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By Ernest Y. Baafi

This paper describes the results of a series of comparative studies in which polygonal, IDS, and kriging were compared for their local estimation accuracy. The specific objective of this study was to determine the impact that the particular nature of the mineralization has on the results of such comparative studies. The study was performed on simulated coal deposits and the evaluation parameter chosen was the coal thickness. For this study, many conditionally simulated deposits having different degrees of seam thickness continuity were first developed. Each simulated deposit covered an area of 30,000 ft x 30,000 ft which was, in turn, subdivided into 100 mine planning blocks of 3,000 ft x 3,000 ft in size. Thickness estimation was made for these mine planning blocks using surrounding DDH assays. In all cases tested, e.g., from a perfect continuity to a complete lack of continuity in coal seam thickness, kriging gave the best estimates among the three, followed by IDS and polygonal methods. As expected, the relative efficiency (i.e., superiority) of kriging over other estimators was highly dependent on the nature of mineralization.

Jan 1, 1982

By R. R. Smith

The meaning of the title, "Blank Piece of Paper," refers to the need for management to take a completely fresh viewpoint to the problems facing our industry. These problems are so severe and some so new that conventional thinking may not be adequate to resolve them. Innovation has to be a part of every company's approach to the solutions, our concept is to start with a "Blank Piece of Paper.' The objective of 'this paper is to outline steps which can be taken to improve the profitability of a mining business. This is not an examination of technical solutions to individual problems, but rather recommendations for overall change in management thinking. This philosophy is based on our actual, hands-on experience in major open pit operations worldwide over the past 25 years.

Jan 1, 1987

By William Gleason

There was a time, not too long ago, when the most daunting challenges facing those in the mining and mineral processing industries could be solved through better technologies and better practices. But now the challenges that come from the actual acts of mining and processing are just part of the bigger picture. SME?s Colorado Section of the Mineral Processing Division (MPD) hosted its 63rd annual meeting at the Broadmoor Hotel in Colorado Springs, April 25-27 and, while the conference had its fair share or mineralolgy and processing presentations that were heavy on the technical side of things, this year?s conference was also focused on the issues of permitting, regulation compliance and legislative issues. The so-called ?softer? issues, that, if not addressed, can lead to very real and very hard challenges. Under the theme ?Mine your own business - permits, startups, expansions and resources,? even the most dedicated metallurgists were drawn into the discussions of politics and legislation, and how those issues affect their business. Fittingly, Colorado Mining Association (CMA) president Stuart Sanderson was honored with the Arthur C. Daman Lifetime Achievement Award. Sanderson, an outspoken proponent for the mining industry in Colorado and beyond, also presented the keynote address to the lunch crowd where he spoke about framing public opinion toward mining and the efforts of the CMA to move the public opinion dial in a direction more favorable to mining. Sanderson explained that Colorado, once a Republican stronghold, turned after 2002 and now is controlled by Democrats who are traditionally less supportive of the mining industry. Sanderson said the deciding factor in the power shift was money, as supporters of Democrats outspent Republicans in the most recent election cycles. CMA has done its part to keep mining going in the state with a broad marketing campaign that was outlined by Sanderson.

Aug 1, 2013

By H. F. Ghezzi

The indirect method of drying coal fines is applied to filter cakes which ordinarily contain 22 to 30% moisture and are not readily transportable. The "Thermal Dryer", which operates on the mass transfer principle, has found wide use in coal preparation plants. The thermal dryer is penalized in operation by the necessity of adding coarse coal to the wet fines before entering the dryer body in order to produce a permeable bed, and thus enable hot gases to uniformly contact the wet mass. The ratio of coarse coal to fines varies from 2:1 to as much as 4:1, depending on the average particle size, moisture, and ash content of the fines.

