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By David C. Oyler, Hakan Gurgenli, Gregory M. Molinda

Historically, miners have known that roof rocks originally composed largely of mud were prone to slaking and deterioration when exposed to water and humidity. Mine Safety and Health Administration (MSHA) records show that roof falls are more prevalent in summer and late fall. Field data shows higher bolt loads and increased room convergence in summer months. Laboratory data shows that very high internal pressures can be generated by significant strain in clay-rich rocks. In summer months humidities ranging from 70-100% can cause rock strains up to 7%, and rock pressures of 14,000 psi, more than enough to break apart weak shales and fireclays. The National Institute for Occupational Safety and Health (NIOSH) conducted wet/dry immersion cycling of clay-rich rocks. Results show that the rocks most prone to moisture deterioration are fireclays, claystones, and sandy shales, all of which have disrupted bedding. Of the 7 mudrocks with a weatherability index above 40%, none showed consistent fissile bedding. Black shales were surprisingly resistant to wet/dry water immersion cycling. Generally, mixed rocks (stackrock), typically susceptible to horizontal stress, are more resistant to moisture-deterioration. Mine roof rocks tested with moisture sensitivity ratings above 50% (moisture sensitivity index ranges from 0-100 with 100 being the most sensitive) all came from mines which had roof skin problems and used supplemental support to prevent rock fall injuries. Some roof rocks showed lateral variability of moisture sensitivity values, suggesting the need for more samples in highly varying roof rocks. Swelling strains of mudrocks showed that almost all of the swelling occurred in the first 24 hours after immersion. The wet/dry immersion cycling test used provides an accurate, quick and inexpensive method for estimating the moisture sensitivity of mudrocks. With this information mine operators can begin to anticipate hazardous ground and prepare appropriate roof support.

By Mark I. Copeland

A study was conducted to determine if commonly used alloying additions or coating materials can prevent the formation of a liquid-copper phase during the reheating of copper-containing steels. If so, the tendency of such steels to surface-crack during hot-working might be eliminated. Steel specimens were scaled by heating them either isothermally or in a programed manner that simulated industrial furnace practice. Metallographic examination of the heated specimens showed that molten fayalite (Fe2Si04) completely prevented the formation of liquid copper at the surface. Fayalite, which melts at 2,200° F (1,205° C), was formed by internal oxidation of the silicon contained in the steel. By forming complex molten oxides, coatings of borax glass were also effective in preventing the occurrence of liquid copper at the steel surface.

Jan 1, 1972

By M. Stephton, L. A. Cornish, R. Süss, N. B. Maledi, J. H. Potgieter, L. Chown

In today?s gas turbines, the emphasis is on saving energy and reducing the amounts of pollutants emitted. This can be attained only by designing alloys with higher melting points and the capability to retain mechanical integrity at increased temperatures. The development of nickel-based superalloys (NBSAs) has reached its limit, as the alloys are operating at critical temperatures close to their melting points. Further increase in the operating temperatures will result in dissolution of the strengthening phases and even melting. Recent trends are towards developing materials that are adequately strong but have much higher melting points and corrosion resistance than the NBSAs that are currently in use. Studies conducted on Pt alloys with similar structure to the NBSAs have presented mechanical results that are promising. This has led to further development of these alloys as a replacement for NBSAs. The operations of gas turbines are usually limited by hot corrosion, which could lead to catastrophic failures. Increased temperatures have an adverse effect on the corrosion of the alloys by making the environment more aggressive. Hence, during a material selection process, the corrosion behaviour of any selected material for a highly specialized application such as gas turbines needs to be assessed. Generally, coatings are applied to combat degradation by salt deposits, hence coated and uncoated NBSAs were selected as benchmark alloys. Corrosion mechanisms and kinetic studies of the Pt alloys were conducted. High temperature hot corrosion (HTHC) tests were conducted at 950°C for540 hours. Analysis of the corrosion products was conducted using a Raman spectrometer, scanning electron microscope with energy dispersive X-ray spectroscopy (EDS) optical microscopy, and X-ray diffraction study of the phases that formed. Both coated and uncoated NBSAs failed under the test conditions. Samples were covered with a porous non-adherent greenish layer which is characteristic of NiO. Pt alloys displayed superior corrosion properties compared with the benchmark alloys.

