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By P. L. Padgett, J. C. Hower

Five coals blended at a Midwestern United States power station were subjected to detailed analysis of their Hardgrove grindability. The coals, representing four distinct coal beds, are a low-sulfur, high-volatile A bituminous Upper Elkhorn No. 3 coal (Pike County, Kentucky); a medium-sulfur, high-volatile A bituminous Pittsburgh coal (southwestern Pennsylvania); a low-sulfur, subbituminous coal from the northern Powder River Basin (Montana); and two low-sulfur, subbituminous Wyodak coals from two different mines located in the eastern Powder River Basin (Campbell County, Wyoming). All samples that were processed in the Hardgrove grindability tests were also analyzed for their maceral and microlithotype content. The high-vitrinite Pittsburgh coal and the relatively petrographically complex Upper Elkhorn No. 3 coal exhibited different grindability behavior. The petrographic compositions of the Pittsburgh raw feed, the 16 x 30-mesh fraction (HG! test fraction) and the -30-mesh fraction (HGI test reject) are similar, suggesting that the HGI test fraction typifies the whole feed. The eastern Kentucky test sample is not as representative of the whole feed, with the HGI test fraction having lower vitrinite amounts than the rejected -30-mesh fraction. The Powder River Basin coals are high in vitrinite content and show behavior similar to the Pittsburgh coal.

Jan 1, 1998

By G. Hargrave, K. W. Moloney, M. R. Stokes

In recent years drivage advance rates in the UK have in- creased from 35m per week in the 1980's to 100/150m per week possible today. These extended rates of advance have resulted in an increase in the potential methane, dust and heat generation at the drivage face. In order to disperse this additional pollutant load requires an increase of fresh air at the face. Although advance rates have changed, current auxiliary ventilation practice has not. UK mining law requires that the fresh air must be delivered to within 5m of the face. This has lead to the wide spread use of overlap auxiliary systems, since a pure forcing system set at this distance would lead to excessive airborne dust. UK mining law does not at present consider on-board mounted exhaust scrubber fans to constitute an effective overlap fan within mechanised drivages. In an attempt to determine whether working conditions could be safely and economically improved within mechanised drivages, a series of preliminary full scale gallery trials were con- ducted. A summary of the principal findings of these trials are presented together with an outline of a series of representative CFD simulations, scale model experiments.

Jan 1, 1997

By Uday Kumar

This paper presents details of an availability study for a fleet of diesel engine operated load-haul-dump (LHD) machines used in a Swedish mine. For the purpose of this study, the LHD machines have been considered as a system comprised of many subsystems like engine, brake, transmission, etc., in series. As availability is dependent on both the reliability and maintainability characteristics of the system, together with reliability, the concepts of maintainability are also discussed. The need for exploring the data for the presence of any structure, which is very common in repairable system data sets, is emphasized with suitable examples. Simple graphical techniques are used for verifying the independent and identically distributed (IID) assumption for the data set. The error introduced due to the use of the exponential distribution in place of more appropriate distributions in estimation of availability and reliability characteristics is analysed.

Jan 1, 1989

By William H. Dresher

World trade has increased significantly during the last quarter century. However, a new rational for protectionism is emerging which argues for the restriction of trade as a means of preserving and protecting the environment. Fearing lower environmental standards in the Third World, environmentalists are calling for new trade barriers between the developed countries and the developing countries to combat what they see as "eco-dumping." The "greening" of protectionism and the merging of environmental standards into international trade agreements could fundamentally change the world trading system as well as seriously impact the availability of raw materials to provide for the needs of the peoples in both the developing and the developed worlds. This discussion will deal with the agreements and regulations that promise to influence the trans boundary shipment and recycling of scrap metals and wastes containing metals and their projected impact on world trade and metal prices. Emphasis will be placed on the Base1 Convention, whose restrictions concerning trans boundary shipment of scrap metal and metal-containing wastes for recycling took effect on December 31, 1997.

