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By Aldo Cipriano, Fernando Estrada

The mining industry is in search of control strategies that allow considering a global optimization of their processes, ensuring their stability. This has led to the application of recently developed control techniques on large-scale systems in the mining processes. One of the most important process of the mining industry is the mineral grinding, as the product particle size impacts, in a significant manner, the recovery rate of the valuable mineral in the separation stages. As a solution, a centralized hybrid model predictive control (HMPC) is presented; this control approach maintains the product particle size on a defined range and minimizes energy consumption, maintaining the grinding plant in a stable operation. As a comparison, a conventional model predictive control with an expert system to handle discrete events was developed, showing HMPC is a suitable solution that can used in the grinding process, with the benefit that it handles in the same controller both discrete and continuous dynamics and events.

Jan 1, 2014

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 Rainer M. Lotzien, Michael J. G. Battersby, Jan Kleefeld, Julian V. Brown, Rainer M. Imhof

A new flotation system has been developed to improve the generally slow separating differentials of fine bubbles and fine particle suspensions. The new technology is based on established pneumatic flotation designs called Imhoflot which use intensive in-line pre-aeration to aerate the flotation pulp prior to its introduction to the separating cell. In the new system (see figure 1) this separation is speeded up dramatically by the introduction of centrifugal motivation in the separating vessel, without the use of internal moving parts. The design focuses on providing increased differential forces on buoyant mineralised bubbles and hydrophilic fines. The commercial benefit to industry is much reduced residence time, less than 30 seconds, which offers considerable cost savings in equipment and infrastructure.

Jan 1, 2003

By Rogerio C. Guimarães, Antonio E. C. Peres

The production of phosphate concentrates (phosphate rock) from slimes represents a challenge to the phosphate industry worldwide. In Brazil, this challenge is particularly relevant due to the consistently low P2O5 grades and the igneous origin. The first industrial experiences of producing phosphate rock from slimes (-44µm or -325#) fraction started at Arafertil, currently Bunge Fertilizantes SA, in Araxá, in the 1980.s. This production corresponds, nowadays, to 35% of the total production of concentrates in the company (830,000t/year) in a circuit consisting of desliming in 40mm microcyclones and concentration in flotation columns, corn starch and fatty acids being utilised as reagents. The performance of slimes flotation and the process control, at Bunge´s concentrator, were improved after the introduction of column flotation technology, in the first half of the nineties. The column flotation technology for slimes recovery was expanded to other Brazilian concentrators still in the nineties: Ultrafértil (Catalão - GO), Bunge (Cajati - SP), Fosfértil (Tapira - MG) and Copebrás (Catalão - GO). At present the Brazilian production of phosphate rock is approximately 4.5Mt/year, with a strong trend for a market increase. Genuinely Brazilian technology is utilised for the processing of slimes, the concentrates representing 11 to 13% of the overall production. The production of apatite concentrates from slimes was relevant to increase phosphate recovery and reduce costs, contributing to the growth of the fertilisers industry.

Jan 1, 2003

By James Y. Oldshue

"Very seldom is it possible when contacting a gas with a slurry to measure the dissolved gas concentration in the slurry, and even where possible, equilibrium data with a suitable Henry.s law constant are seldom available.In general, by assuming a reasonable value for the dissolved gas concentration in the slurry and a corresponding equilibrium gas partial pressure P*, KGa values can be calculated for the pilot plant and then scaled up. Then, with the same P* value at various reaction conditions, a mixer can be designed which is quite satisfactory, having a reasonable design factor for full-scale performance."

Jan 1, 2003

By Sudhir Srivastava

India hosts a wide range of globally significant mineral resources, including four fuel minerals; 11 metallic minerals; 22 minor minerals and 52 non-metallic minerals. The country ranks among world?s top five nations for its commodity reserves of coal and iron ore. Interestingly, only small part of country's landmass has been explored that provides opportunity for future substantial mineral discoveries. India plans to double infrastructure investments to US$ 1trillion. Despite the challenges in infrastructure project implementation, mining sector remains a key driver of demand growth for commodities in the years to come with a good prospect to grow in future.

