Dynamic Modeling and Simulation of SAG Mill Circuits with Pebble Crushing

Grinding is one of the most energy-consuming processes in the mining industry. As a critical part of the comminution process, autogenous grinding (AG) or semi-autogenous grinding (SAG) mills are often used for primary grinding. However, the breakage mechanism of an AG/SAG mill is inefficient in grinding particles of a certain size, typically in the range of 25-55 mm, i.e., pebbles. Therefore, cone crushers are often used as pebble crushers and integrated into AG/SAG mill circuits to break the critical size particles that accumulate in the mill and to increase the performance of the primary grinding circuits.Many studies have been carried out, mainly focusing on optimizing of SAG mills and cone crushers, respectively, but only a few have investigated the dynamic interactions between a SAG mill and its pebble crushers. The scope of this thesis is to examine the dynamic relations between the SAG mill and the pebble crusher in a closed circuit and thus to optimize the circuit efficiency by controlling the pebble crusher operational settings.In this thesis, two modeling techniques are proposed for simulating the dynamics in the grinding process. The first method is the fundamental modeling method, where the underlying physics of the comminution process has been considered. The proposed mill model is divided into sub-processes that include breakage behavior in each sub-division, particle transportation within the mill chamber, and the discharge rate from the mill. The dynamic cone crusher model describes the crusher chamber as a surge bin and predicts the product particle sizes based on crusher CSS and eccentric speed. In the simulation model, other production units such as screens and conveyors are included to describe the dynamics of the circuit better. The flexibility of this method allows one to apply this simulation library to a variety of plants with different configurations.The second modeling technique presented in this study is based on data-driven methods, where two SAG mill power models are developed. The first model calculates the mill power draw by combining several individual data-driven algorithms. The second model uses historical data to forecast the mill power draw in advance. These data-driven methods can make high accuracy predictions based on a specific plant dataset, and find complex nonlinear relations between input variables and target outputs.The results from both simulations and industrial data analysis show that significant dynamic impact can be induced by altering the pebble crusher operational settings. Therefore, the performance (throughput or specific energy) of an AG/SAG closed circuit can be improved with the optimized utilization of its recycle pebble crusher. While the present work is based on simulation and analysis of plant data, full-scale tests and further model development are needed as part of a future study

Optimization and performance of grinding circuits: the case of Buzwagi Gold Mine (BGM)

