revolution in the eighteenth century, there was an intense territorial occupation requiring infrastructure works and complementary works, becoming the soils improvement usual. One of the in situ soil improvement techniques is the eletrokinetics associated with injection of chemical solutions. This technique is characterized by the application of a low electrical gradient through electrodes in a porous media flooded with chemical solutions. In this study, tests were carried out associating the solutions of calcium chloride with soda water, calcium chloride with sodium bicarbonate, and calcium chloride with sodium silicate. To verify the occurrence of the cementation among the sand particles, after the samples flooded with the appropriate solutions, but prior to the application of electric potential difference in the soil, three exploration tests were performed with a Miniature Cone, developed in this study. These tests were compared to other three tests that were carried out after the application of the technique. All associations resulted in not homogeneous cemented regions, and the best results were obtained with the combination of the solutions of calcium chloride and sodium silicate. The application of the eletrokinetics technique associated with injections of chemical solutions is proved to be complex and difficult to be predicted due to the number of variables that can change its final result.

Geopolímeros são uma nova classe de ligantes cimentícios obtidos a partir da reação química entre um aluminossilicato amorfo (precursor) e um ativador alcalino. Esses materiais tem se tornado uma alternativa interessante no desenvolvimento de novos cimentos devido sua reduzida emissão de CO2, bem como pelo potencial de valorização de resíduos. Além disso, apresentam algumas vantagens técnicas como elevada resistência mecânica inicial, baixa permeabilidade e estabilidade química em certas condições de uso. Como precursores utiliza-se normalmente aluminossilicatos provenientes de resíduos como cinza volante, escória de alto forno ou argilas calcinadas como o metacaulim. Como ativadores, os mais tradicionais são os hidróxidos e silicatos solúveis. A pesquisa de novas fontes de silicato provenientes de resíduos industriais gerados em grande volume pode facilitar a adoção desses materiais na indústria da construção. Com isso, esse trabalho avaliou a produção de diferentes ligantes geopoliméricos a partir da utilização como precursores de lodo de caulim calcinado (LCC), e cinza pesada (CP). Da mesma forma foi desenvolvido um ativador alcalino alternativo baseado na dissolução da sílica amorfa presente na cinza de casca de arroz (CCA). Os precursores foram ativados individualmente, bem como em combinações binárias, utilizando silicato de sódio comercial, silicato de sódio alternativo e hidróxido de sódio como ativadores. Os geopolímeros foram sintetizadas a partir de relações molares e critérios de síntese utilizados pela literatura. Os produtos de reação foram avaliados perante algumas técnicas de caracterização como calorimetria isotérmica, difração de raios-X, espectroscopia de infravermelho com transformada de Fourier e análise termogravimétrica entre 1 e 90 dias de cura. Complementarmente a resistência à compressão foi avaliada até 90 dias de cura. Os resultados das análises micro e macroestruturais mostram que é viável utilizar ambos resíduos avaliados como precursores para geopolímeros, sendo possível obter resistências à compressão potencial de até 80 MPa. O conteúdo de silicato solúvel apresenta uma função importante perante a cinética de reações, possibilitanto um material mecanicamente mais resistente. O uso do ativador alcalino alternativo é uma alternativa viável para a produção de um material ambientalmente mais amigável, proporcionando características mecânicas e microestruturais similares aos geopolímeros produzidos com ativadores tradicionais. / Geopolymers are a new class of binder obtained through a chemical reaction between an amorphous aluminosilicate (precursor) and an alkaline activator. This material is a good alternative to the development of more environmental friendly binders, as well as the opportunity to valorize industrial wastes. These materials also show some technical advantages, including high compressive strength at early times of curing, low permeability and higher chemical stability under certain condition of exposure. As precursors, aluminosilicates from industrial wastes such as fly ash (FA), granulated blast furnace slag (GBFS) and/or calcined clays such as metakaolin (MK) are typically used. As activators, the most commonly used are hydroxides and soluble silicates. Therefore, the search of novel aluminosilicates sources from industrial wastes locally available in large volumes could facilitate the adoption of geopolymers by the construction industry. This study assessed the production of different geopolymer binders using as precursors calcined kaolin sludge (CKS) from the Brazilian mining industry and a bottom ash (BA) generated during coal combustion. An alternative alkali activator produced by the dissolution of rice husk ash (RHA) was also evaluated, in order to optimize the environmental benefits of these materials. The precursors were activated individually and also blended using sodium hydroxide, commercial sodium silicate and alternative sodium silicate as activators. The geopolymers were produced based on literature review. The reaction products formed upon alkali activation were evaluated using different characterization techniques, including isothermal calorimetry, X-ray diffractometry, Fourier transform infrared spectroscopy, thermogravimetric analysis coupled with mass spectrometry. Complementary, the compressive strength of the geopolymer pastes produced was evaluated up to 90 days of curing. The micro and macro structural characterization results show that these waste are suitable precursors to produce geopolymer binders, with compressive strengths as high as 80 MPa after 7 days of curing. The content of soluble silicates plays an important role in the kinetic of geopolymerization, favoring a high compressive strength development. The use of an alternative alkali activator based it is a feasible alternative to produce more environmental friendly geopolymers with similar mechanical performance to that of geopolymers produced with traditional soluble silicates based on commercial sodium silicate solutions.

