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By Roberto C. G. Oliveira, Scott C. Brown, Brij M. Moudgil

"The wettability or surface energy of particle surfaces dictates a number of multiphase ensemble interactions that have a significant impact in mineral processing. Dispersion, bulk powder handling and flotation are just a few of the processes that are largely influenced by the degree of hydrophillicity or hydrophobicity on particulate surfaces. Because of the importance of surface wettability, a number of simple, precise and accurate techniques for accessing surface wettability or contact angle on macroscopic flat surfaces have been developed. However, these techniques cannot be directly applied to the particulate surfaces that are often in query. Though a number of techniques are available for accessing the wettability of particulate surfaces, these methods are either relative, application specific or prohibitively tedious. In the present study, key features of existing techniques are combined to formulate an improved method to delineate particle wettability that is simple, versatile and capable of providing reproducible measurements in an industrial environment.Through the use of an inert adhesive and an inert macroscopic surface as a support, it is illustrated that precise measurements of particle wettability are obtainable under suboptimal or ‘shop floor’ conditions. The measurement of the maximum external meniscus height formed between a test liquid and a particlecoated rod is employed to estimate phenomenological contact angles on particles ranging form a few nanometers to several hundred microns in size."

Jan 1, 2003

By Johan F. W. Kock

"Hearing loss due to excessive noise exposure is the most prevalent industrial disease. It is ranked on the World Health Organization’s (WHO) priority list for major work related injuries. Uncontrolled noise not only has a physical effect, but is also a psychological hazard affecting the performance and well being of man. Noise induced hearing loss (NIHL) is irreversible, yet it is preventable. The first defence against noise (noise control engineering) is a high priority in the mining industry. Second defences should be a last resort when the engineering control of noise is inadequate. Hearing conservation programs and the use of conventional hearing protection devices seem to have failed in the prevention of noise induced hearing loss. If compensation payouts that quadrupled in the past ten years are used as a barometer for the success of existing hearing conservation programs, then new strategies and technologies need to be investigated. The best practice Hearing Protection Device (HPD) may be seen as the minimum standard for second defence noise control.Conventional hearing protection is widely applied, but also misused in the industry as well as in the mining sector. Empirical research results, ownership, general attitudes of workers as well as qualitative aspects will be explored. The paper provides reasons, evidence, case studies and strategies regarding the best practice hearing protection philosophy (the Noise Clipper Model) as implemented in the Implats Mining Group. Worldwide tendencies towards custom-made HPD’s, findings that indicate improvements in hearing conservation programs and finally the successful application of Custom-made Hearing Protection Devices, will be outlined."

Jan 1, 2003

By Jochen Petersen, Harro von Blottnitz

"The landfill disposal of slags is common practice in the metallurgical industry. Chromium may be a minor constituent in many cases. It is present mostly in the form of chromites, which are considered environmentally benign and hence safe for disposal. Wastewaters from metal finishing operations are most commonly treated by reduction and precipitation of dissolved metals, including chromium, by lime addition, and subsequent landfill disposal of the resulting sludge. The metals contained in such sludges are mostly in the form of hydroxides, and as such considered environmentally stable.Thermodynamically, trivalent chromium, which is the predominant form in these waste materials, can be oxidised to the hexavalent form by atmospheric oxygen. Detailed research work on both slags and sludges has shown that a gradual emergence of hexavalent chromium can indeed be observed. The mechanism is governed by close physical contact between chromium oxide (or hydroxide) phases on the one side and calcium oxide (or hydroxide), which is present as flux in slags and residual lime in sludges, on the other. If oxygen can migrate to the points of contact, gradual formation of calcium chromate ensues.Hexavalent chromium is associated with high environmental toxicity, and hence undesirable in landfilled materials. Moisture migrating through landfill deposits can mobilise the highly soluble chromates and thus potentially transport them into natural waterways. Such gradual release from stainless steel and ferrochromium slag deposits has been demonstrated in a column experiment."