Jan 1, 1998

By Victor Rudenno

Cut-off grade is one of the most critical parameters affecting project cash flow. Its sensitivity is due to the number of other parameters that are correlated with any change in its value. Changes in cut-off grade, average grade and ore tonnage vary and they in turn can affect such parameters as capital and replacement costs, recovery, life of the project and operating costs. Perhaps one of the best definitions of cut-off grade is that of Taylor (1), "... any grade that, for any specific reason, is used to separate two courses of action, e.g. to mine or to leave, to mill or to dump ... . Obviously the most likely specific reason is one governed by economics, involving the return of investment and sufficient profit to motivate development and mining of the deposit. In this paper the cut-off grade is defined as that mining limit which will maximise the economic return for a projected mining venture. The following brief literature survey indicates that when computing the optimum cut-off grade there is a need to be able to directly compute the Discounted Cash Flow Rate of Return (DCFRR) or Net Present Value (NPV), as economically as possible, while allowing for parameter dependencies and variation in project structure.

Jan 1, 1979

By William Petruk

Performance assessments are carried out to monitor operations, to evaluate performance and to identify processing problems. The assessment involves collecting and analyzing representative samples from critical points in a flowsheet and interpreting the data. Sample analysis techniques include chemical analyses, mineralogical investigations, mineralogical analyses, and materials balancing. Chemical analyses provide the lowest cost assessment and should be used liberally, particularly in monitoring a process. Materials balances performed on chemical assays for a suite of samples are used as a first step in evaluating a process. Mineralogical investigations are more expensive than chemical analyses but need to be used only at the beginning of mining and metallurgical operations and as a second step in assessing processing problems. Quantitative mineralogical analyses combined with materials balancing provide the most complete performance assessment, but the procedure is expensive. On the other hand, the assessment has the potential of a large payback when carried out where warranted.

Jan 1, 1991

By Peter H. Grimley

It is important to realize that lending institutions have a very different risk-profile from that of an equity investor. For bank financing, a feasibility study must address the concerns of the lender and these can be summarized under the four 'PI Is: Project, Performance, Product and People. Generally, feasibility studies focus on the measurable project risks associated with a new venture, but frequently insufficient emphasis is placed on key risk areas such as ore grade and metallurgical recovery. Before accepting full or even partial non-recourse risk, financial institutions will demand evidence that the project was constructed according to specifications and within budget and that its Performance within agreed limits has been demonstrated. Product risk should be discussed in detail in any feasibility study. For industrial minerals, penetration of the market can be critical to success and for commodities with volatile prices, the sensitivity of the cash flow to a range of prices should be carried out. Methods of reducing price risk such as long term contracts or, in the case of gold, forward selling should be carefully evaluated. The People risk is rarely discussed in feasibility studies, but can be a key element. Few projects turn out to be faithful copies of the study and the ability of the operator to identify

Jan 1, 1988

By Mark S. Stagg, Michael J. Nutting, Douglas R. Barlet

Single-row bench blasts at a reduced scale in the field were used to study the effects of delay time on fragmentation. Nine shots with a spacing of 21 in. and a burden of 15 in. (S/B = 1.4) and nine shots with a spacing of 30 in. and a burden of 15 in. (S/B = 2.0) were completely screened to determine particle size distributions. Delay intervals between holes ranged from 0 to 45 msec, corresponding to effective delay intervals ranging from 0 to 36 msec per foot of burden. Each shot was instrumented with strain and pressure gages to measure in situ blast dynamics and to evaluate interactions between blastholes. Finer overall fragmentation was produced for shots with delay intervals between 1 and 17 msec per foot of burden. Only for shots within this optimum delay range was it observed that the strains induced by stress waves constructively interacted with strains induced by gas pres- sure from an earlier detonated hole. Coarsest fragmentation resulted at delay intervals less than 1 msec/ft, where stress waves from each hole were observed to interact destructively, and at delay intervals greater than 24 msec/ft, where no inter- action between holes was observed, indicating a condition that can be considered as the firing of single hole shots independently.

