Dissertations / Theses on the topic 'Ore grinding'

Includes bibliographical references.
The objective of this study was to determine the power losses occurring on a tyre-mounted ore-grinding mill designed by Dorbyl Heavy Engineering for Mintek. In order to understand the type of losses occurring on this mill it was decided that a scaled model be built and tested. Such a model mill was designed through the dimensional analysis and similitude technique. This technique enables the reduction of the number of variables to be tested by grouping them into a set of dimensionless parameters, and also allows the results obtained by means of experimentation with the scaled models to be related to the full-scale prototypes. The model mill was constructed in the Mechanical Engineering Workshop at the University of Cape Town. The overall dimensions of the model are 1400 mm long, 1070 mm wide and 892.5 mm high. Its drive-train comprises an electric motor, the wedge and timing belts with the appropriate pulleys, a differential gear set, the tyres, a shell and a disc brake sub-assembly. The tyres used to drive the shell can either be of the pneumatic or solid rubber types. The model mill was designed such that the tyre parameters required in the theoretical solution for power losses, which utilises the Light Vehicle Dynamics Simulation tyre model, could also be measured.

Efficient measurement methods for comminution properties are an important prerequisite for testing the variability of an ore deposit within the geometallurgical context. This involves the investigation of effects of mineralogy and mineral texture on the breakage of mineral particles. Breakage properties of mineral particles are crucial for the liberations of minerals and the energy required for that. For process optimization and control purposes, comminution indices are often used to map the variation of processing properties of an entire ore body (e.g. Bond work index). Within the geometallurgical approach this information is then taken up when modelling the process with varying feed properties. The main focus of this thesis work has been to develop a comprehensive geometallurgical testing framework, the Geometallurgical Comminution Test (GCT), which allows the time and cost efficient measurement of grinding indices and their linkage to mineralogical parameters (e.g. modal mineralogy or mineral texture, mineral liberation). In this context a small-scale grindability test has been developed that allows estimating the Bond work index from single pass grinding tests using small amounts of sample material. Verification of the evaluation method and validation was done with different mineral systems. For selected samples the mineral liberation distribution was investigated using automated mineralogy. By transferring the energy-size reduction relation to energy – liberation relation new term liberability has been established. As part of the experimental investigations, mineralogical parameters and mineral texture information were used for predicting breakage and liberation properties. Patterns for describing the breakage phenomena were established for a set of iron oxide ore samples. The determined breakage patterns indicated that the specific rate of mineral breakage slows down when reaching the grain size of mineral particles, thus allowing maximizing mineral liberation significantly without wasting mechanical energy.
CAMM

A run-of-mine (ROM) ore milling circuit is primarily used to grind incoming ore containing precious metals to a powder fine enough to liberate the valuable minerals contained therein. The ground ore has a product particle size specification that is set by the downstream separation unit. A ROM ore milling circuit typically consists of a mill, sump and classifier (most commonly a hydrocyclone). These circuits are difficult to control because of unmeasurable process outputs, non-linearities, time delays, large unmeasured disturbances and complex models with modelling uncertainties. The ROM ore milling circuit should be controlled to meet the final product quality specification, but throughput should also be maximised. This further complicates ROM ore grinding mill circuit control, since an inverse non-linear relationship exists between the quality and throughput. ROM ore grinding mill circuit control is constantly evolving to find the best control method with peripheral tools to control the plant. Although many studies have been conducted, more are continually undertaken, since the controller designs are usually based on various assumptions and the required measurements in the grinding mill circuits are often unavailable.
To improve controller performance, many studies investigated the inclusion of additional manipulated variables (MVs) in the controller formulation to help control process disturbances, or to provide some form of functional control. Model predictive control (MPC) is considered one of the best advanced process control (APC) techniques and linear MPC controllers have been implemented on grinding mill circuits, while various other advanced controllers have been investigated and tested in simulation. Because of the complexity of grinding mill circuits non-linear MPC (NMPC) controllers have achieved better results in simulations where a wider operating region is required. In the search for additional MVs some researchers have considered including the discrete dynamics as part of the controller formulation instead of segregating them from the APC or base-layer controllers. The discrete dynamics are typically controlled using a layered approach. Discrete dynamics are on/off elements and in the case of a closed-loop grinding mill circuit the discrete elements can be on/off activation variables for feed conveyor belts to select which stockpile is used, selecting whether a secondary grinding stage should be active or not, and switching hydrocyclones in a hydrocyclone cluster. Discrete dynamics are added directly to the APC controllers by using hybrid model predictive control (HMPC). HMPC controllers have been designed for grinding mill circuits, but none of them has considered the switching of hydrocyclones as an additional MV and they only include linear dynamics for the continuous elements. This study addresses this gap by implementing a hybrid NMPC (HNMPC) controller that can switch the hydrocyclones in a cluster.
A commonly used continuous-time grinding mill circuit model with one hydrocyclone is adapted to contain a cluster of hydrocyclones, resulting in a hybrid model. The model parameters are refitted to ensure that the initial design steady-state conditions for the model are still valid with the cluster. The novel contribution of this research is the design of a HNMPC controller using a cluster of hydrocyclones as an additional MV. The HNMPC controller is formulated using the complete nonlinear hybrid model and a genetic algorithm (GA) as the solver. An NMPC controller is also designed and implemented as the base case controller in order to evaluate the HNMPC controller’s performance. To further illustrate the functional control benefits of including the hydrocyclone cluster as an MV, a linear optimisation objective was added to the HNMPC to increase the grinding circuit throughput, while maintaining the quality specification. The results show that the HNMPC controller outperforms the NMPC one in terms of setpoint tracking, disturbance rejection, and process optimisation objectives. The GA is shown to be a good solver for HNMPC, resulting in a robust controller that can still control the plant even when state noise is added to the simulation.
Dissertation (MEng)--University of Pretoria, 2018.
National Research Foundation (DAAD-NRF)
Electrical, Electronic and Computer Engineering
MEng
Unrestricted

