Thesis (MEng)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: A desire to increase the efficiency of the comminution process in mineral process systems has led to the need of determining the size distribution of ore particles at various stages in the system. The objective of this research is to investigate the feasibility of the use of an acoustic sensor for measuring particle size distribution. The acoustic signal generated when the particles impact on a cantilever bar is analysed using digital signal processing techniques. As rocks fall onto a metal bar, the bar vibrates. The vibrations contain information th a t is extracted to determine the size of particles tha t impacted on the bar. The bar is modelled as a linear system which is excited by impulses (impact of particles). The response of the bar is deconvolved from the acoustic signal to obtain an impulse whose amplitude is proportional to the energy of the impact. In order to improve size estimates, deconvolution is performed using a statistical model of the impulse sequence (Bernoulli-Gaussian) and then estimated using MAP estimation. Size estimates are not only a function of the mass of particles, but also on the exact position of impact on the bar. Since there is always a variation in the position of impact, size estimates are erroneous. It was found that the position of impact can be determined as to reduce variances dramatically. Due to physical sampling in space, the sensor has a bias towards larger particles. We show how this can be represented mathematically and removed. This project is mainly concerned with rocks in the +8-25mm (+0,7-22 gram) size range. / AFRIKAANSE OPSOMMING: Vergruising van erts in die mineraalbedryf verg groot hoeveelhede energie. Daar is ’n behoefte gei'dentifiseer orn hierdie proses meer effektief te maak. Aangesien die effektiwiteit van ’n meul ’n funksie is van die ertsgroottes wat gemaal word, kan partikel grootte inligting aangewend word om effektiwiteit te bevorder. Die doel van hierdie tesis is om die lewensvatbaarheid van ’n akoestiese sensor vir die doel van partikelgrootte estimasie, te ondersoek. Erts partikels wat val vanaf ’n vervoerband op ’n kantelbalk, veroorsaak dat die balk vibreer. Deur hierdie vibrasies te meet en verwerk, kan inligting aangaande partikel grootte verkry word. Die stelsel word gemodelleer as ’n lineere sisteem met impulse as intree. Die geobserveerde sein is die konvolusie tussen die intree impulse en die impulsweergawe van die sisteem. Deur gebruik te maak van ’n statistiese model en MAP-estimasie, word die effek van die sisteem gedekonvuleer vanaf die geobserveerde sein om ’n benadering van die intree impuls sein te verkry. Die amplitudes van die impulse word gebruik as ’n aanduiding van partikel massa. Partikelgroottes soos benader deur die stelsel, is ’n funksie van die die posisie waar die partikel die balk tref. Deur van patroonherkenning tegnieke gebruik te maak, word die posisie van impak bepaal om sodoende grootte benaderings aan te pas en die variansie van grootte verspreidings te verminder. As gevolg van die feit dat partikels gemonster word deurdat slegs ’n klein persentasie van die hele omvang van partikels ondersoek word, onstaan daar ’n oorhelling ( “bias” ) na groter partikels. Die kans dat groter partikels die balk tref is groter as vir klein partikels. ’n Wiskundige model vir hierdie verskynsel word voorgestel en gewys hoe die die oorhelling geneutraliseer kan word. Hierdie projek het te doen met ertsgroottes +8-25mm (+0,7-22 gram).

Thesis (MScEng)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Metallurgical processes are often high dimensional and non-linear making them difficult to understand, model and control. Whereas the human eye has extensively been used in discerning temporal patterns in historical process data from these processes, the systematic study of such data has only recently come to the forefront. This resulted predominantly from the inadequacy of previously used linear techniques and the computational power required when analysing the non-linear dynamics underlying these systems. Furthermore, owing to the recent progress made with regard to the identification of non-linear systems and the increased availability of computational power, the application of non-linear modelling techniques for the development of neural network models to be used in advanced control systems has become a potential alternative to operator experience. The objective of this study was the development ofa non-linear, dynamic model of an autogenous mill for use in an advanced control system. This was accomplished through system identification, modelling and prediction, and application to control. For system identification, the attractor was reconstructed based on Taken's theorem making use of both the Method Of Delays and singular spectrum analysis. Modelling consisted of the development of multi-layer perceptron neural network, radial basis function neural network, and support vector machine models for the prediction of the power drawn by an autogenous mill. The best model was subsequently selected and validated through its application to control. This was accomplished by means of developing a neurocontroller, which was tested under simulation. Initial inspection of the process data to be modelled indicated that it contained a considerable amount noise. However, using the method of surrogate data, it was found that the time series representing the power drawn by the autogenous mill clearly exhibited deterministic character, making