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By J. W. Craven, M. Katom, K. M. McCaffery

At Ok Tedi, ore type and SAG feed size distribution vary widely and frequently. This makes control of the SAG mills by application of the power/pressure relationship difficult. Power logic has traditionally been conservative due to power spikes associated with rapid size-distribution changes. A new expert system was installed in early 2000. The system incorporates multiple state fuzzy logic to deal with frequent and radical ore type and size variations, along with monitoring of motor temperatures. A short-term power spike no longer warrants immediate radical action. This has resulted in increased mill throughput and improved circuit stability. Key words: SAG mills, Mill control, Fuzzy logic

Jan 1, 2003

By F. Forbes

For many years, the Machinery Division of Dravo Corporation has been designing and constructing bins and hunkers as part of overall plant facilities. We have designed bins to handle a variety of materials including coal, coke, iron ores and concentrates, sintered and pelletized ores, calcined and raw limestone, bentonite, alloys for BOF shops, and even cast iron chips from machining operations. We, along with everyone else in this business, have had our bin problems. The bins either plug, rathole, segregate, wear out, flood the discharge device, or overload it. Surprisingly, sometimes they have worked. As engineers, it has long concerned us that something as important as bin design should be so imprecise and that it has been so conspicuously avoided in research and in literature. In past years, rule-of-thumb design criteria had been to keep the sides of the bins as steep as possible and the outlets of the bin as large as possible. This criteria led to the design of bins with 600 to 700 side slopes and table feeders which were very large. Unfortunately, this meant trying to fit tall, skinny bins into a layout where minimum building height was required for obvious economic reasons. Like everyone else in the industry, we found that this design procedure was expensive and ineffective.

Jan 1, 1968

By Jakub Nalaskowski, Vamsi K. Paruchuri, Marcin Niewiadomski, Jan D. Miller

Spherical oxide particles can be used as mineral fillers, paint pigments, polishing materials and catalysts. They can be prepared using various techniques involving precipitation and spray drying. Melting of particles in a high-temperature flame is a simple technique which produces particles with a high degree of sphericity and high smoothness from non-spherical feed material. In current research the preparation of alumina particles by melting the feed material in a hydrogen- oxygen flame is described. The spherical particles obtained were characterized using scanning electron microscopy, atomic force microscopy, energy dispersive spectroscopy, X-ray difiaction, Fourier transform infrared spectroscopy and electrokinetic measurements. The particles pre- pared exhibit a high degree of sphericity and a low level of roughness. The chemical composition of the material after preparation is unchanged, however the crystallographic structure is different. It is suggested that alumina changes from pure a-alumina to a mixture of different transitional forms. Changes in the electrokinetic behavior were also observed for alumina which can be attributed to the strong dehydration of the oxide surface and/or change in the crystallographic structure. Also, the possible accommodation of trace amount of impurities in the surface zone during melting cannot be ignored.

Jan 1, 2003

By H. J. Marais, P. C. van Aswegen

The Biological Oxidation (BlOX®) Process for the treatment of refractory gold ores was commercialized in 1988. During the last decade, the technology has developed into a mature, commercially viable process, with five additional operations commissioned, including operations at Sao Bento in Brazil, Harbour Lights and Wiluna in Australia, Ashanti in Ghana and Tamboraque in Peru. With ongoing development, the efficiency and cost effectiveness of the process have both improved, making it an attractive alternative to conventional refractory treatment processes such as roasting and pressure oxidation. The bacterial culture is robust and can withstand the normal fluctuations experienced on an operating plant. The plants are simple to operate, making it ideal for remote areas. The scale-up potential of the process has been proven, and it can be applied to large refractory ore bodies. The process is environmentally friendly. Neutralization of plant effluents produces precipitates that comply with the most stringent environmental regulations.

