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A panel discussion on carbon-in-pulp processing of gold and silver ores was one of the highlights of the 1981 AIME Annual Meeting in Chicago. The session generated considerable interest and discussion among panelists and the audience. For those unable to attend the panel, the program was recorded and the discussion appears in this two-part report. The panel was co-chaired by Robert S. Shoemaker, vice president of San Francisco Mining Associates, and Laurence D. Hartzog, principal engineer with Bechtel Civil and Minerals Inc., San Francisco, CA. Panel members included: George Potter, consultant, Tucson, AZ; Kenneth B. Hall, metallurgical superintendent, Homestake Mining Co., Lead, SD; and Donald M. Duncan, resident manager, Pinson Mining Co., Winnemucca, NV. There have been several types of carbon-in-pulp adsorption vessels in use, such as the Dorr-type agitator, the simple propeller agitated tank, the Pachuca tank, and, lately, the draft tube-type of agitated tank. Which one of these is best and why? Potter: On the selection of the most appropriate adsorption vessel, there is a considerable difference of opinion that stems largely from the fact that every ore is different. The mesh of grind, the pulp solids, and the apparent viscosity of the pulp as caused by its clay content and chemical conditions all differ. The traditional Dorr agitator with the slow speed center sweep and either peripheral or center column air lifts has worked quite well on the finer grinds of all minus 65 and probably 70-80% minus 200 mesh. Pachuca tanks have also been successful and they may be capable of handling a coarser feed than the traditional Dorr tank. One uranium mill, for example, handles minus 28 mesh sandstone ore in a Pachuca. The most recent development and one that commands consideration is the draft tube agitator in which there is a turbine which closely fits inside a draft tube. Velocity in the tube is carefully calculated to avoid undue shear and thus abrasion of the carbon. The objective in all cases, of course, is to mix the granular carbon, which is typically 6 x 16 mesh, very gently but thoroughly in a slurry with minimum carbon abrasion. I do not know that there is one outstanding choice just yet and I have been unable so far to get information on C-I-P service for ore grinds as coarse as 35 mesh. Duncan: The major advantage of draft tube-type is the ease of startup. At the Pinson plant we installed draft tube-type agitators but it is too early to quote experience with them. We also haven't operated long enough to determine just what our carbon loss is. The advantage, of course, in the draft tube design is that it requires only about one-third the horsepower input of a conventional agitator. If it has no other advantages, it has that. Hall: The type of vessel most suitable for C-I-P adsorption depends on the type of ore treated and the prevailing operating conditions. In most cases, a deep tank with turbine-type mechanical agitator and low speed tip velocities would be satisfactory. Turbine-type impellers give a positive type of agitation which assures optimum ion contact and reduces short circuiting. Thorough aeration is possible with an air sparge properly located. A mechanical agitator can easily be started up after an outage, but it is usually necessary to drain and wash out a Dorr rake-type or Pachuca before restarting. The turbine-type impeller requires more power, but maintenance costs are negligible if rubber covered impellers are used. Carbon losses are minimal. In smaller plants, Pachuca type agitators provide adequate aeration and agitation. Bob Polak, Occidental Minerals (from the floor): Mr. Hall, you favor the mechanical-type agitator with the preface that the proper design is critical. Could you elaborate on this for us? Hall: The most important thing is low tip speed to prevent carbon attrition. I think the impeller should be sized so that you get a good sweeping action toward the bottom of the tank, across its bottom, up the sides, and back to the center. The advantage of the draft tube is that you get a more positive agitation and you probably get improved aeration too. Polak: Do you know of anyone using an upflow mechanical agitator rather than a downflow unit? Hall: I think that Bob Wilson at Custom Equipment has designed one where he has located the sparge directly beneath the impeller. The air bubbles are broken up by the impeller as the slurry passes through it. The slurry flows upward, outward, down the sides, and, again, back to the center of the tank. I don't know that any tanks of this design are in commercial use. Hans Von Michaelis, Randol International (from the floor): A question to any of the panelists on flat bottom versus conical bottom Pachucas. Hall: I would say the conical bottom would be most suitable in most cases. Some plants have experienced problems with flat bottom Pachucas in that they have a tendency to sand in on the sides of the tank so only the center of the tank is active. Duncan: With our draft tube tank we placed an inverted cone in the center of the tank bottom and blanked off the bottom comer around the circumference of the tank to facilitate movement of the pulp. Other than that, as far as conical bottom tanks are concerned, I'm generally opposed to them because of the cost and height differential. Larry Kramer, Kennecott Minerals Co. (from the floor): Mr. Duncan, you mentioned that the draft tube-type could be agitated with about one-third the horse-power applied to a conventional propellor agitated tank. I have trouble trying to pin down that kind of number. Could you give a bit of rationale as to why that mechanism has a lower horsepower requirement? Duncan: I think it has to do with the fact that below the propeller you have straightening vanes. The pulp, which is flowing vertically downward, is turned and flows upward again without any recirculation. You have an inherently less horse-power requirement in that type of tank. The one-third horsepower requirement is a number I obtained from Lightnin, which supplied us with details of the draft tube. There is probably much more recirculation with a conventional impeller type that is wasted motion. Potter: Last week I saw some agitators in South Africa with short draft tubes and actual turbine-type impellers. This plant was handling 200 kt of ore per month. The tanks were flat bottomed, and the agitation appeared to be quite satisfactory.

