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By Erico Tabosa, Kym Runge, Peter Holtham

"The distribution of turbulence in an industrial scale mechanical flotation cell and its effect on flotation kinetics was studied using a fully instrumented 3m³ cell. The cell was operated at a copper concentrator in Australia with different combinations of airflow rates, impeller speeds and sizes and cell aspect ratio providing a wide range of hydrodynamic conditions. An analysis of the overall flotation cell performance showed that the overall copper recoveries were very similar for the conditions tested. However, by decoupling pulp effects from froth effects it was possible to evaluate whether the changes made affected the pulp zone and/or froth zone responses. The analysis showed that the overall recovery has the potential to be up to 7% higher, if not limited by froth recovery. The cell hydrodynamics were characterised by the overall energy dissipation rate and, to understand the distribution of turbulence within the cell, localised measurements were made using a piezoelectric vibration sensor. By comparing the metallurgical performance of the cell with the different hydrodynamic conditions it was found that the collection zone flotation rate constant was not directly related to overall energy dissipation, as is commonly observed at laboratory scale, where energy is usually only changed by varying impeller speed. In this study, energy dissipation rate was varied using not only impeller speed, but also the size of the impeller and the cell aspect ratio. In these circumstances, the best correlation was found to be between the collection zone flotation rate constant and the distribution of turbulence, i.e. the size of the turbulent zone."

Jan 1, 2014

By P. Basarova

The attachment of bubbles onto a collecting surface is an ubiquitous natural phenomenon, playing a critical role in numerous practical processes. The goal of the project is to broaden the knowledge about hydrodynamic interactions between small bubbles and large solids that occur in nature and industrial processes. Focusing on collision processes between a single rising bubble (Db<1 mm) and a larger falling spherical particle in stagnant liquid, the theoretical model describing the bubble trajectory is given here. The model is based on analysis of forces acting on the bubble, and utilizes equation for the bubble motion. Mobile and immobile type of bubble surface mobility are considered. The calculated results are compared with the experimental data; here a high-speed video camera was used to capture the bubble motion and bubble-particle interaction. Very good agreement between experimental and calculated data was found. For both types of surface mobilities, the bubble deviation in the horizontal direction is nearly linear. The proportion constant is bigger for immobile bubble surface and increases with the bubble size. Furthermore, particular forces acting on bubble were studied. A similar course of relative bubble velocity and force impact was observed for identical bubble position. For cases when the bubble centre is close to the particle axis, only deflection in one direction is observed. When the bubble is reaching the maximum trajectory, the force ratio is changed. The bubble is firstly pushed away from the particle, but when it is within close distance from the particle, the bubble is pushed towards the particle.

Sep 1, 2012

By Jorge Misle, Daniel Silva

"This paper addresses the need for advanced control technologies and strategies in the mining industry, its potential and actual impact on mining processes and the best practices for their implementation, operation, and long term sustainability. It is well known that advanced process control (APC) can be a very good source for incremental process improvement for the mining industry, yielding to higher production rates or helping maintain consistent production rates despite ore changes. The application and integration of new technology, process knowledge and innovation are key elements in building such a supporting structure. More specifically, and this cannot be emphasized enough, the correct application and assembly of control tools, the in-time presentation of key data to decision makers and the development of relevant statistics and KPI’s (key performance indicators) can and will make a difference not only in terms of production, but also in plant stability, availability and production costs. In deploying such ideas and aiming at the long-term goal of "Operational Excellence", Minera Los Pelambres (MLP) has developed a number of successful control strategies, best practices and technologies, which are not only the application of state-of-the-art automation and computing tools, but rather the assembly of the above presented structuring factors. This work discusses some of the key tools and ideas implemented for SAG & Ball milling and Flotation areas, their performance results and the roadmap taken for the integration of process knowledge and control tools. Also, cases studies are presented and discussed further to not only show the main areas of improvement, but also to highlight the benefits of such strategy that for the most part, deviate from the traditional mining industry control approach. Also, a word is given on the need for innovating in the design of control strategies and leveraging best practices and process knowledge that ultimately, will contribute to long-term reliable operations, improved mineral processing and, although unmeasured, lead to a superior overall performance and productivity of all mining personnel involved."

