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By MAURICE SUNKPAL, Taghi Sherizadeh, Kutay E. Karadeniz, Dogukan Guner, Samuel Nowak

In this study, various rib bolting scenarios were investigated to better understand the effectiveness of the support systems. A coal mass constitutive model is implemented to a distinct element method (DEM) code, and rib factor-of-safety (RibFOS) analyses were performed by applying strength reduction for the coal matrix and explicitly modeled face cleats. Ribs with various overburden depths and mining heights composed of solid banded bright coal were considered. Different scenarios such as rib bolt length and number of bolts were studied to quantify the effect of primary rib support density on rib stability. As a result of the unsupported coal rib analyses, a decaying exponential relationship is proposed between the mining height-overburden depth and the RibFOS. The developed coal rib models clearly show the coal-rib bolt interaction and illustrate how the addition of rib bolts restricts the movement of the coal rib. The results reveal that the strength-reduction method in DEM code with the coal-mass model can aid in the development of practical primary sup- port charts, which can help in the rib support design process.

Feb 1, 2024

By David R. Hargis

Large-scale groundwater withdrawals are necessary to depressurize a confined aquifer system allowing the dry open-pit mining of the overlying phosphate ore. The extent of the existing and planned groundwater development led to the establishment by the State of North Carolina of Capacity Use Area No. l. Groundwater use in the Capacity Use Area is regulated by a permitting system. A two-dimensional finite-difference ground- water flow model was developed for North Carolina Phosphate Corporation. The aim of the model is to aid the Corporation in matters relating to permitting by serving as a predictive tool. The model can be used to project regional water level impacts resulting from various scenarios of depressurization pumping.

Jan 1, 1983

By B. W. Cavender

Capital investments are made for a variety of purposes, from providing incremental capacity at existing operations to developing and implementing new technologies intended to radically improve a company's capabilities. These projects generate very different business opportunities and create value in distinctive ways. For incremental improvements, the capital budgeting process assures at least a loose fit between short-term goals and readily available resources. However, the criteria used to evaluate capital projects often prevent a company from committing to more aggressive goals that lie beyond the firm's current abilities or resources. Such projects may not have clearly identifiable future cash flows, and the degree of interaction with other projects and the nature of the risk incurred may be difficult to estimate. Additionally, by focusing only on quantifiable benefits, the budgeting process often fails to recognize "soft" improvements such as increased operating flexibility or new knowledge generated by such projects. By rejecting these projects, the capital budgeting process may actually harm the company's future competitive position.

Jan 1, 1998

By H. A. Stoess

The Minerals Industry makes heavy demands for and on its Material Handling equipment. It also gives progressive management the opportunity for considerable savings, ad consequently increased profits. In some cases, cost of Materials Handling amounts to 40°/o of the total cost of the ultimate product. Handling costs are hidden in overhead, indirect labor, excessive maintenance, productive workers performing handling tasks, and, a great many more. Even though Materials Handling is the oldest occupation of mankind, it is only within the past twenty years that it has emerged as a specialized field. While this industry has made full use of all types of mechanical and vibratory conveyors, pneumatic conveyors in their proper application can be a distinct asset. me use of pneumatic conveyors by this industry however is limited- to a certain extent by the particle size of your products through the various phases of manufacture, as well as their bulk density. However, with increasing knowledge of the fluidization of dry materials, their use is becoming more wide spread.

Jan 1, 1962

By E. R. Bauer

In response to the mandates in the MINER Act of 2006, the National Institute for Occupational Safety and Health (NIOSH) conducted refuge alternatives research that included characterizing the utility, practicality and survivability of refuge chambers and outby safe havens. NIOSH also prepared and delivered a report to Congress in late December 2007 that summarized the findings of the re-search, included recommendations concerning the design and performance specifications for refuge alternatives, and focused on specific information that could inform the regulatory process on refuge alternatives. This paper highlights NIOSH?s research and recommendations concerning refuge alternatives, survivability evaluations of refuge chambers and presents a brief review of the current deployment of refuge chambers in underground coal mines in the U.S. The research has lead to the conclusion that refuge alternatives have the potential for saving the lives of mine workers if they are part of a comprehensive escape and rescue plan and if appropriate training is provided.

