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By T. Yegulalp, K. S. Lackner

Zero emission coal plants capture their own CO2 emissions. Since they have no smoke stack, they emit no pollutants to the air. Zero emission plants circulate a gas stream, to which fresh fuel is added and from which spent fuel and impurities are removed as solids or liquids. Coal is gasified via hydrogenation, steam reforming or CO2 gasification (Boudouard reaction). The gas is oxidized in a fuel cell and the resultant water and CO2 are partially removed before returning the remaining gas to the gasifier. The high conversion efficiency of zero emission power plants, which exceeds 70% even in realistic designs, stems from combining fuel cells with careful heat management. The paper generalizes the concepts and outlines the thermodynamic basis of zero emission power plants.

Jan 1, 2004

By Brian H. Zelenko, Patricia M. Perry

INTRODUCTION The environmental requirements of the next section of Washington, D.C. METRO subway tunnels present unique challenges to the Contractor. The 14th Street Tunnels contract includes twin 975 m (3200 linear ft) soft ground tunnels. A stringent environmental soil and groundwater monitoring and free product recovery program was specified by the owner. A project-wide dewatering program hinges on satisfactory completion of the environmental requirements. Implementation of the Contractor's environmental program is discussed, including the pros and cons of the program, as they relate to progress of the project. Environmental issues on tunneling projects have become an important part of the urban tunnel construction process. Delays associated with environmental issues can have a major cost impact on tunneling projects. This paper will discuss the first of five Washington Metropolitan Area Transit Authority (WMATA) tunnel and station contracts awarded in 1994. These contracts are part of WMATA's Fast Track Plan to complete the original 166 km (103 mile) system by 2001. As such, stringent environmental requirements have been specified as a part of these contracts to limit delays associated with local regulators in order that the tunnels may be constructed on schedule.

Jan 1, 1995

By C. L. Schneider, R. P. King

The ability to predict the liberation spectra that will be produced by a closed-continuous grinding circuit is of fundamental importance for the design, optimization and control of most operations in an ore dressing plant. The only known approach through which such a calculation can be performed is the population-balance-model equation. The latest, and certainly most significant, advance made in this area is the solution proposed by King (1990), which requires one textural parameter measured directly from the ore being studied. The main advantage of King's solution is that, unlike the conventional solutions, it does not require the estimation of hundreds of arbitrary parameters that cannot be independently measured. However, King's solution relies heavily on a knowledge of the detailed internal structure of the Andrews-Mika diagram (Andrews and Mika, 1975), which has never been measured for any ore. The characterization of the internal structure if the Andrews-Mika diagram requires the measurement of the liberation spectra at several progeny sizes produced by the breakage of monosize-monograde particles at several different grades. In this paper, a procedure based on magnetic fluid fractionation for generating seven narrow-size, narrow-grade samples is presented. Each of these samples was then broken into six progeny size classes in an ultrasonic mill. The one- dimensional liberation spectra of each of the 42 progeny and seven parent particle samples were then measured by image analysis. The measured linear-grade distributions are presented in this paper. The calculation of the correspondent volumetric-grade distributions is discussed.

Jan 1, 1995

By F. P. de Kock, P. West-Sells, B. Wassink, D .. B. Dreisingerl

During the cyanide leaching of gold ores containing copper minerals, aurocyanide (Au(CN)f) is produced and typically recovered using activated carbon. However, free cyanide, as well as cyanide associated with cuprous cyanide complexes, are generally not recovered from the barren liquor. This results in a significant economic penalty in high cyanide consumption due to the dissolution of copper. 1\vo different configurations of a novel method for the treatment of barren liquor streams for cop­per recovery and cyanide recycle are described. Recovery of copper and cyanide is affected using solvent extraction (XI 7950). Loaded organic is stripped with a high copper, high caus­tic solution which is electrowon to produce copper metal. Depleted electrolyte is treated with sulfuric acid to recover cyanide which is returned to the leaching circuit. Results of benchscale and mini-pilot plant experiments are presented.