Jan 1, 2000

By D. A. Norrgran

The recent development of rare earth permanent magnets has revolutionized the field of magnetic separation. The advent of rare earth permanent magnets in the 1980's provided a magnetic energy product an order of magnitude greater than that of conventional ferrite magnets. This has allowed the design of high-intensity magnetic circuits operating energy free and surpassing the strength and effectiveness of electromagnets. New applications and design concepts focused on the mineral and metal processing industries have evolved. This technology also led to the development of various magnetic separators specifically designed for mineral processing applications. Applications which were not previously considered are now being applied to primary mineral upgrading and recycling and secondary recovery.

Jan 1, 1993

By L. F. Zeiler

In the past, health concerns in coal mines have primarily centered on those elements which have been essentially inherent to the mining environment. These would include respirable coal mine dust, respirable crystalline silica, excessive noise levels, and diesel exhaust particulates. Commercially-available chemical products are prevalent on mine property. These potentially toxic materials are chemical formulations that can degrease, clean, and lubricate metal parts, separate coal from rock in float/sink operations, and aid in roof consolidation, among other uses. As the general public has become more aware of the hazards of chemical exposures, miners have likewise become more concerned about working with an ever-expanding variety of chemical products on the job. Often, product or chemical specific hazard communication training is inadequate or ineffective, and miners do not know exactly what the ingredients are in the products they handle, or the health hazards involved with their use or misuse. Currently, the Mine Safety and Health Administration (MSHA), by law, enforces 1972 Threshold Limit Values (TLV). MSHA is making preparations to adopt new personal exposure limits for enforcement. The values given throughout the article are 1994 TLV's and are not enforcement standards, but are used for discussion purposes. They reflect the current scientific thinking regarding personal exposure to these chemical agents. An overview of these products is presented, and the potential health hazards associated with their use are discussed. Controls needed to prevent overexposures, such as proper handling procedures and personal protective equipment, are covered. Methods used to collect and identify contaminants are presented.

Jan 1, 1995

By M. L. Leming

The mechanisms of Alkali-Silica Reactivity (ASR) are briefly reviewed, test methods are examined, and typical specifications are discussed. In addition, views on responsibility of the aggregate supplier regarding specifications are presented.

Jan 1, 1995

By R. C. Fox

The geophysical aspect of reconnaissance marks the beginning of extensive computer applications supporting development of a mine. Although there are some storage and retrieval applications in geology, and some statistical analysis in geochemistry, large-scale compilation, reduction, and interpretation of mineral resource data are initiated in reconnaissance geophysics. The reasons for this fact are quite simple. Geophysics is oriented toward quantitative evaluation of areas of interest, and methods of data collection are automated to the extent that large amounts of analog and digital information are recorded. The large volume of data must be interpreted in a reasonable time. Furthermore, some modeling problems involving complex numerical solutions could not be attempted without the computer. Therefore, the computer is essential to the success of an exploration project using geophysics. For example, aeromagnetics is a common technique for reconnaissance examination of areas associated with sulfide systems and porphyry deposits. An area covering 161 X 161 km (100 X 100 miles) may be flown with a 1.6-km (1-mile) line spacing yielding 10,000 line miles (16,093 km) of data. If only 10 measurements are recorded per mile, 100,000 data points, including location and magnetic field intensity, must be reduced and stored for quantitative interpretation. Computer applications often represent a significant investment in manpower and hardware. It is desirable, therefore, to initiate an engineering approach to the application of computers to geophysics. By this it is meant that computer programs and systems should be formulated, developed, and implemented in a disciplined manner such that their usage is dependent only on the application and not on the individual doing the programming. In other words, computer application, development, and usage should evolve beyond the personal gadget phase to an important applied technology. Geophysics has evolved over the past two decades in a course parallel to computer hardware development. During the sixties, the computer became large enough and fast enough that complex models required by geophysics could be solved. Automation also relieved the geophysicist from routine manual calculations. During the seventies, computing power in¬creased and applications expanded from two-dimensional problems to three-dimensional modeling. Moving into the eighties, as computer hardware costs will significantly decrease, the major expense of computing will be the manpower required to develop, implement, and use an application; therefore, improved programming techniques and applications software engineering methods will be used to optimize and preserve this investment. This chapter presents a general overview of computer methods in geophysical reconnaissance; it is divided into two parts: geophysical methodology and software engineering.

