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By A. Pytlik, W. Masny

"Underground mining is subject to various natural hazards such as seismic events, rockbursts, fire, and gas (methane). In general, an increase in the extraction depth causes an increase in the likelihood of these hazards, especially seismic activity and rockbursts. Dynamic phenomena such as rockbursts and tremors have been recorded on six continents: Europe (Poland, Russia, Czech Republic, Germany, and Slovenia), Asia (India, and China), North and South America (USA, Canada, and Chile), Africa (South Africa), and Australia. To select appropriate mine working supports for such dynamic phenomena, the performance characteristics of such support types must be determined under both static and dynamic load conditions.This article presents information regarding the application of rockbolts in Polish underground hard-coal mines. Dynamic phenomena occurring in the mines from 2004–2013 are also characterized. A methodology developed at the Central Mining Institute (GIG) for the laboratory testing of rockbolts is presented. In this methodology, the bolts are loaded by the direct impact of a free-moving mass (up to 20 000 kg) at speeds of up to 1.2 m/s. The facilities at GIG used to test the support under static and dynamic load conditions are characterized, and the results of laboratory tests on yielding bolts with a nominal capacity of 420 kN are presented. These types of bolts are commonly used for reinforcing steel arches and the surrounding rock mass in Polish coal mines. The results of the laboratory testing of yielding bolts are discussed.IntroductionSeismic events such as rock bumps and tremors occur with great frequency during underground mining. These phenomena have been reported in such countries as Poland, Czech Republic, Germany, France, Slovenia, Russia, India, China, the USA, Canada, Chile, South Africa, and Australia (Brauner, 1991; Potvin, Hudyma, and Jewell, 2000; Kidybin??ski, 2003; Driad-Lebeau et al., 2005; Li, Cai, and Cai, 2007; Whyatt and Loken, 2009; Durrheim and Riemer, 2012; Holub, Rušajova, and Holec?ko, 2011). Descriptions of the dynamic events and their effects in the form of damage to or destruction of supports have been presented in many publications, both for hardrock mines as well as for coal mines (Brauner, 1991; Dubin??ski and Konopko, 2000; Heal, 2010; Heal and Potvin, 2007; Simser, Joughin, and Ortlepp, 2002; Kaiser and Cai, 2012; Cai 2013; Nierobisz, 2013; Mark, 2014; Masny and Prusek, 2015). One of the main goals of the research has been to develop methods, criteria, and guidelines for the selection of an optimal and safe support for mine workings located in areas of rock bumps or tremors. Example of such studies include the Canadian Rockburst Support Handbook (Kaiser, McCreath, and Tannant, 1996), or the principles presented in the literature (Li, 2010; Cai, 2013)."

Jan 1, 2016

By P. M. Swash

A mineralogical investigation of the main causes of refractoriness of some metalurgicaly complex gold ores in South Africa is reported. It is shown that this refractoriness is related to the presence of submicroscopic gold, carbonaceous material, pyrhotite, and base-metal sulphides. Gold ores can be classified according to their content of these components. Electron-microprobe analysis shows that gold occurs in arsenopyrite and pyrite, the gold contents of which can be up to 2700 gft. The gold and arsenic contents of these minerals are closely corelated. Furthermore, within zoned arsenopyrite grains, the concentration of gold closely folows that of arsenic. Mossbauer spectroscopy caried out on samples of concentrate from the Barberton area indicates that the submicroscopic gold within the sulphides is in a non-metalic form. The mineralogical examination of beneficiation products is important, since it sheds light on some fundamental aspects of the behaviour of the ore and gangue components during milling and flotation. Such basic information will lead ultimately to a better understanding of the problems in the beneficiation of these ores. Investigations have shown that the overmiling of the auriferous arsenopyrite and the disseminated nature of the sulphide mineralization are the main problems during beneficiation.