Jan 8, 1981

By David M. Stearns

Introduction Millions of tons of coal are shipped by rail each year in the US. Loading those trains efficiently is a topic being studied by coal producers and railroads. Alternatives range from volumetric loadouts to systems that weigh the product, using either belt conveyor scales, track scales, or weighbins. Each system has its proper application and each has pros and cons, depending on the volume, nature, and layout of the specific loading facility. In recent years, a batch weighing system has been developed that offers significant benefits to higher volume operations shipping by a unit train. The Unitrain Loadout System (ULS) features a precision electronic batch weighing system married to a mechanical loadout system by a microprocessor-based digital control system. A batch weighing loadout could be designed using analog electronics or even a mechanical weighbin. But it is the adaption and use of a microprocessor that provides the primary benefits of a unit train loading facility. Those benefits are accurate weight determination, optimum car use, overload prevention, speed in loading, optimum labor use, and documentation of the loading process. Unitrain History The first ULS was erected for iron ore applications in Canada during the 1960s. The first domestic system on coal was installed at Pittsburg and Midway Coal Co.'s McKinley mine at Gallup, NM, in 1978. At present, there are more than 20 Unitrain Loadout Systems in operation worldwide. They are loading minerals, concentrates, and coal. Eleven systems are presently in service or under construction in the US. In the last several years, a number of comparable systems have also been installed. As a result, the concept has been well proven and is now commercially available from several sources. Unitrain Operation The basic operation of a ULS involves loading a unit train with individually weighed batches of coal while it moves slowly under a loadout tower. Typical coal systems are designed to load at rates of 2.7 to 6.3 kt/h (3000 to 7000 stph). The contents of each car can be accurately weighed. This meets the requirements of the National Bureau of Standards Handbook No. 44 for static weighing. Also, cars can be loaded within very close tolerances. This optimizes railcar usage and prevents overloads. Principal components of the loadout system are the main feed conveyor, the surge bin, surge bin gates, weighbin, weighbin gate, flood loading chute, control room, calibration weights, and hydraulic and electrical systems (Fig. 1). Main feed conveyor: Coal is delivered from a storage area by the main feed conveyor. The conveyor fills the surge bin. It should be capable of conveying coal at the same rate at which it is being loaded. Usually the feed conveyor is equipped with a conveyor scale that can display rate in the control room and control feed to the belt. The surge bin will typically store 227 to 272 t (250 to 300 st) of coal. If the loadout is installed in an over-the-track silo, there is no need for a surge bin. Four double-bladed, hydraulically actuated gates are incorporated into the bottom of the surge bin. These gates open to fill the weighbin. Automatic pre-act points are selected by the control system. They shut these gates as the desired weight is approached. The final amount of coal is added by a single gate that closes. This results in a weighed batch of coal within ± 0.5% of the selected optimum load per railcar. Thus, if loading 91-t (100-st) capacity cars, the system is set to batch up 90.2 t (99.5 st) batches. Each car is expected to be loaded between 90 and 91 t (99 and 100 st). Weighbin: The weighbin is next in the flow scheme. Typically, it is

