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By Cheng Gan, Gui Xiahui, Li Shulei, Cao Yijun, Liu Jiongtian, Wu Lun

Flotation rate constant is an essential parameter in the flotation process. The fine coal sample utilized in this investigation is anthracite from the Shenhuo mine in eastern China. Fine coal flotation rate tests were conducted to compare the flotation rate constant at constant power input with that at gradually increasing power input. Results indicate that the flotation rate constant decreases with the flotation process and increases as the flotation energy is increased. In addition, the flotation rate constant is close to the maximum value. The increasing trend of the flotation rate constant gradually slows down as the flotation energy input increases.

Jan 1, 2014

By Alejandro Uribe-Salas, Fabiola Nava-Alonso, Gloria Dávila-Pulido

This paper presents results of an experimental study performed on the role of calcium sulfate present in flotation water on sphalerite flotation in the Pb/Cu circuit (non Cu-activated sphalerite) and in the Zn circuit (Cu-activated sphalerite). In the Pb/Cu circuit calcium ions adsorb on the negatively-charged sphalerite favoring xanthate adsorption and therefore making sphalerite floatable; experimental measurements show sphalerite contact angle increases with calcium concentration while xanthate adsorption onto sphalerite increases with the increase of pH and calcium concentration. Gypsum (CaSO4·2H2O) eventually present due to calcium sulfate precipitation is not detrimental to flotation at this stage since it is negatively charged at pH 9 and therefore, does not adhere onto the surface of negatively-charged sphalerite. In the zinc circuit, Cu-activated sphalerite decreases its negative charge (or even becomes positively charged) and develops some hydrophobicity due to the polysulfide produced by Cu-activation. At this stage calcium ions do not interact with the mineral surface and therefore do not favor xanthate adsorption; nevertheless, precipitated gypsum particles do adhere onto the mineral surface, greatly affecting its floatability (e.g., contact angle). Addition of sodium carbonate to dissolve gypsum and to precipitate calcium as calcium carbonate, which disperses in the bulk of the suspension, effectively restores mineral hydrophobicity. SEM observations coupled with EDS analysis clearly illustrate and support the above sequence of events.

Jan 1, 2014

By Matt Kilburn, Liming Lu, Steve Suthers, Alexander Edenton, Rodney Smyth, Matt Adam

"Magnetite concentrate is naturally good for pelletising. However, due to the depletion of reserves of traditional high grade hematite iron ore worldwide, the usage of magnetite concentrate in sintering is expected to increase substantially. Magnetite concentrate is typically high in Fe grade and releases extra heat when oxidised to hematite. This will not only improve the quality of agglomerates produced, but also have a potential beneficial impact on the fuel consumption of the agglomeration process. There are an increasing number of magnetite projects currently being considered and developed. However the concentrates from some of these projects are too coarse as pellet feeds and much finer and denser than normal sinter feeds. Accordingly, special strategies are required in order to utilise the coarse magnetite concentrates at high proportions in pelletising and sintering. This paper discusses various raw material preparation technologies and blending optimization methods demonstrated to be effective for improving the sintering and pelletising performance of coarse magnetite concentrates. Pre-granulation and addition of binders, such as hydrated lime, were found to be particularly efficient in recovering the sintering productivity of sinter blends containing magnetite concentrates. In pelletising, HPGR (High Pressure Grinding Rolls) grinding enabled production of good quality pellets from 100% magnetite concentrates and optimized blends containing up to 70% magnetite concentrates also formed good pellets.INTRODUCTION Magnetite concentrates are often used as feed materials for pellet plants or sinter plants depending on their grades and grain sizes. To achieve the required quality of green and fired pellets, the concentrates often need to be ground very fine (80% passing 38- 45 m), which inevitably consumes a great amount of energy. Therefore, efficient grinding processes are required to reduce the amount of energy consumption needed to achieve the sizing and chemical specification of pellet feeds. The use of magnetite concentrates in sintering has the potential to improve sinter chemistry, which is deteriorating over time due to the slowly decreasing grade of direct shipping iron ores around the world (Yang and Mathews, 1997; Yang and Witchard, 1998, Yang and Davis, 1999; Yang 2005). However, methods are required to allow the utilisation of high levels of concentrates in sintering while maintaining productivity and sinter quality (Han and Lu, 2017)."