Jan 1, 1988

By R. G. Votteler, A. C. Brent

"The business performance of mining corporations in South Africa is adversely affected by the constantly increasing electricity costs. The most commonly used power sources are the national utility supplier via a grid connection, and on-site diesel generators. Previous research has identified the renewable sources of solar photovoltaic (PV), onshore wind, and geothermal energy in hybrid versions with current sources as possible opportunities to counteract rising electricity costs. To provide a clear understanding of the new, developing market of renewable energy sources, this research is divided into two papers. This first paper investigates the internal business structure of mining corporations in order to evaluate electricity generating sources. The multi-criteria decision analysis (MCDA) method is selected as the most suitable approach for this. The paper identifies the criteria used by mining corporations to evaluate possible electricity generation sources for self-generation by means of the corporations’ own investment. Four mining corporations with several mining locations were interviewed. The interviews revealed both new and identical evaluation criteria when the findings were compared to earlier MCDA adaptations analysed in the literature review. The second paper (Part 2) combines current knowledge about the external macroeconomic environment with the findings about the internal environment described here. MCDA is adapted in Part 2 and implemented to analyse and compare current to hybrid renewable sources from the perspective of mines. IntroductionMining corporations in South Africa are currently adversely affected by increasing electricity prices. Electricity is supplied mainly by Eskom1 and, especially in remote locations, by on-site diesel generators (Boyse et al., 2014). Electricity price increases, emanating from diesel price hikes and Eskom, have escalated the total operational expenditure on electricity by the largest mining corporations from 8% to 20% of total operating costs in the past seven years (EIUG, 2015). The reliability of electricity supplied by Eskom has decreased drastically (Govender, 2008), and the prices will increase annually by at least 13% until 2018 (Numbi et al., 2014; Eskom, 2015b). In addition, the South African government plans to introduce a carbon tax on greenhouse gas emissions (Alton et al., 2014)."

Jan 1, 2017

By R. G. Votteler, A. C. Brent

"The first in this series of two papers, on the potential of renewable electricity sources for mining operations in South Africa, investigated the internal structure of mining corporations to evaluate feasible alternative electricity sources that were identified as through earlier research. The purpose of this paper is to combine current knowledge about the external macroeconomic and the internal environments to produce a clear picture of how renewable sources of electricity could perform from the perspective of mining corporations in South Africa. The multi-attribute value theory (MAVT) approach was adapted to structure the research and results. The model was fed with real-time data provided from five different energy companies and four mining corporations operating in South Africa. The results show that the performance of hybrid versions of the currently used electricity sources (diesel generators and Eskom grid connection) with solar PV and onshore wind is favourable compared with the current sources alone. The advantage of diesel generators is significantly greater than that of the Eskom grid connection. By combining the macroeconomic influences with the MAVT results, hybrid solar PV versions are identified as having the greatest potential. In second place are hybrid wind solutions, which have the shortcoming that good wind conditions occur only in coastal regions where there are fewer mining activities. Geothermal hybrid versions are the least favourable owing to the lack of service infrastructure and high initial investment costs.IntroductionRecent developments in the macroeconomic environment necessitate an investigation of the internal structure of mining corporations to evaluate possible alternative electricitygenerating sources (Roehrl and Riahi, 2000). To be able to combine current knowledge of macroeconomic factors and the internal structure of mining corporations, the research process is presented in two papers. The first paper (Votteler and Brent, 2016) investigated the internal structure and argued that a strategic tool should be used to evaluate electricity sources from the perspective of mining corporations. The multi-criteria decision analysis (MCDA) approach was selected as the most appropriate strategic tool. Based on a literature review of previous similar MCDA approaches in energy planning, it was concluded that no adaptation of MCDA methods could be found from a corporate, mining, or South African perspective. Finally, the paper investigated the internal evaluation structure in collaboration with mining corporations, by identifying the criteria they use to evaluate electricity sources."

Jan 1, 2017

By M. Gericke

The microbial leaching of metal sulfides is now an established biotechnological technology. Over the past 25 years, refinements in the engineering design of bioleaching processes have paralleled advances in our understanding of the diversity and role of the micro-organisms driving the process and the mechanisms by which micro-organisms enhance metal sulfide oxidation. Commercial success started with the treatment of refractory gold concentrates using mesophilic micro-organisms, followed by the development of tank bioleaching processes for the treatment of base metal concentrates. This was, initially, a mesophilic process with limited potential for recovery of copper from chalcopyrite concentrates due to slow rates and low copper extractions. The exploitation of thermophiles represents a major breakthrough in the development of bioleaching technology for the treatment of chalcopyrite-containing ores and concentrates. This development also opened the route to heap bioleaching of chalcopyrite ores, which is now a major focus of research programmes and piloting campaigns. This paper reviews the historical development of minerals bioleaching processes and gives an update on the current status of commercial tank and heap bioleach operations around the world.

Jan 1, 2009

By R. D. Lama

This paper presents the results of a study of the mechanics of methane gas flow in coal. Desorption tests carried out on cylindrical coal specimens showed that an analytical formulation can be made to model the process of gas flow in coal based on an integration of Darcy's law, Fick's law and Langmuir's relation. The diffusivity term in the flow equation varies directly with local gas content. Permeability tests carried out on the same coal result in permeability constants with values higher than equivalent permeabilities obtained from desorption tests by many orders of magnitude. The study also revealed that permeability is highly dependent on the applied gas pressure and the rock stress.

