Rare earth mineral recovery from alternative resources such as coal and coal byproducts is increasingly important to provide an opportunity for economic recovery from U.S. sources. Currently, China produces the majority of the 149,000 tons of rare earth elements used annually worldwide of which the U.S. imports 11% or around 16,000 tons. There are no significant mining operations producing rare earth elements in the U.S. However, there are many U.S. sources containing rare earth minerals such as monazite including heavy mineral sand and phosphate operations. Monazite mineral particles of a few microns have also been detected in Fire Clay seam coal. Preliminary attempts to concentrate the rare earth mineral using flotation test results indicated that monazite was floated together with carbonate minerals. The flotation chemistry of a monazite-carbonate mineral system has received limited attention by researchers. As such, a systematic study of monazite flotation chemistry was conducted and the results reported in this dissertation. The surface charging mechanisms of monazite in aqueous systems were studied using electrokinetic tests, solution equilibrium calculation, crystal structure analysis, and electrostatic model prediction. The surface charge of monazite was found to be developed by protonation/deprotonation reactions. In other words, the hydrogen and hydroxyl ions were potential determining ions instead of the lattice ions of monazite. Electrokinetic tests of natural monazite mineral showed that the isoelectric point (IEP) occurred at pH 6.0. Solution equilibrium calculation and electrostatic model predictions of cerium monazite (CePO4) yielded an IEP of pH 7.2. The discrepancy between the two IEP values may be due to the different REE composition and/or the amount of carbon dioxide dissolved in solution. A common collector used to produce a hydrophobic monazite surface is octanohydroxamic acid. Adsorption studies found multilayer formation of octanohydroxamic acid on monazite surfaces at pH values of 3.0, 6.0, and 9.0. A kinetic study showed that the maximum adsorption density and rate for below monolayer coverage occurred at a solution pH value of 9.0, which was attributed to the chemical reaction between octanohydroxamate species and surface active sites (e.g., REE(OH)2+). For beyond multilayer adsorption, maximum adsorption occurred at pH 11.0 due to the abundance of hydroxyl ions in solution. The contributing effect of hydroxyl ions was proven by titration tests and FTIR analyses. When calcium ions existed in solution, specific adsorption of Ca(OH)+ on monazite surfaces occurred in both neutral and basic environments as indicated by the electrokinetic results. At low concentrations, Ca(OH)+ competed with octanohydroxamic acid for P-OH sites. However, higher dosages of Ca(OH)+ served as active sites for octanohydroxamic acid. The monazite floatability was negatively affected by the hydration of the adsorbed calcium species. The calcium ion dissolved from calcite mineral surfaces, which exist in the coal sources, provided an explanation for the depression of monazite in the combined systems. Single mineral flotation of monazite and calcite showed that sodium silicate and sodium hexametaphosphate efficiently depressed calcite while providing minimal effects on monazite recovery. However, in the monazite-calcite combined system, both monazite and calcite were depressed using the two regulators. Electrokinetic data and solution equilibrium calculations indicated that hydrolyzed species of calcium such as Ca(OH)+ interacted with silicates and formed a compact hydrophilic layer on monazite surfaces by hydrogen bonding and surface reaction. The compact layer decreased collector adsorption due to steric hindrance. Using 6×10-5 M EDTA together with 2.5×10-4 M octanohydroxamic acid and 0.05 g/L sodium silicate, monazite recovery of more than 90% was achieved while only recovering 20% of calcite. Based on the fundamental study, rare earth concentrates with 4700 ppm of REEs were produced from the Fire Clay fine coal refuse using column flotation.

