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By Jay F. Colinet

Longwall mining in lower seam heights may necessitate the use of single-drum shearers to overcome size constraints associated with standard double-drum shearers. To avoid the operational problem of clearance in the tailgate entry with one single-drum shearer, two single-drum machines can be operated on the same face, with each shearer responsible for mining a predefined portion of the face. However, utilization of two shearers on the same face necessitates the positioning of one shearer operator and a jacksetter in the return air of the upwind shearer, thus complicating respirable dust control on the longwall. In an effort to evaluate the unique dust control problems associated with this type of mining, the U.S. Bureau of Mines conducted dust surveys on two multiple-machine longwall operations. Sampling was done to quantify major sources of respirable dust and to identify potential solutions to problem areas. Sampling results indicate that the cutting sequences utilized on multiple-machine faces may have to be designed to minimize dust exposure, as opposed to optimizing productivity or facilitating operational requirements. Also, state-of-the-art dust control techniques typically found on double-drum shearer longwalls must be employed to help minimize the exposure of all face personnel to traditional dust sources.

Jan 1, 2010

By Shizhe Liu, Bing Li, Heng Wang, Zuxin Zhao

In this paper, cyclic voltammetry and chronoamperometry have been applied to investigate the effects of Nd2O3 concentration on the anode effects, critical potential for the anode effects and Nd2O3 reduction in LiF-NdF3-Nd2O3 melts at 950℃. The results show that the oxidation peaks in the potential of about 2.7V are attributed to the oxygen ions oxidation and the peak current density increases with Nd2O3 concentration increase from 0 to 0.5wt%. The critical potential caused the anode effects shifts to 0.3V more positive value as Nd2O3 content in the melts decreases from 0.01wt% to 0.5wt%. The cyclic votammograms on W electrodes in the LiF-NdF3-Nd2O3 melts present two pairs of reduction and oxidation peaks, indicating that the reduction of Nd ions in the LiF-NdF3-Nd2O3 melts in two steps rather than one step.

Jan 1, 2014

By L. R. Freitas, A. K. Resende, J. A. Oliveria, K. L. Gonçalves, L. F. D’Assumpção, L. R. Lage, J. D. Neto, F. Viveiros

Pará Pigmentos S.A. (PPSA) is an association between the Brazilian companies CVRD and CADAM, Mitsubishi Corporation of Japan, and the IFC (World Bank) created in 1992 in order to recover kaolin from Rio Capim deposit, northern Brazil. Commercial production at PPSA started in August 1996 using a process comprising mining and beneficiation at the mine site, pumping through a pipeline and drying/loading at the port site on the Amazon river estuary. Presently, all PPSA production is concentrated on 82% <2um, high-brightness coating clay shipped in bulk. In this paper, a detailed description of the development of PPSA beneficiation process is presented. The results of laboratory and pilot plant studies under- taken to develop alternative grades of clay, such as delaminated and calcined kaolins, are also discussed.

