Search Documents

By Andrew B. Cecala

This U.S. Bureau of Mines report provides a detailed description of the Bureau-designed modified shearer clearer system. Engineering drawings are provided for all major components of this system. The modified shearer clearer system is a revised version of the original system and is intended to improve the ventilation around both cutting drums. The original shearer clearer technique was solely a dust control technique that has been effective in lowering shearer operators' dust exposures. The technique uses a series of water sprays that not only knock down a portion of the dust cloud but also act as small fans that move a substantial amount of air and keep the dust cloud from dispersing over the shearer body. The modified version is composed of two additional spray blocks for improved air movement around both cutting drums, thus lowering methane levels and the likelihood of an ignition. A laboratory study performed with the modified version in a full-scale longwall gallery resulted in a 73-pet reduction in methane concentrations at the shearer machine for both cut directions. The air-moving capabilities of the system provide more turbulence at the cutting drums and reduce methane levels.

Jan 1, 1994

By B. Q. Li, S. P. Song

"This paper describes an on-going research on developing coupled boundary element and finite element algorithms for the solution of thermal and electrodynamic problems relating to materials processing. The coupled methods are uniquely suitable for field problems involving composite regions, in which detailed information on field distributions within one particular region is of more interest and yet the solution can be obtained only if the effects of other regions are all considered. Problems of this type include heat transfer in multiple regions and also magnetic induction involving an infinite boundary. The hybrid boundary and finite element formulation, algorithm development and the applications are discussed. Two examples are given to demonstrate the capability and accuracy of the coupled algorithm for heat transfer problems. Various treatments of corner discontinuity are discussed. It is found that the double flux treatment is an ideal choice amongst those tested as it is easy to implement and also gives the most accurate solution. 1. INTRODUCTIONElectrodynamic and transport problems occur frequently in materials processing systems. Accurate solution of these problems is of great importance not only for our fundamental understanding of physical principles governing these phenomena in the processing systems but also for optimization of the existing processes as well as development of new processes. For this purpose, many numerical algorithms have been developed. These computational schemes in general can be classified into three categories, that is, the finite element and finite difference schemes and the boundary element scheme. The former two are domain based numerical algorithms while the latter the boundary-based algorithm.The finite element method, which is based on the variational calculus, is a very useful and yet popular engineering numerical method for boundary value problems defined over irregular boundaries. The use of the method requires the discretization of the entire domain. It can be applied to solve both linear and nonlinear problems, but is particularly powerful for nonlinear problems that involve the field variables defined within the computational domain. On the other hand, the boundary element method, with its root in the Green's function method, is very efficient for linear boundary value problems or nonlinear problems that involve field variables only along the boundaries. The primary advantage of the boundary element method lies in the fact that only the boundaries of the computational domain need to be discretized, and hence the dimension of the problem is reduced by one, compared with the finite element method."

Jan 1, 1994

By B. Mishra

Several reactive metal purification processes using molten salts generate effluent from which significant quantities of metal can be recovered prior to discardinglrecycling the salt. A Salt-scrub [SS] process has been applied where the reactive metals are recovered as a metal-gallium alloy by calciothermic reduction of the metal compounds. The SS alloy compositions were produced by mixing, pressing and sintering the metal-powders. Measurement of metal recovery has been studied for cerium, silver, tin and lead. The process has been optimized for variables such as the metal quantity per kg of effluent salt, amount of excess calcium over stoichiometry, stirring rate and time and holding time at reduction temperature. Over ninety-seven percent metal recovery has been obtained under optimized conditions. The development of an alloy for efficient Salt Scrub processing reduces a major contaminated waste disposal problem as well as recovering the valuable reactive metal. Surrogate metals have been used in this work to study the behavior of plutonium.

Jan 1, 1994

By V. Ramachandran

Under the Resource Conservation and Recovery ACT (RCRA), generators of listed or characteristic hazardous wastes must find satisfactory means for disposal. of wastes. Initially, for many this meant landfills and deep-well injection. Until recently, mining and metallurgical by-products have largely been exempt from RCRA, but now are coming under its jurisdiction. With the increasing closures of landfills, companies in the U.S. such as electroplaters, miners, metallurgical plants and others are turning to recycling as an alternative to treat their wastes. While the cost of recycling has been challenging, the long-term economics prove attractive because recycling interrupts the cradle- to-grave responsibility for the waste generator. The present paper describes the recycling of hazardous wastes at ENCYCLE/TEXAS. Encycle extracts marketable metals from metal-bearing sludges and wastewater using hydrometallurgical processes borrowed from the mining and metallurgical industry.