Jan 1, 2003

By Jan J. Cilliers, Nicolas Barbian, Esther Ventura-Medina

"Froth structure and stability are known to play an important role in determining flotation recovery and selectivity. An industrial sampling campaign was performed to develop a clearer understanding of the effect of flotation variables on froth stability and the role played by the resulting stability on flotation performance.Froth stability was estimated as the fraction of bubbles bursting on the surface of the froth through image analysis and the solids loading on the bubbles at the top surface. The image processing was performed using the Smartfroth software on the top surface of the froth. The system gives measurements of bubble size distribution, average bubble size and froth velocity. The froth velocity was used to estimate the volume of bubbles overflowing the weir yielding to the fraction of air overflowing the cell. This measurement is the complement of the rate of bubble bursting on the top surface. Also samples of the lamellae were taken by touching the top surface of the bubbles with a glass slide. Then, the amount of solids and liquid per unit area in the bubble lamellae was estimated gravimetrically. Both measurements were used to establish stability criteria.It was generally found that high air flowrates resulted in a drop of froth stability showed by a drop in the fraction of air overflowing and a decrease in the solids loading and simultaneously produced low copper recoveries and low concentrate grades. Deep froths only allowed a small fraction of air to overflow and consequently produced low recoveries. An increase to high frother dosage did not result in an improved fraction of air overflowing, hence producing low recoveries. Likewise, low frother addition only allows low recoveries because the resulting unstable froth cannot support itself. Low aeration was found to be preferential as it allowed high particle loading, therefore high bubble stabilisation, and low gangue entrainment, resulting in the highest flotation performance."

Jan 1, 2003

By Chen Shuwen, Yao Zhihua

In the process of thickening dewatering_the motion state of two- phase flow in a thickener has a very great influence on thickening efficiency. The investigation was made using copper mill tailings. In this investigation the authors explored the formation conditions and motion range of density current in the thickening process by model experiments, and analyzed the influence of density current on thickening efficiency. The results have shown that the formation of density current has relations with the structure parameters of a thickener and thickening process. The density current and its forming location affect thickener’s working efficiency. The author measured the motion state of two- phase flow in a 53-m dial. thickener for copper mill tailings under its operation conditions and analyzed the density distribution and motion state of two-phase flow in the thickener. The results obtained by the industry tests have shown that the motion state of two- phase flow in the thickener can be greatly improved by modification of its structure, achieving a great improvement in its thickening efficiency. It is concluded that, a thickener’s working efficiency depends on the formation and motion range of density current in it, which is of great importance to designing and establishment of thickener’s working parameters.

Jan 1, 2003

By Sarah K. DeBono, Alan J. Monaghan, Emmanuel V. Manlapig, Gregory J. Harbort

"The Jameson Cell is a type of flotation machine in which air and pulp are brought together in a vertical tube called a downcomer. Within the downcomer the air and pulp are dispersed into a dense foam of fine bubbles, which creates a favourable environment for bubble-particle collision and subsequent collection of hydrophobic particles. The intense collection zone within the downcomer can be considered similar to the zone between the rotor and stator in mechanical flotation cells.Research into the bubble-particle collision and fluid dynamics of mechanical cells rotor-stator zone has been limited by the difficulty of achieving accurate measurements in production sized machines. With the Jameson Cell the downcomer is largely external and separated from the flotation tank, allowing ready access to the primary contacting zone for measurement and analysis.An investigation has been undertaken into the operating characteristics of the downcomer relating to bubble-particle collision. An effective mapping of the downcomer has been made through measurements of void fraction and bubble size taken across cross sections of the downcomer. Analysis of these measurements has provided an interpretation of the variations in the air and fluid dynamics, bubble size and distribution throughout the downcomer chamber."

