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By D. Mukerjee, Ramen Datta, Sanak Mishra, R. Veeraraghavan, K. L. Rohira

"Recent efforts at Steel Authority of India Limited (SAIL) has led to the successful development of atmospheric and marine corrosion resistant high tensile Thermo Mechanically Treated (TMT) bars with minimum specified yield strength of 50 kg.mm-2. These rebars are increasingly being used for a wide range of end-applications, namely, concrete reinforcement structures, bridges, flyovers, dams etc. Welding is an important processing tool for each of the above applications. In view of the importance of welding, a comprehensive evaluation of the weldability properties has been carried for the two grades of steels using Submerged Metal Arc Welding (SMAW) process; the most popularly used technique of welding of reinforcement bars (re bars).Implant tests were conducted to assess the cold cracking susceptibility of the steels. The static fatigue limit (SFL) value, determined for the atmospheric corrosion resistant (Cu-TMT) rebars under no preheat and no rebalcing conditions was found to be 63.8 kg mm-2, which was significantly higher than the Minimum Specified Yield Strength (MSYS) (50 kg.mm-2). This indicates adequate resistance to hydrogen induced cracking (HIC). On the other hand, the SFL value obtained for the marine corrosion resistant rebars (Cu-Cr TMT) under no preheat, no rebaking conditions was found to be inconsistent. Repeat of the test with fully rebaked electrodes (350°C-2h) resulted in a high SFL value (60.3 kg mm-2)_The rigidity of the structure or restraint influences the susceptibility of the weld joint to cracking. The cracking tendency increases with restraint intensity (K) of an assembly. The critical restraint intensities determined for the two steels were found to be· in excess of 1680 kg/mm.mm, indicating good welding behaviour with the following welding conditions : for Cu-TMT rebars with no preheat and no rebaking and for Cu-Cr TMT rebars with no preheat and fully baked electrodes; that is under low hydrogen levels."

Jan 1, 1998

This paper reviews the historical literature and the author's experience with regard to the effect that the selection of grinding ball size or sizes has on ball mill grinding efficiency. The conclusions presented provide guidelines for single and multi-size charging prac- tices in commercial milling operations.

Jan 1, 1998

By Aïda Espinola

Decontamination of synthetic solutions containing cadmium ions using coconut fibers in natura was investigated in laboratory scale. Cadmium ions, a serious pollutant of water ways, where it is detrimental to the environment, may be absorbed by fish and mollusk used as food, which will, eventually, poison humans; these ions are usually present in minero-metallurgical and electroplating industrial effluents. Usually employed for the aqueous effluents treatment are chemical precipitation, adsorption and electrolytic processes. Precipitation is not effective for cadmium removal, because of the high KpS of the cadmium hydroxide, which requires high pH; only sulfide would be efficient in cases of very small amounts. Some vegetal refuses have shown to be practical for absorption processes of several metallic ions. We have applied coconut (Cocos nucifera) shells, which are extremely abundant over most of the extensive Brazilian coast, in the removal of cadmium: it has been verified, in our laboratory, that the surface of the fiber of this coconut is rich in chemical compounds which are active scavengers for Cd2+. For the optimization of the process, hydrosoluble components existing on the surface of the fiber, which may be deleterious, were previously washed out by water, and variables, such as the pH and the proportion of mass of fiber to volume of solution, were adjusted. As much as 99% of the initial contaminant metallic ion has been eliminated, resulting a solution to be discarded which contains ca. 0.1 ppm; this attends to the maximum impurity legally admitted by the environmental control agency of Rio de Janeiro, FEEMA, for cadmium ions in aqueous effluents to be disposed in rivers and in the Guanabara Bay area.

Jan 1, 1998

The high-shear colloidal mixer is generally recognised as the most efficient method of mixing cement based grouts. Only recently however has this technology been applied to the production of cemented rockfill (CRF) for use in underground mines in North America. Traditionally, paddle type mixers have been used to produce the cement based slurries required for the preparation of CRF. While considerable success has been achieved with these mixers, tremendous advantages are attained with the colloidal mixer. The combined effect of the highly efficient mixing action and the ability to mix low water/solids ratios, allows for reductions in the cement content for a given strength requirement. Cement can also be replaced by cheaper fillers such as flyash, resulting in further cost savings. Although large-scale dedicated CRF batching plants are typical, there is a growing need for mobile plants capable of operating anywhere underground. The compact size and rapid batching speed of high-shear colloidal mixers has allowed them to be incorporated into skid mounted systems capable of producing and discharging cement based slurries onto rockfill aggregate for the production of CRF. In many cases run-of-mine development waste can be used as CRF aggregate with these slurry plants thereby reducing the cost of waste rock removal. These relatively low cost portable plants have now allowed several mines to economically recover isolated pillars and realise positive returns on their investment.