Este trabalho analisou, comparativamente, os aspectos operacionais entre as configurações de circuito fechado de moagem em moinhos de bolas, quais sejam, os circuitos direto e inverso. Foram realizadas amostragens no circuito industrial de prémoagem e moagem primária do Concentrador I de Germano, da Samarco Mineração, ora operando sob a configuração inversa, ora sob a configuração direta. Os históricos de dados industriais entre os circuitos dos Concentradores I e II de Germano foram também comparados, para complementação desta análise. Por fim, foram realizados ensaios de moagem em escala de laboratório, simulando ambas as condições. As comparações entre diferentes índices de desempenho selecionou o consumo de energia por tonelada de material gerado abaixo da malha de controle como o mais adequado para avaliar o desempenho dos circuitos. A comparação entre os históricos dos dados industriais dos Concentradores I (operando sob circuito inverso) e do Concentrador II (operando sob circuito direto) mostrou um histórico consistente em que o circuito do Concentrador II apresenta menor consumo energético por tonelada de material gerado abaixo da malha de controle do circuito. Estes resultados foram diferentes daqueles obtidos a partir das amostragens realizadas no circuito industrial da Samarco, os quais indicaram melhor desempenho do circuito inverso. A diferença foi atribuída à etapa de classificação, cujo desempenho determina a alteração ou até mesmo anula os benefícios, conforme demonstram os resultados de simulação posteriores.
This work compared the performance associated to both direct and reverse ball mill closed circuit configurations. Survey campaigns were carried out in both Samarco Mineração industrial plants ie. Concentrator I and Concentrator II. The former includes reverse configured ball mill closed grinding circuit, while the latter is equipped with ball mills under a direct closed configuration. The study comprised laboratory jar tests as well as comparisons between historical data obtained for both industrial plants. The energy consumption per ton of generated product was selected as the most adequate parameter to access the circuit performance. Comparisons based on historical data indicated that the Concentrator II, configured in a direct mode, showed a better performance than Concentrator I. Such a conclusion contrasts with the results obtained from the survey campaign which indicated a better performance for the reverse configuration. Such a difference was associated to the performance of the classification, carried out in cyclones, as demonstrated by simulations conducted on the basis of previously calibrated models.

O circuito de moagem de Carajás foi originalmente projetado para moagem de sinter feed, obtendose como produto final pellet feed. O processo consiste em etapas de moagem e deslamagem para que se atinjam as especificações de granulometria e área específica. No processo, como um todo, há geração significativa de finos, que são então descartados, acarretando em perdas de material que poderia ser incorporado como produto. O melhor entendimento das características dos vários tipos de minérios, bem como a previsão do desempenho do circuito de moagem em função de tais características permite estabelecer cenários para promover aumentos na recuperação em massa e na produtividade do circuito. O presente trabalho tem por base a caracterização tecnológica dos principais tipos de minério de Carajás e o desenvolvimento de um método para previsão de desempenho do circuito de moagem, em função de tais características. Para o desenvolvimento do método foram realizados ensaios de moagem em bancada e amostragens no circuito industrial. Os resultados dos ensaios de moagem em bancada serviram para definição das condições operacionais em que o ensaio em bancada melhor representou o circuito industrial, denominado ensaio padrão. Os dados obtidos nas amostragens e na caracterização tecnológica serviram de base para a calibração dos modelos matemáticos dos equipamentos de processo. O modelo calibrado constituiu num excelente recurso para previsão de desempenho. O desempenho do circuito de moagem foi avaliado no que se refere à granulometria e área específica dos produtos obtidos. Ainda foram conduzidas simulações pelo ensaio padrão e pelo modelo calibrado integrado do circuito de moagem, que apontam potenciais dos minérios cujo comportamento na moagem era até então desconhecido. Os dois produtos aqui desenvolvidos são, portanto, de aplicação imediata como recursos para previsão de desempenho e melhoria operacional.
Originally designed for sinter feed grinding, the Carajas grinding circuit includes two ball mills in parallel lines in a closed configuration with cyclones. The ground product is further deslimed in hydrocyclone for achieving the final specifications regarding size distribution and surface area. In this process, there is a significant amount of high grade material, not recovered due to overgrind. Ore characterization was here selected for predicting the grinding circuit performance, which in turn was the basis for optimization. The aim of this work is the characterization of the main Carajas ore types as well as the development of a method that includes these characteristics for predicting the grinding circuit performance. Laboratory grinding tests and samplings in the industrial circuit were carried out to predict the grinding circuit performance. The grinding test results were used to set operational conditions in which the laboratory better represented the industrial circuit. Results from industrial sampling and characterization were the basis for fitting the mathematical models. The fitted model was an excellent resource for the prediction of the grinding circuit performance as well as for the grinding test. To assess the grinding performance, products size distribution and surface area were evaluated. Moreover, simulations of the grinding circuit indicated the potential of some ore types. The derived methods were validated as tools for predicting the grinding circuit performance and for operational optimization.

