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By Vincent C. Smith, Agit Singh, Bernard Muller

The control of minerals processing plants is by no means trivial. In order to address some of the difficulties, it was decided to develop and test a model predictive controller (MPC) for a milling circuit. A milling simulator was written to test the MPC controller. Due to the large number of tuning parameters in a controller of this type, an optimising algorithm was written that automatically tunes the controller. Good, robust control was obtained when the controller was tuned using this algorithm. The controller was tested for various scenarios that are often encountered in the minerals processing industry. When problems were encountered, the MPC algorithm was specially adapted to accommodate for these difficulties. Control was further improved by using feedforward control as well as quadratic programming. The movement of the manipulated variables was reduced by using a region of uncertainty that allows the controlled variable to vary within a specified region around the setpoint. Integrators were handled by adapting the algorithm slightly and adding an optional integral error portion in the MPC controller. The performance of the enhanced MPC controller was compared to PI controllers on both the simulator and a commercial plant. The MPC controller showed faster responses with less interaction in both cases.

Jan 1, 2003

By Ramon V. V de Araújo, Roberto B. E Trindade, Pablo R. Fica-Piras

"Lead has been reported to affect blood vessels and kidneys. It also produces adverse effects in the mental and physical development of children and nervous system of adults. It is also considered as a possible cause of cancer. Because of all these threats to the human life, the reduction of its environmental occurrence, by means of recycling, is an important additional advantage to the usual ones derived of the procedures of the secondary metallurgy: lead can be recycled several times maintaining its characteristics equivalent to the primary one.Furthermore, this way of producing the metal avoids the environmental impacts of primary lead melting. Also, as an additional advantage, it triggers the metallurgical process with a raw material in what we observe higher lead content than in the natural ores. Some of the potential sources for these purposes are: ashes, slags, electrode residues, anodic muds, spent electrolytes, solid and liquid wastes, industrial or automotive catalysts, worn-out or obsolete equipment components and/or final consumption products.About 40% of world’s lead production comes from automotive batteries, mainly composed of four parts: plastic box, electrolyte (diluted sulphuric acid), contacts and connectors of Pd-Sb and plates (PbSO4, PbO2 and PbO). The plates represent 75% of the total mass. Metallic parts can be melted at moderate temperatures and then refined. The remaining fraction, constituted by the non-metallic portions, can be recovered by hydro and electro-metallurgical routes. These routes are preferred instead of pyrometallurgical ones due to the ultimate emissions of lead particulates and sulphur dioxide.The principal constituent of the residual paste of batteries is the lead sulphate. In this process, the paste is treated in two stages: in the first, lixiviating with Na2CO3 (desulphurization of the paste), obtaining PbCO3 and Na2SO4; in the second, the lead carbonate is lixiviated with HNO3, producing Pb(NO3)2, soluble, that can be converted to metallic lead by electrolysis. The reaction of PbSO4 with Na2CO3 in aqueous solutions is fast: the global rate is limited by the diffusion of the carbonate ions inside the reaction medium."

Jan 1, 2003

By Francisco Vicuña, Miguel Becerra, Nelson Iglesias

"The following article presents the development of a dynamic tool for the estimation of Jb/Jc rate (ball filling level / total load filling level) of a SAG mil operating in a single stage mode. Using the methodology detailed in this article, it is now possible to have a dynamic estimation tool in the operation, which enables strategic decision making and achieving a continuous development in process optimization. The estimating of the load filling level (Jc) was conducted using a power model, which in this case corresponds to the C-Model developed by (Morrell, 1993) that was calibrated by measuring the load filling levels (Jc) and balls (Jb) using the FARO laser scanning technology by means of Grind-Out and Crash-Stop procedures during the year 2013 and 2014. Finally, to estimate the dynamic filling level of full charge, Jc, three independent models were developed that allowed to feed the adjusted power model: •,SAG mill discharge grate slot wear model •,SAG mill internal volume wear model •,Ball filling level estimation model."