Jan 1, 1996

By J. Fuller, L. Marsden

Windborne dust from alkaline salt flats and mining-related tailings ponds is especially prone to threaten applicable ambient air quality standards. Sodium carbonate crystals, typically present, weather to an exceedingly fine, non-cohesive dust, causing air quality problems for miles downwind. Recently developed specialized polymers react with alkaline dust to form sturdy, wind-resistant crusts with good longevity. An on-going demonstration project at a major trona facility has developed techniques for cost-effective application of these polymers over large areas of soft tailings or sediments in a wide variety of situations. Recently treated areas on the order of 80 acres show effective suppression of dust.

Jan 1, 2004

By L. MacHue

Sulfur containing collectors have been shown over the years to function as strong, selective and non-selective sulfide mineral collectors. Unfortunately, the majority of the widely known sulfur based collectors are of low molecular weight, volatile and subsequently, possess an objectionable odor. Higher molecular weight sulfur based collectors (C9 and higher) are significantly less odiferous due to lower volatility and lower vapor pressures. In this study, a specific proprietary higher carbon number collector, Orfom® MC 37, was blended and used successfully to recover 2-3% additional molybdenum in a laboratory flotation system, when compared to a standard collector blend. Copper recoveries were also positively affected. Further testing is required to give additional conditions favorable to increased copper and molybdenum recoveries, but indications at this time show the proprietary sulfur based collector blend to be a selective collector of molybdenum, while providing a significant increase in copper recoveries.

Jan 1, 2010

By G. Gregory Bryan

G. GREGORY BRYAN 33.1-DEFINITIONS 1. Engineering-Engineering may be defined simply as the science and art of making materials and energy serve the purposes of mankind. There are many fields of engineering, each with specialized branches. The basic fields are: civil, mechanical, electrical and chemical. Others may be specialized phases of one of these or a combination of two or more of them. Mining engineering, for example, requires a working knowledge of construction, mechanics, electricity, metallurgy, geology, accounting and economics, in addition to mining techniques or methods. Mining geology and geological engineering involve rocks and their structure and the forces that act upon them, and chemistry, physics and mechanics also are important to practitioners in these fields. Metallurgical engineering requires chemistry and physics but also a working knowledge of mechanics and electricity. The fields of engineering with which this section are concerned are those primarily involved in the finding, mining, processing and utilization of the natural mineral resources of the earth. They include geology, mining engineering and metallurgy, each with several specialized subdivisions. 2. The Engineer-The engineer is an individual who has had specialized training to qualify him to practice the profession of engineering. The term engineer is used here in its broadest sense to include such professions as certain applied branches of geology, physics and chemistry, whose practitioners may not have acquired engineering degrees but who, nevertheless, by training and experience in some area of the minerals industry, qualify under the above definition. To become a successful engineer, a person should have certain pronounced aptitudes and preferences, even before embarking upon the requisite course of training. Among the chief qualifications that the engineer-to-he must possess are: (a) a natural inclination toward mathematics and the physical sciences, and (b) intellectual and moral honesty. Among the qualities the student engineer must develop are: (a) independence of thought, open-mindedness, sound judgment and the ability to observe, deduce, plan and apply solutions, (b) the ability to articulate and convince, and (c) the ability to organize and direct the activity of others. These qualities are normally developed through sound education, followed by pro¬gressive experience. 3. The Consulting Engineer-The consulting engineer is an engineer primarily in the business of furnishing specialized advice and engineering services on an intermit¬tent, part-time or occasional basis to clients who do not have continuous or full-time need for those services. He must be able to make and take full responsibility for decisions and recom¬mendations where original thought is required. He should not be confused with the engineer, surveyor or technician who also may furnish services on an intermittent basis, such as regular periodic surveys, the overseeing of drilling programs and other such routine work as may require little original thought and planning. 33.2-THE PROFESSION OF CONSULTING ENGINEERING 33.2.1- QUALITIES REQUIRED A successful consulting engineer must first have, as a minimum, the qualities and preparation of an engineer. In addition, he must have sufficient knowledge,

