Over many years, researchers in the field of flotation have developed an in-depth understanding of processes occurring in the pulp phase of flotation machines. Until recently, however, the froth phase has received little attention. The froth phase serves to separate bubble-particle aggregates from suspended slurry in a flotation cell. The mechanism of recovery by entrainment, its relationship to water recovery and particle size dependency is well understood. Froth recovery, (the fraction of particles entering the concentrate launder that entered the froth phase attached to air bubbles), is not well understood. Up until now, there has been doubt over whether this property is dependent on particle size and hydrophobicity. Difficulties in measuring froth recovery had previously prevented researchers from gaining a deeper understanding of the transport of attached particles across the froth phase. A novel device was designed and tested to measure froth recovery by isolating bubble-particle aggregates in the pulp-phase of flotation machines through the determination of the bubble loading in the pulp phase (mass of particles attached per unit volume of air bubbles). This technique can be used with other measurements to investigate froth selectivity by directly comparing these captured particles to those found in the froth phase. Evidence was collected at Red Dog Mine, Alaska and Newmont Golden Grove Operations, Western Australia which showed that the froth phase selectively transported more hydrophobic and smaller sized particles across the froth than less hydrophobic and larger particles. Particles collected in the device were compared to those found in the concentrate stream on a size by mineral by liberation class. Froth recovery was also calculated on a size by mineral by liberation class for two valuable sulphide minerals in a continuous 3m³ flotation cell. These results show that the froth phase is responsible for the upgrading of attached particles across the froth phase as well as for the separation of bubble-particle aggregates from suspended slurry. The pulp phase is responsible for creating bubble-particle aggregates through the attachment of hdyrophobic mineral particles to air bubbles. Many complex factors affect the extent to which this occurs including the size and hdyrophobicity of the particles, the size and number of air bubbles produced by the flotation machine, the rate of collisions between particles and bubbles and the overall chemistry of the system. This measurement of bubble loading presents an opportunity to measure the impact of all these factors on the successful creation of bubble-particle aggregates. Based on a literature review suggesting that there was a high probability of particles being detached at the pulp-froth interface due to the aggregates change in momentum, a three phase description of a flotation cell was proposed. The three phases were: pulp, pulp-froth interface and upper froth zones. A second froth recovery measurement technique (changing froth depth) was used in combination with the bubble load technique to determine the recovery across each of the two froth zones. It was found that the pulp-froth interface appears to be responsible for the selectivity observed across the froth phase as a whole. These findings will enable more in-depth research into the sub-process of the froth phase as well as assisting flotation cell design through a better understanding of the roles of the pulp-froth interface and the upper froth region.

The core of this project was the development of a column flotation dynamic model that can reasonably predict the changes in the concentrations of all solid and bubble species, along the full column height. A dynamic model of a process is normally composed of a set of partial or ordinary differential equations that describe the state of the process at any given time or position inside the system volume. Such equations can be obtained from fundamental material and/or energy balances, or from phenomenological derivations based on knowledge about the behavior of the system. A phenomenological approach referred to as population balance modeling was employed here. Initially, a two-phase model was formulated, which represents the behavior of the gas phase in a frother solution. The column was viewed as consisting of three main regions: a collection region, a stabilized froth and a draining froth. Experiments were carried out, based on conductivity techniques, for obtaining empirical data for model validation and parameter estimation. After testing the two-phase model, the equations for the solid species were derived. Consideration of the effects of bubble loading, slurry density and slurry viscosity on bubble rise velocity and, therefore, on air fraction is included in the model. Bubble coalescence in the froth is represented as a rate phenomenon characterized by a series of coalescence efficiency rate parameters. Auxiliary equations that help describe the settling of free particles, the buoyancy of air bubbles, and the processes of attachment and detachment, were also developed and incorporated into the model. The detachment of solids from the bubbles in the froth zones was attributed to coalescence, and it was assumed to be proportional to the net loss of bubble surface area. Almost all parameters needed to solve the model equations are readily available. The set of differential equations that comprise the model can be solved numerically by applying finite difference approximation techniques. An iteration has to be performed, which involves calculating the product flowrate at steady state, modifying the tailings rate and solving the model again until a mass balance is satisfied. / Ph. D.