Buzwagi Gold Mine (BGM) is operated by Acacia Mining and located in the Lake Victoria Goldfields of central Tanzania. The mine commenced its operation since April 2009 and treats a sulphide copper-gold ore to produce gold in form of doré bars and a concentrate containing gold, copper and silver. The BGM comminution circuit includes a primary crushing stage with a gyratory crusher and a two grinding circuits using a Semi-Autogenous Grinding (SAG) mill and a ball mill. The SAG mill circuit also includes a single-deck screen and a cone crusher while the ball mill circuit utilizes hydrocyclones. Currently, the grinding circuits are inefficient in achieving the aspired product fineness of xP,80 = 125 μm even at low to normal throughputs (450-600 t/h). An evaluation and optimization study of the circuit performance was conducted to improve the product fineness through circuit surveys, experimental lab work and simulations. In three full scale sampling campaigns, size distributions and solids contents of the samples were determined at selected points in the circuit. Further, several types of breakage tests were conducted; standard Bond tests to determine ore grindability and work indices, batch grinding tests to determine parameters for breakage and selection functions , and standard ball mill tests for mineral liberation characterization by an automated mineral liberation analyzer (MLA).The tests were conducted in a size range from 0.063 to 2 mm. Then, mass balance of the circuit was calculated and the models for mills, screens and hydrocyclones were employed in MODSIM (version 3.6.24). Firstly, simulations were conducted to optimize the existing plant. Several options were evaluated such as reduction of SAG screen aperture, adjustment of cyclone feed solids content and reduction of vortex finder and apex diameters. Moreover, simulations were also evaluated for a possible modification of the existing circuit and include; partial splitting of the cyclone underflow back to SAG mill, introduction of a second classification stage as well as introduction of a second ball mill. The evaluation of breakage tests and survey data revealed the following; the Bond work index obtained for the current ore ranges between 17.20 - 18.70 kWh/t compared to 14.50 - 16.50 kWh/t which was estimated during plant design.This indicates a change in hardness of the ore during the last 7 years. Harder ore means more energy requirement for an efficient operation, the consequence of which is increased costs. Thus, a periodic review of the ore hardness for ongoing mining operation is recommended. This will help in establishing better blends as well as prediction of appropriate tonnages for the existing ore types, so as to be efficiently treated by the available plant design. The work indices of the ore blends treated during survey were correlated with their quartz content and showed a strong linear relationship (R2= 0.95). Therefore, the work index for the BGM ore could be predicted based on known quartz content of the material. Further, the model could be used as a control tool for monitoring hardness variation of the SAG mill feed. The mineral liberation studies indicated that the valuable phase (pyrite-pyrrhotite) could be liberated at relatively coarser particle sizes (200-400 µm). This implies that, there could be no problem with the efficiency of the gravity circuit for the BGM operation, where the gold contained in pyrite-pyrrhotite could be easily concentrated. However, the efficiency of flotation and cyanidation processes will still require finer feed. In overall, the liberation characteristics of the ore blends treated during survey showed minor differences. The Bond efficiency factors of 48-61 % were obtained for the BGM grinding circuit, indicating an inefficient operation. This suggests that the operation could achieve targets by lowering the throughput. Further, the SAG mill circuit was characterized by fluctuating feed size of between xF,80 =102 to 185 mm. A need for control of the feed size as well as blending ratios was recommended for an efficient operation in terms of throughput and final product size. This could be achieved through closer monitoring of the primary crusher performance and proper control of the ratios for the SAG mill feeders drawing the ore from the stockpile. The ball mill grinding efficiency was poor and could be indicated by the fraction 400 µm in the mill discharge. This was deemed due to poor hydrocyclone performance which was characterized by higher feed solids content, coarser overflow xP,80: >200 µm as well as cut sizes, xT : > 200 µm. An improvement of product fineness up to 327 µm could be achieved during the simulation and optimization of the existing design. This could be achieved by modification of the operating conditions such as reduction of SAG screen aperture from 12 mm to 10 mm, reduction of vortex finder from 280 mm to 270.3 mm, reduction of apex diameter from 150 mm to 145.6 mm as well as adjustment of the cyclone feed solids content from 66.7 to 67.1 %. Based on this result, it was concluded that the current equipment could not achieve the target product quality (i.e. xP,80 = 125 µm ). Further simulations based on flowsheet modification options showed that a second ball mill (series configuration) can help to achieve the desired product fineness as well as an increase of throughput from 618 t/h to 780 t/h. Although the circulating load increases to approximately 500 % in this configuration, it is outweighed by the benefits. Importantly, this option is cost intensive and hence may be considered as a long term solution and especially after cost-benefit analysis. Finally, the results based on optimization of the existing design is recommended as short term solution for improvement of the BGM operation. Although the fineness achieved is still low (i.e. xP,80 = 327 µm) compared to the target (i.e. xP,80 = 125 µm), this gives additional advantage in the sense that, also better hydrocyclone performance is achieved in terms of overflow product (xP,80 = 105 µm vs. > 240 µm) , cut size (xT =133.1 µm vs. > 220 µm) and circulating load (CL =350 %). The improved overflow fineness will contribute to improved efficiency for the downstream processes

PBM and DEM simulations of large-scale closed-circuit continuous ball mill of cement clinker