Jan 1, 2014

By Janusz S. Laskowski

"Frothers offered by different manufacturers are marketed with some information on their chemical and physical properties (e.g. density, viscosity, color, water-solubility, safety/toxicity, etc.). But frothers are used in flotation to generate fine bubbles and to stabilize the forth, and this information is only provided in a very qualitative description of the visual appearance of bubbles and froths. The terms “powerful” and “selective”, which have been commonly used to characterize frothers, have intuitive rather than scientific meaning.This paper introduces the DFI (Dynamic Foamability Index) plotted vs. CCC (Critical Coalescence Concentration) diagrams to classify flotation frothers (Fig. 1). The frothers characterized by low CCC and high DFI values have properties of strong flotation frothers, while those with high CCC and low DFI values are more selective. The proposed frother classification system, based on simple CCC and DFI measurements, provides, for the first time, a solid ground-work for characterization of the flotation frothers."

Jan 1, 2003

By Tsvetan Damyanov, Nikolay Hristov, Evgeni Kostadinov, Lubomir Kuzev

"The process of grinding in drum mills is directly dependent on the dynamic forces occuring in the free movement of the grinding bodies in the volume. The subject of discussion are the potential impacts between grinding bodies having different shape and equal weight in a drum mill that has a diameter of 1200 mm. The study utilised ball grinding bodies having a diameter of 120 mm and tetraballpebs having a conditional diameter of 120 mm. The study was carried out using the Solid Works Simulation software. The following cases were examined: • Impact between two identical grinding bodies; • Impact between a grinding body and the shell surface. The study provided numerical values for impact force, kinetic energy of impact, linear speed of impact, linear displacment of the center of gravity and duration of impact deformation. The impact force of the balls is approximately 179000 N. The impact force of the tetraballpebs with typical vertices, edges and spherical surfaces depending on the area of impact is 177000 to 185000 N. Upon impact between two spherical surfaces of tetraballpebs, the contact area is 263.55 mm2, which is more than twice the contact area upon impact between two balls, which is 114.39 mm2. This determines better conditions for the transmission of kinetic energy by reducing opportunities for overgrinding."

Jan 1, 2014

By J. D. Miller, C. L. Lin

In general, x-ray computed tomographic (CT) techniques are able to provide 3D images of the internal structure of opaque materials in a nondestructive manner. The unique cone beam geometry allows acquisition of all 2D projections with only one rotation of the sample thus providing for fast data acquisition and better x-ray utilization, as a complete 2-D detector array receives the cone-shaped flux of rays. Thus, an isotropic 3D volume can be reconstructed without the mechanical translation and the stacking of sequential slices as is the case for more conventional CT scanners. In this regard, a state-of-theart, custom designed x-ray microtomography facility to provide very detailed 3D spatial analysis of multiphase particles has been installed and is in operation at the University of Utah. The reconstructed 3D tomographic volume allows for an adjustable spatial resolution from 5 to 20 microns for sample dimensions from 10 to 40 mm in diameter, respectively. For example, a packed bed of coal particles is shown below in which different crystalline froms of pyrite are distinguished in 3D.

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 Xiaodong Jia, Richard A. Williams

"The packing of particles is a fundamental property of a material or system made up of particulates because it underlies many other physical properties of that material or system. Despite being ubiquitous, particle packing has not been an easy subject to study either experimentally or theoretically, except for a few regular shapes.This paper describes the recent developments, arising from research at Leeds, in the computer modelling of packing of complex shaped particles and prediction of physical properties of the structures represented by the packing. The computer model DigiPac, is capable of packing particles of any shapes and sizes in a container of arbitrary geometry. Figure 1 shows a few examples that are relevant to the mining and mineral industry.The ability to predict packing structure of real particle shapes and to compute directly some structuredependent physical properties (such as liquid permeability, mechanical strength/stability, compaction and sintering, dissolution and leaching, etc.) is obviously highly desirable and has significant potential in industrial applications. Examples are presented relating to the packing of granular materials.The mining and mineral engineering industries are well placed to exploit this advance in digital packing and simulation since they deal primarily with asymmetric and complex particulate mixtures. In the future we expect to see a number of developments in this area including:Algorithms that can optimise packing to achieve user-defined propertiesA more rational approach to determining flowability of complex powdersUse of these more realistic packing algorithms linked to blast and crusher design"

