Search Documents

By V. K. Karra

An improvement in the present day screen sizing methods calls for knowledge on i) how material in the size range: 0.5 x 1.5 times the through-fall opening of the mesh on a deck, splits between the oversize and undersize streams of the deck, and ii) how near-mesh content of the feed affects the screening performance. In the throughput based sizing method given here, this is accomplished through the introduction of a generalized partition curve and a near-mesh factor. A newly developed efficiency factor is employed in addition to the traditional screen sizing factors.

Jan 1, 1979

By Pramod C. Thakur

During the past ten years, the US coal industry has experimented with various ways to extract methane from coal seams. Drilling long horizontal boreholes in solid coal from mine workings and vertical gob degas boreholes are becoming standard techniques for methane recovery from coal seams. Prime motivations for such work have always been safety and productivity in mines, but the commercial value of gas so produced is encouraging utilization. The paper reviews various ways to produce methane from coal seams and discusses some utilization projects extant in the industry.

Jan 1, 1984

By J. B. Goddard

Abstract. Leaching of, uranium in situ from sandstone deposits with ammonium carbonate solution containing: dissolved oxygen occurs rapidly compared with the leaching of the bulk of the sulfur present as FeS2. However because of their high reducing, capacity and their relative abundance, the FeS2 minerals consume; the bulk of the oxidants A pressure leach apparatus was-construtted which permitted the measurement of oxygen consumtion by FeS2. Oxygen consumption by FeS2 is best described by a first-order reaction. The experimental rate constants for various cores are roughly proportional to their FeS2 contents.

Jan 1, 1980

By B. K. Cantrell

A miner working in an underground coal mine with diesel equipment is exposed to a wide array of pollutants from the diesel exhaust. These include CO, CO2, NO, NO2, SO2, diesel-exhaust aerosol, and a variety of hydrocarbon compounds. A quantitative definition of the health risk resulting from these exposures remains elusive, but during the past several years, progress has been made in defining the problem. Results from epidemiological studies by Garshick, et al. (1988); animal inhalation studies by Mauderly, et al. (1986); Iwai, et al. (1986); and Brightwell, et al. (1986); and in vitro studies by Lewtas, et al. (1986), have provided sufficient data for the National Institute of Occupational Safety and Health (NIOSH) to recommend that "whole diesel exhaust be regarded as a 'potential occupational carcinogen,' as defined in the Cancer Policy of the Occupational Safety and Health Administration," NIOSH (1988). NIOSH further stated that "though the excess risk of cancer in diesel-exhaust-exposed workers has not been quantitatively estimated, it is logical to assume that reduction in exposure to diesel exhaust in the workplace would reduce the excess risk."

Jan 1, 1990

By Charles Banks Belt

In 1925, Niggli (1925, pp, 1-69), formulated a physico-chemical, explanation for the origin of hydrothermal ore deposits, from a concept that had appeared earlier in the literature in the writings of Von Groddeck, Stelzner, Beck, de Launay, Kemp, and Lindgren. Niggli proposed that pressure at depth could force volatiles from deep-seated magmas. The volatiles would In turn form pegmatites and then ore deposits as the fluids cooled. This is one view of a general theory of ore genesis that gained secondancy for years among such prominent geologists as Fenner (1926, p, 697) and Emmons (1936, pp. 29-70). It was, proposed that ore deposits were precipitated from solutions or fluids that had escaped or been separated from a deep-seated magma by means of liquid immiscibility or crystallization or gas transfer. This theory is based on the presence of igneous rocks close in space and age to hydrothermal ore deposits in many mining districts of the world. As is well known, there are many ore deposits apparently of hydrothermal origin that are neither spatially nor chronologically related to igneous rocks, In still other localities where there are no hydrothermal ore deposits, igneous rocks occur that are similar in composition to those in mining districts. In view of such facts, the applicability of the Niggli theory to all hydrothermal ore deposits may well be questioned. The chief purpose of this paper is to test the Niggli theory by studying the primary petrology, hydrothermal alteration, and distribution of copper and zinc in silicic igneous plutons supposedly genetically related (in the Niggli sense) to nearby hydrothermal ore deposits, Silicic Tertiary plutons in three New Mexico mining districts were chosen, the Hanover-Fierro intrusive at Hanover and Fierro, the Granite Mountain pluton at Magdalena, and the four outliers of the Lordsburg stock at Lordsburg. First, it had to be established whether the observed plutons were or were not the source of the adjacent ore deposits. This was done by studying the relation between the copper or zinc distribution-and the primary or secondary features in the plutons studied, and the time relations between instrusion and ore deposition. Primary igneous features of a pluton are defined as the minerals, texture, shape, and character of the pluton which were formed prior to the complete solidification of the rock, secondary features include all changes that took place in a pluton after solidification. They are identified by their cross cutting nature or as replacing primary minerals, Under the Niggli concept, it is proved that the ore ions did not originate from the parts of the pluton now visible as immediately adjacent to the ore deposits; it must then be established, if possible', that the ore ions were separated from deeper parts of the intrusive, Some idea as to whether the copper or zinc ions originated from a related magma at depth may be gained by a comparison between the primary (that is, pre-alteration) zinc and copper abundances found in ore localizing intrusive studied and the average abundances for copper and zinc in silicic igneous rocks most recently given in the literature. Finally, the relation between ore deposition and hydrothermal alteration was studied on a regional as well as on a local scale.