Jan 1, 1998

By John F. Gamble

Amphiboles are hydrated mineral silicates five of which occur in asbestiform habits as asbestos grunerite (amosite) asbestos, riebeckite (crocidolite) asbestos, anthophyllite asbestos, tremolite asbestos and actinolite asbestos] and non-asbestiform habits (grunerite, riebeckite, anthophyllite, tremolite and actinolite). The asbestiform varieties are characterized by long, thin fibers while non-asbestiform varieties such as cleavage fragments form short fibers with larger widths. The U.S. regulatory method for counting asbestos fibers (aspect ratio [>]3:1, length [>]5 µm) does not distinguish between asbestos and cleavage fragments. The method biases toward increased counts of non-asbestiform cleavage fragments compared to long, thin asbestos fibers. One consequence of this regulatory approach is that workers can be erroneously classified as exposed to concentrations of asbestos (asbestiform amphiboles) above the U.S. 0.1 f/mL exposure standard when in fact they are not exposed to asbestos at all but non-asbestiform amphibole cleavage fragments. Another consequence is that the known carcinogenic effects of asbestos may be falsely attributed to non-asbestiform amphibole cleavage fragments of the same mineral. The purpose of this review is to assess whether amphibole cleavage fragments pose the same risk of lung cancer and mesothelioma characteristic of amphibole asbestos fibers. We identified three groups of workers exposed to non-asbestiform amphiboles: two groups exposed to grunerite (Homestake gold miners and taconite miners) and one group exposed to industrial talc containing non-asbestiform tremolite and anthophyllite in St. Lawrence County, NY. In addition to assessing strength of association and exposure?response trends in the non-asbestiform amphibole cohorts, comparisons were also made with cohorts exposed to the asbestiform counterpart (positive control) and cohorts exposed to the mineral (e.g. talc) that does not contain amphiboles (negative controls). The cohorts exposed to non-asbestiform amphiboles had no excesses of lung cancer or mesothelioma. Similar results were observed in the negative control groups, in stark contrast to the excess risks of asbestos-related disease found in the asbestos cohorts. The only possible exception is the twofold increased risk of lung cancer where exposure was to industrial talc containing cleavage fragments of tremolite and anthophyllite. However, this risk is not considered attributable to the talc or amphibole cleavage fragments for several reasons. A similar increased risk of lung cancer was found in Vermont talc workers, studied in the same time period. Their exposure was to relatively pure talc. There was no relationship between lung cancer mortality and exposure measured as mg/m3 years and years worked. A case?control study reported that all the lung cancer cases were smokers (or former smokers) and attributed the excess to smoking. There were two mesothelioma cases among the NY State talc workers exposed to cleavage fragments of tremolite and anthophyllite, but talc is not a plausible cause because of too short latency and potential for previous asbestos exposure. The positive controls of tremolite asbestos and anthophyllite asbestos exposed workers showed excess risks of both lung cancer and mesothelioma and positive exposure? response trends. St. Lawrence, NY talc does not produce mesotheliomas in animals while amphibole asbestos does. In sum, the weight of evidence fully supports a conclusion that non-asbestiform amphiboles do not increase the risk of lung cancer or mesothelioma. ©2008 Published by Elsevier Inc. Keywords: Amphiboles; Cleavage fragments; Lung cancer; Mesothelioma; Asbestos; Non-asbestiform amphiboles; Grunerite; Talc

Jan 1, 2007

By E. E. Maust

The literature on the activation of sphalerite for flotation by short¬chain xanthates leaves unanswered the question of whether a compact surface film of activator sulfide is necessary or merely sufficient for high flotation recoveries. Studies by Guarnaschelli and Plaksin indicate that xanthate adsorption and flotation of sphalerite are increased with increasing hole/ electron ratio. These results, and the known acceptorlike behavior of many heavy-metal impurities in zinc sulfide, suggest that activation may result from a traditional semiconductor doping effect at the surface. Using the theory of chemisorption states on ionic crystals as developed by Levine and Mark, the Bureau of Mines has carried out A calculation to estimate the surface-state energies of various metals when they are substituted at zinc sites on (110) sphalerite surfaces. Based on a simple Madelung-Born treatment of ionic solids, the calculation indicates that many of the metals known to activate sphalerite for subsequent flotation have lower surface-state energies than nonactivators. The results of these calculations are discussed from the standpoint of consistency with the proposed activation mechanism and observed flotation results. The satisfactory agreement obtained is taken to be support for the proposed mechanism, and further elaboration of a surface-doping model is attempted.

