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By S. M. Bradshaw, C. Dorfling, F. Ngandu

"Selenium removal and platinum group metal (PGM) recovery from copper sulfate leach solutions form an integral part of platinum producers’ base metal refinery operations. Recent studies found that substantially higher PGM recoveries can be achieved if excess thiourea instead of sulfurous acid is used as precipitation reagent; however, the impact of the proposed process on downstream processes was unknown. The objective of the current study was therefore to investigate the effects that excess thiourea and residual selenium present in the rich copper sulfate electrolyte have on copper electrowinning. This was achieved by performing cyclic voltammetry tests using a platinum rotating disk as working electrode, a graphite auxiliary electrode and a saturated calomel reference electrode. A synthetic copper sulfate electrolyte containing 0.01 M Cu2+, 1 M H2SO4 and varying amounts of selenium (20 – 150 mg/L) and thiourea (10 mg/L and 100 – 300 % excess) was used. The results obtained have shown that both thiourea and selenium interact with the cupric ion cathodic reduction reaction. Thiourea polarized the working electrode and lowered the efficiency of the cupric reduction reaction. Tests on the solutions with high selenium concentration showed simultaneous reduction of copper and selenium, which led to copper selenide formation. Nodule formation on the deposit surface also became significant at higher selenium concentrations. Based on these results, it was concluded that precipitation of PGMs from the copper sulfate solution with excess thiourea is not feasible due to the detrimental effect on downstream electrowinning operations.INTRODUCTION During the high pressure oxidative leaching stage in a typical base metal refinery (BMR) circuit, selenium, tellurium and some platinum group metals (PGMs) are dissolved along with the desired copper ions. The impurities (selenium and tellurium) may pass to the copper electrowinning circuit where it can result in the formation of nodular copper electrodeposits or reduced current efficiency. The presence of PGMs in solution, on the other hand, increases the precious metal inventory and potential losses of the operation. Currently, sulfurous acid is widely used for selenium and tellurium precipitation from copper sulfate leach solutions. Sulfurous acid is capable of reducing cupric ions to cuprous ions; the generated cuprous ions then react with Se4+ and Se6+ to precipitate selenium as a copper selenide (Bello, Dorfling, 2014). Recent studies have, however, proposed the use of excess thiourea as a precipitating agent for the removal of selenium and tellurium; it has the advantage of improved PGM recovery in the Se/Te precipitation step (Lottering, Eksteen et al., 2012; Mulwanda, Dorfling, 2015)."

Jan 1, 2018

By Javier Baladron, Mijail Villar, Brandt Henriksson

"In this presentation an overview will be given of what has been observed by the authors in the copper concentration industry, with a large diversity of tailing thickeners operating under different conditions, although many of them are located in the same neighborhood. A closer look will be taken at the reported performance from different sites and from different thickener designs, either conventional or high rate, including those that were retrofitted, regardless of the thickener brand. An analysis is also made of the generic correlation of the size of the thickener and the performance in terms of solids loading (or unit area) and % solids. The paper envisions a technology development route, makes a brief analysis of the economic impact of the suggested route and points out the need for development in technologies around tailings thickeners, such as automation, yield stress measurement, slurry pumping and construction methods."

Jan 1, 2014

By Derek Caizergues, Hurman Eric

Experiments have been conducted at around 1700°C to determine the possibility of carbothermic reduction of alumina under the presence of a metallic solvent. Total pressure of the system was reduced to around 30kPa and metallic nickel, iron, copper and tin were selected as the solvent. The highest recovery of aluminium was achieved with the nickel solvent followed by iron, copper and tin. This ranking for the first three was also in accord with the extent of negative deviation form ideality in the respective binary solutions of these solvents with aluminium. The tin-aluminium system displays positive deviation form ideality. The rate and extent of reduction was found to be highly dependent on temperature and pressure. The pseudo first order reaction rate was found to be applicable to the process in all the solvents used. Rate constants were calculated and it is also suggested that the reduction was controlled primarily by the chemical reaction rate.

