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By B. C. Paul, R. Q. Honaker, M. Huang

Froth flotation is now, the most commonly used method for cleaning fine-coal fractions in coal-preparation plants. Past research and industrial practice have demonstrated that froth flotation achieves excellent separation efficiencies for fine coals having only a small fraction of middling particles. However, the efficiency of froth flotation decreases sharply as the concentration of middling particles increases. This is due to the flotation of high-ash particles that have a small amount of hydrophobic coal present at the surface. Because gravity-based processes are much more efficient for the treatment of middlings, the application of centrifugal washing for fine-coal cleaning was studied with an emphasis on the primary cleaning of fine-circuit feed. Results are shown of a parametric study that used a semibatch Falcon centrifugal concentrator. The results of the study revealed that separation performance is a function of particle size, bowl geometry, feed solids content and feed rate.

Jan 1, 1996

By M. Jawed

Coking coal reserves in India are distributed geographically in Giridih, Raniganj, East Bokaro & Jharia Coalfields (J.C.F.). 97% of prime coking coal in JCF coming through underground mines is credited to Bord & Pillar mining systems inspite of the fact that it results in heavy mining losses. The cost of mining in B & P mines has been much higher due to various factors. In this paper, O.R. model has been discussed with case study for optimizing the cost of production in operational underground mines. Also, a computer algorithm has been discussed using a schematic flowchart, which provides the trend of mining-losses 'in different mining, systems with changing design parameters and finally selects, the optimum mining system for undeveloped seams based on economic appraisal criteria.

Jan 1, 1989

By E. D. Attanasi

Exploration for non-fuel minerals has declined since 1988 as recessionary pressures have slowed growth in the industrialized economies. By most accounts, however, 1990 expenditures were still significantly greater than the low levels experienced in the mid-1980s. The Persian Gulf crisis introduced instability in energy prices and greater uncertainty into an already cloudy economic picture. As 1990 unfolded, the US savings and loan problems spread to the commercial banking system, leading to the failure of several major US commercial banks. The Japanese stock market also suffered significant losses as Japan's Central Bank raised interest rates. The Soviet Union experienced shortages of food and other basic items. Its government faces resistance to changes leading to a market economy. Individual Soviet republics also are seeking more control of their own destiny. The cost of German reunification, in terms of the capital required to bring the east's infrastructure and industrial base to western standards, also appears to have been underestimated.

Jan 1, 1991

By Alva L. Kuestemeyer, Randall J. Scott

INTRODUCTION Pincock, Allen & Bolt, Inc. (PAH) has developed a series of cost models for Western U.S. Gold Mines. The models indicate the economic potential of developing gold properties at various production rates and ore grades. Various combinations of mining and processing methods are also analyzed. The conclusions shown in this paper are taken from PAH's 600 page study titled, "Capital and Operating Cost Models for Western U.S. Gold Mines." PAH decided to develop the cost manual as a result of our perception of the industry's need for such a document. It was our impression that exploration development decisions were being made on the basis of limited economic information. PAH has compiled a substantial database on unit cost information. That database and the engineering capabilities of the firm allowed us to develop a reasonably detailed analysis of capital and operating costs and overall development economics. The study has developed a series of algorithms for underground and open pit mining, processing, G&A, and infrastructure costs. The capital and operating cost data served as a basis for performing after tax discounted cash flow analysis for the various development alternatives. For the base case scenarios, a 15% DCFROR was assumed and the required ore grade was back calculated using the computer. The ore grade versus production rate graphs summarize the economics of developing gold projects in the Western U.S.