The SAG Power Index test (SPI) is a tool for forecasting autogenous mill performance. Much effort has been directed towards the development of the process models relating SPI to throughput estimates, but little has been directed towards ore body modeling. Blending studies are presented showing that the SPI is not additive, affecting the geostatistical procedures. A method is given to ensure that additivity is respected during geostatistical interpolation. A procedure for relating mean SPI precision to sample spacing is given. This procedure is combined with a study of the process model error to estimate the precision of the mean throughput forecasts. A case study from Chino Mines is discussed. The relative throughput error is between 20 and 26 percent for perfect knowledge of SPI. For 100 m sample spacing at Chino, one third of the error is due to the process models and the rest to the SPI estimates.

Sulphate-rich wastewater is an increasing concern for industries as LKAB. The water chemistry of the LKAB Kiruna water system is characterized by high alkalinity, high pH (pH 7.5-9.0) and high concentrations of chemical species and soluble minerals. The sulphate content in the water system of Kiruna is associated with the dissolution of calcium sulphate as anhydrite (CaSO4) and gypsum (CaSO4 2H2O). However, the high concentrations of sulphate in the effluents from the LKAB Kiruna operation are unique for iron ore mining.    The aim of the thesis was to study and evaluate the behavior of sulphate in the process water system of the Kiruna concentrator plants. This was done by laboratory grinding (leaching tests), equilibrium calculations with the HSC software and mass balancing of the concentrator KA3 in Kiruna. The highest concentrations of sulphate have been detected in the process water of KA3, hence the focus has been on KA3 regarding sampling, evaluation and comparison. Water treatment technologies for sulphate and the effect of process water on ore processing have not been included in this project.   The laboratory grinding was done using process water and ore from the concentrator KA3. During the experimental work with laboratory grinding the parameters pH, temperature and operating times for primary- and secondary grinding, respectively, were varied. The observations from the experimental work were further confirmed by equilibrium calculations and mass balancing. The following conclusions were drawn.     Anhydrite/gypsum is not leached from the ore during ore processing with process water having concentrations of sulphate already close to the saturation point at approximately 1800 mg/L. If the process water is diluted with water with lower sulphate content, e.g. mine water or a diluted return water from the pond system (e.g. during spring flood), anhydrite/gypsum in ore will be dissolved until the sulphate concentration reaches the saturation point. The ionic strength of the process water controls the saturation point and thus the sulphate concentration. Leaching of anhydrite/gypsum in saturated process water, with respect to sulphate, is not affected by grinding time or adjusted conditions in the process water, such as temperature or pH value.    For further work, it is recommended to investigate the behavior of sulphate in the tailings pond system to increase knowledge of the overall behavior in the water system. In addition, a similar investigation of the behavior of uranium in the process water is recommended in order to face future environmental standards.

Enhancing mineral processing techniques is a permanent challenge in the mineral and metal industry. Indeed to satisfy the requirements on the final product (metal) set by the consuming market, control is often applied on the mineral processing whose product, the ore concentrate, constitutes the input material of the extractive metallurgy. Therefore much attention is paid on mineral processing units and especially on concentration plants. As the ore size reduction procedure is the critical step of a concentrator, it turns out that controlling a grinding circuit is crucial since this stage accounts for almost 50 % of the total expenditure of the concentrator plant. Moreover, the product particle size from grinding stage influences the recovery rate of the valuable minerals as well as the volume of tailing discharge in the subsequent process.

The present thesis focuses on an industrial application, namely the Kolwezi concentrator (KZC) double closed-loop wet grinding circuit. As any industrial wet grinding process, this process offers complex and challenging control problems due to its configuration and to the requirements on the product characteristics. In particular, we are interested in the modelling of the process and in proposing a control strategy to maximize the product flow rate while meeting requirements on the product fineness and density.

A mathematical model of each component of the circuit is derived. Globally, the KZC grinding process is described by a dynamic nonlinear distributed parameter model. Within this model, we propose a mathematical description to exhibit the increase of the breakage efficiency in wet operating condition. In addition, a relationship is proposed to link the convection velocity to the feed ore rate for material transport within the mills.

All the individual models are identified from measurements taken under normal process operation or from data obtained through new specific experiments, notably using the G41 foaming as a tracer to determine material transport dynamics within the mills. This technique provides satisfactory results compared to previous studies.

Based on the modelling and the circuit configuration, both steady-state and dynamic simulators are developed. The simulation results are found to be in agreement with the experimental data. These simulation tools should allow operator training and they are used to analyse the system and to design the suitable control strategy.