Jan 3, 1985

By V. R. Degner

Comments Summary It is very interesting to review the technical changes which have occurred in the industrial practice of minerals flotation over the past two decades. In 1972, worldwide industrial flotation was dominated by 'mechanical' flotation machines having an individual cell volume less than 500 cu.ft. Manufactures, such as DENVER Eqpt. Co., OUTOKUMPU, WEMCO, GALIGHER (AGITAIR), AKKER, and later DORR-OLIVER, produced flotation machines featuring a mechanical rotating impeller which served to mix pulp and air, prior to flotation, and to keep the solid ore particles in suspension. While sharing this common mechanical impeller feature, the machine design of the various manufactures differed in detail; particularly in regard to the vertical location of the impeller in the cell and the means by which flotation air was brought into contact with the pulp within the rotor mechanism. A review of the existing technical literature in 1972 would identify academic research studies, particularly at Columbia University (N. Arbiter, C, Harris ...) aimed at comparing flotation cell design concepts, of the various machine manufactures, on a hydrodynamic basis. These research studies were confined to very small, laboratory bench size, flotation machines, and the benefits of incorporating hydrodynamic considerations in the scale-up of the existing 300 cu.ft. mechanical flotation technology to larger cells was not commonly practiced industrially. Technological advances in minerals flotation, over the past two decades, have been influenced by a variety of economic factors including the increasing development of lower grade ore bodies, the attractions of producing a higher grade final concentrate, and the economy of tails retreatment to improve overall plant recovery performance, and flotation system “optimization" became increasingly important through the 1970-80 time period. The trend toward processing lower grade ores led to higher tonnage mill operations, and stimulated the development of the very large capacity mechanical flotation machine for roughing and scavenging duty. In 1972, the 500 cu.ft. size flotation machine was being pilot tested and introduced to the industrial market. Today, 1993, individual cell volumes of 1500-3000 cu.ft. are operating successfully throughout the world, and well planned plant test programs have concluded that the very large flotation machine can achieve the same metallurgical performance level of its smaller predecessor. The large flotation machine development record clearly credits the incorporation of internal cell hydrodynamic considerations in guiding the scale-up of the mechanical flotation machine to large sizes. This guidance eliminated, or reduced significantly, costly in-plant prototype machine changes which increase Dramatically with increasing flotation machine size. Early in the 1980's, at approximately the time that flotation machines in the 1500 cu.ft. class were being introduced into the market, it became evident that the availability of the very large mechanical flotation machine brought with it the need for a systematic means to "optimize" the flotation system by relating flotation cell size, row length (i.e. number of cells per row), and flotation rougher, scavenger, and cleaner system configuration to the economic objectives of the concentrators' operating management. Flotation system optimization consists of quantifying the flotation process performance using a suitable model which relates the kinetic response of the trace specie and the gangue material to the cell overflow, and produces a numerical relationship between product grade and value recovery. The computer analysis technique has proven to be an invaluable tool in determining the kinetic model coefficients which characterize a given application, and is also used to apply the resulting model to a proposed minerals beneficiation situation seeking to "optimize" the flotation system by relating metallurgical grade-recovery performance, flotation cell size, and circuit arrangement, to plant space, installation, and operating costs. It is interesting to note that these same computer based kinetic flotation analysis techniques can be easily applied to quantitatively evaluate the effect of different chemical reagent strategies, and flotation air transfer, on process performance for a variety of candidate feed ore types.