Jan 1, 2003

By S. S. Indi, D. Santhiya, S. Subramanian, K. A. Natarajan

"With the gradual depletion of the high-grade ores and finer dissemination of values in the leaner samples, it has become imperative to develop innovative approaches to process such complex ores. The beneficiation of complex sulphide ores containing copper, lead and zinc minerals, remains one of the most important challenges in base metals metallurgy. The advent of biotechnology in mineral processing has opened up immense possibilities to exploit such difficult-to-treat ores. Bioprocessing techniques thus hold promise as potential substitutes for the conventional technologies in vogue. Several types of autotrophic and heterotrophic bacteria, fungi, algae and yeasts are implicated in mineral beneficiation processes. Adopting a bioprocessing route to mineral beneficiation has attractive benefits, such as lower cost and energy requirements, environmental acceptability and operational flexibility.The interaction of sphalerite- and galena-adapted Bacillus polymyxa (B. polymyxa) cells with sphalerite and galena has been investigated through adsorption, electrokinetic and flotation studies. The amount of sphalerite-adapted cells adsorbed onto sphalerite and galena is found to decrease with increase in pH. On the other hand, the adsorption density of galena-adapted cells onto galena shows a feeble maximum around pH 8, and the amount adsorbed is marginally higher in the pH range of 8 – 11.5. In the case of sphalerite the amount adsorbed is higher in the pH range of 5 to 7. The adsorption density of both the adapted cells is higher for galena vis-à-vis sphalerite. Electrokinetic studies indicate significant surface chemical changes on the chosen sulphide minerals and the bacterial cells, consequent to microbemineral interactions. Selective flotation tests on a synthetic mixture of galena and sphalerite confirm that sphalerite could be preferentially floated from galena, using galena-adapted cells, but not with the sphalerite-adapted cells. The cells adapted to galena assay a higher polysaccharide content and are more hydrophilic, while the sphalerite-adapted cells have a higher protein content and possess greater hydrophobicity. Transmission electron microscopic studies have provided evidence in support of the differences between the cell surface characteristics of sphalerite- and galenaadapted cells (Figure 1). Possible mechanisms of interaction between the minerals and the bacterial cells are discussed."

Jan 1, 2003

By Leena Vesa, Antti Remes

Design of thickeners is based on laboratory test work, characterizing the material and determining the optimal reagents, dosages and settling regimes. Several methods for dimensioning plant scale equipment exist. Kynch and Talmage-Fitch design procedures has been applied widely for a long time. Nowadays, besides them, a dynamic laboratory test work is applied for design of high rate thickeners. In that the laboratory unit is operated with known solids load per area, feed and flocculation conditions and with raking of the underflow. All these test methods afford useful data for setting up and calibrating a dynamic simulation model of a plant scale thickener. This paper presents a flocculation kinetics based dynamic thickener simulation model and a procedure to calibrate the model parameters. With the model, the underflow stream composition can be simulated over time as a function of the thickener operating parameters, which are: the feed rate and composition, underflow pumping rate, flocculant dosage and dilution of the feed. In addition, the model incorporates calculation of the slurry bed level, the cone pressure, the yield stress and the rake torque. Such a dynamic modeling scheme enables setting up simulation aided operator trainings and developing and testing of advanced control strategies, for example. The unit model can be integrated as a part of concentrator-wide flow sheet simulation model as well. Here, calibration of the kinetic flocculation model based on a laboratory test case data and further the operation of a simulated plant scale thickener are presented.

Jan 1, 2014

By James A. Finch, Linda Restrepo, Mitra Mirnezami, Amy Buchanan, Maryam Hashemi

Settling rate studies on slurries from Cu/Zn flotation plants occasionally reveals two aggregation maxima at pH 8-10 and 10-12 (Figure 1). From measurements on sphalerite and silica suspensions the double maxima could be replicated. These maxima correspond to the effects of Zn and Mg ions. The aggregation mechanism of both ions is related to the formation of the corresponding hydroxide precipitate. A combination of chemical and electrostatic bridging by the hydroxides is considered to be the aggregation mechanism.