Jan 1, 1976

By J Zhang, O Ostrovski, C Zhang D Cai, Q Wang

The conventional CaO-SiO2-based mould fluxes are not suitable for high-Al steel casting because of the strong reaction between silica in the flux and aluminium in the steel strand. In the process of casting of high-Al steel, flux composition changes; with the decrease of the silica concentration and increase of alumina. Knowledge and understanding of the effect of the Al2O3/SiO2 ratio on flux structure and properties are useful for flux design for the high Al-steel continuous casting. This paper investigated the effect of the Al2O3/SiO2 ratio on structure, viscosity, phase composition of fluxes quenched at different temperatures and heat transfer of CaO-Al2O3-SiO2-B2O3-Na2O-Li2OMgO- F fluxes. It was found that flux melting temperature increased with the increase in Al2O3/SiO2 ratio. Viscosity of the flux melts increased significantly with the increase of the Al2O3/SiO2 ratio from 0.7 to 1.2, reaching the maximum value, and then decreased with further increase of the Al2O3/SiO2 ratio. Raman spectroscopy analysis revealed that the change of the Al2O3/SiO2 ratio led to the change of aluminate and silicate structural units. The turning point for viscosity was attributed to the change in the degree of flux polymerisation. X-ray diffraction (XRD) analysis showed that increasing Al2O3/SiO2 ratio increased crystallisation tendency of the fluxes. Heat transfer measurement by infrared emitter technique (IET) revealed that increasing Al2O3/SiO2 ratio led to the decrease in heat flux which is correlated well with the increased crystallinity of the flux. The results suggested that the flux with Al2O3/SiO2 ratio 4.3 is the best candidate among the studied CaO-Al2O3-based mould fluxes for casting of high-Al steel.

Aug 21, 2024

By Joaquin Marti, Peter A. Cundall

This paper reports on some recent work in which several schemes were developed to model jointed rock under high stress, with particular reference to the phenomenon of "block motion" observed during dynamic loading of underground structures. Three approaches were made, corresponding to an increasing relative importance of internal block deformations as compared to rigid block movements. The first one uses distinct element method and assumes internally rigid blocks, which can break, repeatedly, whenever an empirical crack criterion is met. In the second approach each block is allowed three degrees of freedom to deform internally. The third approach, still in the development stage, permits arbitrary deformation of all blocks, which are internally decomposed into finite-difference zones and automatically rezoned during slip to preserve the calculation accuracy on joints. The last two schemes allow arbitrary constitutive relations for the intact rock, and all three schemes permit the geometrical arrangement of joints to be arbitrarily complex, in contrast to normal Lagrange, finite-difference programs, which are unsuited to model discontinua.

Jan 1, 1979

By Daniel Abbott Albertacci, Celso Luiz Moraes Alves, Fernando Paulucio Quinelato

No cenário econômico atual do mercado siderúrgico, otimizações de processo que aumentem o rendimento metálico estão no alvo das empresas competitivas. Além disso, cada vez mais os clientes exigem níveis mais elevados de qualidade e menor índice de recusa. Neste contexto, desenvolver trabalhos que conciliem otimização e garantia de qualidade são prioritários para o negócio. O objetivo deste trabalho é definir o menor descarte de início de lingotamento para aços com aplicações severas com total garantia de qualidade. Foi elaborada uma metodologia específica para avaliação da qualidade dos produtos: placa e bobina laminada a quente. Primeiramente, avaliou-se a quantidade de inclusões não metálicas em placas, o que permitiu determinar o comprimento de descarte mínimo necessário para garantia de qualidade das placas. Posteriormente, análises de inclusões também foram realizadas em bobinas para confirmar os resultados da ação de alteração de tonelagem de descarte. Os resultados mostraram que as placas produzidas após o descarte determinado pelo estudo resultaram em bobinas aptas para atendimento das aplicações, sem nenhuma perda de qualidade.

Oct 1, 2019

By Richard F. Roethe

Surface coal mining productivity in the U.S. and Illinois has shown a general declining trend since 1969. The U.S. Department of Energy conducted an analysis in 1980 of the causes of declining productivity in different states. This paper presents a detailed analysis of changes in overall productivity and productivity in different functions such as overburden preparation, overburden stripping, reclamation, coal handling, etc. during the period 1970-1982. Statistical analysys techniques including multiple regression were utilized in the study.