Jan 1, 1987

By B. Erdem

This article introduces a computer model, which emphasizes panel design for draglines deployed in direct side-casting mode. The study covers flat and inclined coal-seam conditions with the dragline operating along the strike-line. Two casting methods are embedded in the model: material is placed in the open set adjacent to the one on which the dragline is located (the DNS method) and material is placed in the open set adjacent to the one the dragline excavates (the DND method). While in the first method the unproductive walking time is reduced as the set is enlarged, in the second method the cycle time is lessened as the dragline swings along an acute angle. The side-casting model is shaped so as to provide several panel configurations instead of a single one to conform to the characteristics for an opencast mine. This is achieved by assigning the pit width an interval of values ranging from a minimum to a maximum. The model includes solutions to other critical design parameters such as: set length, swing angles at key cut and main cut positions, and required dragline reach at key cut and main cut positions. The model outcomes reveal the following: the stripping operation is largely affected when the coal-seam is inclined. The downhill spoiling mode should be applied wherever possible. The DNS pattern allows wider pit width intervals as well as longer sets and longer reaches.

Jan 1, 2004

By R. Armstrong, C. Ware, P. Sudan, G. Whitmore

The northern KwaZulu-Natal (KZN) coastal dune cordon, South Africa, extends from north of Durban into Mozambique. The Quaternary dune cordon, which can be up to 2 km wide, comprises a series of stacked, unconsolidated dunes that in places attain a height of over 100 m. Mining of the dunes produces much of the world’s supply of ilmenite, rutile and zircon. This paper documents the age of zircon grains separated from dune units, identifies likely source rocks and presents an evolutionary history for the dune cordon. Between 30 and 60 detrital zircon grains from three distinct units from the northern KZN coastal dunes were analysed for U/Pb isotopic ages using the SHRIMP II at the Australian National University. The samples represent units from the base (ca. 250 ka; luminescence age1),middle (ca. 190 ka2) and upper (ca. 20 ka2) portions of the coastal dune cordon. Zircon grain ages identify three source populations: (1) a 1 000 to 1 200 Ma group correlated to the Natal Metamorphic Province, (2) a 500 to 650 Ma group representing a Pan-African belt, which may correlate to the Mozambique Belt and (3) a ca. 650 to 800 Ma group of unknown provenance. Surprisingly, the presently exposed basement, comprising the Kaapvaal Craton and Archaean volcano-sedimentary sequences, has not supplied a significant amount of zircon grains (< 5%).This suggests that unroofing of basement rocks in the region has only occurred during the last 20ka. In addition, the absence of zircon grains younger than 500 Ma indicates that the bulk of zirconis not reworked from the Karoo Supergroup cover succession, but may be sourced by reworking of the Natal Group sandstones.

Jan 1, 2003

By B. K. Loveday

A model for the leaching of non-porous particles by B. K. LOVEDAY*, Ph.D. (Fellow) A model has been developed for the prediction of the rate of leaching for an assemblage of non-porous particles in terms of size-distribution parameters. Expressions are developed for batch and continuous operation, and an example of the application of the model is given.

Jan 9, 1975

By M. R. L. Blackwell

Over the period 1964 to 1969 Conzinc Riotinto of Australia undertook and completed an evaluation of a large low-grade copper orebody on Bougainville Island in the Territory of Papua and New Guinea. From the outset it was clear that the geographic, climatic and topographic characteristics of the area would necessitate a heavy capital outlay on production and support facilities. Both the physical problems and the magnitude of the investment amplified the need for a thorough and rigorous evaluation of the various strategies for exploiting the orebody. In view of the number of independent and inter-related variables and the flow of new data, a computer-based evaluation process extended the scope and depth of the analysis considerably. The system used permitted an iterative assessment and re-assessment of the various strategies with the results becoming increasingly refined with time. This process encompassed the modelling of the orebody, the simulation of alternative operating strategies and the determination of the financial profitability of the project,

Jan 1, 2014

By J. A. L. Napier

An essential requirement for the planning of the global capacity of a mine is a knowledge of the functional relationship between the production level and the capital expenditure necessary to establish that level. An underlying mechanism connecting capital expenditure and mine production capacity is proposed in terms of a characteristic profile of the expenditure that both precedes and succeeds production expansion. By the assignment of a representative shape to this profile, the capital expenditure of individual mines can be modelled. The empirical values describing the characteristic profile are computed for a number of gold mines, and an attempt is made to explain variations in the model coefficients from mine to mine in terms of physical parameters such as shaft depth, shaft concentration, and average rate of depth increase during the life of the mine.