Jan 1, 2009

By J. L. Furtney, C. Fairhurst

"Although global mineral resources are considered to be adequate to meet the needs of a rapidly growing world population, the United States is becoming increasingly dependent on imports. This could have implications for both the economy and national security. The US is a country with a strong tradition of leadership in science and technology. Impressive advances in autonomous underground mining systems reduce the adverse effects of heat and humidity in deep mines and focus renewed attention on ground control. Developments in computing power open opportunities to develop improved understanding of the important role of discontinuities (faults and fracture systems) and more effective design of deep excavations. Establishment of mining R&D Centers at leading US research universities, jointly funded by industry and US federal agencies is recommended as an effective step for the nation to remain an influential partner in world mining. INTRODUCTION. “None of the arts is older than agriculture, but that of metals is no less ancient.. . for no mortal man ever tilled a field without implements. If we remove metals from the service of man, all methods of protecting and sustaining health and more carefully preserving the course of life are done away with.” Agricola (1558)i Homo sapiens, generally acknowledged as the species from which modern Man has evolved, is considered to have originated in Swaziland some 100,000-200,000 years ago. Evidence of use of minerals in that region has been dated to earlier than 40,000 BC.ii Today, a large fraction of the elements of the Periodic Table are derived from minerals, and finding new applications in development of innovative technologies. Agricola’s comments are as applicable today as ever.iii Metals such as copper, tin, lead, iron and aluminum were mined and smelted several thousands of years BC. It was not until the Industrial Revolution, started in the latter half of the 17th Century in Northern England, where coal was available as an energy source, and iron as the basis for fabricating machinery, that dramatic change to society began to occur. Human toil was replaced by far more powerful machines. Rural communities migrated to work in factories in urban areas. Rapid transportation over long distances became possible, leading eventually to the world of today. The change spread to other parts of the world, bringing wealth and power. Although now well established in some regions, the Revolution has still to arrive in many other parts of the world. This can be seen in Figure 1, which shows the relative wealth, or ‘Standard of Living’ as measured by the GDP/capita, of regions around the world. Regions such as North America, Europe, and Australasia iv are seen to have the highest standard. Thanks to today’s global communications systems, regions with relatively low GDP/capita are well aware of ‘how others live’ – and eager to emulate them."

Jan 1, 2018

By R. R. Klimpel

Introduction The grinding of coal-water slurries has received increasing industrial attention during the last decade. In particular, there is long-term interest in the use of pulverized coal-water slurries to replace oil in combustion equipment and in the development of coal gasification/liquefaction processes that require coal-water slurries as feed. More specifically, the use of coal-water slurries in gasification requires grinding a high-density slurry containing the smallest amount of water consistent with slurry pumping and spraying. As part of a fundamental engineering research support program aimed at the industrial implementation of dense coal-water slurry grinding, this author has published several papers on how specific rates of breakage vary as a function of slurry rheology (Klimpel, 1982,1982/83). These papers demonstrated that there is a consistent pattern of change in specific rates of breakage of coal in dense slurries with controlled variation in slurry rheology. By matching rheological data with laboratory grinding results, it was possible to identify directly slurry conditions that correspond to: 1) slowing down of breakage rates, 2) the occasional acceleration of breakage of some sizes, and 3) conditions where chemical additives will increase rates of breakage. In brief, these conditions were analyzed using two different criteria: a) the net production rate of material less than some specified size (e.g. kg/min of minus 325 mesh) in a standard batch laboratory mill test as a function of controlled changes in grinding conditions, and b) the use of the one-size-fraction feed method, which consists of following the disappearance of this largest size over grinding time in a batch laboratory mill to arrive at well-known specific rates of breakage (Austin et al., 1984). Detailed references to the methodology used as well as the conclusions are available (Klimpel, 1982, 1982/83) and will not be repeated here. The purpose of this paper is to further demonstrate several additional characteristics of dense coal-water slurry grinding that were shown in a simplified sense in the earlier publications of the author but which have clearly demonstrated themselves as being very important in the industrial simulation and scale-up of such coal-water grinding systems. In particular, this includes the clear and unambiguous demonstration of how the simultaneous acceleration of breakage of some size fractions and slowing down of the breakage of other size fractions is occurring as a function of changes in coal-water slurry density. In the earlier publications (e.g. Klimpel, 1982), it was shown by specially designed experiments that the addition of fine material and/or the use of a chemical thickening agent accelerated the specific rates of breakage of coals of coarser size fractions using the one-size-fraction method. There were also numerous examples given of non first-order breakage (the slowing down of coal breakage rates) using also the one-size-fraction method due to the presence of excessive amounts of fines which corresponded to the development of a rheological yield value. The problem with the simulation and scale-up of any laboratory and/or pilot-scale mill data to an industrial scale using the mechanistic modelling approach involving specific rates of breakage and breakage distribution parameters (e.g. Austin et al., 1984) is the number of assumptions involved in translating the smaller mill breakage parameters to the predicted larger mill breakage parameters. It is apparent, at least to this author, that to accurately simulate and predict larger scale equipment performance from smaller scale data (given that the larger scale data performance is known and hence predictions can be thoroughly checked) requires a better knowledge of breakage parameters than is currently available. More specifically, it was felt that one of the chief problems was the inability of the one-size-fraction method of determining breakage parameters to sufficiently represent the actual magnitude and sometimes even the directions of. the complicated interactions involved with slurry density changes in coal-water slurry grinding. Thus, a special set of experiments was conducted in a somewhat larger batch ball mill (0.457 m diam x 0.610 m length) than the 0.203-m-diam mill used in the original rheology characterization paper (Klimpel, 1982) so as to minimize any unusual effects due to wall-ball interactions (2.54-cm-diam balls used in both mills). More importantly, the measurements of specific rates of breakage were done using a proprietary tracer method on a portion of a given size fraction, which was then remixed into a natural feed size distribution before grinding. The experimental procedure and analysis of subsequent data was done in exactly the same manner as the radioactive tracer technique on coals as originally developed by Gardner (1962). The advantage of such an approach is that it makes no assumptions such as the independence of the specific rate of breakage of any size on the absolute sizes and amounts of other sizes present (both larger and smaller) in the mix of natural feed material. It will be shown that the measured rates of breakage using the direct tracer technique and the one-size fraction method on the same coal are indeed different. In fact, an accurate assessment of what is happening to the rates of breakage as a function of changing slurry density can only he made by measuring particle breakage under grinding conditions approximating the size distributions actually being produced in practice. Experiment procedures and results The pilot mill used was 44 cm diam x 60 cm long with a volume of 91,250 cm3 and was fitted with six 0.5-in. lifter bars.

