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Jan 1, 1885

By Melinda Channel, Alan W. Weimer, Jonathan R. Scheffe

"There is a need to develop cost effective renewable energy processes for the production of clean fuels that can simultaneously mitigate the U.S. energy/global environmental security issue. If H2 can be obtained cost effectively via the splitting of water using concentrated sunlight, then it’s possible to operate a fuel cell using renewable H2 or to synthesize other fuels based on renewable H2 for generating electricity or for running internal combustion engines. For example, H2 can be reacted with sequestered carbon dioxide (CO2) to produce syngas (H2/CO) via reverse water gas shift (RWGS), i.e. H2 + CO2 ? CO + H2O. The syngas can be catalytically methanated to form synthetic natural gas (SNG) or it can be catalytically reformed to produce liquid fuels such as “green” gasoline via the MTG process (syngas? methanol ? gasoline). The desert SW United States is home to world class sunlight. Fundamental ferrite thermodynamics will be reviewed, an example of the beneficial effect of ferrite surface area on reaction kinetics will shown, and process economics will be investigated for a 100,000 kg/day facility to produce H2.Introduction and Background ThermodynamicsSpinel ferrites of the form MxFe3-xO4, where M generally represents Ni, Zn, Co, Mn, or other transition metals, have been shown to be capable of splitting water according to the two step cycle shown below:MxFe3-xO4 + solar thermal energy ? xMO + (3-x)FeO + 0.5 O2 (1)xMO + (3-x)FeO + H2O ? MxFe3-xO4 + 2H2 (2)This is an inherently clean and sustainable process, as the only net inputs are solar energy and water, and the net outputs are hydrogen and oxygen. Ferrite water splitting cycles are advantages compared to other high temperature water splitting cycles, such as the ZnO/Zn and Mn2O3/MnO cycles, because thermal reduction has been demonstrated at significantly lower temperatures[1, 2]. As a result, overall efficiency may be increased due to the fact that radiation losses increase as the fourth power of temperature, and material considerations for reactor design should be more flexible. Additionally, cycle repeatability has been demonstrated with relative ease as compared to other thermochemical cycles [3-6]. However, the amount of hydrogen per mole that is generated is significantly less than for other high temperature thermochemical cycles due to the fact that only Fe3+ is capable of being reduced at the temperatures of interest[6]. In addition, water oxidation kinetics appear to be very slow, likely due to diffusion or surface area limitations created by near surface oxidation [6, 7]."

Jan 1, 2010

By Zhiye Zhao, Jianping Sun, Zhipeng Xu

"The subsea rock cavern project is an underground storage facility. For cost-effective and safe excavation, the risk caused by the groundwater seepage into the rock cavern must be addressed. As one of the essential steps of the assessment work, the hydraulic conductivities of the fractured rock masses should be reliably determined based on the limited measured data and geological information from the few boreholes. On the basis of site investigation data and monitored water flow and water pressure data during excavation, this paper presents an estimation method for hydraulic conductivities of the rock masses containing water bearing zones.INTRODUCTIONIn the development of underground rock caverns/tunnels, the uncertainty of hydro-geological conditions plays a critical role in terms of construction cost and construction safety. Excessive groundwater seepage has been identified as one of the key safety factors which always lead to vast loss, such as the Seikan Tunnel in Japan which encountered sudden water inflow and then catastrophic face collapsing, tunnel flood during excavation (Xu et al., 2013). As a key factor in the risk management associated with the groundwater leakage into rock cavern, the hydraulic conductivity determination is very important for cost estimation, reliable water control and construction management.The case presented in this paper is an underground project consisted of a cluster of rock caverns/tunnels for storage of hydrocarbon products. These caverns are located in heterogeneous sedimentary bedrock, at a depth of 130 m beneath a basin, and the crowns of caverns are located at about 100 m below the sea bottom. The caverns/tunnels are designed at two levels, the water curtain tunnels are at the upper level, and oil storage caverns are at the lower level, as shown in Figure 1. A number of horizontal and vertical water injection holes drilled from the upper water curtain gallery tunnel will establish continuous horizontal and vertical water curtains for providing a stable pressure distribution around the caverns, to keep oil/gas inside the lower storage caverns. As the hydrostatic pressure of groundwater around the storage caverns is higher than the pressure of stored oil and gas, the stored oil and gas will not leak out of the cavern (Lu, 2010; Xu et al., 2015). Groundwater pressure gauges are installed in the water curtain gallery tunnels, and water from the operational and access tunnels is injected continuously into the curtains to maintain the pressure. Some monitoring data are recorded at different construction stages. This paper proposes suitable methods to predict the hydraulic conductivity in rock mass and to determine the hydraulic conductivity in the water bearing zones."

