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By Shoji Taniguchi, Lifeng Zhang

"In this paper, firstly the 3D single-phase turbulent steady fluid flow in a vessel with four baffles stirred by a single impeller is mathematically simulated. Turbulence is modeled by using the standard k - e model. Sliding-grid method is used to model the impeller. The flow domain is divided into two cylindrical, the inner one rotates at the same speed as the impeller, and the outer one is fixed with the baffles. Results indicate that the high-speed zone is near the paddles, and larger stirring speed generates larger fluid flow velocity. The calculated stirring intensity data are used to analyze the experimental results. Secondly the effects, such as filter pore size, gas flow rate and NaCl concentration, on bubble size are studied by experiment. For the particle removal rate by bubble flotation in this vessel, first order kinetics is adopted. The effects of initial number of the particles, gas flow rate, particle and bubble size, stirring speed and surface condition, on the removal rate constant are discussed, and an empirical equation is derived by experimental data. At last, a simple model is developed to study the particle attachment probability on bubble surface under turbulent flow conditions. IntroductionIt is well known that inclusions have a bad effect on steel quality. Trying to remove inclusions from liquid steel as many as possible is one of the main objects for the metallurgical workers. Lots of ways are developed to remove inclusions from liquid steel. Gas injection is an effective one. This technique is used to achieve homogeneity in the temperature and metal composition and to assist in the removal of second phase and dissolved impurities from molten steel. Gas injection is commonly applied to the secondary metallurgy processes and continuous casting, for example the ladle argon gas treatment, RH vacuum degassing, and the gas injection in the Submerged Entry Nozzles (SEN) of continuous casting mold, etc. The development of these processes focuses on achieving two conditions: fine bubbles and good mixing. Fine bubbles provide a large gas/liquid interfacial area and a high attachment probability to inclusions, and good mixing enhances the efficiency of impurity transfer."

Jan 1, 2000

Zinc produced by pyrometallurgical processing techniques suffers the disadvantage of restricted market potential because of its impurity contents, typically lead and cadmium. Market zinc to the Special High Grade (SHG) standard can only be produced by reflux distillation refining, which is costly in terms of energy and equipment, and potentially capacity limiting. Recent published laboratory work suggested that molten salt electrorefining of zinc metal is a potentially much cheaper alternative to the reflux distillation refining. The extrapolation of the laboratory results to an industrial configuration, however, resulted in an estimated power consumption for electrorefining and associated costs offering no advantage over current reflux distillation practice. A review of this estimate now shows that a serious error in calculation was made, and that the energy consumption for the electrorefining of molten zinc would be an order of magnitude lower than that for reflux distillation refining. While this is a promising indication, further research is required before development towards an industrial scale operation is warranted. This would particularly relate to the extent to which adverse electrolyte deterioration may take place and its potential effect on the anode and cathode efficiencies of the process. This paper considers the laboratory investigations required to explore the industrial potential of the molten salt electrorefining of zinc and foreshadows some of the practical problems to be solved in further development.

Jan 1, 2000

By Fabiola Alvarez, Ana E. Bote, Daniel Pasquevich

"The oxidation of aluminum and its alloys was extensively studied for improving the corrosion resistance in structural materials having high specific strengths. But this reaction involves the formation of a very thin barrier layer on the metallic pieces. Furthermore, the ·recent development of the directed melt oxidation process for producing metal-ceramic; composites has renewed the interest in the study of interaction between gases and metals. Oxidation experiments in the presence of different chlorine partial pressures and at different temperatures were performed in ·a thermogravimetric balance, and microstructures were analyzed by electronic microscopy and X-ray diffraction. The oxy-chlorination kinetics was determined and the oxide formed W(IS amorphous at temperatures below 600 °C and crystalline .at higher temperatures. The appropriate experimental conditions for the fastest completed oxidation was further determined.IntroductionThe use of fine powders for the manufacture of ceramic components has significant advantages. They include excellent sinterability; low sintering temperature and better microstructure leading to improved mechanical properties. The conventional method of producing fine oxide powders involves controlled precipitation and pirolysis of suitable salts. The main limitation of the high temperature decomposition route is the evolution of environmentally unacceptable and corrosive gases. Controlled precipitation of hydroxides from solutions of salts, followed by thermal treatment involves large volumes of solutions and the calcination step that can induce grain growth (1).Direct oxidation of aluminum metal for producing alumina powder requires high temperatures for the direct oxidation of molten Al alloys by a vapor phase oxidant process (2, 3) or high technological process like thermal plasma reactor ( 4).Oxidation of high purity aluminum (5, 6) below the melting temperature· is initially characterized by a nearly linear reaction rate, followed by a rate which decreases rapidly with further weight gain. However, the oxidation rate of an aluminummagnesium alloy is much faster and it does not conform to any common oxidation law, but it is nearly parabolic at temperatures between 200 and 400 °C, an nearly linear· above 400 °C."

