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By S. K. Kawatra, S. J. Ripke, T. C. Eisele

"An estimated 600,000 tons of bentonite clay are used annually in the U. S. as binder for production of iron ore concentrate pellets. Since this is a significant cost item for the plants, and the addition of bentonite to the pellets contributes undesirable silica into the finished pellets, there is considerable incentive for finding methods to reduce bentonite use. One way to reduce bentonite levels is to selectively use those bentonites that are most effective in this application, so that a lower dosage will still produce a sufficiently strong pellet. Unfortunately, there are no satisfactory methods available for accurately predicting which bentonites are actually most effective, short of using them to actually make pellets. One of the popular methods for attempting to evaluate bentonites is the “Plate Water Absorption” (PWA) test. While some plant operators accept the PWA results as indicating the relative quality of bentonites, others disagree and claim that, over a fairly broad range of values, PWA does not correlate with bentonite performance.Since both Ca+2 and Mg+2 ions are known to reduce the swelling and water absorption capacity of bentonite, it was believed that the presence of these ions in plant recycle water could be changing the bentonite performance. Since the standard PWA test uses only distilled water for its measurements, it could not detect these effects. Experiments were therefore carried out on a number of different bentonites using a modified PWA tests, with plant recycle water replacing the distilled water. These experiments showed little effect of the plant water on the PWA value, and chemical analysis of the water showed that the levels of dissolved salts were quite low.Water and accompanying salts were then extracted from a magnetite concentrate filter cake by rinsing with distilled water. Analysis of this water showed an extremely high level of dissolved salts, particularly salts of calcium and magnesium. When concentrations were compared with the recycle water from the plant filters, it was determined that levels of Ca+2 and Mg+2 retained in the filter cake were over 500 times higher than levels in the recycle water. This extreme elevation of soluble salts in the filter cake is believed to be due to adsorption of these ions into the electrical double layer of the magnetite particles."

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 Elzbieta Mielczarski, Jerzy A. Mielczarski

"It is well documented that xanthate adsorption on sulphide minerals is electrochemically controlled process. Under well controlled potential conditions the adsorption of xanthate takes place at different potential on each mineral, hence, each mineral component can be selectively separated from ore. This was demonstrated in the past for single mineral systems. In real flotation this concept never works out for two reasons: the potential of single mineral particle results from its interaction with solution as well as from galvanic contact with other particles present in the flotation pulp. Thus, the potential of a single particle results from complex surface reactions controlled by solution chemistry and the presence of other mineral particles that also interact with the solution. In flotation it is not possible to control mineral particle potential as it was demonstrated in voltametric studies of single mineral.In this study adsorption of xanthate on pyrite, galena and chalcopyrite has been investigated in the presence of those minerals. The second mineral was in solution: (i) without any physical contact with the first one, (ii) in direct contact (non-liberated grain or connected by wire), (iii) in collision type contact similar to that observed in real flotation.The adsorption of amyl xanthate on pyrite, galena and chalcopyrite was monitored by infrared external reflection technique directly on mineral surfaces. Type of the adsorbed species and their amount were concluded from the recorded reflection spectra. The presence of second mineral in solution without any physical contact does not influence adsorption. The minerals behave as if they were separated (at least during 30 min of the experiment). However, any type of galvanic contact between grains of two different minerals has tremendous consequence on the adsorption of collector on the both minerals. The detected changes are dramatic, from no adsorption to a few monolayer coverage formation.For example, pyrite that adsorbs amyl xanthate strongly in single mineral system in its galvanic contact with galena practically shows no adsorption of the collector in the same solution conditions. On contrary adsorption of xanthate on galena is tremendously enhanced during the galvanic contact with pyrite. The observed changes in the surface reactions are discussed and mechanisms of xanthate interactions in different galvanic contact are proposed."

Jan 1, 2003

By Rhulani F. Maluleke, Francis W. Petersen, John H. Marsh, Johann de T. Steyl, Allan Nesbitt

"Pressure leaching of chalcopyrite and nickeliferrous pyrrotite at temperatures between 105 and 200 ºC has been proposed as a potentially viable route for the extraction of mineral elements from sulphide concentrates. In general, these concentrates contain iron, and the economic success of the processes is partially dependent on the choice of the environmentally acceptable iron-removal technique. One of the most widely used methods for the removal of iron from sulphate liquors is precipitation as hematite, goethite, or jarosite. The nature of the iron precipitate formed, dictates downstream dewatering and residue treatment and disposal options. However, a better understanding of iron precipitation under the defined process conditions would consequently be of benefit in process design and optimization.This study investigated the precipitation of iron in the autoclave at temperatures between 105 and 200 ºC. The effects of temperature, acid concentration, iron concentration, and the presence of other metal cations on the nature and composition of the precipitates were determined."