Jan 1, 1994

By Lloyd R. Nelson

Selective carbothermic reduction is the preferred method of treatment of electric arc furnace (EAF) dust (listed hazardous waste, K061). The process maximizes the recovery of recyclable constituents by concurrent production of saleable zinc metal (directly condensed from the furnace off-gases), an innocuous, disposable iron oxide-rich slag, and some metallic iron. Results of a mineralogical investigation of a foaming slag produced during selective carbothermic reduction treatment of EAF dusts are presented. Wiistite and tricalcium silicate were identified by reflected light microscopy as the primary crystalline phases contained in a glassy matrix, but this technique failed to reveal any solid phases that could have significantly contributed to foam stability. It was concluded therefore, that the foam had been unstable, and had been primarily generated by copious gas evolution associated with the sudden reduction of the slag by an inadvertent addition of carbonaceous reductant. This is consistent with the susceptibility to foaming, when subjected to sudden excesses of carbon, of the slags produced by selective carbothermic reduction, because they still contain unreduced components such as iron oxide.

Jan 1, 1994

By R. L. Russell

Production at Freeport Indonesia's Ertsberg open pit copper/gold mine started in 1972 at a rate of 7500 t/d. Mill throughput remained at that rate for a number of years until the discovery of the Ertsberg East (GBT) orebody. This discovery prompted three successive expansion stages from 1981 to 1988 that boosted production to 20,000 t/d. The discovery of the huge Grasberg porphyry copper deposit in 1988 launched a new era of much larger expansions. The first of these involved installation of a fourth primary mill in 1989 to bring production up to 32,000 t/d and was immediately followed by an expansion of the crushing and screening plant and the addition of a new south concentrator to bring production to 57,000 t/d in 1991. The addition of a primary ball mill and the changeout of the original Denver flotation cells in 1993 has served to optimize current production at a level of 66,000 t/d. A major expansion is now in progress. This includes construction of another new concentrator to house a SAG mill circuit and large Wemco flotation cells in an area created by the removal of 6,000,000t of glacial material. This current expansion, with a planned completion in 1995, will take production to 115,000 t/d. This paper describes the evolution of the Freeport Indonesia (FI) concentrator to-date and will then go into an in-depth discussion of the 66,000 and 115,000 t/d expansions.

Jan 1, 1994

By Michael J. McGuire

Rostoker, Inc. has developed a process to smelt solid hazardous/non-hazardous inorganic wastes. Near seven hundred experiments were performed. Actual industrial wastes as well as reagent grade chemicals were used. By mixing a multiplicity of these wastes to proper formulations, then furnacing them, it was determined that saleable end products could be reclaimed; metal, fume and slag. The slag, due to its siliceous structure was tested to be leach resistant (40 CFR). This formed the essence of our patent, #5,180,421 "Method and Apparatus for Recovering Useful Products from Waste Streams". What is unique is that a HTMR (High Temperature Metal Recovery) process has been developed that can treat a multiplicity of wastes within the same furnace. The discussion will include a list of waste streams we have treated, details of proper waste formulation and experimental results.

