Search Documents

By M. Gous

Keywords: Pyrometallurgy, Namakwa Sands, ilmenite, DC arc furnace, titania slag, pig iron Namakwa Sands is a heavy minerals mining and beneficiation business in the Anglo Base Metals Division, and operates along the West Coast of South Africa. The business encompasses mining, mineral concentration, separation, and smelting operations. The smelting process comprises the carbonaceous reduction of ilmenite to produce titania slag with a TiO2 content of 86%, and iron with a carbon content of 2.5%. The Namakwa Sands smelter, situated near the Saldanha Bay harbour, commenced smelting operations in 1994, when a 25 MW DC arc furnace was commissioned. The smelting operations were expanded in 1999, with the commissioning of a second 35 MW DC arc furnace. Despite the fact that ilmenite smelting poses a technical challenge in terms of the high temperatures required, the physical characteristics of the slag, the constraints placed on the feedstock, and the tight product specifications, Namakwa Sands has continually increased slag production since 1995. High furnace feed-on utilisation and furnace stability, complemented by continuous improvement drives, will be the vehicle to drive performance in the short term, with longer-term performance enhancements due to strategic process development.

Jan 1, 2006

By Cade Mweemba, Alex Mwanza, Jackson Sikamo

"The Zambian Copper mining industry as we know it today has its genesis from early in the 20th century in the 1920s. Consistent private sector-driven investment in the industry over a period of over 50 years in exploration, mine development and operation, development of minerals processing facilities, building of infrastructure for pyrometallurgical and hydrometallurgical processing, with attendant support facilities, including building of whole new towns, resulted in copper production going from zero to a peak of 769 000 tons of copper in 1969. At the same time, the industry created jobs to the extent that in 1972 the industry had over 62 000 direct jobs. The industry was nationalized in 1973 and remained in government hands for just over 24 years. During this period, the industry experienced a serious decline in production levels, reaching the lowest level at the dawn of the 21st century in the year 2000 when production was 250 000 tons. In terms of jobs, an average of just under 2000 jobs were lost every year in the 24-year period, reaching just over 22 000 direct jobs in 2000. Following the return of Zambian politics to pluralism and liberalized economic policies, the government decided to privatize the mining industry. The process started in 1996 and by the year 2000 all the mining assets had been privatized. The new investors embarked on serious investment to upgrade the assets and to develop greenfield mining projects. Fourteen years later and investments of over USD 12 billion, the industry production levels increased year- on-year to reach a peak of 763 000 tons in 2013 with direct jobs reaching 90 000. This paper discusses the impact of the mining industry in Zambia on the economy in areas such as employment, support to other industries, direct contribution to the national gross domestic product (GDP), foreign exchange earnings and social amenities. The paper also focuses on the performance of the mines during these periods vis-à-vis mineral availability, mineral grades and complexity, new technologies and human capital. This is looked at particularly in the light of current challenges the industry is facing and makes suggestions on how the industry can be nurtured to continue being a major driver for the Zambian economy and a major player in the international copper mining business."

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 O. Celep, T. Uslu, Savas

This study investigates the enrichment of a low-grade colemanite concentrate (-3 mm) using a Knelson centrifugal gravity concentrator. Due to its low boron content, the concentrate is unsaleable and has to be stored under appropriate conditions to avoid potential environmental problems. The low-grade colemanite concentrate was comminuted to size fractions of-1 mm, -0.5 mm, and -0.15 mm before treatment in the Knelson Concentrator. The effects of particle size, fluidizing water velocity, and bowl speed on the enrichment process were examined. The B2O3content of the concentrate was increased from 33.96% to a maximum of 45.52%. B2O3recovery increased with increasing bowl speed and particle size, and decreased with increasing fluidizing water velocity. The enrichment process also rejected arsenic and iron to some extent, with a maximum reduction of arsenic from 1360 g/t to 765 g/t and iron from 0.88% to0.33%.

Jan 1, 2015

By D. F. Malan

In deep level hard rock mining the rheological behaviour of the rock is important as time-dependent aseismic processes can lead to a stable dissipation of energy thus reducing violent outbursts. Underground closure measurements, observations of time-dependent fracture formation and siesmic data indicate that the rock in deep South African gold mines shows significant time-dependent behaviour. The objective of this work is to quantify the time-dependent rock behaviour for laboratory specimens and underground conditions. Laboratory experiments indicated that lava and quartzite specimens undergo measurable creep strain at stress magnitudes below the failure stress. Quartzite is however prone to more significant creep at lower stress levels. A viscoelastic analysis showed that laboratory creep results can not fully explain the behaviour observed underground. The in situ behaviour is governed mainly by the rheological behaviour of the fracture zone and the resulting time-dependent formation of new fractures. A viscoplastic discontinuity model implemented in a boundary element program is used to simulate this behaviour.