Jan 1, 2003

By Trevor Saldanha, Stephen Grano

A key uncertainty in flotation modelling is determining, a priori, the proportion of each mineral which will develop a certain rate constant for different feeds of variable liberation and hydrophobicity. First and foremost is the ability to predict the proportion of minerals that will not be recovered, even at very long flotation times, and which therefore report to the tailing stream as the non-floatable fraction (i.e., having a zero rate constant). Recent empirical evidence has shown there are at least two factors which contribute to heterogeneity in flotation rates and, in particular, the appearance of a non-floatable fraction - heterogeneity in the distribution of adsorbed collector amount on a particle-by-particle basis, even for the same liberated mineral in the same size fraction, and the existence of a critical contact angle below which the bubble-particle union is unstable. In this paper, inferred measures of the critical contact angle for liberated particles are compared with stability model calculations. This has demonstrated that the dependency of the critical contact angle with particle size and mineral specific gravity are explicable by bubble-particle stability considerations. This argument is further extended to the flotation behaviour of composite particles, as a function of liberation class, in which the wetting perimeter of the attached bubble on the composite particle surface is constrained by the presence of a surrounding hydrophilic domain for the case of simple binary composites. Reasons for the different flotation behaviour of composite particles having different textures, as noted in the literature, are also discussed in terms of the stability of the bubble-particle union.

Jan 1, 2014

By Sergio Castro, Janusz Laskowski

In the flotation in highly concentrated electrolyte solutions not only ionic strength but also chemical composition, flotation pH and mineral properties play an important role. As a result an improvement or depression may be observed. A strong improvement in the floatability of hydrophobic bituminous coals and other inherently hydrophobic minerals is characteristic for the "salt flotation process", which is carried out in concentrated electrolyte solutions at natural pH and without addition of any flotation reagents. However, pH is a key factor when saline and hipersaline waters with hydrolyzing metallic ions are used as process water. In the case of flotation of Cu-Mo sulfide ores in seawater, molybdenite is strongly depressed by the Mg2+ hydrolysis products when pH is raised to depress pyrite. Process water with a high content of Mg2+ and Ca2+ ions, and this also includes seawater, have deleterious effect on the anionic flotation of industrial minerals with fatty acids. The flotation of potash ores is carried out in NaCl-KCl saturated brine (6-7 mole/L of NaCl and KCl) with the use of long-chain amines. Such a high electrolyte concentration changes dramatically the amine Krafft point making the collector insoluble in brine; its mode of action entirely differs from that in conventional flotation processes.

Jan 1, 2014

By Gabriel Barrios, Juan Pérez-Prim, Marcelo Tavares

"The application of High Pressure grinding Rolls (HPGR) has been growing in the mining industry for the last 10 to 15 years. The major benefits generally supporting this trend are better energy efficiency, improved grinding capacity, less sensitivity to ore grindability variations and higher metal recovery in downstream processes such as heap leaching and flotation. The HPGR machine comprises a pair of counter-rotating rolls mounted in a sturdy frame. One roll is fixed in the frame, while the other is allowed to float on rails and is positioned using pneumohydraulic springs. The feed material is introduced in the gap between the rolls and is crushed by the mechanism of interparticle breakage. Comminution performance is largely determined by the pressure exerted on the bed of particles by the floating roll hydraulic system. The operating bed pressure depends on the hydraulic system start-up parameters and the loading response of the feed material. The work describes how the coupling of the multi-body dynamic simulation with Discrete Element Method in which particle breakage is described using the particle replacement method, can be effectively used to predict the performance of the HPGR. The model considers important variables as the HPGR rolls geometry and design, the hydraulic spring system start-up parameters and the material loading response, to describe operational key outputs as material throughput, operating gap and roller pressure distribution. The preliminary version of the model has been used to predict the effect of material properties on the operating gap and the load distribution on the surface of the rolls, demonstrating that it can describe qualitatively the HPGR operation, indicating that the model will be a power full tool for the simulation and selection of industrial HPGR units."

