Batch sedimentation is a method that enables us to understand the mechanism of compaction and compression of sedimenting slurry. However, batch settling behaviour is a very complex phenomenon that is not easily described fully by a mathematical model. This causes unrealistically large empirical calculations when the thickener size estimations are required. Channelling, reverse concentration gradients and the initial concentration of the slurry have large effects on batch settling. Existing procedures do not provide clear relationships involving these three significant variables. In this study, batch sedimentation phenomena are examined in detail and possible explanations are given to clarify the complex behaviour using recent theories. Modern research has shown that channelling is an unwanted formation because channels can change the concentration at the bottom and top of the bed by carrying a great amount of flocs upwards. Batch sedimentation tests were performed using flocculated slurry of Calcium Carbonate at various initial concentrations such as 250 g/l, 500 g/l, 750 g/l and 1000 g/l to observe channelling and reverse concentration gradients. Flux plots for the batch system reveal behaviour which can be attributed to the upward flow of solids. In addition, photographic methods were used to observe settling processes, channelling mechanisms and flocs in the channels. One of the purposes of this work was to examine the phenomenological solid-liquid separation theory of Buscall and White (1987), which employs the material properties of the local volume fraction, compressive yield stress Py ()ö and hindered settling function R()ö to identify the material behaviour in batch sedimentation. Stepped-pressure filtration and batch settling tests were used to measure the material characteristics for the flocculated CaCO3 suspension. Experimental data were demonstrated using Height versus Time and Height versus Concentration graphs and displayed the possible region of reverse concentration gradients and channelling in the settling bed. Mathematical predictions adopted from Usher (2002) were performed employing material characteristics of the material and graphical documentations were presented. The results of mathematical predictions were compared to the experimental results and the modes of sedimentation explained by Lester et al. (2005). Fundamental theoretical models and experimental observations highlight that the main driving force for channelling is the high-pressure gradient at the bottom of the bed and the most important factors that cause channelling are high initial concentration of slurry and settling time. The predictions also show that the material and flocculant used for the batch settling tests demonstrate important effect on the settling process. The knowledge and information gained from this study is valuable to maximize the thickening process.

De la pâte à dentifrice au moût de fermentation en passant par la peinture, le lit d’une rivière, le propergol d’un réacteur de fusée et le sang, les suspensions sont présentes dans de nombreux usages de notre vie courante. La maîtrise de leur mise en œuvre notamment nécessite la compréhension de leur comportement et constitue un des challenges de la recherche. Dans le présent travail de thèse, nous nous sommes intéressés au processus de sédimentation de suspensions concentrées de particules non-colloïdales et inertes dont la distribution de taille est mono, bi ou tri-disperse. Deux types de sédimentation ont été étudiés : la décantation et l’alimentation continue. L’objectif est de mener une étude expérimentale et dans une moindre mesure numérique pour caractériser de la façon la plus complète possible la sédimentation avec une attention particulière à la structure de l’écoulement et du dépôt, aux profils de concentration et à la détermination des modes de sédimentation. Les moyens expérimentaux utilisés sont les techniques usuelles de mesure bidimensionnelle (vélocimétrie laser et visualisation directe) qui autorisent l’acquisition de données d’intérêt pour des configurations où les particules évoluent dans le plan. Ces techniques laser ont été améliorées pour permettre le suivi simultané de populations de différentes particules et l’accès à des grandeurs diverses telles que le champ de vitesse de l’écoulement, la fraction volumique locale, et les vitesses des divers fronts de sédimentation. En parallèle, un outil numérique simple a été construit, utilisant la Dynamique Stokesienne et saisissant l’essentiel des phénomènes physiques mis en jeu menant à la modélisation des interactions hydrodynamiques. / From toothpaste to must of fermentation passing by painting, bed of a river, propellant of an rocket engine and blood, suspensions are present in many uses of our everyday life. The control of their implementation requires comprehension of their behavior and constitutes one of the challenges of nowadays research. In this work of thesis, we were interested in the sedimentation process of concentrated suspensions of non-colloidal and inert particles whose size distribution is mono, bi or tri-disperse. Two types of sedimentation were studied: decantation and thickening. The objective is to do an experimental and in a lesser way numerical study to characterize sedimentation the most completly possible with a detailed attention to flow and deposit structure, concentration profiles and determination of sedimentation modes. Used experimental means are the usual techniques of two-dimensional measurement (laser velocimetry and direct visualization) which authorize the data acquisition for configurations where particles evolve in the plan. These laser techniques were improved to simultaneously follow various particles populations and access to various outpouts such as velocities field, local volumic fraction, and velocities of various sedimentation fronts. A simple numerical tool was also built using Stokesian Dynamics and seizing the main part of the physical phenomena driving sedimentation leading to the modeling of the hydrodynamic interactions.