Thesis (MSc (Earth Sciences))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The Bushveld Complex of South Africa contains three of the most important platinum deposits in the world namely the Merensky Reef, the Upper Group Two (UG2) chromitite reef and the Platreef. These three ore bodies are principally beneficiated by froth flotation. During the beneficiation of chromite hosted PGE’s by froth flotation, chromite represents the principal gangue mineral. This is particularly true for the UG2 main seam. An excess of more than 3% in mass of chromite in the PGM concentrate is known to result in significant problems in the downstream processing and extraction of PGEs. The variability in texture and composition of chromite due to its primary crystallization and subsequent modification by the development of potholes or through IRUP intrusions are thought to influence the flotation behaviour of the UG2 main seam chromitite ore. This study conducted at Waterval Mine investigated the role of mineralogical characteristics of chromites on the flotation performance of three different environments for the UG2 main seam: (1) “normal” UG2 main seam; (2) UG2 main seam affected by pothole formation; and (3) UG2 main seam affected by IRUP intrusion. This was achieved through an extensive petrographic investigation of the chromites from each environment, to individually characterise their primary textures. This was followed by compositional characterisation of the chromite from each environment. Finally the flotation performance of the ore from each environment was investigated, using small scale batch flotation experiments, to establish any linkage between the textures, the composition and the flotation performance of the chromite from different environments. In this study it was found that the UG2 normal reef and the UG2 reef affected by pothole formation are both principally characterised by primary mineralogical features comprising mainly fine‐grained chromite as the cumulate phase and orthopyroxene and plagioclase as intercumulate phases. These two reef types were also found to be identical in the composition of the chromites present. In addition, in both of these almost unaltered reef types it was found that chromite showed small recoveries by flotation. On the other hand, it was found that the UG2 affected by IRUP intrusion was affected by post‐magmatic alteration that had overprinted primary textures and compositional features. This resulted in the replacement of primary minerals by secondary alteration assemblages. Orthopyroxene was iii replaced by serpentine, chlorite, amphibole and talc, while plagioclase is replaced by sericitic alteration. Furthermore, this alteration also resulted in modification of the chromite compositions. The compositional change in the chromites from the IRUP reef type resulted in Fe and Ti enrichment of chromite with increasing magnetic properties, and Cr, Al and Mg depletion. The alteration also resulted in the coarsening of chromite in the IRUP affected main seam reef particularly at the bottom and the top of the main seam. These compositional and textural modifications, principally the post‐magmatic alteration of intercumulate orthopyroxene, resulted in a greater recovery of chromite by flotation in the concentrate from the IRUP affected ore compared to the two other two ore types where there was small amount of chromite recovered. The characterisation of the recovered chromite revealed that the principal reason for chromite flotation was caused by the mineral association of chromite with hydrophobic Si, Mg, Fe rich phases, principally altered orthopyroxene and associated serpentine, chlorite, amphibole and talc. This investigation showed that the difference in mineralogical and flotation performances of chromite from the different UG2 main seam reef types was caused by the postcrystallisation alteration of cumulate and intercumulate phases due to the emplacement of IRUPs. Although IRUP affected UG2 main seam ore is not currently processed, it could be processed much more rapidly than the other two types of UG2 main seam ores because of its softer character resulting in shorter milling times. This is most likely a function of the presence of alteration phases and the presence of coarser chromite grains, as well as already brecciated chromite grains. Savings associated with the shorter milling time of this ore type are perhaps offset by the cost of the higher dosages of depressant required to suppress the floatable chromite in this ore type. However, given the energy cost of longer milling times, the cost of the depressant is likely to be insignificant. Moreover, the processing of the UG2 main seam ore affected by IRUP intrusion would also require a different approach to extraction of the ore to keep it separate from the normal reef ore.

