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By Johan F. W. Kock

"Hearing loss due to excessive noise exposure is the most prevalent industrial disease. It is ranked on the World Health Organization’s (WHO) priority list for major work related injuries. Uncontrolled noise not only has a physical effect, but is also a psychological hazard affecting the performance and well being of man. Noise induced hearing loss (NIHL) is irreversible, yet it is preventable. The first defence against noise (noise control engineering) is a high priority in the mining industry. Second defences should be a last resort when the engineering control of noise is inadequate. Hearing conservation programs and the use of conventional hearing protection devices seem to have failed in the prevention of noise induced hearing loss. If compensation payouts that quadrupled in the past ten years are used as a barometer for the success of existing hearing conservation programs, then new strategies and technologies need to be investigated. The best practice Hearing Protection Device (HPD) may be seen as the minimum standard for second defence noise control.Conventional hearing protection is widely applied, but also misused in the industry as well as in the mining sector. Empirical research results, ownership, general attitudes of workers as well as qualitative aspects will be explored. The paper provides reasons, evidence, case studies and strategies regarding the best practice hearing protection philosophy (the Noise Clipper Model) as implemented in the Implats Mining Group. Worldwide tendencies towards custom-made HPD’s, findings that indicate improvements in hearing conservation programs and finally the successful application of Custom-made Hearing Protection Devices, will be outlined."

Jan 1, 2003

By Jan J. Cilliers, Nicolas Barbian, Esther Ventura-Medina

"Mineral froth flotation is one of the most widely used processes to separate particles of valuable mineral from its associated gangue. It involves the selective separation of the hydrophobic particles from the slurry into the froth. The hydrophobic particles attach to the air bubbles and rise up to the froth phase on top of the slurry. The valuable mineral is collected when the froth overflows the cell wall. The separation performance of the process can be linked to the amount of solids and valuable material loaded on the bubble shells. In addition, it is well known that in most mineral systems, the presence of solids can enhance the stability of the froths. How the solids get to be distributed and what proportion is actually attached and stabilising the bubbles is not well known.This study aims to establish the relationship between operational variables, solids loading on bubbles and flotation performance. For this purpose, a series of industrial experiments to sample the solids in the bubble films under different operational conditions were carried out in two copper concentrators under steady state conditions. Samples of the lamellae were taken by touching the top surface of the bubbles with a glass slide. The amount of solids and liquid per unit area in the bubble lamellae can subsequently be estimated gravimetrically and by image analysis. The grade of the attached particles was also measured by adequate sampling. This gives an indication of the maximum grade that could be achieved from the process under the operating conditions."

Jan 1, 2003

By Kang N. Zhong, Hui H. Luo, Yunan Phosphate Chemical Co., Yi H. Wei, Yao J. Li, Yu L. Wang

"The three kinds of phosphate ores (igneous, metasedimentary and sedimentary) found in China have great differences in flotation flowsheets and reagents suite because of their crystal structure and mineral composition. The igneous and metasedimentary apatites have good floatability with fatty acid as collector and waterglass, sodium hydroxide or sodium carbonate as conditioners. The sedimentary phosphate is very difficult to beneficiate by direct flotation because of their poor floatabilities and relatively high content of MgO and SiO2, even though the dolomite depressants are used sometimes.The differences in floatability of apatites in China are closely related to their differences in specific surface area. The amount of collector to float apatite increases with the specific surface area. Apatite with lower specific surface area showed good floatability at lower collector concentration. Apatite with a higher specific surface area needed a higher concentration of collector. The content of CO3 2- will affect the specific surface area of apatite by distortion of its crystal structure and consequently affect its floatability.Dolomite can be easily rejected from apatite in a weak acidic medium (pH=5), especially in phosphoric acid medium by reverse flotation. Quartz and siliceous gangue in sedimentary apatite can be removed by direct flotation using fatty acid or by reverse flotation using amine. Amine is not practically applied because sedimentary apatite in China is usually very fine and needs fine grinding, which always results in excessive, very fine, stable and non-flowable foam.Based on the floatability of phosphate ore in China, a two-stage flotation process, direct and reverse flotation (D+R), was developed to beneficiate sedimentary ore. For the Haikou phosphate ore containing 25.11% P2O5, 3.46% MgO and 16.5% SiO2, a concentrate containing 31.84% P2O5, 0.48% MgO and 14.8% SiO2 can be obtained through a continuous D+R test at a recovery of 89%."

