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By David G. Hulbert, Daniël J. Oosthuizen, Bernard Muller, Daniël de V. van der Spuy

"OVERVIEWExpert Online is a software system that aims to mimic an informed expert on a minerals processing plant. The primary objective of Expert Online is to provide operators with effective training and on-the-job assistance. Training will mostly be done off-line (e.g. using simulators of the plant), while on-the-job assistance will help the operator during normal operation to run the plant in an effective manner. Although Expert Online focuses on the operator, it is expected to also be of value to other plant personnel, including supervisors and plant managers.Expert Online will make use of novel artificial intelligence technology (developed by MINTEK) known as the Interpreting Expert System (IES). Previously the IES was only able to explain the actions taken by the controller. Expert Online will extend this functionality to also take the process dynamics into account.Expert Online is being developed by a South African consortium comprising MINTEK (focusing on the research and development of the system as a whole), Lonmin (globally one of the biggest platinum producers, with plants suitable to test Expert Online on) and the University of Natal (academic partner, providing consultation and focusing on complex process modelling). The initial application of Expert Online will be on milling- and flotation plants.This paper discusses the structural design of Expert Online for implementation on the latest version of MINTEK’s open control platform, PlantStar, as well as several advances and additions since the previous implementations of the Interpreting Expert System."

Jan 1, 2003

By Katarina Theander, Robert J. Pugh

In the flotation process, control of the stability of the froth is extremely critical. In the case where the froth is too stable then mechanical entrainment of particles can occur but in the opposite case, where the froth is too unstable and difficult to skimm-off, then a reduction in recovery can result. In minerals and deinking flotation, commercial fatty acids are used and may act as both both collectors and frothers. However, frequently the fatty acids are mixed with nonionic ethoxylated surfactants to give more effective froth control and increase the flotation performance. It is of interest to note from the surface chemistry literature, that such mixtures may cause synergistic effects in surface activity which may explain changes in bubble size, foaming and carry over of particles. In the present study, we have carried out foaming and drainage experiment with oleic acid and model nonionic surfactants; hexa(ethylene glycol) mono-dodecyl ether, C12E6 and tetra (ethylene glycol) mono-dodecyl ether, C12E4 both in separate and mixed systems. Frothing was carried out in a column, equipped with a series of conductivity electrodes which enabled the water content of the froth to be measured along the length of the column, during various stages of the drainage process. The variation in water content of the froth enabled the process to be characterised by distinct three stages; (a) an entrainment state where the water transfer from the bulk phase to the froth was dominant (b) a steady state when entrainment and drainage are balanced and no water is transferred to or from the froth and (c) the drainage step when drainage predominates and the volume of the bulk phase increases. We also carried out surface tension measurements on the oleic acid/ nonionic systems and related the results to the frothing and drainage performance. From the surface tension data, the adsorption interaction parameter of the mixed systems at the air/solution interface could be calculated and was found to depend on the oleate/ nonionic surfactant ratio. This value was related to the frothing performance and the results indicated a positive interaction parameter for the mixed surfactant systems which could explained the synergistic effects in frothing performance.

Jan 1, 2003

By M. H. Moys, M. M. Bwalya

"INTRODUCTIONThe grinding rate prediction scheme makes use of the energy spectra output from the DEM simulations and the statistical quantification of material strength, which can be done using the drop-weight tester or some other similar equipment. The prediction scheme is evaluated using milling experiments performed under well-defined conditions.MATERIAL STRENGTH QUANTIFICATIONUsing the drop weight test machine, particles of a wide size range were broken singly using different energy inputs. A characteristic equation key to milling rate prediction that relates the probability of fracture with energy input and number of impact attempts was obtained and is stated as follows:"