Jan 1, 1979

By Luis Dr. Sobral

In this study, the removal of zinc, cadmium and copper from an aqueous sulphate solution, derived from the biomass desorption process, was examined by using a reaction system with a three-dimensional high surface area electrode (RNiF). This reaction system was found to be extremely effective in reducing metal concentrations to the ppb range. The effect of cathode potential and flow rate were studied for three different nickel foam porosities. In addition, current- potential curves were recorded, at a rotating vitreous carbon electrode, to deter- mine the possibility of depositing the aforementioned metals separately.

Jan 1, 1998

By David G. Chedgy, Edward A. Zawadzki, Robert D. Stoessner

Extensive research and testing in commercial facilities has clearly demonstrated that heavy medium cyclones are the most effective process for cleaning a 0.6 x 0.15mm (28 x 100 Mesh) coal at low separating gravities, less than 1.35. This paper describes testing performed to deter- mine system characteristics at these lower gravities and the type of circuitry required to maximize performance. The results of these studies include both pilot and commercial scale tests of cleaning 0.6 x 015mm (28 x100M) coal.

Jan 1, 1988

By George D. Tikkanen

The world supply of zinc and lead is reviewed. The nature of zinc and lead deposits, production constraints, current production and reserves, new developments, possible future developments, and closures are considered. Lead sup- plies for the future are adequate. Zinc supplies are expected to tighten in the longer term due to growth in zinc consumption and orebody depletion.

Jan 1, 1986

By M. G. Hester, G. S. Adisoma

To address the problem of grade estimation in a general three-dimensional shape and the uncertainty associated with the estimate, the technique of jackknifing/ block-kriging shortcut is proposed. A new estimator called jackknife kriging is introduced first. Through the jackknife variance, a confidence limit for the reserve-grade estimate can be calculated. Unlike the kriging variance, which is more a measure of data configuration and which is independent of data values, the jackknife variance reflects the true variability of the data. This approach provides a simple way to set a confidence level for global estimation of resources.

Jan 1, 1997

By J. C. May, G. M. Elliott, J. J. Brady

Increased clearance was required in two railroad tunnels that were built about the time of the Civil War. Clearance infringements, whether they be excavation tights or caused by ice accumulation, reduce tunnel serviceability. Achieving increased clearance often means disturbing the ground and old ground support structures. Access and transportation needs dictate how and when the work can be carried out, and strongly influence the design approach and the methods used by the contractor to execute the work. This paper explores the pertinent considerations of the owner, the designer, the field inspection team, and the contractor in bringing this project to a successful conclusion.

Jan 1, 1997

By Majid Ataeepour, Ernest Y. Baafi

High level programming languages such ass C, FORTRAN and BASIC have been used in the mining industry to simulate truck-shovel systems. In addition, some special languages for simulation such as GASP, GPSS, SLAM, PROOF and SIMAN are commonly used. The most recent simulation system ARENA uses graphical modelling approach as well as animation notion. In this paper, the main elements of ARENA required to perform a truck- shovel simulation and to view the simulation results by means of the model animation are presented. The layout of the haulage system including shovels, trucks and dump sites was generated using draw tool in ARENA. All the components of the haulage system were represented by graphical modules. Animation tool was used to depict the performance of the haulage system as the simulation progressed.

Jan 1, 1996

By D. J. Dunn

Grinding balls, simple in shape, are actually sophisticated machine components and essential elements of mineral grinding mills. Their physical properties and quality must be adequate to achieve design life and grinding mission with few failures. Consistent properties and freedom from breakage are essential. Size, mass, hardness profile, chemistry, and microstructure are important variables that should be designed, specified, controlled, and verified to achieve optimal mill performance. Failure to specify ball properties in detail or failure to obtain required ball properties and quality can cause milling productivity losses and excessive costs that could endanger a milling operation's survival in the competitive mineral industry.

