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By Yuqing Feng, Ping Fang, Dezhou Wei, Zichuan Guan, Shuling Gao, Baoyu Cui

"Air core, as an inevitable phenomenon of rotational flow field inside hydrocyclone, has a major impact on hydrocyclone’s separation characteristics. The air core formation process, its structural features and its influencing factors were investigated systematically in this paper. Numerical study on the air core of a f50 mm hydrocyclone was carried out using a commercial computational fluid dynamics (CFD) modelling software package ANSYS/Fluent with the selection of Reynolds Stress Model (RSM) for the turbulence model and Volume of Fluid (VOF) for capturing the air-liquid interface. Physical experiments were conducted under the same geometry and operation conditions and the particle image velocimetry (PIV) technology was used to measure the liquid flow. The CFD results are compared with the experimental measurement with good agreement demonstrated. The air core was formed generally at around 0.7 s, air outsides of the air core was eliminated completely after 1.7 s. The centreline axial velocities and the water blocking hydrocyclone simulations showed that air of the air core entered the hydrocyclone from the underflow area and exhausted from the overflow area, but there was also some air flowing into the air core from the overflow area. The largest swing of the air core occurred on the top of the underflow pipe, and a protuberance similar to the shape of Adam’s apple appeared when the air entered the vortex finder. CFD simulation results also showed that the air core diameter was decided by axial position and parameters of hydrocyclone. The structural parameters have more effects on the air core diameter than the operational parameters."

Jan 1, 2014

By Prasad Kopparthi, Narasimha Mangadoddy, Balraju Vadlakonda, A. K. Mukhurjee

"Column flotation (CF) is widely using equipment in mineral processing since many years. ERT technique facilitates non-invasive and nonintrusive visualization of different parameters in a column flotation. The hydrodynamic investigation of two-phase and three-phase are studied using electrical resistance tomography (ERT) coupled with pressure transducers in laboratory column flotation. Bubble size distribution, bubble rise velocity and gas and solids hold-up hydrodynamic parameters are extensively used for column flotation design and performance evaluation. The effect of superficial gas velocity, feed flow rate and slurry height in the column on mean gas holdup and its radial distribution has been analyzed for both two-phase and three phase flows. Influence of solid particles on gas hold-up and its complete elucidation of dispersion in the column are assessed. Experimental results show ERT coupled with PT is suitable as an online monitoring tool to provide useful information on the hydrodynamic parameters of the column flotation. The tomography images, which were generated using a modified sensitivity back projection algorithm, were employed to explore the parameter study in two phase flow in column flotation.Furthermore, the results also indicate that ERT is a very powerful tool for diagnosing the `inside' flow behaviour of gas-liquid two-phase and gas–liquid–solid three-phase flow in columns operating for a wide range of flow regimes.INTRODUCTIONColumn flotation is being widely used in mineral processing industries in last few decades. There has been a lot of attention in understanding the various mechanisms that take place during operation. Due to many reasons column flotation has been found to yield better performance than conventional flotation cells, particularly with fine particles (Honaker and Mohanty, 1996). Due to complex flow behavior in nature, the performance of column flotation influenced by on flow characteristics of the process, (Jena et al., 2008). Previously basic research is carried out to evaluate the effect of the hydrodynamic parameters on the performance of column flotation (Finch and Dobby, 1991)."