As the KZC wet grinding process is a Multi-Input Multi-Output (MIMO) system, we propose a decentralized control scheme for its simplicity of implementation. To overcome all the control issues, a Double Internal Model Control (DIMC) scheme is proposed. This strategy is a feedforward-feedback structure based on the use of both a modified Disturbance Observer (DOB) and a Proportional-Integral Smith-Predictor (PI-SP). A duality between the DOB and PI-SP is demonstrated in design method. The latter is exploited to significantly simplify the design procedure. The designed decentralized controllers are validated in simulation on the process linearized model. A progressive implementation of the control strategy is proposed in the context of the KZC grinding circuit where instrumentation might not be obvious to acquire./

Améliorer les techniques de traitement de minerais est un défi permanent dans l'industrie des minéraux et des métaux. En effet, pour satisfaire aux exigences du produit fini (métal ) fixées par le marché de consommation, la commande automatique est souvent appliquée à l'usine du traitement de minerais dont le produit, le concentré, constitue la matière première de la métallurgie extractive. Une attention particulière est donc dévolue aux unités de traitement de minerais et en particulier aux concentrateurs. Comme le processus de réduction des dimensions granulométriques du minerai est l'étape critique d'un concentrateur, il s'avère que la commande d'un circuit de broyage est cruciale, car ce stade représente près de 50 % des dépenses totales de l' usine de concentration. De plus, la dimension granulométrique du produit de l'étape de broyage influe sur le taux de récupération des minéraux utiles ainsi que sur le volume des rejets du processus ultérieur.

La présente thèse porte sur une application industrielle, à savoir le concentrateur de Kolwezi (KZC qui est un circuit de broyage humide à double boucle fermée. Comme tout processus industriel de broyage humide, ce procédé présente une problématique de commande complexe et difficile en raison de sa configuration et des exigences relatives aux caractéristiques du produit. En particulier, nous nous intéressons à la modélisation de ce procédé et à proposer une stratégie adéquate de commande dans le but de maximiser le débit de production tout en respectant les exigences quant à la finesse et à la densité de la pulpe produite.

Un modèle mathématique de chaque composant du circuit a été déterminé. Globalement, le processus de broyage de KZC est décrit par un modèle dynamique non linéaire à paramètres distribués. Dans ce modèle, une description mathématique de l'augmentation de l'efficacité du broyage en milieu humide est proposée. En outre, nous avons proposé une relation liant la vitesse de convection au débit d'alimentation de minerais dans le modèle du transport de la matière à l'intérieur des broyeurs.

Tous les modèles mathématiques ont été identifiés à partir de mesures prises sur le procédé en fonctionnement d'équilibre stable ou à partir des données obtenues grâce à des nouvelles expériences spécifiques, notamment en utilisant le moussant G41 comme traceur pour déterminer la dynamique de transport de la matière dans les broyeurs. Cette technique a produit des résultats cohérents par rapport aux études antérieurs réalisées au moyen du traceur colorant ou radioactif.

Les simulateurs statique et dynamique ont été développés sur la base de la modélisation mathématique et de la configuration du circuit. Les résultats des simulations sont en accord avec les données expérimentales. Ces outils de simulation devraient permettre la formation des opérateurs et ont été utilisés pour analyser le système et concevoir la stratégie de commande la plus appropriée.

Comme le processus de broyage humide de KZC est un système à plusieurs grandeurs d'entrée et plusieurs grandeurs de sortie, nous avons proposé une structure de commande décentralisée en raison de sa simplicité de mise en œuvre .Afin de surmonter tous les problèmes de commande, un schéma de commande à double modèle interne (CDMI) est proposée. Cette stratégie est une structure à anticipation - rétroaction basée sur l'utilisation d'un observateur de perturbations (OBP) et d'un Prédicteur de Smith doté d'un régulateur Proportionnel-Intégral (PS-PI). Une dualité entre l'OBP et le PS-PI est démontrée dans la méthode de conception. Cette propriété est exploitée pour simplifier considérablement la procédure de conception. Les régulateurs décentralisés ainsi conçus sont validés en simulation sur le modèle linéarisé du procédé. Une mise en œuvre progressive de la stratégie de commande est proposée dans le contexte du circuit de broyage de KZC où l'instrumentation peut ne pas être évidente à acquérir.

Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

In der Erzindustrie findet ein Umdenken statt. Der Einsatz der bewährten aber energieineffizienten Sturzmühlen zur Mittel- und Feinzerkleinerung wird hinterfragt. In der Zementindustrie hat bereits ein vergleichbarer Technologiewandel stattgefunden. In diesem Bereich haben sich vor allem Wälzmühlen auf Grund ihrer Vorteile durchgesetzt. Diese Maschinen stellen auch für die Mahlung von Erzen eine Alternative zu konventionellen Sturzmühlen dar. In der Dissertation werden die Ergebnisse von systematisch durchgeführten Mahlversuchen mit einer Wälzmühle im Pilotmaßstab vorgestellt. Ziel der Untersuchungen mit drei verschiedenen Erzen war es den Einfluss ausgewählter konstruktiver und betrieblicher Parameter auf wichtige Zielgrößen wie Produktfeinheit, Energiebedarf und Verschleiß mit Hilfe von Regressionsmodellen zu quantifizieren und damit die Grundlage für eine Optimierung der Mahlanlage für den neuen Anwendungsbereich zu schaffen.

Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.13.07 – Автоматизація процесів керування. Національний гірничий університет. Дніпропетровськ, 2010
Диссертация на соискание ученой степени кандидата технических наук по специальности 05.13.07 – автоматизація процессов управления. Национальный горный університет. Днепропетровск, 2010
Dissertation on scientific degree of Candidate of Technical Science on specialty 05.13.07 – Automation of processes of commanded. – National Mining University, Dnipropetrovsk, 2010
Дисертація присвячена вирішенню актуальної науково-технічної проблеми автоматичного контроля ступеня здрібнення руди в технологічних комплексах флотаційного та магнітного збагачення на основі встановлення нових закономірностей розділення та кореляції продуктів здрібнення руди у робочих зонах збагачувальних апаратів та використання промислових флотаційних машин та магнітних сепараторів як природних аналізаторів ступеня здрібнення руди. Науково обґрунтовані функціонально-алгоритмічні структури та технічні вимоги до систем автоматичного контролю ступеня здрібнення руди та до систем автоматичного управління технологічними комплексами флотаційного та магнітного збагачення. Результати роботи впроваджені в проект і можуть бути використані на флотаційних та магнітозбагачувальних фабриках руд кольорових та чорних металів.
Решена актуальная научно-техническая задача научного обоснования метода автоматического контроля степени измельчения руд черных и цветных металлов, а именно недоизмельчения, оптимального измельчения и переизмельчения руд при их обогащении на основании косвенной оценки степени раскрытия минералов, что позволило разработать функционально-алгоритмические структуры систем автоматической оптимизации процессов измельчения и классификации руд, повышающие эффективность процесса обогащения. Это позволило повысить извлечения металлов в концентраты, повысить металлургическую ценность концентратов руд черных и цветных металлов. Предложен новый критерий оптимизации процессов измельчения и классификации руды – минимум коэффициента корреляции между массовыми долями металла в концентрате и хвостах обогатительного аппарата, который предложено использовать в качестве анализатора раскрытия руды. Получены новые уравнения регрессии связующие критерии эффективности разделения при обогащении руд и коэффициент корреляции между массовыми долями металла в концентрате и хвостах обогатительного аппарата, что позволяет обосновать новый критерий автоматической оптимизации процессов рудоподготовки и обогащения руд. Научно обоснованы технические требования к функционально-алгоритмическим структурам систем автоматического контроля и оптимизации крупности помола руды в цикле измельчения и классификации, что позволяет повысить извлечение металлов в концентраты руд черных и цветных металлов и их металлургическую ценность. Разработана система автоматического контроля массовой доли железа в хвостах магнитного сепаратора, которая прошла экспериментальные исследования в промышленных условиях. Точность контроля массовой доли железа составила менее 5%относительных единиц. Разработана система автоматического контроля степени измельчения железной руды, построенная на базе промышленного магнитного сепаратора. Выполнены сравнительные экспериментальные исследования системы автоматической оптимизации технологического комплекса флотационного обогащения медной руды в условиях горно-металлургического комбината «Эрдэнэт». Сравнивалась эффективность двух критериев оптимизации: максимальная производительность по готовому (– 0,074 мм) классу крупности продукта измельчения и предлагаемый критерий косвенной оценки раскрытия руды – минимум коэффициента корреляции между массовыми долями металла в концентрате и хвостах. Предложенный критерий оптимизации позволил повысить извлечение меди в концентрат на 6,07%, а извлечение молибдена на 10,09%. Выполнены сравнительные испытания предложенной автоматизированной системы автоматической оптимизации цикла измельчения железных руд по критерию минимума коэффициента корреляции между массовыми долями железа в концентрате и хвостах с системой автоматического регулирования массовой доли железа в концентрате магнитного сепаратора в условиях Лебединского ГОКа. Предложенная система повысила извлечение железа в концентрат на 7,2% относительных единиц и качество концентрата на 2,19%.
The dissertation is devoted to solving actual scientific problem of increasing efficiency of automated control of degree of ore grinding for optimizing of teсhnological complexes of flotation and magnetic concentration of ore by using industrial magnetic separator and flotation machine as technical means of automation and establishing new regularites of separation in working zones of separator. Technical requirement to the systems of automated control and optimization of technological complexes of flotation and magnetic concentration are established. Functional schemes of the systems of automated control and optimization of technological complexes of concentration are suggested. The results of experimental researches the systems of automated control and optimization have shown their efficiency.

The grinding models developed previously are concerned with size reduction only. Although they have proven to be useful in the simulation and design of grinding mills, they do not provide information on liberation which is the main objective of most comminution operations. In the present investigation, a population balance model describing the combined processes of size reduction and mineral liberation has been developed for batch grinding operation. The model parameters include conventional breakage rate and breakage distribution functions, along with a new parameter i.e., liberation function that is used to describe changes in particle composition. These parameters have been determined experimentally by examining mill products under optical microscope using a SEM-IPS image analyzer. The areal assays, obtained from the image analysis of monosized particle mounts, have been found to correspond quite closely to the actual chemical assays. It has been found that the method used to prepare particle mounts is critical in achieving accuracy. In the present work, it has been shown that the breakage characteristics of component minerals can be determined by examining the mill feeds and products using an image analyzer. The model parameter analysis has shown that while the breakage rate functions are sensitive to the grinding environment, breakage distribution functions are independent of it. Furthermore, the breakage distribution functions have been found to be normalizable with feed size, thus reducing the number of parameters that must be estimated. The study has also shown that both the breakage rate and the liberation function suggest a preferential breakage of sphalerite over dolomite gangue. The model has been validated by simulating the batch grinding of a sphalerite ore from ASARCO's Young Mine in eastern Tennessee. The model can predict the product size distributions for the total ore and its components, including gangue, sphalerite, and composite particles. An excellent agreement between the model predictions and the experimental results has been observed for both monosized and multisized feed materials. The model is capable of handling multiple classes of composite particles for a binary ore; however, the model has been verified against experimental results by considering only two composite classes. The method of determining liberation functions has also been discussed. The liberation function has been found to be useful for analyzing the liberation mechanisms of composite particles.
Ph. D.

