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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 Takashi Furuyama, Sukeyuki Mori, Takafumi Okuma, Norio Hashiguchi

"In order to achieve a high recovery of particles finer than 10µm, three types of dry Tower Mill (VD-1, KD-1, KD-2 and KD-3) have been developed. These mills differ from each other in the size of the comminuting part, the inside diameter and shape of the classifying part and the system involved in the collecting process. The last version (KD-3) of tower mills in which the comminuting and classifying operations has been separated, can produce particles finer than 10µm from a limestone ore sizing from 420 to 3360µm. In this tower mill, products in comminuting section are blown up and transported into the classifying column, made of an inverted cone on top of a cylinder, before they agglomerate and settle down. Fine particles are deported and recovered in a cyclone with a central spiral ribbon.Previous studies on the grinding efficiency of the tower mill KD-3 have shown how the maximum size of collected products increased with the airflow velocity, disturbing in the same way a smooth regulation of the grinding operation with the tower mill KD-3. A complete knowledge of factors that influence the maximum size of collected products is needed, therefore, to increase the efficiency of the grindingclassifying operation and ensure a better control over the collected products. The present study deals with this issue and, assuming that the structure of the classifying column could be one of these factors, its internal structure was modified (insertion of vertical plates, cone or horizontal nets) before carrying out comminution tests that would establish a relationship between the inward shape of the column and the maximum size of collected products. It was found that the weight of products collected in the cyclone decreases when a cone or some horizontal nets are inserted inside the column. At the same time, the weight of products collected in the column increases. This is due to the fact that coarse particles blown up from the comminution section collide with the base of the cone or the nets and settle down the bottom of the classifying column. Therefore, the cone and some horizontal nets inserted inside a classifying column, have the particularity to stabilize the maximum size of particles (15.1-17.5µm and 8.4-11.3µm) in the cyclone even when the airflow velocity in duct increased. These tools could of great help in the production of particles of definite size to fit for instance the paper industries requirements (production of limestone material sizing - 10µm as paper filler)."

Jan 1, 2003

By Kari Moen, John Rasmus Leinum, Jarle Hjelen, Terje Malvik

"Industrial minerals may contain the same elements in approximately the same amount. In these cases backscatter electron imaging or chemical analysis are not sufficient to identify the minerals. Another problem arises when micro textures are not detectable in traditional imaging or the grain size is smaller than the X-ray spatial resolution.As a supplementary technique in these cases, application of crystallographic information by electron backscatter diffraction (EBSD) in the scanning electron microscope (SEM) may be a suitable method. The technique has been demonstrated on three Norwegian mineral raw materials and one Italian marble and shows that it has some advantages compared to traditional techniques.• quantitative measurements by ebsdCommon automatic techniques describing the mineral contents and the occurrence of minerals in free and locked particles, are based on optical-, backscattered electron (BSE)- or X-ray-signals. There are various commercial software systems on feature analysis by backscattered and X-ray signals in combination with image analysis (e.g. Oxford Inca Feature, CSIRO QemScan).Especially in silicates, the occurrence of similar elements in the different minerals is common. Sometimes the various minerals not only contain the same elements, but also approximately the same amount of each element. In these cases BSE imaging and chemical analysis are not always sufficient for identification."

Jan 1, 2003

By Máximo Pérez, Julio C. Videla, Rosa Dzioba

"This paper reports the hydrometallurgical treatment of gravity concentrates of gold samples and outcrops associated with graphite ores obtained from:• flotation tailings of crystalline graphite minerals• outcrop samples of graphitic rock associated with auriferous minerals and free gold located in the Villa Union district and surrounding areas - La Rioja Province - Argentina.Previous studies of the flotation potential of crystalline graphite minerals failed to consider the presence of noble metals.The samples represent a mineralized zone of crystalline graphite which is distributed in different formations with a NE - SW trend in Maz, Punta Colorada and Las Ramaditas hills, covering an area of about 300 square kilometers."

Jan 1, 2003

By Wayne I. van Drunick

"Energy balance modeling has recently been shown to be a competent tool in the estimation of SAG mill discharge rheology. Work performed by van Drunick and Moys (2001) validated the ability of an energybalance filter to estimate the slurry density from an operating SAG mill. The importance of rheological data is highlighted by several authors who show the effects on load behaviour and thus mill performance. Energy balance models were developed to account for the dynamic energies in the mill discharge sump. The models then made it possible to infer the mill discharge density. A sampling campaign was performed and the errors from the sump energy balance were within tolerable limits.Since the initial results were published, it has been decided to further develop the modeling techniques in order to focus on balancing the energies around the entire mill. The critical measurements for the energy balance will be the temperatures of all the streams entering and leaving the mill, including energy losses to the environment. Metso’s OCS© (Optimising Control System) currently controls the 3 SAG mills at Anglogold’s Mponeng Gold Plant (South Africa). The OCS has built-in Kalman filtering tools to effectively handle variances and noise in the models and the mill circuit data respectively. The new models are therefore constructed in the OCS platform, and will be run in parallel with Metso’s current modeling and filtering systems. The work is a collaborative effort between Anglogold, the University of the Witwatersrand and Metso. The benefits of energy modeling, compared to mass modeling, are that energy data are more accurately measurable than mass data. The inferred mill parameters can therefore be improved provided that a competent set of models is produced to process the (accurate) thermal measurements."