Jan 1, 2014

By A. J. Lynch, L. Ergun, M. Oner

"A research program on modelling cement grinding circuits has been in operation at Hacettepe University, Ankara, for four years. It has concentrated so far on tube mill and air separator grinding circuits for cement clinker, with emphasis on plant sampling surveys, including axial sampling inside the tube mills. The data used for model development have come from 33 surveys in 9 plants.The operating conditions have been:- mill sizes - 3.2 to 4.8 metres diameter and 8.5 to 15 metres long,- mill feed rates - 46 to 158 tonnes per hour,- air flow through mills - 25000 to 125000 cubic metres per hour,- cement clinker work indexes - 10.3 to 18,- separator sizes - 2. to 3.1 metres diameter,- separator feed rates - 132 to 689 tonnes per hour,- separator speeds - 12.3 to 21 metres per second.The ball mill model is Whiten’s perfect mixing model and the separator model is the Tromp curve with a fish-hook. This paper emphasises the importance of calculating the breakage rates and the discharge functions with three case studies at five different circuits which were selected for discussion because they show how particular features of circuit operation can be included in the general models. Size distribution graphs are used to illustrate every aspect of the discussion"

Jan 1, 2003

By W. Fander, Zhonghan Zhang, T. Choo, J. Enraght-Moony

"This paper describes the mineralogical and metallurgical procedures used to determine the recovery and concentrate grade of heavy oxide minerals occurring in lode deposits. The data produced also provide vital information to the processing engineers, which allows them to develop the most suitable flow sheet for that particular heavy mineral, here called an Economic Oxide Mineral (EOM). It demonstrates how results are interpreted to ensure that the proper process is used at each treatment stage to optimise recovery and to produce the most suitable concentrate at that point. Reference is made to some of the current equipment and techniques that can be used to process EOMs. The paper shows that when assessing the economic potential of a new ore body, or existing ore treatment plant, ore characterisation (OC) is necessary. This is especially true for EOMs such as cassiterite (SnO2), wolframite ((Fe, Mn, WO4,) pyrochlore ((Na,Ca)2Nb2O6(OH,F)), and tantalite (MnTa2O6) where often what seem to be small changes in ore types can have major effects on recovery and concentrate grade. Due to advances in flotation technology scheelite (CaWO4) in some deposits can be less vulnerable to OC variability than other EOM’s. Thorough mineralogical examination is shown to be the fundamental basis of correctly undertaking OC. This is because mineralogical analysis identifies each of the steps required to ensure that all ore types and zones are recognised, and differences explained, and shows the benefit in using reference samples to compare differences in the ores. The OC methods used for EOMs containing metals such as tantalum, tin, tungsten and niobium are similar; if two or more of these EOMs occur in one deposit as separate minerals, then OC will show when and how these minerals should be separated. The OC techniques described for EOMs can also be tailored for other heavy minerals, precious metals and graphite."

Jan 1, 2014

By Johan Nell, Paul den Hoed

"Carbochlorination tests were conducted with matched particle-size fractions of rutile, ilmenite and hightitania slag in a small bubbling fluidized-bed reactor. The effects of temperature, the type and proportion of solid reductant in the charge, and the fraction of Cl2 in the fluidizing gas were investigated. Tests confirm the need for solid carbon in the bed if chlorination is to run at high rates. With solid carbon in the bed, CO supplied with the fluidizing gas does not increase significantly the degree of chlorination after 75 minutes.When large proportions (30 wt%) of carbon are added to the charge, then the reactionTiO2 + 2C + 2Cl2 = TiCl4 + 2COis favoured overTiO2 + C + 2Cl2 = TiCl4 + CO2Ilmenite is chlorinated more quickly than titania slag, which in turn is chlorinated more quickly than rutile. Rates of chlorination at 1100°C and 1000°C are much the same and significantly higher than at 900°C. Chlorination is associated with significant increases in particle porosity (even for rutile), which is brought about by the rapid initial chlorination of FeO and MnO (in ilmenite and slag) and (it is argued) by the chlorination of Ti2O3 which forms at high-energy surface sites."

