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By R. Karl Zipf, Suresh Bhatt

Highwall mining is an important coal mining method. It appears that upwards of 60 highwall miners are presently in operation, and they may account for approximately 4% of total U.S. coal production. A review of the Mines Safety and Health Administration (MSHA) data over the 20 year period from 1983 to 2002 identified 9 fatalities attributable to auger and highwall mining of which inadequate ground control accounted for 1/3. In the past 5 years, 1 fatality occurred in highwall mining. Estimates of the manpower requirements in highwall mining suggest that its fatality rate is essentially the same as for surface coal mining, thus highwall mining appears to be a very safe modern mining method. Highwall stability is the major ground control related safety concern, and operators are required to develop and follow an appropriate highwall mining ground control plan. The plans usually specify the following geotechnical parameters: hole width, maximum hole depth, maximum overburden depth, seam thickness, web pillar width, barrier pillar width and number of holes between barriers. Calculated web pillar stability factor exceeded 1.3 for most designs evaluated. This study examined records from 5,289 highwall miner holes with a total completed footage of about 2,560,000 feet to understand the reasons for early pull out. Average lost footage is typically about 20% of planned footage. Only 35% of the holes reached planned depth, and 20% were short due to rockfalls. Water and adverse geology accounted for 15% of the losses. Mechanical/electrical problems, guidance, and slope stability problems accounted for the remaining 30%. Web pillar stability factor for these holes also exceeded 1.3 in 95% of cases. Best practices to avoid trapped miners include: avoid mining in stream valleys, avoid mining near outside corners, careful alignment of each hole and the use of an onboard guidance system. Several issues in highwall mining ground control require further investigation including highwall mining through old auger workings, highwall mining near old underground mines, multiple-seam and multiple lift highwall mining and finally the size and frequency of barrier pillars.

By J. T. Tanner

The research activities of the Minerals Research Laboratory, which is a part of North Carolina State University, is normally confined to solving beneficiation problems, and developing flotation processes for the mining industry. In recent years the laboratory has veered from its main purpose somewhat and has placed some emphasis on the manufacture of products from mineral concentrates. This has been the result of requests for help from industry. One such request came to the MRL from a talc producer in North Carolina who was having a difficult time competing with foreign imports of steel marking crayons. He felt that if a process could be developed whereby a satisfactory crayon could be produced from powdered talc at a low cost that he could compete.

Jan 1, 1986

By Tiago Silva Costa

O processo que envolve soluções aquosas para remoção do metal de valor de uma grande massa de ganga, com um beneficiamento mínimo, é denominado Lixiviação. A especificidade do agente lixiviante empregado define a capacidade de tratar soluções com baixos teores do metal de interesse e o sucesso do processo. A lama da aciaria, recolhida no sistema de limpeza dos gases oriundos do convertedor LD, e a lama da eletrogalvanização, gerada após a neutralização da solução de zinco contaminada com ferro, são resíduos sólidos gerados nas usinas siderúrgicas com potencial de serem reutilizados ou reciclados. A fim de se remover o óxido de zinco presente nas lamas, amostras foram coletadas e preparadas para sofrerem o processo de lixiviação em escala laboratorial usando soluções de hidróxido de sódio (NaOH) e ácido sulfúrico (H2SO4). Os resultados obtidos nas análises mostraram que é possível remover óxido de zinco através da lixiviação das lamas.