Sep 1, 2012

By Kazutoshi Haga, Atsushi Shibayama, Kosuke Nishioka, Yasushi Kihara, Altansukh Batnasan

The aim of this study was to investigate the feasibility studies of seawater in flotation of a 1.5 mass % of copper containing copper sulfide ore. Effects of seawater, various frothers, and different distilled water/seawater ratio on flotation of copper sulfide ore were studied. Surface properties of native copper ore and sea water soaked were examined by using FT-IR spectrometry. Chemical contents of the copper sulfide ore and after flotation were identified using XRD studies. XRD pattern showed that the main constituents of the copper sulfide ore are chalcopyrite (CuFeS2), bornite (Cu5FeS4). Flotation experiments were carried out using mechanical agitation flotation equipment with a mineral separation type flotation cell. Froth flotation experiment was conducted using calcium hydroxide was used as a pH adjuster, using methyl isobutyl carbinol (MIBC), dow froth 250 (DF 250) as frothers and potassium amyl xanthate (PAX) as collector for the copper recovery from the copper sulfide ore containing chalcopyrite and bornite. The results showed that the copper recovery by flotation was dependent on the flotation medium and frother. The main results showed that the copper recovery by flotation was dependent on the process water and frother. The copper recovery reached 97 % and 87 % in the distilled water flotation and seawater flotation with MIBC, respectively. For seawater flotation with DF 250, the Cu recovery achieved near 95 % and grade of Cu in the froth product after 5 min flotation was reached 29.8 mass %.

Jan 1, 2014

By Peter Rubie, John Russell

"For many years, optimizing the relining of hard rock grinding mills has been complicated by the large number of variables, the low frequency of relines (resulting in a slow relining experience assessment and review cycle), and the potential economic risk associated with some changes to relining equipment or work practices. A technology that has its roots in the automotive manufacturing industry is being utilized to construct a statistically accurate, configurable, and dynamic simulation of the mill relining process. The detailed effects of various mechanization and process changes can be rapidly modeled and compared. Application of this discrete event analysis technology in the mineral processing industry delivers a range of benefits to many industry stakeholders. For example, mill maintenance managers and contract relining companies can embrace the opportunity to benchmark current performance against world’s best practice. Concentrator plant designers and mill manufacturers, informed by this technology’s scientifically defensible data set, can accurately plan for maximum plant efficiency when designing an infrastructure and equipment combination that truly maximizes annual plant availability. Time-motion studies of grinding mill reline data at mills of varying dimensions, liner configurations, mill relining equipment, operator and tool variables, have been integral to the development of this dynamic simulation tool and its associated data set. Access to mill relining simulation technology will enable mineral processing industry professionals to take advantage of an increased capacity to develop mineral concentrator performance optimisation initiatives within the given financial, physical and technological constraints of the individual concentrator plant."

Jan 1, 2014

By G. V. S. Murthy

Beach Placer Ilmenite is an important source for production of titanium metal, titania slag and pigment grade titanium dioxide. Besides, these well known applications for which Ilmenite is mined and processed, there are other emerging processes that are being tried for obtaining highvalue products. Synthesis of Ilmenite based materials for varistor applications and direct electrochemical reduction of Ilmenite to produce ferrotitanium are two such attempts being discussed in this work. In this paper, recent efforts undertaken to study the electrical and magnetic characteristics are discussed. Ilmenite, FeTiO3, is one of the mixed-valence transition metalbearing minerals, inwhich Fe can be in two different oxidation states, Fe2+ and Fe3+.. Similarly, Ti can be in Ti3+ and Ti4+.Ilmenite is inherently suitable for making Varistors, which are devices, used for limiting the transient voltage surges in a circuit. Varistors produced from Ilmenite can withstand harsh environments seen in nuclear reactors and outerspace. Electrochemical reduction of Ilmenite can be used to prepare ferrotitanium directly without any reductant. The process essentially involves removal of oxygen from the mineral through electrolytic action using calcium chloride as electrolyte and graphite as anode. At a temperature of 950°C, it is shown to be possible that all the oxygen can be removed from the Ilmenite sample, which passes through the electrolyte, to form CO/CO2 at the anode. The process has immense potential for cost effective production of titanium metal as well. Results of the above developmental works are presented in this paper. Keywords: beach placer ileminite, varistor applications

