Search Documents

By Brian Hester

Many Third World African countries are well-endowed with minerals - especially gold and diamonds - while only a few have important base metal deposits. For decades since colonial rule, political and economic conditions discouraged interest by Western capital. Influence from Soviet Bloc countries, however, has declined with the move toward multi-party rule. And the left wing orientation, once widely favored by Third World African countries, has almost disappeared. With International Monetary Fund (IMF) encouragement, these Third World African countries now encourage representational government and solicit western finance to expand their industries. Mining is especially encouraged. The North American mining industry is following the same trail as other capital intensive industries and looking abroad for opportunities. The Prospectors and Developers Association of Canada released figures that show exploration expenditures in that country were halved between 1987 and 1990. Figures for the United States are not so easily found but every indication points to a downward trend. While total annual expenditures on US exploration by corporations as a group are either declining or remaining constant, expenditures away from North America is increasing. Gold exploration expenditures in 1991 by the major companies tracked by Minerals Economics Group were less in the United States than for Latin America and the Southwest Pacific combined. The same study showed as much was spent in the Republic of South Africa and "Other" areas combined as in the United States. Expenditures by major corporations in these "Other" areas amount to only 5.2% of their total budget. Third World Africa is a major component of these "Other" areas.

Jan 1, 1993

By Evans U. Jegbefume

A plane strain two-dimensional finite element model employing the method of negative reaction loading has been used to model roof collapse and subsidence resulting from the underground gasification of coal in regions of soft overburden such as that found in Texas. The model included dry zones of rock around the cavity. Roof collapse was included by considering the final state of stress in the elements and removing those that had undergone tensile failure. The two-dimensional plane strain model was extended to include thermal loading and thermal softening of the roof rock. Roof collapse initiation and growth of the cavity were modelled by examining the portion of the rock immediately above the cavity under thermal and hydrostatic load. The model was extended to include linear creep using the method of incremental strains. The overburden was modelled as a generalized Kelvin material.

Jan 1, 1982

By Shaning Yu, Yosry A. Attia

The purpose of this work was to investigate the feasibility of using column flotation as a floc separation technique. In this study, the ultrafine coal (minus 25 microns) slurries were cleaned by using the Integration of column flotation with selective flocculation. It was found that using column flotation as a floc separation technique during the "cleaning" stage, achieved much better results than that either using column flotation as a rougher separation technique for coal flocs, or using It directly to recover the ultrafine coal from the slurries without adding selective flocculant. Thus, the ultrafine coal slurries were first separated by selective flocculation process to reject a certain amount of the dispersed ultrafine ash minerals, and to aggregate the ultrafine coal particles as flocs. Thus, the entrainment of ultrafine ash minerals Into the coal floc-froth concentrate during flotation could be considerably reduced. Subsequently, the coal flocs were further "cleaned" by column flotation. The experimental results Indicated that this approach was technically feasible and particularly suitable for a slurry containing a large amount of ultrafine particles. The effect of flotation time, and collector dosage on column flotation of coal flocs were also Investigated and reported In this article.

Jan 1, 1988

By Swati Mohanty, G. V. Rao

Sedimentary dolomitic phosphate ores are difficult to treat by flotation, and high-grade phosphate concentrates with high recoveries are difficult to obtain. The literature indicates that the reagents required for beneficiation of such ores are generally dictated by the nature of the gangue. In this paper, the optimum flotation parameters necessary for enhancing the grade and recovery of a typical low-grade dolomitic rock phosphate ore from Jhamarkotra, Rajasthan, are highlighted. The standard design-of-experiment (DOE) technique was used to obtain empirical models for both grade and recovery. The model equations were then used for optimizing the flotation parameters, including pH, percent solids, collector dosage and depressant dosage. Laboratory experiments demonstrated that a phosphate concentrate containing about 36% P205, with a recovery greater than 95%, can be obtained in a single-stage by the reverse flotation of carbonaceous minerals at the optimized conditions. Key words: Phosphate, Flotation, Dolomite

Jan 1, 2003

By Misra M., P. Grimes, Chen. S.

The combustion of petroleum products produces emissions which contain oxides of nitrogen (NOx), hydrocarbons (HC), and particulate matter (PM) which have adverse health and environmental effects. In recent years there has been increasing interest in the use of water-fie1 emulsions as a substitute for conventional fuels. Emulsified fuels are emulsions of water in fuel, which are typically made of 10 to 20 percent of water mired with certain additives and fuel. Studies have shown that the emulsified diesel can significantly reduce the emissions of NO, PM and car- bon monoxide and increase the fuel efficiency. In order to produce a stable diesel emulsion, the development of an effective surfactant additive is critical. The stability of diesel emulsions is influenced by many factors, including size distribution of the droplets, the viscosity of the continuous phase, the physical properties of the interfacial film, and temperature. This paper describes a method to produce emulsified diesel and combustion results obtained from various tests. It has been found that the diesel emulsion made with this additive package was stable during the test, and the emissions were lower in NO, CO, and PM compared to the baseline diesel.