For future development of automated sensor-based sorting in the mining industry, an improvement in the separation efficiency of the equipment is desirable. This could be achieved through a better understanding of the identification and separation aspects of the automated sorter. For automated sorters that undertake separation through the use of compressed air jets, the problem of poor separation efficiency has been linked with co-deflection losses. Co-deflection losses occur as particles meant to pass on to the ‘accept’ bin are co-deflected with the particles (which are to be deflected) meant to go to the ‘reject’ bin. To study co-deflection losses and suggest means of improving automated sorter separation efficiency, this research investigates the effects of particle size, shape, throughput, together with the proportion of particles (out of the total test batch) required to be deflected on separation efficiency. The effect of the air valve configuration on separation efficiency was also studied. Presented also is a mathematical model which could be used to predict automated sorter separation efficiency. All separation efficiency investigations were undertaken using a TiTech Combisense© (BSM 063) automated sorter. Samples of granite were sized into -20+15mm, -15+10mm and -10+6mm size fractions and grouped into cubic and flaky shape fractions. These fractions were then divided into two with one portion painted for colour separation efficiency investigations. The separation efficiency results confirmed earlier research indicating that particle size and the fraction requiring deflection affects separation efficiency, with separation efficiency decreasing with a decrease in particle size and an increase in throughput. It was observed that co-deflection loss occurs when correctly identified ‘accept’ particles are co-deflected due to their close proximity to ‘reject’ particles that are to be deflected. Observations from the tests indicate that an increase in the proportion of particles requiring deflection increases the probability of finding ‘accept’ particles in close proximity to ‘reject’ particles leading to co-deflections. Monte Carlo simulations were used to produce a random distribution of particles on the conveyor belt as would be obtained from actual investigations. From these simulations particle proximity relationships and particle co-deflections were studied. Results indicate that the Monte Carlo simulations under-predicts particle proximity associations. The effect of shape on co-deflection was investigated with results indicating that flaky shaped particles produce higher number of co-deflections compared to cubic shaped particles. It was also observed that the valve sensitivity determined from valve opening and closing times is of importance to the selectivity (precision) of the separating air jets. A mathematical separation efficiency model is presented which contains two variables, the belt loading (calculated using particle size, shape and throughput) and the particle fraction of the total test batch that are to be deflected (% deflection). The separation efficiency can be calculated once these two variables are determined.

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A produção de ferroníquel está intimamente ligada à indústria siderúrgica. Todas as operações pirometalúrgicas pertencentes à rota de processo (calcinação, redução e refino) visam o melhor aproveitamento energético e a menor quantidade de impurezas no produto final. A etapa de refino pirometalúrgico produz escória rica em ferro e níquel, que normalmente é processada para recuperação destes metais e reinserção no processo, na própria etapa de refino ou no forno de redução, dependendo da quantidade de impurezas. Ensaios realizados com a escória granulada da Mineração Morro Azul mostram que é possível recuperá-los por processos físicos, de maneira similar à existente no local, porém com resultados superiores, mediante algumas alterações propostas para o circuito. / Ferronickel production is intimately connected to the steel industry. All pyrometallurgical operations which comprise the process route (calcining, smelting, refining) aim at better energetic usage and smaller amount of impurities in the final product. The pyrometallurgical refining stage produces slag rich in iron and nickel, which is usually further processed for metal recovery and reinsertion back into the process, in the refining or smelting stages, depending on the amount of impurities. A series of tests carried out on the Mineração Morro Azul granulated refining slag shows that it is possible to recover the metallic particles through physical processing, similarly to the existing facility, but with improved results due to some alterations proposed for the circuit.

