Search Documents

By J. M. Ortiz

Grade control and short-term planning are usually based on the samples obtained from blastholes. These samples may carry a large sampling and sample preparation error. At El Tesoro copper mine in northern Chile, an advance drilling grid is used for short-term planning and grade control. These drill holes are sampled well in advance, and a short-term model that incorporates several variables and sophisticated estimation methods can be prepared for decisionmaking. An additional advantage of the advance drilling samples is that reverse circulation can be used instead of conventional down-the-hole equipment, and a very careful sampling and sample preparation process can be implemented, reducing the total sampling error. Advance drilling can be performed on a wider grid than blasthole drilling, hence the decision about the grid requires assessing the economic benefit of different sampling grids. Furthermore, this process allows the cost of poor sampling and the effect of different estimation procedures to be quantified. We demonstrate the optimization of the drilling grid for short-term planning and grade control at El Tesoro mine by means of the economic evaluation of the performance of different drilling grids, with different drilling techniques (which differ in the sampling error). The methodology is based on creating dense (exhaustive) geostatistical simulations of the grade distribution over a volume defined for a production period in respect of the geological model, and assuming each simulation as the true grade distribution. Then, samples are obtained from the exhaustive simulations at a spacing similar to the advance grid to be evaluated, and a sampling error is added. The short-term estimation procedures used on the mine are applied to determine the destination of each block and the profit obtained. This profit can be compared with the maximum profit (unachievable) and with the profit under different sampling errors and grids. The results show that the current 8 x 8 m drilling grid is appropriate and by reducing the sampling error, misclassification is also reduced, leading to an increase in profit of about US$ 5 million in 4 years.

Jan 1, 2012

By C. G. Anderson

"As demand for copper and precious metals continues to grow, the need to develop new supplies increases. In the imminent future, the new large global ore bodies are more complex, with enargite, tennantite and tetrahedrite as the abundant contained mineralogy. These resources also contain considerable gold and silver. As such, direct treatment by conventional smelting is prohibitive due to the potential environmental impacts and copper quality issues. This paper outlines the effective application and associated economics of industrially proven Alkaline Sulfide Leaching (ASL) hydrometallurgical technology to an enargite concentrate for selective removal and recovery of arsenic, antimony, gold and silver, leaving a clean high-grade copper concentrate. The fundamentals behind the technology are described, along with those of hydrometallurgical arsenic fixation and stabilization. Flowsheets and unit operations are elucidated, along with an in-depth economic analysis. INTRODUCTION Hydrometallurgical methods can be employed for treatment of gold-, arsenic-, antimony-, tin- and mercury-containing materials, concentrates and ores, as well as complex ones containing any number of metals (Conner & Anderson, 2013). The alkaline sulfide leaching (ASL) system is one of these. It is essentially a mixture of sodium sulfide and sodium hydroxide with other meta-stable alkaline species as required. This is a unique hydrometallurgical system beause it is a very selective lixiviant for the distinct leaching of tin, gold, antimony, arsenic, tellurium, silver and mercury (Anderson, 2000, 2001a, 2001b, 2002, 2003, 2012, 2014; Anderson & Twidwell, 2008a, 2008b, 2010; Anderson et al., 2004, 2005; Glazkov & Tseft, 1961; Gnatyshenko & Polyvyanni, 1961; Nadkarni et al., 1975; Nadkarni & Kusik, 1988; Polyvyanni, 1963). Worldwide, ASL technology has been employed industrially in the former CIS, China and the United States for the production of antimony (Anderson et al., 1992, 1994; Anderson & Krys, 1993; Holmes, 1944; Kaloc, 1967; Nordwick & Anderson, 1993; van Stein, 1971)."

Jan 1, 2015

By P. Foster, A. Burton

Over the past decade there has been a great deal of research into the use of virtual reality (VR) and computer graphics in the mining industry. Much of this has led to developed applications including training simulators and accident re-construction. One other area where there is considerable potential for virtual reality is that of mining ergonomics. This paper identifies those common ergonomic limitations associated with mining equipment that can be effectively modelled using VR techniques. From this, two simple models have been developed namely (i)remote control continuous miner operation and (ii) free steered vehicle sightlines, which demonstrate the practical use of VR in this area.

