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By Venkata S. Buddhiraju

Pelletization of iron ores involves balling on a rotating disc to produce wet pellets and induration of wet pellets on a moving grate to produce fired pellets. The quality of pellets produced and the productivity of the pelletization process depend strongly on the characteristics of the feed to the pelletization disc, especially the particle size distribution and the moisture content. The upstream processes involved in the preparation of pelletization feed include grinding, thickening and filtration of the iron ore slurry. The focus of the present work is the closed circuit wet grinding of iron ores. The circuit consists of a primary ball mill, a regrind mill and a hydrocyclone. A population balance model was developed to predict the grinding kinetics and an empirical model was fitted for the separation of fine particles from the coarse particles in the hydrocyclone. Batch grinding kinetics experiments were performed on a laboratory scale ball mill to obtain the ore breakage parameters which were subsequently used for the simulation of the industrial mills. The models were customized for the industrial operations and the effects of different process variables like feed flow rate, water flow rate, etc., on the size distribution of product from the grinding circuit were studied. Additionally, different circuit configurations were simulated to determine operating conditions that could result in the desirable product particle size distribution. The results of simulation were in close agreement with plant observations and the new circuits explored through simulation have helped in identifying potential opportunities for process optimization and control

Sep 1, 2012

By Bronwynne K. Williams

"In deriving flotation kinetic models, the froth phase was, until recently, either ignored or treated entirely empirically. The behaviour of the froth is now known to be usually important and sometimes dominant in determining flotation performance. Hence numerous methods have been developed for sampling the flotation froths and models incorporating the effects of the froth behaviour have been derived.Such models will assist in determining more accurate estimations of the kinetic parameters utilised in the designing of industrial scale plants thus reducing the incurred costs of over designing. In particular, improved models for batch tests may lead to more effective use of batch testwork for prediction of continuous plant behaviour. A more detailed model is thus proposed which allows for a more realistic approach to the flow distribution in the froth phase.PROPOSED MODELThe batch flotation process is split into two stages in time, namely before the froth begins to overflow and after. The assumptions made, and hence the calculations, are different for each stage.The air enters the slurry at t=0 and generates froth. The superficial velocity of the air through the cell is given by go. It is assumed that the rate of froth breakage (gb) is constant during the first stage. The froth rises with a uniform net velocity throughout the cell and no mixing is assumed to occur.After the froth begins to overflow, the velocity distribution of the gas is modeled by segmenting the froth phase as shown in Figure 1. A model for bubble breakage rate or measurements of froth velocity allows one to obtain the volumetric rate of concentrate froth production. The entrained water and associated particles and a drop-back mechanism are also allowed for in the model."

Jan 1, 2003

By Dingwu Feng, Jannie S. J. van Deventer

"The effect of ultrasonication on reactions at solid/liquid interfaces was investigated by using an ultrasonic probe in two slurry systems, i.e. cyanidation of a refractory sulphide ore and geopolymerisation of metakaolinite. The surfactant dithiophosphate was used to render the gold bearing sulphide particles hydrophobic, in an attempt to induce the formation of cavitation bubbles directly at the desired surfaces. Oxygen was injected into the cyanidation system to improve the attachment of oxygen bubbles to the hydrophobic sulphide surfaces. Geopolymerisation occurs in highly alkaline solution with waste aluminosilicate oxides and silicates as the reactants. The process of geopolymerisation is believed to involve dissolution of Al-Si oxides from solid particles, diffusion of dissolved Al-Si complex from the solid surface into the gel phase, condensation of gel phase and hardening of the gel phase. It has never been investigated how ultrasonication affects the above steps in synthesising geopolymers, despite a number of papers dealing with sonochemical synthesis of materials. The introduction of power ultrasound into such slurry systems is expected to result in advanced geopolymer materials.In the cyanidation of the pyrite concentrate, the kinetics of gold extraction were significantly enhanced in the presence of ultrasound, due to the prevention of passivation and the enhanced dissolution of sulphides. Cyanide consumption was significantly reduced with ultrasonication, owing to the oxidation of soluble sulphides to sulphate, minimising the cyanide consumption by sulphides. With oxygen injection, ultrasound significantly enhanced the leaching of gold from the pyrite concentrate, as oxygen could enhance the formation of the oxidation radicals by ultrasonic cavitation. In the presence of dithiophosphate, ultrasound further improved gold leaching in the oxygen-aerated system. Dithiophosphate could selectively adsorb at gold host sulphide surfaces, and make the surfaces hydrophobic. As a result, the ultrasonication effectiveness could be enhanced through forming cavitation bubbles directly at the interfaces."

