Search Documents

By E. R. Bobicki

"Low-grade ultramafic nickel ores, while representing a large potential nickel resource, are difficult to process due to their serpentine content. Microwave treatment is proposed as a technique to improve the beneficiation of ultramafic nickel ores by converting the constituent serpentine to olivine. The present paper reviews the microwave heating response of ultramafic nickel ores and resultant changes in mineralogy, as well as effects on grinding and slurry rheology. Beyond nickel extraction, microwave treatment improves the mineral carbon storage capacity of ultramafic ore tailings, providing a potential source of additional revenue via the sale of carbon credits. The combined positive effects, considered in the context of the whole operation, suggest an economically viable process is possible.INTRODUCTIONAs high-grade deposits become depleted, the processing of low-grade ores has become increasingly important. One such resource is low-grade ultramafic nickel ores. While representing a large source of nickel, these ores are difficult to process due to their serpentine content. Serpentine is a phyllosilicate mineral consisting of 1:1 stacked sheets of silica tetrahedra and magnesium hydroxide octahedra. There are three primary polymorphs: lizardite (platy), antigorite (corrugated) and chrysotile (coiled, fibrous). The anisotropic nature and non-spherical morphology of serpentine particles leads to complex rheology. Suspensions of serpentine minerals, especially those of chrysotile, exhibit high viscosity and yield stress, which can have a negative effect on comminution, flotation and dewatering operations. In flotation, serpentine is known to slime-coat pentlandite, a valuable nickel mineral, and form bubble-fibre aggregates that report to the froth, reducing nickel concentrate grade and recovery. Methods used to counteract the effects of serpentine in processing include desliming, the addition of chemical dispersants, salts or acid, and dilution (Bobicki et al., 2014a). Microwave pre-treatment has been proposed as an alternative way to eliminate the deleterious effects of serpentine in ultramafic nickel ore processing by converting the serpentine to olivine via dehydroxylation, which occurs at 600-700oC (Reaction 1). Olivine is isotropic, consisting of isolated silica tetrahedra linked by octahedrally coordinated magnesium ions, and has the same surface potential as pentlandite at the pH of flotation (~pH 9). Furthermore, since olivine is more reactive to CO2 than serpentine, microwave pre-treatment creates an opportunity to store more CO2 in tailings, an attractive option for mining operations looking to increase their bottom line where carbon pricing exists."

Jan 1, 2018

By R. A. Kleiv, H. Havskjold, N. Church, T. Malvik, M. Tro, E. Larsen

Liberation is one of the major purposes of comminution in mineral processing. In the simplest form, two or more minerals are present in a particle and have to be reduced such that the individual particles contain only one mineral. The complexity of the mineral intergrowth varies from ore to ore. Poor magnetic separation of iron ore may have many causes. In this paper, the emphasis is given to the problem of fine magnetite inclusions in quartz or other gangue minerals. This is highlighted by two Norwegian cases: one on a magnetite ore and the other on a hematite/magnetite ore. The inclusions in question are so small that they are not liberated by reasonable grinding. In both cases, the result has been either poor recovery or lower grade concentrates than desired. The first example concerns production of direct reduction concentrates from magnetite. Magnetic inclusions in gangue particles will be magnetized enough for the particles to pass into the concentrate. The second example is given a more detailed study, where the problem is caused by silicates with small inclusions of magnetite in a combined LIMS and WHIMS separation. This study included microscopy, Davies tube testing, and magnetization measurements. In particular, large gangue particles with magnetite inclusions were shown to have a tendency to bypass the LIMS separators as drag forces in presence of hematite are large. Such particles will then be picked up by the WHIMS as their magnetization is higher than for hematite. This was demonstrated by Davies tube tests, which indicated that such particles were picked up in preference to hematite particles. However, the Davies results did not give a good quantification. Magnetization measurements of gangue particles with magnetite inclusions was shown to be a better tool to quantify the magnitude of the effect of magnetite inclusions in magnetic separation.