Jan 1, 1992

By M. Ghiani

Biohydrometallurgy originated, some forty years ago, from an environmental problem, namely the serious pollution of the Ohio river by acid drainage water coming from neighboring subbituminous coal mines. Studies aimed at elucidating the cause of the intensive oxidation of the iron sulfide (pyrite) inclusions of those coals, led to the discovery of a bacterium, Thiobacillus ferrooxidans (Temple and Colmer, 1951), capable of acting as a catalyzer, accelerating the otherwise very slow chemical oxidation of iron sulfide to rates many orders of magnitude higher. However, it is now recognized that the biotechnology of microbial mining dates back to 1963, when the ability of this bacterium to solubilize copper from sulfide ores was ascertained (Razzell and Trussell, 1963). Much research has been carried out on biohydrometallurgy over these last 25 years and is still being actively conducted all over the world. The interdisciplinary nature of this young branch of science and technology is reflected by the variety of experts involved: microbiologists, mining engineers, hydrometallurgists, physico-chemists, mineralogists, solid-state physicists and biochemists. This intensive research effort has provided a solid background on the fundamentals of this technology, although many important issues have still to be solved, amongst which the enzymatic mechanisms controlling biocatalysis of mineral sulfides dissolution, the influence of bulk- and surface solid-state physics of metal sulfides on dissolution mechanisms, the interaction of the various strains composing natural microbial floras. Their elucidation should permit the rationalization of biohydrometallurgical techniques and the optimization of commercial processes. Biohydrometallurgy has already achieved satisfactory results: copper recovery from submarginal copper sulfide run-of-mine ores (i.e. assaying less than 0.3% Cu) by in-situ, dump and/or heap leaching is successfully practised in many countries and uranium recovery through bioleaching is competitive with other leaching processes.

Jan 1, 1987

By R. D. Hansen

This paper discusses the influence of frother type and dosage on recovery/selectivity in coal/sulfide mineral flotation as a function of particle size. It is shown that different frother structures do exhibit quite different but consistent performance characteristics depending on the underlying particle size ranges involved as well as the dosage levels of both the frother and collector. The data presented on existing commercial frothers end some new special purpose experimental frothers is used to illustrate some general operator guidelines on proper frother selection and use.