Jan 1, 1993

By E. Steel, V. S. Znamensky, A. Wylie

The asbestiform habit is most commonly developed in certain amphiboles and chrysotile, but other minerals also may crystallize with this unusual habit. The habit may be characterized by (1) a fibril structure, single or twinned crystals of very small widths (generally less than 0.5 pm), which have grown with a common fiber axis direction, but are disoriented in the other crystallographic directions; (2) anomalous optical properties, primarily parallel extinction; (3) unusual tensile strength; (4) high aspect ratio; and (51 flexibility. In addition, there is evidence to indicate that some amphibole asbestos may have unusual surface properties. ASBESTOS AND THE ASBESTIFORM HABIT Asbestos is defined as a group of highly fibrous silicate minerals that readily separate into long, thin, strong fibers of sufficient flexibility to be woven, are heat resistant and chemically inert, and possess a high electric insulation, and therefore are suitable for uses where in- combustible, nonconducting, or chemically resistant material is required (Gary, et al., 1974). The most common minerals that may occur with the asbestiform habit are chrysotile, grunerite (amosite], riebeckite (crocidolite), actinolite, anthophyllite, and tremolite; although the development of this habit among these minerals is rare. Other minerals, most notably other amphiboles, can occur in this habit, but no others have been mined commercially as asbestos. All asbestos is confined to metamorphic rocks, even though other habits of the amphiboles are common in igneous rocks. Slip fiber veins are the most common deposits (South African amosite, Canadian chrysotile, etc.), but mass fiber deposits also may occur such as California chrysotile or mountain leather. Field relations and experimental data support the hypothesis that metasomatism is the dominant process in the formation of asbestos fibers, amphibole as well as serpentine. The crystal habit of a mineral is the shape or form a crystal or aggregate of crystals take on during crystallization. The asbestiform habit has a number of characteristics that differentiate it from other habits. Chief among these is the fibril structure.Afibri1 is a single or twinned crystal with a very small width, generally less than 0.5 pm, and an extremely high aspect ratio; bundles of fibrils may have lengths reaching into the cm. Fibrils share a common crystal growth direction along the long axis of the fiber, but appear to be disoriented with respect to one another in the other crystallographic directions. The structure of the individual fibrils, and the organization of fibrils within a fiber may differ among the various types of asbestos. The fibril structure of asbestos is probably a factor in controlling a number of secondary properties that include high tensile strength, flexibility sufficient for weaving, and anomalous optical properties. The high tensile strength of asbestos is quite remarkable, exceeding that of the ordinary varieties by a thousand fold (Zoltai, 1978). In part, this may be attributed to the lack of defect on the fibril surfaces (Zoltai, 19781, but some contribution also must come from the existance of bundles and the nature of the ordering of and forces among the fibrils. The flexibility is not only enhanced by the fact that the fibrils may slip past one another, but by their small widths and extreme aspect ratios. However, structural defects parallel to the fiber axis also may contribute to this property. Among the common commercial asbestos types, the greatest flexibility is found in chrysotile and the least in grunerite asbestos (amosite), varying inversely with fibril thick- ness. In addition, at least for chrysotile, composition also may affect the flexibility of the fibers. Finally, most asbestos minerals are mono- clinic, but optically display parallel extinction (Heinrich, 1965, and Wylie, 1978). This also must be due, in part, to the ordering or lack of ordering of the fibrils. The fibril structure is probably a random

Jan 1, 1986

By W lethlean, Laurie Smith

When coarse gold is present in an ore, there are advantages in physically recovering this gold in the grinding section of the ore processing plant. This reduces the risk of the coarse gold being locked up in the grinding section equipment, reduces the quantity of activated carbon to be eluted and reduces the risk of gold passing out of the cyanide leaching circuit only partially dissolved. The free gold may be recovered by various mechanical means utilising the significant difference between the specific gravity of the gold and waste minerals. Frequently, sulphide minerals and ball mill attrition steel in the form of fines and chips are present in the ground ore and behave in a similar manner to the gold in the concentrating process. These materials must be removed to produce a concentrate suitable for direct smelting and several stages of cleaning, sometimes utilising different physical principles, may be required. The removal of these materials invariably results in a loss of gold from the final concentrate. The rejected materials containing significant quantities of gold are returned to the grinding section, consequently the opportunity for a high and early recovery has been lost. The quantity of gold returned to the grinding section will vary according to the number and type of cleaning stages and the physical characteristics of the materials and the gold but surveys of the gravity concentration processes suggest that it may be as high as 50%. To maximise the recovery of gold from the primary gravity concentrate, some operations batch cyanide leach this concentrate with or without additional reagents. The method of agitation and solution recovery vary. The most common method of agitation is by a high-speed propeller mixer and the least expensive but time-consuming method of solution recovery is by decantation after settling and by repeated decant washing. The pregnant gold solution is either introduced into the main ore leaching circuit or the gold is recovered by direct electrowinning. After commissioning in 1994, Union Reefs Gold Mine (URGM) experienced below expected recovery of gold from the gravity concentrate generated from the Knelson Concentrators. It was shown that the recovery into the Knelson Concentrate was high but that the subsequent mechanical concentrating techniques of tabling and magnetic separation resulted in significant gold being returned to the grinding circuit.