Sep 1, 2012

By Brochot. Stephane, Manuel Gonzalez Fernandez

"HPGR (High-Pressure Grinding Rolls) is widely used today for grinding of various kinds of ores such as iron ore or base and precious metal ores. It can be used as first stage of grinding replacing tertiary crusher and SAG mill, but also as regrinding stage to enhance mineral liberation. In addition to better energy efficiency, the advantage of HPGR is to produce much more internal particle fractures allowing faster leaching as it has been demonstrated for some gold ores. This grinding mode of compression and fracture generation also promotes mineral liberation without overgrinding. Mineral processing modelling and simulation associated to detailed ore characterization constitute a powerful tool for plant design and optimization. The mathematical models of the units of operations (grinding and separation) have to reproduce the mineral deportment for which the mineral liberation plays a central role. The present paper is focused on the HPGR modelling with the objective of plant optimization or advanced design from pilot plant tests. The traditional approach of the population balance linked to the energy dissipation and the residence time distribution is generalized in association with a mineral liberation model. The effect of the specific HPGR breakage matrix and grinding function on the mineral liberation rate is discussed and compared to the tumbling mill. The implementation of this mathematical model into a plant simulation tool is illustrated by the example of the optimization of an iron ore concentrator."

Jan 1, 2014

By Paolo Bevilacqua, Paolo Antonini, Lorenzo De Lorenzi

"Ceramic production requires large quantities of K-feldspar, which is commonly sourced from granites, alkali-granites, and feldspathic sands. These rocks contain other minerals, such as quartz and plagioclase, which are undesirable for ceramic production. Due to the coarse mineral grains that constitute these rocks, a reasonable liberation is achieved at a relatively coarse particle size.The feasibility of feldspar-quartz separation using a dynamic dense medium separation system has been investigated as an alternative to flotation techniques. The use of a two stages cylindrical vessel (Tri-Flo) was preferred to a conical vessel, due to the improved separation efficiency.In a full-scale processing plant, a dense medium separation process can be used as a K-feldspar preconcentration step. This reduces the amount of material to be treated in the more expensive processes, such as finer comminution, flotation or magnetic separation.A comparison between commercial raw materials for the ceramic industry and the “rich in feldspar” products of the Tri-Flo process is reported, and the validity of the process is demonstrated."

Jan 1, 2003

By M. Maldonado

A flotation bank is a serial arrangement of cells. How to optimally operate a bank remains a challenge. This article reviews three reported strategies: air profiling, mass-pull (froth velocity) profiling and Peak Air Recovery (PAR) profiling. These are all ways of manipulating the recovery profile down a bank, which may be the property being exploited. Mathematical analysis has shown that a flat cell-by-cell recovery profile maximizes the separation of two floatable minerals for a given target bank recovery when the relative floatability is constant down the bank. Available bank survey data are analyzed with respect to recovery profiling. Possible variations on recovery profile to minimize entrainment are discussed.

Sep 1, 2012

By A. Sand

Within stamp-charged coke making a large volume of coal is compacted to one single coal cake before entering the coke oven chamber. This is done by means of several falling stampers in a stamping machine having a mold nearly of the oven?s dimensions. Producing a high quality coke also from inferior coals requires a cake density of approximately 80% of the coal density. Besides that the industrial stamp-charging process demands a minimum mechanical strength of the coal cake to move it from the stamping mold into the oven chamber without failure. Densification and the build-up of cake strength were investigated earlier in stamping tests using a micro-stamping device. The quantities derived from these tests (as e.g. cake density or porosity) represent average values for the entire cake. Statements describing the local compaction state at different heights are difficult to achieve without destructing the cake. In order to gain better insight into the densification process and the inner structure of the coal cake a computational model based on the discrete element method (DEM) has been set up using 2 and also 3-dimensional simulation software. The stamper?s position and velocity as well as the force acting on the stamper were monitored and the model?s response was compared against measurement data from laboratory stamping tests. It was possible to reproduce the force and displacement pattern of the stamper in response to the viscoelastic properties of the cake using standard DEM bonding and contact models. Furthermore, the rearrangement of particles in response to the compaction by the stamper was tracked by calculating their displacement at the point the stamper hit the coal surface. The latter can also be used as indicators of particle deformation or breakage. By defining control points at different heights the particle displacement, stress and strain rates, porosity could be studied at different heights. Keywords: coke making, coal stamping, compaction, agglomeration, DEM, simulation