Jan 1, 2003

By P. J. Petit

Changing mining conditions, legislative issues, rising costs, and the constrained supply of skills and electricity in South Africa, have been some of the criteria forcing mine operators and engineers to review the traditional use of compressed air to power underground hand-held drilling operations in narrow-stope, hard-rock mines. In answering the question, 'What is the best way to power this mine?', they have resorted to trade-off studies with results of limited usefulness, because they are site-specific, and use only a few comparative parameters, based on a small data set. This paper aims to provide definitive, objective, and quantitative decision-making approaches to evaluating alternative energy-delivery systems for stoping in narrow-reef hard rock mines, based on primary and relevant criteria. These include quantifiable criteria such as capital expenditure, operating costs, resulting financial returns, energy and water usage, production performance, life-of-mine, etc. Other important criteria with qualitative aspects are integrated. These are safety, health, and environmental concerns, legislative requirements, business risk, technology change, etc. The paper begins with a review of decision-making processes available, and proposes the use of the analytical hierarchy process (AHP) method as a multiple-criteria decision-making tool and the decision tree based on milestone-driven uncertainties, to validate the selection of the energy delivery system. The results of a multiple-criteria questionnaire completed by a variety of industry experts and professionals, such as production and operation managers, consultants, suppliers, and techno-financial analysts, are discussed. The evaluation indicates the potential for hydropower to be the best solution for narrow-reef hard rock mines, based on current information, mine design layout and production.

Jan 1, 2013

By S. M. Rupprecht

Transportation accounts for some 26% of all mine accidents in South Africa. Although this figure may not be as prolific as fall of grounds accidents or accidents caused by seismic events, the enormity of transportation accidents demands attention, especially as many of these accidents are avoidable. This paper investigates vertical (i.e. shaft), horizontal (i.e. haulages), and in-stope transportation systems and their function as it applies to safety. Recent transportation accidents are discussed looking at current trends within the three transportation areas. In the shaft area, discussions will focus on handling of material cars, loading and off-loading of the workforce and management of shaft orepass systems. The horizontal component will focus on personnel transportation, safety around trains and hoppers, and handling of material in the cross-cut. The discussion on in-stope transportation will focus on the general congestion of the stope environment and how it affects the overall movement of personnel, material, and rock. Of concern are the large numbers of material handling and scraper winch accidents that occur and which will be discussed in some detail. The paper will conclude with a section on proposed guidelines within the three above-mentioned systems for mine engineers to consider in mine design and life of mine planning and scheduling. Keywords Underground logistics, safety in material handling.

Jan 1, 2011

By M. Jacobs

Keywords: Smelting, converting, sulphide, sulphide smelting, platinum, platinum group metals, PGM, base metals, nickel, copper, matte, slag, furnace, electric furnace, Söderberg, electrode, granulation, converter, flash drier, sulphuric acid, acid plant, Ausmelt, Sirosmelt, pyrometallurgy, metallurgy, Anglo Platinum, South Africa Waterval Smelter complex is situated in Rustenburg, in South Africa?s North West Province. The smelter objective is to process wet concentrate to produce crushed, slow-cooled, sulphur-deficient nickel-copper matte rich in platinum group metals (PGMs), gold, and base metals for despatch to the Magnetic Concentration Plant at the Base Metals Refinery. Throughout its history, the smelter complex has been continuously upgraded in line with increasing production demand, changing feeds, environmental initiatives, and advances in available technology. The smelter receives filter cake and slurry from Anglo Platinum concentrators and joint ventures. Wet concentrate is fed through a flash drying process utilising coal-fired, fluidised bed hot-gas generators, to produce dry feed material for the electric furnaces and slag-cleaning furnace. For primary smelting, two electric furnaces are used, each with a rated capacity of 34MW. Furnace matte, containing the bulk of the base metal sulphides and PGMs, is tapped periodically into refractory-lined ladles and granulated using high-pressure water jets, then dried through electrically powered pneumo-driers to become the main feed to the Anglo platinum Converting Process (ACP). Slag is tapped semi-continuously, granulated, and treated through the slag mill. The ACP treats the combined matte output of Waterval, Polokwane, and Mortimer smelters. It is a top-blown furnace, with furnace matte, air, and oxygen being injected into the converter via a lance submerged in the slag. Converter matte is tapped and bottom cast into moulds, slow-cooled, crushed, and despatched to the refineries. Slag is granulated and dried for recycling to the slag-cleaning furnace. ACP slag is fed to the slag-cleaning furnace along with a reductant and a sulphur source. Slag-cleaning-furnace matte is granulated for processing by the ACP, while slag is granulated and processed in the slag mill. The slag mill and flotation circuit treats granulated slag from the electric furnaces and slag-cleaning furnace to recover entrained matte containing valuable PGMs and base metal sulphides.