Jan 1, 2018

By Mohammad Mainul Hoque, Linhan Ge, Ai Wang, Geoffrey Evans, Subhasish Mitra

"Dispersed phase interactions involving bubbles and particles in the turbulent environment play a significant role in the flotation process. The conventional collision models only account for the deterministic rather than the stochastic behavior of turbulenct flow. What the bubble-particle collisions would be like remains an open problem due to the complex nature of turbulent flow. To address this research question, the present study aims to quantify the bubble-particle collision efficiency incorporating turbulence using the computational method. Multiple solid particles were released to interact with a single stationary rigid bubble (non-deformable interface). Effect of particles Stokes number, turbulent intensity (TI) and integral length scale on the bubble-particle collision efficiency (Pc) was examined. Large Eddy Simulation method (LES) was used to compute the continuous phase. Fluctuating velocity required at the inlet boundary condition was derived from Gaussian energy spectrum to generate the upstream turbulence. Discrete Phase Model (DPM) is used to simulate particle trajectory. The characteristics of turbulent flow were analyzed through Energy spectrum and energy dissipation rate. The critical initial releasing radius of the annulus, where Pc equals zero, reaches up to 1.5(Rb+Rp) under high turbulent intensity (TI) 20.48% compared to 0.23(Rb+Rp) calculated from the traditional Pc model. Pc decreases as the distance of initial releasing annulus between bubble centre increases. Pc increases as particle Stokes number increase up to 0.66. The collision efficiency for particles of St less than 0.38 is higher under TI 11.78% compared to TI 4%.INTRODUCTION To increase mineral recovery, interactions between bubbles and particles are essential. All flotation devices achieve it through introducing some level of turbulence into the system by increasing specific energy dissipation rate. Figure 1 shows three different flotation equipment, traditional floatation cell, Concorde cell and cyclonic-static micro-bubble flotation column (FCSMC), with different turbulence generation mechanisms – impeller, down-flow liquid jet and pump recirculation, respectively."

Jan 1, 2018

By A. V. Zimin

It is a well-known fact that usage of reverse cationic flotation in magnetite ores processing enables to improve the quality of magnetite concentrates. We designed an iron ore concentrate technology (with 70 -71 % of iron) including reverse cationic flotation in pneumo-mechanical flotators RIF (developed by RIVS Corporation, Russia) with good biodegradable etheramines as collectors for flotation of quartz. Practical application of high biodegradable flotation reagents decreases environmental impact risk of objects and enterprises of mining industrial complex. This work presents results of development of flotation technology for production of high quality ferruginous concentrates from magnetite ores of Russia and Ukraine deposits. Keywords: magnetite ores, reverse cationic flotation, ferruginous concentrates, pneumatic-mechanical flotation machines, environmental impact

Sep 1, 2012

By M. Ghiani, R. Peretti, S. di Giovanni, G. Zonnedda, A. Serci, A. Zucca

"Beneficiation of the epithermal gold mineralizations associated with an extensive alteration zone in the Serrenti-Furtei region on the island of Sardinia, is proving a complex issue. Experimental investigations have in fact demonstrated that while the ores contained in the upper parts of the deposit are amenable to conventional cyanidation, the gold contained in the refractory ores in the lower portions needs to be recovered by means of flotation, combined with leaching where necessary.The results of commercial heap leaching, carbon-in-leach (CIL) processing and flotation, designed on the basis of the experimental findings and applied to the oxidized portions and transition zones of the deep sulphide mineralizations, confirmed the expectations emerging from the laboratory tests."

Jan 1, 2003

By V. Hudecek

Problems of sudden outbursts of rock and gas present in deep mine mining ones of the most complicated interrogation. It is searching for the methods of prediction and prognosis that can be most useful for the government of these phenomena. Till now the pressure and the desorption of gas in bore holes was consider to be the decisive criteria. By the work of authors with using of statistical date was verify that for considerable reliability of forecast and prevent outbursts is necessity investigate characteristics of workplace and other indicators. These indicators were analyzing and assemblage into mathematical dependences which represent active and passive force asserting with in the process of rush. It was validated by using the equations which are presented in the manuscript that the accuracy of pre-diction of the phenomena is higher and methods of preventions are better also.