Jan 1, 2018

By V. A. Masloboev, A. V. Svetlov, D. V. Makarov

"The methods of heap leaching are considered to be the most promising for the low-grade copper-nickel raw materials. The article presents intensification capabilities of the process. Objects of research: the low-grade copper-nickel ores of Moncheplutone deposits (Moroshkovoye Lake, Nyud Terrasa, Nittis-Kumuzh’ya-Travyanaya (NKT), as well as the copper-nickel ore dressing tailings of the “Kola MMC” JSC. The following directions for the intensification of the low-grade copper-nickel raw materials heap leaching have been considered: preliminary electric pulse destruction (EPD) of ore; ore crushing and further sulfuric acid agglomeration. The impact of sulfuric acid concentration (1-3%) on the extraction of non-ferrous metals kinetics from the copper-nickel ore dressing tailings under various conditions of the percolation leaching has been studied. INTRODUCTION The low-grade grade sulfide ores at the abandoned and producing deposits, overburden rocks, mill tailings and non-ferrous slag are thought to be one of the large-scale sources for non-ferrous metals, on the one hand. On the other hand, they are known to be the subjects of emergency environmental danger. For this reason, the use of mine dumps and tailings, as well as the remained ores left in the ground as raw products, and at the same time decreasing the load on environment, are considered to be the pressing ecological and economic issue (Chanturia et al., 2012). Methods of heap hydrometallurgical and bacterial leaching are sure to be potentially productive for processing such low-grade and technogenic raw materials (Petersen, 2016). The early studies of hydrometallurgical method possibility to process copper-nickel ores of the Murmansk region deposits were launched in the seventies of the previous century (Golovko et al., 1978). For referencing purposes, the main types of impregnated ores from the deposits Zhdanovskoye, Kaula, Sopchinsky Plast and Lovnoozerskoye were selected. The metal content varied, as %: 0.46-1.49 of nickel, 0.01-0.62 of copper. In the first experiments, the solution containing 150g/l of H2SO4 and 135g/l of NaCl, was used in the capacity of leaching reagent. The possibility of underground metals leaching from the ores of the Lovnoozerskoye deposit was justified due to the performed laboratory and further large-sized tests."

Jan 1, 2018

By H. Lieberwirth, M. Hesse

"Selective comminution (SC) is beneficial for the treatment of primary raw materials, especially if it is utilized in the pre-concentration process. Pre-concentration processes are applied in mineral processing to relieve subsequent processes and to achieve a higher efficiency. SC is also a promising method for the treatment of low-grade ores and waste dumps. With SC, various components can be separated such as valuable minerals from waste, ore from wall rock and different ore varieties within a deposit. SC is a property of a comminution system and leads either to a preferred crack propagation in one component (called preferential breakage) or to a preferred crack propagation along the grain boundaries (called interfacial breakage). SC results from different comminution behavior of various components in the feed material. For mechanical comminution, the preferential breakage seems to be the most important case of SC. Hereby SC generates only the difference in the particle size which can finally be used as a sorting parameter. A sorting process which uses SC depends on three parts: the feed material, the comminution machine and the separation machine. The feed material defines the potential for SC. Differences in properties like strength, toughness and density which are related to comminution are often used. The comminution machine has to exploit this potential. The extent of the exploitation can be influenced by the machine design, material and operational parameters. After SC, the various components are still combined in the product. So ultimately, a separation machine is needed. At preferential breakage, a simple screening machine can be used. The basics about SC will be presented at first. This contains relationships between material properties, the kind of loading in the comminution machine and the SC effect. These basics can be used for example to exploit a potential to SC for a pre-concentration step or to avoid the SC for a higher efficiency of subsequent processes. Based on recent investigations with impact load, the influence of the important parameters compressive strength, density, particle size and impact velocity to the SC will be shown, using examples of lead-zinc ore comminution and fluorspar processing."

Jan 1, 2018

By Takashi Furuyama, Sukeyuki Mori, Tetsuo Ikejiri, Abel Bissombolo, Yoshitsugu Koga, Masamichi Hata

In Japan, the increasing number of automobiles newly put into circulation is followed by a larger amount of end-of-life vehicles from which valuable metals are being recovered in shredder and related plants. Nevertheless, the processing of these scrapped automobiles which has reach a recycling rate of about 75%, generates a huge volume of waste, locally known as .shredder dust., which is commonly dumped on landfills. The saturation and depletion of valuable disposal sites in the near future, as well as the social and environmental problems related to the accumulation of these residues disposals are a major challenge for the automobile shredding industry. To promote an alternative way for the management of these disposals, the authors have initiated and developed a system for their processing, on the basis that more than 90% of these residues are combustible materials that could be used as refuses derived fuel. The developed processing system points out the mechanical/physical separation of shredded automobiles residues into two streams by means of an ascending airflow passing through a vertical zigzag separator and, the compaction of the light-density fraction of materials (that is about 60% of auto shredder residue recovered as float products and mainly composed of cotton, sponges and light plastics) to form a refuse derived fuel (RDF), the density, calorific value and ignition loss of which are 1.19 g/cm3, 4470 kcal/kg and 60.7%, respectively.