Jan 1, 2006

By Hanns J. Billmayer

Optimized Operator Compartment layouts based on previous Bureau of Mines activities in standardization and optimization of controls were designed and installed in three operating vehicles. Two National Mine Service 48A-36 TorKars were modified in production prior to delivery to the Quarto Mining Company. An Elkhorn AR-4 scoop owned by Adanac Coal Company was modified in a local rebuild shop. The modified vehicles were then evaluated underground under normal production conditions for a 60 day period. Vehicle operators and management appear well satisfied with the compartment modifications.

Jan 1, 1976

By Brian Stump, David Anderson, D. Craig Pearson, Robert Martin

Mining explosions designed to move, bulk or fracture rock are often composed of a number of explosions arranged in a complex spatial and temporal pattern. The effects of the explosions are strongly dependent upon the design and implementation of this blasting pattern. This paper describes the collection, combination and visual display of multiple types of data from these explosions for the purposes of understanding the relationships between the blast design, implementation, and observations. Data sets consist of three-component ground motion, acoustic, video and high speed film, three-dimensional topography, geological and geophysical properties, design blast pattern and timing, and velocity of detonation in the explosive for individual borehole detonation times. The explosions studied include simple single-fired contained explosions, ones designed to bulk and fracture rocks and those that cast material.

Jan 1, 2000

The past four years since the 2008 MINExpo have been a roller coaster ride for the mining industry, with highs and lows and everything in between. One of the natural consequences of this uncertainty has been a number of significant consolidations and mergers, and this trend has trickled down into the crushing industry. And while there have been some significant changes to this sector of the mining industry, many of the big players have weathered the storm. The following is a look at some of the mineral processing companies that will be at MINExpo. McLanahan Corp. McLanahan Corp. is an example of the changes in the sector. The crushing and grinding stalwart acquired Universal Engineering, expanding its traditional focus on soft mineral crushing to hard rock crushing. At MINExpo, it will be showing off three new pieces of equipment, the LabMill Crusher, the Rocker Tooth Crusher and the Recessed Filter Press.

Jan 1, 2012

By Dolly Chakraborty, S. Ranganathan, S. N. Sinha

Pre-reduction of chromite outside the submerged-arc furnace (SAF) can significantly lower the specific power consumption in the SAF process. Conventional processes for the pre-reduction of the ore operate at relatively high temperatures, at 1400-1500°C. It is possible to enhance the rate of reduction at low temperatures by optimizing the flow rate of inert gas over the reaction site. The influence of the flow rate of inert gas on the rate of reduction of chromite ore was investigated. The rate of reduction initially decreased wit the flow rate of the gas. It increased subsequently at higher flow rates to be followed by a decrease again. There was an optimum flow rate at which maximum reduction could be obtained. It was possible to achieve high levels of reduction at 1200°C by optimising the flow rate of the gas. The degree of reduction obtained was comparable to that obtained at 1400-1500°C, by conventional process routes.

Jan 1, 2007

By F. N. F. le Roux

This paper describes the method used for excavating the upper 33m of emergency access shaft E2 for the underground single track tunnel running between Park and Rosebank station of the Gautrain Rapid Rail System. The soil was decomposed shale and diabase from the Witwatersrand Supergroup. The location was in the car park of The Wilds (a public park) in Johannesburg. The method proved very simple and required less complex plant and equipment than normal when excavating the shallow soil sections in shafts. It involves driving steel sheets ahead of the shaft sump into the soils and then excavating inside the ?tub? created by the sheets whilst supporting the sheets above with regularly spaced circular Steel Rings. It is the intent of this paper to discuss the method and design approach to the method. This will be done at the hand of experiences at E2 shaft..

