Modeling and simulation of spiral concentrators

Les spirales gravimétriques ou « spirales » sont des équipements de séparation par gravité utilisés pour la valorisation des minerais pour lesquels la densité des minéraux de valeur est significativement différente de celle de gangue. C'est le cas du traitement du minerai de fer discuté dans cette thèse. Les spirales sont préférées à d'autres séparateurs car elles sont peu coûteuses, simples à utiliser, pratiquement sans entretien, peu exigeantes en énergie et n'utilisent pas de réactif. Malgré ces qualités attrayantes et contrairement à la flottation, peu d'études sont consacrées à examiner l'opération des spirales. En effet, ce n'est que récemment que l'analyse de ce procédé a démontré que les spirales ne réussissaient pas à récupérer les particules minérales denses et grossières au produit lourd alors qu'elles le devraient en théorie. Il a également été démontré récemment que l'eau de lavage, qui est la principale variable de contrôle pour les spirales, est en partie responsable de la perte des particules grossières. Pour compenser cette perte, d'autres variables de contrôle doivent être utilisées, dont l'ouverture des couteaux de concentré et la position des portes du diviseur à la décharge de la spirale. L'étude de stratégies alternatives de contrôle des spirales ne peut difficilement se faire en milieu industriel, car l'opération des usines de traitement des minéraux est soumise à des contraintes imposées par la production et la qualité du produit final. Par ailleurs, l'impact des perturbations dues aux variations du minerai et/ou aux problèmes mécaniques dans l'usine est inévitable. Tester de nouvelles stratégies de contrôle dans une usine pilote est une option certainement trop coûteuse. Les opérateurs d'usine recherchent donc des approches rapides et peu coûteuses pour identifier des stratégies qui pourraient ensuite être testées sécuritairement dans l'usine. La simulation de procédé offre cette possibilité, mais une étude de la littérature a rapidement révélé l'absence d'outils de simulation pour les spirales et plus particulièrement pour les circuits de séparation gravimétrique utilisant des spirales. Pour construire un tel simulateur il faut donc trouver ou développer des modèles mathématiques pour les unités du circuit. Pour pouvoir tester des stratégies de contrôle, il est important que le modèle développé prenne en compte les variables de fonctionnement de la spirale, dont l'ouverture des couteux de concentré et du diviseur à la décharge de spirale ainsi que l'ajout d'eau de lavage. L'objectif de ce projet de recherche est de proposer un tel modèle pour les spirales. Le modèle mathématique proposé décrit la trajectoire des particules distribuées en classes de minéraux/taille lors de leur descente dans la spirale. Cette prédiction est réalisée en introduisant le nouveau concept de Fonctions de Déplacement de Particules (FDP) pour décrire les mouvements des particules. Le modèle est calibré en utilisant des données générées à partir d'essais réalisés sur un montage à l'échelle pilote construit autour d'une spirale Mineral Technologies WW6 +, installée au Laboratoire de Traitement de Minerai de l'Université Laval. Le modèle est ensuite validé avec des données obtenues avec une spirale WW6E opérée au COREM. Le montage, mis en service à l'Université Laval, utilise une distribution contrôlée d'eau de lavage dans les tours de spirale pour surmonter le problème observé de distribution inégale de l'eau de lavage lorsque le système intégré à la spirale est utilisé. Le montage est également conçu pour échantillonner simultanément le produit de chaque couteau de concentré de la spirale, de sorte que la progression de la séparation des minéraux dans la spirale puisse être utilisée pour calibrer le modèle. Le simulateur calibré prédit de manière adéquate la réponse de la spirale aux changements des états des variables manipulables. Le modèle est capable de simuler l'opération d'une spirale nettoyeuse bien qu'il ait été calibré à l'aide de données collectées à partir d'une spirale ébaucheuse. Le modèle proposé est prêt à être implanté dans un simulateur pour une usine de traitement de minerai de fer, bien qu'il reste du travail à faire pour finaliser la méthodologie de calibrage