it suitable for predictive modelling. It was subsequently found that, when using the data for attractor reconstruction, a connection existed between the embedding strategy used, the quality of the reconstructed attractor, and the quality of the resulting model. Owing to the high degree of noise in the data it was found that the singular spectrum analysis embeddings resulted in better quality reconstructed attractors that covered a larger part of the state space when compared to the method of delays embeddings; the data embedded using singular spectrum analysis also resulting in the development of better quality models. From a modelling perspective it was found that the multi-layer perceptron neural network models generally performed the best; a multi-layer perceptron neural network model having an appropriately embedded multi-dimensional input space outperforming all the other developed models with regard to free-run prediction success. However, none of the non-linear models performed significantly better than the ARX model with regard to one-step prediction results (based on the R2 statistic); the one-step predictions having a prediction interval of 30 seconds. In general the best model was a multi-layer perceptron neural network model having an input space consisting of the FAG mill power (XI), the FAG mill load (X2), the FAG mill coarse ore feed rate (X3), the FAG mill fine ore feed rate (X4), the FAG mill inlet water flow rate (X7) and the FAG mill discharge flow rates (X9, XIO). Since the accuracy of any neural network model is highly dependent on its training data, a process model diagnostic system was developed to accompany the process model. Linear principal component analysis was used for this purposes and the resulting diagnostic system was successfully used for data validation. One of the models developed during this research was also successfully used for the development of a neurocontroller, proving its possible use in an advanced control system. / AFRIKAANSE OPSOMMING: Metallurgiese prosesse is gewoonlik hoogs dimensioneel en nie-lineêr, wat dit moeilik maak om te verstaan, modelleer, en te beheer. Alhoewel die menslike oog alreeds wyd gebruik word om temporale patrone in historiese proses data te onderskei, het die sistematiese studie van hierdie tipe data eers onlangs na vore gekom. Dit is hoofsaaklik na aanleiding van die onvoldoende resultate wat verkry is deur van voorafgaande lineêre tegnieke gebruik te maak, asook die beperkende berekenings vermoë wat beskikbaar was vir analise van onderliggend nie-lineêre dinamiese stelsels. 'n Verder bydraende faktor is die onlangse vordering wat gemaak is met betrekking tot die identifikasie van nie-lineêre stelsels en die toename in beskikbaarheid van rekenaar-vermoë. Die toepassing van nie-lineêre modellerings tegnieke vir die ontwikkeling van neurale netwerke om gebruik te word in gevorderde beheerstelsels, het 'n potensiële alternatief geword tot operateur ondervinding. Die doelwit van hierdie studie was die ontwikkeling van 'n gevorderde beheerstelsel vir 'n outogene meul gebaseer op 'n nie-lineêre, dinamiese model. Dit is bereik deur middel van stelsel-identifikasie, modellering en voorspelling, en laastens implementering van die beheerstelsel. Vir stelsel-identifikasie is die attraktor van die stelsel bepaal soos gebaseer op Taken se teorema deur gebruik te maak van beide die metode van vertraging en enkelvoudige spektrum analise. Modellering van die stelsel vir die voorspelling van krag-verbruik deur die outogene meul het bestaan uit die ontwikkeling van multilaag-perseptron-neurale netwerke, radiaalbasisfunksie-neurale netwerke, en steunvektor-masjien-modelle. Die beste model is daarna gekies vir validasie deur middel van toepassing vir beheer. Dit is bereik deur 'n neurobeheerder te ontwikkel en te toets deur middel van simulasie. Die aanvanklike inspeksie van proses data wat gebruik sou word vir modellering het egter getoon dat die data 'n aansienlike hoeveelheid geraas bevat. Nietemin, deur die gebruik van 'n surrogaat-data-metode, is dit bevind dat die tyd-reeks wat die krag verbruik van die outogene meul beskryf, duidelik deterministiese karakter toon en dat dit dus wenslik is om 'n nie-lineêre voorspellings-model, soos 'n neurale netwerk te gruik. Gevolglik is gevind dat, wanneer die data vir attraktor hersamestelling gebruik word, 'n verband bestaan tussen die ontvouing-strategie wat gebruik word, die kwaliteit van die gerekonstrueerde attraktor, en die kwaliteit van die daaropvolgende model. As gevolg van die geraas in die data is gevind dat die ontvouing gebaseer op enkelvoudige spektrum analise 'n beter kwaliteit attraktor hersamestelling lewer. So ook is gevind dat 'n groter deel van die toestandruimte gedek word in vergelyking met die metode van vertraging-ontvouing. Deur gebruik te maak van enkelvoudige spektrum-analise, het die dataontvouing ook beter kwaliteit modelle opgelewer. Vanuit 'n modellerings-perspektief is gevind dat die multilaag-perseptron-neurale netwerk-modelle in die algemeen die beste gevaar het. 'n Multilaag-perseptronneurale netwerk met 'n gepaste ontvoude multidimensionele invoer-spasie het die beste gevaar van al die ontwikkelde modelle met betrekking tot vryloopvoorspellings. Geen van die nie-lineêre modelle het egter beduidend (op 'n R2 basis) beter gevaar as die ARX model wanneer daar na die eenstap-voorspellings (oor 'n 30 sekonde interval) gekyk word nie. Die multilaag-perseptron-neurale netwerk met 'n invoer-spasie bestaande uit die meul krag-verbruik (XI), die meullading (X2), die meul growwe-erts voertempo (X3), die meul fyn-erts voertemp ('4), die meul inlaat-water vloeitempo (X7) en die meul uitlaat vloeitempo's (X9, XIO) het in die algemeen die beste gevaar. Aangesien die akkuraatheid van emge neurale netwerk afhanklik is van die data waarmee dit aanvanklik opgestel is, is 'n diagnostiese proses modelontwikkel om die proses-model te vergesel. Lineêre hoofkomponent analise is vir hierdie doel aangewend en die gevolglike diagnostiese stelsel is suksesvol aangewend vir datavalidasie. Een van die modelle ontwikkel gedurende hierdie navorsing is ook suksesvol gebruik vir die ontwikkeling van 'n neurobeheerder wat dien as bewys dat die model goed gebruik kan word in 'n gevorderde beheerstelsel.