Sep 1, 2012

By G. M. Wolfaardt, B. C. Qi

"From a lifecycle point of view, biologically digested sludge is a valuable product that should be reused if possible. In contrast to landfill and incineration, application of digested sludge comprises the recycling nutrients and organic matter and reflects the policy of resource conservation and sustainability in waste management. Sludge may be applied to agricultural land for further sludge treatment and improvement of the characteristics of the soil. The characteristics of sludge that affect its applicability for soil conditioning include moisture content, pathogens, nutrients and metals. In this paper, the use of solid anaerobic digestion sludge of the lignocellulosic residues to condition soil was investigated in regards to nutrient composition, water content/retention capacity, hygienic quality (contamination of pathogenic bacteria) and heavy metal adsorbing/releasing characteristics of the sludge.The digested sludge had approximately 44.5% free and immobilized water and 46.9% bound water. The water-holding capacity of the sludge was high. This was the first merit to apply the sludge to agriculture in dry areas. Secondly, the sludge was rich in macro-nutrients (N, P, K) and a series of micro-nutrients (Ca, Mg, Mn, Na, Fe, Cu, Zn, B). The water-soluble fractions of macro-nutrients in the sludge were found considerably low. This implied that the loss or leaching of the macro-nutrients from the anaerobic sludge to the aqueous environment be slow. The nutrients loss owing to leaching could be reduced. However, because of a lower macro-nutrient content of the anaerobic sludge, comparable to the chemical fertilizer, it is advisable that the anaerobic sludge be applied together with commercial fertilizer to the agriculture land. Thirdly, the anaerobic sludge had strong selective adsorption affinity for heavy metal ions; non-heavy metal ions such as K(I) and Ca(II) could be released easily from the sludge in a wide pH range, such as pH from 1.0 to 8.0. Since the metal toxicity to the environment mainly comes from the mobile heavy metal ions, the selectivity to adsorb heavy metal ions of the anaerobic sludge can be utilized to reduce the availability of heavy metal ions to plants and humans in aquatic environment. Fourthly, the anaerobic digestion under thermophilic conditions showed a promising disinfecting effect to the sludge, in contrast to the landfill digestion."

Jan 1, 2003

"The effect of operational conditions, such as air flow rate, impeller speed and solid concentration, as well as the effect of solids concentration and frother dosage, on the bubble size distribution produced in a lab scale flotation cell, were investigated. The cell was operated under batch conditions. The measurement of bubble size was accomplished using an automated photographic technique. The technique enabled fine and coarse bubble distributions to be measured in two-phase (liquid-gas) and three-phase systems (solid-liquid-gas). In each experiment, around ten thousand bubbles were characterized.This paper discusses the main results obtained using the new photographic technique and compares these with previous findings available in the literature. The results indicate that photographic techniques combined with digital imaging processing might become a standard technique for measuring bubble size distribution in flotation machines.HUT BUBBLE SIZE ANALYSERThe importance of having precise and reliable equipment for measuring bubble size distribution in industrial flotation machines has been widely recognized. The measurement of bubble size, particularly in three-phase systems, is rather complex due to the opaque nature of the pulp. However photographic techniques combined with ingenious sampling techniques are utilized for overcoming this difficulty. The technique named HUT, combines previously developed visualization methods with digital image processing procedures. In this technique bubbles and aggregates are exposed to a monochrome progressive scan camera. The acquired images are directly stored in a computer connected to the camera for post-processing. The sampling apparatus consists essentially of a vertical tube for collecting bubbles, a viewing chamber and a collection chamber, where particles carried by the bubbles are released. The function of the collection chamber is to maintain the viewing chamber clear for imaging purposes. Each image is automatically processed off-line, using digital image tools. In this paper the advantages and limitations of this new technique are described."