Jan 1, 1994

By George S. Austin

Mud is one of the oldest building materials used by man, but it is not only of historic interest. Even today in many parts of the world, particularly lightly forested areas, it is the chief building material. Many authorities believe that at least 30% and perhaps 50% of the world's present population lives in earthen dwellings (Dethier, 1985, Coffman et al., 1990). Not all of these people are members of primitive societies or live in third world countries. European, African, Asian, and both North and South American countries contain a large number of such structures. In the United States, the American West, and particularly the Southwest, is known for this type of construction. Some of the earliest remains of adobe structures are those discovered in the ruins of Neolithic farming villages in Mesopo¬tamia dating as far back as 7000 BC (Steen, 1972). The word adobe has its roots in Egyptian hieroglyphs denoting brick and evolved to its present form through Arabic and Spanish (Lumpkins, 1977). The Spanish conquest of the New World spread the use of wooden molds to produce a standard adobe brick. Today, the word adobe is used to describe various earth building materials and techniques, usually referring to sun-dried adobe brick now used in the United States, but is also applied to puddled adobe structures, mud-plastered logs or branches (Jacal or waddle-and-daub), pressed-earth blocks, and rammed-earth walls or pisé (Smith and Austin, 1989, Ferm, 1985). Modern mud construction is used in many countries in various parts of the world. In the United States, the states from Texas to California are perhaps best known for this type of construction. Of these states, New Mexico has the dominant reputation for adobe use. Indeed, in New Mexico the Santa Fe style (Fig. 1) has made adobe not only acceptable, but preferred. RAW MATERIALS Adobe soil used by present day adobe producers, and probably past adobe producers as well, is principally sandy loam (50% clay and silt), although clayey silts are used in some areas (Coffman et al., 1990). In New Mexico, the best adobe soils are those developed on stream deposits, particularly Holocene (Recent) terrace deposits and older, loosely compacted geologic formations, such as the Santa Fe Group (Tertiary) located in the Rio Grande Valley. Some modern adobe producers use a mixture of materials from the screened fines of aggregate operations and mud from irrigation ditches in the river valleys combined with varying amounts of sand to produce the proper blend. Mineralogy Bulk Mineralogy: X-ray diffraction analyses of whole rock samples from many parts of the world where adobe is the dominant construction material show the major constituents of adobe are quartz and feldspar, with lesser amounts (in order of abundance) of calcite, clay minerals, and gypsum (Coffman et al., 1990). Adobes from and climates contain considerable calcite; in some cases calcite is second only to quartz in volume. Quartz, feldspar, most of the clay minerals, and some calcite commonly are derived from the mechanical/chemical breakdown of older rocks units. Some of the clay minerals, much of the calcite and perhaps all of the gypsum are precipitated from evaporating water. Clay Mineralogy: Clay-size minerals consist dominantly of clay minerals, but nearly clay-size fractions contain minor amounts of quartz and calcite, and occasionally other nonclay minerals. In earth construction materials from New Mexico, clay-size particles are the most compositionally variable in commercial adobe soils. However, the clay mineral groups in this size fraction consist of about equal parts of expandable clay minerals (smectite and mixed¬layer illite/smectite or I/S) and non-expandable clay minerals (ka¬olinite, illite, and chlorite), with minor quartz, calcite, and feldspar (Smith and Austin, 1989, Austin, 1990). In the and American Southwest, smectite is commonly calcium-rich and the I/S is dis¬organized and randomly interstratified. In a study of 42 New Mex¬ican commercial adobe soils, only two contained chlorite, and vermiculite, sepiolite, and palygorskite were not found. Soils in temperate climates, as are found in the midwestern and northeastern United States, contain an abundance of illite (Potter et al., 1975). The clay minerals in earthen structures of that region and in Europe commonly contain illite with less amounts of kaolinite, smectite, I/S, chlorite, and vermiculite. In contrast, the clay-size fractions of soils of humid tropical areas are typically acid, with kaolinite as the dominant clay mineral and lesser amounts of I/S, illite, smectite, and others (Chamley, 1989).

Jan 1, 1994

By G. T. Lineberry

The Work Crew Performance Model (WCPM) is a method for designing, implementing, and evaluating? performance improvement strategies for machine operators and other mining personnel. The WCPM offers a practical approach for measuring job proficiency and identifying costly behaviors. It enables interventions aimed at performance improvement, especially training, to be assessed monetarily. Two interrelated elements of the WCPM are emphasized: observational techniques for establishing performance baselines and measuring performance outcomes and cost linkages between job competencies and measures related to profitability. Inter-and intra-subject differences in performance-related behaviors of regular and incidental shuttle car operators were detected during field validation of the WCPM. Downtime data were used as outcome measures to test linkages between performance error rates and cost consequences. Use of a simulation program for analyzing continuous mining face operations showed how common shuttle car operating parameters (e.g., payload, tram rate) can be used as cost-conscious indicators of performance variability and therefore as targets for performance improvement.

Jan 1, 1994

By R. K. Mensah-Biney, M. T. Hepworth, K. J. Reid

The loading characteristics of gold-bromide species onto activated carbon were evaluated using a batch system. The overall loading of gold onto activated carbon was rapid for the first few hours, but it continued without cessation as a result of the reduction of gold. Therefore, conventional equilibrium considerations were not applicable. Although loading continued slowly after several days, an abnormally high, loading capacity value of 10-12 meq/g carbon (650-800 kg Au/t) could be attained in 72 hours. The loading of gold-bromo species by activated carbon was by the mass transfer of (AuBr4)- species to the external surface to be reduced to metallic gold by carbon. Elution of gold from loaded carbon was feasible provided the carbon had not been loaded to high capacity values. If loading is carried to high levels, complete elution becomes impractical, and the gold may be recovered by ashing the carbon. For the high loading capacities observed, this option would appear to be cost effective. The effect of several variables on the loading capacity of the activated carbon for gold-bromo species is discussed.

