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By C. Wade, A. Swart, M. Dworzanowski

AngloGold Ashanti operate a pyrite flotation plant at their East Gold Plant, Acid Plant and Flotation Plant (EGAF) metallurgical complex within their Vaal River operations in the North West province in South Africa. The flotation plant feed is reclaimed pyrite rich tailings and the concentrate produced is used as the source of sulphur for the EGAF acid plant. The sulphuric acid produced is in turn used for the recovery of uranium at the Vaal River South uranium plant. The original flotation plant built in 1960 was based on the use of many small volume flotation cells and was becoming very expensive to operate and its age severely limited further operation. A decision was taken in 2005 to replace this plant with a new one based on fewer, larger volume flotation cells. This paper describes the benefits of using larger volume flotation cells in this new flotation plant when compared to the smaller volume flotation cells in the old plant. The benefits of the new plant include a smaller plant footprint, fewer flotation cells, fewer pumps, no distribution boxes, simpler piping, a greater flotation volume and a reduction in installed power. The saving in capital cost could not be quantified because of the age of the old plant. The savings in operating cost will arise from fewer operators, less maintenance and reduced power consumption. The new plant has not been in operation long enough to quantify the benefits in operating cost and metallurgical performance. However, recovery improvements can be expected given the greater flotation volume (increased residence time) and the installation of larger, more efficient flotation cells.

Jan 1, 2007

By C. Musingwini

An often overlooked factor in the analysis of mine layouts and schedules is technical operating flexibility (or tactical flexibility), mainly due to its nebulous nature. By glossing over technical operating flexibility the resultant mine layouts and schedules maybe suboptimal. The need to incorporate technical operating flexibility into the analysis and comparison of mine layouts and schedules is increasing in importance. The nature of technical operating flexibility is illustrated, previous work on valuing of operating flexibility reviewed, and a proposal made on how technical operating flexibility can be quantified for tabular reef mines by using a platinum reef deposit as a case study. Once technical operating flexibility has been quantified it becomes possible to explore its incorporation into the analysis of mine layouts and schedules and subsequent optimization processes. This paper is a revised version of a paper presented in the Proceedings of the Second International Platinum Conference, ?Platinum Surges Ahead? in 2006. The work described in this paper is part of a current PhD study at the University of the Witwatersrand. Keywords: mine plans, layouts, schedules, technical operating flexibility/tactical flexibility, ore availability.

Jan 1, 2007

By M L. van Kampen

The Resource Management Act 1991 provides for activities to be classified as permitted, controlled, restricted discretionary, discretionary, non-complying or prohibited in district and regional plans. This paper looks at the use of the prohibited activity status to restrict, in particular, mining. Often the use of prohibited activity status for mining appears to have no basis other than the negative perceptions that the local community and/or the planner drafting the plan has toward mining and quarrying.   The paper will address the current appeal regarding the use of prohibited activity status now before the Court of Appeal, and the history to the litigation. The relevance of the outcome of the appeal to the minerals sector will also be explained.

Jan 1, 2007

By Dave Bulled

"This paper describes the design of a molybdenite flotation circuit using FLEET technology applied to kinetics data produced from laboratory flotation testing and distributed across the blocks of a mine plan using a geostatistical approach. The geostatistics assigned the statistical error that arises from having a limited amount of sample testing data to the kinetics estimates of each block of ore in the mine plan. The final design then included a quantification of risk based on the accuracy of the block flotation kinetics and model fitting. The design made reference to the extensive technical reports describing earlier metallurgical test work including some pilot plant work over thirty years ago.The testing involved conducting MinnovEX Flotation Tests (MFT) to determine the rougher flotation kinetics at the specified reagent conditions and rougher-cleaner tests to determine the change in kinetics resulting from regrind. These flotation kinetics were used within FLEET simulations to create a full-scale flowsheet and plant design including recommended equipment sizes and the forecast of operating results. Measurement of detailed flotation kinetics for a wide range of samples allowed the effect of size of grind and efficiency of classification (i.e. width of size distribution) to be predicted for the whole ore body.INTRODUCTIONAdanac Moly Corp. proposed to develop a 20,000 ton per day mill to produce high quality molybdenite concentrate from its Ruby Creek resource in north-western British Columbia. It is a relatively clean low grade porphyry-monzonite occurrence containing minimal quantities of other sulphides such as chalcopyrite, pyrite, sphalerite and galena. Molybdenite occurs mainly as coarse flakes with lesser amounts of finer sized values. An optimum plant design was required to can achieve the predicted operating results, at a known level of risk, while treating the variability inherent in the ore body."