The aim of this thesis is to design a one-purpose machine for grinding concrete light-permeable bricks LiCrete. The bricks LiCrete are a new interior design component. The final step of manufacturing is wet grinding with high quality and accuracy. At the same time it is grinded the concrete and light-permeable parts made by polymethylmethacrylate (PMMA). It is important to keep size and quality appearance of the bricks. The research part contains description of the problems related to the grinding of the bricks LiCrete. The next part is about conceptual variants of the solution. The construction contains the complex solution of one-purpose machine with technical drawings. The last part include a conceptual design of continuous high-productive machine for grinding LiCrete bricks.

Les matières colorantes sont des vestiges encore mal connus de nos jours. L'intérêt qu'elles suscitent tient à ce qu'elles sont susceptibles de révéler des pratiques techniques diverses et complexes, mais il tient aussi à leur forte potentialité à traduire des pratiques symboliques du fait de leur pouvoir colorant intense et des couleurs exploitées : le rouge et le noir qui sont encore aujourd'hui investis d'une forte valeur symbolique. Dans un contexte aussi particulier que celui de la transition entre le Paléolithique moyen et le Paléolithique supérieur, ces vestiges ont été mis au jour en abondance et demandent à être analysés pour restituer les modes de vie des derniers hommes de Neandertal. C'est sur le gisement châtelperronien de la grotte du Renne à Arcy-sur-Cure (Yonne), fouillé de 1949 à 1963 par André Leroi-Gourhan, que les nombreuses matières colorantes découvertes ont conduit à échafauder des théories concernant leurs transformations et leurs utilisations qui méritaient d'être éprouvées. En effet, il est supposé, depuis leur découverte, qu'elles ont fait l'objet d'un chauffage contrôlé qui visait à en modifier la couleur, le chauffage permettant de transformer les matières colorantes jaunes en orangées, en rouges et en violacés. De cette hypothèse découle la théorie selon laquelle les Néandertaliens ont exploité les matières colorantes en tant que pigment pour des réalisations symboliques, voire d'ordre esthétique, ce qui n'a pas encore pu être prouvé. Notre étude, fondée sur le croisement des données issues des analyses de la nature physico-chimique et pétrographique des assemblages de matières colorantes, mais aussi sur leur intégration dans le gisement, en association avec des structures d'habitat dont la conservation est exceptionnelle, et sur une série d'expérimentations visant à caractériser les poudres obtenues par différents moyens (broyage et concassage d'une part, abrasion d'autre part) ont permis de définir les choix techniques qui ont présidé à l'approvisionnement en matières colorantes dans tous les niveaux d'occupation châtelperroniens de la grotte du Renne. Il a ainsi été possible de démontrer qu'aucune des matières colorantes, rouges ou noires, n'a fait l'objet d'un chauffage préalablement à son utilisation, bien au contraire de ce qui avait été supposé jusqu'ici. Ces matières colorantes ont fait l'objet d'un approvisionnement raisonné auprès de formations géologiques affleurant ponctuellement à plus de 10~km et à environ 5~km de la grotte. L'exploitation de ces gîtes de matières premières colorantes a été la même durant toute la séquence châtelperronienne et s'est orientée préférentiellement vers des matériaux que l'on peut aisément réduire en poudre. Une partie était grossièrement réduite en poudre afin de recouvrir de grandes surfaces (sols, peaux de bêtes) dans le but de les assainir, alors qu'une autre partie des matières colorantes était destinée à des activités plus minutieuses nécessitant leur emploi sous forme d'une poudre fine, régulière et extrêmement colorante. Dans ce dernier cas, les Néandertaliens de la grotte du Renne ont entrepris d'exploiter ces produits en association avec le travail des matières osseuses (os et ivoire de mammouth) mais aussi pour leur couleur. L'assemblage des matières colorantes de la grotte du Renne révèle un profond ancrage des connaissances et de la compréhension des multiples propriétés et qualités des matières colorantes intensément mises à profit de telle sorte que le gisement châtelperronien était tout de rouge et noir et la chaîne opératoire qu'il été possible de restituer relève d'inventions techniques abouties, très élaborées dans leur genre pour l'état des observations ingénieuses, des découvertes et donc de la pensée qu'elles supposent et des capacités dont elles témoignent
Despite an increasing number of studies, colouring materials are still poorly understood among excavation remains. Their attraction lies in their capacity to bring to light diverse and complex skills, but also in their intense colouring power and their contrasting colours: red and black, which still possess a symbolic value. These highly-symbolic materials may, therefore, highlight the “conceptual” practices of prehistoric men and give access to their symbolic world and thought. In such a particular context as the transition between the Middle and the Upper Palaeolithic, these remains, which are very abundant in most excavations, offer the possibility, through analysis, to get an exceptional insight into the way of life of the last Neanderthals. The Châtelperronian site of the “Grotte du Renne”, in Arcy-sur-Cure (Yonne), is a landmark. It was excavated beween 1949 and 1963 by André Leroi-Gourhan: Numerous colouring materials were discovered there, and Leroi-Gourhan developed theories about their transformation and uses which so far have not been tested, and have remained unchallenged. Since their discovery, the assumption is that those minerals were heated in a controlled way, in order to modify their colour. It is indeed well-known that heat transforms yellow materials (iron oxides) in orange, red or purple materials (other iron oxides). From this hypothesis originates the theory according to which Neanderthals exploited colouring materials as pigments for symbolic or even aesthetic purposes. But the theory has so far never been proved true. Our study combines several sets of data, obtained from different methods. Physico-chemical and petrological analyses were carried out on the colouring materials. These data were related to their location on the site, in association with exceptionally well preserved “hut” structures. Furthermore, a series of experimentations, aimed to characterize powders obtained via different methods (grinding and crushing on the one hand, abrasion on the other hand). The comparison of all these data enabled us to identify the various technical choices which informed the supply in colouring minerals in all the Châtelperronian levels of the Grotte du Renne. It was thus possible to demonstrate that none of these materials, either red or black, was heated before being used, contrary to what had been assumed so far. The supply in colouring materials was as carefully organised as for other materials (flint, for example); they were collected in geological formations occasionally showing on the surface, at more than 10 km from the cave. The exploitation of these geological sites did not vary during the whole Châtelperronian period, and privileged materials which can easily be ground into powder. Part of their supply was ground coarsely in order to cover large surface areas (soils or hides) as preservative or to clean them up. The remaining materials were destined to more meticulous activities, which required a fine, regular, and highly-colouring powder. In this latter case, the Neanderthals of the Grotte du Renne used those products when working on bone materials (bone or mammoth ivory), and used them also for their sheer colour. The set of colouring minerals from the Grotte du Renne reveals Neanderthals’ in-depth knowledge of materials; they understood perfectly well their properties and qualities, and used them extensively, so that the Châtelperronian site must have been a literally dazzling sight, all red and black. The “chaîne opératoire” which transpires from our analysis shows very sophisticated techniques, and an advanced “technological” knowledge. They are witness to surprising capacities and a highly-evolved pattern of thought. Keywords: Colouring materials; Ochre; Haematite; Manganese; Middle/Upper Palaeolothic transition; Châtelperronian; Arcy-sur-Cure; Grotte du Renne; Heating; Grinding; Skhul; Les Maîtreaux; Combe Saunière

