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By J. C. Agarwal

Do large-scale projects in mining and smelting start up and achieve expected capacity on schedule? In most cases not. Regardless of worldwide location, company know-how, or financial backing, unforeseen delays occur. A comprehensive CRA study for the World Bank shows that delays are the rule, not the exception, in most mining and smelting projects. When delays are not factored into analysis and planning, financial projections are, literally, not to be believed. Returns on investment will seldom achieve their targeted level because of startup delays. This paper reviews the results of our analysis of startup of new mines, mills, and smelters; provides a detailed discussion of why delays occur in the smelters and refineries; presents the cash flow implications of startup delays; and discusses preventive measures that should be taken to avoid financial shortfalls,

Jan 1, 1983

By J Centofanti, D Conti, R Riske, C Morley, A Cook

Why is it so difficult? Why are there differences throughout the resources industry in how reconciliation factors are reported and calculated? Why is there no standard formula to use? These are common questions asked when mining companies try to compare reconciliation results across operations or attempt to undertake internal or corporate governance reporting processes. For many mining companies the calculation of reconciliation factors is often a very time and resource intensive part of mandatory reconciliation reporting. Some major mining companies, that move millions of tonnes of material per annum, dedicate full time resources to the calculation of reconciliation factors. The willingness of these companies to set aside resources demonstrates the value that operations place on good reconciliation reporting. Reconciliation is about measuring the variance between two like measures at different points along the mining sequence. It can be undertaken between predictive models, forecast plans and actual measured performance. Calculations are used to derive a variance between two sections within the mining sequence, with the result being commonly known in the resources industry as a æfactorÆ. Mining companies use the calculation of reconciliation factors as key performance indices (KPIs) to provide a æhealth checkÆ of their operation, with variances often pointing to issues either with the accuracy of the original estimate or the quality of the measurement being used in the comparison. There are many reconciliation factors that can be calculated and reported. This paper will set out, clarify and provide a recommended standard means of calculating each specific factor that, where adopted by a company, will ensure compliance with the international reporting codes, such as JORC. Using case studies from Rio Tinto Group (Rio Tinto) and BHP Billiton Mitsubishi Alliance (æBMAÆ), and the authors experience across a wide range of mine sites, the outline of a generic solution for tracking a parcel of material from the pit through to the port along with appropriate reconciliation factors is provided. The intention of proposing standardised reconciliation factor terminology and methodology is to provide the foundations of a system to enable communication and comparison across different commodities, companies and mines sites.

Jan 1, 2009

By Myles E. Robinson

Significant changes in the markets for coal have taken place since World War II, As used in this study the term ?coal? will refer to bituminous coal, The anthracite industry in size, characteristics, and problems differs materially from the bituminous coal industry, These changes have both influenced and been influenced by the mechanization of mines, and by decreased distribution costs, especially in transportation. It is the purpose of this paper to examine these post-war changes, to assess their impact upon the production and distribution of coal, and to explore future market developments in the light of past and present trends and relationships. The layman lacks adequate informatian on the production, demand, and distribution of coal. There are two reasons for this. First, there is a relative lack of statistics coveting the industry, Coal operators and distributors are not required to file with any government agency the type of much more complete statistics filed by the railroads and public utilities with national and State agencies. The Bureau of Mines assembles much useful information on the coal industry, but several areas, including that of investment and finance, have no central depository which can be used to keep the public informed of the nature and extent of the industry and its problems.

Jan 1, 1964

By F. L. Ransome

The following paper aims to present in a much condensed form the salient results of a detailed geological study of the Bisbee quadrangle, Arizona, carried on during the latter part of the year 1902. It is essentially an abstract of the final official report which will shortly appear in the series of professional papers of the U. S. Geological Survey, accompanied by maps, sections and illustrations. I. Geography. The Bisbee quadrangle, which includes the Warren mining district, lies in Cochise county in the southeastern part of Arizona. It is inclosed between the meridians 109" 45' and 110" 00' and the parallels 31" 30' and 31" 201, the latter being locally the Mexican boundarg line. The area of the quadrangle is about 170 square miles, and includes the southeastern half of the Mule Mountains, one of the smaller of the isolated ranges characteristic of this part of Arizona. The Mule Mountains, while less markedly linear than the Dragoon, Huachuca, Chiricahua, and other neighboring ranges, have a general NW-SE. trend. They may be considered as extending from the old mining town of Tombstone to the Mexican border, a distance of about 30 miles. On the northwest they are separated by the broad, flat floor of Sulphur Spring Valley from the Chiricahua Range, and on the southeast by the similar broad valley of the Rio San Pedro from the Huachuca Range. The maximum width of the range is about 12 miles, and its greatest elevation attained by Mt. Ballard, west of Bisbee, is 7,400 ft. above sea-level. An index-map, showing the geographical position of the Bisbee quadrangle, is shown in Fig. 1. The town of Bisbee (Fig. 2), with an estimated population of 6,000, is crowded into a few narrow confluent ravines near the