Jan 1, 1985

By Richard E. Hucko

The U.S. Department of Energy (DOE) Coal Preparation Program focuses on providing the technical and process-development basis that can be utilized to produce environmentally acceptable clean-coal feedstocks for use as market conditions permit. A major objective of the Coal Preparation Program is the development of physical coal-cleaning technologies capable of significant removal of mineral matter and pyritic sulfur at high energy recovery levels.

Jan 1, 1989

By A. L. Wilder, S. N. Dixon

Introduction Coeur d'Alene Mines Corp.'s largest precious metals property is located in the historic Rochester Mining District 40 km (25 miles) northeast of Lovelock, NV. The property encountered cold weather operational problems soon after its fall start-up in 1986 due to its elevation of over 1830 m (6000 ft). The problem of ice buildup on the heaps because of sprayed solution application was faced immediately. It was felt that allowing ice to build up all winter long until a spring thaw was impractical due to the large area under leach. Further, the operating cost and delivery schedule for a solution heating system was unacceptable. The development and installation of a leach solution distribution system using drip emitters made efficient, cost-effective winter operation possible. Other benefits of this system have also been observed and are discussed here. General process description 15,422 kt/day (17,000 stpd) of - 1.27-cm (-1 /2-in) crushed ore from the three-stage crushing plant are delivered to the leach pad using 77.1 t (85 st) rear dump haul trucks. The ore is drifted into place with a D-9 bulldozer. Leach panels are contiguous and are approximately 8861 m'(90,000 square ft) in area built in 6-m (20-ft) lifts. New panels are built on top of older areas to a final height of 61 m (200 ft). Each panel is ripped and cross-ripped prior to leaching. Barren solution is distributed to the heap using drip emitters at rates of 0.02 to 0.41 L/min/m2 (0.0005 to 0.01 gpm per sq ft), depending on the age of the panels. The pH of the leach solution is 10.7 with a cyanide concentration of 0.75 kg/t (1.5 lb per st). Approximately 50% of the silver and 80% of the gold are finally recovered. Pregnant solution percolates though the heap and flows by gravity into one of two 9.46 ML (2.5 million gal) pregnant solution ponds. The solution is then pumped to a conventional Merrill-Crowe process plant. Clarification takes place in three 9464 L/min (2,500 gpm) capacity filters. The solution is then pumped to a packed vacuum deareation tower for the removal of dissolved oxygen. Typical deareated solution contains 0.7 parts per million dissolved oxygen. Precipitation of gold and silver is accomplished by adding a zinc dust slurry to the deareated solution at the suction of the filter press feed pump. Precipitated gold and silver are recovered in three recessed plate and frame filter presses. Barren solution is discharged into a 11.7 ML (3.1 million gal) pond where cyanide makeup occurs. This solution is pumped back to the heap for further leaching. The precipitate filter cake, containing approximately 75% dore (Ag + Au), is then fluxed with anhydrous borax, soda ash, sodium nitrate and fluorspar to yield a neutral, bisilicate slag. The fluxed precipitate is then charged into a propane-fired melting furnace and heated to 1150° C (2100° F) for 3 1/2 hours. Slag and dore bullion are poured into conical cast iron pots yielding buttons of 800 to 1000 troy oz. The dore typically contains 98.5% silver and 1 % gold. Slag is crushed and tabled to recover the trapped dore blebs and beads. Concentrate from the table is returned to the furnace. Table tails are sent to the crushing circuit and out to the leach pad. Solution application The area kept under leach at Rochester is approximately 130 000 m2 (1.4 million sq ft). Barren solution is delivered to the pad at 21.2 kL/min (5600 gpm) for a resultant application rate of 0.16 L/min/m2 (0.004 gpm per sq ft). A traditional solution sprinkling system using No. 12 Senninger Wobblers with individual pressure regulators was installed at the onset of leaching activities. The Wobblers were placed at 9.1-m (30¬ft) staggered centers and were fed off of a gridwork of Yellowmine plastic piping. Solution flow rates were moni¬tored to each panel. The onset of cold weather with an average nighttime temperature of -12° C (10° F) made it apparent that continual operation would not be possible with the sprinklers. A significant amount of ice was built up on top of the heap, making maintenance and pipe removal dangerous, if not impossible. Leach solution application was restricted to daylight hours to inhibit ice formation. Process plant flow rates were reduced to maintain steady-state operating conditions. However, as daylight temperatures dropped below freezing, ice continued to accumulate due to the sprays. Besides the obvious operating hazards brought on by the growing icefield, there was also the potential environmental hazard associated with an early thaw melting the ice too rapidly for the solution containment facilities. One other option for preventing ice formation was heating of the barren solution prior to spraying. Initial plant design allowed for expansion of the propane storage and distribution system as well as modification of the barren piping for a solution heater. This option was not exercised because the operating costs for an adequate system would have been prohibitive, and timely delivery of a system was not available. An investigation was conducted on the various drip irriga¬tion products available, since subsurface solution applicators would eliminate ice formation altogether. Systems utilizing external flow emitters were ruled out because of their ten¬dency to clog when buried. Emitter systems using perforated tubing were also eliminated from consideration due to their inability to adequately control flow over required lengths of tubing. An in-line emitter system was finally selected which demonstrated clog resistance and adequate flow control, enabling direct burial.