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 J. Y. Tian

In view of the fact that many domestic iron ore-dressing plant applying flotation cells in the re-verse flotation, to improve the technical level of magnetite reverse flotation, we apply such a technological process of one stage rougher and two stages scavenger flotation column respectively. The middling from the two stage scavenger process are returned to magnetic separation for condensing. By contrast, the technological process of one stage rougher and one stage cleaning flotation cells is made up of by multi-magnetic separation and magnetic middling regrinding separations. It has been proved that the flotation column we offer can simplify the technological process structure, obtain advanced technical indexes, run the system smoothly, reduce energy consumption, and be environ-mental friendly.

Jan 1, 2014

By Kauko T. Ingerttilä, Jouko O. Kallioinen, Jaakko O. Leppinen, Alexander V. Lashkul, Vladimir E. Nenno

"Separation in Froth (SIF) is a process for the separation of mineral particles during their descent downwards through a moving froth layer, generated on the surface of water or some other liquid media by means of a bubble generator and frother. Due to the special operation principles of SIF it is possible to separate mineral particles that are about 10 times coarser than the optimal particle size for conventional flotation. In this paper the performance of the SIF technique is presented in the separation of apatite, calcite and silicate minerals from various industrial sources, based on tests with laboratory and pilot plant-scale SIF machines. Basic laboratory test results of the flotation of pure diamonds are also presented.It was shown that calcite, apatite and diamonds with particle size up to about 3 mm can be successfully floated with SIF at high recovery and grade, provided that the degree of liberation is sufficiently high. Coarse calcite (+0.25-2.8 mm) was concentrated with reverse SIF in one flotation step at 87% recovery with better than 99% grade. Apatite particles coarser than 0.2 mm are not well floated in the conventional flotation circuit leading to high P2O5 content in the coarse size fractions of flotation tailings. On the contrary, SIF is capable of recovering such coarse particles at high recovery. However, P2O5 content of the SIF tailings starts to increase at about 0.7 mm due to insufficient liberation of apatite. At higher particle size the lack of hydrophobicity of apatite particles is also likely to lower the recovery.The pilot plant testwork showed that SIF can be successfully used at operating plants not only for preliminary upgrading of the feed of conventional flotation, but also for producing final grade calcite concentrate (>99.5%) from the screen overflow or from the cyclone underflow in a particle size range up to 1 mm. It was particularly promising that the separation took place in one SIF flotation step, instead of several stages of the conventional flotation circuit, with over 90% calcite recovery. The specific capacity determined with the 1 m2 pilot plant unit was approximately 30 t/m2h. Simultaneously the consumption of chemicals was significantly lower than for conventional flotation."

Jan 1, 2003

By Xie Jiyuan, Hu Yuehua, Yang Songrong, Zhu Zhansheng, Qiu Guanzhou

"By the end of 2000, the first bio-oxidation plant in China that designed by ENFI come successfully into commercial operation in Yantai Gold Smeltery. Its capacity is 50t/d of refractory gold ore concentrate. After the extension, the capacity of bio-oxidation plant reached 80t/d of refractory gold ore concentrate at end of 2001.The refractory gold ore concentrate treated is from different gold mines. After proportionate feeding, the feed typically consists of Au (52.7g/t), S (24.42%), As (3.58%).The bacterial culture used in the bio-oxidation circuit is taken from a mine in south of China, and has been grown over 20 years on a variety of sulfide concentrates in a laboratory of mineral processing, and has shown to be adaptive to growth in a high concentrations of arsenic. It is a mixture of mesophilic microorganisms. The nutrients used in the bio-oxidation process are (NH4)2SO4, KH2PO4, KOH.Before feeding to bio-oxidation circuit, the concentrate would be milled to minus 43µm. The biooxidation product is fed to solid/liquid separation system that consists of a thickener and two press filters, solid from the system is fed to CCD circuit, liquid from the system is fed to neutralization area. The neutralized product is fed to another solid/liquid separation system, and the solid from the system is disposed of on a wasted quarry pit, the liquid from the system is returned to bio-oxidation circuit for reusing."