Jan 1, 1987

By Jack S. McPartland, Gene E. McClelland

It is advisable, for any heap leach project, to develop an historical metallurgical data base to predict production heap performance before ore is mined and placed onto the heap. A data base would include results from: interval assays, cyanide solubility tests, and bottle roll tests on exploration drill cuttings samples; and those results plus column leach test data on diamond drill core or bulk ore composites. Subsequent larger scale heap leach test data can then be compared to the historical data base, to blast hole composite data during mining, and eventually to production data. This paper does not discuss metallurgical comparisons between assays, cyanide solubility tests, and bottle roll tests on exploration drill cuttings samples, but does discuss metallurgical comparisons from bottle roll tests, laboratory scale column leach tests, and pilot scale heap leach tests on core and bulk ore samples with operating data for three U.S. commercially producing heap leach operations. Provided that representative core or bulk samples are used for evaluation, heap leach test results accurately predict or understate the success of the commercial operation and remove most of the uncertainty from the investment decision.

Jan 1, 1990

By John A. Herbst, Per-Olaf Samskog, Jan Bjorkman, Yi Chang Lo

The study described here is concerned with the development of a model for the simulation and optimization of a rod milllpebble mill circuit. A series of laboratory tests was conducted to investigate the effect of critical operating variables. The pebble mill model structure used was a population balance type which accounta for impact breakage and fines production from pebble wear. Model parameterization and verification were performed using data obtained in batch tests and in a plant test campaign. The model developed was found to provide accurate predictions of plant-scale grinding. The prediction errors are less than 21 for the product size and 31 for the mill power required to achieve that product with a mill volume scale-up of 14,000 to 1. These results indicate that accurate extrapolations from laboratory batch data to plant scale performance are poaaible using the population balance model and scale-up prediction procedures for pebble mill circuits as well as ball mills. Preliminary indications are that the new model developed here will provide vital input for pebble mill optimization and process control as well as pebble mill design.

Jan 1, 1990

By James S. Hanson

Existing models proposed for the bacterial leaching of metal sulfides generally fail to predict solubilization rates at times greater than a few tens of hours. The reasons for this may be that these models are empirically based and use first order bacterial and chemical oxidation rates. This type of model is satisfactory for short time predictions (on the order of 20 hours) when the bacterially catalyzed dissolution is relatively minor. However, when bacterial action becomes more pronounced, these models consistently predict higher dissolution rates than those commonly observed in laboratory experiments. The present model uses several fundamental chemically and biologically based assumptions to predict the dissolution rate of a chalcopyrite concentrate for extended leach times up to the precipitation of jarosite. The main assumptions made are that Monod growth kinetics prevail, T. ferrooxidans adsorb onto the surface of the mineral (not necessarily mineral specific), and that during periods of high growth oxygen transport may become rate limiting. The model also relies on the energy efficiency of the bacteria in fixing carbon (growth yield) and correlates this value with available surface area of the mineral particles and the bacterial growth rate.

Jan 1, 1989

By F. A. Camisani-Calzolari

South Africa has adopted its own code for public reporting of Mineral Resources and Mineral Reserves in 2000. The South African Code for Reporting of Mineral Resources and Mineral Reserves (SAMREC Code or Code) (SAIMM 2000) is presented here in its local and global context. The main aspects of the Code are listed and elaborated upon. The Code has been written with the participation of the major South African stakeholders in the field including Government institutions, the legal confraternity and the mining industry. The Code is modelled on, and is 90% compliant with, the Australasian Code for Reporting of Mineral Resources and Ore Reserves (JORC Code) (AusIMM 1999). The paper also elaborates on the duties and responsibilities of Competent Persons signing off resource and reserve reports and on the listing requirements of the Johannesburg Securities Exchange (JSE), formerly the Johannesburg Stock Exchange, which has officially adopted the Code. The listing requirements were updated in 2000 to incorporate the SAMREC Code and subsequently in 2002, effective 2003. The ongoing obligations of the JSE for the exploration and mining companies are being compiled and are expected to be effective from early 2004.