pour améliorer la prédiction de la distribution granulométrique des minéraux dans le flux mixte de la spiraleSpiral concentrators are gravity separation devices used for the valorization of ores for which the specific gravity of the valuable minerals is significantly different from that of the gangue minerals. This is the case of iron ore processing discussed in this thesis. Spirals are preferred to other mineral separation devices because they are inexpensive, simple of operation, practically maintenance free, low energy demanding and do not require the use of reagents to separate minerals. Despite these appealing qualities and unlike flotation, few studies are dedicated to the analyze the spiral operation. Indeed, it is only recently that basic process analysis has shown that spirals fail to recover coarse dense mineral particles to the heavy product. It has also been recently found that wash water, as the main control variable for the operation of the studied spirals, is partly responsible for the loss of coarse valuable particles. To make up for this loss and to maintain a satisfactory operation of spirals, other control variables such as the concentrate cutter openings and position of the splitter gates at the spiral discharge should be used. The study of alternative control strategies for spirals implies testing these strategies in the industrial environment, which is practically impossible considering that the operation of mineral processing plants is subjected to constraints imposed on the production and on the quality of the plant product. Besides, the impact of disturbances due to ore variations and/or mechanical problems in the plant is unavoidable. Testing new control strategies in pilot plant is possible but it is certainly costly if one can find a pilot plant equipped for such testing. Plant operators are thus seeking for rapid and inexpensive approaches to carry out such investigation to identify strategies that can subsequently be safely tested in a plant. Process simulation offers this possibility, but a literature survey rapidly revealed the absence of simulation tools for spirals and more particularly for gravity separation circuits that use spiral concentrators. The first step in building such circuit simulator is to find or develop mathematical models for the units of the circuit. With the objective of testing control strategies, it is thus important that the model to be developed be able to account for the usual spiral operating variables, namely the cutter opening, the discharge splitter position and the wash water addition. The objective of this research project is to propose such model for spirals. A mathematical model is therefore described to predict the trajectory of particles distributed in mineral/size classes as they flow down a spiral. This is achieved here by introducing the new concept of Particle Displacement Functions (PDF) in spiral modelling to describe the movements of the particles flowing down the spiral. The model is calibrated using data generated from tests conducted on a pilot-scale test rig built around a Mineral Technologies WW6+ spiral, installed in the Mineral Processing Laboratory of Université Laval. The model is further validated with data obtained from a WW6E spiral operated at COREM. The test rig commissioned at Laval University uses a controlled wash water distribution within the spiral turns to overcome the observed problem of unequal wash water distribution when using the spiral built-in wash water distribution system. The test rig is also designed to sample simultaneously the product from each concentrate cutter of the spiral, so that the progress of the heavy mineral concentration down the spiral can be monitored. This information can be used to calibrate the model. The calibrated spiral simulator predicts adequately the spiral response to changes in the states of the operating variables. The model can simulate a cleaner spiral operation although it is calibrated using data collected from a rougher spiral operation. The proposed model is ready to be implemented into a simulator for an iron ore processing plant, although work remains to be done to finalize the calibration methodology to improve the prediction of the mineral size distribution in the spiral middling stream