Jan 1, 1904

By A. Tosun

"The size distribution of the muckpile formed as a result of open pit blasting operations has a considerable effect on the efficiency of loading, hauling, and crushing. Various researchers have developed specialized computer software that uses image analysis methods for determining the size distribution of the muckpile. However, these methods have some limitations. One of the most important of these limitations is that the very fine fragments in the muckpile cannot be used in the size distribution calculation. In this study, 18 test blasts in total were carried out in two limestone quarries belonging to Batiçim Corp. in Izmir, Turkey. A new model was developed in order to ensure that very fine fragments are used in the size distribution calculation. The size distributions of the test blasts were calculated by both the Wipfrag computer program and the new model. Correlations were established between the muckpile size distributions determined by both methods and the parameters determining the efficiency of the loader. IntroductionThe size distribution of the muckpile formed as a result of open pit blasting operations has a considerable effect on the efficiency of loading, hauling, and crushing. Various researchers have established certain correlations for predicting the efficiency of the operations according to the muckpile size distribution so that production can be carried out economically (Tunstall and Bearman, 1997; Nielsen and Kristiansen, 1996; Workman and Eloranta, 2004; Michaud and Blanchet, 1996; Frimpong, Kabongo, and Davies, 1996; Osanloo and Hekmat, 2005; Molotilov et al., 2010). In these studies, the 50% passing size (X50) is generally used. These methods rely on the correct measurement of the size distribution of the muckpile formed by the blast. The most reliable measurement method would be to subject the entire muckpile to a sieve analysis, but this is obviously impracticable. Therefore, computational method based on image analysis have been developed. These include IPACS (Dahlhielm, 1996), Tucips (Havermann and Vogt, 1996), Fragscan (Schleifer and Tessier, 1996), Cias (Downs and Kettunen, 1996), GoldSize (Kleine annd Cameron, 1996), Wipfrag (Maerz, Palangio, and Franklin, 1996), Split Desktop (Kemeny, 1994), PowerSieve (Chung and Noy, 1996), and Fragalyst (Raina et al., 2002). In these methods, the size limits of the fragments forming the material are determined by image analysis on photographs of the muckpile. However, the computer software has some limitations. It does not take into account the third dimension of the muckpile, nor the size distribution of very fine fragments. In particular, the fragment size ranges below 2.5 to 3 cm cannot be determined, and therefore these cannot be included in the muckpile size distribution. However, the muckpile formed by a bench blast contains a wide range of particle sizes (Tosun et al., 2015)."

Oct 1, 2018

By Charles E. Robertson

As it becomes more and more apparent that our nation must place a great deal of reliance on coal as an energy source in the coming decades, prospecting for new reserves Un Missouri and other states in the Western Interior Region is increasing. As more and more of the known reserve becomes committed to existing or planned projects operators will be forced to look beyond the fringes of existing coal fields for additional reserves. Perplexing geologic problems invariably confront all prospectors and are particularly bothersome to those new to a particular area. It is the purpose of this paper to alert prospective operators to geologic problems likely to be encountered and to offer guidance in the recognition and solution of these problems. Particular emphasis is placed upon geologic structure and washouts. Other geologic problems have been discussed in a previous paper.