Jan 1, 2003

By Fedotov Pavel

"Today the main objective of improving the process of ore dressing is to reduce energy consumption and performance of the basic rule of auxiliary enrichment processes. One of the modern means of ore destruction with a minimum of energy consumption is the interparticle fracturing, for example in the roller press. There still remain the unsolved problems of the energy consumption determination and the particle size distribution of the crushing product .Existing methods for determining these parameters are empirical and require considerable expenses and time. The improved finite element was developed to solve these problems using finite element contact interaction of the rock. Also it was developed to clarify the stress-strain and the rock fracture energy in a layer. These elements are used to study ore destruction in the layer and allows to create a model taking into account the interaction of crushing particles surfaces. The same algorithm was developed determining crushing product particle size distribution in the layer on the base of the Bond’s theory of crushing. The presented finite element model allows to determine the quantity of strain energy and particle size distribution of crushed product during the destruction processes of the material in the roller press with fair accuracy."

Jan 1, 2014

By D. W. Fuerstenau

Understanding how cationic surfactants affect the interfacial behavior of quartz is important in mineral processing and environmental engineering. This paper presents the results of a study of the effect of the molecular structure of cationic surfactants on the interfacial behavior of finely ground natural quartz. Most of the experimental work involved the determination of zeta potentials and the stability of quartz suspensions. Some measurements of induction times and the flotation response of coarser particles are also included. How these surfactants affect interfacial behavior is discussed in terms of adsorption mechanisms. The molecular structure (number of hydrocarbon chains, type of ionic head group, number of ionic head groups on the molecule) of these reagents was found to significantly affect their surface activity.

Jan 1, 2014

By Robert Peretti, Antonio Zucca, Andrea Manni, Silvia Serranti, Paolo Massacci, Marcello Ghiani

"This research study aims to identify the best way of processing colemanite concentrates, which is sometimes characterised by a high content of As sulphides, finely disseminated in the matrix of the boron mineral.Scanning Electron Microscopy analyses have been carried out to identify all the mineralogical constituents and to evaluate their distribution, frequency and mutual relationships.Colemanite concentrates are mainly used by chemical plants producing boric acid and gypsum. A high As content is unacceptable for further use of tailings coming from the leaching process and is very dangerous if the tailings are released into the environment.Grinding tests were conducted under dry and wet conditions in order to assess how As sulphide minerals are released from colemanite minerals.Some of the difficulties involved in obtaining selective liberation of As sulphides from colemanite minerals were overcome, although a certain decrease in As grade in the higher size classes was registered.All comminution products have been analysed by SEM, monitoring the degree of liberation of the mineralogical constituents.Flotation tests have been carried out, following different comminution flow sheets and 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 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 avoid segregation of Asbearing particles together with colemanite ones;- solid/liquid ratio of the pulp to minimise the water flow into the plant.Information obtained from SEM analysis has been adopted to evaluate segregation phenomena in pulp and in flotation products."

Jan 1, 2003

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 Masakazu Niinae, Kenji Aoki

"Electrokinetic soil remediation by electroosmosis and ionic migration is restricted to soluble substances. At a higher pH, the soil particles sorb more heavy metals than at a lower pH and the precipitation of heavy metals are promoted. Both mechanisms make heavy metals immobile, rendering cleanup more difficult and electrokinetic extraction inefficient.In this study, the effectiveness of introducing a complexing agent to enhance the removal of cadmium from kaolinite in the region of neutral pH by ionic migration is examined. The complexing agent selected was ethylenediaminetetraacetic acid (EDTA). The investigation was carried out in a laboratory-scale column containing kaolinite contaminated with cadmium. As the results of the study, cadmium migrates toward the anode without accumulation of cadmium and is successfully removed at the anode reservoir."