Jan 1, 2003

By Vladimir S. Zharov, Vyacheslav A. Tsukerman

"Conceptual imitative dynamic model of developing enterprises for medium and long-term period permitting to ensure coordination of interests of the enterprise and territorial environmental authorities has been developed to enable the process of the prognostication and management of a concentrating mill development, in which a symbol language and terminology familiar to the manager of the company are applied. An algorithm of practical application of this model of company development was elaborated as well as a general methodological approach to the prognostication of the development and procedures of its implementation. The general methodological approach to the implementation of the model has been defined. Within the framework of system approach, a concentrating mill is considered as a subsystem of an ore mining and processing company or a mining and smelting one. A concentrating technology is considered in dynamics, its change is determined by the task of making the company operation profitable. Technological indicators are secondary relative to financial and economical indexes. At the same time, technological and economical indexes are determined in their interrelation with ecological parameters. The elaborated model allows us to estimate all necessary economic, financial and technological indexes in their interrelation both for the company as a whole and as separately redistributed estimating the basic prognostication documents - accounting balance-sheet, profit and loss report, as well as the funds flow statement. When varying the managing parameters, all necessary result-producing financial and economical indexes are estimated and a need in and a possibility of an external funding by various sources are considered.The implementation of the model enables one to determine the required scale of production capacity, as well as the amount of raw-material resources needed. In case of shortages of the latter, there should be considered various scenarios of the production capacity enhancement or the possibility of commissioning of new sites or deposits and introduction of improved technologies."

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 Stefan Mutz, Thomas Pretz, Jörg Julius, Frank Hilbk-Kortenbruck, Aachen, Hartmut Harbeck

"The annual global production of primary aluminium was about 22 million tons in the year 2000. This represents the second largest production rate in the world market after steel. Experts are predicting that the global demand for aluminium will rise in the near future.In contrast to other metals such as copper, the recycling of aluminium is considered relatively difficult. There are two main alloying groups, namely cast and wrought. In the case of aluminium it is important that the constituents within the scrap aluminium to be smelted are clearly identified. Within the secondary remelting process alloying does take place, but a removal of unwanted metal constituents is problematic. Therefore mixed aluminium scrap (not genuine in-house collected material) can only be used to produce cast aluminium. Thus, in other words a down-cycling of wrought (extrusions and rolled) products occurs. However, in spite of these difficulties there is an increasing trend to produce aluminium from secondary scrap (approx. 35% in Germany). Similar trends have been identified in the USA and other industrialised countries. This development is mainly caused by the high energy consumption for the production of aluminium from bauxite. Producing aluminium from scrap is saving about 95 % of the energy in comparison to the processing of primary raw materials.An improvement in sorting technology is necessary to separate wrought and cast alloys of aluminium as the absolute amount of recovery from old scrap is higher than the demand for cast.This contribution presents some alternative methods, utilizing automatic picking technologies, which will be used to separate secondary aluminium in the future. During the recent years, some major progresses have been made in automatic picking technologies for different applications in the processing of primary and secondary materials.For the sorting of aluminium scrap a special additional sensor will be necessary. The best detection will ultimately be based on online elemental analysis of single particles. First investigations in the field of laser based systems for these applications have already been performed several years ago. One of the laser based techniques is the laserinduced breakdown spectrometry (LIBS)."