Jan 1, 1994

By Hugh K. Taylor

"With some justification, people have long complained about the indefinition of ore reserves. Perhaps they were led to expect too much; from former and easier definition practices in the once common underground mines with exposed and available assets, where the obsolete term 'ore in sight' was at least partly literal. But such mines have become rarer, and their underground development less affordable. For most projects, valuations and its definitions have thus been advanced from actual to prospective mines, leaving a very wide gulf between 'what is there' and 'what may happen to it'. This brings the double challenges of reduced geological and technical assurance and the protraction of economic uncertainties.This paper avoids the popular field of regional resources, being confined to what may possibly be mined within single or closely grouped deposits. For these, many estimates of tonnage and grade must be made, defined and declared long before assessment of feasibility; and the uncertainties of the latter make it an unsound base for defining the earlier quantities. Despite the best of intentions, implied or inferred promises may proveimpossible to honour.A simpler framework of definitions is suggested, to some extent reverting to an earlier dependence on supporting work rather than on opinions of economic assurance or future events that are more properly the functions of production and cash flow schedules."

Jan 1, 1994

By J. A. Lombardi

Innovative hard rock narrow-vein, longwall, and stope leach mining systems concepts are described and evaluated economically. The principal tool proposed for use in these systems for both mine development and production is the U.S. Bureau of Mines radial-axial splitter. The mining systems concepts are prefeasibility level costed and projected to be cost competitive for steeply dipping veins, 0.6-1.2 m wide, for horizontal tabular ores 2 m -5 m thick, and for leachable ores with greater than a 1.7:1 stripping ratio. In all of the systems the orebody, less swell, is retained underground for use as backfill.

Jan 1, 1994

By D. T. Smith, L. M. Hsiung, J. J. Schmitt, J. W. Golz, R. L. Lankey, H. N. G. Wadley, J. Z. Zhang, B. L. Halpern

"The microstructure and mechanical properties of Al/AI2O 3 metal-oxide nanolaminates fabricated by' a novel Jet Vapor Deposition (JVD) process at substrate temperatures of ~25° and -250°C have been investigated using transmission electron microscopy (TEM) and nanoindentation methods. The thickness of the oxide layer was held constant between 2 and 5 nm, whilst the Al layer thickness was systematically varied from -3 to -50 nm. Continuity of the Al layers was significantly improved when the nanolaminates were deposited at an elevated substrate temperature (-250°C). The yield strength of the nanolamintes with Al layers greater than -25 nm follows a Hall-Petch type relationship, whereas that of the nanolaminates with Al layers less than -25 nm is better predicted by a Koehler-Lehoczky strengthening model. IntroductionAluminum-aluminum oxide (presumably A12O3) nanolaminates have been recently fabricated using a novel Jet Vapor Deposition (ND) process developed and patented by Jet Process Corporation [1-4]. ND uses sonic, high purity helium (He) gas jets to entrain atomically dispersed vapor and deposit films. It is of interest here because it can deposit multilayered structures (laminates) inexpensively at high rates. Materials with a thin, multilayer structure are of interest because they potentially offer novel mechanical and physical properties [5]. Koehler in 1970 used an image force model to investigate the strength of laminated materials and proposed the use of alternating layers of high and low shear modulus metals to produce high strength composite materials [6]. He predicted that dislocations would have to overcome a large repulsive image force in order to move from metal layer B of lower shear modulus (uB) into metal layer A of higher shear modulus (uA)' The image force (F) is given by the relation:"

Jan 1, 1994

By Robert B. Hopler

The history of the first twenty years of the high explosives industry in the United States begins as an illustration of the free enterprise system at its best and ends with the industry virtually taken over by a single company: a company which strongly opposed the new explosive material at the beginning of the period. In the world of the late Twentieth Century we could almost compare this history to the opposition of the mainframe computer manufacturers to the introduction of the personal computer, and their later entry into, and attempted dominance of, that market. With computers in the twentieth century the attempt to dominate the market has not been particularly successful: with dynamite in the nineteenth century it was.