Jan 1, 2014

By T. B. M. Himawan

In this study, effect of thiosulphate and oxidation using oxygen were studied in arseno copper ore flotation. Single mineral study of chalcopyrite and tennantite in regard to the aforementioned techniques was also studied. Zeta potential, XPS, contact angle and floatability of single minerals were conducted for each treatment to understand the mechanism. It was revealed that the separation is best conducted in alkaline condition at where there will be interaction between thiosulphate and the mineral surface as well as the formation of hydroxide species in the oxidation using oxygen. From zeta potential of both thiosulphate and oxidation conditioning, it can be found that the reactivity of tennantite is much higher rather than chalcopyrite resulting higher rate of depression on both techniques as shown from contact angle and floatability of each mineral after treatment. XPS spectra confirmed qualitatively and quantitatively the existence of species responsible for the depression of each conditioning techniques. As for the copper ore flotation test, it is the oxidation using oxygen provides best performance after 60 minutes of oxidation. Keywords: tennantite, chalcopyrite, arseno copper ore A, thiosulphate, oxidation using oxygen

Sep 1, 2012

By X. H. Zhou

Column flotation is being widely adopted for fine particle treatment by the mineral processing industry due to its simplicity of structure, high efficiency and good separation performance. Cyclonic static micro-bubble column flotation (FCSMC) is an innovative column separation technology that has been successfully applied in the coal preparation industry in China. Recently, the application of this equipment has been further expanded to the separation of several minerals such as fluorite, copper, iron, etc. The bottom of the FCSMC is a cone in which cyclonic field is generated when circulating pump is injected tangentially into the column. The unique cyclonic structure is believed to help enhance the column separation performance. Since the FCSMC is a new flotation device, little work has been done to understand the fundamentals of this technology. In this research, a computational fluid dynamics software, ANSYS/ FLOTRAN, was employed to simulate the flow field of a lab FCSMC system (F0.2 m, F3.0 m by length.) The distribution patterns for velocity field and flow field were investigated under single phase condition. It has been found that axial velocity of the slurry decreases and becomes stable along the height of the column from bottom to top, and the slurry performs as a descending flow pattern. Another observation is the velocity fluctuates vigorously near the wall due to wall effect. Compared to axial velocity, the radial velocity distribution is smaller and more complicated. The basic pattern is that on a given cross section of the column radial velocity increases from the wall to the center and it the velocity changes greatly around the center. Under the condition of column height less than 0.8 m, the axial velocity is negative and it directs from the wall to the column axis. When column height is higher than 0.8 m a reverse pattern is obtained, i.e., axial velocity is positive while directing from column axis to the wall. Special efforts were directed to investigate the tangential velocity pattern. Results indicate that the tangential velocity patterns of different cross sections are similar and showed a symmetrical distribution. Tangential velocity distribution concluded two zones: outer whirlpool and inner whirl-pool. And, interestingly, it has been found that on different cross sections the highest tangential velocity always occurs at the same position of the cross sections.

Jan 1, 2014

By Brian Hart, Liuyin Xia, Staman Dimov

The recovery of rare earth elements (REE) is fast becoming of significant interest globally. Modern research and development programs (outside China) towards the optimization of REE mineral recovery by flotation have been lacking. Due to the mineralogical nature of many hosting deposits, the separation and recovery flotation flowsheets can be very complex. As part of a research project, a selected suite of hydroxamic acid collectors (Naphthoyl, Cyclohexyl, Benzoyl, Octyl, Terta-butyl benzoyl, Salicylic) were tested in order to examine their potential for recovery and selectivity. Micro flotation tests were conducted on a feed sample, recovery and grade of the products were used to evaluate their relative flotation efficiency and selectivity and these results (flotation with the hydroxamate collectors) were compared to a phosphoric acid/sulphonate collector mix(shorten as "mixed"). In the testing, the flotation response with the hydroxamate collectors was significantly better than the "mixed" collectors on freshly ground (no slimes removed) samples. Furthermore the tests revealed that for most of the hydroxamate reagents tested, their dosage requirements to achieve recoveries at the same levels was less than that for the "mixed" reagents. Product assays show that recovery of both La and Ce is significantly better for using the salicylic hydroxamate and that Nb, Y and Zr recovery are favored by using octyl hydroxamate. These results indicate mineral flotation selectivity could be achieved by using selective hydroxamtes. Spectral fingerprinting by TOF-SIMS surface analysis has allowed for the identification of reagent species. TOF-SIMS surface analyses of grains analysis confirmed that REE bearing grains reporting to the concentrates are doing so in response to collector attachment whereas grains reporting to the tails are doing so in response to a lack of collector. The TOF-SIMS surface data bas been used to examine the factors promoting flotation stream partitioning.