Jan 1, 1958

By C. B. Daellenbach

The influence of reduction roasting and thermal shock on the grindability of a refractory low-grade Michigan iron ore was examined in bench scale tests. The quantitative effects of the various treatments were evaluated at three sieve levels: 48, 100, and 400 mesh, using ball mill grindability and work index parameters as response indicators. Data from the testing program were analyzed statistically as a means of isolating the effects of cooling rate, roasting temperature, and ore chemical condition. All three variables were found to have an important influence on the grindability of the treated ore; ore chemical condition and roasting temperature had the most pronounced effects.

Jan 1, 1970

By Dianne C. Marozas

The U.S. Bureau of Mines is conducting research to evaluate the potential for developing an in situ leach mining process that will selectively extract manganese from oxide ores, leaving gangue relatively undisturbed. To accomplish this, a geochemical approach, based on deposit-specific information such as mineralogy and geology, is used to constrain the operating parameters of the system. Among the studies being conducted are (1) leaching experiments to define reaction mechanisms and kinetics, (2) detailed petrologic characterization at the microscopic scale to assess Mn distribution and leaching efficiencies, (3) deposit characterization and evaluation, and (4) development of potential Mn recovery schemes. Data from these studies are being used to develop engineering design information for an in situ mining process. Specific details of the Bureau's research project are discussed, including results obtained to date.

Jan 1, 1991

By P. H. S. W. Kulatilake

The presence of discontinuities strongly affects the mechanical and hydraulic behavior of rock masses. Joint geometry networks play a vital role in civil, mining, and petroleum engineering projects associated with jointed rock. The need for a realistic representation of joint geometry in rock masses has been recognized. The first part of the paper shows how to build three-dimensional stochastic joint network schemes and also shows how to perform validation studies for these schemes using joint data from the Stripa mine, Sweden. Due to the existence of complex joint patterns, mechanical behavior of jointed rock masses usually exhibit scale effects and an-isotropic properties. A correct understanding of the mechanical properties (strength and deformability) of jointed rock masses is important for designing and performance estimation of structures build in and on rock masses. Beyond a certain volume, the mass proper-ties of the rock may remain essentially constant with respect to the effect of joints. This minimum volume may be used as the element size to represent the equivalent properties of a statistically homogeneous rock mass volume which contains a significant number of joints. This volume may be termed as a "Representative Elementary Volume" (REV) and may be of great importance for engineering purposes. Investigations are underway at both the 2D and 3D levels to look into the possibility of establishing relationships between REV mechanical properties and joint geometry parameters. Recently developed joint geometry modeling schemes are linked with existing distinct element codes (both 2D and 3D) to create a stochastic/deterministic stress analysis approach in achieving the goal. Results obtained so far in this direction are presented in the second part of the paper.

Jan 1, 1992

By Robert W. Row

Advanced physical coal cleaning processes that are now under development may remove significantly greater fractions of pyritic sulfur and ash than do commercial coal cleaning processes at comparable heating value recoveries. These processes may be useful for reducing sulfur dioxide emissions from electric utilities and other emission sources. However, little work has been done to determine their applicability to any major coal market. The northeastern states of the United States are interested in burning more coal, but with further sulfur dioxide emission restrictions. Their nearest coal sources are relatively high sulfur Northern Appalachian coals. The project discussed in this paper, which is scheduled to be completed in June 1985, has the objective of technically and economically evaluating various coal supply scenarios involving five selected advanced physical coal cleaning processes; and comparing the economics of them with alternative fuel supply options open to the northeastern users.