Jan 1, 1983

By J R. Manuel, J M. F Clout

The importance of goethite to Australian iron ore production is steadily increasing as the proportion of goethite-rich, martite-goethite bedded and channel iron deposits increases at the expense of declining production from high-grade microplaty hematite deposits. For this reason, an improved understanding of goethite in iron deposits, its genesis, goethite types and their physical and metallurgical properties is vital to maintaining optimum sintering and blast furnace performance in Asian steel mills.The terminology used to describe goethite in Australian iron deposits is currently highly variable. The discredited mineral name ‘limonite’ is still in widespread use as a field term for goethite and there are many misconceptions concerning goethite chemical grade and downstream physical and metallurgical properties. The goethite classification proposed here is based on geological and physical properties from which three types are recognised including brown goethite, dark brown-black vitreous goethite and highly microporous, friable yellow ochreous goethite.In practice, typical vitreous goethite with highly reflective surfaces and conchoidal fracturing, characteristic of the hard cap zone appears from X-ray fluorescence (XRF) and electron microprobe analysis to be significantly higher in Si (up to 18.7 wt per cent), Al (up to 3.5 wt per cent) and S (up to 0.14 wt per cent) compared to the generally very low (&lt;1 wt per cent for Si and Al) levels of these elements in ochreous goethite and brown goethite. The data dispels the common misconception that friable earthy or yellow ochreous goethite is high in Al and Si and other chemical impurities. However, P was found to be consistently higher (mean of 0.112 wt per cent and up to 0.296 wt per cent) in ochreous goethite than brown goethite (mean of 0.011 wt per cent) or vitreous goethite (mean of 0.031 wt per cent). The highly porous microstructure of ochreous goethite is thought to have a much higher surface area, which may aid in preferential adsorption of P onto the ochreous goethite mineral surface.CITATION:Manuel, J R and Clout, J M F, 2017. Goethite classification, distribution and properties with reference to Australian iron deposits, in Proceedings Iron Ore 2017, pp 567–574 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 24, 2017

By Tapiwanashe Chenje, David Hewitt, Peter Radziszewski

"Steel media wear is a major cost component in mineral processing. In the case of existing operating mill, steel media wear prediction can be used to help compare the performance of steel media from different suppliers before completing marked ball tests. It can also be used to investigate how ores from different site of a given mine affect steel media wear. In the case of Greenfield cases, steel media wear prediction can be used to estimate the cost of steel media for a given feasibility study.This paper presents a wear testing and prediction methodology that ties together abrasion wear and corrosion wear testing results through the use of a simplified discrete element charge motion model. The experimentation dimension to this methodology takes samples for steel media, mine site ore and water to determine abrasive and corrosive wear parameters of a given media, ore, water set.The test methodology development is illustrated along with a comparison of wear predictions with observed wear rates in some operating mills. A case study is included that illustrates how this methodology was used to estimate steel media wear performance. The paper closes with a discussion on the use of parts of the experimental methodology to investigate other abrasive wear conditions such as liner wear, paste backfill piping and ore breakage as well as avenues for future test development.INTRODUCTIONThe cost of comminution processes represents a significant part of the overall costs of a mining operation. Grinding media/liner wear alone accounts for 15-25% of the total operating cost. The annual steel grinding media consumption is approximately 2.5 mtpa or 0.3% of total world steel production [Smorgon Steel Group, 2005]. Using an estimated grinding media cost of about US$0.75/kg [Halbe and Smolik, 2002], gives a media cost of over US$1.875 billion per annum. Mining continues to shift towards exploitation of lower grade ores as the higher grades get depleted. These low-grade ores require finer grinding for the liberation of the value minerals, and hence it can be assumed that grinding media consumption will also continue to rise.The Bond abrasion test, dating back to 1963, [Weiss, 1985] is still used to estimate the total mill media wear. This is a purely empirical test based on the ore. From Bond abrasion index tests, it is possible to determine a wear rate using the following function:"

Jan 1, 2009

By O. Barbosa F.

The thermochemistry of the systems SCN-H2O, Au-SCN-H2O and Ag-SCN-H2O is discussed. Potential-pH diagrams at 25°C are drawn for each system considering several sets of concentrations of the species involved. The information provided by the potential-pH diagrams is.complemented by distribution curves for each series of gold and silver complexes with thiocyanate. The analysis includes comparisons between the thiocyanate systems and the analogous cyanide systems, pointing out analogies and differences between the leaching of gold and silver with thiocyanate and with cyanide. The possibility of using soluble oxidizing agents such as ferric ions, hydrogen peroxide and Caro&apos;s acid is evaluated. The thermodynamic data used in the calculations and the chemical reactions represented in the Pourbaix diagrams are all reported in three Appendices. The overall results indicate the thermodynamic conditions for gold and silver leaching by thiocyanate.