Jan 1, 2003

By Henrique Kahn, Daniel Uliana, Carina Ulsen, Guilherme Nery

"Gold has been a material in high demand since the dawn of humanity. After hundreds of years of exploitation, the increasingly search for gold occurs in lower grade deposits with greater extraction difficulty. Therefore, for maximum efficiency, deep knowledge of the characteristics of these minerals and their associations is crucial, which is acquired through an accurate and rigorous routine of process mineralogy and batch extraction tests. The industrial gold process extraction occurs by gravity concentration, sulphides flotation and cyanidation. For gravity concentration, it is fundamental to establish the proportion of free or coarse gold grains and its association to heavy minerals; regarding flotation, the most relevant data are the proportion of gold associated to sulphides and their liberation by the surface area; for cyanidation, it is crucial to evaluate gold accessibility and the kinetics of leaching. Thus, the characterization of gold associations and liberation is vital to establish the plant design, to optimize operating plants and to reduce gold losses. Our aim is the characterization of gold occurrence in low-grade Brazilian deposits with complex mineralogical assemblages to support processing flowchart definition and to predict metallurgical recoveries. Gold distribution in light and heavy minerals was evaluated by heavy liquid separation and the occurrence of gold in free or locked particles was carried out on heavy products by SEM-based automated image analysis using the MLA system. All the products of heavy liquid separation were cyanidated in head samples with different milling conditions to evaluate the reaction kinetics and maximum recovery."

Jan 1, 2014

By Svetlana Krashenina, Nebojsa Petrovic, Oscar Lopez

"As easily mined gold deposits are becoming increasingly rare, gold producers are turning to the processing of ores with polymetallic and copper mineralization. These base metals can create metallurgical and waste handling/disposal challenges, which can render the project uneconomic. Base metals such as copper compete for the cyanide reagent used to extract gold, necessitating the need to increase cyanide volumes and consequently, cyanide consumption costs. Copper will also stabilize in tailings water as weak acid dissociable cyanide, a form that is both difficult and costly to destruct. SART (sulphidization-acidification-recycling-thickening) process technology can be applied to remove base metal interferences in gold projects. SART breaks the copper-cyanide complex and precipitates the copper as a saleable copper sulphide concentrate. With the copper removed, the cyanide can be regenerated as free cyanide for recycle to the gold recovery process. This improves cyanide utilization efficiency and mitigates copper presence in tailings. Additionally, copper recovery generates an incremental revenue source to further improve project economics. Engineering Dobersek GmbH together with BioteQ developed a SART and AVR testing program to recover cyanide and maximize operational efficiencies at a gold processing plant in Kazakhstan with high cyanide consumption in the leach circuit. Results from on-site testing demonstrated that up to 99.98% of copper can be removed and precipitated as copper sulphide and 60-90% of cyanide can be recovered from the AVR and recycled for leaching, reducing total overall cyanide use. This paper provides an overview of the testing methodology and results together with a discussion on the potential of SART to improve gold production operations to deliver both environmental and economic benefits."

Jan 1, 2014

By Dilip. Makhija, Asim. K. Mukherjee, Tamal Ghosh, Abhay Patra

In India around 15-20% of Run of Mine (ROM) from any iron ore deposit reports to slime dams as byproduct of iron ore beneficiation process. The proportion of iron ore slime to ROM will increase in future with higher proportion of lean grade ores in ROM. Furthermore, tonnages of iron ore slime will also increase with increasing demand of iron concentrate. Presently, this slime is stored in the dam in the absence of beneficiation technology. A beneficiation flowsheet has been developed at Tata Steel. This process produced concentrate of 2.2% alumina with 40 % yield from slime of 7-9% alumina. The iron content in the reject will be less than 40% thus adhering to the regulatory norm. Pilot scale study show waste from slime beneficiation is a good raw material for making a variety of building materials. Waste from slime beneficiation also has soil amendment properties. Pilot scale studies show productivity of rice increased when the waste of slime beneficiation process is mixed with soil. On commercialization of this zero waste technology slime generated from the iron ore washing plant will be completely used. In this paper the result of the pilot scale studies on slime beneficiation and utilization processes towards soil making and making of building materials are discussed in detail.