Jan 1, 2000

By K. A. Smith, X. Cheng

Introduction The separation of minerals from complex sulfide ores by flotation requires careful control of the surface chemical behaviors of the minerals constituting the ores. When the minerals in the ore are finely disseminated, extremely fine grinding is needed to liberate the minerals. Fine grinding is not only an energy-intensive operation, but also influences the flotation behaviors of liberated minerals. Steel balls are commonly used for grinding. Galvanic interactions occur not only between sulfide minerals and grinding media but also among the different sulfide minerals themselves. The electrochemical characteristics of chalcopyrite and pyrrhotite when they are independently coupled with steel grinding media and the relevance of these characteristics to the flotation behavior of these minerals have been exten¬sively studied (Cheng and Iwasaki, 1992: Li and Iwasaki, 1992). These studies dealt with reactions in two electrode combinations, simulating mineral-grinding medium and mineral-mineral interactions. In practice, however, it is more common to involve more than one sulfide mineral. In a study of a pyrite-pyrrhotite-mild steel system, Pozzo et al. (1989) provided evidence that a mineral having an intermediate potential could behave differently, depending on the condi¬tion of galvanic contact. This investigation was undertaken to study a chalcopyrite-pyrrhotite-mild steel system to gain better in¬sight into the mechanism of multiple galvanic interactions. A three-electrode system was chosen to simulate a typical copper sulfide ore. The sulfide minerals were represented by chalcopyrite and pyrrhotite. The grinding medium was rep¬resented by mild steel. The nature of galvanic interactions involving these minerals and grinding medium in an oxygen atmosphere was investigated in a three-electrode combina¬tion, and an attempt was made to relate the laboratory flotation results of pyrrhotite-chalcopyrite ores. Possible implications to the differential flotation of complex sulfide ores are discussed. Key words: Electrochemistry, Flotation, Sulfide ores Experimental The pyrrhotite (57.74% Fe, 0.09% Cu, 4.84% Ni and 36.54% S) sample was obtained from Falconbridge Ltd.'s Strathcona mine, Ontario, Canada, and the chalcopyrite (26.00% Cu, 28.57% Fe, 0.05% Ni and 31.52% S) sample came from Transvaal, South Africa. Mild steel (AISI 1020, 0.2% C) was chosen to represent grinding media. A conventional three-electrode cell was used in the elec¬trochemical measurements. The working, counter and refer¬ence electrodes were, respectively, sulfide minerals or mild steel, graphite rod and saturated calomel electrode (SCE, 0.245 V vs. standard hydrogen electrode). The exposed areas of the sulfide minerals and grinding medium electrodes were approximately the same (0.17 to 0.19 cm2). The preparation methods of working electrodes, the reagents used, the experi¬mental procedures and the instrumentation were the same as those described previously (Cheng and Iwasaki, 1992). Rest potentials of pyrrhotite, chalcopyrite and mild steel were measured individually in 0.05-M sodium sulfate solu¬tions. Combination potentials and galvanic currents of the sulfide minerals and grinding medium were measured in short-circuited two- and three-electrode systems. All poten¬tials in this study are quoted in volts with respect to the standard hydrogen electrode (SHE). To simulate the constantly abrading conditions in a ball mill, rest potentials, combination potentials and galvanic currents were also measured by rotating a porcelain ball against chalcopyrite, pyrrhotite and mild steel electrodes in

Jan 1, 2000

By Nora M. Hutt, Kevin A. Morin

One technique for controlling ongoing acidic drainage is to relocate and submerge net-acid-generating waste rock in a lake or water-retaining impoundment. This can lead to the overall improvement of water quality and the reduction In short-term environmental liabilities. A case study of this technique is the Eskay Creek Mine in northern British Columbia. Some findings of the study are: (1) the addition of lime to each truckload of rock, based on its rinse pH, neutralized the accumulated acidity and suppressed the accumulated-metal release, (2) only 10-20% of the dump's neutralization potential had been consumed when acidic drainage appeared, (3) water chemistry in the watershed recovered roughly three years after relocation, and (4) environmental liability was reduced due to the cessation of on-land acidic drainage with no degradation of lake chemistry.