Jan 1, 2000

By P. J. Hyde

Cyanide is a significant contributor to the cost of producing gold. Any reduction in consumption that can be achieved through more reliable measurement and/or more efficient management of dosing rates can have a significant financial impact. An automated analyser, by its mechanical nature, is not prone to the variations of human operators, particularly notice­able from shift to shift. Reducing the standard deviation of the measurement (ie, reducing noise ), the automated measurement will give the metallurgist a truer picture of the underlying patterns of usage. The combination of automated analysis with on-line operation and a control loop provides timely information that is efficiently utilised in the management of the plant. Until the release of the Chemtronics On-Line Cyanide Analyser (OTA3000) about 12 months ago, the Australian experience with automated analysers (especially on-line) had been substantially negative. Since its release, the Chemtronics instrument has outperformed both manual titrations and other automated instruments, gaining an enviable reputation for accuracy and reliability in the process. The instrument is built around the technique ofpotentiomet­ric titrations, in which the potential of an indicator electrode is measured as a function of the volume oftitrant that is added to the sample. As the cyanide in the sample is depleted, the potential on the indicator electrode changes rapidly, producing a typical sigmoidal curve. The OTA3000 takes the first differ­ential of the curve, identifies the apex of the peak as the endpoint and reports the result in parts per million of sodium cyanide. The OTA3000 accepts the peak as valid only if it exceeds a certain minimum height. That minimum height is a programma­ble parameter and is used to optimise the relationship between sensitivity and the rejection of spurious peaks. The instrument will track cyanide trends through both positive and negative slopes of any magnitude, but it will provide a warning if it the slope becomes excessive, not because it affects the instrument but because it means that something unusual is occurring in the tanks. There are a limited number of conditions under which the instrument will produce a result of zero. In these cases the OTA3000 holds any output lines at the last valid result while it repeats the titration. This feature was incorporated for reasons of stability in a feedback loop.

Jan 1, 1995

By Cyril W. Draffin

Introduction Americans have long been proud of their ability to recognize a need, define it, and then develop workable solutions. The U.S. underground coal conversion (UCC) program is a good example. In 1974, the need to utilize coal resources that could not be mined was recognized, and Congress gave the Bureau of Mines $1.7 million to gain a better understanding of the UCC technology and its potential applications. Since 1977 when the U.S. Dept. of Energy (DOE) was formed, workable technologies have been tested, the market for underground coal conversion has been recognized, and extensive industrial interest has developed. Perspective The U.S. is blessed with extensive coal resources. Coal supplies about 19% of our national energy needs, yet recently promulgated environmental standards and increasing mining costs have limited direct coal use. UCC potentially can use coal that is economically or technically infeasible to mine because the coal is too thick, deep, dirty, high-ash, and wet; has an excessive angle of dip; or has unpredictable and poor overburden characteristics that make mining unsafe. Coal can be gasified underground or perhaps liquefied below the earth’s surface. Underground coal gasification (UCG) is the prime element of the underground coal conversion program. It enables coal to be converted to gas underground. UCC Coal Resource Recent data show a total U.S. coal resource base of about 6.4 trillion tons. Of this, 1.8 trillion tons might be accessed by UCC, including some minable coal. A commercial UCC process could quadruple roughly the 450 billion tons of U.S. coal reserves, which presently are recoverable by mining. The U.S. coal resources are divided into five sectors. The two most eastern sectors contain relatively thin, swelling bituminous coals that are difficult to gasify. Of the two, the bituminous coal in the Eastern Province is the most difficult because it is deeper than , in the Interior Province and the terrain is more rugged. The sector along the Rocky Mountains contains huge amounts of thick low-rank coals that are the most promising for early development by UCC. The coal has good continuity and the terrain is suitable. Low-rank coals such as subbituminous and lignite are highly reactive and tend to shrink and disaggregate when heated. Most of the coal in the Pacific

Jan 1, 1980

By John S. Timmons, Eivind B. Jensen

The Henderson mine is an underground panel-caving molybdenum mine located in the mountains of central Colorado. All development and primary production operations are performed using diesel-powered, rubber-tired mobile equipment. The growth in manpower and equipment was rapid in the five years following the July 1976 start-up, reaching about 250 machines and 2000 people to produce 9 Mt/a (10 million stpy) of ore. However, due to dramatic improvements in productivity, production is currently at a rate of 8.1 Mt/a (9 million stpy) with about 570 people and a much smaller equipment fleet. The mine's high degree of mechanization and accompanying maintenance costs have focused increased attention on the maintenance function as a cost center with potential for improvement. To realize some of that potential, several approaches to equipment maintenance have been adopted. None of these stand alone effectively, though, and their success relies on their working together in the overall program. The approaches that characterize the equipment mainte¬nance philosophy at Henderson are described here. Preventive maintenance The value of preventive maintenance as an alternative to breakdown or emergency repair is widely accepted in industry. When production began in 1976, few people at Henderson had experience maintaining diesel-powered, rubber-tired equipment. Other company operations such as its previous Urad operation and the Climax molybdenum mine near Leadville, CO used rail and Blusher technology. A maintenance consultant was hired to establish a formal preventive mainte¬nance program. The initial program contained four different preventive maintenance services, "A," "B," "C," and "D." Each was keyed to a different operating interval. • "A" service was the most frequent. It was a quick, general inspection and greasing of all fittings. •"B" service added a more detailed inspection. • "C" service included changing all filters and most fluids, such as engine oil. • "D" service was originally designed as a comprehensive inspection and testing of major component systems over a period of 24 hours during which the equipment was removed from operation. It was believed that most problems uncovered by the inspection could be reported and scheduled for repair at some later date, with only critical repairs being done during the service. In addition to these scheduled preventive maintenance services, a schedlle of minor and major rebuilds at intervals of 2500 to 5000 hours was established.