Jan 1, 2014

By K. Lillkung

The use of secondary sources has become a very attractive option in the production of platinum group metals as the demand for these metals has increased. One of the promising sources are the spent catalysts, which provide an attractive source as they have relatively high metal content compared with the ores where the metal is originally extracted from. The concentration of platinum group metals in catalytic converters is in the range of 0.1-1 mg/g as the concentration in ores is usually less than 10 ppm. Aqueous chloride solutions are claimed to be a cost effective way in which platinum group metals can be brought into solution and concentrated. In this work the effect of different parameters on the dissolution rates of Pt, Pd and Rh were investigated. The parameters investigated were the Cl- concentration, the temperature and applied potential. Chloride concentrations used were 62.5, 90, 125 and 250 g/l. Temperatures were 25, 40, 60, 80 and 94°C. Potentials were 950, 1050, 1150 and 1250 mV vs. SCE for Pt and Rh and 380, 410, 440 and 470 mV vs. SCE for Pd. Dissolution rates were calculated from the current densities determined by potentiostatic measurements. Thin wire electrodes were used in the measurements. As expected, higher temperature, higher potential and higher chloride content generally increasedthe dissolution rate. However, the effect was nonlinear and slightly different for different metals. The results show that strongly oxidizing conditions are needed in order to achieve reasonable dissolution rates. With the highest chloride content and at potential of 1250 mV vs. SCE and 94°C the dissolution rate of Pt was nearly 1 mm/h, whereas in similar conditions Rh achieved a rate of only nearly 100 µm/h. Similarly, with the highest chloride content and at potential of 470 mV vs. SCE at 94 °C the dissolution rate of Pd was nearly 1 mm/h. Keywords: Pt, Pd, Rh, redox potential

Sep 1, 2012

By Lj. D. Andric

By the micronization-milling of the material, the size and the structure of its particles are changed and it comes to the increasing of the potential energy of the system as well as to the chem-ical activity of the material what is the result of an increased free surface and of the concentration of the grate defects, that is of the internal energy of the system. All these changes that are reached, show that new characteristics of treated materials are got by micronization process. Controlling the process of the micronization and by purpose directing of the new characteristics of the activated materials, we can have the positive effects and use them in more technologies. Talc is important nonmetallic mineral raw material that is widely used as either the basic raw material, or as filler. This has stimulated its technological investigation, as well as the investigation of its physical-chemical characteristics. In this paper are shown experimentally reached results of the physical-chemical characteristics of the talc during the process of the micronization in high energetic mill. In this paper, the optimum conditions of miconization of talc in high-energy-speed rotary mill and its influence micronization on a degree of Fe2O3recovery by hydrometallurgical methodes, are presented. The X-ray analysis of the obtained products showed that high quality talc with low content of can be obtained by these physical-chemical processes In this paper, the principles and application or fine and ultra-fine grinding high-energy attriton mill with small balls, enabling fast, efficient grinding, low energy consumption, short grinding time and easy handling will be described.

Jan 1, 2014

By Ljubisa Obradovic, Baisui Han, Batnasan Altansukh, Zoran Stevanovic, Atsushi Shibayama, Jonovic Radojka, Daizo Ishiyama, Kazutoshi Hag, Radmila Markovic, Ljiljana Avramovic

This paper discussed a combined froth flotation and high pressure leaching (HPL) process to recover copper from mine tailings. At first, froth flotation were carried out using the mine tailings sample under various conditions in the presence of different pH (3.5-10) and sulfurizing reagent value (0-1000 g/t), respectively. As a result, optimum condition (sulfurizing reagent of 1000 g/t, pH of 10, PAX (collector) of 100 g/t and MIBC (frother) of 200 g/t) was found for froth flotation of copper. The effects of sulphuric acid concentration, leaching temperature, total pressure (steam pressure plus oxygen pressure) on high pressure leaching (HPL) of mine tailing were investigated using sulphuric acid solution in the presence of oxygen. The best conditions for HPL were obtained to be sulphuric acid concentration: 0 mol/L (water), leaching temperature: 170 ?, total pressure: 2 MPa, leaching time: 1 hr and pulp density: 100 g/L. The leaching rate of copper reached nearly 99 % and the concentration of copper in pregnant leach solution (PLS) was 0.24 g/L. Finally, copper in the mine tailing was recovered using froth flotation followed by HPL. As a result of a combined froth flotation and HPL, the vast majority of copper (99 %) from the mine tailings was extracted.