Jan 1, 2003

By Leon Lorenzen, Rodrick M. Lamya

"Leaching behaviour of nickel – copper matte in a CuSO4–H2SO4 solution during the repulping stage of a matte pressure leaching process has been studied. The base metal recovery process investigated in this study consists of a matte repulping stage prior to a series of pressure leach stages. The repulping stage is essentially an atmospheric leach stage in which the Ni-Cu matte, containing small amounts of cobalt and iron, is leached in copper spent electrolyte from the tankhouse, resulting in dissolution of the nickel with simultaneous precipitation of almost all the copper.Effects of various process parameters on the kinetics and extent of the leaching reactions, as well as on the cementation of copper from the solution have been quantified. The parameters investigated were temperature, particle size, pulp density, stirring speed, residence time, initial copper concentration and initial acid concentration.Leaching characteristics of the preleached matte during the subsequent pressure leach operation has also been studied. The effects of variations in the conditions in the repulping stage on the kinetics and degree of base metal dissolution during the pressure leach stage have been investigated. Any transformations that occur in the mineral phases of the matte during the leaching process have been studied, and a leaching mechanism proposed."

Jan 1, 2003

By Dominic Howarth, Diana Drinkwater, Don McKee

At a time when the mining and minerals industry across the world is undergoing unprecedented change, the very fabric of the tertiary education system which is the principal source of trained professionals to the industry is in decline in many countries. The change sweeping the industry is globalisation as evidenced by the emergence of a relatively small number of increasingly dominant corporations with operations in most of the major mining countries. The education sector is struggling to provide sufficient graduates as the viability of small mining schools declines. That is only part of the problem as the global operating industry is increasingly seeking graduates who are comfortable working in different countries and cultures. One obvious response to the industry needs and developments is for the education sector to consider how it can best respond to the global opportunities. This paper presents the case for a global education network which is based on a network of international thinking Universities and which makes use of the latest in educational thinking and technologies to provide a quality education and in the process produce graduates fitted for international careers.

Jan 1, 2003

By Harri J. Lehto, Marja I. Oja

"The purpose of grinding circuits is to produce a particle size distribution that has as much as possible the wanted particle size class. In practise, however, the production of the wanted size class is not at all as simple as it sounds. In the case of industrial minerals for example the end user may give very tight specifications for the particle size distribution and for the chemical composition of the product. This leads in many cases to a very demanding grinding process, if we want to reach and maintain these specifications. In other words, the required size distribution is not necessary the best possible for the chemical composition.Screen models aim to predict the size distribution and flow of the products when a feed size distribution, feed tonnage, and grade efficiency curve are known. The approach used in this study was to select the most suitable empirical model for classification. Suitability of the existing models has been evaluated and accuracy compared. The tests showed that best grade efficiency model was the Rosin-Rammler model.The performance of a screen was evaluated in order to minimize the amount of fine material in the screen overflow. The experiments were carried out using Derrick single-deck screen, first alone with recycling and then in the closed circuit with a rod mill using two different scales. The separate screen tests showed the expected behaviour of the grade efficiency curves. In the pilot tests the Leonard screen efficiencies stayed almost constant. This suggests that the screen works better in a milling circuit. However the loading of the screen turned the product of the mill coarser that helped screening. The grade efficiencies obtained from the pilot tests had the same general shape. The regression analysis of the pilot test runs did not give an acceptable correlation for the parameters. This suggests that pilot tests cannot be directly used to scale or to optimise industrial milling circuits. However they can be used to predict the trends of behaviour of an industrial circuit."