Jan 1, 1985

By James B. Meredith

The European Economic Community (The Common Market) is now shifting from I a coal oriented to an oil oriented economy. The proportion of energy supplied by oil has increased from only 13% in 1950 to 38% in 1962, and will approach 50% by 1970. In the past five years Common Market petroleum demand has in- creased 15% per year compared with only 3% per year in the United States. This rapid shift to oil can be explained by looking at oil's competition, First; there is simply not enough other energy - European coal, natural gas and hydro-electric power - to meet the demand, Secondly, oil?s primary competing energy in the Common Market is coal, and Community coal is high-priced - it costs more than two and a half times as much as U. S, coal at the pithead. The third reason for the shift to oil is consumer preference for the ease of handling, convenience and cleanliness of liquid fuels. As these reasons suggest, much of the shift to oil and the resulting growth in demand would have occurred whether or not the Common Market organization had existed. On the other hand, the Common Market has stimulated the use of oil by causing a higher rate of energy consumption, and oil has been the beneficiary of most of this growth.

Jan 1, 1963

By Walter C. Labys

This paper reports on recent modeling efforts to analyze the eastern U.S. steam coal market with a cross-sectional econometric as well as a quadratic programming approach. The background to coal modeling is examined first. The particular aspect of the steam coal market to be modeled are then presented and the corresponding coal model described. Both empirical results and rigorous mathematic pertubation analysis are presented. Conclusions are then drawn regarding potential modeling applications in the policy area.

Jan 1, 1979

By R. L. Weigel

As Florida phosphate mining gradually moves from the Bone Valley formation to the Hawthorn formation, a greater portion of the minable deposit contains dolomitic diluents which result in lower product grades that can be detrimental to the production of phosphoric acid for fertilizer uses. One beneficiation technique found applicable to the phosphate pebble size range (3 X 16 mesh) is heavy media separation using suspensions of magnetite and ferrosilicon. As part of an ongoing investigation of dolomite removal technology, a pilot heavy media cyclone system was constructed by IMC and used in the testing of a variety of drill core composites and hulk samples. The results of these tests were used to develop a predictive model for heavy media cyclone separation based on pebble fraction assays and heavy media operating parameters. This model is currently being used in the evaluation of specific future mining areas.

Jan 1, 1984

By J. D. Grenia

The Buick Mine is a joint venture of American Metals Climax, Inc., and Homestake Mining Company located 120 miles by road southwest of St. Louis, near the village of Boss, in the 'New Missouri Lead Belt' (See Figure 1). Since start-up in 1969, over four million tons of lead-zinc ore have been mined and milled at Buick. Situated about 1,100 feet below the surface at an elevation 270 feet above sea level, the flat lying sinuous ore bodies are up to 250 feet wide, 85 feet high and several thousand feet long. Mineralization is galena, sphalerite and chalcopyrite in dolomite, Access to the mine is through two 18'Ø concrete lined vertical shafts - one for servicing and the other for hoisting ore (See Figure 2). The mine is being worked by a modified room and pillar method using both rubber tired equipment and a sub-level rail haulage. Ore is broken from first pass headings, back and bench faces and transported by load-haul-dump units to ore passes located on 900 foot centers. The ore is pulled from chutes on the sublevel 90 feet below into 15 ton bottom dump cars and delivered in 10 car lots by a 15 ton diesel locomotive to a 42" gyratory crusher (See Figure 3). A recent innovation has been the introduction of two 50 ton trucks with plans to haul up to 60% of the ore on the mining level to an ore pass feeding directly to the primary crusher (See Figure 4). Ventilation raises up to 16'Ø, which were originally planned for 900 foot centers, are now driven on 450 foot centers.