Jan 1, 1990

By Zhiyuan Ma, Yong Liu, Xianjin Lyu, Jianfang Lyu, Jikui Zhou

A stable and continuous leaching process for niobium and tantalum extraction from ferrocolumbium tantalum (FT) was developed. The effects of initial concentration of HF and H2SO4, grinding fineness, leaching time, and temperature on the leaching rate of Ta, Nb, Fe, and Si were studied. Experimental results show that the leaching rates of Ta, Nb, Fe, and Si were enhanced by the increase of acid concentrate, fineness, leaching time, and leaching temperature. The optimum process conditions are HF initial concentration of 5 mol/L, H2SO4 initial concentration of 2.5 mol/L, − 74 μm percentage of 65%, leaching time of 20 min, and leaching temperature of 25 °C. Continuous leaching of FT was carried out by feeding ore and acid every 20 min. By leaching with HF − H2SO4 for 4 h, then adding appropriate amount of HNO3 into the solution and keeping for another 1 h, a high Nb extraction rate of 99.8% was achieved. The established method provides a promising technique for the high-efficiency separation of niobium and tantalum from FT.

Jun 5, 2022

By Stefan Mede

Robot Supported Moulding—this is the name of Herrenknecht Formwork’s entry to the world of automated segment production. What had been considered impossible for a long time, has been achieved by Herrenknecht experts together with the Swiss company Marti AG: unmanned segment production on the working line. The moulds open and close autonomously with the help of a hydraulic system. A robot cleans and greases the moulds at one work station and inserts the injection sockets at another. The next step will include further automation and digital networking of all processes from production to installation in the tunnel.

