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By Y. Foucaud, C. Eswaraiah, L. Filippov

Enhanced gravity separators such as Falcon concentrator which uses additional centrifugal force, are the most common gravity concentration techniques used for fine particles processing. Hence, understanding the kinetics and separation mechanisms within these separators is of paramount interest. Recent research yielded a predictive physical model for the Falcon Ultra Fine (UF) which however does not explain some results obtained with industrial ores. This study aims to identify the mechanisms involved in Falcon UF separation with the objective of confirming or rejecting the hypotheses on which the current model is built and suggesting potential points of improvement. The Falcon UF kinetics is investigated through the processing of complex low-grade and fine-grained ores from the Altenberg tin deposit (Germany), the Tabuaço tungsten deposit (Portugal) as well as a synthetic iron ore. Saturation tests are performed on the Falcon UF by controlling the separation efficiency in terms of recovery and enrichment ratio with time or feed mass. Results show an evolution of Falcon UF performance with time in contradiction with the stationary separation hypothesis on which the physical model is based. Observation of the concentrate bed suggests the presence of erosion figures in furrows which may play locally an active role in the separation. In terms of Falcon UF separation timing, three phases can be distinguished. First, upon initial feeding of the bowl, a bed quickly grows unselectively and ultra-fine particles are ejected from the bowl until the bed reaches its final profile. Next, actual separation occurs with selective concentration of dense particles. Finally, capture sites saturate and recovery drops. The evolution of partition curves over time confirms the existence of two separation mechanisms. First, differential particles settling within the flowing film responsible for the ejection of small size particles during the whole separation cycle which is already accounted for in the physical model. The second mechanism involved may be explained by the action of lift force, neglected in the physical model, which acts preferentially on coarse particles deposited at the surface of the bed resulting in coarser particles being rejected in the tailings. Hence, the addition of a lift force component to the existing model is suggested to account for this second separation mechanism.

Jan 1, 2018

By Nóra Schreithofer, Zoltán Jávor, Kari Heiskanen

"One of the challenges the mineral processing industry is facing is caused by the fact that water resources in mining areas are becoming very limited and the cost of water is increasing. The water sources in arid regions often have high salt content. Environmental regulations are forcing plant operations towards completely closing the water cycles within plants. This means that impurities (salts, reagents, ions dissolved from minerals, etc.) accumulate within the circuit that will affect the flotation performance. Water purification can significantly increase the operating costs therefore it should be carefully considered weather the impurities need to be completely removed or is there a tolerable level of impurities that can still be left in the process water without significant deterioration of the flotation performance? Several additional questions arise: what are the tools that help identify what is a tolerable level of impurities? How do the different impurities interact and what is their effect on the process? The effect of frothers on the dynamic properties of air/liquid interface in different size-scales has been extensively studied by the authors in the past. Based on these studies a frother characterization framework was developed that systematically examines the dynamic surface properties of the air/liquid interface in relation to the bubble size. This work can be considered as tool that could be used for the above mentioned purpose. The present study investigates weather the same frother characterization framework can be applied for systems where both frother and different types of salts are present. Nasfroth 240 was used as a frother, in combination with structure-breaker KCl or structure-maker NaCl and CaCl2. Bubble size measurements in laboratory scale mechanical flotation cell and laboratory flotation column and dynamic surface property measurements (dynamic surface tension and dilatational elasticity) were performed. The results highlighted the addition of salt to the frother solutions significantly decrease the bubble size and increase the froth high. The coalescence behavior of bubbles showed correlation between the D32 and ionic strength of salts. The results highlighted that the studied structure maker and structure breaker salts effect the dynamic surface properties in different way."