Jan 1, 1997

Models are used in engineering to reproduce reality as faithfully as possible so that the expected response of a system for given actions or inputs can be determined. In the field of rock engineering, both empirically based and numerical models are widely used to determine the likely response of the rock surrounding excavations. Many of the empirical models are developed from statistical analysis of case histories or from direct observation; however, empirical models are limited because they should be used only within the range of conditions of the observational database. Synergy exists between empirical and numerical models, because empirical models can be used to calibrate and validate numerical models. The empirical approach can benefit from the capability of numerical models to investigate specific mechanisms, which would not be possible using observations alone. Two cases are presented in which the synergy between empirical and numerical models is demonstrated. The first case examines the analysis of discontinuity effects on the strength of slender pillars in limestone mines, and the second case evaluates the effects of stress orientation on coal mine entry stability. It is concluded that numerical model calibration and verification comprises an important first stage in the successful application of models in rock engineering design. Application of numerical models allows mechanisms and interactions of various parameters to be analysed, greatly improving the understanding of the system. The improved understanding can be used to extend the application of empirical design methods, resulting in improved safety and efficiency of rock engineering designs.

Jan 1, 2014

By C. Kruger

Anglo American Platinum has adopted a strategy of best practice principles (BPP) for sampling, mass measurement, analysis, and metal accounting for more than a decade now. When new plants are designed, the most suitable sampling equipment and sampling protocols are implemented and material flows and plant layouts are designed around sampling strategies. A few years ago, a crushing plant for a high-grade matte stream was commissioned. The design called for the high-grade material to be crushed to 95% passing 2 mm, and the design allowed for a single-cutter primary Vezin sampler taking increments from a gravity flowing stream at regular intervals while filling a tanker for pneumatic offload at the base metal refinery. This was a single point of sampling and analysis that would measure the wanted output from the smelting complex and the input to the refineries. In addition, the design incorporated the functionality to collect increments in an ?interleaved? fashion from the Vezin sampler for internal precision checks. The metal accounting strategy for Anglo Platinum involves the ongoing measurement of all inputs, outputs, and stock levels for all operations for platinum group metal (PGM) and base metal (BM) content. Included are yearly stocktakes, usually done on 1 February, across the smelters and refineries (at least the base metal refinery). In the accounting period immediately following the introduction of the new crushing and sampling facility, a trend was developing whereby the absolute difference between the physical stock and theoretical stock (PGMs predominantly) increased for the two respective sites on an ongoing basis. The smelter showed an increase in physical stock compared to the theoretical stock (sender) and the base metal refinery showed an increase in theoretical stock against physical stock. Because of this anomaly, an additional stocktake was held in September for the period in question, and it was confirmed through the physical stock measurement results that the PGM accounting problem was indeed pointing towards the evaluation of the high-grade matte stream. This paper showcases parts of the process that took place to explain the poor accountabilities for the two sites. Previous results from the sampler ratification process (of the interleaved sampling design) were reanalysed, a physical inspection was carried out on the sampling system again, and the sampler performance was monitored (quality control parameters) for the period. From these investigations, it was found that airflows inside the Vezin introduced the sampling bias. A change in sampling protocol was introduced, as well as certain physical changes to the sampling equipment, to eliminate the airflow and thus the bias conditions significantly. The accounting period that followed the phased upgrading process showed that the accounting between the smelter and base metal refinery had been restored to within statistical limits (difference between physical and theoretical stock below 5% relative to theoretical stock). Keywords sampling, metal accounting, Vezin sampler, sampler bias.

Jan 1, 2014

By S. Z. Pethö

Pillar extraction at shallow depths with small pillars that were not originally intended for secondary extraction can provide a huge benefit to the coal mining industry in those areas where a significant percentage of the remaining coal reserves are locked up in small pillars at shallow depths and where opencast mining methods are simply not as cost-effective and practical to implement. A system considering all of the pertinent geotechnical and mining aspects for the safe and efficient pillar extraction of small pillars at shallow depths at Xstrata Coal South Africa (XCSA) has been further developed and implemented as part of an ongoing improvement process addressing all of the relevant legal and associated risk aspects. This work follows on from the previous pillar extraction work carried out at the ATC, Boschmans, and Spitzkop Collieries. The process involved a number of in-house workshops and sessions arranged with all key personnel from Tavistock Colliery, and also included Professor Nielen van der Merwe of the University of the Witwatersrand, a world renowned authority on pillar extraction, towards reviewing and developing the Modified NEVID pillar extraction system employed previously at Boschmans Colliery. The system is currently being employed at Tavistock Colliery with success and no major accidents, with around 655 000 t of coal having been successfully extracted from the pillar extraction panels.

