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By K. W. Stöckelhuber, A. Wenger, H. J. Schulze

"An important elementary step of the flotation process is the forming, drainage and rupture of a thin intervening liquid film between bubble and mineral particle.After the encounter of the bubble with the solid surface a wetting film is formed. The initial thinning of this film is driven by the capillary pressure inside the bubble. When the film has reached a certain thickness rupture can take place. There are two possible mechanisms describing this process:(a) Gas nucleation, caused by nano bubbles inside the film.(b) Growing fluctuation waves (spinodal dewetting) on fluid interfaces under the influence of any kind of attractive forces (electrostatic, van der Waals).Metastable wetting films on negatively charged, hydrophobic glass surfaces (gaseous phase methylated), or on hydrophilic, positively charged glass surfaces (with Al3+ ions), have been analysed by means of the kinetics of film thinning according to the Reynolds law. These experiments demonstrate that both mechanisms can be responsible for the rupture of a thin wetting film."

Jan 1, 2003

By Paul W. Cleary

"Particle scale simulation of industrial particle flows using DEM (Discrete Element Method) offers the opportunity for better understanding the flow dynamics leading to improvements in equipment design and operation that can potentially lead to large increases in efficiency, throughput or product quality. DEM has been used for modelling many industrial applications, particularly milling. This includes ball and rock motions and power consumption in ball mills, AG and SAG mills, vibrational segregation, flows in rotating drums, operation of dragline excavators and hopper flows. In mineral processing, DEM has been concentrated on mills because of their critical importance. However DEM also offers the opportunity to improve many other parts of mineral processing operations. These areas often do not receive the attention that the key comminution equipment commands, but can become critical when they fail or under-perform. Importantly their assessment/improvement using DEM is often much more feasible because of smaller problem sizes and the absence of poorly understood physics such as breakage. In this paper we describe DEM simulations of four important pieces of non-comminution equipment that are commonly found in or near mineral processing plants (these are shown in Figure 1):"

Jan 1, 2003

By A. Collings, A. Farmer

"Power ultrasound may be used in the processing of mineral suspensions to clean the particle surfaces of oxidation products and fine coatings, mainly through the large, but very localised forces, produced by cavitation, which is the formation and sudden collapse of bubbles in a fluid. Cavitation occurs preferentially at solid surfaces in a liquid: at container walls, inserted objects or suspended particles. When the cavitational bubbles collapse near a solid they do so by forming a very high energy jet directed from the point on the bubble furthest from, and directed towards, the surface of the solid, in effect micro jet blasting.This paper highlights some of the major mineral processes where ultrasonics is beneficial namely: Surface cleaning of detrital mineral particles, where container quality glass sand was upgraded to tableware quality and up to 20% improvements in the sharpness of high tension separation of mineral sands was achieved"

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 K. Malysa

Bubble collisions with ore grains and a selective formation of the bubble-grain aggregates are necessary steps for flotation separation of useful and gangue components of an ore. For the attachment of valuable mineral grain to the colliding bubble a liquid film, separating the bubble and the grain needs to rupture during short time of their collision. High hydrophobicity of the grain surface is favorable because stability of the separating (wetting) film is much lower at such surfaces, that is, the film ruptures faster and at greater thickness. Simultaneously, it needs to be kept in mind and taken into consideration that high affinity to air is a typical feature of hydrophobic surfaces. Thus, when the hydrophobic surface is immersed into aqueous phase the air can stay attached to such surfaces and affect kinetics of the bubble attachment. The paper presents results and analysis of dynamic phenomena occurring upon the collision of the rising bubble followed by its attachment to hydrophobic (Teflon) plates of different roughness. The influence of the Teflon surface roughness, solution concentration, bubble size and impact velocity on bouncing of the colliding bubble, time of the three phase contact (TPC) formation and drainage time of the liquid film, formed between the solid and bubble surfaces, is described. High hydrophobicity, as showed earlier (Malysa et al, 2005), does not assure that each collision leads to the TPC formation and attachment of the colliding bubble. Roughness is the parameter of crucial importance for kinetics of the bubble attachment to hydrophobic surfaces (Krasowska and Malysa, 2007; Krasowska et al, 2009; Kosior et al, 2011). Enlarged roughness of the Teflon plate, from ca. 1 to 80µm, results in shortening the time of the TPC formation (bubble attachment) by over an order of magnitude - from 105 to a few milliseconds only. Higher surface roughness means that larger amount of air can be entrapped in bigger scratches and cavities of the Teflon plate during its immersion into aqueous phase. Results documenting importance of the air presence are showed and mechanism of the air facilitated TPC formation and bubble attachment to hydrophobic surfaces is described. Keywords: bubble collisions, hydrophobic surfaces, teflon plate roughness, TPC formation