Jan 1, 2003

By Sun Chuanyao, Jia Muxin

Generally, if the bond valence (BV) between metal ion and oxygen of the mineral is greater than 0.8, only surface species –Me-O-H or –Me-O exposures on the mineral interface, if the BV is between 0.2-0.8, the metal ion exposures on the interface, and if the BV is less than 0.2 the metal ion dissolves into water. The PZCs of oxide minerals and island silicate minerals are determined by the bond valence of the bond in the mineral crystals, the higher the bond valence the lower the PZC of the mineral. So the PZC sequence of Al2SiO5 minerals is kyanite> andalusite> sillimanite. The general rule for framework silicate minerals is as: The higher the Al content, the lower the PZC of the mineral, when the ratio of Al to Si in the tetrahedron skeleton is below 1:3. The higher the Al content, the higher the PZC of the mineral, when the ratio of Al to Si in the skeleton is between 1:3 and 1:1. The general rule for layer silicate minerals is summarized as: the three-layer silicate minerals have much lower PZCs than that of the two-layer silicate minerals. The threelayer silicate mineral with the octahedron layer occupied by lower charged cations has lower PZC than that of the three-layer silicate mineral with the octahedron layer occupied by higher charged cations. The twolayer silicate mineral with the octahedron layer occupied by lower charged cations has higher PZC than that of the two-layer silicate mineral with the octahedron layer occupied by higher charged cations. The layer silicate mineral with Al substitution in the tetrahedron layer has lower PZC than that of the layer silicate mineral without Al substitution in the tetrahedron layer. Such pyroxene minerals whose M1 is occupied by a trivalence cation and the M2 is occupied by a monovalence cation has lower PZCs than those both M1 and M2 are all occupied by bivalence cations. Such hornblende minerals whose M2 is occupied by a trivalence cation and the M4 is occupied by a monovalence cation has lower PZCs than those both M2 and M4 are all occupied by bivalence cations. There is no Si4+ or 4 coordinated Al3+ exposures on the surface of framework silicate minerals, the metal ions of three layer or chain silicate minerals are compact between tetrahedron layersor chains, they hinder the metal ions to interact with oleate acid radical, the metal ion octahedron layer exposures on the surface of a two layer silicate mineral, but the the oleate acid radical can not attach to a metal ion by replacing a –OH- that connects three metal cations in the same time, So the floatability of such silicate mineral is bad. The metal octahedron chain style of an island silicate mineral affects it floatability, the mineral exposures octahedron chain metals with two dangling bonds in two directions floats better than the mineral exposures octahedron chain metals with two dangling bonds in one direction.

Jan 1, 2003

By Chris A. Fleming

"Interest in the recovery of cyanide from gold and silver plant tailings has heightened in recent years. This interest has been spurred by several factors:Increasingly stringent regulations throughout the gold producing world, governing discharge limits for free and total cyanide to tailings ponds and the environment.The increasing cost of active chemical treatment versus passive (natural degradation) treatment of tailing, to bring them in line with environmental regulations.The worldwide trend to processing of more complex gold ore bodies, which is usually accompanied by higher levels of cyanide consumptions and greater concentrations of cyanide (particularly the copper cyanide complex) in tailings.The growing negative perception of the general public for the gold mining industry, due to several highly publicized cyanide spills in recent years (breaches of tailings dams, accidents involving trucks carrying cyanide to gold plants, etc.).The ability to recover cyanide from gold plant tailings has been known almost as long as the cyanidation process has been practiced, but there has been little incentive to process tailings in this way in the past. With the development of technologies that make it possible to recover and recycle free or complexed cyanide directly from gold plant slurry tailings, which indicates, on paper at least, the potential for significant cost savings compared to cyanide destruction, coupled with the introduction of legislation to seriously limit the discharge of cyanide to the environment in most gold-producing regions of the world, many companies are evaluating the cyanide-recovery alternative."

