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By Ryan Lindmark, Guoxing Gu, Zhenghe Xu, Jacob H. Masllyah

Induction time is often referred to the time required to form a stable three-phase contact between a gas bubble and a flat or droplet surface in a liquid medium. It can be used to quantify the attachment process in aflotation system. Various techniques have been developed to measure this important parameter. Due to its importance in flotation systems and other processes, significant advances in refining the induction time measurement techniques have recently been made. This paper summarizes these recent advances and describes a novel method developed to monitor bubble attachment to a pendant bitumen drop or bitumen-coated flat surface. This visualization-based method offers a higher sensitivity and accuracy than the previously developed apparatuses in the induction time measurement. As an example, the induction time for oxygen bubble-bitumen attachment was measured at a fixed bubble size as a function of temperature in two different aqueous solutions. The results showed that higher process temperature is favorable for oxygen bubble-bitumen attachment and hence bitumen flotation. Addition of calcium to the aqueous solution slightly decreased induction time.

Jan 1, 2005

By F. M. Benavides

The mining complex being analyzed consists of four mines and two processing plants located in an area where there are several existing modes of transportation. Figure 1 shows a map of the general layout of the four proposed mines and the two existing processing plants. The mines are identified by the numerals "I" through "IV" and the plants by the letters "A" and "B". A proposed overland conveyor would collect the product from all four mines and convey it to Processing Plant A. Alternate transportation systems are as follows: Railroad transport from Mines I and II to Plant B; Highway trucking from Mines I and II to Plant A; Off-the-road truck haulage from Mine III to Plant B and from Mine IV to Plant A. River transportation from the mines to the processing plants was not considered in this study under the assumption that the high capital investments for the loading and unloading facilities, in addition to difficult traffic problems, would make this mode of transportation unattractive.

Jan 1, 1980

By Caroline L. Herzenberg

Recently, neutron-induced gamma spectrometry has been introduced and gained provisional acceptance as a method for continuous automated analysis of coal. Instrumentation based on this technique has been under development for and in testing at coal preparation plants and a coal gasifier. To provide a deeper understanding of, and extended capability in applying this method, theoretical calculations have been performed of the absorption of thermal neutrons by various coal compositions, and the thermal neutron capture prompt gamma emission spectra produced by these compositions have been calculated. Selected results of these computer calculations and the computer generated spectra are presented.

Jan 1, 1984

By J. R. Cooper

Since man began beneficiating ores, a limited number of factors influenced the type of treatment. The ore itself has always been a factor. The first form of concentration was probably hand sorting, and the grade of concentrate and recovery had to be considered from the start. The cost of labor as a factor in mill design did not attain importance until the period following World War I. Power was one of the cheapest commodities available, and consequently power consumption was ignored. That no longer holds true. The present work does nothing to simplify the work of the metallurgist, or designer. On the contrary it adds another element to the design considerations. And while this report concentrates on power consumption, the mill designer must take the other factors into account as well. This study is based on a compilation of data supplied by a number of Western United States copper operations, as well as information from equipment manufacturers. Although its conclusiones apply to other minerals and geographic areas, the information is more precise, when applied to similar ores. The discussion has been divided into sections covering crushing, grinding, and flotation as these are the principal power consuming functions.