Jan 1, 1973

By Robert A. Jankowski, George E. Niewiadomski

INTRODUCTION The utilization of longwall mining technology in the United States has steadily increased since the first longwall plow system was installed in 1952. At the errs of FY 1992, some 76 coal mines were employing longwall mining systems for coal extraction, and approximately 78 shearer and 3 plow faces are operating nationwide at any given time. Although the number of operating longwalls has remained relatively constant over the last five years, longwall production levels have increased significantly during this period. During the same timeframe, the number of continuous miner sections has decreased by 13 pct., from approximately 1438 in FY 1988 to less than 1250 in FY 1992. According to Mine Safety and Health Administration (MSHA) data, the average production of longwall sections increased from approximately 2400 tons per shift (tps) in FY 1988 to more than 3100 tps FY 1992. In fact, the average production has more than tripled since 1978, when it was only 850 tps. Approximately 25 pct. of operating longwalls are capable of producing in excess of 4000 tps. Longwall production currently accounts for nearly 36 percent of U.S. underground coal production, compared to 4 pct. in 1978. These improvements are attributed to improved longwall equipment and increased availability, larger longwall panels and automation. While longwalls are highly productive and offer other advantages, operations employing this method of mining continue to experience dust compliance problems more frequently than other mining system. Although dust levels have remained relatively unchanged over the past five years, averaging 1.6 mg/m3 and 1.9 mg/m3 based on results of operator and inspector sampling, respectively, during FY 1992, approximately 25 pct. of the operating longwalls were in noncompliance during any given bimonthly sampling cycle. Although modest gains in longwall dust control technology have been made, these have been overshadowed by significant increases in production rates. As more coal is mined, more dust is generated (Figure 1). Therefore, the increase in longwall productivity has meant that far more dust is being produced which must be controlled. [ ] In view of the current compliance record, any efforts to further increase longwall output, as has been forecasted, must be accompanied by: (1) the reduction of dust levels at existing operations through the proper installation and maintenance of suitable engineering dust controls; and (2) the advancement of dust control technology for today's and future longwalls that will enable all face personnel o work in an environment that is free of excessive levels of respirable coal mine dust. MSHA'S RESPIRABLE DUST CONTROL PROGRAM Since 1972, federal regulations have required each coal mine operator to continuously maintain the average concentration of respirable dust in the mine atmosphere during each shift in the active workings at or below 2.0 mg/m3 through the application of environmental dust control methods. The regulations provide for further reduction in the dust standard whenever the

Jan 1, 1993

By Alan J. Solomon

The function of advertising is communication. Viewing the advertisements of mineral suppliers exposes the reader to a broad spectrum of purposes: announcements of new products, availability and supply, departmental services, company image, etc. It is the advertiser's hope that the message being conveyed is the same message being perceived by the viewer. To maximize this probability, the advertiser at least must carefully construct precise copy, identify the target audience and select the appropriate advertising medium. A truly successful and efficient ad, however, also must accurately reflect a product's life cycle, i.e., the rise and fall in demand for a product. Buggy whips and radio tubes are classic examples of items formerly in high demand. Industrial minerals are similarly affected by occurrences of product life cycles.

Jan 1, 1983

By Jr. Smith

Industrial minerals are just other rocks, except for the unique characteristics that make them useful in an industrial process. There is not a ready market for this type mineral and one or more uses must be developed to sustain production. The name "olivine" is a generic term used to indicate a group of orthosilicate minerals in a solid solution series, with forsterite (Mg2SiO4) and fayalite (Fe2SiO4) as endpoints. Since neither is found alone in nature, the mineral is always a combination of the two. The commercial deposits are high in magnesium and on the high end of the melting scale in the series. The name comes from the olive-green color.

Jan 1, 1992

By J. Wyn Prior

The seismic refraction technique is probably the most popular geophysical method of bedrock profiling in geotechnical site investigations but is somewhat restricted by the inherent assumptions in the method. This paper describes how Hales' method of profile interpretation is modified to overcome the assumptions of increasing velocity and layer thickness with depth when only first arrival data is available. A further expansion of Hales method enables presentation of refraction data in a form whereby bedrock features, such as changes in velocity, relief and dip in particular, are more readily recognized. Characteristic curves of the more common bedrock features are presented as an aid to bedrock feature recognition.

Jan 1, 1976

By A. Ghosh

Commonly used predictors of ground vibration from blasting, being linear in log-log plot, do not model the underlying physics of wave attenuation. Amplitude of the wave decays with distance due to geometrical spreading and inelastic attenuation producing a nonlinear carve in log-log scale. The nolinear decay of seismic waves has also been observed from non-explosive sources, such as, pile driving, drop hammer, traffic, etc. The improved predictors, by explicitly taking these two mechanisms into consideration, model the data trend extremely well at all distance ranges. Actual field data from different studies have been used to validate the improved models.

