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By G. S. Hansford, G. E. Searby

"Ferrous iron oxidation kinetics was measured in continuous culture at temperatures between 65 and 75ºC, using thermophilic microbes suitable for high temperature bioleaching. The resulting specific oxidation rates were modelled as a function of the ferric/ferrous iron ratio. The results were compared to those obtained by conventional mesophilic microbes.Microbially mediated ferrous iron oxidation is a vital sub-process in the mesophilic bioleaching of sulfide minerals and is expected to be of similar importance at elevated temperatures using thermophilicmicrobes.A thermophilic archaeal culture used in chalcopyrite bioleaching was successfully grown in continuous culture on ferrous sulfate, indicating the capability of the microbes to sustain growth for long periods on the energy provided by the conversion of ferrous iron to ferric iron, the primary leaching agent in sulfide mineral bioleaching.Steady state data was obtained at residence times of between 70 and 10 hours, with washout occurring at residence times between 11 and 9 hours, corresponding to a maximum growth rate (µmax) of between 0.09 and 0.11 hr-1. The reactions were followed by measurements of the solution redox potential, soluble iron concentrations, and offgas analysis of the oxygen and carbon dioxide utilisation rates."

Jan 1, 2003

By Reuter M. A., R. D. van der Weijden, W. F. C. van Wageningen

"Copper(II) can be recovered or removed from acidic copper sulfate solutions as cuprite or metallic copper powder by reduction with carbohydrates. The copper powder characteristics, such as size and shape of particles, determine the tendency to adhere to reactor walls and to agglomerate. In order to make this process suitable for a commercial scale pipe reactor, process conditions and the reactor configuration were varied in order to influence the copper characteristics in a positive way. The aim was to achieve proper particle throughput in the pipe reactor and to obtain a well defined copper powder.In this paper the effect of both, chemical and physical parameters on the shape and size of particles were systematically studied in a number of autoclave experiments. These parameters include mixing, Cu(II) concentration, pH, temperature, seeding, use of additives and reactor materials. Additionally, Monte Carlo simulations of copper growth inside a Kenics static mixer were made. Results show that the use of additives and the use of static mixers influence particle characteristics the most."

Jan 1, 2003

By P. M. Solozhenkin, V. P. Nebera, V. D. Skorohodov

"Aqueous dispersions of air specifically prepared on the basis of flotation reagent solution acquire active properties in relation to the solid surface and may be imply as a medium for flotation ores. Such aerated solutions were defined as Activated Aqueous Dispersions of Air (AADA) with 5-6:1 ratio and the procedure of mineral separation was defined as a flotation process under non-equilibrium conditions. These procedures differ from conventional flotation mainly in reagent interaction with minerals through their adsorption films on gas bubbles simultaneously forming flotation complexes. Gas-liquid mixture is kept till an adsorption layer of reagents close to the limit value is formed on the surface of bubbles. The theoretical basis of AADA is considered.The results of two-phase gas- liquid mixture (AADA) were studied. Two versions of AADA were considered. Electrical surface potential of the air bubbles with the surfactant film, untreated minerals particles in Coulomb attraction and flotation complex formation were analyzed. Special flotation machines were constructed for separation of mineral suspension in air dispersion, whose effectiveness was confirmed in flotation of apatite waste of Kovdor ore. FK-9 machine introduced on Kovdor iron ore combine for the recovery of apatite from current departures of factory. The froth product contained 7.2 % P2O5, with recovery of 44 % apatite, which was processed for getting melted phosphoric-magnesium fertilizers."