Jan 1, 1977

By Stephen Semeniuk

Discussion by Stephen Semeniuk Discussion As a valuator and SME member, I view Ross D. Lawrence's position as based on unproven and faulty assumptions made with regard to the pragmatic evidence presented in his paper. Moreover, his call for the inclusion of all mineral resources in discounted cash flow valuations is redundant, if not irrelevant, as there are procedures that already take all classes of mineralization into consideration for valuation purposes. In my experience as a valuator, I find that Canadian securities regulators are more than accommodating in allowing any valuations of mineral properties to be based on cash flow calculations. In other business areas, the same regulators usually reject discounted cash flow valuations of projects or businesses with no operating history. Instead, the regulators prefer valuations to be based on other transactions tested in the marketplace. Valuations based on actual market transactions are less subjective than discounted cash flow calculations and/or the capitalization of arbitrary, untested or undemonstrated earnings projections. In the mining and minerals sector, such projections may be made by persons not qualified to make such projections. In support of this statement, I direct readers to the article "Valuation of mineral properties which do not contain exploitable reserves" by Lionel C. Kilburn, which appeared in the August 1990 issue of the CIM Bulletin. To quote from the article: "Value of a mineral property depends basically upon metal prices, recoverable grades, mining and metallurgical practices, commodity supply and demand, and political-economic conditions, all of which vary with time. Five fields of expertise influence the value of a mineral property: •geological engineering, •commodity markets, •financial markets, •stock markets and •mineral property markets. The skills of geologists and engineers properly apply to the first field of expertise. Knowledge and consideration of the other four fields is important, but such advice is more properly sought from marketing experts, economists and stockbrokers." Securities regulators have created no hardship for valuators by excluding unsubstantiated resources in discounted cash flow valuations. In the field of engineering, best design practices apply. A margin of safety is built into the design criteria for any new equipment or structure that will exceed normally expected load levels and stresses, even though such considerations imply higher front end costs. In accounting, the comparable operating principle is conservatism. It explains why, for balancesheet presentation purposes, inventory is stated at cost or market, whichever is the lowest value. Similarly, when the engineering or geoscience-based valuator plays in the field of finance, the rules of accounting and applied economics apply. Regulators in their skepticism of income-based valuations are in tune with similar views already expressed in mining literature. To quote H. Van Tingley, in Mining Magazine, July 1996: "... the DCF method has inherent dangers when applied to undeveloped resources. Firstly, it presents an often-undeserved aura of accuracy. A DCF value is no more accurate than the least accurate of the assumptions incorporated into the calculation - and assumptions

Jan 1, 2003

By Paul L. Russell

Numbers, arithmetic, mathematics. Where did it all come from? Who needs it? We all do, but many school children would not agree. Engineers, physicists, accountants, tax collectors, and most of the general public are well aware that modern society in large part is founded on mathematics and could not exist without it. Mathematics developed over thousands of years as part of the everyday life of man. No one area, tribe, or race can claim discovery. In fact, from the records that do exist, it is evident that many facets of mathematics were discovered independently of others who made similar discoveries. While proof may be lacking, the earliest concepts of mathematics may be some 250,000 to 300,000 years old. The first use of numbers as written records is unknown. However, a bone of a young wolf deeply cut with 55 notches-arranged in two rows, one of 25 notches, the other of 30-was found in Czechoslovakia. Dated to be about 30,000 years old, it is perhaps an early record of some kind of counting system. It is assumed that mathematics was developed as an answer to man's practical needs, but anthropological studies suggest that the art of counting may have developed in connection with the needs of primitive religious ceremonial rites. Fingers probably were first used to designate sets of from one to five objects. Using both hands, up to 10 items could be indicated. As civilization developed, so did the need for more flexible systems to record items of trade, measure land, and figure taxes. Aristotle noted that the development of the decimal system comes from the fact that most people are born with 10 fingers and 10 toes. In spite of this obvious fact many early civilizations used binary, ternary, and quinary systems while vigesimal systems (with 20 as a base) and even sexagesimal systems (with 60 as a base) were used by others. A form of writing was in use in both the Mesopotamian and Nile valleys as early as 3000 to 4500 B.C. In Mesopotamia, wedge-shaped marks were impressed upon soft clay tablets that were hardened in ovens or by the sun. Many thousands of such tablets have survived. When the tablets were finally deciphered, some were found to be records of items shipped in trade, inventories, tax accounts, and mathematics exercises for teaching. Mesopotamia is also the source of an interesting board game dating back to about 2500 B.C. Its buttonlike men and triangular dice were apparently used with squares of shell, inlaid with lapis lazuli and red sandstone. Unfortunately, rules of play were not found. In Egypt, record preservation was somewhat better. Discovery of the Rosetta Stone in 1799 eventually led to deciphering the Egyptian hieroglyphics that included a numbering system at least 5,000 years old. These records show a competence in counting and numbering. A calendar of good accuracy may have been in existence as early as 4,200 years ago. Mathematics, as practiced today, developed when the Greeks added logic and proof to arithme-