Jan 1, 1989

By R. L. Loofbourow

In addition, dewatering is seldom complete because of aquifer irregularities and an operator's natural reluctance to start a costly study program, provision of wells, and pumping long before mining begins. In some cases, water pumped from the mine is used in treatment. This use is suggested as a way to minimize effluent effects. The true objective of water supply, however, is to provide water of satisfactory quality at the rate needed and at the least cost. Pumping to permit efficient mining isn't likely to coincide strictly with that objective during much of the mine life. The history of mining is replete with efforts, some highly ingenious, to control mine water. Methods that might be used to tackle the challenge Operators of wet mines are faced with both obvious pumping costs and some unquantified water costs. It is possible to reduce both types of costs, generally by reducing inflow to the mine area-and a surprising number of methods have been used to do this. Both the obvious and unquantified costs at a wet mine are now multiplied by: •Increasing costs of power, labor, equipment, and supplies; •Work at greater depth and, in some cases, in wetter ground; •Increasing use of hydraulic fill; and •Increasing zeal in protection of surface and groundwater quality. There are many easily overlooked ways in which mine water may add to hazards and costs (Loofbourow, 1973). As to their importance, consider these examples: •Increased maintenance of equipment, tires, roads, and ditches; •Increased difficulty in supplying proper ventilation; •Increased hazards from ice and use of electric power; • Loss of friable ore minerals and fines stuck on conveyances and in chutes; •Need to use more expensive methods and explosives; and •Decrease productivity of equipment and personnel. Expressed as cost per unit of ore produced, these unquantified costs can be high. Ideally, advanced dewatering should eliminate most of them. Advanced dewatering is a highly effective water control method, but it isn't problem free. Mines in ideal ground for advanced dewatering are most unusual. To be effective, water must be pumped at a comparatively high rate for a period longer than the life of the mine, from below mining depth. Effects on both groundwater and surface water are likely to be drastic. of increasing mine water costs are listed in the accompanying table. Ten groups of possible methods are cited. Most have been demonstrated in mining; two are known from industries other than mining.

Jan 12, 1980

By Cyril W. Draffin

Introduction Americans have long been proud of their ability to recognize a need, define it, and then develop workable solutions. The U.S. underground coal conversion (UCC) program is a good example. In 1974, the need to utilize coal resources that could not be mined was recognized, and Congress gave the Bureau of Mines $1.7 million to gain a better understanding of the UCC technology and its potential applications. Since 1977 when the U.S. Dept. of Energy (DOE) was formed, workable technologies have been tested, the market for underground coal conversion has been recognized, and extensive industrial interest has developed. Perspective The U.S. is blessed with extensive coal resources. Coal supplies about 19% of our national energy needs, yet recently promulgated environmental standards and increasing mining costs have limited direct coal use. UCC potentially can use coal that is economically or technically infeasible to mine because the coal is too thick, deep, dirty, high-ash, and wet; has an excessive angle of dip; or has unpredictable and poor over-burden characteristics that make mining unsafe. Coal can be gasified underground or perhaps liquefied below the earth's surface. Underground coal gasification (UCG) is the prime element of the underground coal conversion program. It enables coal to be converted to gas underground. UCC Coal Resource Recent data show a total U.S. coal resource base of about 6.4 trillion tons. Of this, 1.8 trillion tons might be accessed by UCC, including some minable coal. A commercial UCC process could quadruple roughly the 450 billion tons of U.S. coal reserves, which presently are recoverable by mining. The U.S. coal resources are divided into five sectors. The two most eastern sectors contain relatively thin, swelling bituminous coals that are difficult to gasify. Of the two, the bituminous coal in the Eastern Province is the most difficult because it is deeper than in the Interior Province and the terrain is more rugged. The sector along the Rocky Mountains contains huge amounts of thick low-rank coals that are the most promising for early development by UCC. The coal has good continuity and the terrain is suitable. Low-rank coals such as subbituminous and lignite are highly reactive and tend to shrink and disaggregate when heated. Most of the coal in the Pacific