Jan 1, 2003

By J de Cuyper, S. Ramachandran, L. A. Vazquez, N. L. Grauerholz, W. Freyberger

A novel process is described for the selective flotation of scheelite from low-grade (- 0.5% W03) tungsten ores having appreciable quantities of calcareous and siliceous gangue minerals. Specifically developed for the Tempiute, Nevada facility of Union Carbide, the process yields tungsten concentrates exceeding 15 percent W03 with at least 85 percent recovery. This condition was not achieved through conventional processes. This process consists of conditioning the ore pulp with judicious amounts of lime, followed by soda ash and sodium silicate as modifiers. The scheelite is then floated using a mixture of oleic and naphthenic acids as collector. Contrary to the common observation as to the deleterious effects of calcium in fatty acid flotation systems, lime addition is found to be beneficial in achieving satisfactory results. The process has also shown excellent results on a Brazilian scheelite ore.

Jan 1, 1976

By S. K. Kawatra, T. C. Eisele

Microorganisms, such as the bacteria Thiobacillus ferrooxidans, have been reported to depress pyrite flotation (Elzeky and Attia, 1987; Atkins, 1990). However, the depen¬dence of the depression on the type of organism or on suspension pH is still being determined. In this study, the relative effectiveness of various microorganisms (chemolithotrophic bacteria, chemoorganotrophic bacteria and yeast) over the pH range of 2 to 12 was studied. Screen¬ing tests using microflotation showed that every microorgan¬ism tested was capable of depressing naturally hydrophobic pyrite at acidic pH. Larger-scale experiments with both mineral pyrite and coal pyrite using Thiobacillus ferrooxidans and Saccharomyces cerevisiae as depressants, showed that these microorganisms are very effective depressants for mineral pyrite at acid pH, but they are largely ineffective at neutral and alkaline pH, where the mineral pyrite surface is not naturally hydrophobic. The flotation response of the coal pyrite was completely different from the mineral pyrite. The coal pyrite was most floatable near neutral pH, with the floatability decreasing in acidic or alkaline solutions. De¬pression of the coal pyrite by yeast was not selective between the pyrite and the associated coal under the experimental conditions.

Jan 1, 2000

By D. Lelinski, R. Bokotko, J. D. Miller, J. Hupka

Air-sparged hydrocyclone (ASH) flotation is a new, promising technology, and, since its conception, numerous applications have been successfully tested. Nevertheless, research and development efforts have continued to improve the technology with respect to operating conditions and design considerations. Results, from experimental studies on bubble generation in the ASH system are presented in this paper. Bubble size distributions generated during ASH operation were determined using a high-speed photographic technique. The influence of many factors, including surfactant concentration, water flow rate, and porous-tube pore size have been studied. Test results indicate that these process variables have a profound effect on the bubble size distribution. With an increase in surfactant concentration or water flow rate (shear field), the bubble size distributions become narrower and shift toward smaller average bubble diameters. However, the influence of pore size is more complicated. Depending on the experimental conditions, the average bubble size was found to range from about 100 to 300 µm in diameter.

Jan 1, 1997

By George Bárdossy

Most of the bauxite deposits in Europe belong to the karst type. They are located mainly ill Southern Europe along the Mediterranean Sea and in the Ural Mountains. Lateritic bauxite deposits occur on the Russian Platform, in Poland, Northern Ireland and in Turkey. Tikhvin-type deposits arc found on the Russian Platform. Bauxite formation in Europe started in the Middle Devonian. The main bauxite forming period was the Upper Cretaceous. Very few bauxites are younger than Eocene. Most deposits are covered by overburden of up to 1000 m. Prospecting is carried out by drilling. Several geophysical methods are used to detect the hidden deposits. Geostatistical methods were introduced in several countries for evaluation of the reserves and the geometry of the deposits. Data on bauxite production are given for 1982 and since the beginning of mining in Europe.