Jan 12, 1982

By Diane Moody

I have been asked to give you the National Coal Association's (NCA) view of the future of the coal industry. However, before discussing the outlook for the future I would like to set the stage by taking a brief look at how the industry has changed over the last decade. In 1977 the coal industry was in the midst of a period of steady growth. Although most of the gains in the early and mid 1970's occurred in the west, the industry was still predominately eastern, with eastern production accounting for 76 percent of the 697 million total tons produced in 1977. The labor force was nearing a high - at over 220,000 workers, and the number of active mines was also at a decade high of over 6,000. Productivity on the other hand was at a low. The average miner produced 1.80 tons per hour, and labor relations were also at a low point. Projections for coal's future were very optimistic, mainly because of the unprecedented growth in coal use by the utility industry. In 1977 the 477 million tons of utility coal accounted for 68 percent of U.S. coal production, and the utility industry planned on 129,000 MW of new coal-fired capacity over the next decade. Consumption of metallurgical coal at coke plants was the second largest market at 78 million tons; the industrial and residential market consumed 70 million tons and exports were at 54 million tons. But in retrospect, a lot was happening in 1977 that signalled many changes in the coal industry: - Amendments to the Clean Air Act were passed, which required that utilities take an entirely different approach to meeting New Source Performance Standards at new plants, and required that standards be set for industrial boilers as well; - the Surface Mining and Reclamation Act became law; -electrical generation, despite the optimistic forecasts, was nearing the end of a period of close to five percent annual growth; -1977 ended and 1978 began with the longest coal strike in U.S. history. -crude oil imports in the U.S. reached an all time high as did both total consumption of petroleum products in the U.S. and oil consumption at utilities. The high level of oil imports set the stage for the oil price increases of 1979 and 1980 which resulted in an immediate increase in demand for coal, not only in the United States, but world wide. Labor strikes in Australia and Poland sent foreign buyers to the U.S. literally in droves, and quickly made the U.S. a force in the world steam coal market. The U.S. coal and transportation industries responded to this overwhelming potential demand for coal. In a very short time, the capability had been developed to mine and transport the 1.2 billion tons of coal that forecasters said would be needed by the mid 1980's. What was not anticipated was that the economic effects of sharply higher oil prices would dampen demand for energy, especially for electricity, as quickly as we have seen; that coal industries in other countries would respond as rapidly as the U.S. coal industry, and at a rate

Jan 1, 1988

By R. A. Matuszak

Historically most mine management teams have been forced to operate in a more or less subjective manner. The objectives of mine management are simple and clear. Like other operational managements, mine management teams have the traditional well defined goals of improving efficiency and production while decreasing costs. Unlike other operational managements however, mining teams deal regularly with a vast assortment of uncertainties caused by: - Key production tools being mobile and widely dispersed, and - Non-uniform mining conditions At best in most operations these conditions cause obstacles to productivity and at the same time cause long delay in managment awareness of the obstacles. Planning with delayed feedback of information about necessary deviations is incomplete planning. For these reasons increased operational efficiency remains a constant though somewhat elusive goal.

Jan 1, 1985

By J. Drelich

The adsorption of oleate at the surface of titanium dioxide from aqueous solutions was examined by Fourier transform infrared (FT -IR.) spectroscopy using a germanium internal reflection element coated with a thin film of TiO2. This thin film, with a thickness of 100-200 A, was deposited on the surface of a germanium single crystal by RFIDC magnetron reactive sputtering. It was found that significant adsorption of oleate from a 0.02-0.03 mM aqueous solution on the surface of TiO2 thin film occurs at neutral pH, from about pH=5.5 to pH=7.7. Adsorption of oleate at the surface of the amorphous TiO2 thin film appeared to be reversible, involving soap-acid dimers.