Jan 1, 2006

By B. P. Watson

Crush pillars have been incorporated into a mechanized, low-profile trackless system at South Deep Gold Mine. These pillars had to be designed to fail near the face and to ensure that pillar failure is contained within the pillar, to avoid bursting and the risk of high loads being generated during a seismic event, respectively. PoweRite backfill bags were recommended to maintain the integrity of the pillars; except in the main access drives, where the sidewalls were to be supported on 5.6 mm diameter weldmesh and yielding anchors. The results of a trial site investigation exceeded expectations, showing a residual pillar strength of about 37 MPa for a newly formed pillar and 8 MPa for a pillar subjected to seismicity and a closure of more than 300 mm. The introduction of these pillars has improved the rock mass conditions because of the active nature of the support, compared to the previous passive backfill method. Importantly, the pillars have increased mining efficiencies and improved face availability. A potential cost saving to the mine of R140.9 million could be realized over a period of 10 years.

Jan 1, 2014

"Exploitation of an ore deposit can be optimized by adapting the beneficiation processes to the properties of individual ore blocks. This can involve switching in and out certain treatment steps, or setting their controlling parameters. Optimizing this set of decisions requires the full conditional distribution of all relevant physical parameters and chemical attributes of the feed, including concentration of value elements and abundance of penalty elements. As a first step towards adaptive processing, the mapping of adaptive decisions is explored based on the composition, in value and penalty elements, of the selective mining units.Conditional distributions at block support are derived from cokriging and geostatistical simulation of log-ratios. A one-to-one log-ratio transformation is applied to the data, followed by modelling via classical multivariate geostatistical tools, and subsequent back-transforming of predictions and simulations. Back-transformed point-support simulations can then be averaged to obtain block averages that are fed into the process chain model.The approach is illustrated with a ‘toy’ example where a fourcomponent system (a value element, two penalty elements, and some liberable material) is beneficiated through a chain of technical processes. The results show that a gain function based on full distributions outperforms the more traditional approach of using unbiased estimates."

Jan 1, 2015

By M. Abdellatif

The Mintek Thermal Magnesium Process (MTMP) process is based on DC open arc metallothermic smelting of calcined dolomite at normal pressure and temperatures of 1650?1750°C. The process was demonstrated at the pilot scale in the period 2000?2004. Major changes to the MTMP pilot plant were made throughout the development period, which lasted for about five years. The changes included design and installation of new equipment, modification of existing equipment, changes in the metallurgical approach in terms of feed rates, feed recipes, furnace operating temperatures, cold and hot dolime feeding, and steady and systematic changes in the operating procedures and maintenance of the plant. As a result, the performance of the pilot plant gradually improved from one campaign to the next, in terms of availability and in particular the condensation efficiency. In Run 10, the process was successfully demonstrated over an 8-day campaign. Keywords Magnesium, condensation efficiency, DC arc furnace, silicothermic reduction.

Jan 1, 2011

By J. D. Steenkamp

Keywords: Thermal, conductivity, diffusivity, expansion, history, density, specific heat capacity, industrial rich high-carbon manganese slag The thermal conductivity of slag is an important parameter in the design of furnace-containment systems based on freeze-lining technology. Literature indicates that the crystal content of a slag has a significant influence on its thermal conductivity. Industrial, rich, manganese-bearing slag was cooled at different rates to create samples with different microstructures. The coefficients of thermal conductivity of these samples were measured in a nitrogen atmosphere from room temperature to 990°C at 100°C intervals. The laser-flash measurement technique was used for this purpose. Follow-up investigations included XRF and XRD and modelling in FACTSage.

Jan 1, 2011

By P. van Dorssen

In South African metalliferous mines, stoping operations are largely confined to narrow, tabular orebodies making mechanization extremely difficult. Limited flexibility in terms of stope width has necessitated drilling by means of handheld, pneumatic rock drills at most of our operations. As the largest producer of platinum in the world, we drill in excess of forty million stope blast holes per annum. Cleaning of the broken ore is also done by conventional means?utilizing scrapers and scraper winches. Conventional methods such as these carry high costs in terms of risk exposure as well as labour intensity. The purpose of this paper is to describe the development of a long hole stoping system suitable for the narrow platinum reefs. The new system had to be substantially safer and more cost effective than conventional mining. We selected a site that was conducive to mechanized mining and set out the parameters that we considered would meet our requirements. We then conducted a feasibility study to evaluate the conceptualized long hole stoping system in terms of specific goals. An analysis of the proposed system identified the Key Performance Indicators (KPIs). One of the most critical goals was to be able to create a man-free stope. This would mitigate the safety risk associated with normal stoping operations, as well as the inefficiency cost previously referred to.