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 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

By Victor V. Karmazin

"The appearance of the precise equipment for analysis of results of the laboratory tests with using of the computer processing allows raising accuracy of the estimation of the expected indexes of the mineral processing. Certainly, laboratory tests will not be able to substitute completely industrial ones, but allow reducing the amounts of the industrial tests, that vastly reduces the cost of technological forecast and preparation of data for projection.Calculation of the potential indexes of mineral technology (mass yields and the metal content in products) is fulfilled on the base of results of measurements of the mineralogical liberation parameters using special formulas.The quality of the concentrate ßc = a + ?l • ?s • ?i (ßt - a) can be achieved on a level of the theoretical metal content of a mineral - ßt only if coefficients of mineral processing, of liberation ?l and selectivity ?s of grinding, effectiveness of separation, will reach 1 (a - metal content of the row ore).Increase ?l by overgrinding automatically decrease ?s, and only by destroying of particles of ore along surfaces of accreting of minerals (?i = 1) and when values of all three coefficients will aim to 1, then ßc ? ßt.The degree of liberation of the useful mineral is the ratio of mass of free grains of the useful mineral in the product to general mass of the same mineral in this product. The factor of the liberation, which is defined by curves of dressability by angle of slop of the curve of the elementary faction - ?, is Kr=1 – tga. Kr changes from 0 to 1 when a changes from 45o to 0o. The liberation is reached by grinding of the material, although degree of the liberation, as a rule, is lower than the degree of the grinding."

Jan 1, 2003

By Tim Suljada, Mary Stewart, Jim G. Petrie, Damien Giurco

"The minerals industry is being challenged to reduce the amount of virgin ore that is mined, and to replace this material through the recycling of used commodity items and scrap, or by the reprocessing of waste materials. It is argued here that the existing technology base of minerals processing and refining offers real potential for handling these secondary resources. The challenge is to develop tools by which the most preferable recycling routes (both economically and environmentally) can be identified from a list of feasible alternatives, taking into account any operational constraints of these technologies.This paper describes an heuristic approach to developing the family of all technically feasible flowsheets to address this challenge, from which a preferred option may be selected according to a set of decision criteria (economic and environmental). Our approach uses conventional flowsheeting techniques of selecting flow variables and splitter functions, supported by design performance information for each unit operation. This set of design decision variables is augmented by knowledge of the suitability of a particular waste or scrap stream for a given unit operation within a flowsheet. We achieve this by comparing the composition of the scrap stream with the range of mineral streams for which the unit operation was designed initially. This is inspired by the “overlap” approach proposed by Legarth, where an “overlap” of 1 would suggest that there is high degree of compatibility between a given secondary resource stream and a primary mineral stream as inputs to a specific technology. The “overlap” concept has been extended to include information about the physical characteristics of secondary resource streams, as well as information relating to synergistic / antagonistic influences of minor elements present in the waste stream. A flowsheet which delivers a product of acceptable quality from a given secondary resource material is built up from a progression of unit technologies. The exercise is repeated to generate the family of all feasible flowsheets from combinations of acceptable unit technologies."

Jan 1, 2003

By Ashton M. Swartbooi, Robert van Hille, Alison E. Lewis

"Nickel production by precipitation using hydrogen reduction generates an ammonium sulphate solution containing approximately 2g/L of nickel, and 1g/L of cobalt as an impurity of the process. Sulphide precipitation is an effective method for heavy metal removal, especially when compared to hydroxide processes: metals can be removed from solution at relatively low pH levels, small quantities of sludge are formed, and due to the high reactivity of sulphides the reactor retention time is reduced. However, the low solubility of sulphide species can lead to spontaneous nucleation of fines (due to higher supersaturation levels which are difficult to separate from solution, leading to reduced process efficiency. Using a fluidised bed reactor, fines formation can be minimised as the pellets provide a large surface area and promote heterogeneous nucleation.A synthetic nickel-cobalt ammonium sulphate solution was reacted with two forms of sulphide reagent: (a) a liquid sulphide solution and (b) gaseous hydrogen sulphide. A range of factors (including pH, reagent concentrations, metal to sulphide molar ratio, flow rates and recirculation rates) influencing the efficiency of the precipitation reaction have been studied. The efficiency of the precipitation reaction was measured using both metal recovery and fines formation as indicators.Figure 1 shows the effect of decreasing the metal:sulphide ratio (at constant SS = 2.725e+17), on the metal removal for liquid sulphide. By decreasing the metal:sulphide ratio, up to 99% removal of both nickel and cobalt could be achieved.These results also indicate that the precipitates that formed were polysulphides, since no sulphide was present in solution after the experiment. This would also indicate that a lower metal:sulphide ratio would be more favourable. However, decreasing this ratio (at constant metal concentrations) would lead to an increase in the fines concentration, because of increased supersaturation levels induced by the higher sulphide concentrations. To decrease the supersaturation, dilute solutions of either reagent would be employed."