Jan 1, 1994

By D. M. Neil

Road-headers are one of the most popular mechanized excavators used in mining and civil under-ground construction. These machines are primarily used in soft to medium hard rocks. This paper reviews the parameters associated with the application and operation of road-headers and presents a method for estimating cutting performance.

Jan 1, 1994

By Walker. P. W. A.

Abstract -The Riviera tungsten occurrence in the Cape Province of South Africa was discovered in October 1979 as a result of stream-sediment panned concentrate sampling. The Cape age granite and late Precambrian Malmesbury Group carbonates and chlorite schists which it intrudes and which host the mineralization are covered by between 10 m and 30 m of Tertiary/Recent alluvium and clay. The scheelite/powellite and molybdenite mineralization occurs in a greisenized granite cupola with an overprint of porphyry-type alteration as well as in minor skarns. The ore reserve is estimated to be 46 million tonnes at an average grade of 0.2160Jo W03 and 0.020% Mo. The deposit is uneconomic at current tungsten prices.

Jan 1, 1994

By R. D. Corrans

"Abstract - Africa is endowed with a number of the world's giant ore deposits which have contributed significantly to the development of their host countries. Mineral exploration has a long history in the continent, but mining on an unprecedented scale took off during the latter part of the 19th century, accompanied by the development of lines of communication and other infrastructure to service the major mining centres .The ""Winds of Change"" which swept Africa in the 1950s and 1960s brought in new styles of government and economic management to a number of regions, often with demise of economic viability and infrastructure. ln recent years, with the end of the cold war, collapse of communism and changes in South Africa, new opportunities for mineral exploration are opening up rapidly in Africa. However, due to the large cost, long lead-in time, and high risk of developing new mineral ventures in the continent, it is necessary for the host countries to draft realistic and favorable mineral laws and fiscal codes in order to attract, and not deter, potential mineral investors.There will be an on-going role in mineral exploration throughout Africa for the artisanal miner, the smaller entrepreneurs and mining companies, exploration aid programs funded by the developed countries through African governments, as well as the major mining houses who have the resources to develop larger viable mineral deposits."

Jan 1, 1994

By M. Beale

Fuzzy logic and neural networks are new technologies being applied in many areas of engineering and business. While it is not always clear which kinds of problems are best suited to these technologies, and which problems are best approached with more standard methodologies, both fuzzy logic and neural networks appear to show great promise in the field of control systems. This paper demonstrates two advantages that these technologies offer: Easy controller design in the absence of a mathematical model of the plant to be controlled, and adaptive control capable of quickly responding to changes in the plant.

Jan 1, 1994

By K. Whiting

In October 1993, the first two of a series of full scale passive biological treatment cells were constructed to treat mine drainage from the Burleigh Mine (located approximately 48 km west of Denver, Colorado in the Clear Creek/Central City Superfund Site). The two cells are each 19-21 m long, 10.7 m wide and 1.2 m deep. Each cell contains approximately 216 cubic meters of substrate (composted manure) and is designed to treat 60 L/min of mine flow. One cell is designed as an upflow reactor and the other cell is designed as a downflow reactor. The differences in flow hydraulics and treatment efficiencies will be tested in these two cell for approximately nine months before the remaining cells are built to treat all the discharge. The substrate material was selected based on a series of bench scale tests. During the tests, the amount of metals removed was determined. The design flow rate was based on a sulfide generation rate of 400 nanomoles of sulfide generated per cubic centimeter of substrate per day. Metal removal results for the first three months of operation of the two cells will be presented and compared to results of bench and pilot studies at other sites.

Jan 1, 1994

By Bradford H. Miller

Separation and Recovery Systems, Inc. (SRS) provides on-site waste minimization and resource recovery using its state-of-the-art MX-1500 centrifuge and MX-2000 thermal desorber. The MX-1500 can process over 450 feed tons of material per day, resulting in centrifuged cake containing 20% to 60% by weight. The MX-2000 is a hollow-flite thermal processor indirectly heated by either steam or hot oil. SRS has dewatered and/or deoiled over 1,000,000 feed tons of material in the refining, chemical, and energy industries using the MX-1500. SRS estimates that over 300,000 barrels of reusable oil have been recovered from that material. Additionally, SRS has dried and/or detoxified over 150,000 wet tons of solids or soil to regulatory or customer-specified limits using the MX-2000.

Jan 1, 1994