Jan 1, 2003

By Sergey Ulianov, Arkady Senchenko, Alexey Shvets, Arkady Bakotin

"This paper is devoted to ultrafine grinding of processing products. This process allows one to include into operation complex ores which earlier were considered as inefficient and economically inadvisable to treat. Fine dissemination of valuable component often does not allow its liberation via standard grinding in ball mills, and therefore requires modern methods of ultrafine grinding (UFG). An example of successful ultrafine grinding usage is its application for crude flotation concentrates regrinding before cleaner flotation stages. A problem often arises with a commercial copper concentrate production in the course of copper ore flotation. Crude flotation concentrate regrinding in a ball mill does not provide for good liberation of the material before cleaner stages. UFG application allows one to get commercial copper concentrate with copper grade of 20% and higher. Another example of ultrafine grinding application is its usage for highly refractory pyrite product received after gold-lead scavenger flotation of polymetallic ore. Earlier this product treatment was economically inefficient. At current application of ultrafine grinding down to 85% minus 20 µm and subsequent gravity processing it is possible to pass major part of gold (73.4%) into concentrate. The constraining factor for UFG application in processing may be the chemical activation of minerals. In the result of this, flotation selectivity may decrease. Therefore ultrafine grinding application extends the areas of efficient usage of metallurgical processes. New technologies allow increasing the level of valuable metals recovery."

Jan 1, 2014

By Thomas Mütze, Petya Atanasova, Kai Bachmann, Urs A. Peuker, Thomas Leißner

"A method is presented for the evaluation of mineral processing by liberation and upgrading. The method bases on the plot of recovery of valuables versus the recovery of gangue (Fuerstenau upgrading curve). The locking curve of a feed material was plotted together with the upgrading curve in a Fuerstenau diagram. The assessment of liberation and upgrading is done by a comparison of surfaces formed by the curves and some characteristic lines of the diagram. This plot allows the calculation of two new quantitative measures for liberation and upgrading. Both parameters can be combined to a third parameter describing the quality of the whole technical setup for mineral processing by subtracting the upgrading parameter from the liberation parameter. The third parameter shows a positive value in cases of upgrading determined processes, a negative value in cases of liberation affected processes and about zero for processes affected equally by liberation and upgrading. Thus it is easily possible to distinguish between poor results in the mineral processing caused by insufficient liberation or poor results caused by insufficient upgrading. Preliminary results from two case studies, performed on two different ore types, are very promising illustrating the practical use of such an approach."

Jan 1, 2014

By Jia Muxin

The adsorption behaviors of metal ions on a silicate mineral and the flotability of a metalized silicate mineral with sodium oleate as collector are closely related to the structure of the silicate mineral. The adsorption isothermals of the metal ions on different silicate minerals are studied, the parameters of the isothermal give the information how many surface oxygen anions a metal ions is attached to, from this information and the structure of the mineral the site where a metal ion is attached can be guessed (The adsorption isothermals and adsorption behaviors with pH are fitted with Temkin, Frenudlich and Kurbatov equations respectively). Metal ions as Cu2+, Ni2+, Zn2+ are attached to the oxygen anions of surface species –Si-O– on the quartz surface, most of them coordinate to only one surface oxygen, their adsorption ability on quartz is low, but this metal ions on quartz surface protrude out of the surface perfectly, so their ability to combine with oleate acid radical is excellent. Quartz can be activated well by such metal ions. The isothermal of Fe3+ on quartz indicates these cations coordinates with more than two surface oxygen anions. This means the Fe3+ nucleates on quartz surface in the form of Fe(OH)3 colloid particles. The isothermals of Cu2+, Ni2+, Zn2+ Fe3+ on spodumene shows such ions coordinate with more than two surface oxygen anions, it indicate these ions may attach to the position where Li+ is formerly exists, such metal ions stay in a cave on the mineral surface, their adsorption abilities on spodumene are quite well, but they are affect by the oxygen anions of the two Si tetrahedron chains, the can almost not activate this mineral. These cations may attach on the site where Al3+ exists on the muscovite surface, just like spodumene, muscovite can not be activated well by such cations. Pt2+ has a large ion radius, as Pauling’s rules depicts polyhedron can not attach to Si tetrahedron well, the adsorption ability of Pt2+ on quartz is low and quartz is activated badly by Pt2+. On the other Pt2+ can adsorb well on spodumene and muscovite well and activated them well because it is not affected so bad by the tetrahedron oxygen anions of the minerals for their its large radius. The isothermal of Ca2+ on quartz indicates a Ca2+ coordinates with less than one surface oxygen anion, this means Ca2+ attaches on quartz mainly by physical adsorption. The adsorption abilities on mineral surface and the interaction abilities with oleate acid radical of the transition metal ions with the same valence are guessed to be determined by their d electron number, the rules should be d1<d2<d3<d4>d5<d6<d7<d8<d9>d10. Hydrogen bond may play an important rule in the activation of the mineral by HF and the interaction of the HF activated silicate mineral with collectors. The general rule is high bond valence and small metal ion radius surface species –Me-O can be activated well by HF with sodium oleate as collector. For example – SiIV-OH is neutral while –SiIV-FH+ and –SiVI-FH+0.33 are positively charged, the positively charged surface species are more likely to connect oleate acid radical via hydrogen bonds.