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 Georgios N. Anastassakis

"The depletion of the high-grade chromite ores and the inefficiency of the gravimetric methods to process fine particles has shifted the industrial and research interest from gravimetric separation methods to flotation. However, the response of the minerals to various flotation schemes is not clearly established. In this work, the physicochemical behavior of chromite and olivine is studied using a fatty acid collector.The minerals used were from Vourino area (Kozani, Northern Greece). Macroscopically pure samples of chromite and olivine were selected by hand picking, crushed and subsequently ground to the required size. Each sample was then submitted to panning and magnetic separation for the removal of impurities. The mineralogical and chemical analysis of the purified samples revealed the following: a) The purity of chromite was 95% while the minor constituent was mainly magnetite. Its chemical analysis was: 12.50% Fetot, 2.50% SiO2, 54,54% Cr2O3, 9.31% Al2O3, 0.47% CaO, 13.10% MgO. These analyses show that Cr3+ has been substituted by Fe3+ and Al3+ as well as Fe2+ has been significantly substituted by Mg2+. b) Forsterite is the main constituent of olivine either as pure forsterite (Mg2SiO4), which is the prevailing form, or as iron-forsterite [(Mg,Fe)2SiO4] in less amount. Chrysotile, which belongs to the serpentine group, was also detected at a percentage of 10-15%. The chemical analysis of olivine was: 36.90% SiO2, 0,53% Cr2O3, 7,43% Fe2O3, 0.72% Al2O3, 0.91% CaO, 47.00% MgO, 6.02% LOI.The electrokinetic behavior of the minerals was studied in a electrophoretic mass transport equipment Model 1202 of Micromeritics. The reagents used were sodium hexa-metaphosphate of commercial grade and sodium oleate."

Jan 1, 2003

By Fernando Concha

"Thickening development and innovation in the 20th Century occurred in two decades periods. From 1900 to 1920, Dorr invented the continuous thickener and the first method of thickener design was proposed by Coe & Clevenger. From 1920 to 1940, the operating variables of continuous thickening were discovered by Comings at the University of Illinois. From 1940 to 1960, the first theory of sedimentation was proposed by Kynch and several authors, Talmage and Fitch, Ysioka and Hasset used this theory to develop new thickener design methods. From 1960 to 1980 Shannon and Tory demonstrated that this theory applied exactly for the sedimentation for small rigid spheres in water and Scott showed that it is not valid for flocculated suspensions. From 1970 to 1990 the phenomenological theory of thickening was developed based on the theory of mixtures. Papers by Kos, Bascur, Thacker and Lavelle, Concha and Bascur, Concha and Barrientos, Auzeris, Buscal and White, Landman, White and Buscal show the application of this theory to thickening and Adorjan presented the first thickener design method based on this theory. In 1980s the mathematical analysis and solutions of Kynch’s model for batch and continuous thickeners was obtained by Bustos. The new Century brought solution to the phenomenological thickening model which was applied to thickener design, simulation and control. The method of thickener parameter determination was improved by designing new laboratory and on-line instruments and advanced control strategies was designed and validated in plants. Structural thickener design produced improved feedwells and feed dilution mechanism, stronger raking mechanism and different thickener shapes according to new ambient requirements, such as high rate thickener and paste thickeners that increase the water recovery. New challenges include better flocculation and advanced control strategies."