Jan 1, 2002

Keywords: Pyrometallurgy, furnace, Lonmin, platinum, PGM, UG2 Lonmin, earlier than any other primary platinum producer, had to deal with the concentrating and smelting of UG2-rich ores and concentrates respectively. Smelting was performed at a fairly modest scale compared to its industry peers in the Platinum Group Metals (PGMs) industry, and was focused on smelting concentrates obtained through low mass pulls while still maintaining high recoveries at its concentrators. Lonmin gradually smelted larger quantities of UG2 concentrates. Initially two 2.3 MW Infurnco furnaces were commissioned in 1982, followed by three 5 MW circular 3-electrode Pyromet furnaces in 1991. Deep electrode immersions and moderately high hearth power densities were used in all the designs. Lonmin decided to continue with circular furnace technology when it planned its new high-intensity No. 1 Furnace. Neither Lonmin nor the technology supplier and EPCM company foresaw the challenges that scale-up would bring when applied to the smelting of UG2-rich concentrate blends. Superimposed on the high chromite content, was the low base-metal loading, mineralogical difficulties, and fine particle size that came with milling of all concentrates (especially UG2 and recycle materials within the smelter). Through a process of fundamental diagnoses of furnace run-outs and wear patterns observed during repairs, the main challenges operating this high-intensity furnace were identified as sulphur vapour corrosion of the copper coolers, uneven and unpredicted movements of refractory bricks with associated copper cooler lift and matte tap-block movement, the formation of three-phase ?mushy? zones, high refractory and tap-hole wear rates, uncertainty in matte level and associated insufficient matte buffer height, and high furnace operating temperatures. These factors seldom worked in isolation and will be explored in more detail in the paper. The variability in furnace feed characteristics led Lonmin to re-design Furnace No. 1, to invest in back-up furnace capacity, and to invest in improved monitoring and control. These improvements consisted of online and high-frequency off-line feed chemistry and mineralogy monitoring, online pressure monitoring of water-cooled circuits, an alternative matte liquid level measurement in the furnace, and electrode immersion estimation. Improvements were also made at the converters by installing and utilising optical spectral analysis of the converter flame to characterise converter behaviour and achieve the desired iron end-point for white matte. This paper also briefly discusses the current and future expansion plans, as well as ancillary operations at the smelter such as flue-gas handling and materials handling.

Jan 1, 2011

By B. W. J. van Rensburg, M. J. Schmidt

Bulk materials handling systems are extensively used in the mining and minerals industry, where a fairly high incidence of structural failure is experienced, notwithstanding design compliance with appropriate standards. A number of case studies are explored to demonstrate how insufficient controls or protection systems have contributed to structural failures on mobile bulk handling equipment. The importance of design integration across engineering disciplines is highlighted. The revision of ISO 5049-1 (1994) is proposed to provide specific rules and guidelines pertaining to machine protection systems. It is further recommended that the structural design engineer of the original equipment manufacturer(OEM) fulfils a more prominent role during the final acceptance and handover of mobile bulk handling equipment, with specific reference to protection systems.

Jan 1, 2015

By C. M. Rule

Energy efficiency is currently a significant area of interest due to the Eskom power situation, which led to severe power impacts to the PGM, and indeed whole SA primary industries, in early 2008. Anglo Platinum has focused on energy efficiency for a number of years, especially in the concentrator operational area. New comminution technologies have been aggressively developed, which have shown real metallurgical efficiency gains as well as significant energy efficiency and saving potential for Anglo Platinum?s total electrical consumption as the company expands into a growing PGM demand market. This paper illustrates this programme?s activities, potential and considerable achievements to date.

Jan 1, 2009

By T. Gerritsen, R. C. Delgado, J. Janzen, E. R. Veloza

The paper describes the components of an Integrated Furnace Control system for covered-arc (shielded arc) smelting with results from the recently started 75 MW Cerro Matoso Line 2 Furnace. The paper starts with a review of the mechanisms of power and feed input and heat losses in the shielded-arc smelting process, and describes how the details of the control system are tailored to the process. The control modules of a covered-arc smelting furnace are described including measured results and screen captures. This paper focuses on Integrated Furnace Controls tailored to shielded-arc smelting, but similar approaches have been recently applied to other furnace processes including immersed-arc smelting.

Jan 1, 2004

By P. Bracher

Most efforts to mechanize low seam (narrow reef) mining of platinum ore are presently based on board-and-pillar methods with1.6?1.8 m in reef excavation. This paper attempts to substantiate the benefits of low profile mining: primarily improved head grade with resulting reduced tailings losses. Board-and-pillar equipment supplied by DBT, facilitating1.1?1.2m mining height has been in operation in an Anglo Platinum mine since September 2001. Major aspects of the equipment, battery scoops (LHDs) and rotary bolting rigs, are described and presently achieved results reported. The medium term industry goal is rock breaking without the use of explosives. An outline of present DBT developments is presented.