Jan 1, 2014

By V. Sovmen

The gold-ore Olympiada deposit is located within the Yenissei range (Krasnoyarsk Region, Russia). Primary sulphides ores are metasomatic changed rocks, mica-calcite-quartz structure with impurity amphiboles, chlorites, carbon, the rare thin grains of sulfides (up to 3%~5%) and native gold. The structures of ores are fine-grained, prevailing texture of ores - interspersed, vein-interspersed, band-interspersed, veinlet. The most important minerals in the deposit are: gold, arsenopyrite, pyrrhotite, antimonite, Sb-sulphosalt, quartz, muscovite, calcite, siderite, titanium minerals, chlorite and minor sulfides like chalcopyrite, galena, sphalerite, etc. A common problem in mineralogical studies applied to mineral processing (concentration, cyanidation, etc.) is the characterization of gold in ores and technological products. This paper discusses the behavior of minerals during technological process at operating factory in Olympiada Mine and gold distribution in the ores and products. For the mineralogical characterization of minerals ? combination of analytical techniques was used. Gold is encountered in the primary ores as free grains among rocks, growth with sulfides and nonmetallic minerals, inclusions in sulfides, sulphosalt, and nonmetallic minerals. The gold-sulphide ores of Olympiada deposit can be quite complicated for enrichment. With the purpose to increase the extraction of metal from concentrates by liberating the dispersed gold, forming inclusions in sul-fides, there is used technology of biooxidation of flotation concentrates in Olympiada Mine. Gold and the basic ore-forming minerals in the ores feed, sulphidic concentrates, biocakes, tailings of concentrates of flotation and products of hydrometallurgical leaching have been studied in the mineralogical research. During researches it is established that pyrrhotite was completely oxidized while arsenopyrite was oxidized almost completely in the bacterial oxidation process. Pyrite and antimony minerals behave similarly and were oxidized only partially. The main oxyhydroxides in the bacterial oxida-tion process are goethite, limonite and jarosite. The results of mineralogical researches showed reasons of losses of gold during hydrometallurgical enrichment.

Jan 1, 2014

By Paula Olea, Gonzalo Montes-Atenas

Froth flotation operation is a large tonnage process aiming at selectively separate economically valuable minerals from gangue material. The wellbeing of an industrial froth flotation operation has been historically assessed and understood in terms of many variables known to somehow affect the process performance. Among these variables, air dispersion have been pointed out as key to secure the correct transport of hydrophobic particles to the froth phase and, then, to the concentrate. One of the classic parameters assessed when evaluating the air dispersion in flotation tanks is the superficial gas velocity. Many reports have focused on studying the superficial air velocity profiles across the pulp phase and theories have been based on the fact that the measurements should be performed in the so called "quiescent zone", which is a volumetric region inside a flotation cell of difficult determination. The hypothesis behind this research work is that the reporting of particles to the concentrate would provide a better correlation with the effective air flowrate pattern created in the froth phase. The aim of this study, as a first step towards developing a flotation model fully froth phase-based, is to estimate the effective surface area used in a flotation cell derived from results obtained with a specific setup at laboratory scale. The methodology considers running a thin lateral flotation cell cut at different superficial air velocities, with and without particles. It was found a non-linear correlation between the superficial air flow rate and the characteristic distance between the vertical wall next to the cell lip and the cut point where the foam or froth flowrate almost stops contributing marginally to the overall amount of solid particles transferred to the concentrate. The presence of hydrophobic particles reduced the mobility of the froth phase reducing the characteristic distance.

Jan 1, 2014

By Graeme Jameson

"In current flotation circuits it is customary to grind the whole of the mill feed to an initial size, which is determined by the liberation characteristics of the ore, and the ability of the flotation machines to float the fully liberated particles. Usually, the product of the primary mill will be ground further in a ball mill, to improve the liberation of the values and hence the product grade, before passing to rougher flotation cells. The final grind size is ore-dependent, and is a balance of factors including the relation between surface liberation and grind size, the grain size of the valuable particles within the host rock, and the feed grade. The P80 for the feed to flotation may be as high as 300 µm for free-milling copper ores, and as low as 53 µm for finely disseminated complex ores. The grinding of the feed ore requires considerable input of energy. The rate of replacement of wear components such as mill liners and media, is proportional to the energy input. The costs of these two factors - energy and wear - are usually comparable and together they form the major part of the running costs of a concentrator, and indeed, of the whole mining operation. The energy required increases as the final grind size decreases. This talk will focus on the reduction of milling costs that could be achieved, using a fluidized bed flotation technology that can give high recoveries at coarse particle sizes. A number of different circuit designs will be presented, using the new technology. Calculations show that reductions in the running costs of a mine and associated concentrator of the order of ten to twenty percent could be achieved."