Jan 1, 2003

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 John C. Gathje, Rick Moritz, Wilhelm de Beer, Gary L. Simmons

"Froth flotation has a long history of success for the recovery and concentration of a wide variety of minerals of commercial interest. Both the art and science of flotation have progressed greatly, and as our knowledge has increased so has our ability to improve mineral separations and recoveries.One area of interest in recent years has been the flotation of refractory gold ores to recover the goldbearing sulfides. In many instances, the use of conventional air flotation to concentrate these values has achieved only limited success. However, as a result of intensive research, Newmont Mining has expanded the boundaries of flotation, and it can now be used to successfully treat many gold-bearing sulfide ores as well as platinum and palladium ores. This has been achieved through the use of the patented N2TEC technology, which utilizes nitrogen as an inert gas in the flotation process."

Jan 1, 2003

By Stoyan N. Groudev, Ioannis Paspaliaris, Plamen S. Georgiev, Irena I. Spasova, Kostas Komnitsas

"The uranium deposit Curilo located in Western Bulgaria for a long period of time was a site of intensive mining activities including both the open-pit and underground mining techniques as well as in situ leaching of uranium. The ore was rich in pyrite and, apart from uranium, contained some non-ferrous metals. The mining operations in the deposit were ended in 1990 but since that time the deposit is a permanent source of acid drainage waters. The generation of these waters is connected mainly with the oxidation of pyrite and other sulphide minerals by the indigenous acidophilic chemolithotrophic bacteria.Laboratory and pilot-scale studies revealed that an efficient clean-up of the above-mentioned waters was achieved by means of passive systems of the wetland type. In 2001 a wetland was constructed in the deposit to treat a portion of the acid drainage waters which were discharged to a small ravine. This ravine reaches into the Teina, a small river that is a tributary of the upper reaches of the Iskar river.The wetland was constructed in the ravine and its bottom was located on intrusive rocks with a very low permeability. The rocks were covered by a 30 – 50 cm layer consisting of a mixture of soil, plant compost and crushed limestone. The wetland was characterized by an abundant water and emergent vegetation and a diverse microflora. Typha latifolia, Typha angustifolia and Phragmites australis were the prevalent plant species in the wetland but species of the genera Juncus, Eleocharis, Carex and Poa as well as different algae were also well present.The acid drainage waters treated by the wetland had a pH in the range of about 2.5 – 4.1 and contained uranium, radium, some heavy metals (iron, manganese, copper, zinc, cadmium, lead), arsenic and sulphates in concentrations much higher than the relevant permissible levels for waters intended for use in the agriculture and/or industry. The watercourse through the wetland covered a distance of about 0.2 – 1.0 l/s."

Jan 1, 2003

By Roberto C. G. Oliveira, Scott C. Brown, Brij M. Moudgil

"The wettability or surface energy of particle surfaces dictates a number of multiphase ensemble interactions that have a significant impact in mineral processing. Dispersion, bulk powder handling and flotation are just a few of the processes that are largely influenced by the degree of hydrophillicity or hydrophobicity on particulate surfaces. Because of the importance of surface wettability, a number of simple, precise and accurate techniques for accessing surface wettability or contact angle on macroscopic flat surfaces have been developed. However, these techniques cannot be directly applied to the particulate surfaces that are often in query. Though a number of techniques are available for accessing the wettability of particulate surfaces, these methods are either relative, application specific or prohibitively tedious. In the present study, key features of existing techniques are combined to formulate an improved method to delineate particle wettability that is simple, versatile and capable of providing reproducible measurements in an industrial environment.Through the use of an inert adhesive and an inert macroscopic surface as a support, it is illustrated that precise measurements of particle wettability are obtainable under suboptimal or ‘shop floor’ conditions. The measurement of the maximum external meniscus height formed between a test liquid and a particlecoated rod is employed to estimate phenomenological contact angles on particles ranging form a few nanometers to several hundred microns in size."

Jan 1, 2003

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 Johan C. van Dyk, Johan W. van Zyl, Martin J. Keyser

"Coal is a crucial feedstock for South Africa’s unique synfuels and petrochemicals from coal industry and it is used as the main feedstock to produce synthesis gas (CO and H2) via the Sasol-Lurgi Fixed Bed Dry Bottom gasification process. Detailed coal characteristics are essential to predict gasification behaviour when a specific coal source is to be gasified.The principle aim of this paper is to highlight and discuss those specific coal characteristics, which affect gasification behaviour and stability.In order to determine the suitability of a coal source for gasification purposes, the coal is characterized and the results compared with historical data. Benchmark data, where it was possible to operate the gasifier with ease and relatively high stability, is used as a reference.Coal sources with extreme properties (i.e. low reactivity, ash content <10% as is used by Dakota Gasification Company, or “brown coal” with moisture >30%) can probably be gasified in a Sasol-Lurgi Fixed Bed Dry Bottom gasifier provided that certain operational changes are implemented. Other properties, like high caking and extreme ash content for example, require blending to acceptable levels."