Jan 1, 2014

By Y. H. Hu, X. X. Zhang, Z. F. Dai, H. J. Huang, Q. S. Huang

"In order to get a more comprehensive understanding of the interaction of fine fluorite particles and bubbles, the electro-flotation was conducted, a high speed CCD was used to determine the bubble size distribution, and the results were analyzed using the models of collision and attachment. The electro-flotation was performed in a modified Hallimond tube. The results show that for different fluorite with size of 0 -10µm, 10 -38µm, 38-74um, there is a matching range between the different particle sizes and cathode aperture size (38um, 38um, 74um) to reach highest recovery. In addition, improving the concentration of collector is benefit for the flotation recovery due to the ability of collector to decrease the bubble size and prevent the merger of bubbles. Furthermore, theoretical calculation of collision, adhesion probability and collection probability is in agreement with the experimental data for electro-flotation recovery of fluorite.INTRODUCTIONFluorite is widely distributed, and has been found in more than 40 countries around the world. As fluorite minerals are easy to float, flotation is used as the best method of the current recovery of fluorite (Yang and Ai, 2016; Chen et al., 2017). In the field of mineral processing, the flotation of fine particles is particularly difficult, caused by the small quality and large surface (Sun et al., 2006). Flotation is now considered to contain three subprocesses, including the collision, attachment and detachment between the particles and bubbles (Sun et al., 2011). The collision of particles with bubbles is related to factors such as particle size and density, bubble size, bubble rise rate (Qin et al., 2012). Zongfu Dai et al. (2000) summarized the particle-bubble collisions models in detail and compared the experiment results with the model predictions. However, particle-bubble interactions occur in complex and turbulent flotation environments (Xing et al., 2017). Both thermodynamics and dynamic factors affect the adhesion of particles on bubbles surface (Schulze, 1989; Shahbazi et al., 2010). Scheludko et al. (1976) believes that the necessary condition for successful adhesion of particles on bubbles is that the contact time is greater than the induction time. The probability of adhesion between particles and bubbles increases with the increase of bubble size, but if the particle size is too small, the probability of adhesion decreases instead (Ren, et al. 2014; Norori- McCormac et al., 2017). After the particles adhere to the bubble surface, the particles will slide down to the bottom of the bubble due to gravity. At this point, the gravity, inertial centrifugal force and fluid force promote the desorption of particles from the bubble surface, while the surface tension, surface hydrophobic force maintain the stability of particles-bubble combination (Ralston et al.,2017). In addition, in the process of rising to the foam layer, desorption can also occurs. The purpose of this study is to observe the flotation behavior of fine fluorite with different size and to get a more comprehensive understanding of the interaction of fine fluorite particles and bubbles."

Jan 1, 2018

By A. N. Zagorodnyaya, Ye. G. Bochevskaya, E. A. Sargelova, Z. S. Abisheva, A. S. Sharipova

"In Kazakhstan, there is a unique sulphide copper deposit, in the ores containing the natural isotope of osmium-187 (more than 90 %). In the pyrometallurgical processing of concentrates for the target metal, osmium is mainly sublimated, with wet cleaning of metallurgical gases (dust and gas mixture) 40 % of it together with rhenium passes into washing solutions (wash acid). On the basis of this acid, the production of ammonium perrhenate was organized at the enterprise of the RSE ""Zhezkazganredmet"" and for the first time in the world practice - the isotope of osmium-187. However, the degree of its recovery from solutions does not exceed 8 % of the amount supplied with the charge or 25 % of the amount that was received for extraction. But the bulk of it (~ 75 %) remains in the raffinate, discharged to sewage treatment plants (wastewater). The studies presented in this work are aimed at solving the problem of osmium isotope-187 extracting from wastewater, which are a potential source of increasing metal production in Kazakhstan. The aim of this work is the development and scientific justification of osmium deposition regimes from wastewater using such reagents as thiosulfate and sodium sulphide. The influence of various physicochemical factors on the precipitation of the osmium was studied and optimal conditions for its maximum transition to sediment were chosen. An original method for obtaining osmium concentrate in the presence of sodium thiosulfate with the addition of potassium iodide from a new type of wastewater - man-made ammonia solutions has been developed. These solutions were combined mother liquors of solid-phase stripping operations and dissolution of pulp of crude ammonium perrhenate. On the basis of the obtained results, a settling technology for extraction of the osmium from man-made ammonia rhenium-containing solutions was introduced at RSE ""Zhezkazganredmet"". It should be noted that the degree of extraction of osmium, depending on its concentration in solutions entering on the settlement, and taking into account the addition of sulfuric acid, will vary from 60 to 90 %. The recovery of osmium during the test period was 58 %."