A grinding mill circuit forms a crucial part in the energy-intensive comminution process of extracting valuable metals and minerals from mined ore. The ability to control the grinding mill circuit is of primary importance to achieve the desired product specification with regards to quality and production rate. In order to achieve control objectives an accurate dynamic model of the milling circuit is required. Phenomenological models are preferred over linear-time-invariant models since the latter cannot describe the non-linear behaviour of the process. However, the available phenomenological models of grinding mill circuits are usually complex, use large parameter sets and are mostly aimed towards steady-state design of grinding mill circuits. This study investigates simplified non-linear dynamic models of grinding mill circuits suitable for process controller design. In the first part of this study, the number of size classes in a cumulative rates model of a grinding mill circuit is reduced to determine the minimum number required to provide a reasonably accurate model of the circuit for process control. Each reduced size class set is used to create a non-linear cumulative rates model which is linearized to design a linear model predictive controller. The accuracy of a model is determined by the ability of the corresponding model predictive controller to control important process variables in the grinding mill circuit as represented by the full non-linear cumulative rates model. The second part of the study validates a simple and novel non-linear model of a run-of-mine grinding mill circuit developed for process control and estimation purposes. This model is named the Hulbert-model and makes use of the minimum number of states and parameters necessary to produce responses that are qualitatively accurate. It consists of separate feeder, mill, sump and hydrocyclone modules that can be connected to model different circuit configurations. The model uses five states: rocks, solids, fines, water and steel balls. Rocks are defined as too large to be discharged from the mill, whereas solids, defined as particles small enough to leave the mill, consist of out-of-specification coarse ore and in-specification fine ore fractions. The model incorporates a unique prediction of the rheology of the slurry within the mill. A new hydrocyclone model is also presented. The Hulbert-model parameters are fitted to an existing plant’s sampling campaign data and a step-wise procedure is given to fit the model to steady-state data. Simulation test results of the model are compared to sampling campaign data of the same plant at different steady-state conditions.
Dissertation (MEng)--University of Pretoria, 2012.
Electrical, Electronic and Computer Engineering
unrestricted

In this study, the effect of speed was investigated on the breakage rate of UG2 platinum ore in a batch mill of 5 dm3 and 175 mm internal diameter. One size fraction method was carried out to perform the experiment. Five mono-sized fractions in the range of 1.180 mm to 0.212 mm separated by √2 series interval were prepared. The fractions were milled at different grinding times (0.5, 2, 4, 15 and 30 min) and three fractions of mill critical speed were considered (20%, 30%, and 40%). The target of critical speed below 50% was due to the need of lower energy consumption in milling processes. The selection and breakage function parameters were determined and compared for fractions of critical speed. First the grinding kinetics of the ore was determined and it was found that the material breaks in non-first order manner. Thereafter, effective mean rate of breakage was determined. It was found that the rate of breakage increased with increase of mill speed and optimum speed was not reached in the range of chosen mill speed fractions. Again the rate of breakage was plotted as a function of particle size, the optimum size was 0.8 mm when milling at 30% critical speed. As for 20% and 30% optimum size was not reached. The selection function parameters estimated at 30% critical speed were 𝑎0 = 0.04 min−1 , 𝛼 = 1.36, 𝜇 = 0.9 mm, and Λ = 3. Breakage function parameters were determined and was noticed that the material UG2 platinum ore is non-normalised, i.e. Φ value was changing from 0.25 to 0.90 depending on feed size and mill speed. The parameters 𝛽 and 𝛾 were constant at 7.3 and 1.17 respectively.
College of Science, Engineering and Technology
M. Tech. (Chemical Engineering)