Jan 1, 1991

By David B. Costain

Three dimensional surface approximations are important means of evaluating physical and environmental factors that affect surface coal mining and reclamation. Computer approximated surfaces are projected as an array of square grid cells where individual cells define each parameter value respective to locations on the grid. Grid surfaces or grid cells within a surface can be compared or modified through application of standard mathematical functions. Surface approximations can be used to define the quantity and quality of marketable coal and to evaluate thickness and quality of overburden. Surface approximations also can be used to evaluate overburden swell factors wherein changes in post-mine topographic relief are related to expansion of unconsolidated materials in the backfill. Application of computer approximated surface to analysis of approximate original contour (AOC) standards allows an assessment of the quantity and geographical displacement of overburden and the distribution and numerical level of slope.

Jan 1, 1984

By Egon Pohl, Friedrich Steinhäusler, Werner Hofmann

INTRODUCTION Anticipated increase of nuclear fuel production in the future coincides with growing concern about the occupational health risk of miners from inhaled radon decay products. As a consequence it has been suggested to even lower presently permitted exposure levels (NIOSH, 1980) and implement more stringent control on measurement programmes. Compliance with these regulations requires large investments in new or modified ventilation systems as well as in increased expenditure for staff and instrumentation for health physics operational monitoring. Since both costs are directly related to the overall ore production costs, this can have far reaching implications with regards to the economic feasibility of certain mining operations and consequently reduce estimates of low-cost minable ore reserves. In addition there is increasing evidence that the radon problem is not limited to the nuclear fuel cycle only, but can also represent a significant hazard to non-uranium miners. A key component in the cost-effective implementation of legislative control measures is the monitoring system employed. The choice of system is decisive for the total costs of installation and maintenance, manpower requirements and accuracy of nuclide determination. In the following operational specifications are defined for monitors in mining and milling environments. Different types of available instrumentation are discussed with regard to their suitability for practical radiation protection in underground mines, open cut mines and mills. ATMOSPHERIC CHARACTERISTICS Underground mines Radon in the air of underground mining operations is exhaled from surrounding rock surfaces, crushed material and, to a lesser extent, from water seepage. Whilst in uranium mines radon releasing ore bodies are generally localized in distinct areas, radon sources in non-uranium mines can be very dispersed throughout the system of mine tunnels. The ventilation scheme used influences the absolute atmospheric level of radon as well as the equilibrium conditions between radon and its decay products (factor F). In uranium mines mechanical forced-air ventilation is normally the only way to achieve and maintain legally required nuclide levels. This causes the F-factor to be rather low, e.g. in French CFA-mines F is of the order of 0.2 (Francois, Pradel, Zettwoog, 1975). At the same time the fraction of unattached radon decay products (fp) can increase due to the high air velocities employed. However, it is possible to find non-uranium mines with either natural draught ventilation only or assisted on demand by forced air ventilation during special operations or climatic conditions. Thereby the F-factor is more dependent on seasonal changes of temperature differences between outdoors and mine atmosphere and work routines. As a result F can cover a wide range from 0.02 to 0.95 (Steinhäusler, 1976). The use of filters or electro-precipitators in mine ventilation systems can modify the atmospheric characteristics twofold as it generally decreases the content of radon decay products, but at the same time increases the content of the unattached fraction fp . Average concentration levels of radon decay products are mostly lower in mechanically ventilated non-uranium mines than in equally ventilated uranium mines and are below 0.3 Working Level (UNSCEAR, 1977). However, some working places in non-uranium mines, specially with only natural draught ventilation can occassionally approach maximum permissible levels as defined for uranium mines (Strong, Laidlaw, O&apos;Riordan, 1975; Snihs, 1976; Sciocchetti, Scacco, Clemente, 1981). Open pit- and surface mines Radionuclide levels of radon decay products in the atmosphere of these mines are mostly too low to represent a significant inhalation hazard for miners, ranging typically from 0.03 to 0.1 Working Level (Steinhäusler, 1976). However, personnel using airpurifying respirators or working in cabins ventilated with filtered air can be exposed to a radon atmosphere with low value for the F-factor (F [<] 0.1) and high fp-value up to 80 % (Leach and Lokan, 1979). Mills Atmospheric radon concentration in crushing, grinding, drying and packing sections depends on the radium 226 content of the ore, ore storage methods and ventilation system employed. Providing adequate ventilation ([>] 2 air changes per hour) and control of dust production radon and its decay products represent only a minor problem (Saconney, 1979). MONITORING OF OCCUPATIONAL EXPOSURE Objectives Operational monitoring of the working places provides information on: - confirmation of appropriate control of the routine mining methods employed - indication of abnormal conditions. Although this type of monitoring enables the location

Jan 1, 1981