Jan 9, 1980

By William Hodder, Lisa Smiley, Ehsan Alav

The Don River & Central Waterfront Coxwell Sanitary Bypass Tunnel (CBT) Project in Toronto will extend approximately 10.5 km and be lined using a precast concrete segmental tunnel liner with an internal diameter of 6,300 mm and external diameter of 6,900 mm. The CBT liner was grouted through ports drilled in the segments. The Westerly Storage Tunnel (WST) in Cleveland will extend approximately 2.93 km long and will be lined by using a similar precast concrete segmental tunnel liner with an internal diameter of 7,620 mm and external diameter of 8,230 mm. The WST liner was grouted using both grout ports built into the tail can of the TBM and through segments. Each tunnel was mined primarily in shale with varying levels of weathering and both tunnels had dry and wet sections. This paper will document the means and methods for grouting in each tunnel as well as the methods utilized to proof grout and the results found.

Jun 13, 2021

Horizontal stress is an important factor that contributes to roof failure during a long wall entry development, especially when the immediate roof is weak. In this study, the effects of the three factors, the stress angle between the maximum horizontal stress and entry development, the stress ratio of the maximum to the minimum horizontal stresses, and the sequence of entry development, on the stress distributions in the weak immediate roof of a three-entry system are analyzed using the finite element method, when the horizontal stress is fixed. The results have confirmed that the stress angle has a significant influence on the stress distributions. Generally, the three-entry system is in the worst stress condition when the angle is about 60°_75°. The stress ratio has little effect on the roof stresses. In addition, the sequence of entry development has also little effect on the roof stress for the specific case analyzed.

Jan 1, 1999

By A. S. Ibrado

The adsorption of silver on activated carbon from cyanide solutions was studied as a function of concentration, ionic strength and pH. In cyanide solutions, silver exists mainly as the linear Ag(CN)2 complex and adsorbs on activated carbon following the Freundlich isotherm. The uptake and rate of adsorption increase with the addition of KC1 and KNO3 but changes only slightly with pH. In contrast, the adsorption of Cu(I), Zn(II), Cd(II), and Hg(II) shows marked changes with pH, closely following the predominance profiles of their neutral and singly-charged cyano complexes. Clearly, multicharged negative complexes are repelled by the negatively-charged carbon surface. This sensitivity of activated carbon to the charge of the adsorbing species indicates that silver adsorbs as an anion, not chemically bound to the co-adsorbing counterions. For the same reason, activated carbon is selective to metals that form neutral and Singly-charged cyano complexes, namely gold and silver.

Jan 1, 1988

By E. A. Domínguez

Kaolin deposits of Patagonia (Argentina) were formed by ?in situ? alteration of volcaniclastic rocks or by erosion, transportation, and deposition of residual clays in small basins. The mineralogy, geochemistry, grain size distribution, and specific surface area of natural and washed kaolins were studied in order to point out the relationships with the ceramic process. Primary kaolins are coarse-grained, kaolinite+quartz±halloysite, with a very low specific surface area. Sedimentary clays are either kaolinitic?smectitic and very fine-grained or kaolinitic with a coarser particle size distribution. An interdependence between mineralogy, chemistry, particle size distribution, texture, surface activity and ceramic behavior was found. Plasticity is strictly dependent on surface activity and expandable clay minerals. Slip rheology is affected by soluble salts, smectite, and tubular halloysite. Kaolinite-halloysite play an opposite role versus smectite-I/S in slip casting and tile pressing. Kaolinite and quartz are beneficial for drying behavior while expandable clay minerals increase drying sensitivity. Firing behaviour is mainly affected by minor components supplying fluxing oxides.

Jan 1, 2010

By B. R. T. Simoneit

The formation of petroleum is normally thought of as a geologically lengthy process, involving the accumulation of organic matter, its gradual burial, diagenetic breakdown via geochemical reactions, maturation, heating within a 75-150'C "oil window" induced by normal geothermal gradients in the subsiding basin, and slow product migration into structural traps (Tissot and Welte, 1984, Hunt, 1979). The entire process can take millions of years and, indeed, most oil reservoirs probably formed in this manner. How-ever, today in sedimented, submarine rift basins (Fig. 1), Cl to >C40 hydrocarbons with the chemical and physical properties of crude oil are forming in demonstrably much shorter time by rapid thermal maturation of immature organic matter in hydrothermal regimes that are unusually high for sedimentary basins (Brault and Simoneit, 1988a, b; Didyk and Simoneit, 1988; Kawka and Simoneit, 1987; Peter et al., 1988; Simoneit, 1983; 1984; 1985a,b; 1988; Simoneit et al., 1984; 1987; 1988).