Jan 1, 2003

By Z. Kwela, A. Manhique, W. W. Focke, W. van der Merwe

"The main features of the de Wet improved alkali fusion process for the manufacture of AZST are: Fewer process are steps necessary; radioactivity is removed by leaching rather than by precipitation; fewer waste streams are generated; there is less waste to discard and alkali reagent is recovered in the form of a sodium silicate solution that is essentially free of radioactivity.Here we report on our efforts maximize the alkali recovery in the sodium silicate product stream: Milled zircon, d50 ˜ 9 µm, was fused with caustic soda pearls in open reaction vessels at temperatures between 650°C and 850°C. Fusion times of 1, 2, 4, 24 and 336 hours (with intermittent milling) were investigated. The fusion products were characterized by infrared spectroscopy, X-ray diffraction and by wet chemical analysis.For prolonged fusion times the fusion products approached equilibrium compositions. However, the phases Na2ZrSiO5 and Na4Zr2Si3O12 observed at 850°C did not form at 650°C. Since these compounds do not hydrolyze in water they limit the recovery of alkali in the sodium silicate product stream. For 2-hour fusions a broad spectrum of non-equilibrium reaction-products, that are rich in sodium silicates, is formed."

Jan 1, 2003

By N. Kgabi, F. B. Waanders, E. Vinken, A. Mans

"Mössbauer and SEM identification of the iron mineral phases present in South African coal fractions from the Free State, Gauteng, Mmpumalanga, Natal and Waterberg coal fields, as well as from ash samples from coal used in the Lethabo power plant, containing a large amount of inorganic matter, was conducted. The iron is mainly associated with sulphur in the mineral but the amounts of these and other minerals vary considerably in coals from diverse origins. By means of Mössbauer analyses the iron bearing minerals were identified as pyrite, jarosite, illite and ankerite. In the SEM analyses quartz, associated with various clay minerals was identified with differences in abundance found between the coals from the different locations.The fly ash, produced at the high combustion temperatures in the power plant, gave rise to a spectrum, typical of a glass. SEM analyses showed that agglo- meration of the fly ash was due to the presence of Ca in the coal. The lab. produced fly ash was combusted at temperatures ranging from 200-1 200°C and the pyrite changed partially to hematite and partly into the glass due to the presence of the quarts and the clay minerals. A similar spectrum as the power plant fly ash spectrum was obtained.In the weathering experiments the pyrite changed to a sulphate component in a very short time during air drying."

Jan 1, 2003

By R. Imhof, S. E. Sánchez-Pino, H. Sprenger, S. A. Sánchez-Baquedano

"In 1992, Ingeniería de Minerales started with the introduction of pneumatic flotation technology in Chile and South America. This technology consists of vertical cells and gyratory cells, used mainly under actual operational conditions, with pilot units directly installed in the concentrator circuits of the industrial process. Successful industrial applications have been observed at Los Pelambres, in the molybdenum plant; at Codelco Andina in the molybdenum plant as pre-rougher to produce directly a final concentrate; in the copper circuit at Las Luces as pre-rougher producing final concentrate using sea water; at Minera Valle Aconcagua where a full automatic plant produces pre-concentrate from fresh tailings as feed; at the silica and silicate reverse flotation circuit of Compañía Minera del Pacífico; in cleaning the final concentrate of Zn by reverse flotation removing ultrafine carbonate; and in a plant that reprocesses fresh tailings from a copper slag flotation process. Positive operational changes in the design of the flotation circuit have been seen in plants using G-cells and V-cells, improving the performance of flotation circuits and the quality of final products. The high concentration of bubbles and micro turbulence produced by the pneumatic aeration units provide a high probability of collision and attachment, reducing dramatically the residence time. Though it is a pneumatic flotation, no compressed air is needed, and the equipment is characterized by low maintenance costs, full automation, savings in investment and energy."