Jan 1, 2018

By Jussi Liipo, Pertti Lamberg

Image analysis of process samples gives precise data on particles and their composition. The results presented as liberation tables and maximum grade-recovery curves are informative and good for comparing different feed materials, but basing on them it is impossible to predict the results of the mineral separation process (flotation, magnetic separation, gravity separation) in details. The exact and extensive particle data has remained large unused, because there has not been a model nor a modeling program to include particle information in mineral separation processes. This study introduces a method, which incorporates the particle data in the kinetic model of flotation. Similar approach can be used in modeling other separation processes, too.

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 David I. Verrelli, Boris Albijanic

"Froth flotation is an exceedingly complex physicochemical process. The convenience of distilling much of the complexity of the bubble-particle interactions into a single parameter has led to the continuing popularity of the classical ‘induction time’ to quantify the threshold for bubble-particle attachment to occur. Despite this popularity and the simplicity of the concept, there is no single universal method of evaluating the induction period. In this paper, we begin with a critical review of the available techniques for estimating the induction period. These are: back-calculation from experimental (micro) flotation tests; pushing a particle toward a stationary bubble (or vice versa) using an atomic force microscope (AFM); pushing a bubble toward a stationary bed of particles in the ‘Induction Timer’; pushing a bubble toward a stationary solid surface using the ‘integrated thin film drainage apparatus’ (ITFDA); and dropping particles onto a submerged stationary bubble using the ‘Milli-Timer’ device. Each one of these methods has advantages and disadvantages, and the best choice depends on the application. In the experimental section, we present quantitative comparison of the induction periods estimated using two different techniques, namely the Induction Timer and the Milli-Timer. The same particles were tested in each device, under the same conditions. It was found that by tuning the operation of the particle pick-up device, similar estimates of induction period could be obtained to the estimates made by direct observation with the Milli-Timer. In the former device a bubble is driven toward a particle bed at a controlled rate, whereas in the latter a particle’s motion is governed by the hydrodynamics. The potential to match these presents an intriguing prospect for better understanding the bubble-particle interaction, and the possibility to ‘calibrate’ the simpler Induction Timer against direct observations."

Jan 1, 2014

By Jan Svoboda, Toyohisa Fujita

"The current status and history of innovation in magnetic methods of material treatment are reviewed. The milestones and key drivers of innovation are identified, advantages of magnetic separation in comparison to other physical methods of material manipulation are discussed and reasons for failure to live up to its potential and expectations are identified. The future focus in such diverse areas as mineral processing, waste treatment, recycling and biosciences is discussed and the research and development needs are outlined.Our walk through the innovation landscape in magnetic separation illustrates the enormous effort that has been expended over the years to convert a wealth of novel idea into workable techniques. Remarkable progress has been achieved and numerous successful innovations have been introduced into material treatment operations. On the other hand these techniques have experienced their fair share of failures. The reasons for these cover a wide spectrum of risks that accompany any effort to implement new technology."

Jan 1, 2003

By C. Gomez, J. Finch, R. Dalhke, J. Torrealba-Vargas

"The dispersion of gas into bubbles is an essential feature of flotation machines. Three measurements have typically been used to describe the dispersion: superficial gas velocity (Jg), gas holdup and bubble size along with the derived quantity, bubble surface area flux. Measurement devices continue to be developed. The McGill Jg sensor based on accumulating bubbles by natural buoyancy comprises a tube with a valve and pressure transducer (Figure 1). The tube is immersed at a desired location and depth (H1) in a flotation cell. On closing the valve pressure increases to a maximum (P1) when the tube is full of air. The Jg is estimated from the slope of pressure-time curve (dP/dt).The relationship between Jg and dP/dt is derived from first principles. Testing the relationship is difficult in a flotation machine as the spatial variation in Jg is generally not known. This problem is overcome using a specially designed experimental setup and the estimated Jg is shown to equal the known Jg.The derivation reveals the importance of bulk density (?b). The sensor was modified to provide an estimate of ?b (Figure 2). A second tube was added immersed to a different depth (H2) and kept full of accumulated air giving a pressure P2. The estimate of ?b is given by (P1-P2)/(H1-H2) (i.e., at the end of collecting the pressure-time data). This two-tube sensor also helps dampen process noise as illustrated by a sudden change in level when collecting the pressure-time curve. Both the original and modified versions have been widely used in plant test work."