Jan 1, 1985

By Pramod C. Thakur

Coal is a major source of energy in the world today and will, undoubtedly, continue to be so for the next few centuries. Naturally, a great number of studies has been made of its physical and chemical properties. Unfortunately, the work on technical properties which influence the mining of coal and the consequent yield of inflammable gases and respirable dust particles has not progressed at a comparable pace. Coal is a brittle material. Irrespective of the mechanism of breaking coal, some dust is always produced. In mining parlance dust is defined as solid particle, smaller than 100 microns (micron = 10-6 meter), in size Coal dust, when raised into a cloud, creates two well known hazards in mines, namely, the coal dust explosion and Coal Workers' Pneumoconiosis (CMP). The latter is, perhaps, the greatest environmental hazard in U.S. coal mines today. In this context it is not only natural but also necessary to investigate the proneness of a coal seam to respirable dust production. It has been established that the amount of dust produced is a function of two groups of variables (1), (2), viz. (1) Material dependent variables, e.g., moisture content, compressive strength, hardness, etc. (ii) Breaking mechanism dependent variables, e.g., type of machine, depth of cut, etc.

Jan 1, 1973

By Mustafa Akser

Dwindling economic deposits of rutile (TiO2) prompted research on recovering it from secondary sources. One such resource is in Southwestern Turkey feldspar mining rejects that contain 5%-6% TiO2 mostly rutile. Previous studies could only upgrade the TiO2 to 36% TiO2 grade, claiming that the leftover flotation reagents on the surfaces of rutile and host minerals detrimentally affected upgrading of the rutile. As a potential remedy to this concern, a laboratory sample (from an operating feldspar mine in Milas, Turkey) was first caustic scrubbed, then air calcined at 400°C to evaporate the oily reagents. Subsequent physical separation of rutile included wet screening, gravity, magnetic, and electrostatic separation technologies. Such processes indeed improved the grade of the rutile concentrate up to 83 % TiO2 Low recovery of the TiO2 (<20%), was attributed to lack of full liberation of rutile, even at 125x44 micron range; interference with impurity minerals such as sphene and zircon; and simply the process inefficiency in upgrading the fine grains through conventional separation technologies for heavy minerals.

Jan 1, 1999

By Todd Clarke, Ralf Winterberg

For more than a decade the tunneling industry has explored the potential and benefits of macro synthetic fiber (MSF) reinforced concrete solutions for precast tunnel segments. Parallel to industry investigations, academic research is being undertaken to better understand this material when subjected to the typical loads expected during mechanized tunneling. This paper investigates the performance of MSF reinforced precast concrete tunnel segments by means of an experimental program comprising testing of full-scale tunnel segments. The presentation of the satisfactory results of the experimental testing regime will be complemented by a brief case history from a successfully executed project—an America’s First.

Jun 13, 2021

Sedimentation is used to clarify process effluents or to thicken process slurries. The sedimentation cycle of a suspension is presented as a settling curve. This curve is simply a plot of the height of the interface between the settled suspension and clear liquor versus time. Figure 1 shows a series of graduate cylinders which contain a suspension at various stages in its settling cycle. Cylinder 1 shows the suspension completely mixed at time zero. After a brief period of time (see cylinder 2), the suspension is observed to settle from its initial height Ho to height H1, leaving behind a volume of clear (or turbid) liquor, called the supernatant. The interface between the supernatant and suspension is termed the mud line. It is also possible to distinguish at the bottom of the cylinder a layer of sludge representing solids which have settled from the suspension. The interface between it and the suspension is called the sludge line. The sludge line moves upward in the cylinder.

Jan 1, 1992

By Horst H. Gielen

Bong Mining Company/Liberia provides the rare opportunity to compare two generations of grate kiln pelletizing plants operating on the same magnetite/hematite ore basis. In this paper advantages and drawbacks are compared: mechanical aspects, energy-savings, pellet quality. Plant I with up- and down-draft drying gas flow. Plant II runs only on down draft drying and incorporates a heat-recoup system. Ferteco Mineracao/Brazil operates a Lurgi straight grate plant since 1977 on hematitic pelletfeed. Energy-political situation and char- coal as energy source in Brazil are reflected also in the search for alternative fuels for pelletizing. First measures and results are reported as well as intended further steps towards a 100 % oil replacement.

Jan 1, 1983

By John B. Goddard

The discovery of rhenium on the ion exchange resin used at the uranium in-situ leach operations at Palangana (Texas) led to a laboratory study on the possible methods of recovery. Rhenium, present in small amounts in the ammonium carbonate leach liquors as the perrhenate anion, Re04-, concentrated on the anion exchange resin, which was a factor of ten more selective for rhenium than for uranium. Various elution systems were investigated for stripping the rhenium from the columns after the uranium had been eluted with chloride or nitrate solutions. Although the perchlorate ion was most efficient on a molar basis, nitrate ion combined the benefits of efficiency and low cost. A 3[N] or stronger concentration of nitrate containing up to 0.5[N] H+ was found to be the system of choice. A rhenium sulfide concentrate containing up to 14% Re was obtained from these effluents by hydrogen sulfide precipitation. Preliminary experiments were run to produce rhenium metal powder by oxidation of the concentrate to NH4Re04 followed by hydrogen reduction at elevated temperature.