Aug 16, 2017

By H. L. Miaw, A. M. Gaudin, D. W. Fuerstenau

A quantitative method for evaluating density of slime coatings has been developed and applied to formation of iron oxide slime coatings on quartz and on corundum. Slime coating density is related to flotation recovery and to properties of the electrical double layer at mineral surfaces. IN spite of considerable study, the nature of slime coatings in flotation is still not completely understood. However, phenomena that control floc-culation and dispersion of colloidal systems are now interpreted in terms of electrical double layers.",' Colloids will flocculate even though the particles carry the same charge, but when two dispersed colloids of opposite charge are mixed. flocculation ensues even more rapidly. Analogous phenomena seem responsible for slime coating on minerals in flotation systems. To shed new light on the issue it was considered desirable to devise a tool that would measure slime coatings. The usual method has been to examine photographs of presumably representative surfaces, after. an intervening washing in running water. But such an examination is non-quantitative, and the changes in chemical environment represented by the washing may have removed the slime coatings that existed during flotation. To provide the possibility for a correlation with electrical double layer phenomena, the experiments were made with quartz, corundum, and iron oxide, for which elec-trokinetic data are available.'-" Since the properties of the electrical double layers of these oxides depend on the pH of the solution, pH will be the most important variable. Furthermore, because the zero point of charge for silica, iron oxide, and alumina occurs at pH 3.7, 8, and 9.5, respectively, the relative charge on the slime and mineral can be changed over wide ranges. Because of its practical importance in quartz flotation, iron oxide powder was chosen as the slime. Also, its uniform composition, contrasting color, and ease of analysis make experimentation simple. In this investigation, correlation was sought between the effect on flotation recovery of slime addition and slime coating density. Materials and Methods Details are available in a thesis by Miaw." The quartz was selected from pure Brazilian crystalline quartz, crushed, sized (65/150 mesh) acid-cleaned, washed, and stored in conductivity water. The corundum (synthetic alumina of high purity prepared by Linde Co., Chicago) was crushed, sized (65/100 mesh) deslimed, boiled in nitric acid, washed, and stored in conductivity water. The iron oxide slime, reagent-grade ferric oxide (—400 mesh) from Allied Chemical & Dye Corp., was heated to 160°C, cooled, and stored in a vacuum desiccator. In the electron microscope the slime particles appeared to be about 0.3µ in size, but their large specific surface (87,900 cm per g, by gas-adsorption method, using krypton) suggests that the actual particles are smaller than 0.3r. Had they been perfect nonporous spheres, they would have had a diameter of 0.13µ.

Jan 1, 1959

By Donald J. Murphy

Longevity of structural units, as compared to the planned useful life of a facility, always is a design consideration. Typical concerns include slow decay due to environmental factors, and changes in constitutive relationships governing the performance of the material involved. With respect to foundations, the usual items of interest are corrosion of steel and concrete, and time dependent behavior of the soil/structure system. For piles, as with other foundations, deterioration is precluded, mitigated or otherwise accounted for by assessing properly the ambient situation (sulphates, pH, stray currents, resistivity) and providing safeguards, such as resistant construction products, oversizing, coatings, and/or cathodic protection. On the other hand, long term performance of the pile foundations, as affected by time dependent characteristics of the supporting soil or rock, can be predicted and controlled only with a synergetic coupling of analyses and field tests. The history of a project for which this approach was followed forms the basis for this paper.

Jan 1, 1986

By Stanley F. French, Bruno F. Koch

Although the amount of dust that will be actually recovered in the six main dust-control systems cannot be accurately stated until the tests mentioned previously are carried out, it is estimated that the average air entering the wet collectors will contain around 5 grains of dust particles per cubic foot. This means that the six systems handling a total of about 133,000 cu.ft. of air per minute will return about 68 1/2 tons of dust to the concentrator per day and since the copper in this dust will average around 2 per cent, the total recovery is approximately 1.37 tons of copper every 24 hours. This important copper recovery is not due entirely to the dust-control system since in a plant without control only the duct that is dispersed to the atmosphere represents a loss. A conservative estimate of the recovery of copper solely due to the dust control system would be about half of the total or approximately 0.70 tons of copper per day.

Jan 1, 1942

By Konstantinos Modis

According to recently established theoretical analysis and under certain conditions, a critical sampling density can be determined for an earth-related space-distributed natural variable. Sampling above this critical limit adds little to the mapping results. The objective of this paper is the application of the above theory to the Sesklo clay quarry in Greece, where Heracles General Cement Company had conducted a sampling campaign to estimate its reserves. The structural analysis of Al2O3 values generated a variogram model, from which the critical sampling density was identified. This critical number was by far lower than the existing sampling density. Clay reserves were then estimated using geostatistics and inverse distance squares in different data schemes with variable densities. The results of the comparisons between the various models revealed that, when the sampling density was greater than its critical value, geostatistics and deterministic interpolation gave similar estimations, which is also in agreement to the theory. The optimal sampling grid finally proposed here, will result to significant cost savings in the next drilling program which is now in plan by the company.