Jan 1, 1997

By James D. Hervol, Josepph W. III Leonard, Barbara J. Arnold

INTRODUCTION Dry concentration or pneumatic cleaning uses air currents as the separating medium. Pneumatic cleaning in the United States today is limited to three or four operations. In fact, the quantity of bituminous coal cleaned pneumatically has declined from its peak in 1965 of about 25.4 million tons (23.1 Mt) to its current level (1988) of less than 4 million tons (3.64 Mt) annually, as shown in Fig. 7-9 1. In 1940, pneumatic methods accounted for 15% of the bituminous coal and lignite cleaned in the United States as given in Table 7-32. Currently, pneumatic methods account for less than 2%. The largest air plant was built in Pennsylvania about 1968 with 14 units processing 1400 tph (1280 t/h) of 3/, in. X 0 (19 mm X 0) raw feed and two additional units retreating middlings. This same plant is one of only three or four plants still operating air-cleaning devices in the US. A wet plant was added in 1985 to increase the efficiency of cleaning the fines. The air plant is still used as a scalping operation for the coarse material. Five additional operations are either no longer in production or have discontinued the use of air tables within the last year. Wet cleaning methods are now being employed at the facilities that have discontinued air table operation. he advantage of dry cleaning techniques is the low moisture content of the clean coal product. However, to decrease respirable dust, mining operations must use water sprays on modem mining equipment. This water adds to the moisture content of the run-of-mine coal and decreases the effectiveness of dry cleaning processes that rely on low surface moistures in the feed to allow for good separations. Wet cleaning methods are preferred, especially since they also allow for much sharper separations. The advantage of dry cleaning techniques is the low moisture content of the clean coal product. However, to decrease respirable dust, mining operations must use water sprays on modem mining equipment. This water adds to the moisture content of the run-of-mine coal and decreases the effectiveness of dry cleaning processes that rely on low surface moistures in the feed to allow for good separations. Wet cleaning methods are preferred, especially since they also allow for much sharper separations. Despite dry concentration's drawbacks, research has continued into dry concentrating methods, including both electrostatic and magnetic separation techniques. The real application for future dry cleaning processes is probably at the power plant between the pulverizer and the boiler feed where particles are already dry and ground to fine sizes (- 200 mesh [ -0.075 mm]), increasing the effectiveness of the separation and also, possibly, increasing the liberation of clean coal from finely disseminated impurities. From a utility's viewpoint, pneumatic cleaning offers the best delivered Btu cost, based on the premise that a percent of moisture is just as detrimental as a percent of ash. Additionally, several other advantages are inherent in dry concentration techniques. The main advantage is that dry concentration re-

Jan 1, 1991

By J. L. Schroder, William J. Halvorsen, Wiliam W. Lyons, Kent C. Ware, Sheridan A. Glen, Donald C. Simpsom

The prospects for near-term growth in coal demand are exceptional: the federal government recently targeted 141 oil- and gas-fired generating units for mandatory conversion to coal; coal-to-synfuel developments are proceeding at a steady clip, with construction of a $1.2 billion gasification plant to begin this year in Beulah, ND; uncertainty over nuclear power and stratospheric oil prices enhance the steam coal market; the export market is ripening; and an influential new political force (the Senate Coal Caucus and Congressional Coal Group) is flexing its muscles on Capitol Hill. But the rosy picture is muddled by signals, often conflicting, sent out by federal agencies. Although EPA can be credited with relaxing its grip on the Clean Air Act, its sulfur dioxide control strategy is still often at odds with the Administration's call for domestic energy (coal) development. B. R. Brown, president of Consolidation Coal Co., sums up the situation: "Every mule is pulling in a different direction." Often in the midst of the fray is the small operator who has been hardest hit by the stagnation of coal markets. Layoffs, shortened work weeks, and mine closures were rampant in the eastern and midwestern coal fields, even among large producers. The longstanding boom in western coal was tempered during 1979 by a noticeable slowdown in announcements of new mine construction. The prognosis: Eastern coal will remain in the doldrums for quite a while to come as it works off some 90 Mt of overcapacity. Midwestern coal will fare no better due to the regulatory-influenced appetite of midwestern utilities for low-sulfur western coal. This displacement should ease, though, as new power plants equipped to burn high-sulfur coal come on line in the years ahead. In the West, the National Coal Association projects production to increase a healthy- 10% this year, although mine-to-market transportation looms as the single largest stumbling block to marketing efforts. Fatalities Up 40% in 1979 The National Coal Association estimated total coal production in 1979 at 671 Mt, an increase of 13% over 1978. Of this total, the East and Mid-west accounted for 476 Mt (71%) and the West produced 195 Mt (29%). With the consistent rise in western production playing against flat outputs in the East and Midwest, underground mining's share of total production continues to slip and is expected to account for only 38-39% in 1980. Incidence of deaths and injuries at US coal mines soared in 1979 over 1978 rates. MSHA figures (still subject to final adjustments) reveal a death rate of 0.07 per 200 000 man-hours, up 40% over 1978's 0.05 figure. MSHA chief Bob Lagather attributed the death incidence to the large number of new coal mines put on line in 1978, which he estimated at between 350 and 400. Nonfatal injuries rose to 8.48 per 200 000 man-hours, up about 15% from a 1978 rate of 7.35. In absolute numbers, MSHA counted 144 fatalities and 18 111 lost-day injuries during the 1979 calendar year. The 144 coal mining deaths in 1979 is the highest number of coal fatalities at US mines since 1975.