Jan 1, 2012

By M. Abdellatif

Keywords: Pyrometallurgy, furnace, DC arc furnace, smelting, silicon The technical feasibility of silicon smelting in a DC arc furnace was investigated. A graphite-lined furnace was operated at power levels of 150 to 160 kW, and 40 to 60 V. The average feed rate during the silicon production period was about 30 kg/h. The recipe consisted of pre-mixed batches of 28% petroleum coke and 72% lumpy silica. The target furnace operating temperature was set at 1600°C and then raised to 1700°C. In total, about 1.6 tons of premixed feed materials was processed over 16 feeding?tapping operations. The feed was manually charged into the furnace in sub-batches of 10 to 40 kg at a time. The total batch mass was set at 90 kg during the initial part of the testwork, and increased to about 120 kg for the rest of the campaign.

Jan 1, 2011

By D. F. Malan

This paper presents an overview of work conducted over several years to investigate the continuous stope closure profiles recorded in tabular excavations and the use of this data as a hazard indicator. In spite of the brittle nature of the rock, measurements in gold mines and intermediate depth platinum mines revealed a significant time-dependent closure component. Various approaches to simulate the time-dependent closure have been investigated. Viscoelastic theory is able to simulate the time-dependent closure behaviour, but there are subtle problems with the use of this theory as it cannot simulate the failure processes in the rock. To overcome these problems, continuum and discontinuum elasto-viscoplastic models were developed by the authors. Discontinuum models have the advantage of being able to simulate the creep behaviour of prominent discontinuities. Development of these models has led to useful insights into rock mass deformation and has made the numerical simulation of parameters, such as rate of mining, possible for the first time. A number of practical applications for the mining industry have been developed from this study. Among these are the delineation of geotechnical areas using closure data, use of the data as a hazard indicator and to give warning of large collapses in the platinum mines, identification of areas to be preconditioned in the gold mines, measurement of the effectiveness of preconditioning and improved da

Jan 1, 2007

By H. Basarir

Due to the environmental constraints and the limitations on blasting, ripping as a ground loosening and breaking method has become more popular in both mining and civil engineering applications. Because of the technological advances in dozer manufacturing techniques, more powerful dozer types are available today. Thus, the ground, previously classified as non-rippable, has become rippable. As a consequence, a more applicable rippability classification system is needed which considers both equipment properties as well as rock properties in all applications. This paper is part of a complementary research work and presents the development of a previously published grading rippability classification system by the application of fuzzy set theory. The integrated rippability classification system considers the combined utilization of the rock and equipment properties, as well as expert opinion. Fuzzy set theory was chosen mainly because it deals well with uncertainty in the choice of variables. Although there are apparent sharp or discontinuous boundaries in existing classification systems, practically most of the factors involved in the ripping process are less well defined and boundaries are more blurred (or fuzzy) or uncertain in nature. Also by means of fuzzy logic it is possible to eliminate bias or subjectivity. The validity of the proposed system was checked by the comparison against existing classification systems and direct ripping production values obtained at studied sites. It is seen that by means of fuzzy logic, the uncertainties are reduced and biased usage of the final ratings that appear in alternative systems are efficiently dealt with. Keywords: Fuzzy set theory, rock rippability, rippability classification system, direct ripping, fuzzy inference system.

Jan 1, 2007

By A. A. Debrah

Artisanal and small-scale mining (ASM) plays a fundamental role in the national and local economies of resource-rich countries in Africa. As such, more effort must be geared towards fostering this type of economic activity to sustain livelihoods in rural communities. Across Africa, efforts to operationalize ASM based on a sustainable development framework have been quite tedious and often ineffective. This is because most of these frameworks lacked context and an understanding of the continuum from the artisanal through small-scale and up to the junior miner, grouped under the general term ?ASM?. Driven by the need to contextualize some of the definitional issues in this niche sector, and gain a clearer understanding of their peculiar challenges, this paper aims to contribute to the debate on ASM by considering two of Africa?s resource-rich countries ? Ghana and South Africa. Since South Africa has made greater inroads in protecting the interests of small-scale miners, we thus draw comparisons from both countries? approach to ASM, outline the lessons learnt, and provide recommendations regarding the ways forward.

Jan 1, 2014

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 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 B. P. Watson

The Bushveld platinum group metal deposits are two distinct, shallow-dipping stratiform tabular orebodies and strike for many hundreds of kilometres. Mining is extensive, with depths ranging from close-to-surface to 2 000 m. The mining method is a variation of planar open stoping. Pillars are widely used to support the openstopes. Little work has been done in the past to determine pillar strength and pillars have been designed using experience and formulae developed for other hard-rock mines. This has led to oversize pillars with consequential loss of ore or undersize pillars resulting in potential collapses or pillar bursts. This paper describes a back-analysis of pillar failures at Impala Platinum, just north of Rustenburg, and provides insights into pillar behaviour. Strength formulae are presented for Merensky Reef pillars at Impala. These formulae may be used cautiously on other platinum mines with similar geotechnical and geomechanical conditions.