Cement milling is known to be inefficient and energy-intensive. Thus, even small improvements in cement milling\u27s performance could significantly reduce operation costs. This dissertation aims to develop a simulation tool for dry milling and generate a fundamental process understanding, which enables process optimization. To this end, a true unsteady-state simulator (TUSSIM) for continuous dry milling is developed and applied to model various processes: (a) open circuit continuous mills, (b) closed-circuit continuous mills, and (c) vertical roller mills. TUSSIM is based on the solution of the cell-based population balance model (PBM) for continuous milling, which consists of a set of differential algebraic equations (DAEs). Moreover, air classifier parameters and ball size distribution for the closed-circuit operation are tailored to maximize production capacity while achieving desirable cement product qualities. Discrete element method (DEM) and PBM are coupled to simulate lab-scale batch milling of cement clinker to gain fundamental understanding of the roles of ball size and material (steel vs. alumina). First, dynamic simulations are performed to investigate the impact of ball mill operation parameters on the full-scale open-circuit ball milling of cement clinker without an external air classifier. Parameters for the simulation are taken from the literature. Simulation results suggest that a single-compartment mill produces the desired cement size, but it requires pre-milled fresh feed. Depending on the ball sizes used, a two compartment mill produces cement sizes similar to those produced by a three-compartment mill. A uniform mass of balls achieves an 8% higher specific surface area (SSA) compared to a uniform number of balls. The classifying liners have negligibly finer cement products compared to a uniform mass distribution. TUSSIM is also incorporated with a variable Tromp curve model for classification to simulate full-scale closed-circuit ball milling with an air classifier. The simulation results suggest that a faster rotor speed or lower air flow rate leads to a finer cement product and increases the dust load of the classifier feed. Integrating air classifiers into open-circuit ball milling increases the production rate by 15% or cement SSA by 13%. Operation failure due to overloading of the entire circuit is detected when dust load is too high. Process optimization with a global optimizer?DAE solver is performed to identify either the air classifier\u27s parameters or the ball size distributions that yield desirable cement quality while maximizing production rate. Optimization results show that the production rate can be increased by 7% compared to the baseline process. Unlike open circuits, a two-compartment mill produces a finer cement product than a three-compartment mill. Optimal ball mixtures are identified in a two-compartment mill, suggesting a 14% increase in production rate at a desirable cement quality. A global optimizer-based back-calculation method, based on PBM, is used to determine the breakage kinetics parameters of cement clinker in a lab-scale ball mill loaded with steel or alumina balls of three single ball sizes and their mixtures. The motion of the balls in the mill is simulated via the DEM. The results show that steel balls achieve faster breakage of clinker than alumina balls, which is explained by the higher total?mean energy dissipation rates of the steel balls. The particle size distribution (PSD) becomes finer as smaller balls are used. The ball mixture is the most effective overall. Significant energy can be saved if steel balls are replaced with alumina balls, but the slower breakage with the alumina balls needs to be accounted for. Finally, steady-state cement PSD obtained from a full-scale vertical roller mill is fitted with TUSSIM. The fitted results show good agreement compared to the experimental PSD. Overall, this dissertation has provided a novel process simulator, TUSSIM, and many fundamental insights into the continuous milling of cement clinker and its optimization

The validation of predictive geometallurgical models for concentrator plant process design