Jan 1, 1990

By H. M. Lima, P. Wathern

There are many different words to describe mine closure, including rehabilitation, reclamation, restoration and decommissioning. Closing mining operations, mainly open pit mines, has required resolution of numerous issues. Mine closure plans involve environmental-protection issues, regulatory issues and community issues. The obvious, and often most expensive of them, is the physical rehabilitation of the disturbances and the elimination of long-term commitments and maintenance. This paper outlines mine closure planning and its important component, mine-site rehabilitation. Community consultation and involvement are also referred to as an important component of the mine-closure plans, which are required to ensure satisfactory mine site rehabilitation. Considerations of socioeconomic impact of mine closure and long-term responsibilities are presented.

Jan 1, 2000

By Robert C. Dunne, Maurice E. Freeman, Denis S. Yan

A laboratory tower mill was used to investigate the effect of some variables on the power requirements of a plant mill. The grinding laws were tested for fine grinding and Charles' law and Rittinger's law found to be most closely satisfy the experimental data. The effects of ball size, ball charge mass and media type were investigated. The screw speed was altered to control the power input as required. The results indicate that changes in these variables will change the grinding kinetics but in terms of the grinding efficiency they have no effect on the size-energy relationship. The main factor in the specific energy efficiency is the transfer of the input energy to the charge by variation of the agitation mechanism. The efficiency of a tumbling ball mill and a pin stirred mill were tested for comparison.

Jan 1, 1995

By P. R. Khangaonkar, G. Bhaskar Raju

Three types of flotation columns were developed with a column dia of 8.0 cm and a length of 160 cm. The first type consists of an ordinary column fitted with a porous plate at the bottom. The second type consists of two electrodes at the bottom to obtain very fine and uniform bubbles generated electrolytically and the third is a combination of first and second types, i.e. to get both electrolytic bubbles and air from the compressor through porous plate. Three different ores were tested-gold tailings for recovery of scheelite, copper tailings (chalcopyrite) and oxide copper ore. In the case of scheelite and copper oxides, good results were obtained with the first type of column itself, whereas the third type column was found fairly effective in the recovery of chalcopyrite. The variables like the effect of reagent concentration, column height above the feed point, feed flow rate, current density, air flow rate, particle size etc. were examined.

Jan 1, 1988

By K. H. McDaniel, D. M. Loring

The underground ventilation system at the Waste Isolation Pilot Plant (WIPP) provides for the unparalleled ability to ensure the safety of the workers, the public and the environment. Although small spatially, the system can vary the airflow from 31.2 to 217.1 m3/s (66,000 to 460,000 cfm). The system can automatically incorporate HEPA filtration in the event of radioactive contamination. Remote-capable regulators individually control the four main splits, and they can be adjusted from the surface if necessary. A ventilation remote-monitoring and control system provides real-time information. Future areas of concern include DPM compliance, system psychrometry, logic-based real-time mine-ventilation simulation and automation using PLC technology. This paper discusses the evolution of this system.

Jan 1, 2003

By J. West-Hansen

The problem of long-term production scheduling in an underground coal mine is approached through the concepts of sequencing theory. Based on a typical layout of mining sections, the principles for the approach are: 1. The definition of mining sections as jobs, and mining methods as machines. 2. The reduction of the overall mining activity to the general problem of nonpreemptive scheduling of precedence related jobs on parallel machines. 3. The simplification of the layout to a general type directed network with the nodes representing jobs and the arcs representing precedence relations. 4. The determination of a feasible and near-optimal job schedule given the objective of maximizing the total net present value of the jobs. A general scheduling heuristic is being developed for implementation on an IBM personal computer (PC) as part of an interactive computer system for long-term production planning.

Jan 1, 1986