Jan 1, 2014

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 S. K. Kawatra, T. C. Eisele

"Coal-fired electrical power generation plants produce 56% of all the electricity in the U. S., burning approximately 860 million tons of coal annually. This results in production of 58 million tons of fly ash; 19 million tons of bottom ash and boiler slag, and 23 million tons of desulfurization sludges. These are a considerable disposal problem, and it would therefore be very valuable to be able to sell these residues and byproducts as useful materials, rather than paying to dispose of them in landfills. However, utilization rates are currently very low, below 32% even for the most thoroughly commercialized combustion byproduct (fly-ash). This poor utilization rate is a result of the high impurity content of combustion byproducts, which make them unsuitable for existing markets. The experiments described in this paper were therefore carried out to study the application of mineral processing techniques to upgrading combustion byproducts.Experiments were conducted to upgrade and purify low-grade combustion products to produce highgrade, readily saleable materials. A process was developed for removing unburned carbon from coal fly-ash by froth flotation, using reagents originally developed for flotation of oxidized coals. This technique could reduce the carbon content of fly-ashes containing up to 11.1% carbon to less than 2%. The froth product was sufficiently carbon-rich that the recovered carbon has value as fuel, or as low-grade activated charcoal.Fly ash was also examined as a binder for producing iron ore pellets, primarily as a substitute for bentonite. It was found that Class F fly ash in combination with an activator (calcium hydroxide) was an effective pellet binder at dosages comparable to the currently-used dosages of bentonite clay. While the flyash worked very well alone, tests in combination with bentonite showed that fly-ash/bentonite mixtures had significantly worse binding performance than either pure bentonite or pure fly-ash-based binder. This was determined to be due to the fact that bentonite and fly ash have profoundly different binding mechanisms, with fly-ash undergoing a pozzolanic chemical reaction while bentonite binds through a physical attachment process."

Jan 1, 2003

By Xiong Dahe

"SLon vertical ring and pulsating high gradient magnetic separator utilizes the combined force field of magnetism, pulsating fluid and gravity to beneficiate weakly magnetic minerals with the advantages of large beneficial ratio, high recovery, matrix not easy to be blocked and excellent performance.We have developed SLon-750; SLon-1000; SLon-1250; SLon-1500; SLon-1750 and SLon-2000 VP HGMS. Now more than 200 of them have been successfully applied in China.Application in Qi Dashan Mineral processing Plant of Anshan Iron and Steel Company: The iron ore consists of magnetite and hematite. In 2001, six SLon-1750 magnetic separators are applied to control the tails grade of fine hematite. The results of flowsheet is: feed grade 30.15%Fe, concentrate grade 67.00%Fe, iron recovery 75.86%. The results set up the historic high record of this plant and the processing coast is greatly reduced.Application in Gushan Iron Mine of Ma Anshan Iron and steel Company: There are 6 SLon-1750 and 4 SLon-1500 magnetic separators applied in this mine to treat refractory hematite ore. The feeding grade is about 45%Fe. The final iron concentrate grade is about 60%Fe and the iron recovery is about 76%. The results are much better than the previous gravity flowsheet.Application in Meishan Iron Mine of Shanghai Baoshan Iron and Steel Company: The mined ore consists of magnetite, hematite and siderite. Because of a relatively high content of phosphorus, the iron concentrate could not meet the market requirements. Now 18 SLon-1500 magnetic separators are applied to reduce phosphorus, which is reduced from about 0.4%P to 0.246%P. The quality of iron concentrate is greatly upgraded.Application in Panzhihua Ilmenite Processing Plant: In the past, the -0.045mm ilmenite fraction was discarded in to the tails because of lack of high efficient equipment. In 2001, the plant built up a magneticflotation flowsheet to recover the fine ilmenite from the -0.045mm fraction with 6 SLon-1500 magnetic separators. The total results are: feed grade 11%TiO2, concentrate grade=47% TiO2, recovery 44%. Each year the flowsheet recovers 60,000t fine ilmenite concentrate."