Jan 1, 1977

By L. L. Sutter

Fly ash is a by-product produced from the combustion of most hels including municipal solid waste. Currently, most combustion residuals are disposed of in landfills at a continually increasing cost and with questionable impact on the environment. Due to the presence of heavy metal compounds, municipal waste combustor (MWC) fly ash has the potential to leach these metals (e.g., lead and cadmium) above regulatory limits. The heterogeneous nature of MWC fly ash makes detailed characterization difficult. This research focuses on the identification of lead compounds in MWC fly ash. Samples obtained from the Olmsted Waste-to-Energy Facility in Rochester, Minnesota were examined in this study. The fly ash was fractionated into six size ranges and prepared as geological thin sections for analysis. The worked discussed in this paper involves using an electron microprobe analyzer to determine phase composition in MWC fly ash. In addition, backscattered electron imaging, digital image processing, and mineral liberation analysis software were used to determine phase distributions and phase associations as a function of particle size. Several lead containing compounds in several forms are identified. The results of this study show that lead can be identified in small sectioned particles which would not be apparent using normal backscattered electron imaging.

Jan 1, 1994

By W. C. Holliman

This report describes apparatus and procedure used for determining the vapor pressure of aviation gasoline in surveys of commercial aviation-gasoline characteristics made by the Bureau of Mines in cooperation with the Coordinating Fuel and Equipment Committee of the Coordinating Research Council, Inc. (CFR-CRC). The method is a modification of the Reid method, in which a mercury manor is substituted for the Bourdon-type gage of the Reid method. The method was used in earlier surveys made by the National Bureau of Standards in cooperation with the CFR-CRC, and was used in the Bureau of Mines surveys at the request of the cooperating organizations. It is designed for special research problems? particularly in vapor-lock studies, which require a precision greater than obtainable by the Reid vapor pressure method. A repeatability of + 0.01 p.s.i. average deviation from the mean may be obtained by method.

Jan 1, 1950

By Chris Roper

The Gavia Autonomous Underwater Vehicle is a two-man portable AUV that is capable of performing seafloor surveys in water depths to 2000 meters. The standard survey sensor suite includes a dual frequency side scan sonar and high resolution digital camera. Additional survey sensors are currently being incorporated into the Gavia AUV, include Sub Bottom sonar, Swath Bathymetry sonar and Multi Beam sonar. The modular design of the Gavia AUV allows the end user to quickly incorporate new sensors including client developed propriety sensors.

Jan 1, 2005

This paper deals with the application of table flotation to two unusual mineral dressing problems. Both problems involved the removal of interfering minerals at sizes too coarse to normal froth flotation.The first problem was the removal of arsenical minerals from Broken Hill gravity concentrates without further size reduction. Table flotation without grinding of the original concentrates gave almost complete rejection of the arsenic from the concentrates. A typical test result was a reduction of arsenic in jig concentrate from 0.75% arsenic to 0.007% arsenic.The second problem was to develop a method to produce a high grade calcium carbonate concentrate from coastal dune sands containing about 10% silica and about 80% calcium carbonate. The sands were about 30 mesh British Standard Screen (B.S.S.), and for economic and other reasons it was stipulated that the separation be made without grinding. Again, table flotation gave excellent results. A concentrate was produced containing 99.62% acid soluble material, representing a recovery of 98.69% of the calcium carbonate in the feed with a rejection of 96.44% of the silica.The investigations' were carried out at the Kalgoorlie Metallurgical Laboratory, under the Department of Mines...

Jan 1, 1954

By Brian Isherwood

TransCanada Pipelines, Calgary (TCPL) is one of North America's leading transporters of natural gas through its energy transmission business. TransCanada also operates significant complementary businesses in energy marketing and energy processing in North America and internationally. The main trunk pipeline crossing Canada comprises as many as six pipes, 30" to 48" diameter delivering up to 7.8 trillion cubic feet of natural gas per day. To maintain the maximum operating pressure of 1000 psi, it is necessary to provide compressor stations at 60 to 100 km spacing. One such station is located at Potter, in northern Ontario, some 80 km north of Timmins, referred to as Station 102. The station contains two compressor plants, 'A' and 'B' Each incorporates a gas turbine driven centrifugal compressor unit. 'A' Plant uses an aero-derived gas generator (jet engine) rated at 15 MW (19,000 HP).

