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By M. J. McPherson, P. Mousset-Jones, G. Danko, I. M. Konduri, F. Calizaya

The flow of air through a bare rock, underground airway is affected by the size and frequency of the micro- and macro-asperities of the rough surface. The focus of this study is to characterize this roughness using the coefficient of friction, the friction factor and the fractal dimension. The rough surfaces were identified by two sets of 177 and 78 transverse profiles measured by a laser profiler along the length of an underground airway at the Sunshine Mine, Idaho. Based on the measurements, the friction factor was estimated from Atkinson's equation and the coefficient of friction from the Moody diagram, and power series and variography were used for computing a fractal dimension for the airway surface. Significant conclusions are reached relating the effect of error in the measurement of cross-sectional and rubbing surface areas of a drift, on the estimated friction factor for the airway. The potential role of the fractal dimension as an alternative to the friction factor for characterizing the roughness of a mine airway is discussed.

Jan 1, 1993

By Jeffery L. Kohler

The characteristics of mine airstreams, such as their magnitude in the time and frequency domain and their spatial distribution, as defined by isovels, must be considered when making a measurement. The possibility for erroneous measurements is greatly increased when fixed- point sensors for mine monitoring systems are used. However, an a priori understanding of the airstream characteristics can be used to reduce the possibility of erroneous readings. This paper describes the problem, presents data to illustrate the nature of the problem, and provides recommendations for alleviating the problem.

Jan 1, 1987

By Julie Mitchell

The U.S. Bureau of Mines is conducting research on the application of expert sys tens technology to mining equipment diagnostics and predictive maintenance, to increase mining productivity and efficiency. One of the greatest hindrances to mining productivity is the breakdown of equipment, causing lengthy and costly delays. A diagnostic maintenance expert system (DIMES) is being developed for the hydraulic system of a continuous coal mining machine. Through the use of such a system, the frequency of equipment failures and repair time should be significantly reduced. This paper describes the application domain, the functional requirements, and the problem approach for DIMES, the design and implement at i on of the knowledge- based system, the sensor work involved with the project, and the future plans for the continued development of this and other expert systems.

Jan 1, 1989

By James K. Grunig, Rodney J. Anderson

A process consisting of leach, continuous countercurrent decantation, resin-in-column ion exchange, evaporative crystallization of beryllium sulfate, and decomposition of the sulfate was developed for Spor Mountain, Utah, ores. The process is metallurgically sound, has a minimum of process steps, and is applicable to a wide variety of beryllium ores. The most novel aspect of the process is a resin system of ion exchange which is highly selective for beryllium and which rejects substantially all impurities except for minor amounts of aluminum, magnesium, fluorine, and sulfate in addition to beryllium. The oxide from sulfate decomposition meets specifications of potential users.

Jan 1, 1983

By Robert S. Setren, Jeffrey L. Ambs

The disposable diesel exhaust filter (DDEF) system developed by the U.S. Bureau of Mines and Industry cooperators for heavy-duty permissible, diesel-powered haulage vehicles, effectively reduces in-mine diesel particulate matter concentrations up to 95%. However, there are concerns about the hazards that exist when the filter is used in situations for which it was not designed. This work investigates the exhaust gas temperature limits to which the filter elements can be exposed without posing a safety or health hazard, such as 6re or off-gassing toxic compounds. A filter approved by the Mine Safety and Health administration and after-market filters were evaluated under varying engine exhaust conditions to determine if after-market filters pose an unacceptable hazard when used in a DDEF system. Filters were laboratory tested at engine exhaust temperatures ranging from 77°C to 290°C. Of the seven filter types tested, six appeared suitable for use on water scrubber-based cooling systems and two appeared suitable for use on dry heat exchanger type exhaust cooling systems with exhaust temperatures up to 150°C. Any filter elements used as exhaust filters on permissible diesel machines must be approved by MSHA for that application. Mine operators who wish to use an after-market filter element should request an MSHA field modification. MSHA will work with the mine and filter manufacturer to ensure its use in this exhaust system application does not pose a health or safety hazard.

Jan 1, 1995

By G. A. Hazen, S. M. Sargand

This study monitored longwall mining subsidence profiles over three panels that were mined beneath state highways in southeastern Ohio. The average maximum subsidence was 1.07 m (3.5 ft). The average maximum compressive strain recorded was 0.008 mm/mm. Three predictive methods for the determination of displacements and strains were compared: the National Coal Board (NCB) graphical method, the profile method with empirical constants determined for southeastern Ohio, and a finite element excavation program. Excellent subsidence agreement was found with the profile method, and reasonable strain agreement was determined with the finite element program.