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 Daniela Venter, Stephen Chryssoulis, Ken Stowe

"A sampling campaign was conducted at Kemess in order to identify and assess the chemical and physical factors, which control free gold flotation kinetics in the rougher and cleaner circuits. The rationale behind this approach was that accurate knowledge of the parameters affecting free gold flotation kinetics, can be used to determine how to accelerate free gold flotation. Collected samples were composites of 5-6 cuts over a four-hour period, at steady plant conditions.In the rougher circuit, coarser equidimensional gold particles floated ahead of the finer grained and the flaky gold. Sulphur followed by molybdenum and to a lesser extent silver enhanced gold flotation kinetics, while hydroxyl followed by carbonate ions induced depression."

Jan 1, 2003

By M. Wright, A. H. Mwale

Opportunities to promote enhanced eco-efficiency (i.e. the simultaneous improvement in economic and environmental performance) for the minerals industry exist across the whole value chain. However, given the current operational models of major companies within the industry, and their focus on refining of primary ore bodies, it is important to understand where such opportunities might lie within minerals beneficiation, as it is here that major environmental pressures are felt. This paper examines the combination of unit technologies in a minerals beneficiation train, and explores the inter-relationship between energy input and water consumption for a given mineralogy and product recovery, as these are two critical environmental issues which affect the overall viability of many minerals plants. In particular, we review constitutive relationships for each of the sub-processes of comminution, flotation, and tailings dewatering, and suggest how these might be integrated into a unified hybrid model, with particle size distribution as the key design variable. Such a model can then be used to explore the trade-offs between different performance objectives (be these technical, economic or environmental) as part of a multiple-objectives optimisation exercise. In this way, it may become practical to envision situations in which concentrate grade and recovery are sacrificed, marginally, in order to reduce energy demand in comminution, and improve overall water recovery. In addition, this work provides a useful baseline against which to analyse the potential for dry processing. This becomes more relevant as the industry commits to advancing the sustainable development agenda in the face of the increasing life -cycle costs and impacts of minerals processing operations, coupled to declining ore body grades, and the desire to maximise recovery of minor and trace elements. Some specific observations for copper are offered, supported by operational data from Zambian copper mines.

Jan 1, 2003

By L. Burdukova

In flotation, depressants are used to reduce the amount of gangue that reports to the concentrate and hence increase the selectivity of the flotation process. At the University of Cape Town extensive batch flotation tests are carried out to evaluate industrial depressants and standard procedures have been developed over the years. This study was conducted in order to develop an improved method for comparing depressants using machine vision as an aid. The modified method of batch flotation involved a test with prolonged intervals between scraping to allow more time for the froth to build up and mature.

Jan 1, 2003

By J. Tian

"BHP Billiton carried out a pre-feasibility study on the LanPing zinc deposit to evaluate the possibility to jointly develop the zinc deposit into a large-scale zinc project with their Chinese partner. The unique characteristics of the complex LanPing zinc orebody and ore are 1) smithsonite (ZnCO3) as one of major zinc bearing mineral besides sphalerite, 2) varying and irregular oxidation degree of zinc (0 ~ +90%) in the different zone and depth of the deposit, and 3) varying host gangue from limestone/calcite dominant to quartz dominant, which requires a robust and flexible flotation process to recovery zinc from both sulphide and oxide efficiently.The conventional mineral processing flowsheets have been tested on the LanPing samples taken from the various orebodies by various parties during the past 20 years that includes a sequential flotation flowsheet that was tested in a demonstration plant using the mixed ore. The results of the demonstration plant runs show that the conventional oxide flotation using Na2S and amine collectors could achieve 50 ~ 75% of oxide zinc recovery at very high sulphidiser consumption for the mixed ore but the highly oxidised ore did not satisfactorily respond to the flowsheet in terms of performance consistency and efficiency of oxide zinc recovery, which is very crucial to the overall economics of the project."