Jan 1, 2018

By Zhongxue Li, Cuiping Li, Xiaoyun Hu, Yiqing Zhao, Huaying Wang

"Under the auspices of World Federation of Engineering Organizations’ Committee on Engineering and the Environment (WFEO-CEE) and Society for Mining, Metallurgy and Exploration (SME) Task Force on Sustainability and Mining (TFSM), and aimed at helping raise global understanding on and promote capacity building of risk management, this paper presents a framework and prototype of toolbox or knowledge warehouse for facilitating the application of risk analysis, mitigation and management techniques (RAMT) in the mining and minerals sector. The conception, design and implementation of the intended system of knowledge warehouse of risk analysis, mitigation and management techniques (KWoRAMT) are outlined. The system architecture of KWoRAMT is based on a browser/server (B/S) structured platform with web oriented interfaces and composed of data base, knowledge warehouse, searching mechanisms, and risk assessment methodologies. The knowledge sources for KWoRAMT will come from the TFSM expertise and Internet, including laws and regulations, codes of practice, standards, guidelines and best practices. The functions and outcomes of KWoRAMT consist of guided navigations with web links, categorized risk tools, annotated best practices with cases, and integrated risk approaches and solutions based on typical risk methods. Risk categories include those impacting on mine safety, mine occupational health, and mine community environment throughout the whole of mine life cycle from exploration, construction, and exploitation and processing to post-mining closure. Mining associated hazards will be identified and linked by vulnerability onto risk receptors through pathways. Risk management techniques for assessing impacts and consequences of mining induced hazards will be categorized with their pros and cons or strengths and weaknesses. Best practices and significant cases including experiences and lessons with problems, solutions, and recommendations on how solutions would be derived will be illustrated. Integrated risk approaches based upon typical methods will be developed for alternatives and actions."

Jan 1, 2014

By B. Mishra, Rahul Mohanty, Swati Mohanty, Swagatika Dash

Wet high intensity magnetic separators have been widely used in the mineral industry for separation of mineral particles based on magnetic properties. Usually, magnetic separators employ ordered array of grooved plates such as Lenoir and Jones plates onto which the magnetic particles get attached in the presence of a magnetic field. In the present work, we have carried out computational fluid dynamic (CFD) simulation, using Eulerian-Eulerian model to study the flow dynamics of magnetic and nonmagnetic particles within a matrix consisting of 2 mm size spheres of magnetic material, which are interconnected by wires, in the presence of a magnetic field. The three phases considered were the water, magnetic particles and non-magnetic particles. Model equations were developed considering each sphere in the matrix as a magnetic dipole, and the strength of the magnetic field at any point in the domain is due to all the dipoles. The size of the magnetic and nonmagnetic particles was 45 and 40 micron, respectively. The feed consisted of a slurry having 25 wt. % solids. The volume fraction of the magnetic particles was 0.04, and that of the non-magnetic particles was 0.045. The simulation was first carried out without the imposition of the magnetic field till a steady state was reached, and then the magnetic field was applied. The magnetic particles, as they flow down the matrix were attracted towards the region of maximum field gradient, which was in the central region of the matrix. A symmetrical pattern in the upper half as well as the lower half of the matrix was observed. As the particles moved downwards, the pattern changed, and near the outlet, most of the particles were found to flow out from the central part of the plane. This study can lead to a better design of a magnetic separator.

Jan 1, 2014

By R. Prakash

Column flotation has now gained wide application in the recovery of various minerals. The performance of the flotation device depends on the mixing characteristics of the phases inside the devices. In this work, quality of mixing in a flotation column has been analyzed by using information entropy theory. Empirical models have been developed for flotation column with the parameters which affect the quality of mixing. The efficiency of the particle separation in the flotation column has been enunciated based on the quality of mixing. The present analysis on the quality of mixing in flotation column may give insight into a further understanding and modeling of flotation devices in industrial applications.