Jun 13, 2021

By D. Akers, R. Dospoy

Introduction The geological processes that form coal can also concentrate trace elements in the coal. For example, the average concentration of arsenic in bituminous coal (20 ppm) is ten times the average concentration found in all the other rocks that make up the earth's crust (2 ppm). Similarly, other elements, such as antimony, cadmium, mercury and selenium, are more concentrated in coal than in the earth's crust. When coal is burned, trace elements can be further concentrated. Although no new constraints on trace clement emissions were placed on the power generation industry under the 1990 Clean Air Act Amendments, the act does mandate a three-year study of air toxics. Any new regulations aimed at electric utilities as a result of this Federally-mandated study will almost assuredly be very costly-an estimated $1 billion per year. Many trace elements in coal are associated with mineral matter. For example, arsenic is commonly associated with pyrite, cadmium with sphalerite, chromium with clay minerals, mercury with pyrite and cinnabar, nickel with millerite, pyrite and other sulfides, and selenium with lead selenide, pyrite and other sulfides (Finkelman, 1980). There are also cases in which some of these elements are organically bound. Just as both organic and pyritic sulfur can be found in the same coal, the same trace element may be both organically bound and present as part of a mineral in the sane coal. Physical coal cleaning techniques are effective in removing mineral matter from coal and can potentially remove at least some of the trace elements associated with specific minerals, thereby reducing the release of these elements into the atmosphere. Conventional coal cleaning to remove trace elements As part of a project funded by the Electric Power Research Institute, CQ Inc., a wholly-owned EPRI subsidiary located in western Pennsylvania, has demonstrated that large reductions in the concentration of many trace elements are possible if conventional coal cleaning techniques are properly applied. Four examples are given in Tables 1 to 4. In each example, the results shown were generated by cleaning the coal at CQ Inc.'s commercial-scale cleaning test facility. Cleaning results for Upper Freeport Seam coal from Northern Appalachia are provided in Table 1. Data are presented in the table in two ways: as a weight-based concentration (parts per million) and as a concentration per heat unit (grams per billion Btu). Grams per billion Btu is analogous to pounds per million Btu, but avoids the use of numbers with many decimal places. The heat-based concentration provides a better measure of boiler impacts, because the increased heating value obtained through coal cleaning reduces the number of tons that must be burned to produce a given thermal output. Reducing the quantity of coal burned reduces the quantity of trace elements entering the boiler. This raw coal is relatively high in several trace elements of environmental concern, including arsenic, cadmium and chromium. Cleaning provided large reductions in the quantity of arsenic, barium, cadmium, chromium, fluorine, lead, mercury, nickel, silver and zinc. The results for tests with a Powder River Basin coal, Rosebud/McKay, are presented in Table 2. Large reductions in arsenic, barium, cadmium, fluorine, mercury, nickel, selenium and zinc were observed with cleaning. The concentration of chromium increased with cleaning, while lead concentration increased in one test and decreased in another. Table 3 presents test results for Croweburg Seam coal from Oklahoma. Large reductions in arsenic, barium, cadmium, chromium and zinc were obtained with cleaning. Smaller reductions were obtained with lead and nickel, while chromium, fluorine and mercury increased in at least one of the tests. Table 4 presents cleaning test data for Kentucky No.11 Seam coal. In this case, large reductions were obtained with all elements measured. In general, these data indicate that physical coal cleaning is effective in reducing the concentration of many trace elements, especially if they are present in the coal at relatively high concentrations. The degree of reduction achieved is coal-specific, relating in part to the degree of mineral association of the specific trace element and the degree of liberation of the trace element-bearing mineral. The extent of trace element removal also depends on the method of cleaning the coal. Figure 1 is a washability plot, by size fraction, of arsenic vs. ash content for Upper Freeport

Jan 1, 1994

By Dan Adams, Thomas Post, Paul Kubera, Mike Preston

Mixing is a common unit operation in the mining industry. Mixers are often used in agitated leach, bio-oxidation, and pressure oxidation. In all of these cases it is important to understand the application and what it requires from a mixer in order to be opti­mized. In the mining industJy, it is obviously important to suspend solids. However, the shear level of each of these three applications is ve1y different. In acid leaching, the mixer needs to suspend solids and produce a good degree of blending. In pressure oxida­tion, the agitator must also disperse air or oxygen by creating fine bubbles. Because of the presence of microorganisms, bio-oxida­tion requires less shear than the other two processes, but the agita­tor must be able to suspend the solids, provide excellent blend­ing/heat tJ·ansfer and distribute the air. Thus, in the mining indus­tiy there is an application spectJ·um that requires different impellers to perfotm different jobs. Specifically, these jobs are blending, solids suspension, gas dispersion, mass transfer and heat transfer. It is important to determine whether the process is mass transfer or kinetic rate limited. Mixers affect a mass transfer limitation but have no affect on the kinetics.