Jan 1, 1981

By M. H. Moys

Accurate models of mill power are becoming more necessary as the design, operational, and control requirements for grinding mills become more stringent. Models of mill power are reviewed briefly, and a new semi-phenomenological model is derived. The conventional torque-arm model for mill power is combined with a model of the tendency of the load in a mill to centrifuge at high speeds, to describe mill power that can be related to several design variables (such as mil geometry, mill speed, and liner design) and control variables (such as load volume, slurry rheology, and mill speed in the case of variable-speed milling). The semiphenomenological nature of the model allows rational conclusions to be reached concerning the effect of various aspects of mill-load behaviour on mill power. The model is shown to be capable of describing reality with much greater accuracy than is achieved by empirical models such as the Bond model.

Jan 1, 1993

By S R Grano

A fundamental model, which considers the subprocesses of particle collection by bubbles in flotation, is applied to two comprehensive flotation surveys in the rougher stages of C3 concentrator, PT Freeport Indonesia. The flotation surveys focused on the collection of: ? cell-by-cell and size-by-size metallurgical, ? cell hydrodynamic, and ? pulp and surface chemistry information. The two surveys were conducted at significantly different feed tonnages, giving rise to significantly different feed particle size distributions, pulp densities and mean pulp residence times. A series of model simulations are performed with the aim of quantifying changes in copper recovery, on both a size-by-size and unsized basis, with changes in values of the hydrodynamic parameters and hydrophobicity of the copper sulfide mineral. This was carried out in an effort to identify the most promising route to increase overall copper recovery in roughing. It was found that by increasing the hydrophobicity of the copper sulfide mineral surfaces it became possible to optimise cell hydrodynamics, which targeted increased fine (-12 µm) copper sulfide mineral recovery but without adversely affecting coarse (+150 µm) copper sulfide mineral recovery.

Jan 1, 2007

By A. Ebrahimabadi

Roadheaders are very versatile excavation machines used in tunnelling, mine development, and mine production for soft to medium strength rock formations. Performance prediction is an important factor for successful roadheader application and generally deals with machine selection, production rate and bit consumption. Among many different parameters, brittleness is also one of the material properties related to breakage characteristics and can be used as a cuttability parameter from a mechanical excavation point of view. The main objective of the research study is to contribute the brittleness of rock excavated to construct a new empirical equation for predicting the performance of roadheaders in different material and operational conditions. In this regard, a new performance prediction model for medium duty roadheaders based on a brittleness index (BI) is presented. In this study, rock mass brittleness index (RMBI) is defined in order to investigate the influence of BI on roadheader performance. RMBI is an index which can be used to relate the intact and rock mass characteristics to machine performance. Results demonstrated that RMBI is highly correlated to instantaneous cutting rate (ICR) (R²=0.94). Moreover, through the further analysis and normalization, the pick consumption index (PCI) was introduced as a parameter having a good relation with pick or bit consumption rates (PCR) (R²=0.79). Finally, the new predictive models for ICR and PCR showed very good correlations with the actual measured values. Keywords Performance prediction, roadheader, brittleness index, mechanical excavation.

Jan 1, 2011

By M. J. Nicol, P. Balestra, E. Schalch

A detailed fundamental study has been made of the various factors that influence the partial reactions comprising the electrochemical model of the cementation of gold from cyanide solutions by zinc. The effects of cyanide concentration, pH, agitation, additions of lead, and the presence of various impurity ions on both the anodic dissolution of zinc and the cathodic reduction of gold have been investigated. The results are used to explain the influence of these variables on the rate of cementation, and possible implications of this work for plant practice are discussed.