Jan 1, 2003

By Nicolás Luis, Qi Liu, Gonzalo Montes-Atenas

"The prediction of froth flotation performance is still an unresolved topic. Classic industrial models based on particle size, elemental and mineralogical information provides recovery results with deviations that may become significant. One possible reason for this deviation may be the fact that the current liberation analysis provided by electron microscope based techniques does not take into account the outmost surface layer composition of liberated particles. In order to complete the description provided by the liberation analysis, other spectroscopy techniques measuring the extreme surface of the minerals can be tested. For instance, X-ray Photoelectron Spectroscopy (XPS) is a technique which measures the first tens of nanometers providing elemental composition over the particle surface and allows resolving the elemental associations present at the surface sample. However, this information needs to be statistically robust, reproducible and most importantly representative of what is occurring in the process. The aim of this research work is to develop a statistical model based on particle population to evaluate the feasibility of turning the XPS technique into a metallurgical tool. The model consists of classic statistical population arranged in a bed of heterogeneous particles with a known grade and mineral liberation. The simulations showed that the XPS results statistically followed a well-defined pattern. The statistical results were confronted with pilot plant results obtained from a rougher bank when processing a copper sulfide ore from a Chilean mine site. It was observed that the probability function distribution was in agreement with the experimental data. Further analysis on how the XPS results provide valuable information improve the computation of froth flotation recoveries is also discussed."

Jan 1, 2014

By A. Otsuki

This paper describes the evaluation method of dispersion and coagulation of silica nano-particles by means of interactive force apparatus. The apparatus measures the size of fine particles in aqueous solution or organic solvent of high concentration and/or low optical transparency. Other conventional apparatus for size measurements (such as, apparatus utilizing dynamic light scattering) are difficult to measure the size of particles in such conditions accurately, due to multi-scattering of light in the sample solution or solvent. The apparatus measures the interactive force between two surfaces, i.e. the gold-coated glass hemisphere and the brass flat plate, (which is fixed at the bottom of the sample cell). The apparatus has three parts, i.e. main part (which consists of electric balance, hemisphere and flat plate), control part (i.e. personal computer, piezo-stage controller and voltage supplier), and detecting part (i.e. multi-meter and oscilloscope). During the measurement, electric field is applied between the hemisphere and flat plate, and thus dielectric particles are arranged toward the direction of electric field in the area between two plates. When the two plates are close to each other, two different forces (i.e. repulsive force and attractive force) will alternately act on particles due to the structure change of the particles. The repulsive force occurs when the structure of particles is stretched by compressive force; whereas the attractive force occurs when the aggregate structure is broken. The cycle of the repulsive and attractive forces is a primary size of particle or size of aggregate, which depends on the degree of agglomeration. The measured size of particles, which is varied depending on their degree of dispersion and coagulation, determined the characteristics of the silica particles. In this research work, the effect of size and concentration of particles in aqueous solution on the degree of dispersion and coagulation of the silica particles were investigated. Spherical silica particles were selected for this investigation due to their variety of size. This apparatus can be used to evaluate the degree of dispersion and coagulation of other nano-particles in various solvents in many process industries.