Esta dissertação está baseada no trabalho desenvolvido para adequar a usina de Conceição 1 (da Vale S.A.) para o processamento de itabiritos compactos e semi compactos, situada em Itabira-MG. Até 2014, a usina de Conceição 1 foi alimentada com hematitas e itabiritos friáveis e produzia cerca de 22 Mt/ano. Com o consumo progressivo das reservas de minérios friáveis, tornou-se necessário que a usina processasse minérios mais competentes e com menor teor de Fe: itabiritos compactos e semi compactos (40%Fe). Até então, este material era considerado estéril, uma vez que os circuitos de beneficiamento não possuíam capacidade para transformá-lo em concentrados, tendo em vista às exigências de mercado. Portanto, o principal objetivo deste trabalho foi analisar o processo de ramp-up para aumentar a capacidade de alimentação da planta para 34 Mt/ano. O dimensionamento dos equipamentos, desenho dos circuitos, bem como as premissas adotadas durante o projeto de adequação serão apresentados neste estudo. Comparando a curvas de ramp-up prevista à praticada, notou-se que houve perdas mássicas consideráveis. Dentre os principais fatores responsáveis, está a grande quantidade de materiais compactos alimentados à usina com granulometria e, talvez, dureza maior do que poderia ser previsto. Os teores de ferro na alimentação da flotação e a qualidade dos concentrados (sínter feed e pellet feed) mostraram-se um pouco abaixo, também, do previsto, porém satisfatórios A estratégia de divisão por fases teve forte impacto positivo, evitando perdas maiores, pois reduziu o número de dias de parada consideravelmente. O desenvolvimento do projeto, denominado FRAGCOM (fragmentação e cominuição), pode ter ajudado a revelar as soluções para os problemas encontrados: este visou a obter melhorias no processo de desmonte e, consequentemente, na cominuição. Os resultados analisados de alguns testes deste projeto mostraram que, na britagem, a usina atingiu maiores taxas de produtividade nesta ocasião. Dado que a britagem é o primeiro circuito de processamento (um gargalo), isto é um fator relevante. Para estes testes foi utilizada uma razão de carga maior no desmonte. Com esta e outras melhorias, uma maior quantidade de material compacto pôde ser processado. Por fim, os resultados mostraram que a falta de aderência da curva de produção prevista com respeito à praticada, deveu-se entre outros fatores, à maior dificuldade de alimentação do circuito de moagem, impactado pelo baixo rendimento operacional da britagem. / This dissertation is based on the work developed to adapt the plant of Conceição 1 (Vale S.A.) to the processing of compact and semicompact itabirites, located in Itabira-MG, southeastern Brazil. Conceição 1 plant was fed with friable hematite and itabirite and produced 22 Mt/year) until 2014. With the progressive consumption of friable ore reserves, it became necessary to process more competent and lower grade ores: compact and semicompact itabirites. Until then, this material was considered waste, since the beneficiation circuits did not have the capacity to transform it into concentrates, especially regarding market requirements. Therefore, the main objective of this work was to analyze the ramp up process in order to fed 34Mt/year. The adopted strategies and their impacts on ramp up process to achieve the production rate were analyzed. Equipment scaling, circuit design, as well as, premises and tests, which were performed during the adaptation project, are presented in this study. Comparing the planned ramp-up curve to the implemented curve, it was noted considerable mass losses. The amount of compacts that fed the plant with particle size and perhaps hardness greater than could be predicted is among main responsible factors The content of Fe in the feed of the flotation and the quality of the concentrates (sinter feed and pellet feed) was a little lower than was expected, but satisfactory. The phasing strategy had a strong positive impact, avoiding greater losses, as it considerably reduced the number of shutdown days. The development of the FRAGCOM (fragmentation and comminution) project may have helped to reveal solutions to the encountered problems: this project aimed to improve the blasting process and, consequently, the comminution. The results of some tests of this project showed that the crushing achieved higher productivity rates at that time. Since crushing is the first processing circuit (a bottleneck), this is a relevant factor. For these tests, a higher blasting load ratio was used. With this and other improvements, a greater amount of compact material could be processed. Finally, the results suggested that the mass losses occurred greater difficulty in feeding the grinding circuit, impacted by the low operational efficiency of the crushing.