Jan 1, 2003

By Rebecca Hope, Derick Moolman, Frikkie Malan

"Despite the lip service that has been paid to pro-active plant maintenance processes over recent years, a significant portion of maintenance in industry is still reactive. The business driving force to prevent expensive production opportunity costs arising from “break-down maintenance” is obvious. Various benefits can be derived from successfully deploying remote equipment diagnosis technology and associated business processes.From an end-client’s viewpoint these include the ability to predict and take actions to prevent equipment breakdowns, increasing the lifetime of equipment by responding to appropriate operating instructions and therefore improving the return on capital expenditure. Better planning and scheduling of maintenance priorities and resources with performance measures like an Equipment Health Index are also possible. The knowledge that a qualified supplier engineer is constantly in touch with the operating conditions of their equipment, albeit remotely, is more than a comfort, and can be translated into quantifiable cost savings and improved supplier service levels."

Jan 1, 2003

By G. Demi, G. Belardi, N. Shehu, S. Cico

The physico-chemical interaction between minerals such as olivine, chromite and serpentine and the ions most commonly present in solution, like Ca and Mg and flotation reagents such as EDTA and oleic acid was investigated. The study was conducted via release tests, electrophoretic measurements and microflotation of selected minerals coming from the Kukes deposit (Albania).

Jan 1, 2003

By J. B. Rubinstein

"The paper gives an overview of the history of flotation machine development. The laws of their evolution are stated and the place and role of column flotation are demonstrated.The major parameters of column cell diameter and height are discussed. Options are proposed for optimization of the hydrodynamic characteristics of large-capacity column cells. The high efficiency of columns with cell height of 4-6 m is demonstrated. The optimum parameters of multisectional column machines are determined. Their advantages compared to monocells are shown. A scaling-up procedure for column machines was developed based on flotation macro- and microhydrodynamics simulation."

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 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 Sarah K. DeBono, Alan J. Monaghan, Emmanuel V. Manlapig, Gregory J. Harbort

"The Jameson Cell is a type of flotation machine in which air and pulp are brought together in a vertical tube called a downcomer. Within the downcomer the air and pulp are dispersed into a dense foam of fine bubbles, which creates a favourable environment for bubble-particle collision and subsequent collection of hydrophobic particles. The intense collection zone within the downcomer can be considered similar to the zone between the rotor and stator in mechanical flotation cells.Research into the bubble-particle collision and fluid dynamics of mechanical cells rotor-stator zone has been limited by the difficulty of achieving accurate measurements in production sized machines. With the Jameson Cell the downcomer is largely external and separated from the flotation tank, allowing ready access to the primary contacting zone for measurement and analysis.An investigation has been undertaken into the operating characteristics of the downcomer relating to bubble-particle collision. An effective mapping of the downcomer has been made through measurements of void fraction and bubble size taken across cross sections of the downcomer. Analysis of these measurements has provided an interpretation of the variations in the air and fluid dynamics, bubble size and distribution throughout the downcomer chamber."

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 P. K. Sen, Mrinal K. Ghose

Tailing slurry is usually abrasive and possesses high viscosity. This paper examines the existing iron ore beneficiation process and focuses on some of the key environmental issues related to the disposal of tailings. It identifies that almost 32% of the iron ore extracted ends up as tailings and they are usually disposed in slurry form in tailing ponds. By the year 2000, 27 Mt of iron ore tailings were generated in India, which has become one of the biggest waste handling problems to the industry. Characteristics of the tailings vary widely. So the physical nature of tailings cannot be considered separately in isolation without considering the mill effluent from the beneficiation plant. In the present investigation, studies were carried out in three iron ore mines in India to evaluate the characteristics of tailings from the beneficiation plant. The tailing samples were collected from different locations during a time period of one year and analyzed. The results will be discussed and the characteristics of the tailings have been evaluated. The disposal system of tailings at the three mines was evaluated. The research on the settling characteristics of tailings indicates that the area provided in the existing tailing ponds in India is much more than that of the experimental results. This paper concludes that sedimentation tests are essential to design appropriate tailings pond with respect to size. In the proposed scheme it is suggested that an additional unit process, i.e. sedimentation tank be added to the process before the disposal of tailings to the tailing pond.