Sep 1, 2012

By Vladimir G. Kochnev

"Autogenous and semi-autogenous grinding (AG and SAG) have been considered a step forward in comparison to conventional grinding circuits with several stages of crushing and using ball (and/or rod) grinding mills. However, existing AG and SAG technologies still can be improved and have an immense potential from the viewpoint of economic benefits.Experience gained by the Technics & Technologies of Disintegration Ltd. (TTD) in the research of grinding processes shows that comminution in AG and SAG mills can be performed in a more effective way. The company’s approach comprises the following elements:- Novel mill design- New liners and lifters- Novel discharge grid design- Technique of treating material of critical particle sizeA novel mill of the cantilever type capable to operate in the AG and SAG mode has been developed. The cantilevertype mill has a high diameter to length ratio, which dramatically increases the throughput rate, and is characterised by high reliability, fast installation and low capital and operating costs.Tests of the new heel-shaped liners, originally aimed at improving the intact condition of diamond, indicated that they play an important role in the grinding process. Tests performed by TTD jointly with ALROSA, MINTEK and Anglo-American Corporation, demonstrated that the heelshaped liners provided the increase in the throughput rate varying from 30 to 80 % and the decrease in power consumption in the range 30-55 % for grinding of kimberlite and platinum-containing ores.Investigation of the influence of the main grid parameters on the efficiency of grinding led TTD to a special design of a mill discharge grid, with a radial location of openings, the slot width varying from the periphery to the centre and the grid surface provided with “heels”. The design allows one to control the particle size distribution of the ground product without affecting the grid throughput rate."

Jan 1, 2003

By K. A. Natarajan

"Interaction with microorganisms results in significant surface chemical changes on minerals. For example, chemolithotrophs such as Thiobacillus ferrooxidans and Thiobacillus thiooxidans significantly alter the surface chemistry of several sulfide minerals such as pyrite, chalcopyrite, sphalerite and galena. Heterotrophic bacteria such as Bacillus sp. could alter the electrokinetic properties of oxide minerals such as hematite, alumina, silica, kaolinite and calcite. Microbe-mineral interactions could thus be beneficially utilised in mineral beneficiation as different from bioleaching. Microbially induced mineral beneficiation unlike bioleaching deals with interfacial phenomena at mineral-solution-bacteria interfaces and surface chemical changes are brought about at very rapid rates amounting to a few minutes resulting in mineral separations in an aqueous medium.In this paper, the role of acidophilic chemolithotrophs such as Thiobacillus thiooxidans and neutrophilic heterotrophs such as Bacillus polymyxa in the beneficiation of sulfide and oxide minerals is illustrated. Mechanisms of bacterial attachment on various sulfide and oxide minerals are outlined with respect to the influence of bacterial interaction in bringing about mineral surface hydrophobicity or hydrophilicity. The role of bacterial cells as well as metabolic products such as bioproteins and exopolysaccharides in significantly altering the surface chemistry of sulfide minerals such as sphalerite and galena and oxides such as hematite, alumina, silica and calcite is discussed with probable mechanisms. Possibilities of generating mineralspecific bioreagents are outlined with respect to bacterial adaptation to mineral substrates."

Jan 1, 2003

By Andrei Kolesnikov

"The results of CFD modelling of complex heat transfer and fluid flow in DC electric arc furnace are presented. The model includes energy and momentum conservation equations for gas phase (freeboard), liquid phase (molten bath) and solid phase (walls and graphite electrode). Simulation revealed the temperature distribution in all elements of the furnace. The influence of the arc and melt resistance on the temperature distribution is discussed.Computational Fluid Dynamics (CFD) becomes a powerful tool for better understanding of the heta and mass transfer processes in industrial equipment. In current work commercial CFD software STAR-CD was used to analyse complex heat transfer in DC EAF, including forced and natural convection, conduction and radiation. The finite volume solver using body-fitted grid was used. The grids are non-staggered hexahedral grids and all variables are evaluated at cell centers. Steady-state calculations were performed with PISO algorithm. For the convective terms in equations the hybrid differencing scheme was used. An upwind differencing scheme was used for other terms. Conjugative heat transfer was taken into account in heat transfer calculations on gas-liquid and gas-solid interfaces. Radiation from the arc and inner surfaces of the furnace was calculated by a “discrete beam” approach. Source term in energy conservation equation was used to represent heat release in the zone occupied by the DC electric arc. The volume of this zone was calculated from semi-empirical equations. The Joule heat and heat due to chemical reaction in the melt were calculated through the source term expression in the energy balance equations for the slag and metal in the molten bath. The gas acceleration in the electric arc zone and stirring of the slag due to gas bubbles motion were accounted for by momentum source terms in the momentum conservation equations.All simulations were carried out using axisymmetric two-dimensional grid. The grid resolution was 20 cm per cell in most part of the furnace, except the arc region, where resolution was 5 mm per cell."