Jan 1, 2008

By R. Cao

Geostatistics was initially developed in the mining sector, but has been extended to other geoscience applications, including forestry, environmental science, soil science, and petroleum science and engineering. This paper presents methods, workflows, and pitfalls in using geostatistics for hydrocarbon resource modelling and evaluation. Examples are presented of indicator variogram analysis of categorical variables, lithofacies modelling by sequential indicator simulation and hierarchical workflow, porosity modelling by kriging and stochastic simulation, collocated cokriging for integrating seismic data, and collocated cosimulation for modelling porosity and permeability relationships. These methods together form a systematic approach that can be effectively used for modelling natural resources.

Jan 1, 2014

By B. Clermont

Ball mills are usually the largest consumers of energy within a mineral concentrator. Comminution is responsible for 50% of the total mineral processing cost. In today?s global markets, expanding mining groups are trying to optimize mill performances. Since comminution is concerned with liberating valuable minerals for recovery in the separation process, it is crucial to run the mills at the best operating conditions which lead to good liberation at competitive throughputs with minimum costs (energy and wear). The high availability of the equipment is also essential to maximize production and profit. To reach this key objective, continuous and reliable information about the mill operation is vital. An innovative tool which can deliver information about in-mill dynamics has been developed by Magotteaux. It can provide online and accurate measurements of the degree of grinding ball fill and pulp position for timely decision making and actions. This tool could be used on its own or linked to an automatic grinding ball loading system named Magoload. Therefore, ball load could be kept constant by using direct measurement. This article describes the Sensomag and presents some of the major improvements that can be achieved with it. Some other promising avenues are still to be explored. Keywords: Comminution, process control, process optimization, process instrumentation, online analysis.

Jan 1, 2010

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 B. S. Xakalashe

Keywords: Pyrometallurgy, silicon, solar cells Silicon has been the dominant material in the photovoltaic (PV) industry since its application in the space industry in 1958. This review focuses on crystalline silicon solar cells, primarily due to their dominance in the photovoltaic industry, omitting other photovoltaic cell technologies such as second generation (e.g. thin films) and third generation (e.g. nano-structured solar cells). The value chain for the production of crystalline silicon solar cells has been reviewed. The primary processing steps for the production of silicon solar cells from quartz are as follows: bulk production of metallurgical-grade silicon via carbothermic reduction in a submerged furnace, refining of metallurgical-grade silicon via the chemical means to polycrystalline silicon, or through the metallurgical route to solar-grade silicon, wafer manufacturing, and, lastly, silicon solar cell manufacturing. During downstream processing, solar cells are interconnected and encapsulated into solar modules (panels), which can be used individually or incorporated into a photovoltaic system for electricity generation and supply. The cost for crystalline silicon based solar cells is approaching one US dollar per watt peak ($1/Wp), while the most cost-effective solar modules in industry have reported costs below $1/Wp, and are based on CdTe thin films. Solar cell energy conversion efficiencies as high as 22% have been reported in industry for crystalline silicon solar cells.

Jan 1, 2011

By W. S. Steinberg

In 1963, the full-scale engineering study for the development of an iron, steel, and vanadium plant was initiated. This was the birth of Evraz Highveld and its process flow as it is known today. Highveld started out as a steelworks that produced steel and vanadium-bearing slag from a titaniferous magnetite iron ore mined from its own mine site near Steelpoort. The process utilized co-current rotary kilns for prereduction, and submerged-arc furnaces for the production of pig iron with approximately 1.15% vanadium. Because of various technical challenges that the submerged-arc furnaces experienced over the years, a decision was taken in 2004 to convert the furnaces to open slag bath (OSB) operation, in order to enable the maximum production of iron and vanadium while improving the control over operational parameters. The conversion proved to be highly successful and, since 2005, three furnaces have been converted to OSB operation. The fourth furnace will be converted in the first half of 2011. The conversion to OSB furnaces not only yields higher vanadium recovery to the metal at the iron plant, but also improves the overall throughput of the steel plant. This is the result of the higher carbon content of the liquid iron from the OSB furnaces, eliminating the need for anthracite addition to the shaking ladle process. This reduces the blowing time by approximately 60%. The conversion of the furnaces to OSB configuration is seen as an enabling technology change and a prerequisite to the implementation of other plant improvements that are envisaged. The long-term vision of EHSV is to convert five furnaces to OSB mode, and permanently decommission the two remaining submerged-arc furnaces. This will allow EHSV to maintain current steel and vanadium production but at a significantly improved overall efficiency.

Jan 1, 2011