Jan 1, 2003

By S. Kelebek, A. Khan, J. Caceres, D. Beckett

"Pyrrhotite in nickel-copper sulphide ores is nickeliferrous and intimately associated with pentlandite. Due to its low nickel content, pyrrhotite rejection is an important step in processing of these ores. In our laboratory, various reagents were investigated for their effect on pyrrhotite depression. Among these, a combined use of triethylenetetramine and sodium metabisulphite was found highly promising.The work described in this paper has two parts. The firs part is a summary of results obtained on process samples from the pyrrhotite rejection circuit at Falconbridge’s Strathcona Mill. The second part involves simulation of the circuit performance based on the reagent conditions used in the experimental work and the concept of split factors.Two sets of reagent conditions were evaluated. The first one involved baseline conditions, simulating the current reagent performance. The second one simulated the impact these new reagents can have on the circuit performance.The simulation results obtained under baseline conditions indicated a good agreement with the current circuit performance (Figure 1). The simulation results suggest that at practically the same pentlandite recovery and tailing grades, the circuit concentrate nickel grade can be doubled through effective pyrrhotite rejection by these new reagents (Figure 2)."

Jan 1, 2003

By Willis Forsling, Prabhakar Swarna, Hanumantha Rao Kota

"The solubility of wollastonite and its Hallimond flotation behavior as a function of dodecylamine concentration and pH are examined. The flotation response is characterized by adsorption and surface energy in the presence of amine. The methods of UV-Visible and FT-IR spectroscopy for adsorption and sessile-drop contact angle for surface energy estimation are employed.The results of wollastonite dissolution clearly showed its non uniform dissolution. The surfaces are depleted with calcium ions and became rich in silicon within 10 min of flotation time. Maximum flotation of wollastonite corresponds to a half monolayer coverage of amine, which is substantiated by the surface energy parameters as shown in figure 1."

Jan 1, 2003

By Markus A. Reuter, Albert Scholte, Ewoud V. Verhoef, Gerard P. J. Dijkema

"A dynamic, interactive map has been developed of the life cycle of a number of metals, from mining through to minerals processing, metal production, product manufacturing, recovery and waste management. Whilst the existing metal process network and waste management infrastructure provide substantial scope for (product) design, these also limit change because of the strong path dependency of industry and infrastructure development. The metal production network is complex, as it consists of an interconnected and integrated system that incorporates multiple production routes for a spectrum of metals. More often than not, the production or recovery of a single metal is related to or dependent on the generation or recovery of another. The effects of these other metals is of great importance. In order to realize the potential economic importance of impurities, research and development have integrated the processes of copper production with those of lead and zinc, and connected the processes to those of among others silver, bismuth, tin and platinum group metals (PGMs), for example. The recovery of these elements from the interconnected circuits is extremely complex, as most of the elements must be circulated between two or more circuits before they are concentrated enough to make their extraction possible, and their recovery as a compound profitable.From such a system’s perspective, it can easily be seen that a complication for solid waste management has arisen through the development of products (consumer goods) that bring together metals that are not linked in natural resources. As a consequence, many of these materials are not compatible with any process in the metals production network that was developed for the processing of primary, natural resources, optimized for the processing not only of the primary metal but also for all mineralogically associated minor valuable and harmful elements. The formation of large or complex residue streams or undesired harmful emissions then inhibits processing and recovery of said products at their end-of-life. Another complication is that any change to the system (in metal production, SWM or product design) affects the system configuration. Due to the changing demands for metals as a result from the changing products made from the metals for example, the relationships between the processes in the interconnected metal production systems change. This affects both the demand for old scrap (required amount and grade) from waste management, and the environmental profile of the metals. Preferably, therefore, product designers, waste processors and metal producers must cooperate to realize optimal metal recovery in processing discarded consumer products."

Jan 1, 2003

By Claudio L. Schneider, Reiner Neumann

Any serious study of stereological conversion procedures must be based on an as accurate as possible complete fractionation of a real mineralogical texture. The original work on the Dolomite- Sphalerite Magstream? separation provided excellent data for establishing a working stereological conversion procedure, which has been successfully applied to a number of ores since its implementation. The linear grade distributions measured from these fractionated particles have been published and are accessible. The procedure for stereological conversion from areal measurements is exactly equal to the procedure for linear measurements. Particle composition from the dolomite-sphalerite density-fractionated particle sets, derived from both linear and areal data (Figures 1 and 2, respectively) are redundant, after proper transformation, and match the particle’s compositional range (plotted against S.G.) expected from Magstream?; direct density measurements by Hemicropicnometry plots within the ranges. Linear data cannot be used without conversion, but areal measurements are often directly applied as liberation spectra. Our areal measurements, without stereological conversion (Figure 3), differ completely from the results after transformation, and its density range falls mostly out of the expected/measured values. Therefore non-transformed areal data cannot be directly applied as useful liberation information.