Jan 1, 2015

By W. G. Davenport

Chapter 10 showed that any given smelting task, e.g. production of 65% Cu matte, 1500 K, from CuFeS2, can be done with many different combinations of: blast%02 hydrocarbon fuel blast temperature. This chapter repeats the Chapter 10 calculations but reports the results in terms of the mass industrial oxygen mass hydrocarbon fuel blast preheat energy combinations that will produce 65% Cu matte, 1500 K, from CuFeS2 concentrate. It also determines the energy inputs equivalent to these combinations.

Jan 1, 2001

By Philip G. Burkhalter

Total yield and backscattered electron coefficients were measured in this Bureau of Mines study in an microanalyzer as a function of atomic number and of primary crier: ;y in the 15- to 35-kilovolt range. The electron coefficients were obtained indirectly from measurements of the specimen electron current and the primary beam current collected in a Faraday cage and were measured with a precision better than 0.5 percent. Secondary electron emission was suppressed with opposing potential applied to a screen grid surrounding the specimen. The values of the backscattered electron coefficients agreed with published values within 5 percent.

Jan 1, 1965

By D Michaelsen, S Miller

The Grasberg Mine is a copper and gold open pit mine operated by PT Freeport Indonesia (PTFI) and located in the high equatorial mountains of the Indonesian province of Papua. The climate is alpine/subalpine with little seasonal variation in temperature or rainfall. The daily average temperature ranges from about 2¦C to 14¦C and the annual rainfall in the vicinity of the mine and overburden stockpiles is about 4000 mm to 5000 mm. Mining of the Grasberg open pit will continue until 2014 at which time approximately 2750 Mt of overburden will have been produced. Current overburden production rates are 200 Mt per annum. The current mill rate is 230 000 t/day from the Grasberg pit (190 000 t/day) and the underground operations (40 000 t/day). The acid rock drainage (ARD) issues associated with overburden from the Grasberg operations were identified early in the mining operation. Almost all overburden placed to date has been Potentially Acid Forming (PAF). Laboratory testing has identified four main overburden types: limestone and non-acid forming (Green waste), PAF low capacity (Blue waste) and PAF high capacity (Red waste), and Heavy Sulfide Zone (HSZ), which contains greater than 20 per cent pyrite. Waste type block modelling indicates that at least 30 per cent of the overburden production from 2003 to the end of Grasberg pit operations will be limestone. Strategies are being developed to maximise the beneficial use of limestone through strategic blending and placement for ARD mitigation and control.

Jan 1, 2003

In 1984/85 financial year Australia produced 529 thousand barrels per day (kbd) of crude oil. By far the major contribution (453 kbd) was light waxy oil from offshore Gippsland, Victoria. When these discoveries were made in the latter 1960s, imported oil was available in abundant supply and at low prices. Because of this, the Gippsland producers persuaded Government to control the marketing and pricing of their crude, and thus provide the required security of offtake. Political events in the middle East created supply shortages during the 1970s, and dragged up government selling prices for OPEC crude oil. Thus Arab Light crude that sold for less than US$2/barrel (bl) in 1970 reached $34/bl in 1981. Following the consequent decline in world oil demand, in 1982, Australian refiners sought to evade their obligation to lift Gippsland crude. Hence, in 1983, the Government was forced to introduce a floor quota of 385 kbd of Gippsland crude liftings and to allow producers to export any additional production refiners did not require. On expiry of the old arrangements, Government introduced a partial free market from January 1985, whereby the balance in excess of 350 kbd may be sold to Australian refiners at negotiated prices, or exported as before. In 1984/85 exports were some 90 kbd and will be higher in the current year. About half this total has been exported by BHP, providing valuable experience and lessons which are described in the paper.