Previous studies have suggested that Davis tube (DT) experiment can used to study wet low intensitymagnetic separation (WLIMS) for magnetic iron ores. But DT process has never been used to mapWLIMS process, specifically in a geometallurgical framework. This thesis work is a step towardsfulfilling this gap by studying the Davis tube experiment performed on 13 different samples fromLeveäniemi iron ore deposit. The methodology adapted to map WLIMS concentrate quality includesstudy and analysis of feed, DT and WLIMS. Analyses were made using experimental data, processingdata using some analytical tools, some data-processing tools and post processing tools. For coveringthe geometallurgical aspect the analysis was done for both elements and minerals. The results fromthis study has reviled that DT can be used to predict WLIMS concentrate quality to an acceptablelevel of confidence. Furthermore, results show that a combination of DT and WLIMS informationproduce very accurate and highly reliable models for predicting and mapping WLIMS concentratequality. This work serves as the first step towards studying an unexplored field pertaining to magneticiron ore concentrate and has opened door to possible future work that could take this work a stepfurther. Supplementing this study with more data from different sample is required not only tovalidate the model but also to make it better. A better modal mineralogy of the samples is needed tounlock the full potentials of mineralogical modelling approach used in this work. / <p>I am a graduate from the of Erasmus Mundus masters in Georesource Engineering, 2017.</p> / Primary Resource Efficiency by Enhanced Prediction (PREP)

Os objetivos principais deste trabalho foram planejar, executar e analisar os resultados de uma campanha de ensaios de concentração de minerais em um jigue centrífugo. O programa de ensaios permitiu a análise da influência de variáveis operacionais do equipamento no desempenho metalúrgico do processo de concentração. As investigações tiveram por meta estabelecer o desempenho metalúrgico por faixas granulométricas discretas tanto em termos de recuperações como de enriquecimentos. Para tanto foi selecionado o rejeito de uma operação de concentração de minerais sulfetados polimetálicos. O método de trabalho consistiu na caracterização tecnológica do rejeito e execução dos ensaios de concentração no jigue centrífugo Kelsey variando três parâmetros principais: velocidade de rotação, freqüência e amplitude de pulsação. Os resultados dos ensaios foram analisados em termos de recuperações e enriquecimentos dos elementos de interesse, como níquel, cobre e enxofre, além de óxido de magnésio, principal contaminante dos concentrados. O desempenho da campanha de ensaios indicou valores significativos de recuperação e enriquecimento dos elementos de interesse, bem como redução importante de óxido de magnésio nos concentrados obtidos. / The present work describes an experimental program designed to assess the metallurgical performance of a centrifugal jig. The variations in the main operating conditions were analysed in terms of both metallurgical recovery and grades by size fraction in concentrates. The tailings of a sulphide mineral concentration plant were sampled, prepared and submited to technical characterization as a preparation for the testing campaign. A Kelsey centrifugal jig was used in the testing program which included variation in rotating speed, frequency and stroke of pulse. The results were analysed in terms of recovery and concentration of nickel, copper and sulphur, as well as magnesium oxide which was the main contaminant. The general performance of the tests indicated high values in recovery of the selected elements, as well as significant reductions of contaminant in the concentrates.

Differential geometric nonlinear control of a multiple stage evaporator system of the liquor burning facility associated with the Bayer process for alumina production at Alcoa Wagerup alumina refinery, Western Australia was investigated.Mathematical models for differential geometric analysis and nonlinear controller synthesis for the evaporator system were developed. Two models, that were structurally different from each other, were used in the thesis for simulation studies. Geometric nonlinear control structure, consisting of nonlinear state feedback control laws and multi-loop single-input single-output proportional-integral controllers, were designed for the industrial evaporator system. The superiority of the geometric nonlinear control structure for regulatory control of the evaporator system was successfully demonstrated through computer simulations and real-time simulator implementation. The implementation trial has verified the practicality and feasibility of these type of controllers. It also re-solved some practical issues of the geometric nonlinear control structure for industrial control applications. In addition, the implementation trial also established a closer link between the academic nonlinear control theory and the industrial control practices.Geometric nonlinear output feedback controller, consisting of the geometric nonlinear control structure and reduce-order observer was proposed for actual plant implementation on the evaporator system on-site. Its superior performance was verified through computer simulations, but its feasibility on the evaporator system on-site has yet to be investigated either through simulator implementation or actual plant implementation. This investigation was not performed due to the time