Abstract. The use of geometallurgical models is becoming more common in concentrator plant design and production phase. Predictive modelling aims to optimize process parameters before ore reaches the concentrator plant. Richest and easiest orebodies are already extracted, and in the future, more low-grade and complex orebodies should be exploited to reach enough metal production level. Mineral processing field should be developed all the time and especially predictive planning should be considered. Geometallurgical model means the model that is developed cooperated between metallurgists, mining engineers and geologists. Geometallurgical model combines data from mine plan, drill cores and metallurgical test works. Metallurgical test works are expensive and take a lot of time. Validation aims to point out that it is possible to save money by doing comprehensive modelling and simulation work. Flotation process itself is very detailed studied but the use of geometallurgical models is still under development work. HSC Chemistry® is simulation software developed by Outotec. HSC Sim is sub-program used in process design and production phase. The main objective of this thesis was to evaluate how experimental flotations with different ore blends will correspond to the current kinetic models of HSC Sim simulations for different ore blends. In concentrator plants the ore feed keeps changing all the time, because ore might be delivered from different parts of mine and feed is always heterogeneous. The concentrator plant should be optimized based on mine plan and the kind of ore will be feed to the concentrator plant. Overall 16 different flotation tests were accomplished during this thesis work. Test work was carried out using four different end-member ore types coming from Rich Metal Group mine site from Georgia. Deposit is distributed to different ore types and geometallurgical units. Flotation test work was conducted in Outotec Research Center in Pori. During experimentation, flotation kinetics were defined for four ore types in rougher and cleaner flotation. Experimental work started with grinding tests and optimal grinding times were defined. During flotation tests the distribution of ore types was changing, otherwise, flotation conditions remained constant. Theory chapter explains the most important terms concerning to geometallurgy, flotation theory and flotation simulation and modelling. Theory chapter introduces the theory of validation due to the simulation model validation is the most important output of this thesis. The correlation between experimental and simulated results is clear and results are close to each other. This means that the results are very promising and HSC Sim simulation software can be used to simulate flotation blends, if ores have similar mineralogy. In the future, more test work should be done with more different ores to validate HSC Sim simulation. Simulation of ore blends requires the deep metallurgical definition of end-member ores.Ennustavien geometallurgisten mallien validointi rikastamoiden prosessisuunnittelussa. Tiivistelmä. Geometallurgisten mallien käyttäminen rikastamoiden suunnittelussa ja tuotannossa yleistyy jatkuvasti. Ennustavalla mallinnuksella pyritään optimoimaan rikastamoiden ajoparametrejä jo valmiiksi ennen kuin malmi prosessoidaan rikastamolla. Rikkaimmat ja suurimmat malmiot maailmalla ovat pääosin käytetty ja tulevaisuudessa entistä köyhempiä ja vaikeammin rikastettavia malmeja joudutaan hyödyntämään, jotta metallien tuotanto saadaan pidettyä tarvittavalla tasolla. Prosessointia täytyy kehittää jatkuvasti ja tulevaisuudessa pyritään kehittämään erityisesti ennustavaa suunnittelua laitosten tuotannossa. Geometallurgisella mallilla tarkoitetaan metallurgien, kaivosinsinöörien ja geologien yhdessä luomaa mallia, jossa on yhdistetty data kaivossuunnitelmasta, kairaustuloksista ja metallurgisista kokeista. Metallurgisten kokeiden tekeminen on kallista ja vie reilusti aikaa. Tässä työssä pyritään osoittamaan, että malmisekoituksille ei tarvitsisi erikseen tehdä metallurgisia kokeita vaan aikaa ja rahaa voidaan säästää mallinnus- ja simulointityöllä. Vaahdotusprosessia on tutkittu hyvin huolellisesti mutta geometallurgisten mallien suunnittelu- ja kehitystyöhön täytyy käyttää tulevaisuudessa enemmän rahaa ja aikaa. Outotecin kehittämä simulointiohjelma HSC Chemistry® on suunnittelu- ja tuotantovaiheessa käytetty ohjelma, joka perustuu Outotecin tekemiin kokeisiin laboratorioissa ja tuotantolaitoksilla. Tämän työn tarkoituksena on validoida sen mallinnusta. Rikastamoilla syötteen laatu vaihtelee jatkuvasti, sillä malmi voi saapua prosessiin eri puolilta kaivosta ja syöte ei ole koskaan homogeeninen. Rikastamo tulee säätää sen mukaan, millaista malmia syötetään laitokselle. Diplomityön aikana tehtiin yhteensä 16 eri vaahdotuskoetta neljällä eri malmityypillä, jotka ovat peräisin Rich Metal Groupin kaivokselta, Georgiasta. Kaivoksen malmio on jaettu eri geometallurgisiin yksiköihin, niiden mineralogisten ja metallurgisten ominaisuuksien perusteella. Vaahdotuskokeet suoritettiin Outotecin Porin tutkimuskeskuksessa. Koetoiminnan aikana jokaiselle yksikölle määritettiin vaahdotuskinetiikat, esi- ja kertausvaahdotuksessa. Laboratoriokokeissa ensimmäiseksi selvitettiin sopiva jauhatusaika vaahdotuskokeita varten. Laboratoriossa vaahdotusparametrejä ovat; vaahdotusilman syöttömäärä, kemikaalien annostelu, vaahdotuskoneen parametrit sekä vaahdotettavan malmin määrä. Vaahdotusten aikana eri malmien osuuksia muutettiin, muutoin vaahdotusolosuhteet pyrittiin pitämään vakioina. Teoriaosuudessa perehdytään tärkeimpiin termeihin liittyen geometallurgiaan, vaahdotukseen ja vaahdotuksen simulointiin sekä mallinnukseen. Lisäksi validoinnin teoriaa avattu yhdessä kappaleessa, sillä simulointiohjelman validointi on tärkeässä roolissa tässä diplomityössä. Kokeiden ja simulointien tulosten vertailu osoittaa, että tulokset vastaavat hyvin toisiaan ja näin ollen voidaan todeta että, HSC Sim simulointiohjelmaa voidaan käyttää malmisekoitusten mallinnukseen, mikäli eri malmien mineralogia on samankaltainen. HSC:tä voidaan käyttää malmisekoitusten mallinnukseen, mikäli vain päätejäsen-malmien metallurginen performanssi on tutkittu huolellisesti