Jan 1, 1973

By Jing G. Yen

When a solid-liquid mixture is conveyed through a pipe,' four hydrodynamic conditions may develop depending upon the properties of the transporting medium, the properties of the transported material, the properties of the pipeline and the flow characteristics. They are classified as homogeneous flow, heterogeneous flow, intermediate flow and saltation. Heterogeneous flow, which is the subject of the present analysis, occurs when solid particles are coarse, of high density, and the mean velocity of the flow is relatively low, such that the combination allows the establishment of a pronounced concentration gradient in the cross-section of the pipe. In this type of system the suspended matter does not change the rheological properties of the conveying fluid, and solid and fluid phases behave somewhat separately. In recent years much work has been directed toward gaining more insight into the hydrodynamics of heterogeneous flow (1,2,3,4,5,) However, almost all knowledge obtained is empirical in nature and limited in scope. Much effort has been extended to collect experimental information on the energy losses associated with systems of slurry flow (6-13) The work of Durand and Condolios(14,15) represents one of the most extensive experimentations in this field. Through systematic test runs, the effects of the major flow-parameters were studied one at a time. From the results, they concluded empirically that:

Jan 1, 1969

By Milton E. Wadsworth

Cost effectiveness in gold and silver leaching has centered mainly on reducing or preventing excessive use of lixiviants. In cyanide leaching practice, the active reactants, cyanide and oxygen, present different problems. The activity of cyanide may be adjusted at cost, but oxygen from air, has a fixed, low activity with an equilibrium concentration of ~7 ppm. Consequently, the use of air in agitation and heap leaching presents distinct kinetic problems. The refractory ores are either high consumers of oxygen or tend to immobilize dissolved precious metal-cyanide complexes. Commercial treatment of refractory ores involves oxidation by pressure leaching, roasting or biooxidation prior to cyanide leaching. Chemical reactions important in preoxidation of refractory sulfide ores by pressure leaching and biooxidation are considered. Major emphasis is given to the role of oxygen in heap leaching of oxidized ores.

Jan 1, 1995

By J. Y. Hwang, M. L. Jeong, R. C. Greenlund

Various aluminum-smelting by-products from three production sources were received and characterized. The waste materials were tested for compound identification and environmental acceptance. A coarse metallic aluminum recovery test using an Eddy Current separator (ECS) was performed using two different Circuit configurations. White dross performed equally well with either Circuit, while black dross processing shows significant difference on the separation results. It was found that ECS technology was effective for particle sizes down to 6-10 mesh.

Jan 1, 2001

By Brent Chamberlain

MARY KORPI: As has been typical today, our next speaker is filling in for one of his co-workers. Scott Lawson will be discussing "The Role of the Supervisor in Mining Operations" written by Brent Chamberlain of Independence Mining Corporation. Scott has more than 25 years in human resources management in the mining industry. He has worked in surface and underground mining environments in both precious and base metal mines. A graduate of Ohio University, Scott is currently manager of human resources at the Independence Mining Company's Cripple Creek and Victor Gold Mining operation located in Victor, Colorado. The only direction that I received from Scott was that he has to leave by 11:45 a.m. as he has a tee-off time with his boss at 1:00 p.m. Thank you to Scott for filling in today.

Jan 1, 1998

By Éder Domingos Oliveira, Leandro Viana Teixeira, Carlos Antonio Morais, Ruberlan Gomes Silva

The purity of rare earth products depends on the ability of the reagents used to selectively promote the precipitation of the rare earth elements (REE) from impurities present in sulfuric liquors. The present study aims at investigating the conditions required to precipitate REE, either as rare earth oxalates or carbonates, from purified rare earth sulfuric liquor with a low Al3+ and UO2 2+ and a very high Ca2+, Mg2+, Mn2+, and SO4 2− impurity content. The rare earth sulfuric liquor was obtained in a previous study by the reaction of a rare earth ore with sulfuric acid, pyrolysis at 700 °C/2 h, cooling at 20 °C, and water leaching. The impurities such as Fe3+, Th4+, and PO4 3− were completely removed from the liquor in two consecutive neutralization steps. In order to recover the REE, the purified rare earth liquor was then treated with oxalic acid and sodium carbonate. Rare earth oxides (REO) precipitated with oxalic acid displayed a very high purity (99.2% w/w) and low impurity content. In contrast, the rare earth carbonates precipitated with sodium carbonate presented a comparatively lower REO content (68.5% w/w) and 94.2% of purity, but with a higher content of impurities. Better precipitating conditions were achieved at 60 °C, compared with 20 °C, and under stoichiometric reagent consumption, with REE precipitation efficiencies higher than 96%. The dosage above the stoichiometric condition caused the precipitation of calcium oxalates and co-precipitation of rare earth sulfates when oxalic acid is used, and precipitation of calcium, manganese, and uranium carbonates and also a co-precipitation of rare earth sulfate when sodium carbonate were used. An integrated flowsheet to produce a high-quality rare earth product from rare earth sulfuric liquor containing some impurities is proposed.