Sep 1, 2012

By Thomas Pretz, Alexandra Pehlken

Sampling of municipal solid waste is known to be difficult to sample if it has to be representative. When dealing with municipal solid waste, the usual method is to study separately waste material below 40 mm and particles bigger than 40 mm. The material < 40 mm cannot be sorted manual and is termed the “fine fraction”. The particles > 40 mm can be separated manually and are usually sorted into pre-defined groups of materials. These groups can be defined depending on the demand of quality assurance. But standardisation of procedures is not far progressed, even for the widely practised sorting methods.

Jan 1, 2003

By Hermann Wotruba, Günther Petzold, Fabian Riedel

"Increased mechanisation in underground stoping operations results in higher waste percentages in the run of mine. A new method of reducing waste is optical sorting. Optical sorters have low maintenance costs and can be installed underground. Rejected waste can be backfilled directly without having to be hoisted, therefore increasing the shaft capacity for a more valuable product.Pre-Concentration by Optical SortingA series of tests with an optical sorter at the laboratories of the Mineral Processing Department of the RWTH Aachen have shown that it is technically possible to sort almost any kind of ROM which has even slight differences in colour (Platinum Reef, Gold Reef, Kimberlites, Industrial Minerals, Aggregates, Coal, etc.).By employing optical sorters prior to conventional sorting plants, it is possible to reduce the amount of waste to be processed. Figure one shows test results of ore which is quite similar in colour to the waste (grey). With increasing waste in the feed, the recovery decreases according to the graph. In figure two, the colour ratio parameter of the sorter was changed with a similar waste percentage in the feed. With increasing loss of ore, a cleaner product can be achieved. Before designing a sorting plant, throughput tests are carried out. Throughputs vary depending on the size range. Sorters have a limit of about 250mm top size. In this upper size range, throughputs of 150t/h can be achieved."

Jan 1, 2003

By Christopher Davey, Professor Emeritus, Marian Mazurkiewicz, Peter Kanjorski

The concept of a high pressure liquid jet mill with highly unsteady flow, has been developed and recently patented by Cornerstone Technologies LLC (CsT), for the purpose of micron and sub-micron particle production. The mill accepts feed sizes up to 15mm for some materials and is capable of sub-micron production. Successful material range from precious metals such as silver and palladium to dielectric components and substrates such as Barium Titanate slips, zirconia, titania and silica. The process has also succeeded in adequately reducing the size of materials for both composite and coating uses such as anthracite coal, graphite, chrome metal, wollastonite and more than 100 others. A unique design approach has been taken to highly maximize the energy flux in the mill’s chambers to create extremely high turbulence and destructive cavitation. This is assisted by shock waves, which cause particles to undergo ultra high frequency pressure pulsations, high frequency collisions and then abrasion, shattering, hydro-wedging, and cleaving. Due to these extreme properties the processing occurs in just fractions of a second allowing throughputs up to 1000 kg/h on a machine that would fit inside a 60 cm box. The technical solution and technological advance, as well as the environmental and economic benefits indicate rapid and wide spread acceptance of high-pressure liquid jet milling in modern industry.

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 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 Douglas W. Fuerstenau

Some historical sketches of the early development of froth flotation are presented. Flotation technology involves several aspects: chemical control of mineral hydrophobicity, selectivity in flotation, flotation kinetics, flotation machines, and process optimization and control. However, only some aspects of the regulation of mineral flotability by the addition of chemical collectors in some selected cases are discussed. The early contributions to flotation science by Langmuir, Gaudin, Wark, and Taggart are briefly outlined. With a firmer understanding of surface chemistry, electrochemistry, and the electrical double layer, progress has been made in understanding the fundamentals of flotation chemistry, although sound theoretical underpinnings still are needed in these very complex systems. Flotation chemistry is related very directly to the type of mineral being floated since the systems depend strongly on the chemical and physical characteristics of the minerals. Full discussion of chemical reagent phenomena would be in terms of the behavior of naturally flotable minerals, sulfides, oxides, silicates and alumino-silicates, and salt-type minerals. At this time, citing a few cases involving salt-type minerals and oxides, the dependence of their flotation surface chemistry will be discussed in terms of the role of adsorption, surface reaction, and the hydrophobic effect.