Jan 1, 2000

By Patrick M. James

Many in mining believe that the industry is slipping behind in public image, in public mineral education and, particularly, in mining's basic right to do business. It is critical to turn things around - to change the rules of the game soon - before mining loses any chance of recovery. In the industry's experience, there is a technique of project development and operation that can help gain ground on public opinion. Only recently has this technique had a name, and that is sustainable development. What is sustainable development? Sustainable development is broadly accepted and supported by the international business community. And significant thought and work has been devoted to the subject. Research into the topic was initially confusing because the definitions of sustainable development are written in terms the writer, and his or her constituency understands. To some, it refers to environmental protection. To others, it is about social responsibility. And to the developer, it is about economic benefit. Slowly a theme emerged from the research that seemed to be part of all the definitions. That theme has three parts. First, the development, whatever or wherever it is, must contribute economic value to the developer and the stakeholders of the development. Stakeholders in this context include employees, neighbors, residents of the surrounding area, citizens of the country, suppliers and all others affected by the development. Next, sustainable development must contribute environmental value. This means that at a very minimum it must be neutral and not cause irreparable damage. And last, and what is new for miners and most other businessmen, it must contribute real social value to the stakeholders. How to use the concept? With that three-part theme as a working definition, the mining industry must find ways to use that “the challenge is for an individual company to translate what sustainable development means for them. There is no one model..." Donald W. Gentry is president and chief executive officer of Polymet Mining and former professor emeritus of mining engineering at Colorado School of Mines. He added: "While simple to state, the concept is anything but simple to implement. Present trends indicate ... one wins the sustainable development argument by staking out the high ground early..." In other words, start using sustainable development principles at the beginning of the project. New ways of doing business The mining industry's challenge is to implement sus¬tainable development universally around the world. Paternalism as a way of doing business is dead and a new model of doing business is emerging. All types of businesses are learning to deal with the stakeholders of new developments. Mining cannot be an exception to these trends. To understand how the international mining business came to sustainable development, it is useful to look back a few years. For many North American mining engineers, there were few opportunities for foreign assignments from the 1960s to the 1980s. American companies had been asked to leave many of the Latin American countries. Africa was going through a continent-wide upheaval. The Soviet Union and China had Eastern Eu-

Jan 1, 2000

By Manqiu Xu, Pete Winn, Steve Wilson

"In the flotation of ultramafic ores at Thompson mill, Inco Limited, CMC is used as both a floatable rock depressant and electrostatic serpentine slime dispersant. CMC, being a high molecular weight polymer, creates a serious handling problem in its introduction into the flotation processes. Typically, it is added as a 1-3% solution. This requires an enormous handling facility and makes its metallurgical gains uneconomical.Laboratory studies have shown that dry CMC addition as opposed to wet addition is feasible, as long as sufficient conditioning time is provided. Dry CMC addition into the grinding mill is also possible but its effectiveness is slightly reduced as compared to dry addition after grinding mills. Dry CMC addition using a vibratory feeder into the mill discharge is successfully applied in the treatment of ultramafic ores at Thompson mill.INTRODUCTIONManitoba Division MineralogyAt Inco’s Manitoba Division, two distinctly different sulphide ores are processed at the Thompson mill - primarily by froth flotation. The Thompson and Birchtree mines are both located within the Thompson Nickel belt. Sulphide mineralogy is relatively simple and includes both hexagonal and monoclinic pyrrhotite, pentlandite and minor chalcopyrite hosted in metasedimentary and metavolcanic rocks. The significant difference between the two mines is the amount of ultramafic rock associations in the host material. Increasingly, more of the ultramafic associated ores from the Birchtree mine are being processed through the mill with a characteristic poor metallurgy."