Jan 1, 2003

By Marco Le Roux, Martha Van Rensburg, Quentin Campbell

Fluidised bed drying is currently receiving much attention as a dewatering option during the beneficiation of fine (defined here as between 1 mm and 2 mm particles) coal. Apart from concerns about safety and combustion, the operating costs can be high if very high gas or air temperatures are used. The aim of this study was to investigate the removal of moisture from fine coal by using air at a lower temperature (25 - 55°C) within a controlled environment by lowering of the relative humidity of the air. It was firstly proven that fluidization has a major advantage over non-fluidized beds, with regards to drying rate and final moisture content. Hereafter several parameters that influence the dewatering rate and final moisture content were tested, from which it was concluded that the relative humidity of air acts as the largest driving force for dewatering. Parameters tested included relative humidity, temperature and coal composition. Energy balances showed a positive nett energy increase in the dried coal during combustion when related to the energy input during drying. In comparison with thermal drying technologies, fluidized bed drying was proven to be less energy intensive. It was therefore shown that this is a viable technology for the dewatering of fine coal.

Jan 1, 2014

By Ljudmil S. Grigorov, Eric Forssberg, Hanumantha Rao Kota, Robert J. Pugh, Lidia B. Alexandrova

"The effects of mixed collectors on some physicochemical parameters (thin film lifetime, kinetics of expansion of the three-phase contact, equilibrium three-phase contact angle and surface tension) involved in the elementary act of flotation were investigated experimentally.We have used the microscopic thin balance developed by Scheludko et al (1970) to study the stability and interactions within the thin film between the silica surface and air bubble with (i) a long chain C10 amine and (ii) a cationic/anionic surfactant systems consisting of mixtures of a long straight C10 chain amine with long straight chain C8, C10 and C12 sulfonates at 1:1 molar ratio. The experiments were performed at a range of concentrations at pH 6.5. The equilibrium contact angle was measured with a microscope technique using the modified Mingins-Sheludko method (Mingins and Scheludko, 1979). The surface tension was measured by the method of Wilhelmy (Adamson, 1960). It was found that the mixed surfactants caused lower contact angles, lower rates of the thin film rupture and longer film lifetime, compared to the pure amine system."

Jan 1, 2003

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 T. A. Penzov

As a result of recent scientific and experimental studies new technical devices have been developed for monitoring and control the process of grinding. The description of microprocessor module MILLCONT 1 for control of the loading of the mill and microprocessor density control module DENSIMETER is given in the paper. The improved variant of the automatic system for ore grinding control in single-stage ball mill working in close cycle with a classifier with above mentioned technical means is shown in the paper. The loops for measuring and stabilization of the basic technological parameters (density of the ready pulp ? and fineness of grinding of the pulp ß) are described in the paper. The nowadays economic results in ore grinding process automation are given as well.

Jan 1, 2014

By P. Knüpfer, B. Babel, M. Rudolph, F. Perez Maldonado, U. A. Peuker, L. Ditscherlein

"In heterocoagulation processes for the separation of mineral particles, the most famous being froth flotation, the main characteristic of separation is a differing wettability of the constituents to be separated. This most crucial property in the economically important process of flotation is often only and incompletely, quantitatively described in terms of contact angles against water. A water contact angle larger than 90° is referred to as hydrophobic and hydrophilic vice versa. Looking at Young’s equation shows that it is actually the surface energy of the solid in interaction with the surrounding phases and their surface energies (or surface tensions for liquids) which describes whether there will be hydrophobic/hydrophilic hydration interactions leading to attraction or repulsion. This, we have previously published for various more or less hydrophobic minerals in correlation to their flotation response, i.e. flotability (c.f. Rudolph & Hartmann, Coll.Surf.A 513, 380-388). In the same paper we also discussed the heterogeneity of wettabilities as assessed with the novel method of inverse gas chromatography. Furthermore we have also reported on hydrophobic force distributions as assessed with atomic force microscopy which are as well due to wettability heterogeneities (c.f. Fritzsche et al., Coll.Surf.A 459, 166-171).In this paper we present wettability distributions of different substrates and particles with various surface roughnesses/shapes and degrees of hydrophobization as assessed with iGC, AFM and dynamic sessile drop analyses. We are putting the results in context in unifying models and present methodologies helpful to make use of the fundamental information and their impact on the actual industrial separation process in fundamental process models. Besides froth flotation we also emphasize the impact on selective hydrophobic flocculation process."