A etapa final da reciclagem do alumínio, após coleta, classificação e limpeza é sua transformação em ligas comerciais através da fundição do metal reciclado e sua correção química. Um dos impactos relevantes deste processo é a geração de escórias que representa um dos principais fatores de custo. A escória é um subproduto que surge na superfície do metal líquido decorrente da sua oxidação, da presença de impurezas nas sucatas e da adição de sais fundentes. Normalmente são ricas em alumínio metálico sob a forma de pequenas gotículas que se aprisionam em seu interior e podem levar a perdas consideráveis de produtividade. Pelo seu conteúdo em alumínio metálico, essas escórias têm valor de mercado para as indústrias especializadas em sua recuperação, normalmente com técnicas piro metalúrgicas. Porém frações granulométricas finas, menores que 0,15 mm, trazem dificuldades para a recuperação do alumínio contido. Neste trabalho foram investigadas duas rotas tradicionais de beneficiamento de minérios para a avaliação da concentração de alumínio contido em escórias de alumínio: (I) atricionamento em tambor rotativo e (II) a britagem. Em ambas utilizou-se de uma sequência de operação auxiliar de separação granulométrica. Para comparar a eficiência entre as duas rotas verificou-se a concentração do alumínio presente em produtos granulométricos obtidos em ambas. Outro fator comparativo foi o indicador energético denominado WI (Work Index). Este parâmetro é característico da indústria de processamento mineral e representa a energia consumida pela técnica ou rota empregada. Para a caracterização do concentrado de alumínio nas duas rotas foram utilizadas técnicas por via úmida com medição de hidrogênio, fluorescência de raios-X e pirometria em forno a indução. As avaliações dos concentrados revelaram aumento do alumínio metálico contido à medida que ocorria a redução na granulometria do material potencializando sua recuperação. / The final step of recycling aluminum, after collection, classification and cleaning is its transformation into commercial alloy using recycled metal and its chemical correction. One of the relevant impacts in this process is the creation of slags that represent one of the main cost factors. The slag is a byproduct that appears on the surface of liquid metal due to its oxidation, from the presence of impurities in the scraps and in addition of salts fluxes. Usually they are rich in metallic aluminum in the form of small droplets which are captured inside and can lead to a considerable loss of productivity. By its content in metallic aluminum, these slags have market value for industries specialized in recovery, usually with pyrometallurgy technique. However slim granulometries fractions, smaller than 0.15 mm, bring difficulties for the recovery of aluminum contained. This paper investigated two traditional routes of ore improvement in order to evaluate the concentration of the aluminum contained into the aluminum slags: (I) attrition in tumbling barrel and (II) crushing. In both were used a sequence of auxiliary operation for granulometric distribution. In order to compare its efficiency between the two routes it was verified, in both, the concentration of aluminum present into the granulometric products obtained. Another comparative factor was the energetic indicator denominated by WI (Work Index). This parameter is a characteristic from the industries of mineral processing and it represents the energy consumed by the techniques or routes applied. For the characterization of concentrated aluminum on the two routes techniques used were wet-way with measurement of hydrogen, x-ray fluorescence and induction furnace pyrometry. The evaluation for the concentrated revealed an increase of metallic aluminum contained as occurred into the particle size reduction of the enhacing material in its recovery.