Oct 1, 2009

By W. G. Pariseau

Face and pillar bursts, bumps and bounces are violent failures that occur in underground coal mines in response to a complicated interplay of face and pillar geometry, seam depth, coal strength and moduli and interactions between roof, seam and floor strata. Additional complications arise from the presence of gas, mainly methane, and associated pressure and flow that vary with time and are further influenced by the rate of face advance. Numerical models provide a means of quantitatively accounting for the various complications of mining geometry, the stratigraphic column, mechanical properties, gas flow properties and associated interactions. A fully coupled hydromechanical finiteelement code, utAH4, serves the purpose well and allows study of the important interaction between stress concentration and gas pressure in determining safety and stability of the face during the advance of a longwall panel in a deep underground coal mine in central Utah. Face advance is relatively fast compared with gas flow and depressurization in coal seams of low gas permeability. Consequently, gas pressure is high at the face. When a longwall is stationary, depressurization occurs at the face, so effective stress and strength increase. thus, when gas flow at the face is high and requires a pause in face advance to bring gas concentration to an acceptable level, a second benefit occurs because of timely depressurization. However, quantitative analysis of a deep coal mine shows that regardless of gas pressure, high stress concentration is more likely to pose a threat to face and pillar wall stability.

Aug 1, 2013

By R. W. Parsons

The over-all apparent single-phase permeability of fracture-rock systems was studied using two different two-dimensional models. In a strict sense the results are applicable only to these models, yet may give some insight into real reseruoir behavior. The regular fracture-matrix model can have any number of regular fracture sets. All fractures within each set have the same orientation, width and spacing. The gross behavior is amlytically equivalent to that of an anisotropic permeable medium. In the heterogeneous fracture systems, individual fracture conductivities vary within a two-dinensioml network pattern. A computer program calculates the overall permeability after the conductivities are randomly placed in the network. The calculated permeability depends upon the distribution of these conductivities and the particular fracture pattern into which they are placed. Although detailed information on actual reseruoir fracture systems is not available, this study shows how some of the possible variables may affect obserued gross reservoir characteristics. INTRODUCTION Characteristics of reservoir rocks are determined by direct (core analysis) or indirect (logging and production tests) examination. Both methods, singly and together, are widely used in reservoir evaluations. For fractured reservoirs a problem exists in relating characteristics of cores to the in situ reservoir properties. Knowing fracture characteristics can be of value in determining production mechanisms. Because of the limitations of observation, the intimate details of a fractured rock system will never be known. One approach in analyzing fractures is to study the behavior of some conceptually simple models. The two models analyzed contain features which may be realistic, yet are mathematically tractable. Flow is considered in two dimensions only, with the plane of interest at right angles with the fractures. This concept represents the horizontal flow in a reservoir system with the fractures oriented vertically. Only single-phase, laminar flow is considered. The regular fracture-rock system permeability is calculable from a simple analytical expression. The heterogeneous system requires a computer program for calculating overall permeability.

Jan 1, 1967

By R. Holmestad, M. Gazizov, S. Wenner, R. Kaibyshev, J. K. Sunde

"Mechanical properties and microstructure of an Al-4.7Cu-0.74Mg-0.51Si-0.48Mn-0.10Cr-0.09Ti-0.02Fe (wt. %) alloy subjected to various thermomechanical processing (TMP) have been investigated and compared to conventional ageing at 170°C (designated T6). Three TMP routes involving cold deformation of solution treated samples were tested. These were (i) 3%-stretching (T8-3%), (ii) equal-channel angular pressing (ECAP) to true strain (e) of ~1 (T8-1) and (iii) ECAP to e~2 (T8-2), all with subsequent ageing at 170°C for 0-96 h. At peak age conditions, both yield stress, ultimate tensile strength and elongation-to-fracture decreased for the T8-3% state as compared to the T6 condition. Intermediate ECAP (T8-1 and T8-2) lead to significant increase in maximum yield stress, ultimate tensile strength and elongation-to-fracture. The changes in mechanical properties were related to microstructure evolution, encompassing changes in grain sizes, dislocation densities, precipitate morphology and phase fractions, which were characterised using transmission electron microscopy. Relations between TMP, precipitation behavior and contributions to different strengthening mechanisms are evaluated.INTRODUCTION Al-Cu-Mg-Si alloys are widely used as structural materials in aerospace industry due to their attractive combination of high specific strength, good fracture toughness and enhanced creep resistance. These properties are largely due to the formation of a large number of nano-sized metastable precipitates during artificial ageing (Polmear, 2006; Eskin, 2003; Gazizov, Dubina, Zhemchuzhnikova, & Kaibyshev, 2015). The precipitation behaviour in these alloys is complicated and depends among other things on Cu concentration and the Mg:Si ratio (Wolverton, 2001; Chakrabarti, & Laughlin, 2004). In general, the precipitation sequence has been presented in a prior study (Eskin, 2003) as follows:"