Jan 1, 2005

By J. A. Brierley, C. L. Brierley

The history, current applications and future of biotechnical developments in the metals' extraction industry are reviewed. Bioleaching of copper minerals continues to be the most significant application. Uranium bioleaching was successfully demonstrated at industrial scale. Developments are now being made in biooxidative pretreatment of refractory gold concentrates, ores and low-grade materials. Advancements are forthcoming in water and solid mine waste bioreclamation, including metals' biosorption, wetland treatment of acid mine drainage, and biodegradation of cyanide in spent, heap-leach operations. Better understanding of the types and functions of microorganisms involved in metal interactions could advance genetic engineering applications in bioleaching and bioreclamation.

Jan 1, 1993

By Monica Pavlik, Thomas Wildeman

Water from the Forest Queen mine adit near Silverton, Colorado drains into a natural wetland. Because the pH of the water averages 5 and the iron concentration averages 18 mg/L, it was thought that the wetland might naturally treat the water. Of most concern with respect to the aquatic environment is zinc whose concentration averages 0.60 mg/L. Starting in October 1997, the surface waters, ground waters in the peat substrate, and the sediments in the wetland were sampled and analyzed four times over the course of four months. The adit water primarily remains as surface water where Fe, minor amounts of Al, and no Zn are removed. After the adit water enters the peat, then it is found that the pH rises to 5.8-6.5 and sulfate is reduced. The removal of Zn and A1 is caused by these two changes. However, Fe in its reduced state is quite soluble and may be remobilized in the reduced environment of the peat.

Jan 1, 2000

By Michel David

Once a mineralized body has been delineated, drilled and estimated from surface samples, it often happens that before the final go-no-go decision is taken, an underground sampling program is decided, very often via a ramp which hopefully will be later used to extract the ore. The cost of such a program can be close to a million dollars. On other occasions, when a property changes hands and is reexamined maybe 20 years after the original drilling program, a "check sampling" program is carefully, designed to make "sure" that the old assays are "correct". One may fear poor sampling practice in old days, or deliberate highgrading by promoters. Again one may be talking of resampling cost which may be in the six-figures range. Other similar situations include the drilling of a few large diameter holes to ascertain the validity of a majority of small diameter drill holes, or auger drilling, or back-rimming. In uranium checking radiometric information is also a problem related to the above ones.

Jan 1, 1979

By James E. Monsees, Richard J. Proctor

INTRODUCTION Los Angeles is one of the world's largest cities in area with a span of 70 km between its north and south limits. The population in the Los Angeles Basin exceeds 11 million people. Los Angeles is second only to New York City in density of U.S. urban population and it operates one of the largest city bus fleets in the world, 2,500 buses. After many years of planning and many consultants' reports, it is planned to initiate a 30 km (18.5 miles) starter line subway -- the "Wilshire Corridor" (Figure 1). Construction is to start in 1985. In several locations, subway routes ultimately will skirt or cross old oil fields, which may cause gassy tunneling. Of particular note are the La Brea Tar Pits, which overlie a part of the old Salt Lake oil field. Tunneling through tar sands for about 3 km will be unique for subway construction and will occur on the starter line. Experience with previous gassy tunnels in the greater Los Angeles area shows that tunnels can be completed safely if precautions are taken. Abundant ventilation is the main solution, although other precautions are discussed herein.

Jan 1, 1985

By A. C. Noble, D. E. Ranta

Orebodies with intricate three-dimensional shapes (such as porphyry molybdenum deposits) are difficult to model using geostatistics or other computer-assisted methods. The strong trends in their spatial grade distributions occur as mathematically complex shapes and prevent the customary assumption of local stationarity that is required for accurate ore reserve estimation. "Zoned Kriging", a new method developed by AMAX, solves this problem directly by using the geologist's interpretation of the ore zones as a parameter in the kriging equations. The geological basis and methods used in the Climax ore zoning technique are reviewed and discussed relative to their application in zoned geostatistical modeling. The Zoned Kriging technique is described and demonstrated using data typical of mineral deposits.