constraint on the preparation of this thesis and the inavailability of the plant personnel required for this implementation.Robust ++ / nonlinear control structures that are simple and computationally efficient have been proposed for enhancing the performance of geometric nonlinear controllers in the presence of plant/model mismatch and/or external disturbances. The robust nonlinear control structures are based on model error compensation methods. Robustness properties of the proposed robust nonlinear control structures on the evaporator system were investigated through computer simulations and the results indicated improved performance over the implemented geometric nonlinear controller in terms of model uncertainty and disturbance reductions.A software package was developed in MAPLE computing environment for the analysis of nonlinear processes and the design of geometric nonlinear controllers. This developed symbolic package is useful for obtaining fast and exact solutions for the analysis and design of nonlinear control systems. Procedures were also developed to simulate the geometric nonlinear control systems. It was found that MAPLE, while it is superior for the analyses and designs, is not viable for simulations of nonlinear control systems. This was due to limitation of MAPLE on the physical, or virtual, memory management. The use of both symbolic and numeric computation for solutions of nonlinear control system analysis, design and simulation is recommended.To sum up, geometric nonlinear controllers have been designed for an industrial multiple stage evaporator system and their simplicity, practicality, feasibility and superiority for industrial control practices have been demonstrated either through computer simulations or real-time implementation. It is hoped that the insights provided in this thesis will encourage more industry-based projects in nonlinear control, and thereby assist in closing the widening gap between academic nonlinear control theory and industrial control ++ / practice.Keywords: geometric nonlinear control, input-output linearization, multiple stage evaporator, robust geometric nonlinear control, control performance enhancement.

In recent years there has been growing interest in bio-mineral processing due to its low operating costs and its application in processing lean-grade ores. Bioprocessing is a good alternative to conventional hydrometallurgy process in mineral processing. In recent times microorganisms have been used as surface modifiers in processes such as froth flotation and flocculation. The surface properties of microbes and minerals such as zeta potential and surface hydrophobicity play a major role in determining adhesion of microorganisms to minerals and hence, the efficiency of flocculation and flotation. These properties also depend on solution conditions such as pH and ionic strength. Adhesion of microorganisms to mineral surfaces can alter the surface properties of the minerals. Such surface modification imparting hydrophobicity or hydrophilicity is used in flocculation and flotation of fine particles. In this research work the effect of ionic strength and pH in deteraiining the surface properties and hence adhesion of the bacterium Bacillus polymyxa to minerals such as hematite, quartz and coal has been studied in detail. The effect of the ionic strength and pH on the electrokinetics of the minerals and bacteria and its subsequent effect on adhesion and flocculation were investigated in detail. Contact angle measurements along with the zeta potential results were used to calculate the interaction energies between the mineral and the microorganism to establish a mechanism for the interaction. The following major conclusions can be drawn from this study. Results indicate that increase in the ionic strength significantly changes the zeta potential of hematite and bacteria without varying the isoelectric point. Increase in the ionic strength caused very little change in the zeta potential of quartz and coal. The adhesion of bacterial cells on to the minerals was found to be dependent on pH, ionic strength and conditioning time. Adhesion of bacterial cells was found to be more on hematite and coal when compared to quartz. The adsorption isotherms of Bacillus polymyxa cells with respect to all the three minerals were found to obey Langmuir isotherm. Flocculation studies demonstrated that the settling rate of hematite and coal was enhanced in presence of bacterial cells and electrolyte. However quartz settled much slower under the same conditions indicating that the quartz particles are being dispersed. Thus, selective flocculation of hematite and coal is possible which can be used in separating them from quartz effectively. The different components of total interaction energy arising from Lifshitz-van der Waal forces, acid/base forces and electrostatic forces were calculated using the van Oss approach. Calculation of the components of the acid base free energy showed that coal and hematite were hydrophobic compared to quartz and the bacterium. From total interaction energy calculation based on the extended DLVO theory, hematite and coal were found to have a net negative interaction energy in acidic pH values and hence attractive forces are predominant. Quartz was found to have a net repulsive energy at all the pH values at low ionic strengths but increase in ionic strength the interaction energy become attractive. The AGLW values of quartz was found to be attractive which is probably responsible for bacterial adhesion onto quartz.