Jan 1, 2003

By M. Gonzalez Fernandez

"If the final goal of metallurgy is the extraction of metals from a given ore, everyone knows that this achievement relies on many separation steps involving much more than a biphasic material made of metal and gangue. Nevertheless, still today, most of the design and follow-up of industrial processes only consider metal grades; in best case metal grades per size class. Working with such heterogeneous material, made of several minerals, with different grain size and texture, implies to consider finer ore models to be able to predict the behavior of material and the subsequent operation performances. Analytical tools are now available to provide such relevant and accurate data which are applied in geometallurgy. To achieve a true geometallurgical approach for process design, but also for optimization, accurate process simulation absolutely needs to combine these fine ore models with the corresponding unit operation models. Based on generic, but configurable, criteria of description and a hierarchical approach, the material modelling tool embedded in the USIM PAC process simulator provides the necessary flexibility to describe any type of ore with almost no limit in the level of details and associated physical properties that can be met in the mining industry. The simulation engine and the mathematical models of unit operations are designed to manage such a diversity of material modelling. The paper present various ore models and some of their applications in flowsheet simulation. It proves the interest of this detailed and advanced approach to accurately predict plant performances. INTRODUCTION Process simulation used for process design and optimization requires accurate unit operation modeling. During the last decades, main efforts of the different teams developing software simulators have been dedicated to those models for comminution and physical separations such as flotation or gravity concentration (Kojovic et al., 2012, Soni and Yoon, 2014). In most case, the ore is modelled with a size distribution and metal or mineral grades. A water phase is considered for wet processes. The association of unit operations and such material models generally allows, after some parameters adjustment, to achieve good agreement between experimental and simulated data. The use of the obtained simulator to test alternative configuration of circuits or settings of equipment devices can be accurate enough as far as the ore processed is close to the ore used for simulator adjustment. However, when the ore gets very different grades, coming from different mineral proportions or grain sizes, the simulation results can be of poor accuracy. Because any physical separations such as gravity, magnetic or flotation, do not sort metal and gangue but particles, made of minerals, containing metals, the only way to be accurate enough for allowing extrapolations, is to model particles. The phase model tools embedded in the USIM PAC process simulator gives this possibility. However, as such level of details are not always available for analyses, the tool has been designed with a high level of flexibility, to adapt the model to the available data. In this paper, the principles of this conceptual modelling tool are presented, and some application cases illustrate the material model flexibility and its interest."

Jan 1, 2018

By D. J. Zhao

The reduction and nitridation of preoxidized ilmenite pellets were investigated with the prospect of creating grain refiners containing titanium oxides and titanium nitride dispersoids. All the reduction and nitridation reactions were conducted in a furnace with a thermogravimetric analysis system under a H2-N2 gas mixture of 5 L/min. The ilmenite pellets were reduced at 1100°C for 4 hours under 80%H2-20%N2 gas mixture, and then respectively nitrided at 700°C, 800°C, 900°C and 1000°C for 12 hours under 10%H2-90%N2 gas mixture. The products were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM), and analyzed by Energy Dispersive Spectrometers (EDS) and Electron Probe Mapping Analysis (EPMA). Iron oxides were reduced into metallic iron, and oxides of titanium were found, but titanium nitride particles were not identified in the products under the prevailing conditions.

Jan 1, 2014

By A-M Ahonen

The paper discusses the experiences of a fast-track curriculum designed to provide the industry with engineers capable of working in minerals processing industry. The course has been done once before and the second course has been started. Students chosen have graduated from other fields of engineering. For the first course, twelve students were chosen from 152 applicants and for the second the twelve students were chosen from 96 applicants. The basic idea of the curriculum is to alternate between theoretical studies at the university and working experience periods at industrial sites. In addition, there are several one week assignment tasks at industrial sites. The theoretical periods are six to eight weeks long and there are three of them. During the first period, the teaching concentrates on unit processes and their chemical and physical background. The theme of the second period is mineral engineering systems; flowsheet development, process dynamics, control systems etc. The last theoretical period teaches environmental issues, leadership, project work and other similar topics. Each of the theoretical periods ends with an assignment week at industrial sites. The assignments are designed to wrap up the teachings of the period. For the industrial periods, the students are given learning goals, which have been discussed and designed with their industrial mentors. They are required to find relevant literature, make experimental designs, implement those designs, present the data, and make conclusions of their results. During these periods, a weekly meeting over the Internet is compulsory. Keywords: mineral processing, flowsheet development, process dynamics, control systems, constructivism, zone of maximal development, Vygotsky

Sep 1, 2012

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 Danuta Szyszka

This paper presents results of tests performed to determine minimum concentration of a surfactant used at which coalescence of air bubbles during flotation has low probability to occur. The measurements of the critical coalescence concentration, also known as CCC, were carried out in a device consisting of glass cell into which air was pumped by peristaltic pump through capillaries. The flotation foam was recorded with a high resolution digital camera. Basing on the video records, average diameters of the air bubbles were measured and the values obtained were subsequently used to determine the CCC values. The author of paper determined the CCC values of surfactants tested using the linear regression method, and subsequently analyzed the results obtained. To define initially the capability of a tested surfactant to flotation, efficiency of multiparticle model flotation and flotation of individual size fractions were determined in a flotation apparatus for laboratory use in the presence of only foam making agent at CCC value pre-determined during the tests previously carried out. The tests of coalescence phenomenon were carried out with use of selected flotation frothing agents.

Jan 1, 2014