Jan 1, 2003

By M. Ghiani, P. Massacci, A. Manni, R. Peretti, Center for Mining and Mineralurgical Studies, S. Serranti

"The research study has been devoted to point out the better way to process a colemanite concentrate characterised by a high content of two kind of As sulphides (realgar and orpiment) finely disseminated in the matrix of the boron mineral.Scanning Electron Microscopy analyses have been carried out to determine all the mineralogical constituents and to evaluate their distribution, frequency and mutual relationships.There is a not neglectable part of realgar highly disseminated into the colemanite crystals.The orpiment recurs in small acicular crystals of 20÷30 µm in length and 5 µm in width, very difficult to liberate from the colemanite mineral particles.The colemanite concentrate, in fact, has been addressed to a chemical plant which products were boric acid and gypsum, the contaminated by As. It was unacceptable for further applications and very dangerous if rejected in the environment.Grinding tests under dry and wet conditions have been carried out in order to evaluate the liberation modality of the As sulphide minerals from the colemanite.Some difficulties have been overtaken in order to obtain a selective liberation of the As sulphides from the colemanite even if a certain decreasing in As grade in the higher size classes has been registered.All the comminution products have been analysed by SEM monitoring the liberation degree of the mineralogical constituents.Flotation tests have been carried out after different comminution flow sheet adopting different modulating conditions in order to evaluate the influence of the following parameters:• collector concentration versus contaminants concentration (As minerals) in the froths;• kind and quantity of the frothing agent to maximise the mineral recovery in the froths;• kind and quantity of the modulating agents to maximise the selectivity of the process;• conditioning modalities in order to obtain a suitable dispersion of fines and to avoid segregation of Asbearingparticles together with colemanite ones;• solid/liquid ratio of the pulp to minimise the water flow into the plant."

Jan 1, 2003

By Claudio Bisso, Javier Vargas, Charles Lozano

"This paper summarizes the activities performed to predict SAG milling throughput at Minera Esperanza. Having highly reliable geometallurgical models aided by the new computer tools and specific metallurgical testing to rely on has become a major issue in recent times due to their impact on the business. Minera Esperanza’s SAG throughput model was constructed by characterizing the ore feed and operational parameters of the plant. Producing a robust model required satisfying number of requirements for the parameters used for both the ore and the plant as follow: 1) geologic and geometallurgical characterization parameters; and 2) parameters of a plant running at the rated production under optimum operating conditions. Obtaining these parameters required increasing the quantity of samples and metallurgical testing through drilling campaigns, mapping the drill holes and putting samples through various comminution tests while sampling all operational flows at the plant to obtain the metallurgical information for the operational parameters. The information was entered on the JKSimMet software to enable a throughput model to be developed to output SAG mill throughput predictions that are very close to actual throughput figures, i.e., accurate within a range of 2% on a monthly basis."

Jan 1, 2014

By Weiguo Xie, Malcolm Powell, Lian Liu, Ping Yu

"In order to develop a common mathematical and simulation platform for tumbling mills, a review of existing mechanistic models was made identifying the key aspects of grinding and slurry transport which are common to all tumbling mills. A mill model structure has been developed for all types of tumbling mills based on the population balance framework by incorporating breakage characteristics, slurry and solids transport, product classification and discharge, and energy consumption. A size-dependant breakage model developed by the JKMRC is applied. Transport is separated from breakage events and treated as a main sub-model in the new model structure. The model structure is based on dynamic time-stepping technique to enable dynamic simulation capability for non-steady-state simulation and control modelling. It is envisaged that the new model will cover a full range of milling conditions. It should enable a smooth transition between different mill types, such as from AG (Autogenous Grinding) to SAG to ball mill. The dynamic mill model structure developed here is the first step towards mechanistic modelling of grinding mills and provides great potential for the optimization of the comminution process."