Optimization of Operating Conditions and Design Parameters on Coal Ultra-Fine Grinding Through Kinetic Stirred Mill Tests and Numerical Modeling

This study investigated the ultra-fine coal grinding performance of four low- to moderate-cost grinding media: ceramic balls, granular sand, alumina beads, and silica beads. The kinetic grinding tests were conducted using a stirred mill, while different operating conditions, including the media size, solids concentration, and the addition of viscosity modifiers, were examined. Characterization studies in terms of particle size, shape, and surface morphology were further performed to support the experimental findings. Moreover, using population balance modeling, grinding simulation was performed in Matlab to forecast the particle size distribution based on the specific energy input and experimental size-related data. The results showed that silica beads generated the finest product size with a P80 of 5.9 µm from a feed size of 24.4 µm while having a specific energy (SE) input of 309 kWh/ton, compared to ceramic balls and alumina beads. Nonetheless, the least energy consumption of 109 kWh/ton was achieved by alumina beads; however, yielding a coarser product size of 15.5 µm. In addition, test results indicate that choosing suitable media sizes, reducing the solids concentration, and using viscosity modifiers enhance coal ultra-fine grinding performance. Under the optimized testing conditions, a P80 of 2.7 µm was produced with a corresponding SE input of 270 kWh/ton using silica beads ranging from 420 to 850 µm and a dispersant dosage of 14 kg/ton. Moreover, the mathematical models, generated based on the breakage function, selection function, and particle swarm optimization, provided an accurate forecast of the particle-size distribution at the end of the study

Doctor of Philosophy

dissertationThis research was undertaken to investigate the impacts of finer rock fragmentation (arising from higher energy blasting) on the unit costs of a hard-rock surface mine. The investigation was carried out at a copper operation in southern Utah, which exploits its deposits by conventional methods, including drilling, blasting, loading, and truck haulage. The run of mine is processed in a three-stage crushing circuit and a two-stage grinding circuit, which feed a flotation plant that produces a copper concentrate. The research was carried out using modeling and simulation techniques. Fifty-five blast designs in total were developed for ore and waste units, with energy inputs ranging from 100 kcal/st to 400 kcal/st. For each design, fragmentation was predicted using the Kuz-Ram method. Crushing of the predicted ore fragment size distributions was simulated using MODSIMTM. Data from pit face imaging and timed motion studies were collected and analyzed for the influence of fragmentation on shovel and truck productivity. Analyses indicated that fragment size distribution alone does not significantly impact this productivity. From simulation of the crushing circuit, it was found that the impact of differences in the blast-generated fragment distribution on the crusher energy is limited to the primary crusher, where a vast range of feed size distributions are introduced. No such relationships were evident at the secondary and tertiary crushers. Energy savings from increasing blasting intensity proved negligible and would not justify the costs of higher energy blasting. There was no evidence from this work that any beneficial influences of blast-generated fragment size distribution reach the grinding mill. Costs were estimated for drilling, blasting, and crushing, which were the principal unit operations inferred to be affected in some meaningful way by the varying intensities of blast energy input. The research shows that, principally as a result of jaw crusher gape restrictions and the significant unit costs of secondary reduction for both ore and waste, the net of all breakage (primary blast, secondary reduction, and crushing) does reduce to a transient minimum before they begin to ramp up again, thus fitting a classical mine-to-mill curve

Dynamic simulation of industrial grinding circuits : mineral liberation, advanced process control, and real-time optimisation