Jan 1, 1986

By Yuexin Han, Wenbo Li, Yan Shan, Yanjun Li, Shumin Zhang

"With the accelerating pace of resource extraction, the quality of resources is decreasing, and the old tailing dams which have served for several decades have become the focus of attention. The secondary recovery of valuable metals in the tailings is an important aspect of the comprehensive utilization of tailings. The average iron content of iron tailing is 8%-12% in China. The research aimed at exploring the low-cost and efficient technical route to recycle eastern tailings of Anshan iron mining area. The purpose of the research is to scientifically find the rational conditions of magnetizing roasting and to provide an increase in recovery and quality of concentrates. The eastern tailings of Anshan mining area belong to high silicon bearing iron tailings, iron mainly exists in form of hematite-limonite with an iron grade of 10.60%, the main component of gangue is SiO2 with a grade of 76.22%. In order to reduce the influence of the tailings on the environment, fluidized magnetizing roasting and low intensity magnetic separation for the eastern tailings of Anshan mining area were carried out to improve the utilization of the tailings. The results indicated that an iron concentrate with an iron grade of 65.30% and a recovery of 85.85% could be obtained under the conditions of gas flow rate 8 m3/h, H2 concentration 50%, fluidized magnetizing roasting temperature at 600? for 20s. Phase analysis, magnetism analysis and XRD analysis on roasted materials indicated that hematite-limonite could be transformed to magnetite during the fluidized roasting, then the effective separation of iron and gangues could be made easily by the weak magnetic separation. INTRODUCTION It is universally acknowledged that the grade of iron ore in China is low, the output rate of iron ore tailings is high, usually more than 60%. At present, the comprehensive utilization rate of iron ore tailings is low in China. Generally, the iron ore tailings are stockpiled in the tailings dam. The tailing dams not only occupy a lot of land, but also takes a lot of money to construct and maintain. In addition, the noxious substances in the tailings, such as residual flotation agents and heavy metals, have a severe impact on the ecological environment. There is little doubt that tailing dams have a visual impact on the environment due to their regular geometric shape. Iron tailings can be treated as compound mineral, which is an important component of comprehensive utilization of mineral resources, and is an has been widely concerned. Lots of scholars have done a large amount of research work on a large number of iron ore tailings. Since the iron mineral crystal grain size is fine and the iron grade is low, the iron tailings have failed to achieve good selection criteria."

Jan 1, 2018

By J. Roth

The increasing demand of the filler industry regarding fineness and better delaminated products led to the development of a series of different grinding machines, which differentiate basically by the grinding mechanism as well as the kind of classification. Spiral jetmills grind, as it is well known preferably by delamination, therefore a spiral jetmill with integrated dynamic classifier has been developed. Especially the enhancement of the functional properties of the used industrial mineral fillers is a factor of highly increasing importance. These properties are very often bound to the platy shape of the minerals expressed by the aspect ratio. The developed Spiral Jetmill shows sufficient ability for such delamination and therefore increases in aspect ratio. In a series of comparative tests the suitability and advantages of this system regarding achievable fineness down to the submicron range as well as the conservation or even improvement of the aspect ratio of different minerals has been studied. As an emphasis on the results application tests with certain materials in the plastics field have been conducted. Due to the fact that in this range the required specific energy for achieving the necessary fineness increases exponentially another target is to optimize the grinding efficiency. A special feed control system provides on one hand a sufficient load inside the mill to obtain maximum utilization of the applied energy and on the other hand to prevent the mill from overfilling and coming with this a poor classification. The integrated classifier is a combination of a high speed motor with directly attached classifier wheels. This unit on one hand grants the necessary high circumferential speed of up to 190 m/s for providing an exact top cut of the ultrafine products and on the other hand gives the required operational reliability for continuous operation. Hard grindable impurities, which enrich inside the mill chamber, can be rejected from the process leading to an even cleaner product. Comparative tests on a talc product with certain free quartz impurities showed a significant improvement of the final product with respectively low loss on rejected material. This effect again had a beneficiary impact on the suitability of the final product when used in plastics application.