<div><br></div><div> Today, autoinjectors are developed for more viscous drug solutions, which require larger forces for actuating the syringe and impose larger stresses on the drug solution during the administration of autoinjectors. We developed experimentally validated high-fidelity simulations to investigate the liquid jet formation, liquid slosh and cavitation during the insertion process of an autoinjector. </div><div> </div><div> The jet formed due to an acceleration-deceleration motion of syringe is found to be governed by the interplay between inertial, viscous, surface tension and gravitational forces. A scaling for the jet velocity and a criterion for the jet breakup in a simplified geometry are proposed.</div><div> </div><div> When the syringe accelerates and decelerates during the insertion, liquid slosh occurs and there is a vehement motion of the air-liquid interface. Here, we quantified the area of air-liquid interface and hydrodynamic strain rate, which increase with the air gap size, syringe velocity, tilt angle and inner wall hydrophobicity, and decrease with the solution viscosity and hardly change with the liquid column height and surface tension. The strain rate is not sufficient to unfold the protein and the air-liquid interface is more likely to cause protein aggregation.</div><div> </div><div> In a spring-driven autoinjector, the plunger is actuated by the impact of a driving rod, which generates a strong pressure wave and can cause cavitation inception. The cavtiation bubbles can be impeded by the syringe walls and form a re-entrant jet shooting toward the syringe wall. During the process, the protein molecules are focused in the jet, pushed toward the syringe wall and spread across the wall, which can be the reason for the protein aggregation and adsorption on the syringe walls. The impedance effects of the wall decreases with the wall distance and increases with the maximum bubble size. The maximum bubble radius also increases with the liquid column size and nucleus size and decreases with the air gap pressure. Since inertia effects dominate in the cavitation process, the liquid viscosity and surface tension hardly changes the cavitation bubble dynamics. Small bubbles can also form in the bulk, which may generate aggregates in the bulk solution. Bubbles in the cavitation bubble cloud may coalesce with nearby bubbles and induce a higher pressure at the collapse (up to 1000 bar). This high pressure can potentially generate hydroxyl radicals that oxidize the protein molecules.</div><div> </div><div> The current study presents a detailed picture of fluid flows in autoinjectors and provide recommendations for mitigating the liquid slosh and cavitation generated in syringes. The results can be combined with future experiments to understand the implications of fluid flows on protein drugs and the performance of autoinjectors.</div>

Mechanisms of three reactions catalyzed by microporous materials were investigated computationally; the reactions investigated include Friedländer and Knoevenagel reactions catalyzed by Cu3BTC2 metal organic framework (MOF) and an intramolecular cyclisation of unsaturated alcohols catalyzed by zeolite H-ZSM-5. It was found that the reaction mechanisms of all three reactions are controlled by a high concentration of active sites in materials. Reaction intermediates interact with more than one active site simultaneously. This novel concept of "multiple-site" interactions is described. The concerted effect of two catalytic sites leads to a decrease of activation barriers on reaction paths of Friedländer and Knoevenagel reactions. On the contrary, a simultaneous interaction of reactants with two active sites has a negative effect on reaction rate in case of alcohol cyclization catalyzed by H-ZSM-5; it was found that the interaction with dual sites results in the increase of activation barriers and diffusion limitations. In case of Knoevenagel reaction catalyzed by CuBTC, the adsorption of reaction precursor to the reaction site allows the creation of a dynamic defect in the MOF framework that subsequently catalyses the reaction. Both, the multiple sites effect and the dynamical defect formation effect...

The current requirements in automotive lubrication impose complex formulation. Among all the additives present in oil, the presence of molybdenum dithiocarbamate and zinc dithiophosphate, both tribological additives containing sulfur and phosphorous is found. For environmental reasons, it is important to reduce or eliminate the presence of these two elements contained in oil. Organic molecules based on carbon, oxygen and hydrogen seems to be good candidate. The lubrication mechanism of fatty acids (e.g. stearic, oleic and linoleic acids) is revisited with a new approach combining experimental and computational chemistry studies. First, the adsorption mechanisms of fatty acids on iron-based surfaces are investigated by Ultra-Accelerated Quantum Chemistry Molecular Dynamics simulations. The adsorption of fatty acids on iron oxide surface occurred through the acid group. Depending on the nature of the substrate, on the density of the film and on the tilt angle between the molecule and the surface, different adsorption mechanisms (physisorption and chemisorption) can occur. Stearic acid molecules form a close-packed and well-arranged monolayer whereas unsaturation acids cannot because of steric effects induced by double carbon-carbon bonds. The friction process favors the formation of carboxylate function. Results are confirmed by surface analysis (XPS and PM-IRRAS). Tribological properties of pure fatty acids, blended in PAO 4 and mixture of saturated/unsaturated acids are studied by MD simulations and tribotests. Low friction coefficient with no visible wear is reported for pure stearic acid and single stearic acid blended in PAO 4 at 1%w at high temperature. This lubricating behavior is inhibited in the presence of unsaturated acids, especially at 150 °C. MD simulation results show a faster diffusion toward the surface for unsaturated fatty acids than for stearic acid at all studied temperature.