Sep 1, 2012

By V. Avzian Belozersky reg 453524, Vasily V. Lodeischikov, Adolf F. Panchenko, Til E. Vidusov, Olga D. Khmelnitskaya, Vladimir E. Dementyev

"Presently, there is a number of gold deposits which cannot be developed using the conventional technologies with acceptable economic indices due to low gold content, high depth of ore occurence and other conditions. For such ores, an innovation technology of underground gold leaching in the place of their occurrence is of special interest. The technology excludes ore mining and hoisting to the surface. This enables the production cost of 1 g of gold to be considerably reduced in comparison with conventional methods of gold recovery.The Maminskoye deposit oxidized ores were chosen as the subject of underground leaching because they are ideally suited for this purpose due to their composition and hydrological parameters. The ore reserves within the underground leaching block are 90, 000 t with 0.7 g/t average gold grade.An experimental system for underground leaching with a throughput of 15 cubic m solutions per hour was developed. A combined filtration-and-infiltration system of the ore massif development by holedrillingwhere pregnant solutions are air-lifted was worked out.The underground leaching flowsheet includes Au dissolution by chlorine-containing solutions, Au adsorption from solution onto active carbon, carbon concentrate ashing and calcine melting to produce Dore metal."

Jan 1, 2003

By N. Panteleeva, E. Konoplev, I. Michailova, S. Titkov, T. Gurkova, T. Chumakova, Sylvinit Co.

"INTRODUCTIONFlotation of mineral particles by cationic surfactants – namely alkyl amines and their derivatives – is finding ever growing application in processing of various ores and in quality refinement of the benefication end products, iron concentrates for example. In the recent years application of cationic collectors - alkylmorpholines - enabled the development of new highly efficient procedure of water-soluble mineral processing, being also the one with low energy consumption. This procedure is a reverse flotation of carnallite from bay salts of salt-pans and from carnallite ores.The efficiency of cationic SAS influence depends upon colloid-chemical state of the collector in flotation liquid phase, especially if the latter comprises mineral salts. Availability of clayey impurities or slime particles of iron oxide in cation flotation feed, which actively sorb the cationic collector, deteriorate considerably the cation flotation performances. In Halurgy Institute the investigations of cation flotation under potash and carnallite ore processing have been carried out, and new reagent modes, enhancing cationic surfactants sorption at mineral particles, have been developed. Application of new reagents enables one to decrease considerably the consumption of expensive cationic collectors and to enhance the floatability of coarse mineral particles."

Jan 1, 2003

By Rod Hocking, Nenad Djordjevic, Randolph A. Pax

"Semi Autogenous (SAG) mills exhibit complex interactions between the competing processes occurring inside them. Traditional practice is to measure the operation of the SAG mill at an operating point in terms of its load, power draw, steel load, ore throughput rate, water addition rate and more recently the feed size distribution. However significant departures from standard operating conditions can occur due to changes, for example, in ore hardness, the quest for higher throughputs and mill internal geometry.Fundamental to SAG mill operation are the internal processes that ensure that a given ore throughput and discharge grind size are obtained and maintained. These processes can be measured using non-contact acoustic emissions from the SAG mills which utilise the information rich noise that is generated by the grinding, flow and charge movement inside a mill. Non-contact acoustic in-mill measurements can be used for the validation of discrete element modelling (DEM). The approach being reported in this paper is to model the individual physical processes and then to simulate the assemblage of a physical mill.By modelling the assemblage of steel balls in a 1 m pilot mill and duplicating the experimental arrangement exactly with the PFC3D model, it was possible to replicate the pattern of falling balls in the experimental mill. Furthermore, the key features of the acoustic emission spectrum that was calculated compared favourably to the measured spectrum at low frequencies. The experimental spectrum is shown in Figure 1."

Jan 1, 2003

By Renato S. Costa, Afonso H. Martins, Flávia D. Mendes

"This paper presents some important aspects regarding the ion exchange treatment of an Ni and Co sulphate acidic liquor using chelating resins. Chelating resins possessing iminodiacetic or bis-picolylamine functional groups were compared in terms of nickel and cobalt recovery. The experimental resin with bispicolylamine functionalities (Dowex M4195) was evaluated with respect to Ni and Co uptake, and compared with Rohm &Haas commercial chelating iminodiacetate acid resin.The use of selective ion exchange to recover metals from sulphuric acid liquors has been studied for a long time. Companhia Vale do Rio Doce (CVRD) has been actively involved in hydrometallurgical applications of IX and has researched in selecting the optimum resin for nickel and cobalt selective removal and the design of a suitable IX circuit. When an IX operation is contemplated for a specific application, it is followed a screening process which generally involves consideration of the solution composition and pH, speciation of the metals in the liquor to be treated and other possible techniques that can be applied to achieve the desired specifications or recoveries. Once a decision has been made to use IX for a specific application, relevant testwork should be done to select the most cost-effective resin and design the IX circuit to achieve the desired criteria. The experimental part dealt with the working conditions, resin characteristics and the influence upon the resin maximum exchange capacity of the following factors: nickel concentration, temperature, pH and resin-to-solution ratio. Based on the experimental data obtained, it has been proposed a innovative technological treatment"