Jan 1, 2014

By Hernán Menares, Diego Hernández

"Over the last few years, the copper mining industry has been facing a changing scenario with respect to both the market and society which has resulted in taking a closer look at the way in which mining is being done. The cycle of high metal commodity prices of the last decade left the industry with high costs. Together with increased environmental and social requirements, a decrease in ore body quality, scarcity of resources such as human capital, water and energy, has resulted in an ever-increasing challenge to make a profit out of new ore bodies but also to maintain the current operations in the longer term competitive. The major challenge is to create value for all stakeholders, exploiting ore bodies that nowadays are not considered economically attractive, which applies to both new ore bodies and existing operations, but in a sustainable way. In order to achieve this objective, it is necessary to approach the mining business differently in five main areas: (1) operational efficiency through better use of installed equipment and skilled labor force; (2) efficient use of energy; using opportunities for alternative energy sources and efficient design; (3) efficient use of water; diminishing losses and use of seawater as an alternative source; (4) minimizing environmental impact by eliminating effluents and controlling dust emission; and (5) a more closer, proactive and collaborative relationship with the communities allowing them to be an active player in the solution to assure a sustainable business in the long term. This presentation will show how Antofagasta Minerals is facing these challenges with a long term strategy that includes all of the above mentioned aspects and that is allowing the company to exploit its mineral properties in an efficient and successful way."

Jan 1, 2014

By Sami Makni, Ahmed Bouajila

"To remain competitive in an open market, mining companies are more and more requested to optimise their complex and highly multivariate processes. The increasing amount of process data, brought about by intensive use of instrumentation and the progress in computer data acquisition, enhances the need for more and more powerful and robust tools for the analysis and modelling of the process data. Now, with the emergence of multivariate data analysis (MDA) techniques, on-line clustering of mineral process behaviour is possible and could help in the extraction of valuable process operation indicators. MDA can be used in different mineral processes such as flotation, grinding, smelting etc. In this paper, the focus will be on grinding process as it is the one of the most costly node in the mineral processing scheme (i.e. power consuming) and it is a highly multivariable process. Particularly for primary grinding mills (SAG/AG), more instrumentation outputs and more powerful and significant process indicators are needed for efficient control and optimisation.MDA is a novel approach suitable for understanding mineral process behaviour compared to the traditionally approaches based on empirical and phenomenological modelling. Multivariate techniques can be used for several purposes. In this paper, the following objectives will be addressed:operation diagnosis: Shift differentiation and operation test differentiation can be showed by using MDA tools such as principle component analysis and factorial discriminant analysis.operation performance monitoring: operation regimes can be evaluated by clustering based on an economic criterion performance such as costs, tonnage, product quality, profit, etcIdentification of operation behaviour (monitoring) and selection of drift correction trajectories (control):MDA can be used to identify periods of unusual or abnormal process behaviour and to diagnose, if it is possible, causes for such behavior."

Jan 1, 2003

By Francesco Montanari, Gianni Schena

"Recent improvements in X-ray computed tomography allow investigation of objects several tens of millimetres in dimension with spatial resolutions in the order of a few microns. These improvements are made possible by coupling the micro-focus technology adopted by some of the latest cone-beam X-ray sources with an increase in the efficiency of the detectors. The micro-focus technology allows the production of clearer images at high magnification by reducing the penumbra (fuzziness) associated with larger focal spot size.Even higher resolutions can be expected in the next few years with the commercialisation of nano-focus X-ray tubes. In practice one can inspect a system of fine composite particles and analyze the different mineralogical phases in each individual particle. Computed tomography allows accurate liberation studies, e.g. providing liberation spectra or washability data in tens of minutes. However, on-line application of micro-focus computed tomography is unlikely in the foreseeable future, despite rapid development.Dual-energy (DE) radiography is another X-ray technique, which allows retrieval of the volumetric content of valuable components in two-phase particles in a fraction of a second. A digital radiograph of a single two-phase particle produces a grey level image, where the luminosity of the pixels is determined by the sum of the attenuation levels of all the structures. Thus morphological and compositional effects concur to produce the radiographic image, which does not allow retrieval of the composition of the particle, as the 3D-structure of the particle is compressed into a 2D-image, with an obvious loss of information. Thus, in principle it is not possible to discriminate between thick, comparatively penetrable, and thin, comparatively impenetrable mineralogical components."

Jan 1, 2003

By Jochen Petersen, David G. Dixon

"Although heap leaching may be perceived as a somewhat low-tech route for the extraction of low-grade minerals, the underlying physical, chemical and biological processes are in fact extremely complex. There has been increased interest in heap leaching of sulphide minerals in recent years with the advent of controlled bio-heap leaching, and the need to mine more marginal ore deposits.A detailed investigation into the dynamics of heap leach processes has provided much insight into the underlying complexities, and has led to the development of a sophisticated modelling tool, HeapSim. Some of the sub-processes that are modelled include mineral kinetics, particle size effects, bacterial growth, oxidation and adsorption, gas adsorption, pore diffusion, bulk advection, gas balance and heat conservation. The interplay of these various sub-processes is illustrated in the paper.Two case studies are presented which illustrate specific features of the model for different applications and how these have helped to identify key areas of concern. The first is focussed on chalcocite heap bioleaching, which shows that by nature of the reaction the process is strongly dependent on the initial supply of acid to the mineral site. In heaps this acid supply can be severely limited by the rate of diffusion from channels of flowing solution into stagnant zones of the heap, whereas in narrow-bore laboratory columns this effect is not observed."