Jan 1, 2003

By L. Tavares

The significant capital and operating expenditure of size reduction operations have maintained comminution on the spotlight of mineral processing research during the last century and, more recently, the concerns about the impact of these operations on the sustainability of the minerals industry, will remain to do so in the 21st century. One of the most popular approaches that have been used to deal with these challenges is the application of simulation both to reduce the uncertainty in the design and improve the operation of size reduction operations. From the initially purely empirical approaches, including the energy size reduction ?laws? and the phenomenological approaches, of which the traditional population balance model is, arguably, the best example, comminution modeling now reached a point in which more fundamental and mechanistic models are sought. The paper analyzes some of the advances that now make multiscale modeling of comminution processes realizable. On the microscale, greater understanding of the phenomena involved in fracture and fragmentation of single particles under different stressing conditions now exists. Particle breakage testing methods are currently used in a routine basis by industry and good quantitative descriptions of different breakage mechanisms are now available, although research is still required to develop appropriate models for a couple of them. On the macroscale phenomena, the discrete element method (DEM) has been successfully used not only to provide insights but also quantitative information on the transfer of mechanical energy from the machine to the grinding media in mills and to particles in crushers, while smoothed particle hydrodynamics (SPH) and computational fluid dynamics (CFD) to describe fluid flow. The paper also analyzes the importance of modeling mesoscale phenomena in size reduction, which is the interaction of particles forming assemblies or beds of particles, demonstrating some of the areas requiring further attention. Examples of application of the multiscale modeling approach to the inadvertent comminution of ore lumps during handling, to the comminution in vertical impact crushers and tumbling mills are demonstrated. Keywords: comminution modeling, DEM, SPH, CFD, multiscale modeling approach

Sep 1, 2012

By Grigori I. Voiloshnikov

"The long-term studies on development of the technology for precious metals recovery using activated carbons executed by Irkutsk Research Institute of Precious and Rare Metals and Diamonds (IRGIREDMET) were finished by successful introduction of ""Carbon-In-Pulp"" process in Russia (1984).The review of some studies, accompanied by development, testing, introduction and subsequent improvement of considered technology, carried out by IRGIREDMET is submitted in this paper.The basic regularities of gold and silver adsorption onto activated carbons from cyanide, thiourea, chloride and other solutions are investigated using various phisical-and-chemical methods ( X-ray photoelectron spectroscopy, Voltammetry, X-ray microanalysis etc.). Using voltammetry it was found that gold cyanide is adsorbed onto activated carbon without chemical changes and partial reduction of gold is possible only during drying of carbon samples before analysis. Metallic gold and silver may be dissolved in boiling cyanide solution at argon atmosphere when they are in contact with activated carbon surface. Gold adsorption mechanism for activated carbons has great differences from that for the ion exchange resins. So the most probable mechanism for gold adsorption from cyanide solution is adsorption of neutral molecules Me n+[Au(CN)2-]n.X-ray quantitative microanalysis technique was developed to investigate gold adsorption kinetics onto spherical activated carbon. Gold profiles in granules of activated carbon for various adsorption conditions were tested (carbon particle size, mixing efficiency, adsorption time etc.). Mathematical methods were used to determine gold diffusion coefficient within activated carbon granule.The properties of various types domestic and foreign activated carbons were tested and the demands to activated carbons suitable for gold extraction were determined. As a result foreign and Russian activated carbons AG-90, AG-95 were recommended for use at Russian gold plants. Domestic adsorbents are cheaper in comparison with foreign activated carbons. The methods to restore carbon adsorption activity including acid treatment and thermal reactivation were tested and implemented."