Jan 1, 1998

By S. Makni, C. Bazin, D. Hodouin

This paper reviews approaches for the real-time estimation of mass flow rates and assays using data from on-stream analyzers and flowmeters in a flotation circuit. Results obtained using one algorithm operating on-line with an industrial flotation circuit are presented.

Jan 1, 1998

By M. Manrique, S. A. Pirzada, P. R. Taylor

A thermal plasma-assisted laminar flow reactor was used to evaluate the kinetics of converting alumina to sodium aluminate in flight. Free energy minimization calculations were used to determine experimental conditions. The experimental variables included alumina particle size, alumina/sodium nitrate molar ratio, temperature and residence time. A mathematical model for the conversion was developed and validated. Experimental and mathematical results are presented.

Jan 1, 1998

By Milton Manrique

The thermal decomposition of ilmenite concentrates in a non-transferred arc; thermal plasma flow reactor was investigated. The plasma torch was operated using argon-helium and argon-nitrogen mixtures as plasma gases. The effect of power, feed rate and particle size was studied. Products were characterized by XRD, SEM, TEM and ICP techniques. Free energy minimization plots were used to predict the thermodynamic behavior of the system under different operating conditions. The results of this investigation showed a significant segregation process where titanium-rich products are collected in the reactor, while iron-rich products are collected in the quenching box and filter. The average size of the product is in the sub- micron range. Titanium nitride was formed and condensed in the reactor zone when using an argon-nitrogen mixture as the plasma gas.

Jan 1, 1998

By M O. Tade, M W. Sze

The particle dynamics of a mixture of coal and zircon system wasstudied in a scaled-down cold model of an industrial kiln. Thefactors investigated in the study were rotational speed (N),zircon-to-coal feed ratio (B), coal particle size (dpc) and the angle of inclination (*) of the kiln. The technique used is the residence time distribution (RTD) method. It was found that rotational speed and angle of inclination are important parameters that affect the residence time of particles in the kiln. A mathematical model for predicting the mean residence time of particles in the rotary kiln was developed. Comparisons with reported models for such systems are discussed.

Jan 1, 1998

During the past decade, international mining companies have descended on South America. Countries like Chile, Brazil and Peru have seen billions of dollars in exploration and development funding turn their once meager mineral industries into mining giants that have become the envy of the world. Part of this outpouring of foreign investment in those countries has been because each has privatized its state-owned mining companies and has liberalized its foreign investment laws. In addition, they have rewritten their mining codes to encourage minerals development and passed new tax laws that have made natural resource development more attractive. Now these same international mining companies are turning their attention to Argentina. This a country that, like Chile, Brazil and Peru, has a wealth of largely un- tapped mineral resources. And Argentina wants its share of the foreign investment that its neighbors have enjoyed. With that in mind, ministers of Argentina's natural resource agencies came to Denver, CO to meet with mining executives and pitch their country's mining industry. The meeting, attended by about 200 people, was sponsored by the US Trade and Development Agency and organized by the World Trade Center Denver. Others involved were the Colorado Mining Association, the Colorado International Trade Office and the Secretariat of Industry, Commerce and Mining of Argentina. The following is a summary of a report on Argentina's mining industry. It was prepared by Anderson & Schwab Management Consultants and distributed to attendees as part of the meeting's program.

Jan 1, 1998

By Mark R. Stephenson

Everyone knows that mining is a noisy job, but did you know that you are nine times more likely to lose your hearing than someone who works in a quieter job? If unprotected from noise on the job, by age 50, you will probably need hearing aids. Obviously, the best solution is to engineer out the noise, but that isn?t always im­mediately possible. Until mines are quieter, one way you can help save your vital sense of hearing is to use hearing protectors whenever the noise around you is hazardous. Even if you already have some hearing loss, you can use hearing protectors to prevent your hearing from getting worse. When loud noise is present, proper use of hearing protectors will help miners pre-vent most or all noise-induced hearing loss.