Jan 1, 2003

By Tamara F. Kondrateva, Evgenia E. Savari, Galina V. Sedelnikova, Rauf Y. Aslanukov, RAS (INMI), Grigori I. Karavaiko

"The investigation is dedicated to study of biohydrometallurgical processing of refractory gold-arsenic concentrate with the large content of pyrrhotite. Sulfide concentrate of chemical constituents: 75g/t Au, 4,7g/t Ag, 6,3% As, 29,3% S, 2,3% Sb, 0,5% ? (organic) and of mineral composition, %: 11,8 arsenopyrite, 39 pyrrhotite, 12 pyrite, 2,9 antimonite and the rest – aluminosilicates, carbonates and quartz, was studied. The recovery of gold from concentrate by cyanidation is 51,2%. The rest of gold is embedded as finegraded segregation in sulfides.Sulfide oxidation process study is described. Bacterial oxidation was executed on a pilot laboratory unit using combined autotrophic bacterium: A. thiooxidans , A. ferrooxidans, Leptospirillum ferrooxidans and sulfobacillus thermosulfidooxidation, pH=1,5-2,2, t=28-32?C, oxidation time 120 hours. Pyrrhotite is the least stable sulfide mineral with electrode potential 0,45V versus arsenopyrite (0,55 V) and pyrite (0,55-0,6 V) and is oxidated primarily. Pyrrhotite oxidation is followed by large amount of elemental sulphur, which has a bad influence on cyanidation.It’s established that the rate of arsenopyrite (for the first 48 hours) from concentrate containing 39% pyrrhotite is 2-3 times as less as the rate of arsenopyrite bio-oxidation from concentrate without pyrrhotite. The arsenopyrite bio-oxidation is accelerated only after the elemental sulfur was oxidized by bacterium A. thiooxidans and elemental sulfur percentage was reduced from 6,8 to 3,9%. The bacterium concentration is increased from 2,5x107 to 2,5x109 cells/ml. Almost full oxidation of arsenopyrite (98%) and pyrrhotite (98- 99%) is finished in 120 hours. We have studied two pretreatment methods for elimination sulfur content influence on cyanidation: aeration in lime and electrochemical treatment. Such an operation enables to have supplemental oxidation of elemental sulfur and other oxygen and cyanide absorbants before cyanidation. After treatment the content of elemental sulfur was decreased from 3,9 to 2,2%, gold recovery from 90 to 96% and cyanide consumption from 16,2 to 7,2 kg/t decreases. The content of toxical rhodonite-ions in liquid phase of pulp and disinfection reagents consumption were decreased as result of elemental sulfur content in bio-oxidated product reduction."

Jan 1, 2003

By Frank Cappuccitti, Stephen Chryssoulis, Stamen Dimov

Surface organic microanalysis of platinum (Pt) and palladium (Pd) minerals by TOF MS1 is an attractive complement and potential alternative to conventional collector screening methods. Its attractiveness lies on its ability to focus on individual Pt and Pd mineral particulates, therefore providing a more targeted approach. The only requirement is knowledge of the occurrence (mineral composition, grain size and association) of Pt/Pd in the feed sample. This newly developed technique can detect, and identify collectors and quantitate loadings on individual Pt/Pd mineral particulates at plant concentration levels. Using this technology, collector loadings were measured on Pt and Pd metal plates and on PtS2 and PdS particulates which had been exposed together to aqueous solutions of different collectors. Thus, data were obtained on collector selectivity, the effect of sulphur; and of depressants, the latter in combination with TOF-LIMS2 results. Staged rougher tests on North American and UG-2 ores linked Pt/Pd flotation kinetics with collector loadings and ultimately grade/recovery.

Jan 1, 2003

By Elzbieta Mielczarski, Jerzy Mielczarski, Jan Drzymala, Yann Duval

"The monoalkyl ethers of polyethylene glycols are universal flotation reagents because they can be used as collectors, frothers, surfactants, and depressants. Their collecting power was demonstrated for different minerals including coal and quartz.It was confirmed in this work that monoalkyl ethers of polyethylene glycols could be used as collector in flotation of quartz in a monobubble Hallimond cell. Since feldspar does not float in the same cell, it was also shown that selective separation of quartz and feldspar in the Hallimond tube is possible. However, a trail to use the monoalkyl ethers of polyethylene glycols compounds for separation of quartz and feldspar by flotation of mixture of these minerals in a Mechanobr laboratory flotation machine was futile, indicating that these reagents required special environment for flotation.Most probable parameter responsible for a decrease in quartz flotation in the flotation machine is the hydrodynamics of process, and different adsorption/desorption conditions. To prove this, another series of experiments was carried out to separate quartz and feldspar, in which a laboratory flotation column was utilized. The performance of the flotation column was in between that of in the Hallimond tube and flotation machine. These experiments confirmed that the hydrodynamics of flotation plays a vital role in flotation of quartz with monoalkyl ethers of polyethylene glycol compounds."