Jan 1, 1987

By N. L. Piret, R. J. Wesely, A. E. Melin, A. D. Zunkel

At the end of the sixties new iron precipitation techniques as jarosite, goethite or hematite brought about the new generation of electrolytic zinc plants, thereby terminating the multitude of existing neutral leach residue treatment schemes. Since the eighties, increasing environmental impact considerations urge the conversion of these contaminated waste generating precipitation processes to techniques which either produce environmentally acceptable residues or minimize their formation thereby generating iron-bearing byproducts. Technologies identified and economically assessed include the hematite process either suitably improved or with subsequent upgrading, the iron extraction process and the direct smelting of neutral leach residue to slag and fumed zinc oxide.

Jan 1, 1993

By S. R. S. Sastri, G. V. Rao

Because the nickel contained in lateritic nickel ores does not occur in an identifiable mineral, it is generally accepted that these ores are not amenable to beneficiation. For this reason, such ores are either directly smelted or leached to extract the nickel. In this paper, a process for enriching the nickel content of the lateritic nickel-bearing chromite overburden, normally a waste material generated during chromite mining, is described. In this flotation process, a nickel preconcentrate containing >1.1% Ni was obtained from material containing as little as 0.36% nickel. An empirical relationship was developed to predict the grade of nickel that can be obtained.

Jan 1, 1997

By B. R. Green, Ms. M. H. Kotze

Ion-exchange fibres (IEF) were prepared by the ir­radiation grafting of styrene onto polypropylene, which was then subsequently functionalized. Strong- and weak-base exchangers were prepared and evaluated Tor their ability to extract gold cyanide selectively. The IEF prepared had loading capacities similar to those of the corresponding resins and they had good selectivities for gold cyanide when contacted with a mixed metal-cyanide solution. The expected advantage of IEF over granular exchangers, that of faster kinetics, was illustrated. The strong-base Iibre in particular seemed to be very effective for the extraction of gold cyanide from dilute solutions such as return-dam waters.

Jan 1, 1990

By Roy E. Williams, Muriel S. Robinette

Ground-water contamination from uranium operations could be avoided with proper site analysis techniques. Contamination from tailings disposal sites is carried downgradient within permeable hydrostratigraphic units which can be located and delineated with a combination of drill holes and borehole geophysical logs. Engineering safeguards can be designed into a disposal site by determining if permeable hydrostratigraphic units exist which will dominate the flow system and provide seepage paths for contaminates. It is more cost-effective to accurately assess seepage potential with geophysical logs before contamination becomes a problem than to be faced with a major clean-up effort after contamination has occurred. If a uranium waste impoundment already has a ground-water contamination problem, then borehole geophysical logs may be used to delineate the contaminated zones which need to be cleaned up. It is less expensive to withdraw the contaminated plume from only within the affected zones rather than attempt to dewater the entire area. Consequently, the geophysical logs are invaluable in assessing which zones should be pumped and where packers should be set for construction of piezometers to allow monitoring of water-quality changes. A surface geophysical technique is being tested and developed for monitoring of seepage frum uranium tailings impoundments. Geoelectric soundings and profiles from direct current resistivity surveys can locate anomalous areas for the placement of drill holes to better assess seepage. This reconnaissance technique should eliminate random hit-or-miss drilling at sites where monitoring is required. Tests and experiments are being done on developing the capabilities of this technique to incorporate complex resistivity data to assess cultural impedence noise which complicates simple resistivity data.

Jan 1, 1980

By V. K. Karra

Research by various workers has shown compressive comminution to be significantly more efficient than impact comminution. Based on the work being done at Nordberg, wet compressive crushing in cone crushers producing finer and finer products, shows the feasibility for partial substitution of conventional tumbling mills. For further substitution, major challenges are processing of fine feed slurries in cone crushers to realize a significant size reduction of the particles, and understanding the limitation of the gyratory type units in terms of finest product achievable. The paper addresses the challenges involved, efforts at Nordberg, and the implications to conventional comminution flowsheets.