Jan 1, 2014

By Alex Joseph

A tertiary amine containing polyamine in its back bone was grafted to exfoliated graphite oxide by means of a series of chemical reactions.The synthesized amine functionalized polyaniline grafted to exfoliated graphite oxide (EGAMPANI) was characterized using various techniques such as, FTIR, TGA, Raman, and X-Ray diffraction.The synthesized EGAMPANI was blended with carbon paste electrode, and used to study the response of Hg2+ in acetate buffer solution.Preliminary analysis showed that the anodic current intensity using the EGAMPANI modified electrode was higher during a potential sweep and 10-4 M concentration of mercury could be detected which could be improved to 10-6 M using anodic stripping voltammetric technique. Keywords: metal sensor, exfoliated graphite oxide, functionalization, polyaniline

Sep 1, 2012

By S. Banisi, A. Ghasemi, S. Zare, F. Ghorbani, E. Nematollahi

"Comminution is the most energy intensive operation which constitutes the major portion of operating and capital costs of the mineral processing plants. Working at the maximum operating capacity of comminution equipment plays a significant role in the efficiency of the circuit. Appropriate design of cone crusher feed box could result in the choked crushing which is known as a vital factor in achieving target performance. In this research, the non-uniform cone crusher feeding at the Sarcheshmeh copper complex was studied and appropriate measures were taken to solve the problem. The problem resulted in non-uniform and high wear rate of crusher liners and high fluctuations of power draw. In recent decades, the discrete element method (DEM) has been applied successfully to study the effect of different factors on the behavior of particles flow. In this work, various designs for feed box were tested using an in-house developed DEM software called KMPCDEM©. The best feed box design obtained from the simulations was selected, constructed and installed in of the cone crushers. The new feed box design resulted in more uniform feed distribution on the distributor plate of crusher indicated by a reduction of the standard deviation of power draw measurements from 13 to 3 kWh. The better control of the crusher, 49% increase in the crusher throughput and finer and narrower product size distribution were the main outcomes of the installation of the new feed box. Furthermore, the wear rate on mantle and liners of crusher not only decreased but it also became uniform.INTRODUCTION Comminution is the most energy intensive operation which constitutes the major portion of operating and capital costs of the mineral processing plants. Reaching the maximum operating capacity in comminution equipment is a key sign of approaching the nominal productivity of the process. Due to the effect of crusher efficiency on the downstream circuit performance, optimization of the crushing circuits has received considerable attention (Herbst, & Potapov, 2004; Quist, & Evertsson, 2010; Li, Huiqi, McDowell, Glenn R, Lowndes and Ian, 2014; Cleary, Sinnott, Morrison, Cummins, & Delaney, 2017). Improving the performance of crushing circuits not only decreases the capital and operating costs but also increases the efficiency of downstream grinding circuits (Jacobson, Janssen, & Urbinatti, 2010). In cone crushers particles can be subjected to two different modes of compressive breakage; single particle breakage (free feeding) and inter-particle breakage (choked feeding). The maximum efficiency of the cone crusher directly depends on the type of feeding arrangement (Operation Manual, 1977). An appropriate feeding must lead to choked feeding the cone crusher. If the rate and method of feeding the crushers are correctly be executed, the maximum efficiency of the crushers could be available (Jacobson et al., 2010)."

Jan 1, 2018

By S. Castro, L. Uribe

Seawater can be considered as a particular process water with a high concentration of NaCl (about 0.5- 0.6 mole/L) and high concentration of hydrolyzing metal cations (mainly, Mg2+ and Ca2+ ions). Micro-flotation tests, induction time measurements, and zeta potential measurements have been used to investigate the effect of these ions on the natural floatability of molybdenite. The results demonstrate that molybdenite is strongly depressed in the alkaline pH range over which hydrolysis products of Mg2+ and Ca2+ ions are formed. At pH 10, colloidal magnesium hydroxide seems to be responsible for molybdenite depression in seawater and in Mg2+ solutions. This is also supported by the measurements of the effect of Mg2+ ions on the zeta potential of molybdenite. The mechanism of depression of molybdenite with Ca2+ ions is different, and depression takes place in the pH range were Ca(OH)+ complexes are formed, below the pH of precipitation of calcium hydroxide. Adsorption of the cationic hydroxy species and/or hetero-coagulation of the positive charged colloidal hydroxide on the negative charged molybdenite particles seem to be the main mechanisms involved.