Jan 1, 2003

By Slobodan B. Vujic

"For the requirements of the mining company “Rudnik-Rudnik”, engaged in undergr-ound exploitation of polymetallic ore and lead, zinc and copper concentrates production, the Department of Computer Application of the Faculty of Mining and Geology, University of Belgrade, designed a computer supported and integrated information-management system. This paper presents a concept of this system covering both monitoring and management of production in ""Rudnik-Rudnik"".The ""Rudnik"" Rudnik, Yugoslavia is a mining company, engaged in underground exploitation of polymetallic ore and production of ore, zinc and copper concentrate as well as other metals such as silver, bismuth and cadmium. This mining company runs stable business activities and undergoes a permanent growth of valuable production volume.The basic characteristics of production-technical system of ""Rudnik"" company are: uniform and up-todate technical-technological solutions: linking of production chain from underground exploitation of ore to flotation, namely final product - concentrate of lead, zinc and copper; complete mechanization of production; relatively low level of computer technics implementation; namely, ununiformed implementation of different application of computer-supported information technologies in production and business activities of the Company.These are the assumptions on the basis of which the management of the Company made a decision, in 1999, to upgrade information-management functions through development and application of modern integrated and computer-supported production-business information-management system (hereinafter: IMS, namely IMS Rudnik). For this purpose the Company requested the Department of Computer Application, Faculty of Mining and Geology, University of Belgrade to make the Project on IMS for their needs."

Jan 1, 2003

By S. M. Marr

"Water availability and water-related environmental impacts are now one of the most significant challenges facing primary production within the global minerals industry. Whereas the industry has, to a large degree, been able to demonstrate a collective response to greenhouse gas emissions and global energy demand, no such strategy exists for water. In part, this is because water quality and availability are regional issues, but also too because water quality cannot be defined by a single attribute, and extrapolation of any set of water quality indices to their associated environmental impact is no trivial matter. In design situations specifically, the situation is exacerbated by the fact that process engineers typically focus on site water management, and consent authorities are primarily in catchment level issues. As a result, an integrated approach to water management is difficult. This does not stem from an unwillingness by members of the professional team to engage with the total picture of water quality and availability, but principally from the fact that there is no common language through which to approach the problem.It is imperative for process engineers to extend their design system boundary, to reflect the geographic scales over which water impacts need to be quantified. It is not suggested that chemical engineers and metallurgists should become experts in geochemistry, hydrology and limnology. Rather, the challenge is to develop tools through which better communication of the relevant environmental impacts can be achieved.It has been estimated that 50% of the capital for new plants is devoted to handling wastes. The integration of mass exchange processes, adopting a life cycle analysis framework for considering environmental impacts and shifting the emphasis from effluent concentration to environmental impacts should be adopted in the framing of the design problem have been suggested as techniques of Environmentally Conscious Design. Shifting the focus from effluent concentrations and legislative requirements to evaluating the environmental impact is an important step towards improving the overall environmental performance of a process facility."

Jan 1, 2003

By Andrew D. McCallum, Russell A. Heins

"Until the advent of intensive cyanidation, gold gravity concentrates were generally treated by tabling. The table concentrates were smelted while table middlings and tailings were recycled to the milling circuit for further grinding and subsequent leaching in the CIP/CIL circuit. Gold recovery on production tables is relatively low, often only 30 percent, and rarely above 60 percent. Significant factors in tabling performance are; mineralogy and the operator’s experience and ability. Units have been developed by Gekko Systems to treat both batch and continuous gold concentrates. Unit sizes are determined by leach kinetics and the required residence time of the concentrate in the unit.Gekko commenced the commercialisation of intensive leaching of gravity gold concentrates in 1997 with the first commercial prototype of the InLine Leach Reactor (ILR). Over 20 units are now installed worldwide with half that number on the African continent. South African mines, South Deeps (Placer Dome WAJV) and Target (AvGold) have both installed InLine Leach Reactors. Ashanti Goldfields have placed the ILR on their standard equipment list and have six operating units with a seventh on order. AngloGold installed one of the first ILR production units at Morila in Mali.Gekko Systems successfully installed an ILR1000 Batch unit at the Antapite Mine in Peru in December 2002. The unit was installed to treat gravity concentrates and to replace a shaking table. Following installation, gravity gold recovery increased from 15% to 40% of total gold. The unit was operational from start up and the first gravity batch treated achieved 98% gold recovery. The gravity concentrates also have a high silver content and 95% recoveries on silver were also achieved.Preliminary testwork identified that the concentrates required additional oxygen to achieve peak performance. As a result of optimisation work in the laboratory, leach kinetics in the ILR have been excellent with only 6 hours residence required to achieve maximum gold extraction."