Jan 1, 2018

By Seungwoo Park, Gaurav Soni, Roe-Hoan Yoon, Hyunsun Do, Kaiwu Huang

In a flotation froth (and foam), air bubbles become larger due to coalescence, causing bubble size to increase, bubble surface area to decrease, and hence casing less hydrophobic particles to drop off to the pulp phase below. Thus, bubble coarsening provides an important mechanism by which product grades are increased. On the other hand, excessive bubble coarsening results in low recoveries. In the present work, a model describing the process of bubbles becoming coarser in a foam as they rise to the top by deriving a mathematical relation between the Plateau border area, which controls film drainage rate, and the lamella film thickness, which controls bubble-coalescence rate. The model has been derived by assuming that liquid drainage rate increases due to slip at the air/water interface, and that the critical rupture thickness is determined by the capillary waves created by thermal motion. The model developed in the present work can predict the bubble size ratio between the top and bottom of a foam as functions of aeration rate, foam height, and surface tension (frother dosage). The model predictions are in good agreement with the changes in bubble sizes measured using a high-speed camera.

Jan 1, 2014

By Ghislain Bournival, Seher Ata, Yesenia Saavedra Moreno

"In froth flotation, frothers are commonly added to the pulp to modify the interfacial properties of bubbles. These properties may be modelled using commercial software packages. The volume of fluid (VOF) method was used to track the interface motion during the post-rupture oscillation of the newly formed bubble. The aim of this research was to provide an insight into the modelling of viscoelastic phenomena through the coalescence dynamics of two bubbles in solutions of various surface tensions using a three-dimensional computational study. Different surface tensions were used to simulate changes in methyl isobutyl carbinol (MIBC) concentration. The computational results were evaluated by comparing the oscillatory motion of the newly formed bubble for the different MIBC concentrations. For known MIBC concentrations, the deviations of the computational damping constants from the experiments were quantified, revealing possible deviations in the VOF surface tension model. In addition, the analysis provided insight into the flow patterns of the fluids and the effect of frother concentration on the velocity magnitude in the liquid and air phases. This analysis provided a further understanding of coalescence dynamic and post-rupture oscillation in froth flotation. Such a process is believed to affect the stability of particles at the interface due to the release of surface energy when the bubble surface is reduced.INTRODUCTIONIn froth flotation, bubble coalescence is an important phenomenon that is highly dependent on the interfacial properties of the liquid film between bubbles. It is known that the frother adsorption at the liquid-air interface changes the interfacial properties, resulting in an increase of surface elasticity and reduction of surface energy (Pugh, 2016). However, in a two-phase system, it is the frother type, concentration, frother molecule conformation at the interface and viscoelasticity properties that dictate film stability (Pugh, 2016). The viscoelasticity phenomena can be explained in terms of surface viscosity, which quantifies the energy dissipation at the interface and surface elasticity that represents the energy absorbed at the interface as result of bubble oscillation (Pugh, 2016). In the case of systems stabilized by nonionic frothers, it has been shown that surface forces alone do not account for film stability, but the viscoelasticity represents the ability to damp external disturbances in the thin film separating the bubbles and prevent coalescence (Santini et al., 2007)."

Jan 1, 2018

By Michael Young, Rodrigo Araya, Cesar Gomez, Le Huynh, James Finch

The performance of flotation machines is closely related to the gas dispersion characteristics achieved in their operation. It is known that frothers play a major role not only in the size distribution of the generated bubble population, but also on the swarm rise velocity. A program to characterize frother effects on two-phase hydrodynamics (air-water) of Jameson cells was undertaken in a fully instrumented pilot unit installed at McGill University. Gas dispersion parameters (gas velocity, gas holdup and bubble size distributions) of the gas-liquid mixture generated in the downcomer were measured after its release into the separation chamber. The unit was operated under different conditions including gas velocity, liquid jet velocity and frother concentration (MIBC). Bubble size distributions for concentrations above the critical coalescence concentration (CCC) were narrow with Sauter mean diameter between 0.6 to 1.3 mm. The bubble size followed the general trend as encountered in other types of flotation machines, i.e., rapid decrease with increasing frother concentrations below 10 µL/L, and almost no change in size for concentrations above 30 µL/L. The CCC was between 10 and 15 µL/L. Strong correlations were found between bubble size and air-to-liquid flow ratio (APR), and between the bulk density of the aerated solution in the separation tank and the vacuum inside the downcomer. An equation is proposed to estimate gas holdup in the separation tank from vacuum and bulk density readings.