Jan 1, 2014

By I. D. Shah

A roasting procedure for synthetic copper sulfide which results in a reproducible transient melting at 450° and 470°C is described in this paper. Possible causes for this melting phenomenon are suggested, and also a procedure to avoid it during the roasting. This melting is believed to be responsible for the occasional occurrence of stickiness in the commercial roasting of copper sulfide concentrate. Many workers have studied the roasting of copper sulfides, but only Lewis et al. have reported that fusion and, in some cases, fusion with "boiling" occurred in the neighborhood of 450°C. The DTA and TGA apparatus, the materials used in this investigation, and the discussion of chemical reactions occurring during the CuS roasting are described in an earlier publication. CuS, in the form of either pellet or powder, was heated at 280° to 330°C in a flowing air or 30% 02: 70% N2 atmosphere. Heating was continued at this temperature until no further weight increase due to sulfates formation was observed on the TGA thermogram. This is believed to be due to the inability of SO, to diffuse out from the sulfate layer on the surface of the pellet, thus halting the sulfate-forming reactions. Hereafter, the sample oxidized in this manner will be referred to as "partially oxidized CuS." X-ray analysis and microscopic examination of a polished cross section of a partially oxidized CuS pellet showed the following order of layers starting from the center of the pellet: Cu2S, Cu2O, CuO • CUSO4, and CuSO4. A bare thermocouple inserted in the center of a partially oxidized CuS pellet (2.5 g) did not indicate any noticeable change in the temperature of the pellet when melted at 450° to 470°C in an inert or oxidizing atmosphere. During the preparation of a partially oxidized pellet, the temperature of a CuS pellet increased by 50°C due to the exothermic formation of sulfates in air at 320°C. The endothermic peak associated with the melting phenomenon at 450°C is shown in [Fig. 1.] A CuS pellet (0.2 g) was oxidized in flowing air (150 cc per min) at 10°C per min up to 320°C and held there for about 2 hr. Then, N2 replaced air and heating was continued up to 500°C. The exothermic peak at 320°C represents an overall formation of sulfates, and an endothermic peak at 450° to 470°C represents the melting phenomenon. To observe the melting visually, a small (50 mg), partially oxidized CuS pellet was heated (in static air) in a hot-stage microscope. The melting phenomenon was observed on an auxiliary TV screen. The sample

Jan 1, 1976

By F. A. Forward

"IntroductionTHE LYNN LAKE MINE, situated in Manitoba about 150 miles north of Sherridon, has been actively developed by Sherritt Gordon Mines, Limited, during the past seven years, resulting in the establishment of a proven reserve of over 14,000,000 tons of ore containing 1.223 per cent nickel, 0.618 per cent copper, and additional cobalt values. For many years, the Sherritt Gordon Company operated a copper-zinc-gold mine at Sherridon but, as this mine was approaching exhaustion and as it was proposed to use the mining and milling equipment to treat the Lynn Lake ore, a number of unusual problems were faced in transferring plant and operations from the one mine to the other, and particularly in preparing to undertake nickel production.Preliminary investigation showed that the ore could be concentrated by flotation to produce a copper concentrate containing 28 to 30 per cent copper with less than 1 per .cent nickel, and a nickel concentrate containing 11 to 14 per cent nickel, 0.3 to 0.4 per cent cobalt, and less than 2 per cent .copper, with high recovery of the three metals in .the concentrates. It was apparent that, initially, the copper concentrate could be economically smelted and refined in the usual manner. But as the nickel concentrate contained an insignificant amount of precious metals (less than 0.02 oz. per ton) and as .it had a much higher nickel content than comparable concentrates normally produced from sulphide ores, the selection of a treatment process and the location of a plant required careful study."