Jan 1, 1986

By A. E. Hall

INTRODUCTION Underground gold mining operations are found in South Africa, U.S.S.R., Canada, the United States, Zimbabwe, Ghana , Brazil. Australia, China and many other countries. The methods used for extraction differ from highly mechanized trackless mining in the developed countries to the labour intensive systems of the third world nations. The climatic conditions in which mines are situated vary from equatorial to arctic. The rock temperatures and the depth of workings also vary significantly from shallow to extreme depth. The Western Deep Levels mine in South Africa is the deepest and exceeds 4.000 metres in depth with strata temperatures above 55°C. These major differences between mining fields result in significantly different ventilation problems in underground gold mines. The ore types also vary and some deposits have high silica contents while other mines extract sulphide ores. Methane may also be encountered in underground gold mines and can have a large influence on the ventilation practice. Several topics are currently of concern to operating mines and are reviewed here:- a) Air circulation and fans b) Mine cooling c) Permafrost operations d) Mine heating e) Control of diesel exhaust f) Gases, fires and explosions

Jan 1, 1988

By M. R. Peterson, C. R. Ferguson, T. H. Jeffers

The ability of microorganisms such as yeast, bacteria, and various aquatic flora to sorb metals from dilute aqueous solutions is well documented. Although microorganisms have significant potential in decontaminating waste waters, techniques and equipment suitable for bioassisted decontamination are limited. The Bureau of Mines has investigated the use of microorganisms immobilized in porous polysulfone beads for extracting toxic and heavy metals from dilute waste streams. The minus 8- plus 12-mesh beads were fabricated from high-density poly- sulfone dissolved in dimethylformamide (DMF). Dried, thermally killed yeast, algae, duckweed, xanthan gum, and alginates were blended into the polysulfone-DMF, and spherical beads were formed by injecting the mixture into water. Microscopic analysis revealed microorganisms immobilized within the bead pores. The beads had excellent handling characteristics and were tested in stirred reactors, fixed bed columns, and fluidized bed columns for their ability to remove metal contaminants from several waste waters. The effluents resulting from these waste waters met or exceeded the National Drinking Water Standards for cadmium, copper, manganese, and zinc. Other heavy metal contaminants readily sorbed by the beads included arsenic and mercury. Elution of metal values from the beads was accomplished using dilute nitric acid or sodium carbonate.

Jan 1, 1989

By T. X. Ren, J. S. Edwards

Although much work has been carried out in order to understand the mechanism of spontaneous combustion and hence minimise its potential risk, the spontaneous combustion of coal continues to be a problem in coal mining. The Department of Mineral Resources Engineering of Nottingham University has been active in conducting fundamental research into the problem of spontaneous combustion of coal. For years standardised adiabatic oxidation tests have been used to identify coals and other carbonaceous materials liable to spontaneous combustion. Recently the apparatus has been computerised and coupled with an expert system known as ESSH to evaluate the potential of self-heating of coal on the basis of intrinsic coal properties, geological settings and mining techniques. A numerical model has been developed to study the aerodynamics of airflow in the wastes of longwall coal faces. The Computational Fluid Dynamics approach is being explored to simulate airflow behaviour and nitrogen inertisation processes within the goaf. Such a model would be used in locating the areas most liable to spontaneous combustion and improving the utilisation of nitrogen. It would also be possible to determine the most likely path ways of combustion/heating products so as to provide an indication of the most appropriate locations for fire detectors.