Jan 1, 2003

By Ponisseril Somasundaran, H-L. Chen, University of Athens, D. R. Nagaraj, Zhonghua Pan, Jing Wang

Gums are often used as depressants for talceous gangue minerals in the flotation of nickel and platinum bearing ores. However, the mechanisms of gum adsorption on talc are not clearly established. In this work, adsorption of guar gum at the talc-solution interface is investigated using spectroscopic and allied techniques. Guar gum adsorption on talc is not affected significantly by changes in solution conditions such as pH and ionic strength. Electrokinetic studies showed that guar gum decreased the negative zeta potential of talc but did not reverse the charge. Fluorescence spectroscopy studies conducted to investigate the role of hydrophobic bonding using pyrene and dansyl probes showed no evidence of the formation of hydrophobic domains at talc-aqueous interface. Urea, a hydrogen bond breaker, reduced the adsorption of guar on talc to the same extent as that for guar/alumina system, in which hydrogen bond plays an important role. All of the above results suggest that one of the main driving forces for guar adsorption on talc is hydrogen bonding rather than electrostatic or hydrophobic force.

Jan 1, 2003

By L. Burdukova

In flotation, depressants are used to reduce the amount of gangue that reports to the concentrate and hence increase the selectivity of the flotation process. At the University of Cape Town extensive batch flotation tests are carried out to evaluate industrial depressants and standard procedures have been developed over the years. This study was conducted in order to develop an improved method for comparing depressants using machine vision as an aid. The modified method of batch flotation involved a test with prolonged intervals between scraping to allow more time for the froth to build up and mature.

Jan 1, 2003

By Ronald Smeink, Ton de Gouw

"Reagents are an important cost-factor in the flotation of minerals. The mechanism of collectors and frothers has been studied extensively, but on depressants – probably the biggest cost-factor in the reagent suite – very little is actually known. Theories are frequently faced with the bare facts, pointing in another direction. Fundamental research is complicated by the fact that the amount of possible interactions in the flotation cell is almost unlimited and makes “change-one-parameter-at-a-time” experiments questionable and at least difficult to interpret. Also, the adsorption of depressants on the ore is very strong and desorption merely impossible. Detection methods therefore tend to be indirect and – therefore - non-specific about the location of the depressant on the ore.Depressants are supposed to adsorb selectively on gangue minerals; not on the valuable minerals in the froth. In order to be able to develop better and ‘’smarter’’ depressants, an analytical method is therefore required that will enable to detect which (=qualitatively) depressant, in which concentration (=quantitatively) sits where exactly (= selectively) on the mineral surface. (Answering the question: ‘’ Which minerals is located direct under the depressant?’’)And also: does the depressant compete with other reagents for that location? (like collectors) This analytical method is under development. The actual status of the method is promising and the results will be shown."

Jan 1, 2003

By G. Demi, G. Belardi, N. Shehu, S. Cico

The physico-chemical interaction between minerals such as olivine, chromite and serpentine and the ions most commonly present in solution, like Ca and Mg and flotation reagents such as EDTA and oleic acid was investigated. The study was conducted via release tests, electrophoretic measurements and microflotation of selected minerals coming from the Kukes deposit (Albania).

Jan 1, 2003

By Konstantin Fedotov, Victor Beloborodov, Anatoly Potyomkin

"There are areas in Russia, which cover huge territories and they are north, and Siberia. These difficult to access regions with cold climate are rich in a great number of distant deposits of valuable and rare metals, gold and platinum. The development of such deposits requires highly effective technologies of mineral processing which could be realized in modular and quick-built processing plants.The work presented includes the results of long term research in the development of new technologies of processing of zirconium (in the form of rare mineral Baddeleyite – natural zirconium dioxide) bearing ore of the Kovdor deposit which is located in the Polar region of the Kola peninsular and also in Siberia deposits of of ledge ores of gold."

Jan 1, 2003

By T. V. Chnyrenkova, J. Troncoso, V. A. Luganov, G. P. Kluev

"Arsenic-gold bearing ores are used as flux in smelting or are leached out with extraction of gold. For decreasing arsenic content in processed materials and for breaking up the lattice and opening up of gold the raw materials are roasted. Some regularity was established for sulfidizing of arsenic bearing compounds in a presence of pyrite and for oxidation of ores and concentrates in the presence of soda.This article analyses the results of laboratory and pilot testing of dissociating and oxidizing roasting of gold-arsenic bearing concentrates. During the dissociation roasting under vacuum arsenic is sublimated into elemental and sulfide forms. This process allows minimizing the negative influence on the environment but requires costly engineering solutions. Roasting in a limited quantity of oxygen in the gaseous phase makes it possible to sublimate arsenic in the form of oxides and sulfides and may be carried out in fluid bed furnaces."