Jan 1, 2003

By Takashi Furuyama, Sukeyuki Mori, Ltd. Kyushu Metal Industry Co., Abel Bissombolo, Yoshitsugu Koga, Masamichi Hata

"Actually, the recovery of valuable metals such as iron, aluminium and copper is a nowadays practice in factories dealing with the processing of scrapped automobiles (Harder (WERG); Koga et al., 1997). This process has reach a recycling rate of about 75%, and generates a huge volume of waste (including cottons, sponge, plastics, rubber, etc…), locally known as “shredder dust”, which is commonly dumped on landfills; its recycling is either unsatisfactorily or not yet performed (Keller and Schebdat, 2000).The saturation and depletion of valuable disposal sites in the not-so-distant future, as well as the social and environmental problems related to the accumulation of these residues disposals are a major challenge for the automobile shredding industry.To promote an alternative way for the management of these disposals, the authors have initiated and developed a system for their processing, on the basis that more than 90% of these residues are combustible materials that could be used as refuses derived fuel. The developed processing system points out the mechanical/physical separation of a calibrated (–80+5mm) shredded automobiles residues into two streams by means of an ascending airflow passing through a vertical zigzag separator and, the compaction of the light-weight materials (that is about 60% of auto shredder residue recovered as float products and mainly composed of cotton, sponges and light plastics) to form a refuse derived fuel (RDF), the density, calorific value and ignition loss of which are 1.19 g/cm3, 4470 kcal/kg and 60.7%, respectively. A sedimentation tank is used to recover the light-weight materials deported in the heavy fraction stream."

Jan 1, 2003

By Richard K. Komarek, Antonios Zavaliangos, Roman T. Dec

"The work in the paper introduces a 2-dimensional finite element model for analyzing particular material processing in a roller press. Two basic roller geometries are considered: (a) smooth rolls (used for milling and compaction) and (b) rolls with cavities, commonly used for briquetting. A model is presented that is suitable to analyze material behavior through all stages of the rolling process: feeding zone, nip region, neutral plane and release section. It can predict pressure, shear stress, slip of the material over the roller surface, material velocity field, failure of the compact during release and the course of other important process variables.MODEL, RESULTS AND CONCLUSIONSAn associated Gurson model was employed as a constitutive model for the material. The calibration of the model was based on experimental results from an instrumented compaction die. Coulomb friction law was used to describe phenomena on the material/roller surface interface. Powder River Basin sub bituminous coal fines with moisture content 9% was used as a model material.Two finite element models have been set up, one for the briquetting roll and one for the “equivalent” flat roll. Approximately 3200 plain strain continuum elements with reduced integration (CPE4R) were used. Lagrangian-Eulerian (ALE) approach in conjunction with judiciously applied remeshing was employed with the commercially-available, dynamic explicit version of ABAQUS finite element code.Comparison of model predictions with experiment shows that there is an agreement in terms of the general trends of experimental values recorded on laboratory roller presses. Gurson model overpredicts stresses at low densities and, as a consequence, overpredicts roll force and roll torque."

Jan 1, 2003

By M. Barsky, E. Barsky

A study was conducted to elucidate the relationship between the hovering velocity and the particle settling velocity. The experiments were carried out in a water medium on five materials ranging in density from 1.070 to 4.000 kg/m3. Analysis of the results with allowance for the distribution of stream velocities over the cross section of the pipe revealed that the final settling velocity of the particles was equal to their local hovering velocity (on the stream axis), and not to the average velocity of vertical flow as is generally believed. It therefore follows that the kinetic structure of the stream must be taken into account when constructing theoretical models of the process for purposes of computation. In addition, the optimal stream velocity is not always equal to the hovering velocity and in fact is governed by other factors as well. Illustration is provided by the results of a study conducted in a vertical cascade classifier comprising eleven identical stages. The feed material was introduced at each stage successively beginning with the topmost (i* = 1 ) and ending with the lowermost (i* = 11). First, the stream velocity that yields optimum separation conditions at each stage of the cascade (i.e. k=50%, k being the yield of a given size class in the fines for a single stage) was sought. Subsequently the conditions of optimal separation for the instrument as a whole were determined (i.e. F(x) = 50%, F(x) being the yield of a given size class for the entire instrument). The results of the study are presented in the table.