Jan 1, 2003

By Buks Kruger

"After the milling and flotation of the platinum bearing ore, the flotation concentrate is electrically smelted in 6-in-line electric arc furnaces and the resulting furnace matte treated in Peirce Smith converters to remove the iron sulphide. The iron free (less than 1% Fe) converter matte is then granulated and sent to the Base Metals- and Precious Metals Refineries for further processing.During the smelting and converting processes two distinct gas streams are produced.The Peirce Smith converter off gas contains 4% - 9% SO2 which is treated in a conventional Sulphuric Acid Plant to produce sulphuric acid (H2SO4).The electric furnace off gas contains 0.9% SO2 and was (until September 2002) vented through a 91 meter high stack to atmosphere.Off gasses which contain less than 3% SO2 is difficult to handle and quite a few processes had been developed over the years to cope with this gas. A broad spectrum of process suppliers and technology approaches is available and the different technologies can be divided into a few main approaches i.e.Scrubbing of the off gas with an alkaline solution to produce an environmentally friendly and stable waste product which can be discharged onto a tailings dam or permanent landfill site.Physical absorption of the SO2 into a chemical solution to produce high quality chemically pure process chemicals.Catalytic reaction of SO2 with O2 to produce SO3 which is absorbed in water to produce sulphuric acid of less than 90% strength.In October 2002 Impala Platinum commissioned a Sulfacid Plant at its Smelter in Rustenburg which recovers the SO2 from the electric furnace off gasses into a weak sulphuric acid solution.The Sulfacid Plant technology is widely used in the paint pigment industry. This is, however, the first application of the technology on electric furnace off gas.The furnace off gasses contains flue dust which is removed in electrostatic precipitators. The gas exiting the precipitators normally still contains between 40 mg/Nm3 and 60 mg/Nm3 dust and passes through a quench-scrubber before entering the reactors. The quench-scrubber cools the electric furnace offgas down from ± 200 °C to 60 °C and act as a final dust removal stage."

Jan 1, 2003

By Aubrey Mainza, Malcolm S. Powell

"A hydrocyclone with two vortex finders, named the three-product cyclone (3PC), has been successfully tested in the Platinum industry for dealing with the dense Chromite found in UG2 ores. This dense component preferentially reports to the cyclone underflow, resulting in an over-ground fine Chromite component in the final product. The dense media effect caused by a high concentration of this in the cyclone feed produces a coarsening of the cyclone overflow, which results in loss of recovery through over-size silica in the PGM carrying component material in the float feed. The fine barren particles of Chromite that report to the overflow are recovered through entrainment in the flotation process, resulting in detrimental contamination of the slag produced from the concentrate.Data from many industrial scale tests of the 3PC have shown that three distinct products are obtained when the inner vortex finder length (LIVF) is extended to the region either above (normal classification) or below (reverse classification) the transition zone (a region were the inner and outer overflow streams are identical). Due to wear problems arising from extending the IVF deep into the cone of the cyclone, it is advantageous to use the shorter IVF. Only the normal classification results are reported here, but similar outcomes (to opposite overflow streams) were obtained for the reverse classification. The results showed notable differences in the percentage split of the plus 100µm material in the product streams, confirming that three distinct products are discharged from the 3PC. About 12% of the plus 100µm material in the feed reports to the middlings stream, 1% reports to the final product, and the remainder to the cyclone underflow.Results of silica and chrome splits to the three distinct products namely, the inner overflow (INO), the outer overflow (OUO) and the underflow (U/F) are given in Table 1. These show that the 3PC can be used to recover coarse silica through screening the middlings product - which has a high silica content. When the vortex finder ratios (ratio’s of cross-sectional areas) are carefully selected, the split of plus 100µm silica to the middlings product ranged from 2.9 to 9.6%. Large amounts of oversize silica and chrome report to cyclone underflow, explaining their high percentages in the underflow stream."

Jan 1, 2003