Les exigences actuelles en terme de lubrification automobile imposent des formulations extrêmement complexes. Parmi tous les additifs présents dans l’huile, on peut noter le dithiocarbamate de molybdène et le dithiophosphate de zinc, additifs à action tribologique à base de soufre et de phosphore. Pour des raisons environnementales, il est important de diminuer voir d’éliminer la présence de ces deux éléments dans les huiles. Les molécules organiques à base de carbone, oxygène et hydrogène semblent être de bons candidats. Le mécanisme de lubrification des acides gras (acides stéarique, oléique et linoléique) est revisité par une approche visant à combiner l’étude expérimentale et la modélisation moléculaire. Tout d’abord, les mécanismes d’adsorption des acides gras sur des surfaces à base de fer sont étudiés par couplage Chimie Quantique et Dynamique Moléculaire (UA-QCMD). L’adsorption des acides gras sur des surfaces à base de fer se fait par la fonction acide. Selon la nature du substrat, la densité du film et l’angle d’inclinaison de la molécule par rapport à la surface, différents mécanismes d’adsorption peuvent avoir lieu (physisorption et chimisorption). Les molécules d’acide stéarique forment une monocouche compacte et bien arrangée alors que les molécules insaturées en sont incapables à cause d’effets stériques induits par les doubles liaisons carbone-carbone. Le frottement favorise la formation de la fonction carboxylate. Ces résultats sont confirmés par des analyses de surface (XPS et PM-IRRAS). Les propriétés tribologiques des acides gras purs, dans la PAO 4 et en mélange dans la PAO 4 sont étudiées par simulation MD et par des tribotests. Un faible frottement et une absence d’usure visible ont été observés pour l’acide stéarique pur et dissous à 1%m dans la PAO 4 à haute température. La présence de molécules insaturées inhibe les propriétés réductrices de frottement de l’acide stéarique, en particulier à 150 °C. Ceci est expliqué par la diffusion des acides gras insaturés bien supérieure à celle de l’acide stéarique dans la PAO 4 à toutes les températures étudiées. / The current requirements in automotive lubrication impose complex formulation. Among all the additives present in oil, the presence of molybdenum dithiocarbamate and zinc dithiophosphate, both tribological additives containing sulfur and phosphorous is found. For environmental reasons, it is important to reduce or eliminate the presence of these two elements contained in oil. Organic molecules based on carbon, oxygen and hydrogen seems to be good candidate. The lubrication mechanism of fatty acids (e.g. stearic, oleic and linoleic acids) is revisited with a new approach combining experimental and computational chemistry studies. First, the adsorption mechanisms of fatty acids on iron-based surfaces are investigated by Ultra-Accelerated Quantum Chemistry Molecular Dynamics simulations. The adsorption of fatty acids on iron oxide surface occurred through the acid group. Depending on the nature of the substrate, on the density of the film and on the tilt angle between the molecule and the surface, different adsorption mechanisms (physisorption and chemisorption) can occur. Stearic acid molecules form a close-packed and well-arranged monolayer whereas unsaturation acids cannot because of steric effects induced by double carbon-carbon bonds. The friction process favors the formation of carboxylate function. Results are confirmed by surface analysis (XPS and PM-IRRAS). Tribological properties of pure fatty acids, blended in PAO 4 and mixture of saturated/unsaturated acids are studied by MD simulations and tribotests. Low friction coefficient with no visible wear is reported for pure stearic acid and single stearic acid blended in PAO 4 at 1%w at high temperature. This lubricating behavior is inhibited in the presence of unsaturated acids, especially at 150 °C. MD simulation results show a faster diffusion toward the surface for unsaturated fatty acids than for stearic acid at all studied temperature.