Jan 1, 2014

"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 Kobus (J. J. ) Rossouw, P. Chris Pistorius, Johannes Sono

"Different coal properties are important in SL/RN (coal-based rotary kiln) direct reduction of iron ore, and in electrical smelting of prereduced iron ore. Laboratory simulation was used to evaluate two candidate coals, which were similar in volatile content and rank, but differed in reactive maceral content. The tests served to evaluate both the reduction rate (during direct reduction) and the dissolution rate of carbon from the coal into an iron bath.Reduction rates of mixtures of magnetite and devolatilised coal were assessed isothermally, using samples of 55 grams. The off-gas analysis was used to follow the extent of reduction. Results are shown in Figure 1 a). Coal B was expected to be more reactive, based on its higher content of reactive macerals (77%, compared with 61% for Coal A). In line with this, Figure 1 a) does show a higher reduction rate with this coal. However, increasing the reduction temperature increases the reduction rate substantially,especially for the less-reactive Coal A.For the dissolution experiments, samples (mass: 250 g) were melted in an alumina crucible (under a nitrogen atmosphere), to give a starting composition around 1%C. When the desired temperature was reached, 25 g of char was added on top of the melt, through a feeding port. Results are shown in Figure 1 b). The more-reactive Coal B was less crystalline (the graphite crystallite size estimated from X-ray diffraction was 4.6Å, compared with 11.4Å for Coal A). This is associated with a lower dissolution rate in iron."

Jan 1, 2003

By Jorge Menacho

"A typical Chilean producer in the Large Copper Mining Industry today is characterized by high production level with economical results decreasing but still attractive. Operational activities are developed within a low-productivity environment, with high cost and complex relationship between the company and communities, government authorities, providers, clients and their own workers. Decreasing copper grades and limited availability of energy, water and workforce are structural problems which require the State intervention in collaboration with the relevant actors and benefits would be evident in the middle or long term. Main opportunities in the short term are found in the sub optimal conditions we have at many plants today. Robust solutions to control existing operational management system as well as to supply systematic optimization options are needed. These should be oriented toward effective fulfillment of specific operational set points and also to reduce variability in crosscutting tasks. Solutions should include easy connectivity to existing information systems as well as to a suite of simulation and optimization tools settled in a highly interactive communication platform. Relevant issues include minimization of specific energy and fresh water consumption, maximization of the use and performance of critical equipments, minimization of damage to environment and control of effective application of good operational practices. Several specific examples are given."

Jan 1, 2014

By D. Pienaar, B. McFadzean, T. Jordaan

"Dithiophosphate (DTP) collectors have the lowest affinity for sulfide mineral surfaces compared to other common sulfide mineral collectors, such as xanthates and dithiocarbamates. In some cases it has been found that DTP does not adsorb onto the mineral surface at all and yet increases in recoveries and grades are noticed with the addition of DTP. Many studies have investigated the interactive effects of collector mixtures. However, there have been relatively few studies on the interactive effects between frother molecules and collectors. This study investigates the interactions between different types of frothers and sodium diethyl dithiophosphate.The study found that there were large increases in pyrite and galena microflotation recoveries at both pH4 and pH9 when DTP was mixed with small amounts of frother at a constant bubble size, showing that these increases were neither mineral-specific nor pH-specific. The same effect was not present when xanthate was used as a collector. The increases in recovery when using the DTP-frother mixture were similar irrespective of the type of alcohol or polypropylene glycol frother that was used. In an attempt to distinguish the mechanism of enhanced flotation recovery, various supplementary experiments were performed. It was found through adsorption experiments that no DTP was adsorbing on to the mineral surface. Therefore, interactions at the air-water interface were performed. Surface tension and critical coalescence concentration tests showed that, while DTP is a weak surfactant at the air-water interface, it does not have a synergistic effect in the presence of frother. DTP-frother mixtures do, however, show interactions in the froth phase, indicating an interaction in the thin films. It is proposed that there is a DTP-frother interaction on the bubble surface that enhances the rate of film thinning at the 3-phase bubble-particle contact."

Jan 1, 2018