Jan 1, 2009

By F. N. F. le Roux

This paper describes the method used for excavating the upper 33m of emergency access shaft E2 for the underground single track tunnel running between Park and Rosebank station of the Gautrain Rapid Rail System. The soil was decomposed shale and diabase from the Witwatersrand Supergroup. The location was in the car park of The Wilds (a public park) in Johannesburg. The method proved very simple and required less complex plant and equipment than normal when excavating the shallow soil sections in shafts. It involves driving steel sheets ahead of the shaft sump into the soils and then excavating inside the ?tub? created by the sheets whilst supporting the sheets above with regularly spaced circular Steel Rings. It is the intent of this paper to discuss the method and design approach to the method. This will be done at the hand of experiences at E2 shaft..

Jan 1, 2009

By H. J. Glass

Collection, preparation, and analysis of blasthole chippings is expensive. Frequently, interpolation of grades at unsampled locations is considered using techniques like kriging. A pre-requisite for kriging is that an experimental variogram is established. In order to assess the quality of the experimental variogram, a measure is developed in this paper. The measure is derived from analysis of the time-honoured expression relating the variance, semivariance, and covariance. It reflects the weighted average deviation of the summed semivariance and covariance from the biased variance. The proposed measure allows assessment of the influence of key variables on the quality of the variogram. Using simulated data, it follows that the quality improves with an increasing number of samples, increasing density of the sampled locations, increasing regularity of the sampling pattern, and increasing uniformity of grades in the absence of correlation. Application to real data shows that the minimum number of samples could coincide with a marked decrease in the value of the measure. Establishing a threshold value is subject to further research. Keywords: variogram, variance, covariance, semivariance, minimization, sampling.

Jan 1, 2003

By M. Laliberte

"Gold-mine effluents are often characterized by high concentrations of copper, ammonia and cyanide derivatives (mostly cyanates and thiocyanates). While not acutely toxic to birds, this water can be acutely toxic to fishes and invertebrates. In many jurisdictions, the effluent requires further treatment in order to pass a mandatory requirement to be nonlethal to species like the rainbow trout (Oncorhynchus mykiss) or Daphnia magna. Using actual mine water, it has been demonstrated that aerated moving bed biofilm reactors will biodegrade the ammonia, cyanides, cyanates and thiocyanates, thereby removing the toxicity associated with these components. By removing copper by precipitation the water can be made to pass acute toxicity tests. Tests have demonstrated that the process is stable between 4 and 25°C, with no significant changes in the treated water composition. Once the biomass is acclimatized, the process is resistant to upsets and requires very little inputs except for phosphorus and air. Furthermore, it has been demonstrated that an anoxic reactor can be added downstream of the aerated reactors to remove nitrates if required.IntroductionThis paper will demonstrate that gold-mine effluents, which are toxic to fishes and invertebrates, can be made nontoxic by using a combination of chemical precipitation and biological oxidation.The typical composition of gold-mine effluents will first be described. The applicable legislation will then be introduced, with its requirement that the treated effluent be nontoxic. The toxicity of a typical untreated effluent will then be confirmed, and the sources of the toxicity identified. After that, a number of toxicity reduction treatment methods will be presented, and the selected method will be described.The lab tests that confirmed the efficiency of the treatment method will be presented, with three phases of testing as the understanding of the process gradually improved. Toxicity test results showing that the water is nontoxic after treatment through the temperature range will be presented."

Jan 1, 2015

By A Giblett, K Afewu

This paper uses a case study to demonstrate best practices techniques for predicting the contribution of gravity concentration in a gold recovery process flowsheet. The case study was selected as an example of an ore with a marginal gravity gold content, which makes the value of a gravity circuit difficult to quantify. In this instance the value of leveraging a significant knowledgebase of operating gravity circuit performance to support the decision making process was demonstrated. This case study analysis serves as a useful demonstration of best practice methodologies supporting decisions to include or exclude gravity recovery in a gold recovery process flowsheet.CITATION:Giblett, A and Afewu, K, 2015. Do we need a gravity circuit or not? A case study in applying best practice, in Proceedings MetPlant 2015, pp 288–295 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 7, 2015