Jan 1, 2014

By Anatoly N. Vinogradov, Vyacheslav A. Tsukerman

The North-West Russia for 70 years is one the main producers of Cu, Ni, Co, Al, P, REE, Zr, Ti, Ta, Nb, Fe ores and other minerals in the Europe. The largest mining companies locates in the Murmansk region, and they extracts about 100 mln. tons of ores and damps up to 250 mln. tons of waste annually. Nevertheless an environmental situation in the region is stable due to rational management and treatment of wastes on a base of the Noosphere Concept for Nature-using suggested by Vladimir Vernadsky. The Concept was performed practically in the Fersman’ scheme of “non-waste mining and metallurgical complex”, published in the monograph “Minerals of the Kola Peninsula: current status – analyses – prognoses” (1941) and served till now as a sort of “Bible” for industry managers lightening a strategy for an industrial “trophic chain”. The recent status of this scheme is shown on the picture below, and one can see that our concept is coincide with modern ideology known as the “Industrial Ecology”. Moving along this mainstream in the Kola Peninsula since 1929, when the first mining company “Apatit” was established, we provided the water close circuit in mineral dressing plants, hydrometallurgical treatment of slag and tailings, productions of building materials and adsorbents of wastes. The innovation set of technologies designed by the Kola Science Centre allow recently to involve tailing damps in re-exploitation as the technogenic deposits of valuable raw materials for fertilizers, tanning and cleaning agents, pigments, concretes and etc.

Jan 1, 2003

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

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

Jan 1, 2003

By Valery V. Kostjuk, Victor. N. Bredikhin, Alexander I. Shevelev, Evgeny A. Kazban

"The investigations to improve the process data have been done in order to stabilize the functioning of drying units. The scheme of turnings preparation with centrifuging and subsequent thermal degreasing (tandem) is proposed. To improve the efficiency of the process the scheme of reclamation of the centrifuge fugate is developed with production of oil and service circulating water. Empirical dependences of the turnings temperature influence on the lubricant-coolants content in centrifuging are gained. When the turnings temperature is increased to 80 C the residual content of LC is decreased by 1.5%. The investigations aimed to improve the preparation of non-ferrous turnings have allowed to decrease the melting loss by 15-20%; to stabilize the process of thermal drying of turnings; to decrease sharply (by 60- 70%) the volume of LC combustion products; to reclaim the centrifuge fugate and produce oil and servicecirculating water.Non-ferrous turning and primarily aluminum and copper alloys turning is a stable source of secondary raw materials for metallurgical works.Direct by lubricant-coolants (LC) of various types: synthetic, semi synthetic, oily and emulsions.On the base of investigations concerning various methods of the non-ferrous turning processing the favorable one has been selected taking in to consideration the economy, ecology and quality of the finished product (alloy). Two-stage process is developed. The main idea of the process is the elimination of the lubricant-coolants (LC) to the limit specified in advance. The applied method is centrifuging with subsequent final elimination of LC by thermal method.Constant value of LC content at the inlet of the thermal unit excludes practically the oxidation of metal and as a consequence increases the output by 10 –15 % in metallurgical processing."

Jan 1, 2003

By S. K. Pan, M. P. Srivastava, N. Prasad

"Dalli mines of Bhilai Steel Plant, India is fully mechanized iron ore mine having wet processing system. It has a capacity to treat 5 Mt of ROM. In processing circuit of Dalli mines, scrubbing, wet screening and classification operation is being carried out. Average slime generation for the last five years is about 14% of ROM. As the mining has reached to the lower benches, fines generation is more. As a result, very fine and heavy particles, which settle fast, are being discarded with the slime to tailing pond. These heavy and faster settling particles were causing jamming in the thickeners.Laboratory investigations were carried out at Research and Development Centre for Iron and Steel (RDCIS) to suggest a suitable scheme to recover high quality fines so that the availability of thickener can improve. The slime samples were first treated in a floatex density separator. The concentrate obtained from the floatex density separator was treated in hydrocyclone. Laboratory investigations indicated that the slime with 49% Fe, 12.7% silica and 10.7% alumina can be upgraded to 62.1% Fe, 3.3% silica and 2% alumina with 36% material recovery. Based on the laboratory studies ,a system was installed at Dalli minesThe general arrangement of the system is shown in Fig. below."