Jan 1, 1992

By G. E. McCormack

The Development of Water Gel Explosives Water gels are the most recent development in the evolution of commercial explosives. They are replacing dynamite, having proven themselves to be excellent alternatives to this standard explosive. Water gels have steadily displaced dynamite over the past two decades. In 1959, they accounted for only 1 percent of the market they share with dynamite. By 1965, the share taken by water gels had grown to 21 percent. In 1970, it was more than 40 percent, and today it is nearly 70 percent. Black powder, the first widely used explosive, revolutionized mining and quarrying in its day. However, when nitroglycerin dynamite became available about a century ago, it rapidly displaced black powder because it provided greater energy for a given weight, much higher velocity for better rock shattering performance, and water resistance for easy use in wet conditions. During the past 50 years, ammonium nitrate has played a dramatically increasing role in explosives. First, it was used as an ingredient in dynamite, and then as the main component in nitrocarbonitrate blasting agents. About a quarter of a century ago, it began to find use in a simple and inexpensive mixture with fuel oil that has revolutionized the explosives industry and today fills about 80 percent of the requirements for explosives in the U.S., and certainly the bulk of blasting requirements worldwide. Water gels and dynamites share the remaining 20 percent. Water gel explosives based on ammonium nitrate have also been developed during the past quarter century. These explosives contain

Jan 1, 1979

In conjunction with steady increases in production levels, longwall operators have applied greater quantities of ventilating air and spray water in an effort to control respirable dust and/or methane. Air velocities greater than 7.6 m/s (1,500 )fpm) have been measured on longwall faces. Operators have expressed concern over the potential entrainment of respirable dust at these high velocities. The greatest likelihood for entraining dust into the high-velocity airstream may occur as shields are advanced, allowing relatively dry particles to fall from the shield canopy directly into the airstream. Laboratory tests to simulate dust liberation during shield movement were conducted at the Pittsburgh Research Laboratory of NIOSH at velocities ranging from 2.0 to 8.2 m/s (400 to 1,600 fpm). Airborne dust samples were obtained with personal impactors to quantify the size distribution and concentration of the dust entrained at the various air velocities. Statistically significant increases in both total and respirable dust concentrations were measured as test air velocities were increased.

Jan 1, 2002

By B. K. Mishra, R. K. Rajamani, P. Songfack

Primary grinding in SAG mills is gaining more importance with respect to the conventional crushing, rod and ball milling operations. This is due to the reduced operating costs generated by lower steel consumption. However. SAG milling is inherently susceptible to more severe risks and problems since it attempts to combine several stages of the conventional crushing and grinding into a single stage. This paper analyzes the SAG milling operation by predicting the motion of rocks and steel balls. The well-known discrete element method (DEM) is used to calculate the trajectories of individual entities, and their collision with one another. A computer code previously used for studying the motion of grinding media in ball mills is enhanced to handle the interaction between heavy spherical steel balls and light chunks of rocks, usually ellipsoidal in shape. The DEM based software called MILLSOFT can animate the charge motion for different design of liners. A case study of a 9.75-m diameter SAG mill is presented and the effects of lifter bar height and configuration on the overall dynamics of the charge are discussed. Also the effect of spacing between liners on lifting the charge is presented. This new approach has a large potential because it shows in detail the effect of each design or operating parameter on the performance of SAG mills.

Jan 1, 1998

By Claus Becker

Waterbearing, cohesive or non-cohesive grounds with glacial stone deposits are found very often in Europe. The problem consists of destroying the boulders and supporting the face simultaneously. At the example Grauholztunnel Bern ( outer diameter 11,60 m ) the theoretical attempt of solutions for the big machines is described: destroying of the boulders with roller discs, hydraulical support of the front. The problem of coming out of stones of a certain size from the surrounding matrix will be discussed. Further diminishing to the size that can be handled by pumps is executed by a crusher, situated in the center of the machine. At the same example the theoretical attempt for headings in cohesive soil with stone deposits are shown. Surface structure of the cutting wheel and working chamber as well as controllable current movements are the solution here. The danger of clogging discs and stone crusher has to be encountered by right positioning of the tools and jetting nozzles. At the example Sewer MoosstraBe Salzburg the same problems are discussed for the Mikro-Tunnels. The pipe-jacked sewer lines have outer diameters from 485 and 805 mm. With this method, the stones have to be holed through. The wear of the cutting tools determines the [ ]

Jan 1, 1989

By N. Choi, W. D. Cho

Distribution coefficients of gold and silver between matte and slag during the pyrometallurgical treatment of nickel-copper sulfide concentrates were evaluated as a function of matte and slag compositions in the temperature range of 1,250oC to 1,300oC. It was observed that the composition of the matte phase, including matte grade and copper content in the matte, significantly affected the distribution behavior of gold and silver in the matte-slag system. Both gold and silver preferentially concentrated in the matte phase as the matte grade increased With increasing temperature and copper content in the matte, the distribution coefficients of silver increased, while the gold distribution coefficients decreased. It was also, found that slag additives such as CaO, MgO, and A12O3 caused a significant decrease in the solubility of both gold and silver in silica-saturated iron silicate slag. An activity coefficient of gold in matte was derived from the experimenta1 results.