Jan 1, 1997

By G. Van Weert, O. Wang

"As part of a general review of processing double refractory ores through Barrick Gold’s autoclaves / CIL facility at Goldstrike, blanking the preg robbing native carbon in the process solids with hard (m.p. 55 - 60 º C) paraffin wax was studied, specifically in relation to pressure oxidation. The improvement in CIL gold extraction was found to depend on the wax addition point, with hot, dry contacting of the ore in the presence of wax - prior to POX - yielding the largest, most consistent improvement in gold extraction.INTRODUCTIONDouble refractory gold ores present two barriers to gold extraction. The first is generally a physical barrier: the gold is encapsulated or dispersed in a matrix which is impervious to the gold lixiviant. In most cases, including Carlin Trend, NV, deposits, this involves a pyrite or arsenopyrite matrix, although minor gold may also be dispersed in competent silica (quartz) or iron oxides. Gold can be rendered accessible by oxidative destruction of such sulphide matrices. At Goldstrike this is practised by roasting and autoclave oxidation (Thomas, 1994). It is the latter route to which this paper refers.The second barrier refers to the actual gold recovery. Gold may be extracted from the pressure oxidized solids with cyanide, forming a gold cyanide complex. One characteristic of this complex is that it adsorbs on graphitic surfaces. This is taken advantage of on a large scale by gold millers, who use manmade activated, i.e., graphitized carbon particles to remove the gold from solution during leaching: the Carbon-In-Leach, or CIL process. The gold cyanide bearing carbon particles are larger than the ore solids and can be separately recovered by screening. Goldstrike uses the CIL technology to recover gold. The second barrier becomes problematic when the ore naturally contains graphitic orcarbonaceous material, hereafter referred to as native carbon (versus the man-made activated carbon). This material may also adsorb gold cyanide in competition with the activated carbon. Since the native carbon is ground with the ore it is much smaller than the activated carbon. Any competition between the two carbons may produce a loss of gold from the pregnant leach liquor to the process tailings. This phenomenon is called “preg robbing”. Goldstrike ores come from the Carlin trend, which is known for the occurrence of native carbon (Adams & Burger, 1998; Schmitz, Duyvesteyn, Johnson, Enloe & McMullen, 2001; Tretbar, 2004)."

Jan 1, 2012

By M. A. Schimmelpfennig, A. D. S. Gillies

M.J. McPherson Having worked on the thermodynamics of air/liquid-water mixtures passing through the surface fans of deep mines, I find this paper of great interest and congratulate the authors on producing it. There are two matters, however, deserving discussion. First, the authors have described the classical theory of fog formation with fogging occurring at "supersaturation." In fact, the process of fog formation begins well below 100% humidity. The more strongly hygroscopic nuclei in the atmosphere will attract water molecules and begin to grow at a relative humidity perhaps as low as 70%. The process is a dynamic one with both condensation and evaporation taking place throughout the mixture on microscopic liquid surfaces. As saturation is approached, the rate of condensation accelerates rapidly producing the familiar reduction in visibility. Hygroscopic nuclei are present in all natural atmospheres and under the appropriate conditions of pressure and temperature, will produce clean fogs. However, if the air is polluted by particulates from combustion or other processes then the resultant coagulation with growing liquid particles may produce dense (and sometimes photochemical) smogs. It is this process that is likely to occur in underground mines when moist air is cooled below dew point. Second, the authors have summarized very well the individual measures that might alleviate the problem. In particular, I agree that neither heating nor refrigerating the air, by themselves, provides a satisfactory solution. However, there is a combination of these that provides a neat and effective control of fog formation. This involves a small, self-contained refrigeration unit within a duct but without the usual external heat rejection facility. The air is cooled below dew point and, hence, dehumidified on passing over the cold evaporator coils. The heat from the condenser is rejected back into the air downstream from the water eliminator, as shown in Fig. 1. The duct configuration can be designed to create good mixing at the outlet. I have used a climatic simulation program to illustrate the effect, assuming a 500-m (1,640 ft) long airway of cross section 60 m2 (645 sq ft), an airflow of 9 m3/s (318 cu ft per sec), inlet conditions of 19/19.25°C (66/67°F) wet bulb/dry bulb temperatures, a virgin rock temperature of 17°C (63°F) and typical rock thermal properties for a hard-rock mine. I have also assumed that 10% of the rock surface is wet. Figure 2 shows the variation in temperatures along the airway if no measures are taken. The relative humidity remains close to 100% and condensation will occur throughout the length of the airway. Before any such installation is designed, the exercise must, of course, be repeated for each location with accurate data. However, this example demonstrates the potential of the system. The idea is not new - the principle is sometimes used in air-conditioning plants for buildings. Figure 3 shows the effect of removing 30 kw of heat by evaporator coils sited 40 m (131 ft) along the airway and rejecting that heat (plus another 10 kw of compressor and fan power) into the air at 60 m (197 ft). Condensate water is produced, at a rate of 0.45 L/min (0.12 gpm). The result of this sequential cooling/dehumidification/heating process is to separate the wet and dry bulb temperatures along the length of the airway. The relative humidity increases from 80% at the duct outlet to 92% at 500 m (1,640 ft). The airway is maintained free from fog.