Jan 1, 1984

By W. J. Deutsch, W. J. Martin, R. J. Serne

At the termination of mining, the quality of ground water in the ore-zone aquifer must be returned to a condition predetermined by the permitting agency. To immobilize the redox-sensitive elements (e.g., uranium, arsenic, selenium, molybdenum), it has been suggested that a reducing agent be circulated through the leached ore zone. We have conducted laboratory experiments to test the ability of sodium sulfide as such a reducing agent. Sodium sulfide lowered the redox potential of the effluent such that insoluble minerals containing the redox-sensitive elements should be stable. The uranium concentration of the solution decreased by more than three orders of magnitude. In column experiments, by the time 10 pore volumes of the sulfide solution had flowed through, sulfide minerals were forming. The experimental results indicate that the addition of sodium sulfide should cause chemical reduction of the leached sediments, thereby producing long-term stability of the ground-water/sediment system.

Jan 1, 1988

By Jeffrey M. Listak, Gregory J. Chekan

The U.S. Bureau of Mines, in an effort to improve coal conservation and utilization is currently investigating longwall panel layouts to maximize coal recovery and minimize interactive problems in multiple-seam operations. When longwalling coalbeds in descending order, the transfer of stress from overlying gate roads is a major design constraint affecting pillar stability in the lower mine. The lower mine gate road pillars must be properly designed to withstand the additional load transfer if gate roads are superpositioned in successive seams. The Bureau's MULSIM/NL model was used to analyze load transfer mechanics for superpositioned gate road pillars. Analysis of Longwall Pillar Stability (ALPS), which is an empirically based design method for longwall gate road pillars, was used to calibrate model input parameters. The attributes of both the MULSIM/NL model and ALPS were combined to develop a modified method for estimating pillar stress for multiple-seam cases. The modified method uses a multiple-seam (MS) factor to estimate the stress on the lower mine gate road pillars when superpositioning is practiced. Numerical analysis shows that the MS factor is dependent upon the interburden thickness and pillar width and is presented in a series of graphs relating these two parameters. Several examples are included to illustrate the use of the MS factor for estimating lower mine pillar stress and resulting stability factors.

Jan 1, 1992

By G. T. Adel

The selective recovery of fine particles by flotation has been a long-standing problem in the mineral processing industry. Fundamental studies carried out at Virginia Tech since 1980 have suggested that many of the problems encountered in separating fine particles can be alleviated by using significantly smaller air bubbles than those used in conventional flotation processes. The main advantage of using smaller bubbles is found in an increased recovery rate, which can be attributed to an improved bubble-particle collision efficiency. This concept has been applied in column flotation as a means of improving flotation kinetics. A computer simulator has been developed to better study the effects of various parameters on flotation column performance. The simulation results suggest that the use of small bubbles and tall columns improves the recovery of fine particles while a judicious use of wash water greatly improves product quality. Information collected as a result of this analysis has been applied in developing scale-up relationships for column flotation.

Jan 1, 1989

By R. D. Lama

Coal mining is one of the major sources of methane release to the atmosphere by human industrial activities and is believed to contribute to -30% of the total methane emissions from industrial activities. In 1993, world saleable black coal production, attained almost 3.5 billion tonnes from which around 65% was produced underground. Coal in underground mines can contain high quantities of methane and some deep coal seams have methane content as high as 50 cubic meters per tonne of coal. Gas is re- leased during coal mining from the mined seam and in a higher degree from the neighboring unmined seams and gas bearing strata which are fractured as mining advances. This paper de- scribes a study which was undertaken to estimate the extent of methane emissions from coal mining in the world. Measured emission related data were collected from most underground coal producing countries in the world. The data included methane flows in the ventilation system, methane flows in gas drainage system, in-situ gas content, methane utilization and coal production. More comprehensive data were collected from a range of gassy and non-gassy Australian mines. Residual gas content of samples from run of mine were also measured. Using the Australian data, mathematical expressions were established to evaluate methane emissions as a function of coal production and in-situ gas content for other mines. These emission models were then used to evaluate the emissions for the countries or coal basins without measured emission data. Trends in methane emissions from underground mining for the year 2000 and beyond were also estimated.