PhDENV / Department of Ecology and Resource Management / Some industries such as textiles, ceramics, paper and printing are known to use significant amounts of dye to colour their products and during the colouring process, certain quantities of dyes are absorbed by the products, and some of them end up in wastewater. Depending on their application, some synthetic dyes are designed to be chemically or biologically resistant and their presence in the environment can cause severe environmental problems because of their colour impartation to water bodies. Therefore, proper treatment is required to remove these pollutants from wastewater before discharge into the environment. In this thesis, the potential of dye removal from wastewater by calcined magnesite, halloysite nanoclay and calcined magnesite - halloysite nanoclay composite was evaluated. To this end, the study was subdivided to four segments. The first segment of the study focused on evaluating the efficiency of using calcined magnesite to remove Methylene Blue (MB), Direct Red 81 (DR81), Methyl Orange (MO) and Crystal Violet (CV) dyes from aqueous systems using a batch study. To achieve that, several operational factors like residence time, adsorbent dosage, dye concentration and temperature were appraised. The adsorbent was subjected to different kinds of physicochemical characterization to determine the various characteristics that would assist in the dye uptake process. Characterization results showed that the adsorbent material was highly crystalline with magnesite, periclase, dolomite, and quartz as some of the crystalline phases. The batch study proved that calcined magnesite is effective in the treatment of dye contaminated water and moreover it performed well in terms of colour removal, though exceptional results were recorded for CV removal with complete decolourisation occurring in first few minutes of contact. In terms of experimental adsorption capacity, the performance of calcined magnesite was in the order CV (14.99 mg/g) > DR81 (12.56 mg/g) > MO (0.64 mg/g) > MB (0.39 mg/g). Mechanisms of adsorption where explained by fitting the experimental data into adsorption isotherms, kinetics, and thermodynamic parameters. Neither, the Langmuir, nor the Freundlich nor the Dubinin Radushkevich, nor the Temkin model could perfectly describe the adsorption of the four dyes onto calcined magnesite, however adsorption kinetics obeyed the pseudo second order model, implying that, the dye removal process was primarily a chemical process. In accordance with the results of this study, it can be concluded that calcined magnesite can be used effectively for the removal of dyes in aqueous solution and thus can be applied to treat wastewater containing dyes. The second segment of the study focused on the removal of MB, DR81, MO and CV dyes by halloysite nanoclay. Physicochemical characterisation revealed that the nanoclay has a surface area of 42 m²/g and its ABSTRACT iv morphology is predominated by tubular structures, which exhibit some hollow rod like structures. Various important parameters namely contact time, initial concentration of dyes, dosage, solution temperature and solution pH were optimized to achieve maximum adsorption capacity and it was observed that the effect of initial pH and temperature of the aqueous solution was neglibible on removal of the four dyes. The experimental adsorption capacities towards 40 mg/L of MB, DR81, MO and CV dyes were 17.51, 14.11, 0.38, and 4.75 mg/g respectively. The results indicate that natural halloysite nanoclay is an efficient material for the removal of the selected dyes. Due to its low cost and non-toxicity, halloysite nanoclay can be considered a good replacement option of other high cost materials used to treat coloured wastewater especially in developing countries like South Africa. Having observed the performance of calcined magnesite and halloysite nanoclay individually in the removal of selected dyes, a third study was designed with the aim of preparing a nanocomposite adsorbent from the aforementioned adsorbent materials and then evaluating the synergistic influence of the mechanochemical modification by a ball miller on the removal of MB, DR81, MO and CV dyes. Physicochemical characterization was carried out to get an insight of pre- and -post adsorption characteristics of the nanocomposite material and results showed major changes which could be an indication of dye uptake by the nanocomposite material. According to the results, the nanocomposite material outcompeted its component individual constituent materials i.e (calcined magnesite and halloysite nanoclay material) in the removal of DR81, which in turn was the highest removal efficiency observed for the whole batch adsorption study recording a maximum adsorption capacity and percentage removal of 19.89 mg/g and 99.40% respectively. Experimental results fitted the Langmuir and pseudo-second order models perfectly hence