Jan 11, 1983

By Maurice Lacasse, Pierre Legast

GENERAL OUTLINE For more than one hundred years, asbestos ore has been mined on Les Mines d’Amiante Bell's property at Thetford-Mines , Quebec, Canada. In 1878, the first tons of fibre were produced. The mine operated as an open pit until 1951 at a yearly production of about 330 000 mt of ore. Since 1951, the mine has operated underground using a block caving method. The mine produced 725 000 mt per year until 1978, when the rate of production was increased to 1 100 000 mt. The ore was produced entirely fm the first lift on 650 level until 1976. Then, a second lift on 950 level was put into operation to replace production facilities fm the first lift which is now exhausted. Annual fibre production is 72 500 mt with grades £ran 3 to 7. The total work force is 600 people. The host rock is a peridotite partially serpentinized. The asbestos fibre seams occur as stockwork deposit structurally controlled by talcose shear zone. The geological rock formations are heavily jointed and have a wide range of competence. Asbestos ore bodies have an heterogeneous nature which des difficult geological interpretation. THE GRIZZLY METHODS A full gravity method was used on the first level where the caved ore was drawn from finger raises onto grizzly bars spaced at 480 mn. Oversize blocks were reduced by secondary blasting. The ore fell by gravity in- to the ore pass below the grizzly chamber and was loaded into 5.7 mt haulage cars through a 1.2 m wide chute. Access to the undercut drift was fm the grizzly drift through finger raises. The undercut trough was drilled and blasted in a 1.2 m interval ring sequence into a slot situated at the end of each panel. The undercut stope was emptied through the finger raises. The undercut retreated from South to North at blast interval determined by the finger raises spacing. Fig. 1 represents the various steps involved with the grizzly method. Extraction drift dimensions were opened 1.8 m wide x 2.4 m high with anchor rock bolts and wire mesh where safety required them during excavation. Grizzly chambers were excavated at 2.4 x 2.4 x 4.6 m long on a 7.6 x 7.6 m grid spacing. Ore passes with dimensions of 1.5 x 1.5 m were developed from the haulage drift. On the extraction level, headings were drilled with jacklegs and cleaned by slusher into ore passes to the haulage chutes. The support used in the grizzly chambers was square concrete structure with 150 mn H beam reinforcement. The H beam was partially buried in the concrete and had one free face to allow for difference frequency of blast vibration between concrete and steel. The supported brow of the chamber had an opening 1.5 x 2.1 m. Ore passes were ring concreted 150 mn thick without any reinforcement. A 24 MPa compressive strength concrete was pumped and poured in pre-assembled forms. Based on the success of this method on the first level, the same layout was repeated on the second level. With the start of undercutting on the second lift, signs of deterioration were noticed in extraction drifts. At first, there was great concern as the operators were confident that standard repair techniques could cope with such a situation. An intensive program of support repair and a reduction of draw resulted. The following method of repairs were used: 1) Steel square sets of 150 mn H beam at 0.6 m intervals were installed. 2) This was reduced later to 0.3 m interval and eventually to a skin to skin steel structure. 3) Yieldable arches were introduced spaced at 0.9 m intervals, linked laterally with 150 m. H beam. 4) The yieldable arches spacing was then reduced to 0.46 m and eventually installed skin to skin. However, this support was not successful.