Jan 1, 2007

By D. Lunt

This paper describes and sets in context the commercially proven uranium extraction processes. It also discusses some of the technologies that are currently being pursued with the aim of reducing costs and overcoming a number of technical issues that are faced by process designers and operators. In doing so, opportunities for the transfer of extraction technology from other industries/commodities are identified. The key processing areas that are examined include: ?The influence of mineralogy. The type of uranium mineralization and the nature of its association within a particular deposit will have a major impact on process route selection. Uranium minerals are classified according to their influence on extractive metallurgy. As the uranium price has risen in recent times, so opportunities are increasing for the recovery of uranium from less conventional resources such as phosphates and fossil fuels. ?The opportunities for employing techniques aimed at reducing the capital and operating costs of the overall process such as heap leach and beneficiation. Preconcentration by screening, gravity separation and radiometric sorting can potentially reduce the mass flow to the downstream leach and recovery plants. ?Purification or separation of uranium in carbonate systems. While it is possible to directly precipitate uranium from clarified leachate, the presence of impurities such as vanadium, molybdenum and others may dictate that ion exchange or selective precipitation is employed. Advances have been made in other industries in terms of improved ion exchange equipment aimed at reducing resin inventories and hence costs. ?Separation in acid leach systems. Earlier developments included the use of combined SX-IX systems (Eluex or Bufflex) and the introduction of continuous countercurrention exchange (CCIX). Column SX has found a ready application to uranium in view of the rapid extraction kinetics. With the renewed interest in uranium processing, efforts are being redirected towards further development of resin-in-pulp (RIP) as a means of driving down capital and operating costs. ?Extraction in a chloride environment. Australia and Namibia are desert countries where good quality water comes at a cost. However, both have access to saline water from either the ocean or subterranean aquifers. The issues associated with operating a uranium extraction operation in such environments is discussed. ?Extraction from less conventional sources. Recent price increases for U3O8 have resulted in a number of companies examining the recovery of uranium from sources such as fossil fuels and phosphate deposits. Both of these areas were examined in the 1970s and 1980s and a number of approaches were commercialized. The paper reviews the extraction options.

Jan 1, 2007

By Daniel Barkley

Underground coal mining in Illinois has a lengthy history dating back to the early 1800?s. High extraction underground mining has played a significant role in production through out this time. Modern mechanized longwall mining methods were introduced in the 1960?s and have been in continual use ever since. Regulations governing subsidence from underground coal extraction and the mitigation of resulting impacts to surface structures and surface land initiated in 1983. Despite the history of experience with subsidence, recent plans to longwall in Illinois have stirred public emotions and strong opposition. Anti and pro longwall groups formed and divided a community over the potential economic benefits new mining ventures could bring verses the potential problems associated with longwall mining in productive flat farmland. The debate culminated in a county wide referendum vote on the use of longwall mining. This paper provides an overview of the history of underground mining in Illinois, the controversy that has risen in central Illinois regarding longwall mining, and the efforts to educate the public about regulations that govern longwall subsidence.