demonstrating that adsorption took place on a homogenous adsorbent layer via chemisorption. In overall, the results suggested that the nanocomposite is a suitable adsorbent for decolourising industrial wastewater. Based on the overall performance of the adsorbents in removing the four dyes, it was observed that the nanocomposite material had a high affinity for DR81 dye hence it was chosen as the model dye for further application in column studies. The effect of flow rate, bed height and initial dye concentration on the removal of DR81 was investigated. Maximum bed capacity and equilibrium dye uptake were determined and break through curves were plotted. Percentage dye removal increased with decrease in flow rate and increase in bed height. The maximum capacity of column was found to be about 51.73 mg DR81 per gram of the nanocomposite adsorbent for a flow rate of 3 mL/min, initial concentration of 10 mg/L and 4 cm bed height. Data from column studies was fitted to the Thomas model and Adams-Bohart models. The comparison of the R2 values obtained from both models showed a better fit for the nanocomposite material than the individual halloysite nanoclay and calcined magnesite materials. The study revealed the applicability of calcined magnesite- halloysite nanoclay composite in fixed bed column for the removal of DR81 dye from aqueous solution. v The reuse of an adsorbent is essential in order to make the adsorption process economic and environmentally friendly. To recover the adsorbate and renew the adsorbent for further use, a chemical method of regeneration was applied by using 0.1 M NaOH as the desorbent. Regeneration with 0.1 M NaOH proved very efficient for some dyes and less efficient for others depending on the adsorbent material used at the time. The general observation was that the adsorption capacity of the adsorbent materials decreased with successive adsorption – desorption cycles. Furthermore, regeneration with NaOH, favoured the acidic dyes (DR81 and MO) more than the basic dyes (MB and CV) possibly due to electrostatic interactions between oppositely charged molecules allowing for reversible reactions to take place. The three tested adsorbents namely calcined magnesite, halloysite nanoclay and their nanocomposite thereof were applied for the treatment of real wastewater effluent from a printing and ink industry. The adsorbents performed very well in terms of colour removal as recommended by the South African standards of wastewater discharge, However, in terms of pH, calcined magnesite and the nanocomposite produced a highly alkaline solution hence wastewater neutralisation by an acid is recommended before discharge. These findings show that the two natural clay-based materials (calcined magnesite and halloysite nanoclay) and their nanocomposite thereof have a great potential for application in dye wastewater remediation since the materials used in the process are inexpensive, abundant and require minimal modifications. / NRF

La forte augmentation de la population mondiale entraîne une demande croissante en eau potable. La production d'eau potable est accompagnée par la génération de résidus du traitement de l'eau dont la boue d'aluminium qui est donc largement disponible mondialement. Ce travail se concentre sur l'identification des différentes voies de valorisation des boues d'aluminium afin de les réutiliser dans le domaine de l’environnement. Deux sources de boues d'aluminium, collectées en France et en Irlande, ont été étudiées dans divers domaines d’application en fonction de leurs caractéristiques. Tout d'abord, les boues d'aluminium ont été utilisées en remplacement d’une partie de l'argile dans la fabrication des briques, en incorporant différents pourcentages de boues d'aluminium et à différentes températures. Les briques résultantes ont été caractérisées et les résultats ont montré que les briques composées de boues d'aluminium et d'argile sont conformes aux « normes européennes et irlandaises » et démontrent ainsi le potentiel pour une application industrielle des boues d'aluminium dans la fabrication de briques en terre cuite irlandaises. Dans un second temps, les boues d’aluminium ont été utilisées comme adsorbant des polluants présents dans l’agriculture. Le glyphosate est un ingrédient actif dans les pesticides utilisés massivement dans l'agriculture irlandaise et représente une problématique environnementale. La boue d’aluminium et la tourbe irlandaise ont été comparées pour l’élimination du glyphosate lors de tests en pot à l’échelle laboratoire. Les résultats ont montré que la boue d’aluminium permet d’éliminer le glyphosate à plus de 99% et réduire les niveaux de DCO. Cet aspect scientifique a permis d’être dans la sélection des adsorbants possibles pour le traitement des eaux usées agricoles en Irlande. Le co-conditionnement et la déshydratation des boues de station d’épuration avec des boues d’aluminium liquides ont également été étudiés. Pour cela, le Jar