Jan 1, 2003

By Carin Laubscher, Francis W. Petersen, Jaap P. Smit

"Waste streams, such as acid mine drainage, are often characterised by low pH values and high concentrations of heavy metals, dissolved solids, calcium and sulphates. Although lime remediation effectively removes most of the heavy metals as hydroxides, it is less effective at lowering levels of sulphates. Various methods of removing sulphates from effluents exist, such as precipitation with lime, precipitation with barium salts, co-precipitation with calcium carbonate, reverse osmosis, and ion exchange. Mintek developed a chemical precipitation (SAVMIN) process to treat acid mine drainage, which entails the addition of lime to precipitate the metal hydroxides, and the subsequent formation (precipitation) of calcium sulphoaluminate or ettringite. The key to the viability of the new technology lies in the correct use, regeneration and recycling of Al(OH)3 used to precipitate the ettringite. The water produced by this process is suitable for disposal to watercourses or for agricultural, domestic or industrial consumption. No brines are produced as the salts are converted to solid hydroxides, gypsum and calcium carbonate.The SAVMIN process has been tested successfully during several laboratory scale operations, and during two pilot plant operations at Stilfontein Goldmine for Anglogold and Navigation Plant, Witbank for Anglocoal. During the pilot plant campaign at Navigation Plant, metal and mineral precipitation was achieved with lime addition. The sulphate concentration in the water was reduced from 2136 mg/L to an average value of 102 mg/L and the calcium concentration was reduced from 727 mg/L to an average value of 70mg/L.The SAVMIN process generates a number of different waste streams including metal hydroxide sludge from neutralisation, gypsum sludge from the gypsum crystallisation steps, and calcite sludge from carbonation. The metal hydroxide sludge is composed of Mg, Ca, Mn and Fe hydroxide, and could be disposed of on a slimes dam. Gypsum sludge was greater than 99% CaSO4.2H2O. This gypsum could be used for dump or road capping, underground backfilling, production of wallboard and cement. The calcite sludge is pure CaCO3, which is recycled back to the neutralisation stage."

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 John Ralston, Stephen Grano, Yongjun Peng, Daniel Fornasiero

"A specially designed mill which allowed the control of pH throughout grinding was used to study the effect of rgrinding conditions on galena flotation and galena separation from pyrite. The various reactions occurring on the mineral surface were investigated by a range of techniques, including OH- addition to maintain the grinding pH, EDTA extraction, XPS and ToF-SIMS measurements.Galena flotation and galena separation from pyrite were strongly dependent on the metal oxidation species produced on galena and pyrite surfaces under different grinding conditions. Iron oxidation species depressed both galena and pyrite flotation, whilst lead oxidation species activated pyrite but had little effect on galena. Optimum galena flotation and galena selectivity against pyrite were achieved by selecting grinding conditions that enabled lead and iron oxidation production to be controlled."

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 Konstantin Fedotov, Victor Beloborodov, Anatoly Potyomkin

"There are areas in Russia, which cover huge territories and they are north, and Siberia. These difficult to access regions with cold climate are rich in a great number of distant deposits of valuable and rare metals, gold and platinum. The development of such deposits requires highly effective technologies of mineral processing which could be realized in modular and quick-built processing plants.The work presented includes the results of long term research in the development of new technologies of processing of zirconium (in the form of rare mineral Baddeleyite – natural zirconium dioxide) bearing ore of the Kovdor deposit which is located in the Polar region of the Kola peninsular and also in Siberia deposits of of ledge ores of gold."

Jan 1, 2003

By Chris A. Bennett, Glenn S. Dobby, David A. Bulled

Establishing reagent dosing strategies for new ore bodies has traditionally involved a combination of experience and empirical experimentation using standard laboratory tests. The grade and recovery data resulting from these lab tests have historically been used as direct indicators of plant performance despite the obvious differences between the flotation environments. A reagent scheme selected in this way would subsequently be employed to generate the grade and recovery information for the geometallurgical model which in turn was used for metal production and cash flow forecasts. If the reagent scheme was sub-optimal then so too would be the forecasts and the resulting cash flow.

Jan 1, 2003

By T. V. Chnyrenkova, J. Troncoso, V. A. Luganov, G. P. Kluev

"Arsenic-gold bearing ores are used as flux in smelting or are leached out with extraction of gold. For decreasing arsenic content in processed materials and for breaking up the lattice and opening up of gold the raw materials are roasted. Some regularity was established for sulfidizing of arsenic bearing compounds in a presence of pyrite and for oxidation of ores and concentrates in the presence of soda.This article analyses the results of laboratory and pilot testing of dissociating and oxidizing roasting of gold-arsenic bearing concentrates. During the dissociation roasting under vacuum arsenic is sublimated into elemental and sulfide forms. This process allows minimizing the negative influence on the environment but requires costly engineering solutions. Roasting in a limited quantity of oxygen in the gaseous phase makes it possible to sublimate arsenic in the form of oxides and sulfides and may be carried out in fluid bed furnaces."

Jan 1, 2003