Jan 1, 2003

By Sashnee Raja, Mehdi Nemati, Ashley Sissing, Susan T. L. Harrison

"Extreme thermophiles, operating at 65 - 90°C, are finding increasing application in biohydrometallurgy. These micro-organisms have the advantage of exhibiting better oxidation kinetics in terms of reaction rate and extent of mineral solubilisation (Duarte et al., 1993; Norris and Barr, 1988; Konishi et al., 1995). These extreme thermophilic Archae, characterised by a different cell envelope structure (König and Stetter 1986, König 1988, Michel et al. 1980) perceived to provide reduced structural strength in comparison to bacterial envelopes, and customised metabolic pathwaysThe active tank bioleaching process, used for high rate leaching, is conducted in a slurry bioreactor. Here sufficient energy dissipation is required to ensure suspension of the mineral phase as well as to sustain high rates of gas liquid mass transfer. It is well known that subjection to hydrodynamic stress of sufficient magnitude may alter the physiological state of a range of micro-organisms through changed viability (ability of the microbes to grow), metabolic activity and integrity. While limited study on the influence of the solids phase on thermophilic leaching performance is reported, initial reports suggest that the thermophiles used for bio-oxidation appear to be sensitive to hydrodynamic conditions (Jordan et al 1993, Clark and Norris, 1996) and the presence of solids (Norris and Bar 1988, Le Roux and Wakerley, 1988, Escobar et al. 1993, Torres et al. 1995, Nemati and Harrison, 2000)."

Jan 1, 2003

By Williams Calderon, César Arredondo, Gonzalo Montes-Atenas

The quality of final concentrate in froth flotation circuits is largely dictated by the correct implementation of the froth washing operation in flotation cleaning stages, which are commonly installed in column flotation cells. In flotation plants, this aspect has been largely overlooked and the froth washing is restricted to the use of perforated piping through which process water flows producing a similar effect to that observed in "fountains": jet created with low energy crosses the froth phase washing out entrained particles as well as particles weakly attached to bubbles. The aim of this research study is to assess the efficiency of traditional froth washing systems theoretically and experimentally. A theoretical model was implemented using Fluent® software where a jet of variable speed was introduced in a continuous soft matter phase with physical properties similar to those observed in a froth phase in wet and dry conditions. In addition, a simple experimental protocol was designed to validate the model. It was found that the water process jet-like flow influences the behavior of 2 to 3 times the equivalent volume in the froth phase. Such influence zone is dramatically reduced as the froth phase becomes drier. These results were confirmed by the experimental findings indicating that a better froth washing technologies must be assessed and implemented. Some aspects of the ideal froth washing system are derived and discussed in details.

Jan 1, 2014

By Andrzej Luszczkiewicz, Magdalena Duchnowska, Jan Drzymala

A selected flotation system of beneficiation of the copper ore at KGHM Polska Miedz S.A. has been analyzed in the article. It was found that a proper assessment of upgrading must be based on two elements, that is the upgrading process selectivity and working point of the considered flotation unit, both determined, preferentially by means of the Fuerstenau recovery-recovery upgrading curve. The Cu recovery - non-Cu components recovery upgrading curve was selected for calculations because its background lines (no separation and ideal separation) are insensitive to changes in the grade of feed of the processed material. This approach allows a comparison of upgrading results for feeds having different grade, being upgraded in various flotation machines and under different physicochemical conditions. It was shown in the paper that the main criterion for comparison of two working in parallel systems is selectivity of upgrading. However, when two flotation machines, despite of the same selectivity, produce concentrate and tailing of different grades, it is necessary to analyze their working points using upgrading curves. The proper position of the working point depends on the criterion imposed on the process and is a result of not only basic parameters of the upgrading process such as feed, concentrate and tailing grades but also on economic parameters such as costs associated with the production of concentrates and the time needed for their production.