By James L. Hendrix, Michael R. Straka, Emil B. Milosavljevic, Ljiljana Solujic, Neil P. Gallagher

Analysts that utilize the classical distillation procedures for cyanide analysis are often frustrated by the poor reproducibility and repeatability of these techniques. Capital intensive business decisions and environmental management regulations are exas­perated by the fact that the EPA/ASTM approved cyanide deter­mination methods produce data of questionable quality. Reliable cyanide values are important in monitoring the effec­tiveness of the cyanide detoxification procedures. Efficiency and cost of gold and silver cyanidation recovery can also be improved by precise cyanide monitoring in the process itself.

Jan 1, 1996

By J. H. Kempton

The scrutiny given to model predictions of pit-lake water quality has focused attention on the uncertainty associated with long-term predictions. Although comparison of probabilistic predictive modeling of water quality in existing pit lakes indicates that short-term predictions can bracket most parameters, uncertainties in wall-rock reactions and the stability of groundwater composition and climate remain unquantified. This overview of the uncertainties associated with longer-term predictions is presented as support for those considering policy decisions that must be made in the absence of reliable estimates of future conditions.

Jan 1, 1998

Iron removal using biologically produced organic acids was investigated as a treatment option for the production of refractory grade bauxite. A leaching solution containing 98mM oxalic and 67mM citric acid was prepared from a sucrose medium using for fermentation the fungus Aspergillus niger. The leaching capacity of the metabolic product was tested on a bauxite sample containing 16-19% iron (as Fe2O3). Aerobic and anaerobic leaching tests were carried out at pH 3, 50°C and in the absence of light. Results indicated that more than 80% of total Fe can be removed from the ore, when the sample is finely ground and applying a two stage treatment. The presence of oxygen was seen to affect adversely the kinetics of the process, suggesting that leaching follows a reductive mechanism. Experiments that were carried out with different particle size fractions indicated that for obtaining efficient removal of iron particles should be finer than 0.63mm. Reduction of the operating temperature from 50 to 30°C caused a decrease in the rate of iron removal by more than 10 times.

Jan 1, 2006

By D. E. Munson, H. J. Sutherland

Empirical methods for describing the shape of the subsidence trough over coal mines in Europe are tested against field measurements of subsidence over longwall panels in the United States. The graphical methods developed by the National Coal Board in the United Kingdom do not correlate well with the U.S. measurements; however, the profile functions typically used on the Continent give quite acceptable fits to the data. In the case of two longwall panels mined at Old Ben No. 24 in Illinois, a trigonometric profile function appears the best choice; in the case of two longwall panels mined at York Canyon in New Mexico, an error integral function is somewhat superior. Analyses of subsidence development curves show that rate effects occur. A comparison of fitting parameters establish influence functions as an important methodology for future analysis. In conjunction with the evaluation of empirical methods, an analytic model based on material failure and bulking was developed. A key element of the model is the void-volume distribution function which establishes a mechanism for transfer of significant amounts of the mined volume to the surface. Preliminary calculations demonstrate the features of the model and illustrate close correlation to physical observations in the field. Moreover, centrifuge models simulating the subsidence process have been used successfully to demonstrate the dominant or key failure modes necessary to the analytic model. General features of the centrifuge simulations and model calculations correlate well.