Jan 1, 2003

By M. J. Leeuwner

Computational fluid dynamic (CFD) modelling is used to research the complex flow structures that exist in a hydrocyclone. By simulation of a two phase (water and air) flow system, the internal flow and multiphase interactions are investigated. The suitability of CFD modelling as a design tool is further evaluated by examining the effect of varying device dimensions. Three hydrocyclone geometries, used in previous studies, are specified. A transient simulation approach, which employs the Reynolds Stress Model as turbulence model and the Volume of Fluid model as multiphase model, is followed. Results are validated qualitatively against experimental measurements from the previous studies. Keywords: CFD modelling, hydrocyclone, Reynolds stress model, multiphase flow

Jan 1, 2008

By Reginald N. Boryor, Steven D. Woods

1.0 Introduction ?Low grade, high tonnage, open pit gold mine. ?Gold bearing Tarkwaian conglomerates. ?Reverse Circulation percussion drilling (25m X 25m grid). ?Composite 1m intervals, logged and split in the field to provide±2Kg samples. ?Samples used to build grade control block models using SURPAC. ?Approximately 100,000-130,000 meters drilled per year. ?RC samples are assayed using Rapid Cyanide Leach (RCL). ?Check assays are done using Fire Assay

Jan 1, 2005

By M. Machikicho, N. R. Shoko, J. Chirasha

Keywords: Pyrometallurgy, furnace, ferrochromium, alloys, Zimbabwe Zimbabwe Alloys was founded in 1949 by a consortium led by the John Brown Group. It was the first ferrochrome plant in Africa. The establishment of the refinery was necessitated by an increase in world stainless steel demand and the need to reduce cost by shipping alloy rather than chrome ore. The location of the refinery in Gweru was influenced by a number of factors, not least of which were the abundance of chrome ore deposits, access to inexpensive power from Kariba, the availability of reductant coke from Hwange, accessibility to ports (as the town was well served with rail and road networks second to none in the country), and of course cheaper labour costs. The production of Low Carbon Ferrochrome (LCFeCr) was commissioned in 1953 and produced from an Open Arc Furnace with a Submerged Arc Furnace producing Ferrosilicon Chrome (FeSiCr) that is used as a reductant in the production of LCFeCr. An experimental furnace was commissioned in 1958 to help with efficiency and control on larger furnaces. A second Submerged Furnace was commissioned in 1963. Three other Submerged Arc Furnaces were built between 1967 and 1974. Several mines were acquired between 1974 and 1984, as a strategic move to ensure the growth of the refinery. A briquetting plant was commissioned in 1977, enabling the use of friable ores to enhance the capacity of ore supplies and ore cost management. A plant to recover alloy from slag was established in 1994 to capitalize on market demand without large capital outlay that would be required to build other furnaces to increase capacity. Zimbabwe Alloys has created employment opportunities throughout the years. There have been direct employment opportunities at both the refinery and the mining divisions. With time, indirect employment was realised both upstream and downstream of the refining process, enhancing the livelihood of numerous people. Zimbabwe Alloys' involvement with various labour skills has, of necessity, enabled it to develop a culture of safety at work, home, and play. Zimbabwe Alloys has contributed to society by participating and funding various local initiatives primarily to impact positively on societal needs. The latest development was in 1996, when Zimbabwe Alloys entered into a Technical Transfer Agreement with Japan Metals and Chemicals to improve the efficiencies and hence the profitability of the LCFeCr production process. A significant quantity of various alloys has been produced since inception, and significant foreign currency has been earned for the country. This was in spite of challenges that included the cyclic nature of market prices, the upheavals of sanctions affecting the macro-economic environment, and the challenges related to the deteriorating grade of chrome ore and reductant coke.

Jan 1, 2006

By G. I. McPhail

The authors have conducted several investigations into the prediction of the beach profile of high-density tailings and have found that there are a number of important considerations that need to be taken into account over and above the reliability of the beach profile prediction methodology. These considerations relate to the chemistry of the slurry and specifically the influence of pH and flocculation, both of which have a significant influence on the rheology of the slurry at the discharge point. A number of examples are discussed and a potential testing protocol that will assist in assessing the influence of chemistry ahead of the beach profile predictions is presented. A methodology for assimilating the results of the testing into the likely field situation is discussed, and suggestions are made on application of the results in beach profile prediction. The suspected influence of residual flocculation on the stratification

Jan 1, 2012