Jan 1, 1997

By William S. Brack

The mining industry is very capital intensive. Competition for shareholder investment has never been greater. Among our challenges is the need to meet shareholder expectations (return on investment), and one area of focus lies in our ability to deliver value on our capital investments. Our ability to meet project expectations affects not only the economics associated with the immediate project but also directly influences our ability to finance future projects. Moreover, our ability as individual companies to attract investor capital is influenced by how we have done overall as an industry, and our industry track record has not been that stellar. With safety, scope, cost, schedule, and quality as guiding principles, our project managers today must address high expectations on every project. This paper examines some items that should be on today's project management checklist. PROJECT ENGINEERING Herbert Hoover, himself a mining engineer, said Engineering is a great profession. There is the fascination of watching a figment of the imagination emerge through the aid of science to a plan on paper. Then it moves to realization in stone or metal or energy. Then it brings jobs and homes to men. Then it elevates the standards of living and adds to the comforts of life. That is the engineer's high privilege.

Jan 1, 2004

By R. Gerling

A computer program has been developed for finding a near-optimum schedule of the mining sequence for flat lying, tabular orebodies. The deposit is divided in blocks with equal areas and definite grades, thicknesses and ore contents. Mining is done by room and pillar method and trackless haulage to surface. Access from surface is by adits or ramps with additional vent raises. In total eight different general concepts for access and development can be realized. The optimum mining sequence is found by a heuristic method. Criterion is the maximization of the net present value over the lifetime of the mine. Specific stoping costs per t of ore are taken for con¬stant, whereas development and haulage costs for individual blocks and also sequences will be different. Correct ventilation and a technically sensible sequence are guaranteed. Beginning with a single block, neighbouring blocks are tested and an optimum stoping sequence is generated. The net present value of the total mining operation for the planning period is calculated, taking into account ore, which is mined during development. The program can also be used to investigate given mining sequences.

Jan 1, 1986

By E. Woodburn, R. P. King, R. Putman

Flotation plant simulation, a relatively recent methodology in mineral processing, is defined and corresponding uses are discussed. Typical simulation structures are compared. Current problem areas exist although these are not insurmountable. Following a brief state of the art discussion, the N. I. M. simulation program is reviewed. In general, digital plant simulation is expected to be of substantial benefit in the near future.

Jan 1, 1976

By R. Hogg, P. Bunnaul

Sedimentation in highly, flocculated suspensions of fine particles, such as clays, occurs through individual settling units (flocs) that have very open structures and correspondingly low densities (typically less than 5% solids by volume). Such settling processes rapidly lead to the buildup of a bed of flocs that are essentially close-packed, with an inter-floc porosity of perhaps 50%. However, the overall solids content is no more than about 2% to 3% by volume. Consequently, the thickening process is dominated by the bed consolidation rather than by the simple settling of the individual flocs. Experimental measurements of sediment consolidation in flocculated clay suspensions indicate, for a given system, that consolidation rates are essentially determined by the solids concentration and can be evaluated using the classical Kynch treatment. However, these rates are strongly dependent on the physical, as well as the chemical, conditions of the flocculation process. Furthermore, the extent to which gravity consolidation proceeds depends on the total weight of the sediment (i.e., on the bed height and the solids concentration). The implications with respect to thickener operation and the requirements for the laboratory testing for thickener design are discussed.

Jan 1, 1993

By James F. Albus, Vincent C. Grimshaw

High pressure fluid energy grinding, or jet milling, is a versatile method of continuously fracturing solids into fine particles to gain substantial increases in exposed surface area Applications in industrial minerals grinding include calcium carbonate, talc, barytes, mica, diatomaceous earth, bauxite, rutile, coal, kaolin, sepiolite, diamonds, etc The basic principles can be extended to provide continuous drying and delivery of discrete par¬ticles from a wet process slurry The main design and operational features of jet mills and dryers are described, relating energy consumption for both air and steam milling and hot air drying techniques Mean particle sizes in the order of 1 micron are achievable from pre-milled feeds, or maintained from similar slurries in the drying mode Aspects of feed preparation and multi-stage processing are discussed

Jan 1, 1983

By S. Chander

The fundamentals of flotation are reviewed with an objective to understand the limitations in predicting the performance of a sulfide mineral flotation system and in its scale-up from laboratory studies to plant practice. The difficulties can often be traced back to complex interactions between chemical and physical parameters and nonequilibrium effects. The physical and chemical changes that occur during the long sojourn of sulfide minerals that begins with mining, continues through crushing and grinding, and ends when they emerge from the flotation cell as a concentrate, are reviewed. The benefits of new techniques that have become available in recent years to identify and estimate the amount of surface species are discussed.