Jan 1, 2003

By Vladimir P. Nebera, Kostas A. Matis, Piotr M. Solozhenkin, Anastasios I. Zouboulis

"Considered combination of two processes-selective sorptions of metals on biosorbents, inorganic sorbents and their following flotation by dissolved air(DAF). The process of biosorption, using as sorbent suspended non-living biomass (of Streptomyces genus, S. clavulgerus and S. griseus, fungi-Penicillium chrisogenum and Phizopus arrhizus, active slime) in fine particulate dispersion, combined with the application of flotation, for the consequent solid / liquid separation of metal-loaded biomass, has been studied for the removal of toxic and noble metals from dilute aqueous solutions. Biomass of microorganisms possesses great sorptive capacity, exceeding capacity of synthetic and natural sorbents. For instance, Micrococus luteus sorbed gold for 2h Au 253mg/g.The optimal conditions of effective flotation (more than 90%) of actinomyces biomass, loaded with toxic metal-cadmium were found. The adsorpbing flotation technique for copper, arsenic (III, V), chromium removal of metals on pyrite mineral fines (suitable industrial by- product) is an effective process.Dissolved-air flotation was also apllied in the case of dolomite/lead aggregates removal. A fatty acid was used as a flotation surfactant. The presence of dolomite fines aids the efficiency of the process, in comprarison with the flotation of alone lead hydroxide.A laboratory investigation was undertaken on the gold-thiourea system over the whole pH range, aiming at the separation complex of gold [Au(CS(NH2)2]2+ by flotation from dilute solutions. The reagents were found to improve gold recoveries remarkably: the recovery reached over 95%. A separation technique has been investigated, involving gold adsorptionon powdered activated carbon. Foam flotation was employed for the subsequent solid/liquid separation, using sodium oleate as surfactant. The content of Au were 500 mg/L in froth and recovery gold about 100%."

Jan 1, 2003

"The Merensky Reef is a platinum group minerals (PGM) bearing reef in the Bushveld Igneous Complex in South Africa. The reef has been treated by bulk PGM and sulphide flotation with the aim of maximisingthe valuable minerals recovery and gangue minerals rejection.Synthetic water with a calcium concentration of 80 ppm and 500 ppm was prepared and the flotation results obtained were compared to a simple electrolyte in order to determine the effect water quality has on pentlandite and pyroxene surface alteration and, ultimately, floatability. During the study, the possible effect of interactions between the minerals investigated and Ca2+ ions in the presence of sodium isobutyl xanthate was studied at pH 6 and pH 9 by means of zeta potential determinations, microflotation tests and ToF-SIMS analysis.The results obtained on 1:1 pentlandite-pyroxene mixtures showed that the quality of process water plays an important role in flotation. The flotation recoveries of pentlandite and pyroxene were lower in synthetic process water compared to those obtained in a simple electrolyte solution."

Jan 1, 2003

By G. Belardi, N. Shehu, L. Passeri

"This paper illustrates the possibilities of applying what is essentially a physical soil-washing technique for treatment of soil contaminated by semi-volatile hydrocarbons in order to reduce the level of pollution to that permitted by Italian regulations.The ground around a factory producing lubricating-oil additives consists of silty-sandy soils which have long been contaminated by heavy hydrocarbons, especially branched alkyl benzenes and naphthalene derivatives. Pollution is particularly marked in some zones (hot-spots) where Total Petroleum Hydrocarbon (TPH) values are as high as 7000 ppm. The hydrogeological characterization showed the presence of a gravely soil in a sandy/silty matrix, with big stones making preferential paths to the water circulation. The permeability is 10-5 m/s and the water-table occurs at about 3 m below ground level.After laboratory and pilot-scale studies on representative samples of in-situ soils with TPH between 2700 and 7000 ppm a flow-sheet is proposed for reducing TPH values below the acceptable limits in Italy, namely 700 ppm for hydrocarbons with more than 12 carbon atoms and less than 250 ppm for those with fewer.On the basis of indications provided by laboratory tests a mainly physical treatment process of soil washing has been developed. This is used to clean-up soil from a site polluted by non-volatile hydrocarbons with a high TPH value. The process involves a high-density attrition stage followed by wet screening at 0.5 mm and then wet-gravity separation of the minus 0.5 mm fraction in the centrifugal field.The gravity separation products consist of a light fraction with particle size finer than 15 micron which contains most of the pollutants, and a heavy coarse fraction with TPH values conforming to the limits set by Italian regulations (less than 700 ppm hydrocarbons whose structure contains more than 12 C atoms, and less than 250 ppm of hydrocarbons with less than 12 C atoms)."