Jan 1, 2003

By Stephen J. Harker, John Knights, Randolph A. Pax, Glen A. Stewart

"Mineral samples were obtained from different stages of a mineral processing circuit used to extract the copper and gold rich mineralogical phases. The aim of this work is to characterise the quality of the samples at different stages of processing. The samples were taken of the head grade, tailings, cyclone overflow and the final concentrate.Characterisation of the samples was determined using Cu-Ka X-ray powder diffraction and Fe57 Mossbauer spectroscopy. These measurements will be presented and discussed in terms of the enrichment of the ore, showing the removal of magnetite and quartz through the processing, the final concentrate being rich in chalcopyrite and pyrite. This data also shows the utility of Mossbauer spectroscopy to provide mineralogical phase information directly.Mossbauer spectroscopy is a tool to determine the material phases of a sample. It is a nuclear based technique which measures the amount of attenuation of a narrow Doppler shifted source energy as it passes through a sample. The attenuation depends on the amount of resonantly absorbing material in the nuclear radiation path from the source to the detector. Synchronous detection of the doppler shifting velocity and the nuclear radiation count gives a Mossbauer spectrum. By convention, the energy axis of the Mossbauer spectrum is displayed in units of velocity.Figure 1 shows Mossbauer spectra obtained for a sequence of samples throughout a processing plant. These spectra show the removal of magnetite and the concentration of chalcopyrite and pyrite. Optical microscopy results indicated a significant component of bornite not witnessed with Mossbauer spectroscopy. Closer examination showed that optical microscopy assays over estimate the bornite component."

Jan 1, 2003

By Przybycien Krzysztof, Tumidajski Tadeusz

"Materials being the feed to mineral dressing plants are the mixture of ore minerals having different physicochemical properties among others, especially susceptibility on crumbling. During exploitation of material and their preparation to communition the big number of narrow classes comes into being and they have different properties. The determination of common communition laws of multicomponent (on account of size and mineralogy) materials leads to the estimation of mutual influence of narrow classes and their rates, taking into account their endurance and mineral density, on general ratios and their simultaneous crumbling.If we try to accept the grain membership to the certain component as the differing feature, we can write the balance equation as: ( ) ( ) S= = k i i i g x p f x1where: fi – density functions of one type distribution and of different statistical moments (characterising the homogeneous materials grinding), pi – “stirring” proportions of each components, S== k i i p 1 1 . From the point of verification view of detailed versions of this equation the inverse operation should be done: in the base of the components’ mixture grinding results and the results of components grinding the legitimacy of equation should be checked.The using of finished distribution mixtures’ theories to the grinding process analysis allows, first of all, to verify the assumption of grinding independence of individual feed components. Talking more generally it would lead to the comparison of grain size distributions, obtained by individual components grinding from the defined in the mixture distributions theory calculations. One of experimental and calculation results for artificial mixtures of galena and dolomite is presented on figure below (df means distribution function)"

Jan 1, 2003

By P. M. Solozhenkin

"Galvanochemical process (GChP)) cleaning of sewages is realized in the field of shortcirquited galvanic elements from the mixture current the materials place in purification’s solution and form multitude galvanopairs without external electric field in presence oxygen of the air. The galvanochemical process is electrochemical process utilizing galvanic pairs: coke - iron, iron - copper and others and process does not require chemical reagents.The effect of basic parameters of the cleaning effectiveness have been studied depending on oxidizing of galvanopairs. Adjusting nature, type of galvanic pairs and forming three component system possible to enlarge emf circuits to 2.378 V.The role of ?2, as basic agent, for generation of hydrogen peroxide and hydroxyl ions.It was stated, that removing of metal ions from solutions occur mainly on account of sorption and hydrolytic sedimentation of iron oxihydrates.Determined separate stages of the process: coagulation, sorptions of admixtures on freshly formed ferric oxides and oxidizing destruction of organic components of effluents in presence of ?2 ? ?2?2. Shown efficiency of the method for removing of Cu, Cr, Ni, Zn, As ions, as well as fluoride, phosphate and cyanide anions and oil products, surface-active and flotation reagents. Cleaned water can be recycled for some processes non-critical toward residual concentration of admixtures, as total salt contents is lowered on 60-75 % and reaching limits of concentration for toxic components.The concept of high power unit creation was developed, and galvanochemical pulsator is presented. The pulsator is not expensive, and exploitation expences are low, as well as servise is simple with high effectiveness, and capacity. The galvanoflotation process is developing, combining galvanochemistry and flotation of hydrofobic admixtures (oil, surface-active agents).The galvanochemical flotators are presented."