Étant donné que les minéraux apparaissent fréquemment dans des associations complexes dans la nature, la libération minérale est un aspect clé du traitement de minerais et celle-ci est accomplie par comminution. Cette opération est certainement l’une des plus importantes, mais aussi des plus coûteuses dans l’industrie. La réussite globale d’une usine dépend souvent de la performance du circuit de broyage car il existe un compromis pour atteindre la taille des particules libérant les minéraux ciblés afin d’obtenir des concentrés de haute pureté tout en ayant de faibles coûts d’opération, lesquels sont largement influencés par la consommation énergétique. Dans les années récentes, les entreprises ont été confrontées à des objectifs de performance plus exigeants, une concurrence accrue sur les marchés, et des réglementations environnementales et de sécurité plus strictes. D’autres défis supplémentaires sont inhérents aux circuits de broyage, par exemple les réponses non linéaires, le niveau élevé d’intercorrélation entre les variables et les recirculations de matière. Les problèmes ci-dessus soulignent la pertinence d’avoir des systèmes de contrôle et d’optimisation adéquats pour lesquels les praticiens profitent de plus en plus des approches basées sur des modèles pour y faire face de façon systématique. La modélisation et la simulation sont des outils puissants ayant des avantages significatifs tels que les faibles coûts, les temps requis pour réaliser des expériences relativement courts et la possibilité de tester des conditions opérationnelles extrêmes ainsi que différentes configurations des circuits sans interrompre la production. De toute évidence, la qualité des résultats sera aussi bonne que la capacité du modèle à représenter la réalité, ce qui souligne l’importance d’avoir des modèles précis et des procédures de calibrage appropriées, un sujet fréquemment omis dans la littérature. Un autre aspect essentiel qui n’a pas été rapporté est l’intégration efficace de la libération minérale aux systèmes de contrôle et d’optimisation de procédés. Bien qu’il s’agisse d’une information clé directement liée aux performances de l’étape de concentration, la plupart des stratégies se concentrent exclusivement sur la taille de particule du produit. Ceci est compréhensible étant donné qu’il est impossible de mesurer la distribution de libération présentement. Basée sur une librairie de simulation d’usines de traitement des minerais déjà existante, cette recherche aborde lesdits problèmes en (1) développant un modèle de libération minérale visant à coupler les étapes de broyage et de concentration ; (2) programmant et validant par calibrage un modèle phénoménologique de broyeur autogène/semi-autogène (BA/BSA), nécessaire pour compléter la librairie de simulation ; (3) couplant un simulateur de circuit de broyage à un procédé de concentration avec le modèle de libération, et (4) développant un système de contrôle et d’optimisation qui considère explicitement des données de libération minérale pour évaluer les avantages économiques. Les principaux résultats confirment que le modèle de libération est capable de reproduire avec précision des distributions de libération minérale couramment observées dans l’industrie. Cependant, si les données de calibrage correspondent à un point d’opération unique, la validité pourrait être limitée aux régions voisines proches. Le problème de caractériser l’évolution de la libération minérale aux diverses conditions d’opération ainsi qu’aux régimes transitoires reste à être abordé. Le modèle de libération s’est aussi révélé utile pour coupler des circuits de broyage avec des procédés de concentration, en particulier pour une unité de flottation. Quant au modèle de BA/BSA, celui-ci peut capturer le régime statique ainsi que la dynamique d’un broyeur réel et conjointement avec le reste des équipements dans la librairie de simulation, des circuits de broyage industriels. Ceci a été confirmé par le calibrage à partir des données d’opération d’une usine et des tests en laboratoire, tout en suivant une procédure systématique, contribuant aussi au sujet de l’établissement de méthodologies de calibrage standardisées. Pour terminer, les expériences concernant la stratégie de contrôle et d’optimisation basée sur la libération minérale suggèrent que l’utilisation de cette information peut améliorer la performance globale des circuits de broyage-séparation en réagissant aux variations des caractéristiques de libération, qui à leur tour influencent l’efficacité de séparation. L’étude de cas réalisé révèle que cela peut entraîner une augmentation du débit massique et de la teneur du concentré, de la récupération des métaux et des revenus de l’ordre de +0.5%, +1%, +1% et +5%, respectivement, par rapport au cas où ces informations sont omises.As minerals frequently appear in complex associations in nature, mineral liberation is one of the most relevant aspects in ore processing and is achieved through comminution. This operation is one of the most important, but also one of the most expensive ones in industry. The global efficiency of a plant often depends on the performance of the grinding circuit, since there is a compromise to achieve the particle size liberating the targetted minerals in order to obtain high purity concentrates while maintaining low operating costs, which are largely influenced by the energy consumption. In recent years, companies have been facing more demanding performance targets, stronger competition, and more stringent environmental and safety regulations. Additional challenges are inherent to the grinding circuits themselves, e.g. the nonlinear responses, high degree of intercorrelation of the different variables, and material recirculations. The abovementioned issues highlight the relevance of adequate process control and optimisation, and practitioners rely more often on model-based approaches in order to face them systematically. Modeling and simulation are powerful tools with significant advantages such as low costs, required times for conducting experiments are relatively short, and the possibility of testing extreme operational conditions as well as different circuit configurations without disrupting production. Evidently, the quality of the results will only be as good as the model capacity to represent the reality, which emphasises the relevance of having precise models and proper calibration procedures, the latter being a topic frequently omitted in the literature. Another crucial aspect that has not been reported yet is the effective integration of mineral liberation in control and optimisation schemes. Although it is a key piece of information directly related to the performance of the concentration stage, most strategies focus exclusively on the particle size. This is understandable given that it is currently impossible to measure the liberation distribution online. Based on an existing mineral processing plant simulation library, this research addresses these problems by (1) developing a mineral liberation model aiming at linking the grinding and concentration stages; (2) programming a phenomenological autogenous/semiautogenous (AG/SAG) mill model, required to complement the simulation toolbox, and validating it through calibration; (3) coupling a grinding circuit simulator to a concentration process by means of the liberation model, and (4) developing a plantwide control and optimisation scheme considering mineral liberation data explicitly to evaluate the economic benefits. The main results confirm that the liberation model is capable of reproducing accurately mineral distributions observed in industry. If calibration data correspond to a single operating point, its validity may however be limited to the close neighbourhood. Characterising the evolution of mineral liberation in different operating conditions and transient states remains to be addressed. The liberation model proved to be equally useful in coupling grinding circuits with concentration processes, specifically for flotation. As for the AG/SAG mill model, it can capture the steady state and dynamic behaviour of an actual device and, along with the rest of pieces of equipment in the simulation toolbox, of industrial grinding circuits. This was confirmed through calibration from plant data and laboratory testwork following a systematic procedure, contributing to the endeavour of establishing standard calibration methodologies. Lastly, the results of the designed control and optimisation scheme suggest that using liberation data for control and real-time optimisation can improve the overall performance of grinding-separation circuits by reacting to variations in the liberation characteristics, which in turn influence the concentration performance. The case study reveals that doing so can lead to increases in the concentrate mass flow rate and grade, metal recovery, and global profits in the order of +0.5%, +1%, +1%, and +5%, respectively, compared to the case omitting this information