Jan 1, 2000

By K. A. Natarajan, Namita Deo

Strains of Bacillus polymyxa, preadapted and grown in the presence of corundum, were found to be capable of the efficient separation of hematite from alumina. Results of tests performed using binary hematite-corundum and ternary he- matite-quartz-corundum mixtures in the presence of cells and metabolic products separated from the adapted bacterial culture indicated that more than 99% of the hematite could be efficiently separated through selective flocculation after desliming. It was found that alumina-specific bioproteins and other nonproteinaceous compounds were secreted by bacterial cells after adaptation to the mineral. The utility of this bioprocessing is demonstrated in the removal of iron from bauxite ores through selective

Jan 1, 2000

By K. Norrena, E. Magri

An important problem in mine operations is the classification of material as waste, low-grade stockpile and ore. This classification must often be made with blasthole data that are widely spaced and that have sampling errors. Geostatistical-simulation techniques combined with basic economic principles allow a procedure for classification that maximizes the expected profit. Geostatistical-simulation methods (Gaussian, indicator or annealing-based) allow the integration of hard and soft data in the creation of alternative, equally probable realizations of the mineral grades. At each location, for each realization one calculates the "profit" if the block were to be classified as ore or waste. The optimal classification is the one that maximizes expected profit (a maximum profit selec¬tion or MPS procedure). In this paper, the authors discuss the theoretical justification of the method and implementation details. The use of blasthole data from different types of mineral deposits, that is, different levels of continuity, are considered. The authors also show the efficacy of the procedure with different levels of sampling error. The increased revenue due to the MPS procedure and improved sampling is shown. The paper shows the geostatistical-simulation procedure and the uncertainty in block grades that result from incomplete and imperfect sampling. The optimal classification is presented. Optimal block classifications are transferred to realizable dig limits by hand-drawing polygonal boundaries. The results of the proposed method are compared to classification based on kriging. Limitations and areas of future work are identified.

Jan 1, 2000

By P. H. Willis

Since the 14th CMMI conference, held in Edinburgh in 1990, at which a paper was presented by the author (Willis, 1990) reviewing the role of integrating new technology as a survival strategy for South African gold mines, considerable change has occurred in the South African mining industry. This paper reviews the current state of the industry and provides an update on the technologies discussed ten years ago. It reviews available technology and provides a broad economic assessment of these technologies if they were to be introduced in an integrated mining system with a focus on deep level mining below 3000 m. It also reviews possible future technologies currently being researched and developed by CSIR: Division of Mining Technology (Miningtek).

Jan 1, 2000

By D E. Langberg, J S. J va, D R. Swinbourne

Specifications on the types and levels of impurities tolerable in metals are becoming increasingly stringent, and are pushing the limits achievable with conventional refining technologies. Particularly difficult is the removal of electrochemically noble elements with low volatilities, such as copper, from more active host metals such as lead, iron and aluminium. Electrochemical refining, utilising the ability of certain solid electrolytes to selectively transport copper or other impurity cations away from the molten host metal into a separate refining phase, may provide an answer to this problem. Numerous studies on solid electrolytes used in concentration sensors have been reported, as well as a limited number on metal refining. Oxygen anion conducting solid electrolytes have been applied to the deoxidation of copper and steel while cation conductors, eg ¯ -alumina and Nasicon materials, have been used to remove lithium and sodium from aluminium. However, solid electrolytes have yet to be applied to the removal of noble elements. The behaviour of solid electrolytes under the extreme conditions of molten metal refining is not well understood. This paper will examine the potential use of solid electrolytes to remove noble metals such as copper from active host metals such as iron. The suitability, and selection criteria of available solid electrolytes for implementation in the metal refining industry in the future will be discussed. In particular, the stability of Cusicon, a copper superionic conductor potentially suitable for use in metal refining, has been assessed and the results of the experiments are presented.