Jan 1, 2014

By Rodrigo Ladrón, Gonzalo Rund, Gonzalo Montes-Atenas

Modelling ore comminution processes have been a highly fruitful scientific topic. The models have been proved to be largely dependent on the selected comminution technology. Among them, semiautogenous (SAG) mill technology has been widespread implemented in plants but no complete understanding of the mechanisms involved in the process is available. Tracing back in history, SAG models considered only some granulometric cut sizes such as the t10 and attempted to relate these parameters with the energy involved in the impact between particles. Other models evolved towards incorporating physical properties of the material being ground and the mill operating conditions. These material properties have assisted to obtain a more comprehensive description of the breakage mechanisms; nevertheless, the gathering of all known parameters still have not delivered a model able to describe the process. This may be a result of emergent properties or phenomena originated from interactions inside the process which are hard to predict turning the size reduction operation into a complex system. Cellular automata provide one answer to describe complex systems by following simple rules. The aim of this research work is to establish the preliminary rules of thumbs enabling the implementation of cellular automata able to predict the particle size distribution at the exit of a SAG mill. The methodology involved developing a simple 2D model of a ROM sample. Plant data from two mine sites were correctly described by a set of three rules: two rules describing the particle reduction and one rule associated with material transport across the mill. Further analysis related with expanding this model to 3D and its impact on the liberation of valuable material is also discussed.

Jan 1, 2014

By J. W. Ahn

Calcined calcium oxide from limestone is hydrated to manufacture calcium hydroxide, and then precipitated calcium carbonate is synthesized from calcium hydroxide. Precipitated calcium carbonate of various morphologies is obtained by controlled conditions of each step and characteristics of limestone, calcium oxide and calcium hydroxide. Especially characteristics of calcium hydroxide have the most influence on morphology of precipitated calcium carbonate character. In this study, therefore, it is investigated the specific surface area of calcium hydroxide and morphology of precipitated calcium carbonate according to hydration temperature. Calcium hydroxide hydrated at high initial temperature has larger particle size than that hydrated at low initial temperature. And formation yield of aragonite precipitated calcium carbonate has improved by using calcium hydroxide had larger particle size (hydrated at high initial temperature).

Jan 1, 2014

By Rajamani R. K.

The design of tumbling mills has progressed from the Bond work index concept of the 1950s to the population balance concept of the 1980s and then made a quantum leap forward with the discrete element method in the 1990s. The failure of a SAG mill at the Grasberg mine site set in motion the inquiry into the role of shell lifter geometry on the profile of the charge motion within the mill. Quickly, it became evident that this could only be accomplished by tracking individual motion of ore particles and grinding balls and not by study of en masse motion of the charge that had been established previously. The discrete element method (DEM) which was prevalent in the civil engineering literature at that time proved suitable to tackle this simulation problem. In 1991, the two dimensional simulation of laboratory scale mills was validated with the DEM. Later this simulation method evolved into ?MillSoft?? a simulation software package for the design of lifters in ball and SAG mills. MillSoft?simulations proved that cataracting charge motion is not conducive to the life of lifters. The old rule of thumb that the number of shell lifter rows should equal twice the diameter of mill in feet was shattered by simulation results. Instead, the number of rows equal to the diameter of the mill in feet, providing that the lead angle of lifter is around 25 degrees, was established as being more optimal. This bold design change was first implemented and tested by Mark Sherman at Alumbrera Mines in Argentina. Two 36-ft SAG mills responded extremely positively to the design change. This success was immediately repeated at Collahuasi, Pelambres and other mines in South America. The design change has so far exceeded expectation that there is not a single SAG mill around the world today that does not employ a relief angle on its shell lifter. The DEM method has advanced in the hands of the author, mining companies and universities, notably in Australia and South Africa. Today, three-dimensional simulation of charge profile and slurry transport is a standard in the design of mills. There is strong pursuit of a virtual comminution machine with DEM in Australia. In South Africa, an experimental method known as positron emission tracking is emerging as a method for tracking particles in grinding mills. The computational burden of computing with millions of particles in three-dimensional simulations has been eased to less than a day with a technique known as GPU computing. Keywords: DEM method, GPU computing, SAG mill, tumbling mill simulation, discrete element method