Jan 1, 1953

By Xiqing Wu, Liang Dai, Tao Yue, Longsheng Yi, Ruifang Wang

Magnetic seeding flotation (MSF), i.e. adding magnetic seeds and pre-magnetization-flotation, is a new flotation technology especially for fine particles, which improves the flotation performance by enlarging the apparent size of the particles in a way of magnetic agglomeration. Both the fine coal slimes with a size of 66.68% –38µm and the pyrite slimes with a size of 73.95% –23 µm were investigated by the MSF, respectively. Flotation tests with variable of dosages of magnetic seeds and polyacrylamide were conducted, and some measurements, such as laser diffraction size analysis, magnetic susceptibility by vibrating sample magnetometer (VSM) and infrared spectroscopy (IRS), were also applied in order to probe the mechanism of the MSF. Based on the tests, measurements and calculations it was found that both the recovery of coal and the flotation kinetics of pyrite slimes increased with the additions of the magnetic seeds, and in the presence of polyacrylamide the coal flotation was further strengthened due to a synergetic effect of magnetic seeds and polyacrylamide on the flotation and a relatively larger apparent size of slimes after additions of magnetic seeds and polyacrylamide. The reason for the MSF lies in fact that the presence of the polyacrylamide intensified the adsorption of magnetic seeds on the coal particles and increased the coverage of the magnetic seeds on the coal surface from 0.2 to 1.3 wt%, resulting in increased magnetic susceptibility of coal particles from 9.13×10-9 to 22.17×10-9 m3/kg and thus a low magnetic field strength of pre-magnetization needed for the magnetic agglomeration among the coal particles from 602 to 24 mT prior to proper flotation. IRS shows that polyacrylamide chemisorbed on the surfaces of both coal particles and magnetic seeds, thus acting as the bridging media between particles and seeds.

Jan 1, 2016

By A. J. Weinig

IN the accompanying figure consider the classified AB in closed circuit with a ball mill, wherein T = Tonnage of new feed C = Ratio of circulating load Now consider that the circulating load is made up of two portions of ore. One portion is due entirely to the characteristics of the ball mill and the tonnage of new feed impressed on the ball mill. This portion of the circulating load in no way is to be blamed on the characteristics of the classifier and is all composed of oversize. Consider, for illustration, that this portion of the circulating load is handled in the A division of the classifier, assuming that the classifier is divided longitudinally into two divisions by an imaginary line. Because the classifier does not usually make a perfect separation of the undersize, a certain portion of the total circulating load is to be directly blamed on the efficiency of the classifier. Let this portion of the circulating load be considered as being handled in the B division of the classifier. Now if the classifier is operating perfectly (100 per cent efficient), the width due to the B division becomes zero and correspondingly the efficiency of the classifier diminishes as B becomes wider in proportion to A. If E is the mechanical efficiency, then

Jan 1, 1934

By A. A. Dor

Of the numerous methods that have been tested or considered for the beneficiation of low-grade iron ores, this article deals only with proven flowsheets that are adopted in plants in operation or which have been reliably pilot-plant tested. Several recommended layouts are described and discussed. They illustrate recent trends and embody improvements and new features that have resulted from the experience acquired in the operation of the plants already in service. They have been developed, in the last few years, in the course of designing several iron ore beneficiation plants of various types and sizes. Some of the design features in the layouts which are submitted represent, in some respects, personal views and may not meet the full approval of others in this field. It is hoped that this presentation will provide an opportunity for constructive discussion of the problems involved and of suitable solutions.