Jan 1, 2000

By Barrick Pierina, John Frostiak, Igor Gonzales, Kenneth G. Thomas, Ken Manning

"1.0 SummaryThe Pierina deposit was acquired in August 1996 when Barrick Gold Corporation purchased Arequipa Resources, a junior mining company with extensive land positions in Peru. At the time of acquisition, Arequipa had developed two exploration tunnels and drilled 9 exploration holes on the property. Metallurgical tests, conducted on samples taken from the tunnels and the exploration holes indicated that the ore was amenable to heap leaching. Barrick’s exploration team recognised from the outset, the potential of the mineralisation and convinced Barrick’s senior management that this was indeed a world class deposit that should be pursued. On November 25, 1998, the first dore was poured at Pierina, 27 months from the time of acquisition. During that period Barrick completed its exploration programme, prepared a development plan including capital and operating costs, production profiles and cash flow forecasts, and a schedule to develop a mine and construct a leach pad and gold recovery plant, including all supporting infrastructure. All permits and environmental approvals were obtained and all necessary land was acquired. The project was completed on schedule and under budget. This was the first greenfield mine development for Barrick outside of North America.This paper details, mainly, the research and development, engineering, construction and commissioning of the metallurgical process facilities.2.0 The Develonment ProgrammeImmediately after the acquisition, Barrick began the process of gathering information required to prepare a project development plan. Kilborn Engineering was retained to assemble all of the information collected and collated into a development plan document. This document was completed by June 16,1997. The objective was to bring the mine into production as quickly as possible with critical activities identified as follows:"

Jan 1, 2000

By John R. Twining, Michael D. Lawton, Ross A. Jeffree

The Finniss River system in tropical northern Australia has received 'acid-drainage' contaminants from the Rum Jungle uranium/copper mine site over the past 4 decades. Following mine-site remediation that began in 1981-82 the annual contaminant loads of sulfate, Cu, Zn and Mn have declined by factors of 3, 7, 5 and 4, respectively over 1990-93, compared to the 1969-74 pre-remediation loads. Comparison of the frequency distributions of contaminant water concentrations over these pre- and post-remedial periods have shown varying degrees of reduction in the highest levels following mine-site remediation, that are consistent with reductions in their annual-cycle loads. Among the three selected major metal contaminants the reductions in maximum water concentrations are most pronounced for Cu. The demonstrated reductions in the highest water concentrations of all four contaminants are also associated with previously reported ecological improvement in the Finniss River system, compared to the benchmark of environmental detriment established in 1973fl4, prior to the beginning of remediation at the mine site.

Jan 1, 2000

By S. Chander, S. W. Musselman

The molecular structure of hydrophobic and hydrophilic groups in nonionic surfactants has been related to the wetting and dispersion of selected pigments. The nonionic surfactants included in this study are acetylenic diol based surfactants and ethoxylated alkyl phenols. The Langmuir model could be used to fit adsorption data. Further analysis of the data showed that the free energy of adsorption was a function of adsorption density of the surfactants at the interface. The change in free energy with adsorption density could be interpreted by considering a change in the orientation of the adsorbed molecules. Acetylenic diol based surfatants were found to have an area per molecule of 2-3 times that of similarly ethoxylated alkyl phenols. The wetting and dispersion properties of lamp black, a model hydrophobic surface, by these surfactants were investigated by contact angle measurements and particle size analysis. Acetylenic diol based surfactants with ethylene oxide contents between3.5 and 10 moles per molecule and alkyl phenol based surfactants with approximately 9 moles of ethylene oxide per molecule were found to provide superior wetting abilities. Longer ethylene oxide chains were required for superior dispersion capabilities within each family of surfactants. Complete wetting and dispersion was found to occur above the critical micelle concentration of the surfactants.

Jan 1, 2000

Many mining operations generate seismic signals. They come from blasting and from underground mine failures such as rockbursts, longwall first caves, coal bumps and pillar collapses. Traditionally, seismic motions have been of concern on a local scale because they could create damage to structures at the mine site or at neighboring locations. Recently, there has been much interest in the Comprehensive Nu-clear-Test-Ban Treaty (CTBT). It prohibits any kind of nuclear explosion, anywhere. So distinguishing signals of mining operations from a possible nuclear explosion becomes important. An international monitoring system (IMS) is being implemented to verify the Treaty when it is ratified. It includes a large number of seismic stations capable of recording signals at regional (200 to 2,000 km or 124 to 1,240miles) and teleseismic (more than 2,000 km or 1,240 miles) distances.