Jan 1, 2014

The ultimate goal of a mineral processing plant is to recover as much of the target mineral(s) as possible from the ore being treated to achieve the best economics. Selection of the mineral processing techniques is the most important step in achieving this goal. However, due to the complexity of the ore, the recoveries of valuable minerals may be not satisfactory even when the mineral processing technique(s) are well chosen. In other words, minerals of interest can be lost to the tailings for mineralogical reasons. For example, gold is mainly extracted from the ore by gravity, flotation, cyanidation, or a combination of these processes, and high recovery (>90%) can be achieved when gold occurs as coarse grains. However, when a refractory ore is being processed, gold extraction will be challenged by mineralogical factors, which often cause gold losses to various tailings. Mineralogical factors affecting gold recovery mainly include grain size, shape, surface coatings and rimmings, presence of cyanicides, oxygen consumers and preg-robbers, presence of slow-dissolving gold minerals and the refractory nature of submicroscopic gold. Among these factors, locking in sulphide, silicate and other minerals as fine-grained gold inclusions and/or as invisible submicroscopic gold is by far the most common factor leading to poor gold recovery encountered in gold ore processing. Processing of PGE ores faces the same challenges as gold. Small grain size and locking of PGM in sulphide and non-sulphide minerals often cause PGM losses. When silver ore contains significant amounts of pyrargyrite, proustite and stephanite, silver recovery by cyanidation can be very low because of the slow dissolving kinetics of these minerals. In the processing of base metal ores, high content of pyrite, intergrowth of chalcopyrite with sphalerite and presence of clay miner-als may cause problems in recovering Cu-, Pb- and Zn- bearing minerals. Process mineralogy helps address all issues and problems related to mineral processing with predicting and trouble-shooting being two major objectives. It provides useful information on process selection, flowsheet development, recovery improvement and reagent consumption optimization. The information acquired from a process mineralogical study can be used as a guide for a metallurgical testwork program for process design or optimization.

Jan 1, 2014

By M. C. Harris

"In the flotation process the contact angle is an important indicator of the hydrophobicity of a mineral particle. There is considerable literature showing that the contact angle increases when the chain length of the alkyl group associated with the collector molecule used to render the valuable mineral particle hydrophobic increases. The extent to which an alkyl group interacts with surrounding water molecules is quantified thermodynamically by the excess Gibbs energy. In the present paper it is shown that there exists generally a strong linear relationship between the excess Gibbs energy of the alkyl group associated with the collector and the contact angle. The structure-activity of such alkyl groups is in turn related to the total surface area, molecular volume, the molar volume, molecular weight of the functional groups in the molecule and interaction energies. It is proposed that the demonstrated relationship is indicative of the role which the alkyl group component of the collector, which is attached to the mineral particle, plays in increasing the extent to which water molecules at the surface of the mineral are rejected from the surface thus increasing the contact angle. The relationship between excess Gibbs energy and surface tension is further explored with a view to relating the observations quantitatively to the parameters in the Young equation.INTRODUCTIONThe issue of wettability of materials is of great importance to many industrial applications. Wettability studies usually involve the measurement of contact angles which indicate the degree of wetting when a solid and liquid interact. As is well known the contact angle (O) is the angle between planes tangent to the surfaces of the solid and the liquid at the wetting perimeter which is the zone where the air, water and solid phase merge. When the air bubble attaches to the solid surface there is an increase in the air/solid interface area and a decrease in the solid/water interface area. For attachment to occur the cosine of the contact angle should be less than 1 and this will be promoted if the interfacial surface tension between the air and the solid (? SV) is low. Classically the relationship between these parameters has been expressed through the Young equation (1) for a perfectly flat surface:"

Jan 1, 2018

By Wayne I. van Drunick

"Energy balance modeling has recently been shown to be a competent tool in the estimation of SAG mill discharge rheology. Work performed by van Drunick and Moys (2001) validated the ability of an energybalance filter to estimate the slurry density from an operating SAG mill. The importance of rheological data is highlighted by several authors who show the effects on load behaviour and thus mill performance. Energy balance models were developed to account for the dynamic energies in the mill discharge sump. The models then made it possible to infer the mill discharge density. A sampling campaign was performed and the errors from the sump energy balance were within tolerable limits.Since the initial results were published, it has been decided to further develop the modeling techniques in order to focus on balancing the energies around the entire mill. The critical measurements for the energy balance will be the temperatures of all the streams entering and leaving the mill, including energy losses to the environment. Metso’s OCS© (Optimising Control System) currently controls the 3 SAG mills at Anglogold’s Mponeng Gold Plant (South Africa). The OCS has built-in Kalman filtering tools to effectively handle variances and noise in the models and the mill circuit data respectively. The new models are therefore constructed in the OCS platform, and will be run in parallel with Metso’s current modeling and filtering systems. The work is a collaborative effort between Anglogold, the University of the Witwatersrand and Metso. The benefits of energy modeling, compared to mass modeling, are that energy data are more accurately measurable than mass data. The inferred mill parameters can therefore be improved provided that a competent set of models is produced to process the (accurate) thermal measurements."