Jan 1, 1989

The objective of this international conference was to assist the mining and minerals industries in their global transition to sustainable development. The main theme of the meeting, therefore, was the development, monitoring and assessment of sustainable development criteria for mineral operations. Emerging technologies that can assist in the development of criteria and performance measurements were also presented at the meeting. A goal of the conference was also to conclude with a consensus plan and a process, representing a variety of stakeholders, which can provide guidance to the global minerals community on the path to sustainable development. A number of papers were not submitted in time to be included in the printed proceedings. Hence this addendum was compiled and includes last minute paper submissions. The pages of this addendum are numbered consecutively to the main volume of proceedings, so that when a reference is made to a paper, a proper page number may be quoted.

Jan 1, 2003

By Milton E. Wadsworth, Jeffrey S. Thompson

The effect of an activator on gold dissolution in clear solution is examined using a rotating disk gold electrode. Steady state polarization curves for anodic dissolution of gold and cathodic reduction of oxygen indicate that the dissolution rate increases in the presence of the activator. The activator enhances gold disso­lution under standard cyanidation conditions; however, optimum activator concentration at the maximum dissolution rate is a function of the cyanide level. In the presence of an activator, the gold dissolution mechanism is controlled by surface kinetics and may be explained by a metal dissolution over-potential model. The dissolution rate with activator is higher than the dissolution rate at a higher cyanide concentration but without activator. The dissolution rate measurements indicate that 3 PPM of activator in a 500 PPM NaCN solution provides a higher dissolution rate than 1000 PPM NaCN alone. Activator technology may be a cost-effective means to reduce cyanide concentration.

Jan 1, 1998

By Gail I. Bakker, Mark E. Smith, George Sintay, Allan Young

The Snow Caps mine was an open pit and conventional cyanide heap leach gold project located 10 Km east of Independence, California in the Owens Valley. The project is unique in that it is one of the first projects to go full-cycle, from design through closure, under California's Chapter 15 mine waste regulations adopted in 1984. The property was acquired by Sunshine Mining Company in 1985. During 1986, final design and permitting were completed and the facility was commissioned in 1987. Mining continued to mid - 1990, when the minable ore body was depleted, and heap leaching continued into early 1991. Rinsing of the spent ore was completed in 1991, and final closure will be complete in 1992. The spent ore will be left on the leach pad for its final disposition. The focus of this paper is the permitting and closure aspects of the project as required by California's Chapter 15, Article 7 regulations.

Jan 1, 1992

By P. R. Altringer, R. H. Lien, B. E. Dinsdale

The Bureau of Mines, U.S. Department of the Interior, is investigating biodegradation of cyanide as a means of decommissioning heap leach operations. Biological oxidation decreased weak acid dissociable (WAD) cyanide in process solutions from 50 to 170 ppm down to 0.1 ppm. The tests were conducted both in trickling column reactors, using quartz as the growth surface, and in upflow columns, using activated carbon as the growth surface. In addition, exploratory tests indicated that bacteria will destroy residual cyanide in leached ore. A flowsheet has been proposed for closure of heap leach operations in which the metals processing portion of the plant, possibly the carbon adsorption columns, or a collection pond is used as a bioreactor. The cyanide in the process solution is destroyed in the bioreactor and the treated water is used to rinse residual cyanide from the spent heaps. The water is recycled until the effluent WAD cyanide concentratio� meets discharge standards.

Jan 1, 1992

By John E. Litz, Charles W. Kenney, Wayne Carter

Refractory gold ore pretreatment processes continue to receive much attention. This paper compares the relative economics of treating ores by oxygen pressure oxidation, roasting and bacterial oxidation with or without preconcentration by froth flotation. Capital and operating cost estimates for each method of pretreatment were prepared and these estimated costs and ore sulfide grades then are used to compare the process economics. The study indicates that the most significant item affecting the economics is the amenability of the ore to flotation. The cost benefits of flotation are $10-13 per tonne ore processed (2%-4% s=, 10:1 ratio of concentration). In most cases bacterial oxidation has the lowest overall cost, especially if less than complete oxidation of the sulfides will give acceptable recovery, however bacterial oxidation has yet to be practiced on a large scale. In all situations pressure oxidation shows the highest cost. However, the cost differences between the treatments are small, less than $7 per tonne.

Jan 1, 1990