Jan 5, 1980

By W. Jacobi, K. Eisfeld

The primary objective of dosimetric modelling for the inhalation of radon daughters is the evaluation of the dose distribution and of the mean dose to sensitive cells or target tissues in the respiratory tract which are assumed to be responsible for the initiation of lung cancer. The results of such dosimetric models are influencing the practice of radiation protection in a twofold manner: Firstly, they enable us to identify appropriate operational quantities for air monitoring and for the surveillance of individual exposures to radon daughters. Secondly, they can be used to derive secondary and operational limits for these radionuclides from the basic dose limits. The dose to target tissues in the lung from inhaled radon daughters depends on various physical and biological parameters: The unattached fraction of daughter atoms, the AMAD of the carrier aerosol for attached atoms, the geometry of the respiratory airways, the breathing conditions, the parameters for the retention and translocation of daughter atoms in the different lung regions, and the location of the target cells or target tissues, respectively. Therefore, dosimetric modelling for radon daughters has to include a sensitivity analysis showing the influence of these parameters. To meet these objectives we have recently described in a comprehensive report an improved dosimetric model for the inhalation of 222Rn, 22ORn and their short lived daughters (Jacobi and Eisfeld, 1980). In the following this model is shortly described and the main results are summarized. DOSIMETRIC MODEL [Model Structure]. For the geometry of the bronchial airways the model A of Weibel (1963) was used. Each bronchial generation i (i =0.1 .... 16) was considered as a separate compartment i, for which the following transfer pathways for radon daughter atoms were taken into account (see fig. 1): (1) the uptake by deposition (deposition probability wi); (2) the translocation by ciliary clearance (rate constant [A]i); (3) the transfer to blood by diffusion through the bronchial epithelium (rate constant [A]b). To distinguish between attached (Index a) and free (index f) daughter atoms each bronchial generation was divided in two subcompartments (i.a and if) with a transfer rate constant [a]s (ia- if) characterizing the desorption or dissolution rate of attached atoms in the mucus fluid. Thus for daughter atoms primarily deposited in attached form the transfer to blood is a twostep process with the rate constants [a]s and [A]b which were assumed to be independent of the generation number i. [Deposition]. The deposition probabilities wi in each bronchial generation were calculated on the basis of the laminar diffusion model of Gormley et al. (1949); however the deposition in the upper airways was corrected for turbulent air flow, taking into account the results of our deposition experiments (Martin et al., 1972). Figure 2 shows the resulting deposition probabilities per unit surface area of the bronchial generations for nose breathing at a rate of 20 1/min. The values for attached daughter atoms refer to an AMAD of 0.2 - 0.3 µm ([O]g =3) for the carrier aerosol; the deposition values for free atoms were derived with a diffusion coefficient of 0.05 cm2/s, assuming a prefiltration of 50% in the naseopharyngeal region.