Esta dissertação está baseada no trabalho desenvolvido para adequar a usina de Conceição 1 (da Vale S.A.) para o processamento de itabiritos compactos e semi compactos, situada em Itabira-MG. Até 2014, a usina de Conceição 1 foi alimentada com hematitas e itabiritos friáveis e produzia cerca de 22 Mt/ano. Com o consumo progressivo das reservas de minérios friáveis, tornou-se necessário que a usina processasse minérios mais competentes e com menor teor de Fe: itabiritos compactos e semi compactos (40%Fe). Até então, este material era considerado estéril, uma vez que os circuitos de beneficiamento não possuíam capacidade para transformá-lo em concentrados, tendo em vista às exigências de mercado. Portanto, o principal objetivo deste trabalho foi analisar o processo de ramp-up para aumentar a capacidade de alimentação da planta para 34 Mt/ano. O dimensionamento dos equipamentos, desenho dos circuitos, bem como as premissas adotadas durante o projeto de adequação serão apresentados neste estudo. Comparando a curvas de ramp-up prevista à praticada, notou-se que houve perdas mássicas consideráveis. Dentre os principais fatores responsáveis, está a grande quantidade de materiais compactos alimentados à usina com granulometria e, talvez, dureza maior do que poderia ser previsto. Os teores de ferro na alimentação da flotação e a qualidade dos concentrados (sínter feed e pellet feed) mostraram-se um pouco abaixo, também, do previsto, porém satisfatórios A estratégia de divisão por fases teve forte impacto positivo, evitando perdas maiores, pois reduziu o número de dias de parada consideravelmente. O desenvolvimento do projeto, denominado FRAGCOM (fragmentação e cominuição), pode ter ajudado a revelar as soluções para os problemas encontrados: este visou a obter melhorias no processo de desmonte e, consequentemente, na cominuição. Os resultados analisados de alguns testes deste projeto mostraram que, na britagem, a usina atingiu maiores taxas de produtividade nesta ocasião. Dado que a britagem é o primeiro circuito de processamento (um gargalo), isto é um fator relevante. Para estes testes foi utilizada uma razão de carga maior no desmonte. Com esta e outras melhorias, uma maior quantidade de material compacto pôde ser processado. Por fim, os resultados mostraram que a falta de aderência da curva de produção prevista com respeito à praticada, deveu-se entre outros fatores, à maior dificuldade de alimentação do circuito de moagem, impactado pelo baixo rendimento operacional da britagem. / This dissertation is based on the work developed to adapt the plant of Conceição 1 (Vale S.A.) to the processing of compact and semicompact itabirites, located in Itabira-MG, southeastern Brazil. Conceição 1 plant was fed with friable hematite and itabirite and produced 22 Mt/year) until 2014. With the progressive consumption of friable ore reserves, it became necessary to process more competent and lower grade ores: compact and semicompact itabirites. Until then, this material was considered waste, since the beneficiation circuits did not have the capacity to transform it into concentrates, especially regarding market requirements. Therefore, the main objective of this work was to analyze the ramp up process in order to fed 34Mt/year. The adopted strategies and their impacts on ramp up process to achieve the production rate were analyzed. Equipment scaling, circuit design, as well as, premises and tests, which were performed during the adaptation project, are presented in this study. Comparing the planned ramp-up curve to the implemented curve, it was noted considerable mass losses. The amount of compacts that fed the plant with particle size and perhaps hardness greater than could be predicted is among main responsible factors The content of Fe in the feed of the flotation and the quality of the concentrates (sinter feed and pellet feed) was a little lower than was expected, but satisfactory. The phasing strategy had a strong positive impact, avoiding greater losses, as it considerably reduced the number of shutdown days. The development of the FRAGCOM (fragmentation and comminution) project may have helped to reveal solutions to the encountered problems: this project aimed to improve the blasting process and, consequently, the comminution. The results of some tests of this project showed that the crushing achieved higher productivity rates at that time. Since crushing is the first processing circuit (a bottleneck), this is a relevant factor. For these tests, a higher blasting load ratio was used. With this and other improvements, a greater amount of compact material could be processed. Finally, the results suggested that the mass losses occurred greater difficulty in feeding the grinding circuit, impacted by the low operational efficiency of the crushing.