Jan 1, 2003

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 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 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 E. V. Manlapig, M. C. Harris

"The complexity of the flotation process has made the identification of an appropriate model structure for the predictive simulation of flotation circuits far from obvious. Work performed under the auspices of the AMIRA P9 flotation program has indicated that the metallurgical performance achieved from a flotation cell arises from the interaction of two essentially independent property classes, namely the cell operating conditions and the properties of the cell feed stream. These observations have led to the development of a model structure that associates a constant set of flotation parameters to the streams of the circuit, which are transformed into a flotation response depending on the operating conditions within the flotation cell.A variety of alternative model structures exist within the literature which do not make this distinction between cell and stream flotation properties, and many of these models are in widespread use for flotation optimisation and design studies, both in industry and academia.In this paper, circuit survey and laboratory batch flotation data collected from an industrial flotation circuit are analysed. The data demonstrate that streams in an industrial flotation circuit exhibit varying particle floatability – concentrate streams typically float faster than tailing streams (Figure 1(a)). This floatability, however, is generally conserved around the various units within the flotation process (i.e. the effective floatability of the combined feed and product streams of a unit is equivalent (Figure 1(b)))."

Jan 1, 2003

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 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 Heribert F. Broicher, Arne Volland

"The analysis of laser-induced fluorescence (LIF) combines remote sensing techniques with laser spectroscopy. Over variable distances different rock types are identified or changes in the quality of one rock type are recognised. LIF Analysers operate non-destructive, non-contact, on-line and in real-time. Installed over conveyors or over driveways the analysers ""look"" at the moving bulk solids 20 times per second and provide in real-time information for downstream sorting, blending or optimisation of processing. LIF Analysers recognise rock types (hardness information or dilution control), degrees of alteration, degrees of oxidation and –semi-quantitative- content of certain minerals in an ore. Only under favourable conditions quantitative assay information can be obtained, as e.g. the phosphorus content of Kiruna type iron ore.The main application of LIF Analysers is seen in big open pit operations, where the muck is trucked to an in-pit crusher and the crushed rock conveyed out of the pit to its respective destination: e.g. the primary high grade ore to the mill, the low grade or oxidised ore to the leach pads and the internal waste to the dumps.In underground mining and especially in block caving operations dilution control is of utmost importance. Here a LIF Analyser mounted on the back of a pick-up truck can be moved from drawpoint to drawpoint and quickly assess the degree of dilution.Closer to the mill the stockpile management based on LIF analysis will lead to stockpiles sorted according to rock type (hardness), degrees of alteration and oxidation. In case of direct feeding rom ore to the mill the knowledge of the type and quality of all the material between the in-pit crusher and the mill facilitates optimisation of e.g. reagent dosage."

Jan 1, 2003

By Chris J. Martin, Nichola A. McKay

"In mid-2001, North American Palladium commissioned a new 15,000 tonnes per day milling and flotation circuit at their Lac des Iles Mine (LDI), one of only two primary platinum group element (PGE) producers in North America. The mill treats an ore containing 2.3 g/t PGE producing a concentrate assaying 300 g/t PGE, at a recovery of roughly 75%.Top-size control crushing is conducted ahead of semi-autogenous milling. A portion of the SABC circuit feed is crushed to –25mm to increase mill throughput. Product from the SABC circuit is fed to flotation. Flotation consists of roughing and scavenging, with the rougher and scavenger concentrates each being reground using vertimills. Cleaner flotation uses two stages of cleaning using mechanical cells, and a third stage using flotation columns, the column tails being scavenged using a bank of mechanical cells. Rougher concentrate by-passes the first cleaner circuit. Reagents added include amyl xanthate collector, dithiophosphate promoter, MIBC frother and a carboxy methyl cellulose-based gangue depressant.SGS Lakefield Research, together with staff at LDI initiated a structured plant optimisation program comprising on-site testing, bench-scale flotation and mineralogical analysis using QemSCAN. The objectives of the mineralogical studies were 1) to identify feed PGM, their size distribution and mineral associations, 2) establish relationships between the PGM mineralogy and PGM floatability, and 3) characterize the culprit silicate minerals diluting the final concentrate.PGM flotation response at Lac des Iles is clearly bi-modal in nature, with about 60% of the PGM floating quickly, to a high value rougher concentrate. The mineralogical work was able to explain the causes of the bi-modal PGM floatability, which in turn created new opportunities for the metallurgists to optimise the circuit."

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