A run-of-mine ore milling circuit is primarily used to grind incoming ore containing precious metals to a particle size smaller than a specification size. A traditional run-of-mine (ROM) ore single-stage closed milling circuit comprises of the operational units: mill, sump and cyclone. These circuits are difficult to control because of significant nonlinearities, large time delays, large unmeasured disturbances, process variables that are difficult to measure and modelling uncertainties. A nonlinear model predictive controller with state estimation could yield good control of the ROM ore milling circuit despite these difficulties. Additionally, the ROM ore milling circuit is an energy intensive unit and a controller or power optimizer could bring significant cost savings. A nonlinear model predictive controller requires good state estimates and therefore a neural network for state estimation as an alternative to the particle filter has been addressed. The neural network approach requires fewer process variables that need to be measured compared to the particle filter. A neural network is trained with three disturbance parameters and used to estimate the internal states of the mill, and the results are compared with those of the particle filter implementation. The neural network approach performed better than the particle filter approach when estimating the volume of steel balls and rocks within the mill. A novel combined neural network and particle filter state estimator is presented to improve the estimation of the neural network approach for the estimation of volume of fines, solids and water within the mill. The estimation performance of the combined approach is promising when the disturbance magnitude used is smaller than that used to train the neural network. After state estimation was addressed, this work targets the implementation of a nonlinear controller combined with full state estimation for a grinding mill circuit. The nonlinear controller consists of a suboptimal nonlinear model predictive controller coupled with a dynamic inversion controller. This allows for fast control that is asymptotically stable. The nonlinear controller aims to reconcile the opposing objectives of high throughput and high product quality. The state estimator comprises of a particle filter for five mill states as well as an additional estimator for three sump states. Simulation results show that control objectives can be achieved despite the presence of noise and significant disturbances. The cost of energy has increased significantly in recent years. This increase in price greatly affects the mineral processing industry because of the large energy demands. A run-of-mine ore milling circuit provides a suitable case study where the power consumed by a mill is in the order of 2 MW. An attempt has been made to reduce the energy consumed by the mill in the two ways: firstly, within the nonlinear model predictive control in a single-stage circuit configuration and secondly, running multiple mills in parallel and attempting to save energy while still maintaining an overall high quality and good quantity. A formulation for power optimization of multiple ROM ore milling circuits has been developed. A first base case consisted not taking power into account in a single ROM ore milling circuit and a second base case split the load and throughput equally between two parallel milling circuits. In both cases, energy can be saved using the NMPC compared to the base cases presented without significant sacrifice in product quality or quantity. The work presented covers three topics that has yet to be addressed within the literature: a neural network for mill state estimation, a nonlinear controller with state estimation integrated for a ROM ore milling circuit and power optimization of a single and multiple ROM ore milling circuit configuration.
Dissertation (MEng)--University of Pretoria, 2015.
Electrical, Electronic and Computer Engineering
Unrestricted

A study was carried out to improve the flotation selectivity between galena and sphalerite during the flotation of a Cu-Pb-Zn sulphide composite ore from the Rosh Pinah Mine (Namibia). Xanthate collectors were found to be unselective for the flotation of the Rosh Pinah composite sample. It was observed that the recovery of sphalerite increased with both the recovery of galena and the concentrate mass pull. In addition, the recovery of sphalerite increased after activation with Cu(II) ions while that of galena decreased when the composite was dry ground in a mild steel mill with mild steel grinding media. However, the recovery of galena was not affected after wet milling in a stainless steel mill. The recovery of Cu(II)-activated sphalerite was independent of the milling environment (wet or dry) and grinding media. The activation of sphalerite by cuprous cyanide complexes, which are present in the recycled water, was clearly shown in this study. Both batch flotation tests and XPS analysis have confirmed that sphalerite was activated by copper(I) from the cuprous cyanide complexes. The recovery of copper(I)-activated sphalerite increased further when the composite was dry milled as compared to wet milling. Batch flotation tests have shown that the use of cyanide alone is not efficient for the depression of sphalerite due to the mineralogical texture of the Rosh Pinah ore. A large quantity of galena locked and/or attached to sphalerite was observed in the lead concentrate. Their prevalence increased with increasing particle size. The use of both cyanide and zinc sulphate improved the depression of sphalerite much better than cyanide alone. A flowsheet has been proposed to improve selectivity between galena and sphalerite in the lead flotation circuit. It includes the regrinding of the lead rougher concentrate prior to the cleaning stage due to poor liberation between galena and sphalerite.
Thesis (PhD (Metallurgical Engineering))--University of Pretoria, 2006.
Materials Science and Metallurgical Engineering
unrestricted