Jan 1, 2014

By Nina Panteleeva, Elena Afonina, Stanislav Titkov, Jury Buksha

"Flotation processing of water-soluble minerals (potassium ores, sedimentary salts of salt lakes) is currently the main method for production of potassium fertilizers and concentrated carnallite which is the initial product for production of metallic magnesium. Flotation of sylvite (KCl) and halite (NaCl) is carried out in the electrolyte solutions: KCl-NaCl-H2O and KCl-NaCl-MgCl2-H2O. The report presents the results of studies of the effect of concentration and the electrolyte type on the size of air bubbles in a flotation cell in comparison with the floatability of mineral constituents of potash ores. The floatability in electrolytes of various compositions has been studied: - of sylvite (KCl) by alkylamines, - of halite (NaCl) by alkylmorpholines, - of silicate-carbonate slimes contained in the ore by ethoxylated surfactants. The reagent modes (regimes) activating the flotation desliming of potash ores have been developed."

Jan 1, 2014

By J. Y. ` Xie

The paper introduced bio-oxidation plants of refractory gold concentrate in China and CCGRI cultures. CCGRI cultures are composed of bacteria and archaea. Archaea Ferroplasma acidiphilum is very thick and fills whole mineral surface. It plays a more dominant role in CCGRI process. Several years of practice has proved that the operating temperature in bioreactors between 38~52?,gold recovery is almost same. Pulp concentration has been increased each year and reached to 25%.

Jan 1, 2014

By Knut L. Sandvik, Erik Larsen

"Estimated global solar energy demand in 2001 required approximately 5,500 tons of silicon feedstock. This required 65,000 tons of quartz. If the trend continues, the solar energy demand in 2010 would require approximately 30,000 tons of silicon feedstock and 350,000 tons of quartz, although the need for quartz probably will be lower than this due to higher solar cell efficiencies, larger and thinner wafers, more extensive recycling of waste material and new routes for the production of silicon feedstock. The raw material requirements for the production of metallurgical-grade silicon are most likely to change. This may favour increased beneficiation of primary raw materials in the future solar cell production chain.SOLAR CELL PRODUCTION CHAIN SCENARIOSThe major problem concerning solar cells is the production costs. Electricity produced from fossil fuels and hydropower plants are currently much cheaper than the electricity produced from solar cells. Also, limited availability of silicon feedstock for the production of crystalline silicon solar cells is considered a major threat to the further growth of the PV industry. The present route for solar silicon feedstock goes from quartz, through metallurgical-grade silicon (MG-Si) and to electronic-grade silicon (EG-Si). The reject from the EG-Si production are further processed into wafers and solar cells. This situation is not satisfying, however, because it has created a silicon feedstock shortage and a PV energy price that is not competitive in a large scale.Crystalline silicon solar cells are the most important solar cells manufactured today. This will most probably remain the situation the next decade. Also, the future silicon ""feedstock"" is most likely not reject from the production of electronic-grade silicon, as it is today. There will probably be a more direct solargrade silicon route, excluding the very expensive electronic-grade silicon ""detour"". Quartzite has been regarded as the most suitable primary raw material used in the silicon solar cell production chain. This may change as the raw material requirements for the production of metallurgical-grade silicon are most likely to change. In addition, quartz or other silica-containing minerals from other rocks may be of a higher purity or contain lesser amounts of the most harmful elements. This favours increased beneficiation of primary raw materials in the future solar silicon feedstock production chain"

Jan 1, 2003

By W. Pawlos

"The paper will present the methods of visual observation and recording of movement paths of coal grains of different physical properties in the paramagnetic liquid. The paths were recorded with a video camera in the working chamber by means of a specially constructed device, acting as a periscope, which were then transformed into digital images.Experimental movement paths were confronted to the paths obtained in a theoretical way by means of solving differential equations of movement. The outlet level of a grain of the same physical properties from the separator is a random variable with normal distribution which modal value is equal to the outlet level of a spherical grain, calculated from the solution of grain movement equations. At these assumptions it is possible to calculate the height of the passage from the separator working chamber to separate a given product with a given separation accuracy, measured by a probable error and to determine separation conditions."

Jan 1, 2003

By K. W. Stöckelhuber, A. Wenger, H. J. Schulze

"An important elementary step of the flotation process is the forming, drainage and rupture of a thin intervening liquid film between bubble and mineral particle.After the encounter of the bubble with the solid surface a wetting film is formed. The initial thinning of this film is driven by the capillary pressure inside the bubble. When the film has reached a certain thickness rupture can take place. There are two possible mechanisms describing this process:(a) Gas nucleation, caused by nano bubbles inside the film.(b) Growing fluctuation waves (spinodal dewetting) on fluid interfaces under the influence of any kind of attractive forces (electrostatic, van der Waals).Metastable wetting films on negatively charged, hydrophobic glass surfaces (gaseous phase methylated), or on hydrophilic, positively charged glass surfaces (with Al3+ ions), have been analysed by means of the kinetics of film thinning according to the Reynolds law. These experiments demonstrate that both mechanisms can be responsible for the rupture of a thin wetting film."