Jan 1, 1998

By A. Athousaki

The Ecological Footprint is a resource accounting tool used to address underlying sustainability questions. Aggregates consist of natural, artificial or recycled materials. The production of aggregates is the fastest growing activity worldwide since huge quantities are required by the construction industry. This paper presents a parametric investigation of the ecological footprint of transporting aggregates for urban use as a function of tonnage and distance.

Jan 1, 2008

By R. D. Hamilton, W. J. Miles

In 1987, the International Agency for Research on Cancer designated crystalline silica as a 2A probable carcinogen. As a result, crystalline silica is regulated under the Hazard Communication Standard as a probable carcinogen at a concentration of 0.1% or greater in the workplace. Crystalline silica will be listed as "reasonably anticipated to be a carcinogen" by the National Toxicological Program. This designation of crystalline silica as a probable carcinogen has created major issues for the mineral and chemical producer, including labeling, hazard communications, marketing a material with potential hazard exposure, and potential liability. The State of California also regulates crystalline silica under Proposition 65 in products as a carcinogen, based upon the IARC determination that it is a probable carcinogen. More federal and state regulations are anticipated as a result of the IARC classification of crystalline silica and its subsequent federal regulation. Respirable crystalline silica has been regulated as a hazardous dust for many years by OSHA. This regulation was initiated to prevent silicosis, another occupational disease. OSHA has established monitoring devices for determining the concentration of airborne respirable silica in order to measure exposure to this substance. The accurate determination of the crystalline silica content is critical to dealing with these health risks and regulations. In the past, crystalline silica was considered to be safe and, because of its ubiquitous nature, little effort was made to determine or quantify its presence in most materials. The Hazard Communication Standard requires that a1l products containing 0.1% or greater crystalline silica must be properly labeled for this material and its hazard. Unfortunately, the 0.1% threshold was not chosen on the basis of established analytical capabilities for crystalline silica, but results from general limits for potentially carcinogenic chemicals and substances. Numerous methods have been developed for the determination of crystalline silica in a variety of products. However, these methods are not generally applicable since they must be specific for silica in any of its crystalline states and not just for total silica content. Chemical tests for silica are not difficult and quite accurate at the 0.1% level; however, in addition to its crystalline phases, it occurs in amorphous phases and in a wide variety of crystalline and amorphous silicates. In general, there is little correlation between total silica content and crystalline silica.

Jan 1, 1991

By H. L. O. Huyck

A microcomputer equipped with spreadsheet, data management, and FOR- TRAN programming software is used to update and quantify a model for ranking seventeen economically important metal commodities in terms of market potential (Huyck, 1982). Weighted factors are used for the ranking: (1) demand growth trends, (2) end-use substitution vulnerability, (3) recycling trends, (4) price trends, and (5) cumulative demand versus world reserves factor. Price trends are defined using (1) price-vs.-year slopes (with prices in 1967 constant dollars) and (2) standard deviations of slopes (to indicate price volatility). Substitution vulnerability is defined as the percent of end-use which is replace- able by other commodities, and a factor indicating the likelihood of such substitution. Factors are normalized and linearly combined to produce a ranking of the seventeen metals. Microcomputer software is essential for organizing data and calculating statistical parameters and linear combinations of factors.

Jan 1, 1986

By J. K. Hrica, T. J. Orr, J. Navoyski, B. Macdonald, C. L. Hoebbel, J. L. Bellanca, B. Demich

Haul truck fatal accidents and injuries continue to be a significant concern for the mining industry. However, the availability of high-quality training materials continues to be limited. Near-miss incident accounts, if packaged well, could help fill this gap, because for every fatality, there are hundreds of reportable accidents and thousands of undocumented near misses. Researchers from the National Institute for Occupational Safety and Health (NIOSH) collected detailed accounts of 21 near-miss incidents in virtual interviews with mineworkers at surface mining operations across the country. From these interviews, researchers created four simulation videos. The videos bring these events to life through first-person retelling and various visual perspectives of actual events. Each video exemplifies a critical safety message and a common haul truck hazard. This paper describes the process of taking narratives and turning them into impactful visual stories. NIOSH plans to co-release these simulation videos with the Mine Safety and Health Administration (MSHA) to the mining industry to raise awareness and ultimately help reduce haul truck-related accidents and fatalities in mining.