La evaluación de la resistencia al cizallamiento del cemento de ionómero de vidrio modificado con resina con la adición de vidrio bioactivo 45S5 utilizando dos métodos convencionales.

Introduction: There is a high prevalence of enamel caries around brackets due to the young age of the majority of orthodontic patients, and to the difficulty of plaque removal in presence of orthodontic appliances. Recently, protective agents such as bioactive glasses (BGs) were introduced to enhance remineralization and prevent demineralization of tooth structures.  This study aimed to assess the shear bond strength (SBS) of resin-modified glass ionomer cement (RMGIC) with addition of 45S5 BG to enhance its remineralizing potential using two conventional methods. Material and methods: This in-vitro experimental study evaluated three groups (n=20) of orthodontic brackets bonded to enamel using Transbond XT (group 1), light-cure RMGIC (group 2) and RMGIC with BG added (group 3). Samples underwent 7000 thermal cycles and their SBS was measured. The adhesive remnant index (ARI) score was also determined. Quantitative data were analyzed using one-way ANOVA while qualitative data were analyzed using a chi-square test. Discussion: The results showed no significant difference in SBS between study groups, however the ARI scores were significantly different among the groups. The RMGIC group showed the highest ARI while RMGIC doped with BG showed the lowest ARI score. Conclusion: Addition of 30% w/v 45S5 BG to RMGIC does not cause a significant change in SBS of orthodontic brackets bonded to enamel, while resulting in less amount of luting agent remnants on the enamel surface after debonding. Introducción: Existe una alta prevalencia de caries del esmalte alrededor de los brackets debido a la corta edad de la mayoría de los pacientes de ortodoncia y a la dificultad de remoción de la placa en presencia de aparatos de ortodoncia. Recientemente, se introdujeron agentes protectores como los vidrios bioactivos (VB) para mejorar la remineralización y prevenir la desmineralización de las estructuras dentales. Este estudio tuvo como objetivo evaluar la resistencia al cizallamiento (RC) del cemento de ionómero de vidrio modificado con resina (CIVMR) con la adición de 45S5 BG para mejorar su potencial remineralizante utilizando dos métodos convencionales. Material y Métodos: Este estudio expe-rimental in vitro evaluó tres grupos (n = 20) de brackets de ortodoncia adheridos al esmalte usando Transbond XT (grupo 1), CIVMR fotopolimerizable (grupo 2) y CIVMR con VB agregado (grupo 3). Las muestras se sometieron a 7000 ciclos térmicos y se midió su RC. También se determinó la puntuación del índice de restos de adhesivo (IRA). Los datos cuantitativos se analizaron mediante ANOVA de una vía, mientras que los datos cualitativos se analizaron mediante una prueba de chi-cuadrado. Discusión: Los resultados no mostraron diferencias significativas en la RC entre los grupos de estudio, sin embargo, los puntajes IRA fueron significativamente diferentes entre los grupos. El grupo CIVMR mostró el ARI más alto mientras que CIVMR dopado con VB mostró el puntaje IRA más bajo. Conclusión: La adición de un 30% p/v de 45S5 VB a CIVMR no causa un cambio significativo en la RC de los brackets de ortodoncia adheridos al esmalte, mientras que resulta en una menor cantidad de remanentes de agente de fijación en la superficie del esmalte después del desprendimiento. Resistencia al Corte

No-Regret Online Prediction with Strategic Experts

We study a generalization of the online binary prediction with expert advice framework where at each round, the learner is allowed to pick $m\geq 1$ experts from a pool of $K$ experts and the overall utility is a modular or submodular function of the chosen experts. We focus on the setting in which experts act strategically and aim to maximize their influence on the algorithm's predictions by potentially misreporting their beliefs about the events. Among others, this setting finds applications in forecasting competitions where the learner seeks not only to make predictions by aggregating different forecasters but also to rank them according to their relative performance. Our goal is to design algorithms that satisfy the following two requirements: 1) $\textit{Incentive-compatible}$: Incentivize the experts to report their beliefs truthfully, and 2) $\textit{No-regret}$: Achieve sublinear regret with respect to the true beliefs of the best fixed set of $m$ experts in hindsight. Prior works have studied this framework when $m=1$ and provided incentive-compatible no-regret algorithms for the problem. We first show that a simple reduction of our problem to the $m=1$ setting is neither efficient nor effective. Then, we provide algorithms that utilize the specific structure of the utility functions to achieve the two desired goals

The evaluation of shear bond strength of resin-modified glass ionomer cement with the addition of 45S5 bioactive glass using two conventional methods.