Jan 1, 1982

By C. R. McKee

In-situ mining of hard rock deposits will only become successful as we understand the engineering parameters involved and the design limitations they impose. As recognized by Wadsworth1 the most critical area is the enhancement of permeability in a hard rock mass. Along with creating permeability, the appropriate flow and fragment size conditions must be generated to insure economic rates of mineral recovery. In this article our interest is confined to true in-situ processes in which boreholes are drilled from the ground surface or a mine drift to deeper strata. We assume that fractures and permeability enhancement will be due to explosives detonated in boreholes. Other techniques such as hydraulic fracturing do not produce the necessary size distribution to promote economic extract ion rates unless the medium is already highly fractured and interconnected. Notable exceptions where hydraulic fracturing is applicable are many oil, gas and salt deposits. For many in-situ processes, an array of explosive charges offers the opportunity of creating a distribution of many fractures not achievable by other techniques. Such a situation would be suitable, for example, to in-situ mine hard rock gold, uranium, copper or oil shale deposits and may enhance oil and gas recovery in certain situations. The purpose of our article is to review and extend the explosive permeability theory of McKee and Hanson 3,4,5 and to apply its results to derive design parameters suitable for in-situ mining.

Jan 1, 1981

By John J. Stetler

The Companhia Vale do Rio Doce in Brazil operates one of the most extensive systems in the world for the mining, transportation, processing, pelletizing and shipping of high grade hematite iron ore and pellets. Current shipping of unbeneficiated, sized, high grade ore from its ports at Tubarão and Vitória is now at the rate of 17,500,000 metric tons annually. An increase in this annual rate is now under study. Using the technology and facilities of Lurgi (1) and Arthur G. McKee company CVRD undertook a program to process and pelletize two types of fines - "Blue Dust" and ?Itabira Fines?. Blue Dust is a high grade fine ore which was bypassed while mining the direct shipping ores and which, also, exists as a very large ore body called the Conceição Mine. Itabira Fines is a lower grade of fine ore which is comprised of in-situ fines and, also fines which are generated in sizing the direct shipping ores for a rigid specification market.

Jan 1, 1970

By A. Pomianowski

A spectrophotometric study of xanthate solutions alone and their mixtures with equimolar amounts of alkyl trimethyl ammonium bromide (CnTAB) has established the additivity of ultraviolet spectra (190 - 400 my) for potassium ethyl xanthate (KEtX) and C12TAB. No obvious effect of C12TAB addition on the decomposition rate of KEtX was observed. The kinetics of collector abstraction by copper, nickel and sphalerite powders were studied in 10-5 - 10-3M solutions of KEtX alone and in equimolar mixtures of KEtX and C12TAB. Presence of C12TAB caused a 2 - 3 fold increase in the amounts of xanthate (equivalent to many monolayers) abstracted by copper and, nickel powders but had no effect on the abstraction of xanthate by unactivated sphalerite. The adsorption of C12TAB itself from the mixed solutions was very low, at most ore monolayer only, and was not influenced by the nature of the solid powder used. The results are interpreted in terms of molecular associations and synergistic action of xanthates and quaternary amines.

Jan 1, 1963

By Wern-Ping Nick Chen

Durability risks for underground facilities can be underestimated during design phase as compared to well-known geological risks. However, unclear durability requirements can result in construction schedule delay and change orders. Unlike bridges or buildings, a unified underground durability code or standard does not exist. This paper will provide a durability approach for underground facilities, including degradation modes, mitigations, and compliance measures during construction. In addition, this paper will address how to clearly specify durability requirements in a contract document to reduce disputes during construction and discuss key durability tests that are time consuming and will impact construction schedule if not timely planned.

Jun 23, 2024

By G. E. Mellor, R. E. Lippoth, T. B. Faddies

The Little Rocky Mountains host epithermal- gold-silver bearing vein and stockwork deposits in a syenite intrusive complex. Pegasus Gold Ltd. is currently mining these oxidized deposits by open-pit methods and recovering gold and silver by heap-leach processes. A geologic program has been designed to effectively determine the basic ore characteristics; 1) mineralization; 2) oxidation; 3) structural setting; 4) lithology; 5) alteration; and ultimately, 6) the leachability of the ore. Geologic mapping, sampling, drilling, assaying, and testing are routinely used in exploration, development, production control, mine planning, and ore reserve estimations. Timely and accurate assay results are essential for the program&apos;s success.

Jan 1, 1992