Jan 1, 1999

By Robert A. Jankowski, John J. McClelland, Charles Babbitt

The purpose of this study was to develop guidelines to enable mine operators to maximize longwall dust reductions, while optimizing the use of ventilating air and shearer water consumption. A recent investigation by Foster-Miller Incorporated, under a Bureau of Mines contract, quantified the effect of increased face airflow and shearer water supply on face dust concentrations. A 70 pct reduction in respirable dust levels was achieved at the shearer operator's position during tail-to-head cutting by an incremental increase in average face air velocity from 83.8 m/min (275 fpm) to 123.4 m/min (405 fpm), while holding shearer water consumption constant. A 60 pct reduction was achieved through an increase in shearer water pressure and flow from 9.1 kg/cm2 (130 psi) at 0.19 m3/min (50 gpm) to 19.7 kg/cm2 (280 psi) at 0.28 m3/min (75 gpm), holding airflow constant. The combined effects of increasing both parameters produced an 85 pct reduction. Optimal usage of ventilating air and shearer water consumption can be achieved by defining a "point of diminishing returns" above which further increases no longer reduce dust concentrations, proportionately .

Jan 1, 1987

By M. S. Janssen

The development of a design equation for, and the testing of, a constant- flow airlift pump IS described. The predictions of the new airlift model agree with the results of experiments carried out using riser diameters between 0.025 and 0.300 m, submergence depths between 5 and 10 m, suspension densities between 1000 and 1650 kg/m3, and a solids dg of 70 to 100µm. The predictions o the model also agree with data from the literature for submergence depths that reached 130 m. This airlift model was employed to simulate the pulp flow through a series of tanks, each of which was fitted with an airlift pump to transfer the suspension to the next tank. Particular attention was paid to the riser diameter, submergence of the airlift pump, and control of the air supply to the airlift pump during the simulated operation of a series of tanks. The results of the simulation highlight some design parameters that could affect the efficiency and operation of a plant that employs airlift pumps to transfer suspensions.

Jan 1, 1989

Raises are widely constructed underground in hard rock mining for ventilation, material transport or emergency escape. The four major raise excavation methods, Drop Raise, Conventional, Alimak and Raise Bore can be divided into two categories from ground control point of view, one ground support can be installed during excavation, the other not. Excavation method must be chosen carefully to keep the raise wall in stable state during excavation and make sure enough rock stand-up time to install ground support if needed. If rock quality is permitted and there is no strict space limitation, raise bore method which is the only method that ground support can not be installed after the whole excavation is finished should be considered first because it is faster, cheaper, safer and less disturbance to the hosting rock. Support may or may not be needed depends on the purpose of the raise and rock quality. In high quality hosting rocks, if the raise is only for ventilation or material transfer, support may be not needed. If it is for emergency escape or escape and ventilation, which provide or require personnel access, the whole raise must be supported either in high or low quality rock. Based on on site data collection, construction and raise utilization, this paper gave out the rule of thumb how to decide an excavation method. After purpose of the raise, required raise diameter (size) and raise site options being known, geotechnical data collection is the next important step in a raise project.

Jan 1, 2011

By Kenneth Maser, Douglas W. Ounanian, Joseph S. Boyce

Foster-Miller Associates, Inc. (FMA), under contract to the Department of Transportation (DOT) and the Urban Mass Transit Administration (UMTA), is currently developing an Extruded Tunnel Lining System (ETLS). The ETLS would reduce ground support costs in machine bored tunneling by eliminating the need for temporary support, and by slip-forming the final concrete lining directly behind the Tunnel Boring Machine (TBM). The system can advance at variable rates, from 0.6 to 3.7 m (2 to 12 ft) per hr, by combining three systems: a very high early strength concrete, continuously produced and delivered by a concrete process system; a slipform/bulkhead system for supporting the concrete prior to strength gain and exposure; and a control system for form/bulkhead alignment and concrete process control. Large-scale tests are planned to demonstrate the system in a 3 m (10-ft) diameter steel "tunnel".

Jan 1, 1981

By I. G. Ediz, D. W. Dixon, W. M. Fidler

In this paper a new method for the arresting of tunnel explosions is presented. In the proposed technique, the on coming explosion is detected by a pressure sensitive device by a pre-determined rise in static pressure. The sensor then triggers a mechanism which causes the explosion door to be closed in a specially constructed concrete barrier zone. The doors are of a special construction and consist of perforated steel plates that allow part of the blast wave to be transmitted but do not allow the passage of the flame. A number of design parameters have been identified, including: the likely amplitudes of the transmitted/reflected pressure waves that would govern the explosion door pressure loading; thickness of the perforated steel packages; perforation dimensions; heat transfer across the door and other factors.

Jan 1, 1995