Jan 1, 2003

The introduction and subsequent ascendancy of autogenous and semi-autogenous milling for comminution circuits has undoubtedly lead to many economic advantages. From a process viewpoint, however, at least one downside has been the sensitivity of these machines to process input variations. Foremost among these is ore competence, though feed size comes a close second. This sensitivity is due to the reliance of ag/sag mills on the feed ore for their grinding media competence and size. Autogenous (ag) mills are the most sensitive in this respect with semi-autogenous (sag) mills being increasingly less so as the ball charge is increased. Increasingly designers and operators are recognising the importance of feed size and the benefits of manipulating it to improve performance. This has been achieved by installing additional crushing/screening capacity ahead of the ag/sag, better operation of the primary crusher, better control of segregation cased by stockpiles and bins and by changing blast design/practices to modify the ROM size distribution. This paper describes the influence of feed size distribution on ag/sag mill performance with reference to a range of plant data. It particularly concentrates on how changing blasting practice to modify ag/sag feed size can have a considerable overall benefit.

Jan 1, 2003

By P. Huang, D. W. Fuerstenau

Various factors that control the natural flotability of talc, including differences due to crystal face and edge effects, were delineated. For study of talc depression phenomena, dextrin was used as a model depressant. For the enhancement of talc flotation, dodecylammonium acetate (DDAA) was used as the collector. The interaction of DDAA with talc was assessed by flotation experiments and electrokinetic (zeta potential) measurements, from which the role of hydrophobic bonding can be demonstrated. The results presented in this paper provide useful information on how the crystal chemistry and surface chemistry control the electrical double layer, adsorption phenomena, wettability, and flotation behavior of talc in aqueous media.

Jan 1, 2003

By P. Harris

"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

By Pradip, Beena Rai

A molecular modeling study was carried out on an adsorbed oleate monolayer on the surfaces of three calcium minerals, fluorite, calcite and fluorapatite using Universal Force Field (UFF) potentials. The cleavage plane of calcite {104} was the best template for oleate monolayer adsorbed since the surface structure enabled all the calcium sites available on the surface to be occupied by oleate anions. The area occupied per chain of oleate in this well packed monolayer was computed to be 20.2 Å, which exactly matches the value calculated to be the parking area per oleate molecule for a fully packed monolayer based on strictly geometric calculations. On the other hand, the precentage of calcium sites occupied by oleate to achieve a fully packed monolayer in case of fluroite and and fluorapatite was found to be 67% and 75% respectively. The results of this theoretical study suggest that while all the three adsorption conformations, that is unidentate, bidentate and bridging type are equally likely on fluorite and fluorapatite, bridging is most likely on calcite. Interestingly, all the conformations are observed experimentally for calcite-oleate system also. The reasons for this discrepancy between the theoretical predictions and experimental observations are not clear. More work is required to resolve this discrepancy, in particular simulation studies in presence of solvent water molecules on the surface.

Jan 1, 2003

By J. B. Rubinstein

"The paper gives an overview of the history of flotation machine development. The laws of their evolution are stated and the place and role of column flotation are demonstrated.The major parameters of column cell diameter and height are discussed. Options are proposed for optimization of the hydrodynamic characteristics of large-capacity column cells. The high efficiency of columns with cell height of 4-6 m is demonstrated. The optimum parameters of multisectional column machines are determined. Their advantages compared to monocells are shown. A scaling-up procedure for column machines was developed based on flotation macro- and microhydrodynamics simulation."

Jan 1, 2003