Jan 1, 1989

By Hugo M. Checo

Friction-reducing textures for lubricated mechanisms have received much attention since the advent of microtexturing techniques. In this work we consider the piston ring/liner contact, numerically simulating the rings as they slide against a textured liner. This situation has not been sufficiently analyzed because its numerical complexity is much greater than that of texturing the rings. Further, we consider the actual typical geometries of oil-control, wiper and compression rings, under realistic loads and velocities. The results show the possibility of friction reduction when the texture on the liner is properly designed, identifying starvation alleviation as a crucial intervening mechanism.

Jul 31, 2018

By Chang-Ha Ryu, Hyung Yang, Hyung-Sik Yang

Ground vibration by rock blasting causes many environmental problems to adjacent structures and human bodies. Growing concerns have been given to the effects of dynamic loading induced by blasting works near safety-related structure like nuclear power plant, hospital, broadcasting station, research institute and tish farm, etc. In order to ensure the safety, rational safe criterion should be established. It requires development of a model to predict the design parameters through more systematic measurement and analysis. Primary estimation by adequate model with general parameters will be very useful for safe design and understanding the possible hazards in advance.

Jan 1, 2001

By I. H. Warren

The high temperature lubricant molybdenite, MoS2, is usually produced by a complex sequence of processes involving mineral dressing of molybdenite concentrates followed by leaching with hydrofluoric acid to remove abrasive impurities such as silica (1). Many attempts have been made, mostly by techniques involving, direct fusion of molybdenum compounds with sulphur, to produce synthetic molybdenite. However, apart from some experiments of geochemical interest (2) in which aqueous solutions of sodium sulphomolybdate, Nat MoS4, were decomposed under pressure at temperatures between 300°C and 700°C, no attempts to produce the mineral by hydrometallurgical procedures have been reported. Since molybdenite is nominally a compound of tetravalent molybdenum with sulphur, and the most common state of molybdenum is +6, production of molybdenite is likely to involve reduction and sulphidization. The present study, therefore, describes the reduction, with hydrogen and carbon monoxide, of molybdenum in the hexavalent state in alkaline aqueous solutions containing sulphide ion. In these

Jan 1, 1972

By M P. Sandy, R M. Stephenson

Portals to access underground mines are important infrastructure and their design requires careful consideration. Portals are generally expected to last for the life of the mine. Typically, the exposure of personnel and equipment is high, with many hundreds of movements through the portal per day. Consequently, the risk associated with geotechnical instability must be extremely low. Portals are often established from a boxcut. In areas where the weathering profile is well developed, the design and execution of the boxcut can involve significant effort, with the objective of minimizing the volume of the boxcut, whilst ensuring that conditions at the design depth are suitable for establishing a stable portal. Properly designed site investigations are a critical part of this process. Currently available portal design guidelines have not been updated for decades, however the equipment and ground support systems have changed significantly in recent years. Many mine portals have since been constructed in a relatively short time frame with success, often in challenging ground conditions using some of the more modern approaches to ground support. This is beneficial because delays in establishing a portal will generally delay other critical path activities, and lead to cost overruns.