Jan 1, 2003

In this study, selective flocculating of diaspore using anion macromolecular reagent as flocculant was tested to separate diaspore from alum-silicate minerals. Firstly, the effect of pH on settling behavior of diaspore and kaolinite dispersions has been investigated. The results show that the maximum settling speed of diaspore and kaolinite appeared re-spectively at pH7 and pH3.33 which is close to the point of zero charge (PZC) of diaspore (6.8) and kaolinite(3.5). This result is in well agreement with the double electric layer theory. Secondly, the settling behavior of diaspore and kaolinite particles in different anion flocculant solution have been researched. The results indicate that flocculant solution concentration significantly affect the selectivity and the flocculating performance of anion molecular. In high concentration solution, both diaspore and kaolinite have faster settling rate compared to blank solution. How-ever, in low concentration solution, the anion macromolecular can enhance the settling rate of diaspore remarkably but has no apparent effect on the settling rate of kaolinite. This result suggests that the tested anion flocculant is a promising reagent for de-silica of diasporic bauxite. Lastly, FTIR method was employed to probe the adsorption mechanism of flocculant on diaspore and kaolinite. The results reveal that there are anion flocculant characteristic bands on the spectra of diaspore but no obvious characteristic bands of flocculant on the FTIR spectrum of kaolinite. This result is in good correspondence with settling test.

Jan 1, 2014

By Vladimir I. Ryaboy, Konstantin M. Asonchik

"At flotation of sulfide-barite ores of one of deposits sulfide and barite concentrates are obtained. In sulfide cycle potassium xantogenate as a collector in consumption of 200 g/ton, methylisobutylcarbinol (MIBC) as a foaming agent in consumption of 30 g/ton and also liquid glass are used. In barite cycle tall oil as fatty acid collector in consumption up to 400 g/ton is used.Sulfide concentrate represents mainly gold- and silver-containing pyrite. The contents of gold makes not less than 10 g per ton, silver - not less than 278 g/t. Barite concentrate contains up to 86% of barite.Factory is working in water recirculation conditions. Owing to that in barite cycle fatty acid collector is used, technological water from tailing repository contains fatty acids soap up to 25 mg/l. Before submission into sulfide cycle this water is conditioned with active carbon to delete the main part of fatty acid collector. The active carbon consumption makes 0,4-0,5 kg per 1m3 of water or 1,5-2 kg per ton of ore. The above mentioned consumption of active carbon improves reducing of contents of fatty acid collector from the initial concentration of 25-30 mg/l to 4 mg/l. At concentration 4 mg/l fatty acid collector does not render negative influence on flotation index in sulfide cycle. At the absence of active carbon pollution of sulfide concentrate and its irrevocable lost are observed."

Jan 1, 2003

By Hermann Wotruba, Günther Petzold, Fabian Riedel

"Increased mechanisation in underground stoping operations results in higher waste percentages in the run of mine. A new method of reducing waste is optical sorting. Optical sorters have low maintenance costs and can be installed underground. Rejected waste can be backfilled directly without having to be hoisted, therefore increasing the shaft capacity for a more valuable product.Pre-Concentration by Optical SortingA series of tests with an optical sorter at the laboratories of the Mineral Processing Department of the RWTH Aachen have shown that it is technically possible to sort almost any kind of ROM which has even slight differences in colour (Platinum Reef, Gold Reef, Kimberlites, Industrial Minerals, Aggregates, Coal, etc.).By employing optical sorters prior to conventional sorting plants, it is possible to reduce the amount of waste to be processed. Figure one shows test results of ore which is quite similar in colour to the waste (grey). With increasing waste in the feed, the recovery decreases according to the graph. In figure two, the colour ratio parameter of the sorter was changed with a similar waste percentage in the feed. With increasing loss of ore, a cleaner product can be achieved. Before designing a sorting plant, throughput tests are carried out. Throughputs vary depending on the size range. Sorters have a limit of about 250mm top size. In this upper size range, throughputs of 150t/h can be achieved."

Jan 1, 2003