Jan 1, 1981

By M. Ahrens

The paper describes the main drive systems of an iron ore pelletizing plant and related important design aspects. It is shown how today?s drive systems provide the desired flexibility for the process and lead to high energy efficiency and system reliability. With respect to electric drives expansion projects have many technical issues in common with green-field installations. However, there are aspects where important, distinct differences occur. It is shown which considerations for selecting and sizing drive systems for such a plant as well as for integrating them into an overall plant control concept need to be taken into account. Besides the design of the drive systems a key aspect for such an expansion project is the network interaction. Harmonics levels at different points in the plant network need to be checked carefully with simulations during the design phase to avoid problems later-on during operation. The power factor compensation and the harmonic filtering of the new production line cannot be designed independently of the already existing plant. The paper highlights areas where problems could occur and which points need to be paid attention to when a plant is expanded.

Jan 1, 2008

By M. Tirmarche, J. Brenot, J. W. Piechowski

INTRODUCTION Statistical analysis of results obtained by workers survey is very often limited to the determination of the collective dose and mean annual values. This information is not sufficent by itself for radiation protection purposes since the cumulative exposure of a worker during his working life is not taken into account. A more complete analysis would be obtained by considering both: [ ] These two notions are different. The former depends on the evolution of the protection with time and is related to annual limits (ICRP, 1977 and ICRP,1977 a). The second depends mainly on the works performed during the period of survey, the interference of protection evolution is weakened. So it is useful to foresee how the individual average annual doses would be when considering survey periods of 5, 10 years, or more. STUDIED POPULATION In order to analyse the two previously mentionned notions it is necessary to follow up a well defined population of workers which is continuously exposed to the radiological hazards on a long enough period. The selected population is that of the workers of the French uranium mines always present during the 1971-1979 period (9 years). The number of individuals is 937. The radiological hazards are: 1. exposure to radon and short-lived daughters 2. exposure to long-lived ore dust 3. external irradiation. The workers of the uranium mines are exposed to these radiological risks in different ways according to the work performed. It is therefore necessary to subdivide the population into more homogeneous groups with respect to the radiological risks. Three groups are considered: - Group 1 : 227 individuals whose radon and dust exposures are always nil - Group 2 : 449 individuals whose radon and (or) dust exposures are different from 0 every year - Group 3 : 261 individuals represent a mixed category. Some features of these groups are given in table 1. [ ] The 937 followed individuals represent approximatively the half of the whole population of the French uranium mines. Taking into account the procedure adopted to select the studied population, it appears clearly that this population is not representative of the whole miner population. DOSIMETRIC RECORDS Three risk indicators are considered .Individual annual exposures to radon and its shortlived daughters. They are determined by ambient monitoring based on radon concentration measurements and recording of the times elapsed in the various workplaces. For each worker the annual exposure is represented by the mean annual air concentration and is expressed as a fraction of the maximum annual concentration (MAC). Given the administrative arrangements and the effective state of equilibrium between radon and its daughters, the maximum annual concentration is practically equivalent to 1 Working Level = 2.08 x 10- 5 jm-3. (UNSCEAR, 1977). . Individual annual exposures to long-lived ore dust which are also expressed in fraction of the maximum annual concentration. . Individual annual doses of external irradiation (X and [y] rays) expressed in mSv (= 10-3 Sievert). Irradiation monitoring is based on use of individual film badges.