Jan 1, 2000

By T. Tamagawa, S. H. Tabaian, I. Iwasaki, N. X. Fu, M. Kobayashi

A gaseous chlorination process for the hydrometallurgical treatment of a chalcopyrite concentrate was investigated. The overall process is visualized to consist of low-temperature chlorination -selective oxidation, followed by aqueous chloride leaching and SX-EW for producing electrolytic copper, elemental sulfur and ferric oxide. In this article, the chlorination phase of the process is described. Initially, the chlorination behavior of chalcopyrite concentrate micropellets was investigated using a small batch-type fluidized bed reactor. The optimum conditions thereby established were used in continuous chlorination tests. The chlorinated products thus prepared were used in the selective oxidation phase of the investigation.

Jan 1, 2000

Change is inevitable but learning from change is an option. Willingness to learn is one of the first lessons that a leader must learn. Get comfortable and get left behind. I propose to outline the main social changes which are taking place and their impact on the Minerals Industry. Also the changing way we do business and what are the skills needed to manage that change and diversity. How are Associations and Institutes responding to this ever changing environment? More specifically, what is my Vision for the Institute to assist professionals to achieve greater and continuing professional excellence in their chosen professions?

Jan 1, 2000

By 1980, the US mining community had reached a broad consensus regarding coal pillar design. The pillar load could be estimated from tributary area theory, and the pillar strength could be estimated from empirical formulas and laboratory coal strength testing. Then the growth of longwall mining required new thinking. Recently, powerful design methods have emerged from analysis of large databases of real-world pillar successes and failures. These include the analysis of retreat mining pillar stability (ARMPS), the analysis of longwall pillar stability (ALPS), the Mark-Bieniawski rectan¬gular pillar strength formula and guidelines for preventing massive pillar collapses. Sophisticated numerical models have also helped transform the pillar design landscape. In the process, the understanding of pillar mechanics has been greatly enriched. A new paradigm identifies three categories of pillars according to the types of failure that are associated with them. These categories are slender pillars (w/h < 3.0), which are subject to sudden collapse; intermediate pillars, in which pillar squeezes seem to be the most common failure mode; and squat pillars (w/h > 10), which are dominated by entry failure (rib, roof or floor) and coal bumps.

Jan 1, 2000

By J L. Mauk

Golden Cross is a volcanic-hosted, low-sulfidation, epithermal Au-Ag deposit in the Hauraki Goldfield. Irrespective of the rock type (andesite versus dacite), hydrothermally altered wallrocks are enriched in K, Rb, As and Sb around Au-Ag mineralised veins of the Empire vein system and stockwork. Sodium and Sr are strongly depleted around these veins, whereas Mg and Fe are locally depleted. Calcium and Si display mixed behaviour, varying from unchanged to depleted to enriched. Other elements including Al, Ti, Mn, Zr, Y, and Nb show little change or are immobile during hydrothermal alteration. Element enrichment and depletion trends are directly related to the degree of alteration and the alteration mineralogy. Addition of K and Rb and converse loss of Na and Sr in intensely altered wallrock surrounding veins corresponds to the replacement of igneous plagioclase by hydrothermal adularia. Sodium and Sr occur in moderately altered rocks on the margins or in æhard barsÆ that contain plagioclase. Locally, elevated Si concentrations and depletion of Mg adjacent to the Empire vein system reflects intense silicification of the wallrocks and the replacement of mafic minerals by quartz rather than by chlorite. The geochemical zonation patterns at Golden Cross are very similar to those at the McLaughlin deposit California, and shallow levels of the active Broadlands Ohaaki geothermal system. Therefore, determination of K, Na, Rb, Sr, and Ca enrichment and depletion patterns provides insight into alteration intensity and mineralogy that is complimentary to traditional trace element analysis of As, Sb, Hg, Au, Ag, Zn, and Pb used in the exploration of shallow level (&lt; 500 m) epithermal Au-Ag deposits.

Jan 1, 2000

By J. W. Choung, J. A. Finch

Acid rock drainage (ARD) is a recognized environmental challenge facing mining industries. An ambient temperature ferrite (ATF) process has been investigated for treating ARD. Most nonferrous metal and calcium ions present in typical ARDs were found to be detrimental to the ATF process. Three approaches were examined, including C02 aeration, addition of complex agents and use of magnetic seeds. By introducing magnetic seeds in the ATF process, the interferences were minimized and all the precipitates formed with lime neutralization were magnetically recovered from a simulated ARD. The residual concentrations of major metal ions in the treated water were environmentally acceptable. The XRD pattern confirmed the spinel ferrite crystal structure of the products

Jan 1, 2000