Jan 1, 2003

By Markus A. Reuter, Bernardete Castro, Antoinette van Schaik, Han Remmerswaal

"INTRODUCTIONThis paper describes the inseparable relation between product design, liberation, and metallurgical recovery in the optimisation of the recycling of passenger vehicles. This is illustrated by the use of an optimisation model that uses among others a material combination matrix based on metallurgical process data, which depicts the consequences of the quality of intermediate recycling products on the metallurgical material recovery and final alloy metal quality. Various simulations will illustrate the effect of changes in product design and hence liberation on the recycling of end-of-life vehicles. Although this paper focuses on cars, the discussion is equally valid for any end-of-life product. Calibration of the model will be discussed with reference to experiments carried out in order to study the optimal recovery of aluminium applications used in passenger vehicles.OPTIMISATION MODEL FOR LINKING DESIGN TO RECYCLINGImproving the efficiency of the material cycle of the car is essential to ensure a sustainable development of our society as well as e.g. to comply with the recycling targets imposed by EU legislation. In the design of the car various materials are combined and connected in many different ways, making up the complex 'mineralogy' of the car and its components, which is changing rapidly and continuously over time. The liberation of materials during shredding plays an important role in the composition (and quality) of the intermediate recycling streams. In order to include the influence of product design (mineralogy), liberation, and particle composition (quality of the intermediate recycling streams) in the optimisation of the recycling of end-of-life vehicles, a systems engineering tool for optimisation of the recycling of end-of-life vehicles was developed, including a liberation model. The optimisation model predicts the recovery rate as a function of product design (in this case a car), liberation, efficiency of the different process steps, economy and legislation based on a developed recycling flow sheet for end-of-life vehicles. Optimisation can only be achieved through the combination of the knowledge areas of product design, shredding, mechanical separation technology linked to pyro- and hydrometallurgy, composing a complex interconnected network of unit operations."

Jan 1, 2003

By Markus A. Reuter, Jacques J. Eksteen

"The modelling of bath type furnaces tends to be either fundamental in nature or total empirical ""black box models"". While models of the first kind are robust, they tend to lack accuracy, in cases where they are to be used for process control, and may take an overly long in development time. On the other hand, black box models tend to lack robustness of prediction for all circumstances and tend to be limited to interpolate based on historical data. While this may very often provide short-term accuracy, the models may have problems with stability in the long term. Moreover, the model structure may not reflect any of the fundamental properties of the system and remains opaque to fundamental analysis. The aim of the model development is in obtaining a model that have robustness, high accuracy, a short development time and which is adaptive to a changing environment. The models are specifically developed for on-line decision support or control of furnaces. The modelling approach is evaluated for a chromite bath smelting furnace. The role of systems analysis, mass balance smoothing, thermodynamic analysis are integrated into one generic algorithm for bath type furnaces. Not only are fundamental process relationships such the mass and energy balances satisfied through a scientific method of data reconciliation; the proposed modelling approach allows adaptive prediction, the first step towards predictive control or metallurgical decision support.It is shown that neither an ARMAX model only, nor a purely equilibrium model only, could predict the dynamics of the process very well. However, a combination of the two approaches more than doubled the accuracy as measured by the R2. It was noted for carbon dissolved in the alloy, that the improvement in R2 in using a hybrid modelling approach was more than the sum of the R2 of the individual traditional approaches. Similar improvements in modelling performance were noted for all other species.It shows further that process dynamics may totally overshadow the effect of thermochemical equilibrium (even when the thermochemical equilibrium prediction includes the recycled alloy and slag heels as additional feeds). The exclusion of process dynamics therefore leads to erroneous results."