Jan 1, 1997

By P. K. Crane, S. C. Gambrell

The work reported herein compares the support characteristics of two different types of roof truss subjected to the same force in the horizontal tension member. The major differences between the two trusses are in the sequence of tensioning the horizontal and inclined members and in the design of the loading brackets. A photoelastic model was used to compare stresses at points along the roof of the mine opening and at the junction of the roof surface and the rib. The effects of simulated subsidence on stress in the roof and on tension in the horizontal member were analyzed. Results indicate that there are significant differences in the overall support characteristics of the two trusses. Conclusions are drawn relative to which type of roof truss provides the most favorable support if the horizontal members are tensioned equally.

Jan 1, 1986

By A. D. S. Gillies, Hsin Wei Wu

An evaluation of the use of air cooling power as an index of the thermal environment is discussed. A body temperature prediction -. model based on body temperature tests, a concept linked to a maximum safe body temperature and the predicted fourth hour body temperature which depends on the rate of heat accumulation (heat storage) within the body has been developed and tested. This has led to the conceptual development of a personal response heat stress meter calibrated to the physiology of the personnel within the workplace. The proposed heat stress meter will be able to measure workplace environmental parameters such as air temperature, humidity and air velocity and the user can either select or manually enter other heat stress parameters such as work rate, clothing type and subject's personal response to heat. With a built-in computer program, the meter will calculate the ACP of the workplace, the fourth hour body core temperature expected and the maximum safe working time allowed for a pre- defined limiting body temperature. A brief description of the work required for developing the meter is included. The potential benefits of such instrument to the mining industry are also evaluated.

Jan 1, 1997

By G. Bryant, P. Ziemkiewicz

Acid mine drainage (AMD) from both abandoned surface and underground mines is a serious problem. The flow of water and changes in quality over time from abandoned mines is important in determining remediation strategies. Acid mine drainage from surface mines is estimated to last for 10-20 years, while estimates of acid drainage from underground mines vary from 10- 100s of years. Fifteen underground mine discharges in West Virginia were studied to compare water quality changes between 1968 and 1999 to see if our data are consistent with other studies. Each of the discharges were categorized into one of three groups: undisturbed since 1968, affected by surface mining since 1968, and reclaimed. Comparing water quality between 1968 and 1999, the discharges in the undisturbed category showed a 35 to 95% improvement in acid concentration and a 40 to 99% reduction in iron concentration. The discharges affected by surface mining showed the most dramatic improvement. For acidity, iron, and aluminum, the percent improvements were all above 44%, and in most cases in the 70 to 99% range. In the reclaimed category, one of the four discharges declined in water quality. Discharge 82 showed a 76% increase in acidity, and iron and aluminum concentrations worsened by 58 and 96%. However, discharges 15 and 74 improved in water quality with a 94% acid load improvement and a 95% iron load improvement at both sites.

Jan 1, 2000

By Terry P. McNulty

During the last 30 years, at least ten authors have dealt with startup ("ramp-up') times for minerals beneficiation, hydrometallurgical, and/or pyrometallurgical plants. Most have attempted to identity the reasons for delays and some have suggested attributes common to successful startups, as well as those shared by unsuccessful ones. The most recent has advanced a project characterization matrix as a predictive tool for qualified users. This paper will summarize past work, will review cause and effect, will outline an approach for refining our ability to avoid costly delays, and will seek guidance from professionals most likely to use such a tool. INTRODUCTION During the last few decades, many billions of dollars have been lost by investors in mineral industry projects that did not perform as well as their developers had hoped. The most common form of failure has been the inability to generate a profit quickly, and delayed achievement of planned production rate has been the chief cause. Minerals processing projects are by no means the only kind of plant to suffer from startup delays, as some authors cited in this paper considered inorganic chemical plants and other types of facilities. Furthermore, mines are not without fault and there have been many that were closed after years of disappointing performance. However, our interests as a group are most sharply focused on mineral processing and our database for such projects is relatively extensive. It is sufficient to say that the conclusions made or repeated in the following text can be readily extended to most types of projects.

Jan 1, 2004