Jan 1, 1981

By D. S. Kingery, F. F. Kopsch

The practice of using two or more main ventilating fans is common at large coal mines throughout the coal-mining industry. To assure adequate and efficient ventilation at may mines, such multiple-fan systems are necessary. The hazards associated with interrelated ventilating currents if a fan fails are controversial, and to date little effort has been made to study this specific problem and to determine corrective measures. The obvious questions are: 1. Is there a hazard? 2. Under what circumtances does it exist? 3. How serious is it? 4. What are corrective measures? Most members of the mining fraternity agree that reduced quantities of air and changed airflow patterns introduce potential hazards, especially where gaseous conditions exist when mechanized methods are used in concentrated mining 0 The seriousness of the hazard depends on the ease with which methane accumlates in face areas or haulage roads, the quantity of methane in workedout areas, and the extent to which reversed air currents interfere with escape and recovery operations after mine fires or explosions. These studies cover three mines and give the distribution of air for the specific conditions show. Each mine probably has somewhat different airflowpressure relationships between fans. This depends on the number of fans, the

Jun 1, 1959

By E Holloway

The optimisation of an open pit mine can be broadly split into two stages, the first being the ultimate pit optimisation (and subsequent stage designs), and the second being schedule optimisation. Macroeconomic uncertainty clearly impacts on both however interrelationships do also exist. Generally, the opportunity exists for the ultimate pit to be revised during each planning cycle, however when this reprieve is removed the uncertainty for the underlying business increases. As one example, the introduction of an in-pit waste dump can be seen to significantly limit the option to revise the ultimate pit. When in this situation there are two potential risks that present: (i) the long-term price used for the ultimate pit selection is optimistic, and too large of a pit is selected resulting in waste being mined which uncovers material not of a significant value to deliver a profit; (ii) the long-term price used for the ultimate pit selection is pessimistic, too small of an ultimate pit is selected, and ore of realisable economic value left behind. Both of these outcomes are risks and as such can be assessed and quantified. CITATION: Holloway, E, 2018. Incorporating economic variability into a strategic planning framework, in Proceedings Complex Orebodies Conference 2018, pp 88–90 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Nov 21, 2018

Safe, efficient production is a common objective for all large open pit mines. Despite comprehensive policies, procedures and regulations aimed at protecting workers, several people die each year in mining equipment-related collisions. The limited sightlines of heavy equipment operators coupled with difficult operating conditions are major contributing factors to the majority of mining equipment collisions. Off road haul trucks are the most common type of machinery involved in surface accidents. These vehicles represent the primary target for improving safety performance by mine operators. Although several commercial products have been introduced to address these issues, none have achieved significant market acceptance. The current collision avoidance solutions lack integration with onboard fleet management and equipment health systems. To achieve acceptance in industry, any collision avoidance system must offer high reliability, minimal false alarms, and value for money. With these criteria in mind, this paper will examine the pros and cons of the various technological approaches to collision avoidance in an open pit mining environment. The unique global positioning systems (GPS) and camera-based proximity detection solution on offer from Modular Mining Systems will be described. This solution uses intelligent filters to minimise false alarms. Tight integration with fleet management provides context information to enhance warnings and enable back-office near-miss analysis. Available today, this combination creates a practical solution to improve the situational awareness of heavy equipment operators, at a compelling price point. Future directions for maximising heavy equipment operator situational awareness will also be examined.

May 1, 2010

By Linn Bradley

F. H. WILLCOX, Pittsburgh, Pa. (communication to the Secretary*). -We must keep in mind, in balancing the savings-to be anticipated by the most efficient combustion of gas, the best heat absorption by stoves or boilers, and by heat conservation of the thermal equivalent carried in. blast-furnace gas-against the cost in operation, maintenance, depreciation and interest charges of the equipment required to realize the savings, that in boilers and hot-blast stoves we are basing our economies upon two different, combustion phenomena. In a boiler, evaporating water at a heat efficiency of 70 per cent., approximately 47,550 B.t.u. is consumed per boiler horsepower. Taking the blast, furnace gas cited in the above paper, we are using about 38 ¾ lb. of cold-washed gas per boiler horsepower. Using the hot-cleaned gas, the same equivalent heat is furnished by 34 1b. of the gas , This leaves of the 38 ¾ lb. required in the case of cold-washed gas, 4 ¾ lb. or 6,650 B.t.u. available for raising more steam when dry-hot gas is used, which means that an equivalent amount of coal firing can be dispensed with. Per ton of iron, this figure 2/3 X 12,000/38.75 X 4.75 = 980 lb. gas or 1,372,000 B.t.u. or 100 lb. coal. At $1.50 per ton of coal, the net saving per ton of pig iron produced by the use of dry-hot over wet-cold cleaning will, therefore, be about $0.06 2/3. At a stove heating 8,500 lb. of air per toil iron from 150° F., one-quarter of the dry-hot cleaned gas, or 3,000 lb., would heat the air to 1,450° F. 3,000 X 1,400 X 0.70 = (8,500 X 0.255) = 1,300. The cold-wet gas would heat the same amount of air to 1,280° F. 3,000 X 1,225 X 0.70 = (8,500 X.0.255) = 1,130.