Mar 15, 2021

By Fredrick C. Kruger

Introduction This surprisingly little-known group of minerals, the nonmetallics, so-called for their lack of metallic luster, is the largest group of the mineral kingdom, and cinstitutes perhaps 75 percent of all mineral species. For the most part, these minerals are compounds of the common acids, oxides, hydroxides, and two elements, carbon and sulfur. The list of the non- metallic minerals, therefore, is very long. It includes the borates, carbonates, chlorides, fluorides, nitrates, phosphates, silicates, sulfates, and less commonly, arsenates, chromates, molybdates, suliides, tungstates, and vanadates, the latter groups, and many of the oxides, being sought principally for their metal content. Those nonmetallics used commercially are generally called the industrial minerals, although in addition this term also includes a considerable group of rocks. The list of industrial minerals and rocks is continually growing as new uses are found, and it now numbers over 300 commodities. The industrial minerals industry has developed since about 1920. There- fore, the development has been fast, and it has been more or less parallel with the development of the art of minerals beneficiation. General Discussion of the Group This group is so heterogeneous that it has defied logical, or widely accepted, classification, whether by origin, composition, or end use, and perhaps for this reason the industrial minerals generally have received short shrift in both teaching and research. Except for those involved with asbestos, cement, fertilizers, gypsum, salt, sand and gravel, few large companies have deigned to enter the field, and consequently most industrial minerals have been developed for the most part by the small operators or entrepreneurs. Yet surprisingly, except for one war year, the nonmetallics have always surpassed the metals in value and tonnage (Fig. 1). One main characteristic that most of the nonmetallics have in common is direct sensitivity to labor and transportation. In other words they are characterized by large bulk and low-unit value, and hence have what might be termed a "place value".

Jan 1, 1971

COMPARED with the equipment used in most industrial processes, the open-hearth furnace has a relatively short life. The most important quality of an open-hearth refractory, therefore, is its rate of failure. This discussion of the physics and chemistry of the individual refractory materials will keep uppermost the question "Why, how, and where does it fail?" CAUSES OF FAILURE The principal causes of failure of open-hearth refractories are, in their order of importance : 1. Reaction with iron oxides. 2. Reaction with slag. 3. Flow and failure under load. 4. Melting. 5. Spalling. 6. Mechanical breakage. Reaction with Iron Oxides and Slag. Reaction with iron oxides and slag is by far the most important cause of failure. Liquid iron oxide comes near to being the "universal solvent" sought for by the alchemists. Among the materials commonly used in the open-hearth furnace, magnesia has the greatest resistance to this liquid and fireclay the least. The relations of iron and oxygen at high temperatures are illustrated in Fig 14-18. The liquid iron oxide that forms wherever iron is in contact with air or combustion gases cannot be given a definite formula. The percentage of oxygen at steelmaking temperatures may range from 21 to 28 (iron 79 to 72), depending upon the temperature and the oxygen pressure and also upon whether or not the liquid is in equilibrium with metallic iron. Oxide mixtures exist not only in the solid and liquid phases but also in the vapor phase, for metallic iron and its oxides have

Jan 1, 1964

By H. C. de Wet

The predevelopment and preparation of a total infrastructure in a deep level mining environment, prior to the shaft system being commissioned has major advantages. This paper intends to indicate these advantages and outline an understanding of the disadvantages. These benefits can be classified in three basic groups: the financial and timing advantages, a knowledge of the ore body and the development of required technology to meet the design parameters. The required technology in many aspects was still to be developed prior to successful application. Stemming from the technological evolution are some secondary advantages which will be described in each of the groups. Safety and health considerations and some practicalities made some of the new technology redundant prior to the actual application. In each case the actual achievements and the anticipated benefits will be indicated to allow the reader to distinguish clearly between planned and actual achieved advantages.

Jan 1, 1997

By J. A. McLennan, J. M. Ortiz

Nickel laterite deposits are typically formed from tropically weathered mafic-to-ultramafic complexes. The resulting nickel concentration is found within soil horizons and is mineable with regular dozer units. At the time of mining, digging elevations are needed at selective mining units (SMUs) or representative dozer regions (RDRs). Moreover, for mine planning, the costs due to dilution and lost ore require mining elevations to be specified. A conditional simulation approach is used to calculate “optimum” RDR mining elevations. Multiple realizations of the ore base surface are simulated. For a single bottom surface realization, dilution and lost ore costs are calculated over the entire vertical extent of each RDR. The optimum mining elevation is the elevation where the lowest summed cost of “accepting dilution” and “wasting ore” occurs. The reported RDR dilution is the cost of mining the volume of waste located below the bottom surface and above the optimum mining elevation. The reported RDR lost ore is the cost of not mining the volume of ore above the bottom surface and below the optimum mining elevation. For all ore bottom surface realizations, optimum RDR mining elevations and their associated dilution and lost ore costs are calculated and compiled to represent production uncertainty.

Jan 1, 2006