Jan 1, 1982

By M. J. Meulendyke, J. D. Purdue

Within the mineral processing industry, a range of grinding conditions exists which include semiautogenous grinding (SAG),rod milling, and conventional ball milling. Each of these mill environments presents a unique environment for grinding media, requiring the application of specific physical and chemical properties for optimum grinding media performance. The environments are characterized by varying degrees and combinations of abrasive, corrosive, and impact wear. An extensive test program has been conducted to determine the extent wear rates vary between these different applications. Test results are related to production results, ball size, and mill operating conditions.

Jan 1, 1990

By L. C. E. FEIO, R. RAMSDEN

In many parts of the world deep level mining relies heavily on the use of refrigeration for providing safe thermal underground conditions. The trend in South Africa in recent years has been to locate the refrigeration plants on surface and to use these plants to chill water that is then distributed throughout the mine. The surface cooling installation normally consists of a pre-cooling tower in which water is first chilled before it is sent to one or more refrigeration plants for further cooling. Presently, the majority of these refrigeration plants use CFC refrigerants; however, to conform with the Montreal Protocol, these plants will have to be replaced or converted for use with alternative refrigerants. The optimum design criteria for installations using the new generation of refrigerants will be affected by their characteristics and are likely to be different from those currently in use. In light of these developments the industry is examining a number of alternative systems for future installations including water vapour refrigeration. Factors that affect the decision on the type of refrigeration system to be used in mine installations are reviewed. INTRODUCTION Gold mining has been carried out in South Africa for over 100 years and most of the reserves close to surface have been mined out; this has led to mining taking place at greater depths, approaching 4000 m below surface. One of the consequences of operating at these greater depths is that it is necessary to install refrigeration plants to cool the ventilation air so as to provide safe and healthy working conditions. With the current low precious metal prices there is pressure on mines to cut costs and in recent years there has been considerable effort devoted to the design of more cost effective and efficient refrigeration plants and cooling systems. In the last 10 years there have been many studies into the use of ice for specific applications (Eschenburg et al., 1986; Hemp, 1988 and Ramsden and Lloyd, 1992) and at present there are three ice making plants in operation on South African mines, each of which produces ice in different processes. In addition, detailed design studies have been carried out on the "split ammonia system" (Napier and Patterson, 1992). In this refrigeration system the evaporator is located underground close to where the cooling is needed, whilst the condenser and heat rejection system is on surface. As far as refrigeration plants are concerned the trend has been to move away from standard package units to custom built refrigeration installations. This has given the design engineer greater flexibility in the choice of key components for refrigeration installations. For example both screw and centrifugal compressors are used, the heat exchangers for the evaporators and condensers may be either plate or shell and tube, and in a number of installations evaporative condensers are used. In addition, the following refrigerants are in use, R12, R22 and ammonia. The acceptance of the Montreal Protocol and its amendments by the South African government will restrict the use of CFC refrigerants and it will be necessary to re-evaluate various refrigeration systems, including those that do not use conventional refrigerants, such as air cycle and water vapour systems, for new surface installations. Although new systems and refrigerants are being developed, only the following refrigeration installations will be compared in this paper: - a refrigeration system using R134a which has properties similar to R12 - refrigeration system using R22 or a new alternative refrigerant with very similar properties - an ammonia refrigeration system - a water vapour refrigeration system The benefits of new cooling systems are not discussed in detail, since they are largely mine specific and outside the scope of the present paper. Since the optimum design for an air cycle system (del Castillo, 1988) is dependent on the mine layout, this system is also not included.