Jan 1, 1979

By S. Gqebe, A. Lewis, M. Rodriguez-Pascual

"Gravitational sedimentation of suspensions in various precipitation processes is hindered by colloidal stability. This is due to the high surface charge of the suspension and results in strong attraction/interaction between the ions on the particle surface and counter-ions in solution. Moreover, this strong interaction results in a charge build-up that renders the suspension stable. In order to induce gravitational sedimentation of these particles, a redistribution of ions close to the particle surface is required. We therefore sought to redistribute ions close to the particle surface by applying a magnetic field. This results in the reduction of interparticle electrostatic repulsive forces and a subsequent increase in the zeta potential of a suspension. For the purpose of this study, a copper sulphide suspension was used. Copper sulphide particles were exposed to a range of field strengths for set exposure times and their zeta potential was measured before and after exposure. All particles had an initial zeta potential value equal to or less than –40 mV prior to magnetic field exposure. A significant increase in zeta potential was observed, with values reaching a maximum of –16.5 mV when exposed to a 2 T field strength for 40 minutes. This is due to Lorentz ion shifts resulting from the Lorentz force exerted by the magnetic field on the particle surface. IntroductionMetal sulphide precipitation is a process for treating industrial waste streams with high residual concentration of mixed metal ions and acid mine drainage. This process has been reported to achieve higher metal removal compared with the industrially prevalent lime precipitation, due to the sparingly soluble nature of the metal sulphide precipitates formed. However, precipitation is governed by high levels of supersaturation which favour the formation of fine particles (Lewis, 2010). Consequently, some of the metal sulphide fines formed exhibit slow settling dynamics and thus tend to remain suspended in solution."

Jan 1, 2016

By Z. Leng

"After detonation of the explosive, the final blast-induced damage area around the blast-hole falls into three categories, namely crushed zone, fractured zone, and elastic deformation zone. This paper presents a modified model to calculate the size of crushed zone around a blast-hole in drill-and-blast, with the hoop compressive stress and cavity expansion effect taken into account. The material in the crushed zone was assumed to be a granular medium without cohesion, but with internal friction. On this basis, the formula for crushing zone radius was derived. The proposed approach was verified with tests reported in the literature and the simulated results from SPH-FEM coupled models. A full statistical analysis was also carried out, and the predicted values were found to be in better agreement with the test results compared with other models. A sensitivity analysis of the modified model showed that the size of the blast-induced damage area is mainly affected by the following factors: rock mass properties, in situ stress, and borehole pressure. In particular, the roles of borehole pressure and in situ stress are discussed. Finally, suggestions are made on how the size of the crushing zones can be decreased. IntroductionOver the past decades, drill-and-blast has become the most commonly used technology in rock excavation. It is well known that in rock mass fragmentation with explosives, the annular rocks around the blast-hole are converted into fines. The formation of these fines consumes a significant part of the energy of the detonation, which in general is ignored in the determination of the efficiency of detonation (Glatolenkov and Ivanov, 1992; Furtney et al., 2012). Many studies show that only 20–30% of the total explosive energy is effectively used in fragmenting the rock, and up to 50% of the energy generated by conventional charges is wasted in overcrushing of the crushed zone and the inner part of the fractured zone (Ouchterlony et al., 2004; Sanchidrian et al., 2007). How to control the crushed zone to enhance the effective utilization of explosive energy, reducing the unit explosive consumption and the engineering cost, is therefore of great significance."

Jan 1, 2016

By A. Tosun

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

Oct 1, 2018

By A. Muwila

Hercules? is a low nickel austenitic stainless steel developed at Mintek that has a typical composition of 9 wt% Mn, 0.05 wt% C, 2wt% Ni, 0.25 wt% N and 16.5 wt% Cr. A more corrosion resistant version of Hercules? (Hercules? B) with 0.5 wt% Mo has also been developed. Potentiodynamic tests performed on Hercules? B in a 5wt% sulphuric acid solution showed it to have improved corrosion resistance comparable to that of AISI 304. The effect of a varying Mn content on the corrosion resistance of Hercules? B has also been investigated and the results discussed in this paper. From the corrosion test results, it is clear that decreasing the Mn content of Hercules? B increased the corrosion rate, while increasing it decreased the corrosion rate. Keywords: austenitic stainless steel, % ferrite, molybdenum, manganese, nitrogen, electrochemical corrosion tests, potentio-dynamic scans, microstructure, chemical analysis.

Jan 1, 2007

By M. J. Papo, A. Muwila

Hercules? is a low nickel austenitic stainless steel developed at Mintek that has a typical composition of 9 wt% Mn, 0.05 wt% C, 2 wt% Ni, 0.25 wt% N and 16.5 wt% Cr. A more corrosion resistant version of Hercules? (Hercules? B) with 0.5 wt% Mo has also been developed. Potentiodynamic tests performed on Hercules? B in a 5 wt% sulphuric acid solution showed it to have improved corrosion resistance comparable to that of AISI 304. The effect of a varying Mn content on the corrosion resistance of Hercules? B has also been investigated and the results discussed in this paper. From the corrosion test results, it is clear that decreasing the Mn content of Hercules? B increased the corrosion rate while increasing it decreased the corrosion rate. KEYWORDS Austenitic stainless steel, %ferrite, molybdenum, manganese, nitrogen, electrochemical corrosion tests, potentiodynamic scans, microstructure, chemical analysis.

Jan 1, 2006