Jan 1, 2003

By P. A. Harvey

Previous studies have reported that inorganic electrolytes can enhance floatability of coal. The research has shown that the enhancement, if any, is highly dependent on changes in solution pH, type of electrolyte, and electrolyte concentration. The reasons for this are still not clear. In this study the floatability of coal particles in mono and divalent salt solutions was investigated. The zeta potential and hydrophobicity of the coal was measured experimentally, and a modified Hallimond tube was used to determine the floatability of coal particles by single bubbles, where the collision efficiency was equal to unity. The experimental information was used in conjunction with the Hogg-Healy-Fuerstenau equation to quantify the electrical double layer interaction. It was found that for low electrolyte concentration (less than 0.1 M) solutions the flotation recovery of coal particles was less than that for distilled water, and decreased with increase in concentration. Conversely, at electrolyte concentrations above 0.1 M, flotation recovery increased with increasing concentration (Figure 1). Both of these results are consistent with previous observations, but are inconsistent with expectations when considering the possible influence of electrical double layer interaction. Modelling of the system indicates that the electrical double layer is compressed with increasing electrolyte concentration, resulting in an increase in flotation recovery due to a diminishing of the (electrical double layer) repulsion between the bubble and the coal particles. Moreover, for electrolyte concentrations above about 0.1 M the electrical double layer is completely depressed and would have little further influence, if any, on the flotation process. Therefore, the electrical double layer interaction is not the principal determining factor for the flotation of coal in electrolyte solutions.

Jan 1, 2003

By L. G. Schumskaya, ?. S. Yusupov, ?. ?. Kirillova

"It has been shown on the example of cassiterite that grinding in mills of the increased power lead to destruction of the fine crystal structure and consequently to change in physical and chemical properties of the mineral, that is its transition into mechanically activated state. The increase in mineral reactivity is related to both the growth of mineral specific surface and sharp decrease in the sizes of primary crystallites accompanied by essential increase in number of microdefects that is clearly expressed in its increasing solubility during interaction with corrosive mediums, especially with acids. Calorimetric measurements indicate that the thermal effect of SnO2 solubility increases considerably.These observations allow us to propose two techniques of hydrometallurgical treatment of cassiterite: direct dissolution of the mechanically activated mineral in acids, although it is a very power-consuming process, and mechanical activation of cassiterite in presence of metals that are able to release hydrogen from acids. Active hydrogen is released during interaction between the mechanical mixture of SnO2 and metal with acids and reduces tin from the mineral transferring it into solution.In addition to other technological properties, the flotability of cassiterite has been thoroughly studied. It has been found that it steadily decreases as activation proceeds because of increase in the degree of hydratability of particle’s surface. In this case, the mechanical activation is provided through tribotreatment of a surface rather than through fine grinding. On this basis we developed the technique of inverse cassiterite flotation with its subsequent transfer into a chamber product that considerably increase the quality of a tin concentrate.The observed technological effects may be generally explained by occurrence of the valenceundersaturated, strained (deformed) chemical bonds and other active centers on the cassiterite surface while decrease in its flotability - by formation of the hydrolyzed tin species and impurity iron, such as Sn(??)4°, Fe(??)2 +, Fe(??)3° hydroxocomplexes and others."