Jan 1, 2003

By Pradip, Beena Rai

A molecular modeling study was carried out on an adsorbed oleate monolayer on the surfaces of three calcium minerals, fluorite, calcite and fluorapatite using Universal Force Field (UFF) potentials. The cleavage plane of calcite {104} was the best template for oleate monolayer adsorbed since the surface structure enabled all the calcium sites available on the surface to be occupied by oleate anions. The area occupied per chain of oleate in this well packed monolayer was computed to be 20.2 Å, which exactly matches the value calculated to be the parking area per oleate molecule for a fully packed monolayer based on strictly geometric calculations. On the other hand, the precentage of calcium sites occupied by oleate to achieve a fully packed monolayer in case of fluroite and and fluorapatite was found to be 67% and 75% respectively. The results of this theoretical study suggest that while all the three adsorption conformations, that is unidentate, bidentate and bridging type are equally likely on fluorite and fluorapatite, bridging is most likely on calcite. Interestingly, all the conformations are observed experimentally for calcite-oleate system also. The reasons for this discrepancy between the theoretical predictions and experimental observations are not clear. More work is required to resolve this discrepancy, in particular simulation studies in presence of solvent water molecules on the surface.

Jan 1, 2003

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 Harri J. Lehto, Marja I. Oja

"The purpose of grinding circuits is to produce a particle size distribution that has as much as possible the wanted particle size class. In practise, however, the production of the wanted size class is not at all as simple as it sounds. In the case of industrial minerals for example the end user may give very tight specifications for the particle size distribution and for the chemical composition of the product. This leads in many cases to a very demanding grinding process, if we want to reach and maintain these specifications. In other words, the required size distribution is not necessary the best possible for the chemical composition.Screen models aim to predict the size distribution and flow of the products when a feed size distribution, feed tonnage, and grade efficiency curve are known. The approach used in this study was to select the most suitable empirical model for classification. Suitability of the existing models has been evaluated and accuracy compared. The tests showed that best grade efficiency model was the Rosin-Rammler model.The performance of a screen was evaluated in order to minimize the amount of fine material in the screen overflow. The experiments were carried out using Derrick single-deck screen, first alone with recycling and then in the closed circuit with a rod mill using two different scales. The separate screen tests showed the expected behaviour of the grade efficiency curves. In the pilot tests the Leonard screen efficiencies stayed almost constant. This suggests that the screen works better in a milling circuit. However the loading of the screen turned the product of the mill coarser that helped screening. The grade efficiencies obtained from the pilot tests had the same general shape. The regression analysis of the pilot test runs did not give an acceptable correlation for the parameters. This suggests that pilot tests cannot be directly used to scale or to optimise industrial milling circuits. However they can be used to predict the trends of behaviour of an industrial circuit."

Jan 1, 2003

By H. U. R. Kattentidt, W. L. Dalmijn, T. P. R. de Jong

"Research at Delft University aims to develop systems for automatic inspection and sorting of bulk solids which can be applied in the mineral processing and recycling industry. A recent development includes an automatic sorter based on airport X-ray inspection technology. It is designed for continuous inspection and sorting of 5 – 150 mm solids and has as objective a cost effective and high capacity on-line inspection and sorting.Dual energy X-ray transmission imaging provides instantaneous data about particle dimensions and the atomic number distribution. The system provides particle thickness and average atomic number on a pixel level at scanning speeds between 250 and 500 lines / second. With existing X-ray components inspection speeds between 0.5 and 2 m/s at approximately 1-meter inspection width and between 1.5*1.5 and 5*5 mm2 sensor resolution can be achieved.Imaging algorithms that were developed by Delft University for applications in recycling, waste cleaning and other applications acquire shape, size distribution and composition data. Currently on-line processing of a product at a rate of around 200 particles per second is possible using a standard PC. Experiments with a demonstration X-ray unit indicated good potential for various applications in solids processing. They include continuous inspection of organic content, sulphur, chlorine, ash, and metal distribution. It is applicable for coal cleaning, ore sorting, industrial minerals, and various applications within waste cleaning and recycling. Dual energy X-ray transmission fundamentals and recent progress in system development and applications are presented."

Jan 1, 2003