The aim of this study was to study the extraction of zinc from the mineral sphalerite, especially the leaching of concentrate recovered from the Rosh Pinah tailings by means of ferric chloride. To this end, the literature on zinc processing was surveyed and knowledgeable persons were consulted. The study also addressed the leaching kinetics of an upgrade Rosh Pinah tailings dam concentrate as well as those of a synthetic zinc sulphide in a ferric chloride medium. Valuable results were obtained, from the leaching of sphalerite concentrate in ferric chloride medium. An activation energy value of 45.82 kJ/mol was obtained, which compares well with what has been published in the literature. A chemical control model and a diffusion control model were applied to the data obtained. From neither of the models a straight-line relationship could be deduced over the leaching range. At t < 45 minutes it seems that the process is controlled by chemical reaction at the interface; at t > 45 minutes it seems that the process is controlled by diffusion through the product layer. If therefore seems that the rate-controlling step can be related to the process of diffusion through the product layer. The mixed control model proposed by Huang and Rowson, [1-(1-x)1/3+y/6[(1-x)1/3+1-2(1-x)2/3]=kMt, was applied to data obtained during this study. The resultant graphical fit was near perfect, indicating that sphalerite leached in ferric chloride follows a mixed control mechanism for the conditions reported in the study. An activation energy of 20.71 kJ/mol was determined for this model by using the following equation: / Dissertation (MSc)--University of Pretoria, 2006. / Chemistry / unrestricted

Molybdenum is a versatile alloying and refractory metal of strategic importance. In India almost all molybdenite is obtained currently as st byproduct from copper and uranium deposits. The present Indian production is only about 66 tonnes while the demand is over 1000 tomes. It thus becomes important to explore newer deposits of molybdenum and develop efficient beneficiation strategies to recover the metal. A potential source of primary rnolybdenite has been found in the Ham area of Dharmapuri district in Tamil Nadu. In the present investigation, taking into consideration the importance of the problem beneficiation studies have been undertaken on core - drill molybdenite ore samples from the Hanu area. Initially, detailed characterization of the molybdenite ore has been carried out with respect to its mineralogy and chemical composition. The X-ray diffkactogam of the ore has also been recorded These studies have indicated that quartz and sericite are the major minerals followed by carbonates and feldspar. Among the sulphide minerals, pyrite is dominant with trace amounts of galena, sphalerite, chalcopyrite and molybdenite. The molybdenum content in the ore sample has been determined to be about 0.1%. Liberation studies have revealed that molybdenum is more or less uniformly distributed in the different size fractions from 1.7 mm down below to 75 microns. However, mineralogical analysis of the different size fractions has indicated that about 85% of the molybdenite is liberated. from associated silicate and carbonates below 2 12 microns. The results of the flotation kinetic tests have shown that percentage recovery and grade of molybdenum foLZow an inverse relationship with time. Studies carried out to evaluate different reagent - combinations, reveal that optimum values of grade and recovery could be achieved using kerosene and M1IBC. Further, these studies have shown that flotation time of 4 minutes is adequate, as beyond this time the grade of molybdenum is found to deteriorate. Detailed mesh-of-grind studies have indicated that 20 minutes of grinding yields optimum values of molybdenum and lead in the float product and this time was fixed for all subsequent experiments. Preliminary experiments conducted to evaluate djfferent depressants for galena have shown that satisfactory results are obtained only with sodium dichromate. Optimisation studies performed to arrive at the dosage of sodium dichromate have shown that the addition of 0.25kg/t of sodium dichromate gives optimum results with respect to overall recovery and grade of molybdenum, copper and lead in the float and tailing fractions. In a similar manner, the optimum dosage of kerosene (collector for molybdenite) has been arrived at to be 0.8kg/t taking a holistic view of the grades and recoveries of the different metal values of interest. Based on the studies carried out with respect to optimization of the mesh-of-grind, depressant and collector concentrations, it became apparent that a grade of about 0.8% Mo only could be achieved with over 80% recovery. The redeeming feature however was that over 90% of the feed could be rejected at the rougher flotation stage itself with a negligence loss of about 0.02% Mo in the tailings. It was thus considered logical to further upgrade the Mo content by regrinding. An extensive flotation campaign was therefore mounted, adopting the following strategies: (1) Ist stage regrinding and one cleaning (2) IInd stage regrinding and three cleanings (3) IIIrd stage regrinding and two cleanings Based on the first stage regrinding tests it was found that by regrinding to 100% passing 106 microns, the Mo assay could be enhanced to over 32% from a initial value of about 0.1% in the feed. The enrichment ratio at this stage corresponds to about 340.After the second stage regrinding followed by three stages of cleaning, close to 75% recovery of Mo with an assay value of about 52% could be achieved, further enhancing the enrichment ratio to about 540. A few experiments were conducted using sodium cyanide during second stage regrinding tests and it was found that copper assay could be brought down to 0.3% from about 0.8%, without affecting the grade of lead and molybdenum. The results of the third stage regrinding tests have highlighted that a final concentrate assaying about 55% molybdenum with over 70% recovery could be obtained. It is worthy to mention that the concentrate so produced meets the specification of metallurgical grade molybdenite. The overall enrichment ratio obtained, commencing from a feed assaying 0.1% Mo, corresponds to about 580. In order to explore the efficacy of organic depressants, which are more acceptable on environmental grounds, detailed flotation studies were carried out using dextrin with particular emphasis on galena depression. A series of experiments was carried out in an identical manner to those conducted using sodium dichromate. Here again, three stages of regrinding/cleanings test where carried out, akin to those performed using sodium dichromate. A dextrin concentration of 0.01 kg/t was found to be an optimum value from the point of grade, wt. % recovery and distribution of molybdenum, lead and copper in the cleaner concentrate. It is noteworthy that after second stage regrinding followed by four stages of cleaning, the molybdenum assay value has significantly improved from 16% to about 53% with over 70% recovery. Another notable feature is that copper content in the concentrate is only about 0.2% even without the addition of sodium cyanide. The results of the third stage regrinding/cleaning tests have shown marginal improvement in the molybdenum assay values without affecting the grade of copper and lead. On a comparative basis, it can be inferred that dextrin holds promise to be used as a potential substitute for the inorganic depressants such as sodium dichromate and sodium cyanide. On the basis of the extensive investigations carried out on the beneficiation of molybdenite ore, a comprehensive flowsheet has been developed.