Jan 1, 1981

By B. J. Arnold

Froth removal rate is perhaps the most important parameter in scaling up from laboratory tests to plant froth flotation circuits. The WEMCO froth factor, the percentage of the froth height over the lip of the cell, accounts for the difference between laboratory and plant froth removal rates. As laboratory tests are generally run with a high pulp level, laboratory results are directly comparable to plant results only when a high froth factor (high pulp level) is run in the plant. When a plant does not have a high pulp level, laboratory results must be modified by using a ratio between laboratory and plant kinetics to predict plant results. This ratio, which accounts for the froth factor is important in testing any new reagents or reagent dosage levels. CQ Inc. researchers have used predictive scale-up equations using this froth factor coupled with equations for kinetics and the residence time distribution in the froth flotation cells. These equations show that modifying the froth factor in the plant can have a large impact on flotation cell yield and reagent use. EQUATIONS DESCRIBING FROTH FLOTATION Scaling up from laboratory- to plant-scale coal froth flotation has been the subject of much research and debate over the years. Determining the proper rate equation to describe flotation kinetics and an equation to describe the residence time distribution in a bank of flotation cells have been particular areas of study. As shown in Tables 1 and 2, various rate equations and residence time distribution equations have been proposed in the literature. These equations consist of one or two parameters giving the rate constant(s) in units of time-1 and a parameter for recovery at infinite time, [Roo]. Dowling, Klimpel, and Aplan (1985) evaluated the rate equations in Table 1 for their ability to fit froth flotation kinetic data and found that all of the equations give reasonably low standard errors. Several of these equations, however, proved to have superior confidence limits for the parameters. Other equations have also been proposed to describe the recovery versus time profile. Most recently, Diao et al. (1992) proposed a first-order form with a sine wave distribution. As indicated in Table 2, investigators have suggested many equations to describe the residence time distribution in continuous froth flotation. To measure the water residence time distribution in a bank of cells, a soluble tracer is often used, with the level of tracer being measured over time at the tailings discharge. This response is then put on a dimensionless basis as described by Austin et al. (1984) in order to compare mixing behavior between cells or under different conditions. Coal flotation cells are generally of the flow-through or hog-trough variety allowing for some degree of backmixing and short-circuiting. While the water residence time distribution (see Figure 1) at the end of one cell in a bank of 1.4 cu ft WEMCO froth flotation cells may approximate perfect mixing conditions (Arnold, 1989), the water residence time distribution at the end of a bank of cells does not. Figure 2 shows the RTD for various flotation cell types compared to that for perfect mixers in series. To better describe the water residence time distribution in coal froth flotation cells, Van Orden (1986) used an equation similar to the perfect-mixers-in-aeries equation. This

Jan 1, 1993

By G. Whitney, J. Steiner

Introduction The Summitville Mine located in southwestern Colorado is an example of the potential impact that natural weathering and mining activities can have on environmental quality. Acid rock drainage and metals leaching from active and historic mine districts are a major environmental problem facing the mining industry today. Sulfide ore exposed naturally or during mining operations has the potential to produce leachates that contain high concentrations of dissolved metals. These leachates can affect the quality of plant and animal health in surface water used for agriculture, recreation and human consumption. Pintail Systems has developed biological processes for detoxification of cyanide in heap-leached spent ore and process solutions. During application of spent ore cyanide bio-detox processes we have also observed a substantial reduction in many of the leachable metals in biotreatment solutions. These field observations of soluble metal reduction led us to propose that metal bio-mineralization should be a secondary treatment goal of spent ore detox in Focused Feasibility Studies (FFS) for the Summitville Mine. In the FFS (described in a companion paper) for Summitville, spent ore from the heap leach pile (HLP) was loaded into PVC test columns (six inch X ten foot) and was leached with bacteria/nutrient solutions. Two treatment designs were studied: a standard percolation leach (aerobic) and a saturated leach design where the ore was saturated with the heap leach solution to which bacteria and nutrients were applied in a continuous biotreat leach. The bacteria for all column treatment tests were isolated from the spent ore at depth through the Heap Leach Pile (HLP) in the saturated and unsaturated zones. Bacteria isolated from the heap material were tested for cyanide oxidation capacity and were submitted to a bioaugmentation program to improve reaction kinetics and metals tolerance. The final treatment population consisted of several distinct species including aerobic heterotrophs, facultative anaerobes and sulfate-reducing bacteria. The remineralization of soluble metals was observed through a decrease in copper in column leachate solutions and the formation of observable mineral products on ore surfaces in the columns. Several of the tests were run in clear PVC columns to facilitate observation of mineral formation. The column ore contents were photographed before, during and after the biotreatment process which ranged from 10 to 20 days for each test column. Ores were collected from each column after the treatment was complete and were submitted for SEM and TEM study at two laboratories - the USGS SEM Laboratory in Denver, Colorado and the City College of New York SEM laboratory. Treatment Process Description Numerous species of bacteria, fungi and yeasts are capable of accumulating many times their weight in soluble metals. Both living and dead biomass are effective in removing soluble metals from waste streams containing gold, silver, chromium, cadmium, copper, lead, zinc, cobalt and others. Soluble metals may also be immobilized in soils by natural or engineered biomineralization reactions. Several commercial processes using biological reactions are being applied on an industrial scale for metal remediation. Bacteria found in natural and extreme environments have developed a wide variety of metabolic functions to adapt to these environments. These natural microbial functions contribute to global mineral cycling that continuously forms, transforms and degrades minerals and metals in the environment. Biomineralization is described as a surface process associated with microorganism cell walls where the remineralization occurs. The biogeochemical activities initiated by microorganisms in ores, soils, surface and groundwater environments can dominate the formation and transformation of those mineral environments.