Jan 1, 2003

By Vincent C. Smith, Agit Singh, Daniel de V. van der Spuy, Bernard Muller

"Process control in the minerals industry is made difficult by factors such as the multivariable nature of the processes, noise, many disturbances, the changing nature of the processes, nonlinearities, process constraints, slow responses and large deadtimes. A good example of such a process is a milling circuit, where all these problems are experienced. Since model predictive control (MPC) effectively handles most of these difficulties, Mintek decided to develop, customise and test an MPC controller for milling control.Conventional MPC uses a dynamic model of the plant to calculate the future (predicted) plant outputs based on the movements of the manipulated variables in the past. The future moves of the manipulated variables can then be calculated using an optimisation algorithm that will minimise the difference between the setpoints and the predicted outputs. The least squares optimisation method is the quickest, but it does not cater for process constraints. Constraints can, however, be handled explicitly by using a quadratic programming optimisation method. This method ensures that the variables stay within the constraints at all times, but the calculation procedure is much more computationally intensive.• modifying MPC for the Minerals Processing IndustryIt was found that in order to obtain good, robust control using MPC in the minerals processing industry, the conventional MPC algorithm had to be adapted. The MPC controller was first tested on an extensive milling simulator, which was specifically developed for that purpose. Problem areas were identified and the MPC controller was specially adapted to accommodate for these difficulties. Some of the adaptations to the conventional MPC algorithm and special features added were as follows:Since milling plants contain many integrating processes (e.g. sumps), and integrating errors can cause offsets and poor control, it was essential that integrators be handled explicitly. This problem was solved by adapting the algorithm and also using an integrating error portion to compensate for integrating errors.Constraints on the inputs and outputs adversely affected the control. The controller using simple least squares optimisation was tuned with the constraints in place, while the maximum expected setpoint changes were made. This ensured that the process would be able to handle most setpoint changes up to these expected values without violating the constraints. A later improvement on this method was the incorporation of a quadratic programming algorithm to perform the optimisation. This method handles limits explicitly and was shown to perform better than the least squares methods (at the expense of a much higher computational cost)"

Jan 1, 2003

By Graeme Heyes, Warren J. Bruckard, Michael A. Somerville

"Over the past few years CSIRO Minerals has been conducting research aimed at developing a continuous copper converting process to replace the traditional two-stage batch process that is currently used to produce blister copper. Sirosmelt type reactors and calcium-ferrite (lime-based) slags have been used rather than the conventional iron silicate slags. The research work has now been extended to focus on the development of a single-stage continuous copper making process (so-called direct copper converting) in which copper concentrates are converted to low-sulfur blister copper in a single step, that is the smelting and converting steps occur in one continuous stage.One feature of the direct copper converting process is that copper losses to the slag phase can be high, meaning the slag produced needs to be treated to recover the copper value. The feasibility of the whole copper making process will most likely depend on the efficiency and cost effectiveness of the copper recovery stage. Flotation has been identified as the most economical option to recover the copper from direct copper converting slags where it has been estimated that a copper recovery from the slag of above 90% is required to make the overall single stage copper making process economically feasible.A limited series of laboratory batch flotation tests was conducted on a suite of calcium-ferrite-based slags made in laboratory smelting trials. Copper sulfide concentrates from MIM were used as feed-stocks. The objectives of this work were to develop a robust flotation process to maximise the copper recovery and iron rejection from slags made in the process, and to establish operating conditions for future continuous flotation pilot plant trials.The slags treated included a reduced low copper slag, an oxidised high copper slag composite, and a very reduced low copper self-pulverising slag. The copper content of the slags varied from 2.9% to 14% Cu and the CaO/Fe ratio varied between 0.30 and 0.54. In general, the higher the copper content the more oxidised the slag. The copper was present as metallic copper, oxide copper and copper-calcium ferrite phases with the phase mix related to smelting conditions. The slags were crushed, ground, wet-screened at 355 or 210 µm to remove coarse metallic particles of copper, and floated at natural pH (about pH 11) using reagents and conditions appropriate for the selective recovery of the copper phases. Reagent additions were typically 200 g/t KEX and 500 g/t Na2S.9H2O and the grind size was generally a P80 of about 40 µm."