Jan 6, 1962

By Richard H. Johnson

The Castle Mountain Mine (CMM) is located in the eastern por­tion of San Bernardino County, Southern California, 70 miles south of Las Vegas. The CMM is a joint venture between Viceroy Gold Corp. (75% and operator) and MK Gold (25%). The CMM initially started gold production with an 8,000 tpd cyanide heap leach operation in February, 1992 when the first ore was crushed and delivered to the leach pads. Even during construction and commissioning, design work was under way to engineer and construct a 1,200 tpd Mill circuit to process the higher grade fraction of the ore through use of pulp agglomera­tion. The need for a grinding circuit became evident with the quantity of high grade material delineated during drilling and the amount of visible gold that the geologists were finding in the drill core and R.C. cuttings. Viceroy did not want to stack the higher grade ore on the heap, and it was clear that permitting a tailings pond would, at best, be a long drawn-out affair. An alternative to a tailings facility had to be found.

Jan 1, 1996

By H. D. Outmans

The mechanics of filtration are described by a theoretical-empirical nonlinear diffusion equation which, under certain circumstances, may,be linearized and then solved explicitly. For filtration under static conditions linearization leads to a boundary value problem analogous to a heat flow problem with a known explicit solution. The corresponding solution for static filtration is compared with published experimental data. Under dynamic conditions filtration takes place in three successive stages. During each of these the rate of filtration and/or the thickness of the filter cake are different functions of the filtration time. The proposed mechanism explains the observed high resistance of dynamically deposited filter cakes against erosion and also the connection between filtration rate and viscosity of the drilling fluid. Several of the quantities governing dynamic filtration have no counterpart in the static filtration mechanism. The static filtration rate is, therefore, not a reliable measure for the dynamic rate and vice versa. INTRODUCTION Filtration under simulated borehole conditions, i.e.. either from a static suspension or from a suspension flowing parallel to the filter cake (dynamic filtration), has been the subject of several laboratory studies.1-7 This experimental and theoretical work showed that many aspects of the filtration mechanism cannot be explained by an elementary filtration theory based on the assumption that the filter cake is incompressible. For a more satisfactory theory compressibility should be taken into account. This has been done. at least to some extent, in the filtration theory developed for the chemical industry. Surveying the literature (see Ref. 8 for a bibliography) it becomes apparent that, although several properties of filter cakes deposited from many different suspensions have been measured, including compressibility, the filtration equations are essentially empirical in nature. No attempt has been made, for instance, to develop filtration theory along the lines of consolidation theory.12 This theory, upon which a highly successful development in soil mechanics rests, would appear to be an excellent starting point for a filtration theory since the compressibility concept is an essential part of it. As we will use this theory in the following development it is well to state the four assumptions on which it is based: 1. The fluid flow through a compressible porous medium is governed by Darcy's law. 2. The rate of change in fluid content of an element of the porous medium is proportional to the rate of change of solid pressure between the particles. 3. The solid particles are incompressible within the range of pressures considered. 4. The total pressure on a surface normal to the line of flow is equal to the sum of the fluid pressure and the pressure between the particles (solid pressure) at that surface. To calculate the rate of filtration and other quantities of interest it is necessary to know the filter cake compressibility and the permeability as a function of the solid pressure. It has not been possible to calculate these functions from theoretical considerations and they will therefore be introduced in this paper as empirical expressions. Both are determined in a compression cell where the cake is subjected to a mechanical load. Permeability and compressibility are measured after the solid pressure has stabilized, i.e., after the excess fluid pressure has been dissipated and the uniform pressure is transmitted entirely by the solids. The permeability and compressibility thus determined are not the same as during filtration in the borehole, under either static or dynamic conditions, because then, due to frictional drag, the solid pressure and hence also the permeability and compressibility vary along a line normal to the direction of the mean flow and can only be defined locally. DERIVATION OF THE FILTRATION EQUATION FOR COMPRESSIBLE FILTER CAKES As the filter cake in the borehole is thin compared to the radius of the hole the filtration may be considered as linear. Taking the x-axis normal to the wall, with its origin at the formation, we have, according to Darcy's law,