Sep 1, 2012

By C. Dorfling, S. Bradshaw, J. Eksteen, M. Khesa, C. A. Snyders

Titaniferous ores serve as a major feedstock for the production of a white titanium dioxide pigment, a titanium metal and several other titanium-based products. Such ores exist mainly as heavy mineral sands. Ilmenite is upgraded to intermediate products namely synthetic rutile and titania slag through the synthetic rutile route and the reductive smelting route respectively. Tronox KwaZulu Natal Sands (Pty) Ltd recovers high titania slag via the reductive smelting process while slag is used as a feedstock to the pigment industry and furnace dust from the gas cleaning plant is disposed as waste. Previous investigations have shown that such furnace dust can contain significant amount of titanium-bearing minerals. This study looks at the characteristics of the furnace dust obtained from Tronox KwaZulu Natal Sands and investigates a possible high temperature recovery route in detail. The furnace dust was examined by using x-ray fluorescence, x-ray diffraction, microscopy and laser-diffraction size analyses. The characterization work showed that the furnace dust was rich in titanium and iron, containing 49.4 wt% ??????2 and 29.5 wt% ????2??3. These oxides were associated with Si, Mn, K, and Al oxides as impurities. A Carbolite® vertical tube furnace was used to investigate the extent of formation of titania slag and metallic iron on a laboratory scale at 1500°C, 1600°C and 1650°C. The laboratory reduction tests revealed that the slag samples with an equivalent titanium dioxide content ranging from 70.9 -76.9 wt% at 1600°C and 1650°C could be obtained. The Fe content of the metallic iron samples produced ranged between 93.0 and 97.1 wt%. The experimental results were found to be in relatively good agreement with the FactSage simulations, both of which demonstrated the potential of producing a titania slag and a metallic iron from the furnace dust.

Jan 1, 2018

By Chao Li, Kym Runge, Saeed Farrokhpay, Dee Bradshaw

"It is well known that froth phase has a controlling influence on the overall flotation performance. Froth recovery is expected to be affected by froth transportation behaviour. The latter has been represented by different volume balance and energy balance based models. In froth transportation models based on a volume balance, the froth phase is divided into different zones. The total froth residence time is the sum of the time spent in each zone and is dependent on the cell geometry, bubble burst rate and the position that bubbles enter into the froth phase. Alternatively, the froth transportation model based on an energy balance treats the froth phase as a block. In this model, froth height above the concentrate lip is being predicted by minimising the energy of the system which is dependent on the froth geometry, froth stability and froth rheology. The froth height can be used to calculate the froth efficiency of delivering mineralized bubbles from the pulp to the concentrate lip. This paper critically analyses the current models of froth transportation in flotation, and examines the limitations of these models. The importance of froth rheology, which is the resistance to the froth flow towards the discharging weir, in determining froth transportation, is also highlighted."

Jan 1, 2014

By J. Kwon, D. Lee, H. Cho

"The use of the combined grinding and liberation model to predict liberation characteristics of iron ore comminuted by a ball mill was studied. Comminution characteristics were obtained using the one-size fraction method. The iron ore samples were crushed and separated into a number of narrow size fractions by screening. The size fractions were further divided by magnetic separation into three classes: concentrate, middling, and tailings. Subsequently, various size-grade classes were subjected to ball milling, and the results were analyzed in terms of the kinetic grinding model. The mineralogical textures of the grinding products were analyzed using mineral liberation analysis. The distribution of iron content within the size fractions was characterized by the beta distribution combined with the Andrew–Mica diagram. It was found that the grinding characteristics of the iron ore samples varied slightly with the iron content. However, the liberation characteristics were well described by the same set of liberation model parameters, regardless of composition. The variation in grinding kinetics with composition and the liberation model parameters was used in the combined comminution–liberation model to predict the evolution of the size-composition matrix as grinding proceeded. The predicted results agreed well with the experimental results. The developed model can be used to construct the yield–recovery graph and to calculate the liberation efficiency to determine the size reduction threshold for efficient separation. INTRODUCTION In mineral processing, comminution is usually the first step that ores undergo to liberate valuable minerals from gangue minerals. Generally, as the particle size decreases, higher liberation can be achieved. However, excessively small particles are unfavorable to subsequent processes, such as separation. Moreover, comminution is a highly energy-consuming process itself that accounts for approximately 60% of all energy used for processing. Therefore, there is a definite need to increase energy efficiency by applying adequate stress so that a high degree of liberation can be acquired at the coarsest size without overgrinding. To this end, it is essential to develop a model to predict the liberation of minerals as a function of size reduction."

Jan 1, 2018