Jan 1, 1989

By H. D. Freeman

The Pacific Northwest Laboratory (PNL) is developing cover technology for uranium mill tailings that will inhibit the diffusion of radon to the atmosphere. As part of this cover program, an improved radon flux measurement system has been developed. The radon measurement system is a recirculating, pressure-balanced, flow-through system that uses activated carbon at ambient temperatures to collect the radon. With the system, an area of 0.93 m2 is sampled for periods ranging from 1 to 12 h. The activated carbon is removed from the radon trap and the collected radon is determined by counting the 214Bi daughter product. Development of the system included studies to determine the efficiency of activated carbon, relative calibration measurements and field measurements made during 1980 at the inactive tailings pile in Grand Junction, Colorado. Results of these studies are presented.

Jan 1, 1981

By K. Cothern, S. Novack, D. A. Johnson, R. Borden, S. Pavlou

A procedure is presented for ranking hazardous waste sites for remedial decisions, and an example with application to mining waste sites is discussed. Typical contaminant concentrations are calculated from field data. Exposure indices that compare these measured concentrations with allowable limits are then computed. The limits are selected to protect both the health of humans (for both carcinogen and noncarcinogen effects) and the health of key organisms in the ecological food web. The additive exposure index for a site, defined as the sum of all contaminant-specific exposure indices, is then used in ranking the sites and assigning each a priority for remedial action. One key source of uncertainty in the process is the estimation of a typical site concentration from data that include values reported as "below certified reporting limit" (BCRL). This uncertainty is compounded in the additive exposure index and therefore may have a substantial effect on the assignment of remediation priority. A general approach is presented for incorporating consideration of BCRL data into uncertainty evaluation when assigning remediation priority designators to hazardous waste sites.

Jan 1, 1992

By G. S. Adisoma

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

Jan 1, 1995

By P. Otto, G. Borm, Th. Dickmann, F. Amberg, R. Giese

Based on many years experience, the well approved Tunnel Seismic Prediction System (TSP) has been substantially enhanced for online geological prognosis in underground construction. The method provides high resolution seismic images of the rock mass ahead of a tunnel face via an array of standard anchor rods. These contain3D-geophones and can routinely be installed during the excavation process. A further outstanding feature of the system is the newly developed high frequency repetitive seismic source which can easily be fixed at a tunnel boring machine. A user-friendly software package enables online data acquisition, processing, 3D-visualization, and interpretation.

Jan 1, 2001

By Hector M. Valenzuela, Juan H. Rojas

This paper presents a strategic plan for automation, plant integration and process management being implemented at the Chuquicamata mining and metallurgical complex of Codelco-Chile. This five-year plan considers different levels of process control and plant integration, which include instrumentation and direct control, process models and supervisory control, plant information integration, and real time process and plant wide management. The conceptual solution developed defines an architecture for the overall system and the projects to be implemented by each production unit, as part of the proposed solution for the division wide process control, plant integration and real time process management. An estimate of the cost benefit relation of the plan is also given.

Jan 1, 1998

A general form of pore pressure in a saturated porous medium, which is subject to external forces it has the pressurization of a borehole in hydraulic fracturing, is derived. The pore pressure consists of two parts: the preexisting initial pore pressure and the pressure induced by fluid flow due to the pressure difference caused by pressurizing the borehole The initial pore pressure associates with the effective stresses in the stress, fields of crustal stresses and a thick hollow cylinder subjected to internal and external pressures. The pure pressure weaned by fluid flow is implied in Biot's (1941) constitutive equation for three-dimensional consolidation and proved to be the exact effective pore pressure (Nur and Byerlee, 1971). Using this general form of pore pressure, a general poroelastic model for hydraulic-fracturing breakdown (fracture-initiation) pressure was derived. This model was validated by laboratory experimental results on Indiana limestone. Three sets of tests were conducted under the conditions of preexisting pore pressures of 6, 21 and 28 MPa, respectively. The equal horizontal (confining) pressures applied in the tests ranged from 6 to 60 MPa. Hainison and Fairhurst's (1967) model appear to be applicable to rocks having microcracks or flows. Experimental results of fracture reopening pressures on Indiana limestone supported this assertion. The test results also demonstrated that, when the pressure difference between the confining and the initial pore pressure grows larger than 14 to 21 MPa, the breakdown pressures agree well with the general poroelastic model developed in this paper. This indicates that the developed model will be superior when hydrofacturing stress measurements are conducted at great depth.