Jan 1, 2014

By John Ralston, Stephen Grano, Yongjun Peng, Daniel Fornasiero

"A specially designed mill which allowed the control of pH throughout grinding was used to study the effect of grinding conditions on galena flotation and galena separation from pyrite. The changes occurring on the mineral surface during grinding were investigated by EDTA extraction and ToF-SIMS measurements.Galena flotation and galena separation from pyrite were strongly dependent on the type and amount of oxidation species produced on galena and pyrite surfaces under different grinding conditions. Iron oxidation species depressed both galena and pyrite flotation, whilst lead oxidation species activated pyrite flotation but had little effect on galena flotation. Optimum galena flotation and galena selectivity against pyrite were achieved by selecting grinding conditions that enabled lead and iron oxidation production to be controlled.Grinding conditions had a large effect on the flotation of the galena particles of different sizes. Flotation of fine galena particles (-10 µm) was depressed by iron oxidation species derived from the grinding media. Chromium grinding medium decreased the production of iron oxidation species and therefore increased the flotation of fine galena particles."

Jan 1, 2003

Pure camsellite samples were prepared through crushing, sorting and grinding the high-grade iron-containing camsellite ores from Fengcheng, Liaoning, China. The flotation behaviour of camsellite was studied via a systematic investigation of camsellite flotation re-covery changes as a function of choices and dosages of collectors and depressants at different slurry pH. The results showed that at pH 8.5 to 9.5, the recovery of camsellite reached the maximum at 90%~93.5% using dodecylamine as the collector, while under the same condition a recovery of 84%~86% could be achieved with sodium oleate. The adsorption of dodecylamine was not affected by the addition of sodium hexametaphosphate, but the adsorption of sodium oleate could be significantly depressed. This implied that sodium metahexaphosphate could be used as an effective depressant for the other associated minerals during the dodecylamine flotation of camsellite. When starch was used as the depressant, the flotation of camsellite by sodium oleate was almost completely depressed in the alkaline conditions. Significant depressions were also observed when calcium chloride was added in the camsellite-sodium oleate system. The higher the slurry pH is, the stronger the depression. Zeta potential measurements indicated that the flotation was mainly initiated by the electrostatic adsorption of the collector on camsellite. X-ray photoelectron spectrometer (XPS) analysis showed that the adsorption was originated from the electrostatic attraction between the N atom in dode-cylamine and B atom in camsellite. Dodecylamine had a higher coverage on the camsellite surface than sodium oleate.

Jan 1, 2014

"The thiosulfate leaching process developed by Barrick to treat sulfidic high preg-robbing gold ores uses calcium thiosulfate as the leaching reagent for ores pre-treated by pressure oxidation, resin for gold recovery with sulfite/trithionate elution and reverse osmosis as a means of reagent recovery. A large portion of the research that led to the development of the technology was based on previous studies completed by different groups over the years, mainly focused on the ammonium thiosulfate system. Operational limitations in the use of the ammonia-containing recycled water in the pressure oxidation circuit were some of the main drivers for the change from ammonium to calcium thiosulfate for the development of the industrial scale process. One of the main aspects for successful gold extraction and recovery in the thiosulfate system is the pseudo-equilibrium reactions that drive distribution of the different gold species (in solids, solution and on resin) in the system. Previous studies have been focused on the thiosulfate reactions and equilibrium constants for the oxysulfur ions (thiosulfate, trithionate, tetrathionate). However, the literature around the effects of the different metal-oxysulfur complexes (Cu and Hg complexes) that form when the ore is in contact with the leaching reagents, and the related effects on stability of the gold complex is limited. The main changes in the gold complex chemistry and stability in the calcium thiosulfate system as compared to the ammonium and sodium equivalents, as well as related effects on gold recoveries, were investigated in the presence of different types of double refractory ores. INTRODUCTION Barrick has developed a thiosulfate leaching process to treat double refractory gold ores, by combining the use of acidic and alkaline autoclave pre-treatment with thiosulfate resin-in-leach (RIL). The process currently in operation at the Goldstrike mine (the TCM process), uses calcium thiosulfate as the leaching reagent, resin for gold recovery with sulfite/trithionate elution and reverse osmosis as a mean of reagent recycle. The main feed to the process plant is highly preg-robbing sulfidic ore from Goldstrike’s open pit. Prior to feeding the pressure oxidation circuit, the ore is processed through the crushing and grinding circuits and treated in preparation for acid or alkaline autoclave processing (POX)."