A tentativa de modificar algumas propriedades dos solos é antiga. Alguns autores fazem considerações a tentativas ocorridas a três mil anos atrás. Com o crescimento populacional e o desenvolvimento de novos sistemas de produção ocorridos após a Revolução Industrial no século XVIII, houve uma intensa ocupação territorial exigindo obras de infra-estrutura e obras complementares, tornando cada vez mais comum o melhoramento de solos. Uma técnica in situ passível de aplicação para melhorar as propriedades mecânicas dos solos é a técnica de eletrocinética associada à injeção de soluções químicas. Esta é caracterizada pela aplicação de um baixo gradiente elétrico através de eletrodos num meio poroso inundado com soluções químicas. Nesta pesquisa, foram realizados ensaios associando as soluções de cloreto de cálcio com água carbonatada, cloreto de cálcio com bicarbonato de sódio além de cloreto de cálcio com silicato de sódio. Para verificação da ocorrência da cimentação entre as partículas de areia, após a saturação do corpo de prova com as devidas soluções, mas anterior à aplicação da diferença de potencial elétrico ao solo, foram realizados três ensaios de prospecção com um Miniature Cone, desenvolvido nesta pesquisa. Esses foram comparados a outros três ensaios que foram realizados após o período de aplicação da técnica. Todas as associações resultaram em regiões cimentadas não homogêneas, sendo que os melhores resultados foram obtidos com a associação das soluções de cloreto de cálcio e silicato de sódio. A aplicação da técnica de eletrocinética associada a injeções de soluções químicas mostrou se complexa e difícil de predizer devido ao número de variáveis que podem modificar o seu resultado final. / The attempt to change some soil properties of the soil is not new. Some authors describes attempts occurred three thousand years ago. With population growth and the new production systems development that occurred after the Industrial Revolution in the eighteenth century, there was an intense territorial occupation requiring infrastructure works and complementary works, becoming the soils improvement usual. One of the in situ soil improvement techniques is the eletrokinetics associated with injection of chemical solutions. This technique is characterized by the application of a low electrical gradient through electrodes in a porous media flooded with chemical solutions. In this study, tests were carried out associating the solutions of calcium chloride with soda water, calcium chloride with sodium bicarbonate, and calcium chloride with sodium silicate. To verify the occurrence of the cementation among the sand particles, after the samples flooded with the appropriate solutions, but prior to the application of electric potential difference in the soil, three exploration tests were performed with a Miniature Cone, developed in this study. These tests were compared to other three tests that were carried out after the application of the technique. All associations resulted in not homogeneous cemented regions, and the best results were obtained with the combination of the solutions of calcium chloride and sodium silicate. The application of the eletrokinetics technique associated with injections of chemical solutions is proved to be complex and difficult to be predicted due to the number of variables that can change its final result.