By K Afewu, R Dunne, W P. Staunton

The treatment of preg-robbing gold ores has always been a technical challenge in the gold industry. Early solutions included removal of preg-robbing carbonaceous material by flotation, the addition of kerosene to æblindÆ/passivate the surface of the preg-robbing component, and the most effective of all options, roasting the ore. Unfortunately gold ores have become more complex and roasting has environmental challenges, so other methods of treatment have had to be found. This paper will review methods of characterising preg-robbing gold ores, method of treatment and cite examples of actual application in the industry.CITATION:Dunne, R, Staunton, W P and Afewu, K, 2013. A historical review of the treatment of preg-robbing gold ores - what has worked and changed, in Proceedings World Gold 2013 , pp 99-110 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013

By David A. Larson

Preliminary laboratory experiments have been conducted by the Bureau of Mines to define the influence of bit geometry on methane ignitions as a step toward establishing safer mining-machine operating parameters. The experimental system was designed to simulate the operation of a continuous mining machine, using a drum-type cutterhead of normal diameter with a narrow cross section, permitting full-diameter drum cutting tests to be run on material representative of sandstone lenses (or inclusions) in coal seams. Two conical bit types were tested at shallow depths of cut with three drum speeds. Bits that rotated in the mounting block during testing did not produce ignitions. The ignition frequency for used bits was three to four times greater than for new bits at the same kerf depth.

Jan 1, 1983

By Tianjiao Luo

The electroless copper plating process for continuous carbon fiber using CuSO4?5H2O as the main salt and formaldehyde as reducing agent was experimentally studied, including the effects of pH values and concentration of chelating agents, stabilizing agents and reducing agent on the electroless plating process. The surface morphology and the composition of coating were investigated by means of Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS), and deposited the coating thickness was measured by way of dissolution. The results indicated that the pretreatment of carbon fiber before plating was so important. This pretreatment could prevent the formation of the black cores, furthermore, it could form many active absorption cores with Ag as the center on the carbon fiber surface. Used the optimized parameters in this process, which led to a stable solution for plating, a homogeneous copper coating was conducted with the carbon fiber plated with favorable mechanical performance and high adhesion strength.

Jan 1, 2006

The French research institute, INERIS, requested the assistance of the CSIR?s Division of Mining Technology in developing further precautionary measures against explosions in their collieries. In response to this approach, an on-board active suppression system was adapted to meet their mining requirements. This system is used on tunnelling machines in Germany where the machine is positioned in the middle of the tunnel, which is therefore not much wider than the machine itself. With this configuration, the machine is never away from the tunnel face during the cutting cycle. As a result, the possible volume in front of the machine of combustible gas requiring suppression is less than 50 m3. In South Africa this technology has been adapted to suit a two-cut mining method which entails greater distances from the face and thus much larger volumes of methane mixtures requiring suppression. The particular configuration of the Explo-Stop® system being investigated required the suppression of possible methane ignition volumes of up to 180 m3of a 9% per volume methane/air mixture. The volume is a consequence of the large cross-sectional area of French underground workings and of the two-cut mining method used in France. In order to take the second cut in the coal seam, the machine is pulled back a maximum distance of 4 m, leaving an air pocket in which gas can accumulate. The machine-mounted system is required to effectively suppress any flame ignited by such a large accumulated volume of methane. The results of the protocol tests done at Kloppersbos showed that the system was capable of suppressing all simulated methane ignitions for the prescribed conditions. This was achieved with a temperature increase of less than a 100°C at the operator?s position and without any flame being detected at this position.