Jan 1, 2018

By M. Ito

Cobalt-rich ferromanganese crust and nodule ores from seamount areas contain volcanic and sedimentary rocks as substrate or nuclei. These ores require mineral processing to remove the sub-strate/nuclei rock before smelting. This paper reviews experimental results of previous investigations. Observations and analysis of 10 samples from different localities were carried out and it was found that the liberation ratio of crushed product was high even at coarse size fraction, 0.5mm to 4mm. Experimental and calculated results in the smelting stage confirmed that the separation product satisfies the standards of the subsequent smelting process if the substrate/nuclei rock is removed from the 0.5mm to 4mm fraction with high separation efficiency. There was a density difference between the substrate/nuclei rock and the ferromanganese component. Thus the coarse sized sample was treated with gravity separation; air table separation was used as a dry method and jig separation as a wet method and high grade values with high recoveries were obtained by both kinds of gravity separation.

Jan 1, 2014

By Gus Van Weert, Samuel A. Bolorunduro, David B. Dreisingerm

"As deposits of high-grade base metal sulphides become depleted, attention must be focused on the treatment of complex sulphides, which contain significant fractions of precious metals such as gold and silver. Acid pressure oxidation is a promising process for these materials and the recovery of silver and gold will improve the economy of the process. Gold can be recovered from the oxidised residues, however, silver is incorporated into the jarosite specie and the cyanidation of the resulting residue yields very low recovery.Pressure oxidation of various complex sulphides was carried out at 110-150°C in sulphate media with additions of potassium iodide under conditions similar to industrial autoclaving. The resulting residues were subjected to cyanidation. High recovery of silver, up to 98%, was achieved because its incorporation into lead-hydronium jarosite during the pressure oxidation was minimised, while its deportment into the cyanide-soluble silver iodide was favoured. Silver recovery decreased slightly at high temperatures (140° and 150°C) because of the enhanced stability and kinetics of lead-hydronium jarosite, but this could be overcome by increasing acidity and iodide concentration of the autoclave slurry."

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 P. Harris, D Bradshaw

"Comparison of the two most commonly used classes of depressant in the South African platinum industry is complicated by the fact that these polymers induce different effects on the surfaces onto which they adsorb. The use of carboxymethyl cellulose (CMC), which is ionically charged in solution, can lead to increased particle dispersion in addition to the effect of reduced surface hydrophobicity (depression). Guar is typically only slightly charged in solution. Comparison of these two depressants is complicated since it is uncertain whether differences in their action is a result of either depression of dispersion effects.This work investigates the role of dispersion independently to that of depression in the batch flotation of a platinum bearing ore. An inorganic dispersant, sodium hexametaphosphate (NaHMP) was added in parallel to the uncharged guar depressant to simulate the action of depressants with varying degrees of dispersion. By distinguishing between the material recovered by entrainment and the floatable gangue and by including the effects of froth stability it was possible to decouple the effects of dispersion and depression.The results show that both dispersion and depression led to increased grade of the sulphide minerals. Depression leads to a decreased recovery of floatable gangue minerals. Dispersion leads to an increased recovery rate of these minerals and an accompanying decrease in froth stability."

Jan 1, 2003