Esta dissertação está baseada no trabalho desenvolvido para adequar a usina de Conceição 1 (da Vale S.A.) para o processamento de itabiritos compactos e semi compactos, situada em Itabira-MG. Até 2014, a usina de Conceição 1 foi alimentada com hematitas e itabiritos friáveis e produzia cerca de 22 Mt/ano. Com o consumo progressivo das reservas de minérios friáveis, tornou-se necessário que a usina processasse minérios mais competentes e com menor teor de Fe: itabiritos compactos e semi compactos (40%Fe). Até então, este material era considerado estéril, uma vez que os circuitos de beneficiamento não possuíam capacidade para transformá-lo em concentrados, tendo em vista às exigências de mercado. Portanto, o principal objetivo deste trabalho foi analisar o processo de ramp-up para aumentar a capacidade de alimentação da planta para 34 Mt/ano. O dimensionamento dos equipamentos, desenho dos circuitos, bem como as premissas adotadas durante o projeto de adequação serão apresentados neste estudo. Comparando a curvas de ramp-up prevista à praticada, notou-se que houve perdas mássicas consideráveis. Dentre os principais fatores responsáveis, está a grande quantidade de materiais compactos alimentados à usina com granulometria e, talvez, dureza maior do que poderia ser previsto. Os teores de ferro na alimentação da flotação e a qualidade dos concentrados (sínter feed e pellet feed) mostraram-se um pouco abaixo, também, do previsto, porém satisfatórios A estratégia de divisão por fases teve forte impacto positivo, evitando perdas maiores, pois reduziu o número de dias de parada consideravelmente. O desenvolvimento do projeto, denominado FRAGCOM (fragmentação e cominuição), pode ter ajudado a revelar as soluções para os problemas encontrados: este visou a obter melhorias no processo de desmonte e, consequentemente, na cominuição. Os resultados analisados de alguns testes deste projeto mostraram que, na britagem, a usina atingiu maiores taxas de produtividade nesta ocasião. Dado que a britagem é o primeiro circuito de processamento (um gargalo), isto é um fator relevante. Para estes testes foi utilizada uma razão de carga maior no desmonte. Com esta e outras melhorias, uma maior quantidade de material compacto pôde ser processado. Por fim, os resultados mostraram que a falta de aderência da curva de produção prevista com respeito à praticada, deveu-se entre outros fatores, à maior dificuldade de alimentação do circuito de moagem, impactado pelo baixo rendimento operacional da britagem. / This dissertation is based on the work developed to adapt the plant of Conceição 1 (Vale S.A.) to the processing of compact and semicompact itabirites, located in Itabira-MG, southeastern Brazil. Conceição 1 plant was fed with friable hematite and itabirite and produced 22 Mt/year) until 2014. With the progressive consumption of friable ore reserves, it became necessary to process more competent and lower grade ores: compact and semicompact itabirites. Until then, this material was considered waste, since the beneficiation circuits did not have the capacity to transform it into concentrates, especially regarding market requirements. Therefore, the main objective of this work was to analyze the ramp up process in order to fed 34Mt/year. The adopted strategies and their impacts on ramp up process to achieve the production rate were analyzed. Equipment scaling, circuit design, as well as, premises and tests, which were performed during the adaptation project, are presented in this study. Comparing the planned ramp-up curve to the implemented curve, it was noted considerable mass losses. The amount of compacts that fed the plant with particle size and perhaps hardness greater than could be predicted is among main responsible factors The content of Fe in the feed of the flotation and the quality of the concentrates (sinter feed and pellet feed) was a little lower than was expected, but satisfactory. The phasing strategy had a strong positive impact, avoiding greater losses, as it considerably reduced the number of shutdown days. The development of the FRAGCOM (fragmentation and comminution) project may have helped to reveal solutions to the encountered problems: this project aimed to improve the blasting process and, consequently, the comminution. The results of some tests of this project showed that the crushing achieved higher productivity rates at that time. Since crushing is the first processing circuit (a bottleneck), this is a relevant factor. For these tests, a higher blasting load ratio was used. With this and other improvements, a greater amount of compact material could be processed. Finally, the results suggested that the mass losses occurred greater difficulty in feeding the grinding circuit, impacted by the low operational efficiency of the crushing.