On-line sensors for measuring the total ball and charge level in tumbling mills

Includes bibliographical references.Tumbling mills are still the mostly used milling device in the mineral processing industry for both coarse and fine grinding applications. A number of factors affect the performance of tumbling mill. One of these factors is volumetric filling which is the volume of charge in the mill expressed as a fraction of the total volume available. The volumetric filling controls the mill throughput, power draw and product size. The common method of measuring volumetric filling is by taking in situ measurements when the mill is stationary. This method is disruptive to production due to the mill downtime involved. The use of on-line sensors for measuring the volumetric filling using acoustic, inductive proximity and conductive sensors are the new technologies attempting to monitor volumetric filling in situ. The methods are non-intrusive and low cost approach for direct monitoring of dynamic volumetric filling conditions in the tumbling mill. The dynamic volumetric filling was assumed to be directly related to static mill filling conditions. In this study, the volumetric filling was calculated from the toe and shoulder angles estimated by the CSIRO monitor (acoustic) and the Magotteaux Sensomag (inductive proximity and conductive) sensors. The CSIRO acoustic sensor was installed on a run-of-mine (RoM) ball mill at Angloplatinum UG2 Concentrator at Rustenburg, South Africa. The toe and shoulder angles were obtained from the surface vibration caused by the impact of the charge on the mill shell. The industrial scale experiments were performed at varied mill feed rate at constant ball load of 28%. In the pilot scale experiments, the Magotteaux ball mill at Frank Concentrator was equipped with a Sensomag sensor for measuring the toe and shoulder angles of the slurry and ball load based on the principle of conductance and induction, respectively. The mill was configured to operate as a RoM ball mill. The experiments were conducted at varying mill speeds (75%-85% critical speed), feed rate (1200-2800kg/hr) and ball loads (15-26%). The static mill filling was determined from physical measurements after crash stopping the mill