Geopolímeros são uma nova classe de ligantes cimentícios obtidos a partir da reação química entre um aluminossilicato amorfo (precursor) e um ativador alcalino. Esses materiais tem se tornado uma alternativa interessante no desenvolvimento de novos cimentos devido sua reduzida emissão de CO2, bem como pelo potencial de valorização de resíduos. Além disso, apresentam algumas vantagens técnicas como elevada resistência mecânica inicial, baixa permeabilidade e estabilidade química em certas condições de uso. Como precursores utiliza-se normalmente aluminossilicatos provenientes de resíduos como cinza volante, escória de alto forno ou argilas calcinadas como o metacaulim. Como ativadores, os mais tradicionais são os hidróxidos e silicatos solúveis. A pesquisa de novas fontes de silicato provenientes de resíduos industriais gerados em grande volume pode facilitar a adoção desses materiais na indústria da construção. Com isso, esse trabalho avaliou a produção de diferentes ligantes geopoliméricos a partir da utilização como precursores de lodo de caulim calcinado (LCC), e cinza pesada (CP). Da mesma forma foi desenvolvido um ativador alcalino alternativo baseado na dissolução da sílica amorfa presente na cinza de casca de arroz (CCA). Os precursores foram ativados individualmente, bem como em combinações binárias, utilizando silicato de sódio comercial, silicato de sódio alternativo e hidróxido de sódio como ativadores. Os geopolímeros foram sintetizadas a partir de relações molares e critérios de síntese utilizados pela literatura. Os produtos de reação foram avaliados perante algumas técnicas de caracterização como calorimetria isotérmica, difração de raios-X, espectroscopia de infravermelho com transformada de Fourier e análise termogravimétrica entre 1 e 90 dias de cura. Complementarmente a resistência à compressão foi avaliada até 90 dias de cura. Os resultados das análises micro e macroestruturais mostram que é viável utilizar ambos resíduos avaliados como precursores para geopolímeros, sendo possível obter resistências à compressão potencial de até 80 MPa. O conteúdo de silicato solúvel apresenta uma função importante perante a cinética de reações, possibilitanto um material mecanicamente mais resistente. O uso do ativador alcalino alternativo é uma alternativa viável para a produção de um material ambientalmente mais amigável, proporcionando características mecânicas e microestruturais similares aos geopolímeros produzidos com ativadores tradicionais. / Geopolymers are a new class of binder obtained through a chemical reaction between an amorphous aluminosilicate (precursor) and an alkaline activator. This material is a good alternative to the development of more environmental friendly binders, as well as the opportunity to valorize industrial wastes. These materials also show some technical advantages, including high compressive strength at early times of curing, low permeability and higher chemical stability under certain condition of exposure. As precursors, aluminosilicates from industrial wastes such as fly ash (FA), granulated blast furnace slag (GBFS) and/or calcined clays such as metakaolin (MK) are typically used. As activators, the most commonly used are hydroxides and soluble silicates. Therefore, the search of novel aluminosilicates sources from industrial wastes locally available in large volumes could facilitate the adoption of geopolymers by the construction industry. This study assessed the production of different geopolymer binders using as precursors calcined kaolin sludge (CKS) from the Brazilian mining industry and a bottom ash (BA) generated during coal combustion. An alternative alkali activator produced by the dissolution of rice husk ash (RHA) was also evaluated, in order to optimize the environmental benefits of these materials. The precursors were activated individually and also blended using sodium hydroxide, commercial sodium silicate and alternative sodium silicate as activators. The geopolymers were produced based on literature review. The reaction products formed upon alkali activation were evaluated using different characterization techniques, including isothermal calorimetry, X-ray diffractometry, Fourier transform infrared spectroscopy, thermogravimetric analysis coupled with mass spectrometry. Complementary, the compressive strength of the geopolymer pastes produced was evaluated up to 90 days of curing. The micro and macro structural characterization results show that these waste are suitable precursors to produce geopolymer binders, with compressive strengths as high as 80 MPa after 7 days of curing. The content of soluble silicates plays an important role in the kinetic of geopolymerization, favoring a high compressive strength development. The use of an alternative alkali activator based it is a feasible alternative to produce more environmental friendly geopolymers with similar mechanical performance to that of geopolymers produced with traditional soluble silicates based on commercial sodium silicate solutions.