Thesis (LLM.(Management and Development Law)) -- University of Limpopo, 2019 / South Africa, like many African States is faced with an increase in the unemployment rate and decrease in economic growth. In terms of Mineral and Petroleum Resources Development Act 28 of 2002 (MPRDA) as amended, the people of South Africa are the owners of mineral resources such as; Platinum Group Metals, Gold, Platinum, and the State is the custodian thereof. The main problem is that the majority of black people in South Africa remain destitute and marginalized. They revolt by demanding radical socio-economic transformation and beneficiation from mineral resources, as the backbone of their survival. The government rejected nationalisation instead favouring a Mineral beneficiation strategy. In terms of Section 26 of MPRDA, the minister of mineral resources may initiate or prescribe levels of beneficiation of minerals in the Republic. The beneficiation strategy entails that the people must have control and access to their country’s mineral resources; in another context, it entails the transformation of minerals or a combination of minerals to higher value product, which can either be consumed locally or exported. Thus creating economic growth, jobs and alleviate poverty. The study examines legislation and policies that promote beneficiation of minerals and petroleum resources in the Republic. The study also deals with the importance of minerals and petroleum beneficiation as an impetus towards socio-economic transformation in the country. It utilised jurisprudence of Botswana, which has robust legislation, and strategies that promote and deliver resource beneficiation to the citizens equitably. It points out the challenges faced in the transformation of mineral resources beneficiation and legislative prospects that have been put in place to redress them. Key Words: Beneficiation legislation, Minerals resources, Socio-economic transformation and Poverty.

A one-dimensional, physical model describing two-phase fluid flow is used to simulate the effect of boiling on silica precipitation in geothermal and epithermal precious metal systems. The extent to which decreasing temperature and fluid vaporization are responsible for quartz precipitation is dependent on three related factors - the temperature of the fluid entering the two-phase system, the change in fluid temperature with respect to distance of fluid travel, and the extent of fluid vaporization in regions of gradual temperature decline. Boiling contributes to significant quartz precipitation in systems with high-temperature basal fluids, and in deeper portions of systems in which extensive vaporization occurs. Temperature reduction is a dominant precipitation mechanism in near- surface regions where temperature reduction is rapid, and in systems with lower temperature fluids. Owing to the small difference in quartz solubility between the liquid and vapor phases at low temperatures, boiling does not contribute to significant quartz precipitation in low temperature, near-surface regions. Quartz precipitation is most intense in systems with high mass flux/permeability ratios and low initial fluid temperatures. Geothermal systems with high mass flux/permeability and moderately low initial fluid temperatures are most effective in producing epithermal systems with abundant gold. Numerical modeling indicates that sufficient copper can be partitioned from a "typical" calc-alkaline melt into an exsolving fluid to produce an economic porphyry copper deposit. Neither non-magmatic sources nor an additional hidden magma source are necessary to provide copper to the system and an elevated initial copper concentration in the melt is not necessary. Melts in shallow systems with initial water concentrations of at least 2.5 wt.% water and Cl/H₂O as low as 0.03 can produce economic deposits with volumes of 50 km³ or less, regardless of copper compatibility. In deeper systems deposits may be produced from melts of less than 30 km³ if copper behaves incompatibly prior to water saturation or if the initial melt is water-rich and requires only minor crystallization to achieve water saturation. If copper behaves compatibly prior to water saturation very large volumes of melt may be required. High salinity fluids may be produced directly from a crystallizing melt and immiscibility is not necessary to produce the high salinities observed in some systems. Depending on the temperature, pressure, initial water content, and the extent of crystallization of the melt, the bulk salinity of the aqueous fluids exsolved from a melt may vary from < 2.0 wt.% NaCl to saturation levels (84 wt.% NaCl at 700°C). Fluid evolution during the magmatic-hydrothermal transition and coincident molybdenite precipitation at Questa, New Mexico, has been traced using fluid inclusion microthermometry. The lack of cogenetic liquid- and vapor-rich inclusions, plus final homogenization of most saline, liquid-rich inclusions by halite dissolution indicate that high-salinity fluids were generated by a mechanism other than fluid immiscibility. Pressure fluctuations, responsible for the formation of a magmatic-hydrothermal breccia, are capable of producing the observed fluids and inclusion behavior. Solubility data indicate that the crystallizing aplite porphyry generated fluids with salinities as high as 57 wt.% NaCl equivalent. / Ph. D.