Jan 1, 2003

By M. Özer, G. Önal, F. Arslan

"The use of ultrasonic in industrial processes has increased during the last few years. Ultrasonic vibrations are used in sieving, grinding, ore washing, cleaning, and flotation in mineral industry. There are also some attempts for the utilization of ultrasonic treatment in separation and removal of fine particles from gases and liquids. In Kalemaden A.S. (Turkey) four different types of clay mixtures (1. A mixture of clays from Balikesir-Düvertepe and Istanbul-Sile, 2. A mixture of clays from Ukrania and Balikesir-Düvertepe, 3. Sögüt-Kadikelimesi, 4. A mixture of clays from Sögüt and Istanbul-Sile) and kaolin from Balikesir-Düvertepe (Turkey) are concentrated before their use in ceramic production. Dewatering is the important step in those types of concentration plants. Sedimentation of concentrated clay has always been difficult and taken long times due to their nature and having small particle sizes. Flocculants can be used to enhance the sedimentation, but they are not preferred by the ceramic industry since they affect the quality of ceramic products. For this purpose, ultrasonic treatment is used in the sedimentation of clays mentioned above for solving the problems encountered related to the ceramic industry and promising results were obtained.Kaolin sample, subjected to this experimental study, from Balikesir-Düvertepe region of Turkey was brought from the plant as a pulp in containers and throughly mixed with a stirrer before sedimentation experiments. A two liter graduated cylinder and an ultrasonic bath (with 25 kHz frequency and 0.5 KW power) were utilized in the tests. Superfloc A-120 (1% concentration) was used as a flocculant. The settling distance was reported against the settling time during the experiments. Initial and final pulp densities were also determined. The effects of several parameters such as pulp density, flocculant addition, and ultrasonic treatment on the sedimentation of kaolin were investigated and the results are represented in terms of settling distance versus settling time."

Jan 1, 2003

By Wieslaw Wszolek, Kazimierz Trybalski, Ryszard Tadeusiewicz

"The present work is an attempt of neural networks application to the description of complex technological processes of useful minerals enrichment. Neural networks are among the most convenient tools that have been added recently to the professional toolbox of modelling specialists, and they are particularly useful in realisation of multiple practical tasks, characterised by great complexity and relatively low amount of available a priori knowledge about the nature of the modelled processes. They are successfully applied in a wide variety of problems related to data processing and analysis, their prediction, classification or process control. The object of the study was the technological site for copper ore enrichment by floatation, being a part of technological line in the Ore Enrichment Plant ZG „Polkowice”, KGHM „Polska Miedz” S.A.The main floatation is described by parameters measured by the supervision and control system, which can be grouped with respect to the functions performed for the object:a) input function: aFG - copper contents in the feed material for the main floatation [% Cu]b) control: LFG I - level in the first section of the floatation unit [%], LFG II - level in the second section of the flotation unit [%], LFG III - level in the third section of the floatation unit [%], LFG IV - level in the fourth section of the floatation machine [%]. These quantities compose the five elements long input vector.c) output function: ? - copper contents in the waste from main flotation (final waste) [% Cu]The measurement data, containing the above-mentioned parameters, have been collected during the normal operation of the plant. The data contain momentary values of the parameters, registered every 10 minutes, covering the period of 196 hours of the plant’s operation (1176 measurements for each quantity).For construction of the model used in the study classical multi-layer perceptron-type neural network has been used, with one hidden neuron layer, trained by the error back propagation method."