Jan 1, 1998

By Yuri Gelfgat

"This paper presents some results of the investigation of the steady magnetic field influence on hydrodynamics and heat/mass transfer in processes of semiconductor single crystal growth (Si, Ge, InSn). The investigation employed mathematical and physical simulation techniques of relevant processes and full-scale experiments on growth facilities. A number of additional MHD phenomena have been found generated in the melt due to the rearrangement of flow pattern, the formation of specific convective cells, and the origin of MHD boundary and shift layer.IntroductionMagnetohydrodynamic (MHD) means of creating forces by contact-free methods in liquid conducting media have been widely used in the production of volume semiconducting single crystals. The goal of this method is to control convective transfer processes in the melt volume and on the crystallization front [1-3]. This is due to the sufficiently high conductivity of semiconductor melts (s = 104 /106 O1m-1 ) and an obvious relationship between the hydrodynamics in the melt and at interfaces and the conditions of formation of single crystals and their quality [ 1].All types of MHD effects rest upon the generation of volume electromagnetic forces in the melt by various means as well as on the possibility to direct them arbitrary in space and to adjust easily their absolute values. Fig. l presents different means how to implement MHD phenomena during single crystal growth. It should be emphasized that in all the modifications given in Fig. l additional energy introduced into the melt cannot influence directly the crystallization process since it is incomparable to the energy of molecular forces. Both the influence and efficiency of MHD means are determined solely by the change of motion, heat and mass transfer characteristics."

Jan 1, 1998

By F. T. Cawood

?It is in the interest of stability and investor confidence that the healthy and necessary debate on such a (minerals) policy should soon find its way to consensus.? (President Nelson Mandela at the104th (1995), AGM of the South African Chamber of Mines) Inauguration of the new political dispensation in South Africa initiated a dynamic period in the historical development of its minerals policy. The process of substituting the current South African mineral policy framework with an acceptable ?post apartheid? system, started soon after the 1994 election of the African National Congress (ANC) government. The Green Paper on a Minerals and Mining Policy for South Africa released for public discussion in February 1998, calls for radical transformation in mineral rights ownership. A shift towards exclusive state ownership of mineral rights, away from the present dual system of private and state ownership, is the most significant proposal. The current holders of mineral rights, or their nominees, who lawfully enjoyed security of tenure under past and present mineral laws are opposed to this transformation because mineral rights were often acquired at considerable cost. The situation is compounded by poor public record-keeping and passive mineral rights administration over a very long period. This paper represents a summary of the historical developments leading to the current legislative environment and forms the basis for any discussion on which future sculpturing of South Africa?s policy regarding mineral rights can take place. One cannot plan for the future without considering the past!

Jan 1, 1998

By P. Ritsopoulos, A. J. Dentsoras

The objective of this paper is the development of a reliable simulation model for the operation and production capacity of an aggregates quarry. Based on this model, a computer program is introduced that provides the final production outputs according to the defined material gradation and machinery characteristics. The program takes into consideration all operational parameters that may be introduced by the user through the whole machinery network. As a result, all production parameters are properly updated. The structured simulation program can help detect production inefficiencies that result from design ineffectiveness. Additionally, the program can be used for the generation of alternative scenarios for future modifications of a plant's configuration. Finally, a designer can use it as a tool for obtaining optimum solutions concerning newly designed quarries. As a case study, a quarry operating at Heraklion, Crete, was examined. The application of the program to the plant produced a complete image of the quarry's input/output characteristics, along with some suggestions for improvements on certain production processes.

Jan 1, 1998

By R. S. Rogers

Abstract - Forensic geology in a mineral exploration context is concerned with geology and related technical matters as they pertain to legal cases involving exploration and evaluation of mineral properties. Such cases involve the possibility of outright scams that include falsification of data and information, as well as inappropriate application of various technical procedures. Experience in forensic geology in such cases emphasizes the need for systematic quality control procedures during routine exploration/appraisal and indicates the need for more attention to ‘target hardening’ (improving security in the chain of custody of samples and assay results). A number of ‘early warning signs’ that might suggest some form of tampering or falsification of information are listed. These measures will support the work of the "Qualified Persons" (geologists and engineers) entrusted with the scientific and technical aspects of mineral exploration, and facilitate the increased attention to regulatory oversight and enforcement of securities laws recommended in the report "Setting New Standards."