Jan 1, 2003

By M. Barsky, E. Barsky

A study was conducted to elucidate the relationship between the hovering velocity and the particle settling velocity. The experiments were carried out in a water medium on five materials ranging in density from 1.070 to 4.000 kg/m3. Analysis of the results with allowance for the distribution of stream velocities over the cross section of the pipe revealed that the final settling velocity of the particles was equal to their local hovering velocity (on the stream axis), and not to the average velocity of vertical flow as is generally believed. It therefore follows that the kinetic structure of the stream must be taken into account when constructing theoretical models of the process for purposes of computation. In addition, the optimal stream velocity is not always equal to the hovering velocity and in fact is governed by other factors as well. Illustration is provided by the results of a study conducted in a vertical cascade classifier comprising eleven identical stages. The feed material was introduced at each stage successively beginning with the topmost (i* = 1 ) and ending with the lowermost (i* = 11). First, the stream velocity that yields optimum separation conditions at each stage of the cascade (i.e. k=50%, k being the yield of a given size class in the fines for a single stage) was sought. Subsequently the conditions of optimal separation for the instrument as a whole were determined (i.e. F(x) = 50%, F(x) being the yield of a given size class for the entire instrument). The results of the study are presented in the table.

Jan 1, 2003

By Elzbieta Mielczarski, Jerzy A. Mielczarski

"It is well documented that xanthate adsorption on sulphide minerals is electrochemically controlled process. Under well controlled potential conditions the adsorption of xanthate takes place at different potential on each mineral, hence, each mineral component can be selectively separated from ore. This was demonstrated in the past for single mineral systems. In real flotation this concept never works out for two reasons: the potential of single mineral particle results from its interaction with solution as well as from galvanic contact with other particles present in the flotation pulp. Thus, the potential of a single particle results from complex surface reactions controlled by solution chemistry and the presence of other mineral particles that also interact with the solution. In flotation it is not possible to control mineral particle potential as it was demonstrated in voltametric studies of single mineral.In this study adsorption of xanthate on pyrite, galena and chalcopyrite has been investigated in the presence of those minerals. The second mineral was in solution: (i) without any physical contact with the first one, (ii) in direct contact (non-liberated grain or connected by wire), (iii) in collision type contact similar to that observed in real flotation.The adsorption of amyl xanthate on pyrite, galena and chalcopyrite was monitored by infrared external reflection technique directly on mineral surfaces. Type of the adsorbed species and their amount were concluded from the recorded reflection spectra. The presence of second mineral in solution without any physical contact does not influence adsorption. The minerals behave as if they were separated (at least during 30 min of the experiment). However, any type of galvanic contact between grains of two different minerals has tremendous consequence on the adsorption of collector on the both minerals. The detected changes are dramatic, from no adsorption to a few monolayer coverage formation.For example, pyrite that adsorbs amyl xanthate strongly in single mineral system in its galvanic contact with galena practically shows no adsorption of the collector in the same solution conditions. On contrary adsorption of xanthate on galena is tremendously enhanced during the galvanic contact with pyrite. The observed changes in the surface reactions are discussed and mechanisms of xanthate interactions in different galvanic contact are proposed."