test a été effectué sur des boues issues d’une station de traitement des eaux française. Les résultats ont montré que le rapport optimal de mélange des boues est de 1:1 (boues d’épuration : boues d’aluminium). Ainsi, la quantité de polymère utilisée peut être diminuée de 14 fois par rapport aux technologies actuelles. Cette approche a permis de montrer la possible valorisation des boues d’aluminium comme un moyen durable et technique permettant ainsi l’élimination des boues localement pour une même station de traitement des eaux. Une autre voie de valorisation des boues d’aluminium comme adsorbant pour la purification des gaz a été étudiée lors d’expériences d’adsorption de H2S dans un réacteur à lit fixe dans différentes conditions expérimentales. Les données expérimentales d’adsorption du H2S ont été modélisées à l'aide de modèles empiriques basés sur la cinétique des processus d'adsorption. Les résultats ont montré que les boues d'aluminium sont un adsorbant efficace pour l'élimination du H2S (capacité de 374,2 mg H2S / g solide) et que des mécanismes mis en jeu sont l'adsorption dissociative et l'oxydation. Les coefficients de transfert de masse globaux ont également été calculés et pouvant ainsi être utilisés pour la prédiction. Enfin, les gâteaux de boues d'aluminium ont été réutilisés pour la purification simultanée d’H2S et le traitement des eaux usées. Les résultats ont montré la capacité de cet adsorbant pour éliminer tout le H2S présent avec une grande efficacité d’élimination de la DCO, TN et TP. Ainsi, il a été démontré la valorisation des boues d’aluminium en tant qu’adsorbant pour une purification du H2S simultanée avec le traitement des eaux usées. / The production of drinking water always accompanied by the generation of water treatment residues (WTRs). Alum sludge is one of the WTRs, it is an easily, locally and largely available by-product worldwide. This work focuses on the identification of different ways to valorize the alum sludge for environmentally friendly reuse. Two alum sludges collected from France and Ireland have been reused in various fields as a function of their characteristics. Firstly, alum sludge was used as a partial replacement for clay in brick making, by incorporating different percentages of alum sludge and calcined at different temperatures (range from 800 to 1200 °C). The resultant bricks were tested for compression, Loss on Ignition, water absorption, appearance, etc. Results show that alum sludge-clay bricks have met the “European and Irish Standards” and demonstrated the huge industrial application potential for alum sludge in Irish clay brick manufacturing. Glyphosate is an active ingredient in pesticide which is massive employed in agriculture. Alum sludge and Irish peat were compared for glyphosate removal in pot tests, results show that alum sludge present significant glyphosate removal capacity (>99 %) and could reduce the level of Chemical Oxygen Demand (COD). It provided a scientific clue for sorbents selection when considering the agricultural wastewater treatment in Ireland and to maximize their value in practice. The co-conditioning and dewatering of sewerage sludge with liquid alum sludge was also investigated in Jar-test based on the case analysis of a water industry in France. Results show that the optimal sludge mix ratio is 1:1, the use of the alum sludge has been shown to beneficially enhance the dewaterability of the resultant mixed sludge, and highlighting a huge polymer saving (14 times less than the current technologies) and provided a sustainable and technical sludge disposal route for the local water industry. The use of alum sludge as a sorbent for gas purification was studied by H2S adsorption experiments in a fixed-bed reactor with various operating parameters. The experimental breakthrough data were modeled with empirical models based on adsorption kinetics. Results show that alum sludge is an efficient sorbent for H2S removal (capacity of 374.2 mg/g) and the mechanisms including dissociative adsorption and oxidation were proposed. Moreover, the overall mass transfer coefficients were calculated which could be used for the process scaling up. Finally, alum sludge cakes were reused in the novel aerated alum sludge constructed wetland (CW), which were designed for simultaneous H2S purification and wastewater treatment. Results show that H2S was completely removed in the six months’ trials, while the high removal efficiencies of COD, total nitrogen (TN), total phosphates (TP) were achieved. Thus, a novel eco-friendly CW for simultaneous H2S purification and wastewater treatment was developed. In the different approaches and process considered, in particular it was put in investigating and describing the mechanisms involved. Overall, this work demonstrated alum sludge could be a promising by- product for various novel beneficial reuse rather than landfilling and provided a “Circular Economy” approach for WTRs management.