Jan 1, 2001

By D. Tesh

The mining industry worldwide is facing a tremendous shortage of minerals engineers in all fields of specialization. For instance, in Australia the skills shortage in the mining industry has been identified as one of the top risks facing the mining industry. In Namibia most minerals engineers employed are expatriates, with some being Namibians who studied abroad. The minerals engineering programmes at the Polytechnic of Namibia are still in their infancy. These programmes were designed to meet the mining industry skills needs. Being young has its advantages in that lessons can be learnt from older minerals education institutions that went through similar challenges. However, this does not imply just copying and implementing their approaches, since the context differs and, to ensure sustainability of the minerals education programmes, curricula have to be customized to the local context. This paper reviews the interventions made by the Polytechnic of Namibia in order to ensure the sustainability of its minerals education programmes. The methodology consisted of an extensive literature review, a status quo analysis of the mining and process engineering department, identifying the gaps between the current state and desired state, and mapping the goals and strategic actions required to progress to the desired state. The following factors were identified as major threats to the sustainability of minerals education at the Polytechnic of Namibia: the quality of students, low student enrolment rates, low pass rates in science and mathematics, shortage of academic staff, dwindling government funding, and limited involvement of the mining industry. The major outcomes of this research comprise the detailed strategic actions employed by the Polytechnic of Namibia to address the threats to sustainability of its minerals education programmes.

Jan 1, 2014

The coal-based power generation industry faces increased pressure from all sectors to improve its environmental performance. This is due to increased awareness of and concerns regarding greenhouse-and acid-gas emissions, toxic metal releases (to both air and water) and water availability. A methodology to assess this industry?s environmental performance is needed. Such a methodology should assess all environmental impacts accurately, recognizing the irspatial and temporal dependence, and taking into account the social acceptability of technologies employed. Here, we develop a methodology to determine the environ-mental impact associated with solid wastes generated by this industry, and apply this to the specific case of ash management. More specifically, the case study compares the environmental footprint of an ash deposit for a number of operational water management scenarios. The methodology considers leachate generation processes from ash impoundments to obtain a time-dependent concentration profile of mobile constituents at the interface between the ash impoundment and the surrounding environment. This leachate prediction modelling is subsequently linked to plume dispersion modelling tools to determine the fate and transport of leached components, predominantly salts, into groundwater. Together, these provide a measure of the extent to which a land mass is affected by leachate migration from the deposit. To determine the exact boundary between regions of acceptable and unacceptable risk to the environment, we use Ecological Risk Assessment concepts. In this way it is possible to obtain a time dependent affected land footprint which could be used as an indicator of the environmental impact of solid waste management practices. This information can be included in a set of environmental criteria which form the basis of an overall environ-mental impact assessment, using tools such as Life Cycle Assessment (LCA). The value of LCA is that its structure is consistent with accepted models of environmental decision making, where different approaches to valuation in impact assessment assist in prioritizing impacts on the basis of their perceived significance. The proposed ?affected land footprint? metric represents a significant improvement over current LCA impact indicators for solid waste management practices. Keywords: Environmental Impact Assessment, Environmental Risk Assessment; Life Cycle Assessment; coal ash; leachability; salinity

Jan 1, 2002

By Robert Fernie

Demographics and Infrastructure demands have led to a significant increase in construction of: deep basements for buildings and, trough structures for Highway and Rail/Metro. Concrete embedded walls used for temporary works can be incorporated into permanent works and because of this (and geological conditions) tend to be favoured in UK. This paper considers British practice in the provision of diaphragm (slurry) walls secant (true and pseudo) piled walls contiguous piled walls Plant utilisation, construction techniques, reinforcement placement, connections, propping, water tightness, tolerances, general UK practices and their relation to design practices are discussed. [ ]

Jan 1, 2000

By L. B. Berger

From time to time the Bureau of Mines receives requests for information and advice regarding the safety of using internal-combustion engines operated on butane fuel as prime movers for haulage and other purposes in mining and tunneling. The purpose of this, circular is to discuss the properties of butane and to present data in regard to the possible use of this fuel in underground operations. Published information on the use of commercial butane as a fuel for internal-combustion engines indicates that, insofar as performance is concerned, butane may be utilized satisfactorily and efficiently for this purpose. However, the introduction of a volatile, inflammable material such as butane into confined spares such as mines or tunnels would create potential fire and explosion hazards that should be given due consideration by those concerned with the promotion of safe practices.

Jan 1, 1944