Jan 1, 2003

By H. Pearce, A. E. Lewis, A. Ochieng

"Hydrodynamics and mixing are fundamental to the operation of mineral process systems such as flotation cells and metal precipitation reactors. Hydrodynamic conditions influence phase mixing and mass transfer in a multiphase system, and these affect the overall performance of such a system. Detailed information on the effects of the hydrodynamics on the performance of agitated systems is still required for the design and optimal operation of hydrometallurgical systems, which are always multiphase. Computational fluid dynamics (CFD) techniques have been employed to study the hydrodynamics and mixing, most of which have focussed on the performance of axial and radial pumping impellers in agitated tanks. However, very little has been reported on the influence of a draft tube on the flow profile in such systems.CFD simulation of a stirred vessel centres on the way the impeller is modelled. Some of the most recent approaches to modelling an impeller are impeller boundary condition (IBC), snap shot, sliding grid (SG), multiple frame of reference (MFR) and inner outer (IO). The accuracy, with which these models predict experimental results and the corresponding computational demands, form the basis upon which the choice of an approach is made. Most of these approaches (IO, SG and MFR) address the key problem of the stirred tank modelling, namely, the simultaneous meshing of the rotating impellers and the stationary baffles. The MFR is computationally cheap and has been found to give predictions that compare well with experimental data.The CFD technique (code CFX4.4) has been employed in the present work to study the hydrodynamics in a mixing vessel stirred with either a Rushton turbine or a pitched blade impeller. The multiple frame of reference (MFR) approach has been used to model both impellers. A draft tube was used only in the Rushton turbine stirred vessel. The flow profiles for the impellers have been studied in three regions; below the impeller tip, at the middle of the tank, and near the liquid surface. The simulation results were compared with literature data obtained using a laser Doppler velocimetry in the three regions of the vessel, and it was found that the model predictions were better in the impeller region. There was a poor prediction of the experimental results in the region closer to the liquid surface; however, this was improved when the turbulence parameter (C2) in the k-e model was set to a higher value. The value of the impeller clearance at which the Rushton turbine generates an axial impeller type flow has been determined and it has been shown that, at this clearance, a draft tube can be used to enhance axial flow in a Rushton turbine stirred reactor."

Jan 1, 2003

By N. Ahmed

"This paper is concerned with the drainage behaviour of gangue mineral in the froth phase. Experiments were carried out in a continuous laboratory flotation cell in which froth depth and bubble size can be changed independently. The fraction of solids returning from the froth to the pulp zone was expressed using a rate constant by considering the appropriate froth regimes. A mixture of hydrophilic solids (silica) and floatable particles (glass ballotini) was used as a flotation feed. Samples of glass ballotini of different hydrophobicities were obtained, using controlled silanation. Three samples, with contact angles of 50, 66, 82 degrees, were used. The effect of the initial bubble size (pulp bubble size), concentration of gangue mineral in the froth zone, and froth depth on the drainage of silica, were also investigated.Typical results obtained from this study is shown in the figure given below. In this figure drainage rate constant for the entrained solids in the presence of particles of the three hydrophobicities is plotted against froth height. As observed, the drainage rate of the entrained solids increases considerably with an increase in the degree of hydrophobicity. Concerning the effect of pulp bubble size on the drainage rate of entrained solids, larger bubbles always give higher drainage rates due to formation of relatively loose froth structures which allows gangue particles to easily move down to the pulp zone. Conversely, smaller bubbles exhibit lower drainage rate constants, in particular at shallow froth depths."

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 S. Mohanta

The air dense medium fluidized bed separator which has been developed for the dry beneficiation of coal is recognized as a low cost and high efficiency process. The success of this separator for beneficiating any specific coal, alone or in combination with other processing methods, mostly depends on the characteristics of run-of-mine coal. Therefore, a thorough knowledge of the mineralogical composition and washability characteristics of representative coal sample is highly essential for correctly and effectively assess the suitability of this process. Available literature conforms that although the characteristics of Indian non-coking coals are well known, the correlations between the particle compositions with its density are entirely lacking. In the present study the washability, proximate, ultimate and elemental analysis was conducted for four typical Indian high-ash non-coking coals and their elemental compositions were well correlated with the specific gravity of coal. The results obtained in this study provide some essential information to the coal-processing engineer for efficiently operate and control the process. Furthermore, the beneficiation potential of air dense medium fluidized bed was experimentally evaluated and compared with the results obtained from an operating wet beneficiation plant. Based on this comparative study the air dense medium fluidized bed is established to be a possible alternative to the conventional wet beneficiation method for beneficiating Indian coals with Ep values in the range of 0.03 to 0.06