Jan 1, 2018

Ensuring the success of a major resource development project, whether in the Gippsland Basin or elsewhere, is typically both a complex and costly process. It is therefore imperative from the point of view of the proponents of such a project - and in particular the financiers - that everything possible be done to minimise administrative confusion and delay in the establishment phase of the project, and to put systems in place which enable the project to run smoothly and efficiently in the later stages of its development and operation. An essential element in this process is ensuring that the project management is able to come to terms with and deal effectively with the relevant planning and environmental laws.

Jan 1, 1992

By Jin He

Based on the simple-beam theory, a stress analysis model was established for undermining in multiple seam strip-pillar mining when the strip pillars were not columnized; the effects of various mining factors (e.g., mining depth, inter-burden thickness, recovery ratio, etc.) on inter-burden stability were analyzed; the changes in inter-burden stress distribution were investigated; and the important role that the inter-burden spacing and the mining width of the lower seams on inter-burden stability was studied. Finally, the actual practice used in Feng Feng Mine area was used as an example to demonstrate the rational mining width for a fixed mining depth.

Jan 1, 2006

By T. M. Barczak

One of the primary goals of Bureau of Mines research is to reduce the cost of coal mining by improving the efficiency of longwall supports. One method of achieving this goal is the optimization of stress distribution within the support structure, resulting in a lower overall weight, more fully stressed shield. However, before stress optimization can be initiated, load conditions must be defined that cause maximum stress in the various support components. A finite-element model of a longwall shield was used to identify these critical load conditions. These load conditions were then evaluated in the Bureau's mine roof simulator (MRS) by instrumentation of a longwall shield and measurement of strains in each of the shield components. The critical (canopy-base contact) load conditions were identified that can cause structural failure at less than rated shield (hydraulic yield) capacity. Comparisons were made between full-contact and partial-contact load conditions. Other parameters investigated included the stiffness of the contact material, changes in shield geometry, rate of load application, and effects of horizontal constraint. Conclusions were drawn regarding the structural integrity of the major shield components and potential for stress optimization.

Jan 1, 1987

By Larissa Rodrigues de Carvalho Rocha, Mauro Vivaldino Fernandes, Maurício Covcevich Bagatini, Beatriz Fausta Gandra, Adriano Cesar Carvalhido

O combustível com menor granulometria, denominado small, pode ser carregado juntamente com a carga metálica, em substituição ao coque, no intuito de melhorar as condições de permeabilidade do gás e a redutibilidade da carga no alto-forno. Na Usiminas, o equilíbrio na geração e no consumo desse material limita o seu uso em taxas abaixo da média nacional. Nesse sentido, foi avaliado o efeito do coque verde de petróleo (CVP) em substituição ao small coque no consumo de combustível e na estabilidade operacional do alto-forno. Os resultados do teste industrial indicaram a possibilidade de substituição até 45 kg/t gusa, com manutenção do fuel rate, da permeabilidade e da produtividade do alto-forno.

Oct 1, 2019

By R. G. Nelson

The mechanical properties of low-hafnium, arc-melted, Kroll-process zirconium are presented. The effect of temperature on the ultimate strength, yield strength, proportional limit, elongation, hardness, Young's modulus, electrical resistivity, and impact strength are shown, The effects of cold work and annealing on the tensile properties, bend radius, and formability, as determined by cupping tests, are also given, Tensile properties are compared, in part, to those obtained on earlier graphite-melted zirconium and on crystal-bar zirconium. INTRODUCTION The commercial production of high-purity, low-hafnium bearing zirconium has been achieved, and this metal is becoming available for industrial use. However, there is little published information regarding the physical and mechanical properties of this product; and, since there have been many improvements in the production and arc-melting techniques of zirconium in the past 3 years, it was considered advisable to present the properties of the vastly improved zirconium representative of current production.