Jan 1, 2014

By E. D. Gálvez, L. A. Cisternas, R. Acosta-Flores, F. A. Lucay

The optimal design of flotation circuits is a complex task as the mathematical model is nonconvex and includes binary variables, making it difficult to obtain the global optimum solution. Furthermore, there are epistemic uncertainties in the evaluation of the performance of flotation and grinding units. This epistemic uncertainty is generated because semi-empirical models are used with parameters that are a function of the circuit design. Therefore, it is not possible to adjust these models based on experimental data as the experimental conditions are not known at the design stage. This paper analyzed the effect of the uncertainties in flotation units, grinding units, and both units simultaneously. As a result, this paper demonstrated that, for a specific mineral, few structures exist that are optimal for a wide range of values in flotation stage recoveries and liberation fractions in the grinding units. A remarkable aspect of this work is that it introduces grinding, one of the operations that most influences energy consumption in mining and has not been studied in depth in the design of flotation circuits. To demonstrate that there are few optimal structures for a specific mineral when there is high uncertainty in the process units, an a priori approach or first principles was used. Two methods of proof were used: proof by construction and proof by exhaustion. Proof by construction is the construction of a concrete example with a property to demonstrate that something having that property exists. In this work, two examples were considered in the proof by construction. In proof by exhaustion, the conclusion was established by dividing it into a finite number of cases and proving each one separately. Here, 30,000 cases were included for each example. This knowledge can be useful in circuit design including grinding, e.g., after selecting the circuit (or the most promising circuits), and the equipment design parameters and operating conditions can be defined based on simulation and laboratory tests.

Jan 1, 2018

By Thomas Mütze, Anja Hirte, Ursx Peuker, Thomas Kuhn

"The comminution behavior of two ferromanganese nodules samples of the equatorial northeast Pacific has been examined as a basis for the separation of two kinds of metal-rich layers. Those layers were finely grown together during nodule formation and are one reason that the exploration of deep-sea minerals calls for the development of new mineral processing concepts. Therefore fundamental analyses of the fracture behavior have been made under compressive and impact stress. Further experiments took focus on the crushing behavior in a jaw crusher and a small scale impact crusher as well as the milling behavior in a dry vibrating mill, a wet planetary ball mill, and a wet agitated ball mill. The comminuted products were characterized by PSD, particle shape, particle density, and porosity. The experiments show a low stress resistance of the ferromanganese nodules. Compared to compressive stress, impact stress turned out to be the more effective for crushing. Both samples showed no significant difference in the comminution behaviour which makes differing mechanical treatments unnecessary. In both cases particle sizes below 1 µm were achieved by wet grinding. This particle size is necessary to separate the two kinds of metal-rich layers which is part of continuative studies."

Jan 1, 2014

By J. Bouchard, Ali Vazirizadeh, R. del Villar

"The amount of water reporting to the concentrate correlates well with the solid entrainment. It is well known that the frother and collector dosage as well as the froth depth and gas rate influence the amount of water reporting to the concentrate. This is also true for gas dispersion properties such as gas holdup and bubble surface area flux. On the other hand, a positive bias rate, required to reduce hydraulic entrainment, also affects water recovery and thus the particle recovered by entrainment (depending on the their size). Up until now, the effect of the gas rate on the water recovery has been studied, but no comprehensive investigation on the gas holdup, bubble size and bubble surface area flux has yet been reported. This research precisely aims at addressing this issue. The experimental work was carried out under a constant gas flow rate to eliminate the gas volume effect, while other gas dispersion properties have been varied by modifying the frother concentration and the shearing water introduced to the frit-and-sleeve sparger. A constant froth depth and no wash water were used, in order to be able to evaluate the exclusive correlation between the water recovery and the bubble surface area flux and/or the bubble size. It is worth mentioning, that the particle size of the hydrophobic particles did not show a significant effect on the amount of water going to the concentrate. Not surprisingly, experimental results demonstrate that water recovery increases with the bubble surface area flux and with the gas hold-up."

Jan 1, 2014