Jan 1, 1998

By George Owusu

A study has been carried out on the use of solvent extraction, instead of the traditional zinc dust cementation process, to remove copper from concentrated zinc sulphate leach solutions. In a series of experiments using plant solution containing 1.9 g/L Cu, 2 g/L Fe, 173 g/L Zn, 7.9 g/L H,SO,, 0.25 g/L Cd, 15 mg/L Co etc. and LIX 622 in SX-1, up to about 97-98 % of copper present in the zinc sulphate leach solution was extracted with negligible co-extractions of zinc, iron, cadmium, cobalt, etc. pH modification was not required for this reagent. The copper loaded organic was almost completely stripped using 150 g/L sulphuric acid. Investigations into the effect of any possible organiclextractant contamination on zinc electrowinning showed (if any) little effect on current efficiency if the organic contamination is less than 45 ppm; current efficiencies of 95-97 % were obtained. At organic contaminations higher than 45 ppm, the current efficiency dropped to about 92- 94 %. Visually, the organic-contaminated cathode sheets had rough surface morphology, becoming more intense with increasing organic concentration, compared to the non-contaminated cathode sheets.

Jan 1, 1998

By J. E. Golsan

Barrick Gold Corporation installed an expert style control system on the grinding circuit at its Mercur mine. Barrick's main objective was to increase mill throughput by a minimum of 3%. The expert system team collected operating data and then created a knowledge base using Comdale/X expert system development software. The expert system moved from on-line "advisory" mode, testing of expert rules, to full process control in four weeks. Expert system control benefits include a 9-15% increase in mill throughput, consistent mill loading leading to less wear on SAG mill parts, and improved downstream process control.

Jan 1, 1998

By James M. Franklin

Research on modern hydrothermal systems provides quantitative measures of the processes of formation of hydrothermal fluids and of precipitation mechanisms from them. Studies of ancient deposits provide new information regarding volcanological processes that are related to the deposits, as well as data on their spatial and temporal compositional variations. Mew exploration guidelines result from both aspects of research. The most fundamental requirement for large metalliferous hydrothermal systems is an abundant heat supply for the upper two kilometers of the crust. This heat may come from a focused heal source (shallow-level subvolcanic intrusion), but ambient heat also may have provided enough energy for the reactions necessary to effect leaching of metals, especially where heat flow is particularly high (i.e. very large or high-temperature magmatic source, such as ultramafic environments). For most VMS systems, the majority of the metals were derived through leaching from footwall strata; in addition interstratal fluids may enter subvolcanic intrusions during episodes of magma a chamber "cracking," engendering some '?magmatic" component in the hydrothermal system. Direct contributions of metalliferous magmatic fluid also may be significant from arc-related or back-arc felsic or alkalis systems. These latter contributions may form exceptionally high - grade portions in some deposits. Subvolcanic intrusions, which are excellent indicators of high heat flow and may have been the direct driving mechanisms for some stems undergo two stages of alteration: On intrusion emplacernent. fluids may rapidly enter and react with their mesostatic portions, evident in the sills in the Middle Valley. High temperature interactions caused albitization and destruction of oxides and sulfides, releasing metals. During terminal hydrothermal stages, the metalliferous fluid collapsed into the intrusions, forming disseminated and vein sulfides.

Jan 1, 1998

By Richard R. Brochu

At the International Society ofExplosives Engineers Annual Conference held in Nashville, Tennessee in February 1995, a Seismograph Standards Committee was established. The purpose of this wmmittee was to develop objective performance specifications for vibration measurement instrumentation and field use practices. It was also understood that due to geology, temperature, and moisture in the soils, it is not possible to design and build an instrument to give ‘results which are absolutely comparable for ground vibration. It was, however, considered essential to standardize instrumentation by which vibration can be measured under closely defined conditions so that results obtained by users of seismographs are always the same ,&thin stated tolerances.

Jan 1, 1998

Natural gas from the south west Queensland gas fields is now available in north west Queensland to fuel the development of many Carpentaria Mineral Province projects. Like these projects, the south west Queensland gas project, developed under the operatorship of Santos Ltd, has its own æMining CycleÆ. While the project is entering its third expansion phase, it is at the same time actively extending its discovery phase, with large programs of gas exploration and reserves definition. This paper outlines the history of the south west Queensland gas project, with particular emphasis on the relationship of the project to north west Queensland.

Jan 1, 1998

Choosing the correct delay time for many blasting applications is an important and critical blast design parameter for controlling fragmentation, muckpile shape, swell, digability, throw, ground vibration and airblast. BAl and its affiliates have monitored thousands of full scale blasts in a variety of field conditions, spanning over 15 countries, with sophisticated blast monitoring instrumentation. In some blast environments, a small change in the choice of delay times used had a dramatic and pronounced effect on the overall blast results. In other blast environments, large changes in the choice of delays used had absolutely no effect on the final results in terms of specific outputs. In environments which were sensitive to the delay selection, the type of explosive, dynamic response time of the rock mass (TMIN), integrity of the material, burden and rock mass geometry, all played a very important ,role.

Jan 1, 1998