Jan 1, 1993

By B. A. Hancock

It is not at all surprising that causticized potato and potato derived amylopectin starch solutions performed much better than their parent starches. Some preparation is required to rupture the starch granules to effect the polymeric adsorption and interparticle bridging necessary for selective flocculation. In laboratory work comparing the deslime performance of causticized and autoclave cooked laboratory corn starch solution preparations, it was found that higher deslime weight rejections, with attendant proportionally greater iron unit losses, occurred with the causticized starch. These results may be specific to the ore involved but they do suggest that cooking and causticizing cause different starch granule rup- ture and/or starch breakdown, which have an effect on desliming response. I calculated from the data in the article that the slimes product grades were high - 24.3% and 20.3% Fe when 53.7% and 54.5% Fe concentrate products were obtained, respectively, in Table 4, and 21% Fe with a 62.6% Fe concentrate in Table 5 - using the natural tailings sample, which had a head of 34.3% Fe. It may be advisable for the authors to consider different starch preparations in future investigations. The combination of upgrading and selectivity results presented in Table 4 are not as good as the authors suggest. The authors' claim that a system has been developed to produce saleable concentrates from the Kudremukh tailings is quite disconcerting. There are many hurdles yet to be crossed before commercial application of selective flocculation becomes possible because differ- ences between the very small-scale laboratory tests conducted and commercial application are rather large. Among the many differences are varying circuit feed grades that will occur from use of tailings, the apparent face that much lower tailings grades will be encountered in practice (it is much easier to achieve a high concentrate grade with reasonable recoveries using 34.3% Fe tailings as in the study rather than 25.3% Fe tailings grades that the plant apparently averages), the hydraulic nature of the thickeners used in operations compared to the static system used in laboratory tests, the different size distributions that will be obtained from a plant closed grinding- classification circuit, and differences in water used in a plant operation and the laboratory. The authors wrote that it was necessary to overgrind to be sure that the coarse gangue would not settle with the iron oxide floccules. This situation is likely to be exaggerated in commercial operations where it is assumed cyclones would be used for classification. Because cyclone classification is greatly influenced by particle densities, there will probably be an even greater difference in size between the iron and gangue particles in the plant, which would make the gangue slightly coarser still in relation to the iron. This would make the selective flocculation-desliming separations using the procedure employed by the authors even more difficult and, using the dispersant system the authors employed, greater overgrinding would be required. To grind finer to minimize the coarse gangue in the flocculated iron oxides is quite inefficient and appears not to broach the problem. The actual problem appears to be insufficient dispersion of the ground pulp. In this situation, addition of a dispersant would likely be required to attain a sufficiently high pulp dispersion level to efficiently effect a selective flocculation-desliming separation. Although the very coarse particles would still have a tendency to settle with the floccules, it probably would be found unnecessary to overgrind as much as indicated. Use of an optimum combination of dispersant and pH modifying reagents may also significantly improve the selectivity of desliming. Additionally, although it is possible that sufficient dispersion may be obtained by pH control alone in some situations, it is quite probable that added dispersity was obtained in the reported work from using distilled water. It is research experience that distilled water enhances dispersion. In commercial operations it may not be expected that sufficient dispersion will be obtained by pH control alone, unless the water used in the process is by nature quite dispersive. Overall, a change in the Kudremukh tailings dispersant scheme appears necessary where a dispersant is used in conjunction with a pH modifying reagent. With this change, different dispersion-flocculation responses will result that would have to be further evaluated. Therefore, it is still an open question whether an efficient and effective selective floccula- tion separation using Kudremukh tailings may be obtained that will produce saleable concentrates.

Jan 1, 1987

By David J. Brown, Richard C. Fountain, Marc V. Hurst

The Central Florida Phosphate District, one of the most productive phosphate districts in the world, has been mined principally within Polk and Hillsborough Counties, Florida. Recent development is extending the district southward into Hardee, Manatee, and DeSoto Counties. This area is known as the Southern Extension. The combined area of these two phosphate-bearing areas encompasses about 2,000 square miles. Structurally, the district and its Southern Extension lie at the southern end of the Ocala Arch and are flanked by the Hillsborough High to the northwest. South of this area is the South Florida Embayment. The Osceola Low lies to the east. The phosphorite within the Central Florida Phosphate District generally dips very gently (<0.1°) to the south. The boundaries of the central Florida Phosphate District are generally defined by thinning of the phosphorite due the adjacent structurally high areas to the north, west, and east, and by increased clay, CaO, and MgO content reflecting lithologic differences to the east and south. The Bone Valley Member of the Peace River Formation and reworked sediments of more recent age were the primary ore-bearing horizon in the Polk-Hillsborough County area. As those reserves are depleted, the less desirable phosphorites of the Peace River Formation are being exploited in the Southern Extension.

Jan 1, 1993