Jan 1, 2003

By Peter N. Holtham, Geoffrey J. Lyman, The University of Queensland, Matthew S. Brennan, Vijay Subramanian, Rui X. Rong

"The cyclone would have a claim to be the commonest, least understood and most abused piece of mineral processing equipment available for study by researchers. It has certainly generated its fair share of publications – 1,000 in the last 60 years would be a fair estimate. However this remarkable degree of interest and scale of investigation is not reflected in our understanding of how they work; cyclones are still installed inappropriately and run poorly, which suggests that there are still things to learn about this deceptively simple process.In mineral processing there are two broad classes of cyclone: the hydrocyclone, used in classification, thickening and dewatering, and the dense medium cyclone, used for concentration by density. Although rarely studied together, the laws of physics presumably apply equally to both and so it seems that there would be interesting things to learn by considering them as a single class of device. The good news is that in recent years there have been spectacular advances in the computational and measurement tools available to study these devices, including computational fluid dynamics (CFD), tomography, and laser doppler anemometry (LDA), and some good progress has been made in an understanding of the fundamental principles involved.The JKMRC has made many experimental studies of hydrocyclones and DM cyclones, leading to useful empirical models. However some recent CFD and tomographic work, in association with work of other institutions, has thrown important light on the workings of these processes. Progress has also been made in novel designs of cyclone to achieve improved separating efficiency, based on an attack on the subprocesses believed to contribute to inefficient operation. This paper describes the work to date.Modelling of the dense medium and classifying cyclone was conducted using the Fluent computational fluid dynamics code. Three phase simulations of the dense medium application (air/water/medium) showed appropriate medium segregation effects but over-predicted the level of segregation compared to segregation measured by gamma-ray tomography. This is believed to be because the basic Algebraic Slip mixture model in Fluent does not model any back-mixing of the dispersed phase due to turbulence."

Jan 1, 2003

By Jim Petrie, Mary Stewart, Damien Giurco

This paper describes a generic approach to analysing the environmental and economic performance of a generic global mineral/metal value chain, with the express view of improving the quality of prospective decision-making within the industry in order to ensure more sustainable outcomes. As a point of departure we propose that it is not possible to place metals in the context of the sustainable development of society without paying due regard to the entire metals value chain. Thus, the starting point for this analysis is the development of a global stocks flows and transformations model, for the metal of interest. Any aspect of the value chain, e.g. “metals refining, “goods manufacture”, “use and disposal”, can be assessed, either relative to other stages in the value chain, or in more detail by focusing on the technologies used within that stage. The use of this model as a decision support tool is explored here for the case of copper. Both primary and secondary production routes are enumerated, covering a range of processes, for seven distinct geographic regions around the globe. The value of the modelling approach is explored for different energy mixes. In particular, the case study examines the impact of increased recycling on the (re) distribution of global and regional environmental impacts for technologies-in-place in these different regions. The aim of these case studies is to highlight to the minerals processing and metals refining industries their potential role in a more sustainable global society.

Jan 1, 2003

By D. Whittles, S. Kingman, K. Jackson, S. Bradshaw, N. Miles

The influence of microwave energy at high electric field strength on ore strength has been investigated. Two ores of varying mineralogy were treated in both multimode and single mode microwave cavities. After treatment, any change in strength relative to untreated ore was established. It was shown that in the multimode cavity reduction in strength was related to the applied power level. Results of tests carried out in the single mode cavities showed that, for both ores, reductions in ore strength > 50% could be achieved in very short periods (<1 second). Thermal stress analysis showed that the mechanism of microwave induced failure was the development of tangential stresses at the grain boundaries. It was concluded that operation at 915 MHz with high power and short residence times gives feasible scale-up possibilities.

Jan 1, 2003