Feb 1, 2023

By F. Chavan

1. Introduction The new Cleuson-Dixence development project in the Valais region of the Swiss Alps, involves the construction of a new link between the Grande-Dixence dam (still world recordholder with a height of 300 m) and a power house on the banks of the Rhone consisting of approximately 20 km tunnels and shafts, and involving a fall of about 1900 m. This 1200 MW project will replace an existing 900 MW structure built in the 1960s, no longer considered efficient. The new project comprises a head race drift about 15.8 km long, a surge tank, an inclined cascade shaft 4,2 km long, and an underground power station. The work for lots C and D (head race drift from Tortin to Tracouet, surge tank, six adits ans the complete inclined shaft) was awarded to our group (Prader, Locher, SELL, Losinger, Evéquoz, Dénériaz, Imboden and Bouygues). The geological conditions are: Lower part of the shaft (300 m) : sedimentary - sandstone and soft tertiary sandstone. Middle and upper part (2600 m) : metamorphic - upper and lower carboniferous, interrupted by triasic chipping. The horizontal section (7 km) consists of mica

Jan 1, 1995

By Stephen C. Tadolini, Thomas M. Barczak

Western mines have had limited choices for standing support. Wood cribs were often too soft and unstable. The introduction of the Can support in the early 1990’s provided a very effective alternative and remains the dominant form of tailgate support. Water-filled prestressing cells are now used to cap the Can and preload it to provide an active roof load. The Cluster Prop, consisting of three timber wedge props bundled together, provides more capacity than an equivalent sized Can support and improves transport efficiency. However, the Cluster Prop is less stable and does not maintain a consistent load throughout its loading profile. Pumpable roof supports are another alternative support, but they have not been proven in high deformation environments. Alternative supports are also being used in longwall recovery operations. These include the Rocprop and Omni Prop, which are extendable support systems. They also provide active roof loading which can be beneficial in these applications. Specialty supports, such as the Sand Prop and Spider Prop, have also been introduced into western longwall operations. This paper compares the performance characteristics of these various support systems.

Jan 1, 2005

By P. R. Shivdasan, R. D. Hagni

Cathodoluminescence microscopy (CLM) is uniquely applicable to the study of carbonatite-related fluorspar ore deposits. The mineralogy of the carbonatites, sodic and potassic fenites, marbles, quartzites and fluorite ores are readily determined and characterized. Calcite, dolomite, apatite and fluorite were deposited dominantly under high-temperature conditions, and they exhibit strong cathodoluminescence (CL). At the Okorusu, Namibia, carbonatite complex and fluorspar mines, three types of carbonatites have been recognized by field mapping and laboratory CLM. The main carbonatite intrusion is fine grained and consists mainly of calcite. A later phase of pegmatitic carbonatite consists of calcite, magnetite, Fe-rich pyroxene, apatite and pyrochlore. Pyroxene carbonatites were recognized mainly through their study by CLM.

Jan 1, 2002

By Matthew E. MacGregor, Hugh T. Kelly

I.H. 635 (LBJ Freeway) was constructed as a loop freeway around the city of Dallas in the late 1960s and early 1970s with a design capacity of 160,000 vehicles per day (vpd). Today’s facility is carrying over 270,000 vpd. To help mitigate community concerns with regard to right-of-way issues, noise, safety, and traffic disruption, the Texas Department of Transportation (TxDOT) is planning a number of significant improvements. The West Section improvements include the construction of managed HOV/Toll lanes. Within this 8-mile section, TxDOT is planning two mined tunnels(1.5 and 1.9 miles long) beneath the LBJ Freeway. The mined tunnels will connect to cut-and-cover box sections in both the east and west directions. This paper presents an overview of the project development from the design schematic, through the geotechnical investigations, into the current design stage. The project is being planned for implementation by use of a Comprehensive Development Agreement.