Sep 1, 2012

By Derek Caizergues, Hurman Eric

The principle of carbothermic reduction has been around for many years. In principle it is a simple process, yet with a multitude of problems. The temperature required to affect reduction is in the region of 2200ºC and results in aluminium oxy-carbide formation rather than metallic aluminium. From a thermodynamic point of view, reducing the temperatures of reaction which would suppress oxy-carbide formation would only be possible by lowering the total pressure of the system. A decrease in thermodynamic activity of product aluminium by dissolving it in another phase would also help preventing the formation of oxy-carbides and would also increase the yield of the reduction reaction. Thus experiments have been conducted at around 1700ºC to determine the possibility of carbothermic reduction of alumina under the presence of a metallic solvent. Total pressure of the system was reduced to around 30kPa and metallic nickel, iron, copper and tin were selected as the solvent. The highest recovery of aluminium was achieved with the nickel solvent followed by iron, copper and tin. This ranking for the first three was also in accord with the extent of negative deviation form ideality in the respective binary solutions of these solvents with aluminium. The tin-aluminium system displays positive deviation form ideality. The rate and extent of reduction was found to be highly dependent on temperature and pressure. The pseudo first order reaction rate was found to be applicable to the process in all the solvents used. Rate constants were calculated and it is also suggested that the reduction was controlled primarily by the chemical reaction rate.

Jan 1, 2003

By Remmerswaal, U. Boin, M. B. G. Castro

"To design sustainable products that can be recycled with high resource efficiency, low environmental impact and economic feasibility, the choice of materials and materials combinations, made in the design stage, is fundamental. The products we design, manufacture and use now will be the resources of the future. Designers are able to select materials for a product according to the many functional requirements they must fulfil. But they have a limited knowledge of the recycling processes and its requirements regarding quality of the secondary material streams. Resource Engineers have to manage the processing of these streams, that are becoming more complex with the increasing variety of materials and decreasing size of components. After mechanical separation of the materials streams resulting from shredding of EOL (endof- life) products, there is always a degree of contamination, from two possible causes:Incomplete liberation: the bonds between different materials combined in a component are not completely destroyed by shredding, resulting in some particles containing two or more materials attached;Separation efficiency: the mechanical separation processes are not able to separate perfectly the many material particles; there are always a number of foreign particles in the recovered streams.Sometimes, those contaminants cannot be removed by the industrial metallurgic recycling processes, and a more serious problem occurs when the contamination levels compromise the recycling of the material stream by lowering its quality (i.e. the properties of the recycled material will be lower due to the contamination). As a consequence, the material must be diluted in virgin raw material and/or used in a less demanding application (downgrading), causing resource depletion and increased energy use, waste production and recycling costs. In order to make the best choice of materials combinations for a product, a systematic approach is necessary, that can close the gap between the knowledge areas of Product Design and Recycling Technology."

Jan 1, 2003

By Barbara Peszko, Tadeusz Tumidajski

"Various methods are used to identify the grain composition of fine-grained materials because so far the best notion of the grain size has not found and there is no single method to define grain size. In practice the most important are the following grain sizes: sieve diameter dt, effective diameter de, substitute diameter d2 and statistical diameter dst. The mentioned sizes are connected with the methods of analyses. Methods are correct but measure of different diameters of grain and their results are different.The most important methods of granulometric composition analyses are the following: the sieve analysis, the sedimentation method and the conductometric (Coulter-Counter) methods. In each of these methods various physical features connected with the grain size are measured.Sizes of grains defined by different formulas or measurement methods are associated mutually by dependencies, which are results of differences in their determination or calculation ways.In order to determine principles of results comparison the classification analysis results on linearly or non-linearly connected was made. Analyses which results demonstrate the same type of grain size distribution are treated as linearly connected. It is based on the general formulae which determines the probability density function of random variable which is the function of another random variable having the known density function.In order to show the difference in the grain composition of the same material qualified by different methods, three methods of investigations were distinguished. They are: the sieve analysis performed on precise sieves, the sedimentation analysis performed by means of a sedimentation balance “Sartorius” and the microscopic analysis performed after preparing a microscopic slide where the grain size was measured by the Martin’s method.The materials selected for the analysis were quartzite and glass, which are the material of high purity.The obtained results of mentioned above three types of analyses were approximated by distribution function of four distributions: Weibull, log-normal, cut Weibull and Gaudin-Schuhman."

Jan 1, 2003