Jan 1, 2003

By Vladimir G. Kochnev

"Autogenous and semi-autogenous grinding (AG and SAG) have been considered a step forward in comparison to conventional grinding circuits with several stages of crushing and using ball (and/or rod) grinding mills. However, existing AG and SAG technologies still can be improved and have an immense potential from the viewpoint of economic benefits.Experience gained by the Technics & Technologies of Disintegration Ltd. (TTD) in the research of grinding processes shows that comminution in AG and SAG mills can be performed in a more effective way. The company’s approach comprises the following elements:- Novel mill design- New liners and lifters- Novel discharge grid design- Technique of treating material of critical particle sizeA novel mill of the cantilever type capable to operate in the AG and SAG mode has been developed. The cantilevertype mill has a high diameter to length ratio, which dramatically increases the throughput rate, and is characterised by high reliability, fast installation and low capital and operating costs.Tests of the new heel-shaped liners, originally aimed at improving the intact condition of diamond, indicated that they play an important role in the grinding process. Tests performed by TTD jointly with ALROSA, MINTEK and Anglo-American Corporation, demonstrated that the heelshaped liners provided the increase in the throughput rate varying from 30 to 80 % and the decrease in power consumption in the range 30-55 % for grinding of kimberlite and platinum-containing ores.Investigation of the influence of the main grid parameters on the efficiency of grinding led TTD to a special design of a mill discharge grid, with a radial location of openings, the slot width varying from the periphery to the centre and the grid surface provided with “heels”. The design allows one to control the particle size distribution of the ground product without affecting the grid throughput rate."

Jan 1, 2003

By M. H. Moys, H. Dong

"Discrete Element Method (DEM) has become a standard tool to simulate grinding mills in order to gain information about load behaviour, power drawn, etc. However, parameters necessary to run a simulation are not always readily available. For example, the coefficient of restitution used in DEM simulation from the literature ranges from 0.1 to 0.9 due to lack of accurate values. The lack of correct input parameters results in the fact that some simulation parameters are adjusted to match the simulation prediction with the experimental results. It is inappropriate to tune one single parameter arbitrarily in order to fit the prediction with experimental results. The correct value of parameters for DEM simulation should be established, and rigorous validation on simulation results by DEM needs to be done.The objectives of the ongoing project are to measure the coefficient of restitution at conditions analogous to grinding practice. Equipment has been built to measure the coefficient of restitution. A typical case of impact test showing the vertical position of a ball as a function of time is presented in Figure 1. The coefficient of restitution between steel ball of different sizes and the targets including steel liner (e = 0.91), mild steel block (e = 0.57) and rubber liner (e = 0.7) have been measured. The coefficient of restitution reduces to 0.38-0.52 when there is a layer of coal particles (1-2 mm) on the steel liner. The effects of ball size, drop height on coefficient of restitution are investigated. Then a DEM code is developed of several contact models to simulate the impact process. This code can reveal details on velocities (translational and rotational) and forces (normal and tangential) during the brief impact interval. Figure 2 is a comparison of the rebound rotational velocity between experiment and prediction by different models. The results can be used as DEM input and to assess contact models."

Jan 1, 2003

By John A. Herbst, Ming Song, Xiangjun Qiu

"It has been known for sometime that as wear occurs in tumbling mills there is an associated change in mill throughput. These changes have traditionally been simplistically, attributed to “mill volume effects”. New high fidelity simulation (HFS) tools (involving DEM, CFD and Breakage models) are now giving new “microscale” insights into the complex interactions that occur between evolving lifter/liner profiles and breakage. An illustration of this analysis is shown in Figure 1 below.Here we see that after a new lining is installed (Region I) the wearing process reduces the liner thickness resulting in a larger power draw and an associated higher throughput until Region II is reached. By this point the lifter height is reduced significantly changing charge motion (less cataracting) the power begins to decline, but the comminution efficiency increases with this type of “calmer” breakage environment therefore the throughput continues to increase. In Region III the lifter is no longer providing the minimum required charge lifting action, the power and the throughput both drop off significantly. In the last two stages the behavior is especially complex because throughput is not linearly related to power since grinding efficiency is changing.The study described here shows that these new HFS tools allow the design of wear part profiles which will maximize mill productivity over the entire life of liner/lifter systems. A simple example of such a design procedure is shown involving the selection of a sinusoidal profile for a 34 ft diameter SAG mill.The paper discusses how the principles exposed in this simple example can be applied to search for an optimal profile in which non-standard modifications are allowed to compensate for throughput or wear shortcomings of standard profiles."

Jan 1, 2003