Jan 1, 1995

By Donald E. Ranta

Many portions of the mining industry are under intense pressure to reduce costs while commodity prices languish. In response, global Internet-based marketplaces to deliver business-to-business (B2B) e-commerce solutions are being established to reduce costs and improve efficiencies across the mining industry supply chain as well as with customers. Over time these marketplaces will likely evolve to create an integrated supply chain solution, layer in value-added services, and develop mining community portals with industry content. Significant opportunities to help reduce costs and create value are available in mining e-procurement as well as in on-line product sales. The supply chain for the industry is highly fragmented and many mining companies have numerous inefficiencies in procurement. An e-procurement marketplace (or "exchange") can immediately address these inefficiencies and offer numerous benefits to buyers and suppliers. These benefits include improved sourcing options, inventory cost reduction, transaction cost reduction, access to value-added services, lower customer and supplier acquisition costs, improved reach, and improved information flows.

Jan 1, 2001

By Zhongwei Wang, Dong Wang, Feng Ju

The coal seam in the southern coal field of the Ordos Basin serves as the main aquifer, while the region is known for its high-intensity coal mining activities. The coupling effect of mine water and the strong disturbance caused by high-intensity mining have brought serious challenges to the stability of coal pillars. To address this, a formula for determining the reasonable width of coal pillars under the aforementioned coupling effect and establish a criterion for coal pillar instability in this paper. A case study was on the 11,215 working face at the Xiaojihan coal mine in the area to investigate coal pillar stability. Results indicate that the strength and stability of the coal pillar are affected by the water content, with a small water content increasing its strength and large water content weakening it. In high-intensity exploration of watery coal seams, the best stability of the coal pillar is achieved at optimal water content and mining rates. For the Xiaojihan coal mine, the optimum water content and mining rate are 3.31% and 20 m/d, respectively, ensuring the efficient mining of watery coal seams. Furthermore, this study's findings can provide valuable references for the mining design of coal mines with similar geological conditions in the region.

Feb 13, 2024

By Desiree Willis

At 6 percent downgrade to a low point beneath California?s Sacramento River, the Lower Northwest Interceptor Sewer was a difficult project from the outset. Project owner Sacramento County Regional Sanitation District (SRC-SD) planned to excavate the V-shaped tunnel in two sections using an earth pressure balance (EPB) machine in soft ground. Muck removal, due to the steep downgrade, was a tricky proposition. ?We did look at muck cars, but determined they were not the best option due to the relatively steep slope of the tunnel alignment. The safety benefits of conveyors on this job were obvious, as there were not the potential hazards associated with muck cars traveling on an incline or derailing,? said Steve Norris, senior civil engineer for SRCSD The successful project represented one of the first instances of a conveyor system being used for a soft ground tunnel boring machine (TBM) application. Several projects in California, including a recent tunnel completed in 2009, have highlighted a growing acceptance of conveyor muck removal in a variety of ground conditions. Conveyors offer higher system availability than more common methods, such as muck cars, as they allow for continual operation of the TBM. The design of conveyor systems must, however, take into account the differences in material between soft ground and hard rock, including belt cleaning features, sealed transfer points and other elements.

Jun 1, 2010

By James F. Lemons

The potential production of cobalt from nickel sulfide deposits in Canada, from nickel laterite deposits in the Pacific Islands, and from the copper deposits of Zaire and Zambia will be a function of the cost of recovery of the primary nickel and copper products. This cost of production varies significantly for these deposits and is related to the differences in the cost of labor, energy, and supplies, to production technology, and to the grade and recovery of nickel, copper, and cobalt. This Bureau of Mines paper investigates these cost and technology differences as they relate to the cost competitiveness of the deposits in Canada, Zambia, Zaire, and the Pacific Islands.

Jan 1, 1984