Jan 1, 1954

By Georges Delemontex, Nigel Grigg

"Pre-concentration of precious metal and base metal ore types is becoming more relevant with the discovery, development and operation of many lower grade deposits around the world. The fluctuations in metal prices and currencies expose many mines to risks especially dealing with low and variable ore grades. Pre-concentration, the process of concentrating the valuable metal into a smaller mass yield, effectively results in the introduction of higher feed grades to milling circuits. Gangue rejection, the removal of lower S.G. waste rock from the circuit, not only results in higher downstream grades but also potentially removes harder, non-valuable mineral, providing significant power savings within the circuit. The pre-concentration or ‘gangue rejection’ process offers a number of benefits when considering the treatment of marginal ore deposits, especially if it can be performed at a coarse crush size; these benefits include a reduction of the operating costs and the feed of more metal units to the mill. Gekko Systems has effectively utilized the Inline Pressure Jig (IPJ) to pre-concentrate the valuable metal, achieving high primary recoveries into a range of mass yields resulting in upgrade ratios between 2 and 10 times. This paper explores: the benefits of pre-concentrating ‘marginal’ ore deposits prior to the milling circuit; the selective rejection of ore types that may affect either the recovery or comminution process; and also looks into the potential to effectively reduce the ‘cut-off’ grade when considering the mine planning process. Case studies of projects using the IPJ to pre-concentrate and reject gangue are also included. Pre-concentration and gangue rejection provide the potential to develop marginal ore deposits, thus providing higher grades, less gangue and more metal at a lower operating cost to producers."

Jan 1, 2014

By H. Linder, W. H. Dennen

The graphitic carbon content of soils may be used to detect and delimit subsurface graphitic zones. Spectrographic measurement of carbon in C horizon soils from several areas in the northeastern United States shows good correlation with known graphitic bodies. Bodies of graphite and sulfides are readily located by electromagnetic prospecting methods, but these methods cannot generally discriminate between them. Usual practice, therefore, requires follow-up work on electrically anomalous areas by trenching, drilling, or soil sampling in order to determine the mineralogical nature of the conductor. The efficiency and cost of such follow-up is consequently an important factor in prospecting. The presence of buried sulfide deposits is often reflected in concentrations of metals in the superincumbent soil. Simple chemical tests for such metal concentrations have been developed and applied with considerable success. Bodies of graphite or mixtures of graphite and sulfides are, however, very common and a means whereby buried graphite could be detected by soil testing should provide valuable additional information in the search for ore sulfide and graphite deposits. Graphite is a notably stable substance and should persist in soil above graphite-rich horizons. Microscopic examination of soil samples high in carbon, however, failed to reveal any recognizable graphite fragments indicating a grain size in the clay range. Presumably such small particles would have some mobility in a soil by a translocation mechanism similar to that proposed for the movement of clay particles in a soil profile. Experimental data supports this idea since the boundary between background and anomalous soils carbon values is quite sharp, but the anomalous zone is slightly broader than the graphitic source rock. A simple spectrochemical technique for the determination of carbon in geological materials has been described by Dennen,1 and may be directly applied to soils. A modification of this technique which employs an arcing chamber through which nitrogen is passed is recommended to decrease contributions from atmospheric carbon dioxide. Tests indicate that soils over graphitic zones may be strongly enriched in carbon. The spectrochemical determination of carbon depends upon the formation of the cyanogen molecule (CN) from carbon in a sample and atmospheric nitrogen, under the high temperatures associated with a dc arc. Samples for analysis are dried, lumps broken, and screened. A small portion of the -100 mesh fraction is packed into a copper electrode and excited as the cathode of a dc arc. The band spectra of cyanogen are recorded photographically and the density of the bandhead CN 3883A is measured. The limit of detection of the method is about 0.01 pct C and its coefficient of variation is about 15 pct. Soils, of course, contain carbon in other forms than graphite, and the amount of interference from such sources was examined. The C horizon of several soils from Massachusetts, Maine, and Pennsylvania were found to have a carbon content of 0.3 to 0.5 pct by weight. This content is chiefly due to the presence of carbonates and vegetable matter in the sample and may be readily eliminated, or at least