By F Butler, G E. Batley, A C. Hogan, A R. Butler

The ANZECC/ARMCANZ (2000) Water Quality Guidelines (the Guidelines) are the primary reference used in Australia and New Zealand for managing and regulating water quality. For most mining operations in Queensland, the environmental authority (EA – licence) incorporates the national default guideline values (GVs) for ecosystem protection as trigger levels (TLs). Exceedances of TLs ‘trigger’ further investigation and reporting. A review of the surface water compliance history at a metalliferous mine in North West Queensland identified minor exceedances of the cobalt GV as a common trigger for investigation and compliance reporting.The reliability of GVs is dependent on the availability and quality of ecotoxicology data for the relevant contaminant. The current national default GV for cobalt of 1.4 µg/L is classified as a low reliability GV due to the lack of available data at the time it was derived (ANZECC/ARMCANZ, 2000).The Guidelines are presently being revised and the toxicant GVs will be available as a set of web-based values and associated technical briefs. The new platform will enable the timely revision of existing GVs and inclusion of GVs for additional toxicants. Cobalt was considered a priority toxicant for the Guidelines’ revision, but was not included in the revision process.A preliminary review of the international literature indicated that at least 15 additional chronic cobalt toxicity studies had been published since 2000, sufficient to derive a high reliability cobalt GV using the protocols developed for the revision of the Guidelines (Batley et al, 2014; Warne et al, 2015). This presented an opportunity to improve environmental management by increasing the reliability of the performance measure.CITATION:Hogan, A C, Butler, A R, Butler, F and Batley, G E, 2016. Derivation of high reliability water quality guideline values for cobalt in freshwaters – improving water quality guidelines for better water quality compliance management in mining, in Proceedings Life-of-Mine 2016 Conference , pp 205–208 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jun 28, 2016

By Tom Learmont

The emergence of the dragline as the dominant stripping tool is described and reasons for this are noted. Brief comparisons are made with stripping shovels and wheel excavators. Representative output and machine availability figures for draglines are presented. The effect of changes in machine parameters such as boom length, swing power, and hoist power on machine productivity are discussed. An analysis of machine availability and the causes of machine downtime is made. Measures which are being taken to improve machine availability are discussed in detail. These include (1) improved methods of structural analysis, standardization of welded joints and welding methods to increase structural reliability and to develop more efficient structural designs, (2) standardization of gearing and mechanical componentry to permit the use of proven designs, (3) review of fairlead design and bucket hardware to improve rope life and reduce downtime, and (4) modifications to reduce maintenance time. The General Electric Data Logging system is described and consideration given to its use as a tool for improving productivity. Areas for future improvements in productivity are discussed.

Jan 1, 1976

By Welby G. Courtney

The Bureau of Mines conducted an exploratory field survey to determine the amount of airborne coal dust, the size distribution of the dust, and the rate of dust deposition in coal mine airways. The survey was taken at eight underground locations in operating coal mines. The rate of dust deposition in the airways depended upon the concentration of air-borne dust and decreased exponentially with distance from the dust source. The rate was seemingly independent of the size of the airborne dust particles. The rate of deposition, along a return, for the coal dust from a fade being mined with a continuous mining machine closely matched the rate for the rock dust from a trickle duster. A sample rock-dusting schedule for that return is presented; that is, the trickle duster should be operated for 3-112 hours after every five shifts to protect the average deposit of new float coal dust in the return, but operation after every three shifts is preferred, to protect an occasional heavier deposit.

Jan 1, 1982

Many sampling standards arrive at a value for the prescribed sample mass by assuming a specific relation between the sample mass and the relative standard deviation of the fundamental error and assigning a value to the tolerated coefficient of variation. In order to obtain an equation that provides a relation between the minimum sample mass and the particle properties, many different models for the drawing of a sample have been developed. Here, a model for the drawing of a sample is proposed which can be considered to be a generalisation of the model used in GyÆs sampling theory. Using simulations, it is illustrated that the generalised model can lead to a better correspondence with actual sampling processes.

Jan 1, 2005