Jan 1, 1997

By J. A. Organiscak

This paper examines methods for limiting occupational silica exposures for roof-bolting personnel in underground coal mining. A canopy air curtain and an air tube were evaluated as means to provide filtered air over the breathing zone of these personnel. Laboratory testing showed that dust reductions beneath the air curtain and air tube approached 60% and 40%, respectively, with low interference air velocities. The data also showed that dust reductions were highest for positions closest to the device and that these levels decreased with distance. This paper also evaluates a metal rake, a flexible insert and a rigid insert for cleaning the roof-bolter dust collector box. Less dust was produced when using the rigid insert. Surprisingly, the flexible insert was sometimes no better than scraping or raking the dust onto the mine floor. However, little dust got on the workers coveralls when using either of the inserts.

Jan 1, 2003

By Martha Caudill

When planning for the required amount of storage capacity at a proposed open-pit coal mine or determining when additional storage capacity should be added to an existing operation, the decision must be based on a breakeven- analysis relating the discounted cost of capital for storage capacity to the marginal costs incurred for additional crew call-outs on weekends and demurrage charges. The model developed in this paper uses simulation techniques applied to two coal mines in the Powder-River Basin to determine how much storage capacity is needed and when it is needed. The paper also generalizes the simulation model so that it can be applied to any type of open-pit mining operation. Two important results of the model are (1) all of the mines in the Powder River Basin have excessive amounts of storage capacity, and (2) management is provided with estimates of the total number of hours that crews will have to work on the weekends as annual tonnage increases, and the levels of demurrage costs incurred.

Jan 1, 1986

By K. Mulukhov

Introduction The depth of open-pit mines continues to increase. The typical designed depth for large quarries is now in the 300 to 600 m (1,000 to 2,000 ft) range, with some quarries even reaching depths of 700 to 800 m (2,300 to 2,600 ft). The cost of handling material from such deep mines can be 60% to 70% of the total cost. The capacity of using a cyclic means of transport, such as trucks or skip hoists, continues to drop as the depth of the mine increases. In addition to the problem of maintaining relatively low slope angles for haul roads, increases in environment pollution and increased fuel consumption make the use of trucks ineffective below 100 to 150 m (300 to 500 ft). In handling large quantities of bulky materials, i.e., more than 15 to 20 Mt/a (16 to 22 million stpy), under fixed terminal points, belt conveyors are preferable in almost in all cases. An exception is when the lump size of the load is too high for the conveyor to handle. Belt conveyors in mines can handle loads having a maximum lump size of no more than 250 to 300 mm (10 to 12 in.). The use of a movable crusher prior to the belt conveyor in an open-pit mine would make the process very expensive. Such an operation could not compete with truck haulage on a cost basis. Belt-car conveyor The main factor that restricts the lump size for conventional belt conveyors is collision impacts between the load-carrying belt and idlers. These impacts are completely eliminated in the belt-car conveyor, which was previously described by Mulukhov (1977). The unique feature of the conveyor is that the load-carrying belt is supported by moving cars. Each car consists of a troughed cross strap that supports the belt with the load and two rollers, on which the cars move along upper and lower rails. Cars are connected by two endless chains revolving over sprockets. The system uses conventional drive pulleys, tail pulleys and return idlers. There are no fasteners between the carrying belt and the car cross straps. The conveyor belt simply drives the cars along by the force of friction between the belt and the straps. A belt-car conveyor was first installed in 1970 at the Karatau mining operation in Kazakhstan. The system was an elevating conveyor with an inclination of 20° and was located on the final part of the truck haul road. The conveyor transferred blasting phosphate ore from the quarry to the crushing plant. A bunker was mounted between the trucks and the conveyor. The maximum lump size was typically 1,200 mm (48 in.). However, there were some lumps as large as 1,500mm (60 in.), which was greater than even the belt width (Fig. 1). Because the prototype belt-car conveyor was intended only for industrial trails, it had a relatively short length of about 50 m (160 ft). Nevertheless, the conveyor yielded a substantial profit over the cost of truck haulage. Naturally, the first question one might ask is why such a system is not now widely used. The reason was the further development of a huge transporting complex for the whole quarry at the base of the belt-car conveyor. After successful industrial trials from 1971 through 1973, which demonstrated the systems engineering feasibility, the State Planning Committee of the USSR included the development of the belt-car conveyor in its plan for the development of the national economy. However, mistakes were made. First, a single organization was not in charge of the development. Second, a plant that was not specialized in belt conveyors was put in charge of the design and manufacturing of the conveyor system. In addition, the crusher was installed before the stacker, which negated the major advantages of the belt-car conveyor. For loading the conveyor, a special blade feeder with pendulum suspension was developed, but it was found unreliable. The main conclusion was that, in-

Jan 1, 2003