Jan 1, 2003

By Kevin Galvin, Simon Iveson

Fine particles are the most valuable because they are the most liberated. However, they are also the most expensive and difficult to recover and concentrate. The Reflux Classifier is a novel invention that combines many of the virtues of existing fine particle separation technologies in a way that provides profound synergies. Multiple parallel narrow channels create a laminar-shear separation zone. The laminar flow provides a well-defined velocity gradient that exposes particles on the wall to a conveying velocity that is approximately proportional to their size, thus reducing the dependence of elutriation velocity on particle size. The high shear rate in these channels generates a hydrodynamic lift force that selectively lifts low-density particles off the channel wall and thus causes them to be preferentially conveyed out in the overflow. Particles that are not elutriated slide back down into the mixing reflux zone beneath the inclined channels which gives them multiple opportunities to re-enter the channels. The resultant suspension of both coarse and fine high-density particles in the fluidized bed zone at the base of the unit generates a strong autogenous dense medium that helps to direct large low-density particles back up to the overflow. The fluidization water also simultaneously de-slimes the high density underflow product. When placed in a centrifuge, the benefits of these features multiply with the improvements in capacity and selectivity that arise from high G-forces. When inverted, these features can be used to perform flotation well beyond the conventional flooding limit. Hence this invention platform has the potential to dramatically improve both gravity and flotation separation performance across the minerals processing industry.

Jan 1, 2014

By Stephen Simukanga, Jewette Masinja

"Mining has been going on commercially in Zambia for over 100 years. The backbone of the mining industry has been copper production and its by-products of cobalt and gold. Over these years, the mining industry ownership structure has swung from private ownership to state ownership in 1972, and back to private ownership in 1995. Environmental management was first introduced into the body of Zambian legislation in 1991 through the promulgation of the Environmental Protection and Pollution Control Act (EPPCA). The Act’s main functions included the protection of the environment and control of pollution, and in particular to provide for the health and welfare of the people, animals, plants and the environment in general. This Act, was replaced in 2011 by the Environmental Management Act (EMA). The new Act has a number of new elements including: mainstreaming environment in national planning, it provides for the domestication of multilateral environmental agreements, enhances public participation issue, creates a central environmental information depositary, elaborates access to information principles, establishes an environment fund, creates enforcement orders, provides for both Zambia Environmental Management Authority and members of the public to sue for damages following environmental pollution, and provides for the appointment of honorary Inspectors. In addition to this, the Mines and Minerals Act of 1995 provided, for the first time, a section on environmental management in the mining sector. This section also created the Environmental Protection Fund (for mining), and made it obligatory to undertake environmental impact assessment before mining permits could be issued. The Environmental Protection Fund has now been established, as provided for by the law, and currently has more than USD9.0 million in the account. Secondly, environmental auditing is now being carried out annually on mines around the country, the effect of this has been a significant improvement in the environmental management of mining in Zambia. This paper looks at the response of the Zambian mining sector to these pieces of environmental management legislation, and the direction that the mining sector is expected to take on environmental management going forward."

Jan 1, 2014

By Kang N. Zhong, Hui H. Luo, Yunan Phosphate Chemical Co., Yi H. Wei, Yao J. Li, Yu L. Wang

"The three kinds of phosphate ores (igneous, metasedimentary and sedimentary) found in China have great differences in flotation flowsheets and reagents suite because of their crystal structure and mineral composition. The igneous and metasedimentary apatites have good floatability with fatty acid as collector and waterglass, sodium hydroxide or sodium carbonate as conditioners. The sedimentary phosphate is very difficult to beneficiate by direct flotation because of their poor floatabilities and relatively high content of MgO and SiO2, even though the dolomite depressants are used sometimes.The differences in floatability of apatites in China are closely related to their differences in specific surface area. The amount of collector to float apatite increases with the specific surface area. Apatite with lower specific surface area showed good floatability at lower collector concentration. Apatite with a higher specific surface area needed a higher concentration of collector. The content of CO3 2- will affect the specific surface area of apatite by distortion of its crystal structure and consequently affect its floatability.Dolomite can be easily rejected from apatite in a weak acidic medium (pH=5), especially in phosphoric acid medium by reverse flotation. Quartz and siliceous gangue in sedimentary apatite can be removed by direct flotation using fatty acid or by reverse flotation using amine. Amine is not practically applied because sedimentary apatite in China is usually very fine and needs fine grinding, which always results in excessive, very fine, stable and non-flowable foam.Based on the floatability of phosphate ore in China, a two-stage flotation process, direct and reverse flotation (D+R), was developed to beneficiate sedimentary ore. For the Haikou phosphate ore containing 25.11% P2O5, 3.46% MgO and 16.5% SiO2, a concentrate containing 31.84% P2O5, 0.48% MgO and 14.8% SiO2 can be obtained through a continuous D+R test at a recovery of 89%."

Jan 1, 2003