Introduction: There is a high prevalence of enamel caries around brackets due to the young age of the majority of orthodontic patients, and to the difficulty of plaque removal in presence of orthodontic appliances. Recently, protective agents such as bioactive glasses (BGs) were introduced to enhance remineralization and prevent demineralization of tooth structures.  This study aimed to assess the shear bond strength (SBS) of resin-modified glass ionomer cement (RMGIC) with addition of 45S5 BG to enhance its remineralizing potential using two conventional methods. Material and methods: This in-vitro experimental study evaluated three groups (n=20) of orthodontic brackets bonded to enamel using Transbond XT (group 1), light-cure RMGIC (group 2) and RMGIC with BG added (group 3). Samples underwent 7000 thermal cycles and their SBS was measured. The adhesive remnant index (ARI) score was also determined. Quantitative data were analyzed using one-way ANOVA while qualitative data were analyzed using a chi-square test. Discussion: The results showed no significant difference in SBS between study groups, however the ARI scores were significantly different among the groups. The RMGIC group showed the highest ARI while RMGIC doped with BG showed the lowest ARI score. Conclusion: Addition of 30% w/v 45S5 BG to RMGIC does not cause a significant change in SBS of orthodontic brackets bonded to enamel, while resulting in less amount of luting agent remnants on the enamel surface after debonding. Introducción: Existe una alta prevalencia de caries del esmalte alrededor de los brackets debido a la corta edad de la mayoría de los pacientes de ortodoncia y a la dificultad de remoción de la placa en presencia de aparatos de ortodoncia. Recientemente, se introdujeron agentes protectores como los vidrios bioactivos (VB) para mejorar la remineralización y prevenir la desmineralización de las estructuras dentales. Este estudio tuvo como objetivo evaluar la resistencia al cizallamiento (RC) del cemento de ionómero de vidrio modificado con resina (CIVMR) con la adición de 45S5 BG para mejorar su potencial remineralizante utilizando dos métodos convencionales. Material y Métodos: Este estudio expe-rimental in vitro evaluó tres grupos (n = 20) de brackets de ortodoncia adheridos al esmalte usando Transbond XT (grupo 1), CIVMR fotopolimerizable (grupo 2) y CIVMR con VB agregado (grupo 3). Las muestras se sometieron a 7000 ciclos térmicos y se midió su RC. También se determinó la puntuación del índice de restos de adhesivo (IRA). Los datos cuantitativos se analizaron mediante ANOVA de una vía, mientras que los datos cualitativos se analizaron mediante una prueba de chi-cuadrado. Discusión: Los resultados no mostraron diferencias significativas en la RC entre los grupos de estudio, sin embargo, los puntajes IRA fueron significativamente diferentes entre los grupos. El grupo CIVMR mostró el ARI más alto mientras que CIVMR dopado con VB mostró el puntaje IRA más bajo. Conclusión: La adición de un 30% p/v de 45S5 VB a CIVMR no causa un cambio significativo en la RC de los brackets de ortodoncia adheridos al esmalte, mientras que resulta en una menor cantidad de remanentes de agente de fijación en la superficie del esmalte después del desprendimiento. Resistencia al Corte

In Vitro Comparison of Apical Leakage in Root Canals Obturated with 0.04 and 0.02 Tapered Gutta-Percha

INTRODUCTION: Gutta-percha is the most commonly used material for root canal obturation; it has been recently manufactured with different tapers. The aim of this in vitro study was to compare microleakage of canals obturated with standard gutta-percha (0.02 taper) or the new 0.04 taper gutta-percha master cone using the cold lateral condensation technique. MATERIALS AND METHODS: Forty-four extracted single rooted teeth were selected. The crowns were removed and all the canals were prepared using RaCe rotary files. The teeth were then divided into experimental (n=2) and control (n=2) groups. In the first study group, the teeth were obturated with 0.02 taper gutta-percha master cone and lateral condensation. In the second study group, the canals were obturated by 0.04 tapered master cones and the same obturation method. The degree of leakage was measured using fluid filtration method. Data were analyzed statistically by student t-test. RESULTS: There was no significant difference between the mean microleakage of two experimental groups (P=0.558). CONCLUSION: Lateral condensation technique using 0.04 tapered master cones can provide an effective apical seal similar to 0.02 gutta-percha cones

Optimization of the expression of genes encoding poly (3-hydroxyalkanoate) synthase from Pseudomonas aeruginosa PTCC 1310 in Escherichia coli

Introduction: Over the years, the use of plastics has complicated the problem of disposal of solid wastes. One strategy to reduce plastic waste is the use of biodegradable plastics. A group of these plastics are polyhydroxyalkanoates (PHAs). To date more than 250 different microorganisms are known to synthesize and accumulate PHA. Most Pseudomonas strains are able to accumulate mcl-PHA. In previous studies, the phaC1 and phaC2 genes were identified in Pseudomonas aeruginosa (P.aeruginosa) PTCC 1310 and were cloned. The aim of this study was to express these genes and optimize the conditions for their expression.  Methods and Results: The inserts obtained from vectors pTZPHAC1 and pTZPHAC2 were subcloned into pET15b expression vector. After transformation of competent Escherichia coli (E.coli) BL21 (DE3) cells with recombinant plasmids, expression was induced using IPTG. By changing expression conditions such as IPTG concentration, time and temperature of incubation with IPTG, the expression conditions for these enzymes were optimized, and the obtained results were compared using proper statistical analysis. Conclusions: The PHA synthase genes were induced with IPTG and the expressed 62 kDa protein was observed and purified. By changing expression conditions, 1 mM IPTG, 37°C and a 2 hr incubation provided the highest level of protein production in E.coli cells. These results suggest that induction condition of PhaC genes can influence expression of PHA synthase enzymes