Jan 1, 2005

By D. M. Range

Exxon is reclaiming an 80-hm2 (200¬acre) Wyoming uranium tailings basin in accordance with US Nuclear Regula¬tory Commission (NRC) requirements. The reclamation plan is designed to control the tailings and their radioactive emissions for at least 1000 years. Rigorous modeling and analyses of potential erosion by wind and water were used in planning. The use of riprap was minimized and the need for long¬term reclamation maintenance was eliminated. The resulting design is simi¬lar to regions stable from erosion cre¬ated by nature. The concepts used in the design and implementation have wider reclamation application. Highland history Exxon operated the Highland uranium operations from 1972 until mid-1984. Open pit and underground operations mined the roll front, sandstone ore body. The 2.5 kt/d (3000 stpd) mill employed conventional crushing, grinding, sulfu¬ric acid leach, CCD, SX, precipitation, and drying circuits. The mill produced 10 Mt (11 million st) of tailings. An¬other operator began commercial scale in situ leach operations in 1988. The tailings basin was constructed by deposition of mill tailings in a natural ravine dammed with a 30-m (100-ft) high by 1050-m (3400-ft) long clay core earthen dam built entirely downstream of tailings. Figure 1 shows the layout of the tail¬ings basin in 1984. Tailings were de¬posited along the dam face on the east side of the basin as well as in the west end and along the south edge until the early 1980s. This left a deep water pond in the middle of the basin. The deep pond was largely filled with tailings during the last four years of mill opera¬tions by the construction of two tailings causeways and the operation of a float¬ing tailings line. The pond water volume was mini¬mized by recycling tailings water to the mill and by operating a 32-L/s (500¬gpm) evaporation enhancement spray system during the last few years of mill operations. Regulatory requirements Several conceptual tailings basin rec¬lamation plans were prepared during the mine life. In September 1984, Exxon began preparation of a detailed plan in response to an NRC request. Water, Waste and Land Inc. (WWL) of Fort Collins, CO was selected to help pre¬pare the plan that was submitted to the NRC in December 1984. The design had to meet the require¬ments found in NRC regulations (NRC, 1985). These were based on regulations prepared by the Environmental Protec¬tion Agency (EPA, 1983) at the man¬date of federal law (UMTRA, 1978). The NRC regulations contain strict primary standards and a somewhat more flexible set of secondary standards. The primary standards include requiring that: • radiation from tailings be reduced to background levels; • radon gas emitted by the tailings be reduced to 20 pCi/m2/s from the surface of the reclaimed tailings pile; • tailings not be dispersed into the environment; and • these conditions endure without routine maintenance for at least 200 years and for 1000 years to the extent reasonably attainable. The lengthy time requirements pre¬sented a large engineering challenge. Radon is a radioactive, chemically inert gas with a 3.8 day half-life. It is released from uranium tailings by the radioactive decay of radium, which, in turn, is a radioactive decay product of uranium. Radon emissions from ura¬nium tailings can be controlled with an earthen cover thick enough that the radon gas decays to its solid, short-lived radio¬active daughters before the radon dif¬fuses through the cover material into the air.

Jan 1, 1989

By Robert H. Scott

Developments during the past few years have brought coal-based composite fuels to commercial readiness. During the next few years, composite fuels will become available from a number of suppliers. Potential users must evaluate the combustion properties of these fuels to determine equipment and operating changes required for their use. Most work to date has been done with boiler applications. However, many potential non-boiler applications exist in the metals and minerals industry. These applications require specific evaluations appropriate for the processes involved.

Jan 1, 1982