Jan 1, 2003

By O. A. Punishko, G. G. Mineev, Zabaikalsky Ore-Dressing Plant, M. V. Malova, O. V. Belousova, S. A. Bogidaev

"In order to intensify benefication processes (flotation and magnetic separation) for rebellious tantalitecolumbite ores electrochemical machining of pulp (ECM) is suggested instead of costly mechanic-chemical activation and magnetizing roasting. Any change in the surface mineral-semiconductor potential under the action of electrochemical treatment results in the change in the isoelectrical state of the surface and the adsorption property of the mineral with respect to ionogenic reagents-collectors. In this case conditions are created for regulating the ion composition, reduction-oxidation potential and pH of the liquid phase of the pulp without any extra introduction of expensive and often ecologically harmful chemical substances.Ores containing tantalum and niobium are characterized by complex chemical composition, determining their physical properties (conductivity, dielectric penetration, magnetization value, etc.) and their electric susceptibility.The authors investigations show that the pulp electrochemical treatment leads to the increasing magnetic susceptibility of the paramagnetic minerals. The main chemical elements forming the columbite-tantalite minerals except tantalum and niobium are iron and manganese. They determine the rare-metal minerals paramagnets properties. The electrochemical treatment changes the relation of the oxidized and reduced forms of these elements having. The method of cathode pulp treatment before flotation is successfully tested industrially.In the field of noble metals metallurgy new technological proposals are reduced to the following. As is know, the production of noble metals from unusual raw materials demands the elaboration of principally new technologies new technologies in so far as the methods for gold and silver extraction from ores are as a rule low elective and at the existing level of engineering are economically not expedient.The analysis of the main trends in the field of non-standard raw material treatment shows that the perspective ones are the geo- and biotechnological processes (underground leaching and leaching in heaps - UL and HL and microbiological methods of metal extraction)."

Jan 1, 2003

By Barda K. Mishra, Surya P. Mehrotra

"INTRODUCTIONIn a jig, which is primarily a coarse mineral concentration device, the bed of mineral particles is pulsated with a stream of water resulting in the particles of different specific gravities. It operates in a cyclic manner – the jig cycle consists of four stages, namely, inlet, expansion, exhaust and compression. In the inlet stage the bed lifts up en masse. Near the end of the lift stroke the particles at the bottom of the bed start falling resulting in the loosing of the bed which, in turn, causes its expansion or dilation. During the third and fourth stages the particle resettle through the fluid, and the bed collapses back to its original volume. The pulsation and suction are repeated to bring about stratification with respect to specific gravity across the bed height. Various parameters affecting the stratification process include amplitude and frequency of pulsation, bed thickness, rate of hutch water flow, and feed characteristics. This paper first presents a review of various jigging theories and then describes a new approach to mathematical modeling of jigging employing the discrete element method.JIG MODEL BASED ON DISCRETE ELEMENT METHOD (DEM) APPROACHThe jig models based on DEM essentially involve tracking the position of each particle incrementally, applying Newton’s law of motion and a force displacement law at the contact. The model presented here is based on a three dimensional mathematical description of solid-solid and fluid-solid interactions. In this model, the force balance on a particle is extended to account for the effect of continuously varying fluid on the particle. The total force on each particle is made up of a known external body force, fluid particle interaction force and particle-particle and/or particle-wall interaction force. The fluid-particle interactive force is primarily made of drag and buoyancy. Di Felice’s correlation is used to evaluate the drag force. Solid-solid interaction is described by treating particles as discrete elements that are indestructible but interact with each other and any other elements present, such as walls, when they make physical contacts. A pair of spring and dashpot represents a contact The contact forces are computed from the amount and the rate of overlap of the particles at the contact. The motion of the particle is due to movement of the fluid, which transmits its energy through the particle-particle contacts. A computer program incorporating both the contact and the fluid model has been developed. It takes the operating parameters such as amplitude and frequency of the pulsating fluid, pertinent data concerning particle properties and the geometry of the jig bed as inputs."

Jan 1, 2003