Jan 1, 1999

By Lawrence F. Rooney

The wide distribution of limestone and dolomite and the decentralization of the depedent industries give the State Geological Survey a major role in the, development of these mineral resources. The amount of geological information necessary for efficient exploration is so large that few companies can afford to do the necessary basic field work or store the data. The state surveys fill these responsibilities and thus might be said to serve as the geological research departments of the limestone and dolomite industry. At the Indiana Geological Survey, the data of most value to limestone producers are in the form of unpublished measured sections, well records, cores, chemical analyses, directories, and geologic maps. Much of this information is published in summary form. The Survey also assists individual members of industry in exploration and evaluation of mineral deposits. In addition, a progressive State Survey provides the geological infor¬mation necessary for the development of new resources which do not appear to justify industry's own preliminary efforts.

Jan 1, 1966

By Victor F. Hollister

This section includes examples of discoveries of Kuroko- and Anyoz-type massive sulfides, and shale-hosted, zinc-lead deposits, and describes exploration models for each group of case histories. Exploration or empirical models can differ from genetic models, because ore guides and controls are emphasized in exploration models. Genetic models may form the scientific basis for exploration or prospecting models, although factors that are important to the localization of ore are stressed in exploration models. The paper by Sato (abstracted herein) on Kuroko deposits can be used as a general exploration guide for that type of deposit. It is clear, however, that no unambiguous stratigraphic control for Kuroko-type ore is given in the Sato paper. The paper by MacIntyre (an excerpt herein) describing Gataga, Midway, and Windy Craggy includes most of the elements of the shale-hosted and Anyox models. Although more recent work by the Geological Survey of Canada has modified the Windy Craggy stratigraphy, the Anyox model as applied to Windy Craggy is well described in the MacIntyre (1983) paper. Discoveries of ophiolite-, Ducktown-, volcanic-associated Ni- Cu-, and Besshi-type deposits are not included in this section. Conformable massive sulfide deposits are generally assumed to be syngenetic. Sulfides in the crosscutting feeder zones, however, are classed as epigenetic. Therefore, volcanogenic massive sulfides can contain both a syngenetic and an epigenetic component. Vital to the development of the epigenetic component is a heat source that propels the convection cycle that forms both components. In all massive sulfide discoveries described in this section, it is assumed that a volcanic magma fueled the hydrothermal fluids.

Jan 1, 1991

Traditional fine-grinding mills in mineral processing rely on the use of steel medium for particle size reduction. The IsaMill (a horizontal stirred mill with a 3, 000-L net chamber volume and a rated motor power of 1,120 kW) has successfully adopted a novel product-separator design, which has led to a major revision of medium use in fine grinding. The IsaMill separator has successfully operated with a wide variety of medium types, such as silica sands, river gravel, smelter slag, run-of-mine ore fractions and steel shots, with sizes ranging from 0.5 to 10 mm. Great flexibility in the IsaMill operations has been achieved for processing feed as coarse as 120 µm to a product as fine as 5 µm. This paper discusses the performance of two inert grinding media in the IsaMills that are used at Mount Isa Mines Ltd. for the processing of galena- and sphaleritebearing ores to below 10 µm. They are the copper reverberatory furnace slag (CRFS) and the heavy-medium plant rejects (HMPR). A methodology was also demonstrated for comparing the medium performance and for scaling up the IsaMills from a 1.5-L laboratory batch mill to a full-scale 3,000-L mill.

Jan 1, 2002