Jan 4, 1917

By N. S. Dalal, X. Shi

"Electron spin resonance (ESR) measurements provide evidence for the formation of Cr(V) intermediates in the enzymatic reduction of Cr(VI) by glutathione reductase (GSSG-R) in the presence of NADPH, indicating an initial single-electron transfer step in the reduction mechanism. Depending on the pH, at least two different Cr(V) species are generated which are relatively long-lived. In addition, we have detected the hydroxyl (·OH) radical formation during the GSSG-R catalyzed reduction of Cr(VI) by spin trapping, employing 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and a-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN) as spin traps. Superoxide dismutase (SOD) causes only a minor effect on the ·OH radical and Cr(V) formation, indicating that the ~ - is not significantly involved in the reaction mechanism. Catalase enhances the Cr(V) formation and substantially inhibits the ·OH radical formation, indicating the involvement of hydrogen peroxide (H20 2) in the reaction mechanism. Addition of H20i suppresses Cr(V) and enhances the ·OH radical fonnation. Measurements involving N-ethylmaleimide show that the Cr(V) species, produced enzymatically by the reduction of Cr(VI) by GSSG-R, react with H2O2 to generate ·OH radicals, which might participate in the initiation of Cr(VI) carcinogenicity.INTRODUCTIONC(VI) compounds have been found to exert serious toxic and carcinogenic effects on humans and animals [1-4) and to cause mutations in bacteria and transformation of mammalian cells [5-8). In contrast, most Cr(lll) compounds are relatively nontoxic, noncarcinogenic, and nonmutagenic [9, 10]. Cr(VI) and Cr(lll) oxidation states are different in their metabolic pathways: Cr(VI) ions are rapidly transported across cellular membranes [2, 11-13), while Cr(lll) moieties do not easily penetrate cells and are not oxidized by cellular constituents [3]. Since it is known that the reduction of Cr(Vl) is required for its reaction with DNA [2], the molecular mechanisms for the intracellular Cr(VI) reduction have been the focus of studies during the past decade but the details are still not understood."

Jan 1, 1990

By M. K. Larson, J. K. Whyatt

Proper employment of numerical stress analysis design tools is based on the demonstrated ability of a model to capture key elements of the geologic site model and accurately simulate how these elements interact with a mine design. While these tools have progressed markedly, they are, at heart, a gross simplification of the abundant complexity of a natural setting and its response to mining. A generic deep longwall site model was developed that includes aspects of the geology of deep coal mines in the Wasatch Plateau and Book Cliffs coal fields of Utah. The site model contains a set of common features and observations of how these features typically respond to mining. This site model was the basis for evaluating use of empirical, boundary element and volume element stress analysis tools to analyze the distribution of stress around a deep longwall panel. More specifically, this evaluation examined shifting of stress to panel abutments and gob, distribution of stress in the abutment and deformation and failure of bridging strata. Measurements of abutment stress changes at two sites in the Wasatch Plateau region were used to illustrate model calibration. Overall, these comparisons highlight the considerable differences between methods. Volume element tools can incorporate considerable detail and have fewer underlying assumptions, but this detail carries a considerable computational cost. Boundary element tools are much more efficient. However, this efficiency comes at the cost of added assumptions. These assumptions were challenged by the presence of a strong sandstone unit in the overburden, leading to boundary element results that depart significantly from volume element results. Empirical rules are the simplest, but are even more burdened by assumptions, many of which are implicit in underlying cases. Insight into the nature and impact of underlying assumptions in each method is essential to the proper use of results in mine design.

Jan 1, 2009