Jan 1, 1961

By André Desbiens, Jocelyn Bouchard, René del Villar

"The metallurgical performance of the column flotation process is determined by the concentrate grade and recovery. Although the former can be continuously measured using an on-stream analyzer, the latter must be estimated by a material balance calculation based on seldom verified steady-state assumptions. Consequently, the automatic control and optimization of flotation columns should be performed using secondary variables having a strong influence on the metallurgical performance, such as froth depth, gas hold-up or bubble surface area flux and bias. The aim of this paper is to present a model-based automatic control strategy using froth depth and bias measurements obtained from virtual sensors developed at Laval University. Preliminary pilot plant results on two-phase (water– air) and three-phase system (water – minerals – air) will be presented and eventual industrial implementation of such a strategy as well as the possibility of achieving effective real-time optimization from bias and froth depth measurements will also be discussed.INTRODUCTIONFlotation columns have been widely studied and used in mineral processing for about twenty years. Although a great deal of work has been accomplished to understand the influence of different variables such as froth depth (H), bubble surface area flux (Sb) and bias (Jb) on the metallurgical performance, the measurement of some of these variables is still difficult to be performed – except at the laboratory level – because in most cases, no commercial device yet exists.As a result of this, it is almost impossible to achieve neither efficient control nor optimization of the process at the industrial level, even in open-loop operation. This paper aims at presenting a simple control strategy of froth depth and bias. Description of the sensors used to achieved measurements, preliminary pilot plant results for froth depth control, eventual industrial applications and possibilities for process optimization are also treated."

Jan 1, 2003

By Alastair Grogan

In October of 2002, the author was retained by Public Works and Government Services Canada, on behalf of the Department of National Defense, to design, construct and test the effectiveness of a bubble curtain system at an underwater demolition range, near Victoria, BC. The purpose of the bubble curtain was to reduce the potential for fish mortalities at the site. This paper presents some of the elements of the design, along with the results of overpressure monitoring during blasting and compares the results of fish mortality and animal behaviors with and without the bubble curtain in operation.

Jan 1, 2005

"The Archaean komatiite-associated nickel sulphide deposits at Kambalda, Western Australia, exhibit a number of stratigraphic features that are indicative of a strong volcanic control on ore localization, including (1) a restriction to specific basal cumulate metakomatiite host units, (2) confinement within distinctive synvolcanic embayments in the footwall and (3) variations in the internal structure and composition of overlying and adjacent barren metakomatiite flow's and the distribution of interflow metasediments with proximity to the ore zones.The high magnesium content of the host units (up to 45% MgO volatile-free) in comparison with that of aphyric or spinifex- textured lavas (16-32% MgO) has been considered previously to indicate either magmas/lavas rich in intratelluric olivine or selective accumulation of olivine phenocrysts. The marked linear trend of the oreshoots, basal host units, footwall embayments and the volcanic stratigraphic relationships have been used as evidence for local linear feeding fissures. Rare relict igneous olivine in some host units is, however, demonstrably not intratelluric, and there is no direct or indirect evidence of a proximal eruptive site (e.g. footwall feeders, pyroclastic breccias, ultramafic intrusives) at Kambalda such as at some other deposits of this type. Kambalda is interpreted as a distal rather than proximal volcanic environment.Emplacement of the komatiite sequence at Kambalda was probably controlled by the locations of a few specific eruptive sites relative to regional topographic gradients and influenced by the topography of the pre-existing volcanic surface. Olivine enrichment in the basal host units occurred by in-situ fractionation and cumulus crystallization of olivine during longitudinal lava flow within linear lava conduits, possibly centralized on depressions between non-overlapping footwall basalt flows. The distinctive stratigraphic relationships are attributed to localization of lava conduits along the volcanic pitchline, flanked by more slowly moving parts of the flows. There are analogies with the physical volcanology of Modern basaltic and Proterozoic komatiitic lava flows.A corollary of this model is that the lava conduits thermally eroded and assimilated sulphidic sediments, contributing additional sulphur to sulphur-saturated komatiites or possibly inducing sulphide separation in originally sulphur-undersaturated komatiites. The latter would account for the restriction of ores to linear cumulate komatiite host units (thermally active lava conduits) and the locally mutually exclusive, but stratigraphically equivalent, relationship between the ores and sulphidic metasediments at Kambalda."

Jan 1, 1984