Jan 1, 2007

By G F. Brent, R D. Hart, C Carr, F Felipe

In underground operations, where copper, gold and other metals are mined, the open stopes can be backfilled to stabilise surrounding workings. This fill may consist of tailings from the processing plant, usually mixed in slurry with a binder such as ordinary Portland cement (OPC). Extensive use is made of tailings in OPC-based paste fill, cemented hydraulic fill or cemented aggregate fill applications. A large underground operation such as the Mount Isa Copper Operations utilises over three million tonnes of backfill per annum. Geopolymers offer an alternative binder system with significant environmental advantages over OPC. Geopolymers are formed by polymerisation of aluminosilicate precursors in an alkali medium. They generally form products with superior strength characteristics as well as increased resistance to degradation, particularly under acidic conditions. Geopolymers have lower carbon dioxide emissions associated with their manufacture than OPC and offer further potential advantages, such as the use of less water and more waste materials. The application of geopolymers to weak material systems such as mine backfill has not been widely studied. The aims of this investigation were to assess a range of Australian mine process wastes for suitability as feedstocks in fill applications and to construct a range of these cemented minefills using a geopolymer binder. The physicochemical characteristics of each of the wastes are discussed as well as how they ultimately contribute to the geopolymer cement through direct replacement of OPC. Results from various tests on the candidate geopolymer fill formulations are presented and the potential of such fill formulations to replace OPC in mine backfilling operations is highlighted. The significant potential contribution to reducing greenhouse gas emissions from the use of geopolymer-based mine backfill across the industry is noted. Conversion of a single mine, such as the Mount Isa Copper Operations, is shown to match the reductions in greenhouse gas emissions due to the current total installed photovoltaic electricity generation capacity of Australia. A similar examination of wastes available to a gold mine could potentially yield new binders for use in established or new fill systems.

Jan 1, 2007

The importance of the accurate determination and interpretation of the bulk density and porosity of a given iron ore deposit is very often disregarded or neglected. Large amounts of time and money are spent on delineating and testing orebodies, and yet one of the most important factors in resource evaluation is sometimes estimated or, at best, determined from existing data from similar deposits. The Thabazimbi and Sishen South iron ore deposits are two well-known economical occurrences of high-grade iron ore in South Africa. Both these deposits formed as secondary enrichment of banded iron formation lithologies. Ongoing density studies on both these deposits are underway and results thus far proved very effective and necessary. Small-scale methods are used to determine average values for different ore types on both deposits. These values are used in resource estimation and geophysical interpretation.

Jan 1, 2007

By G. V. Fernandez

Sociedad Minera Cerro Verde S.A.A leaches secondary copper sulfides. In recent years, the mine has introduced innovations that have improved the management of mineral crushing, agglomeration, curing, and leaching. The crushing plant, for example, uses the concepts of degree of balance and percentage of time in an operationally balanced state which, displayed in real time, facilitate more intensive and uniform utilization of the crushers. High agglomerate quality is ensured with the correct dose of moisture, which is adjusted to the changing characteristics of the mineral through the use of electrical conductivity measurements. The amount of acid used for curing the agglomerate is also adjusted by using quality control information. Finally, the stockpile irrigation regime is managed using the criteria established by the "Lixiviant Request Rate", which optimizes the addition of leaching solution, creating such benefits as faster recovery, and reduced acid and energy consumption.

Jan 1, 2007

South Africa remains the largest global producer of gold, accounting for 11.3 per cent of total world mine production, which amounted to 2520.2 t in 2005. The benefits and disadvantages associated with hedging practices in general, and among South African gold producers is examined. The wide variety and unique nature of risks faced by the mining industries provide a strong case for hedging. Only the principles of hedging, such as selling ounces of gold in the ground at a pre-agreed price for delivery at a future date as a cost-effective mechanism for price risk management, is discussed. Progressive and cumulative increases in the volume of forward sales in the major producing countries are considered by many to be the cause of the declining gold price over the past decade. In spite of negative publicity, forward selling continued as an industry-wide practice until recently (2002) when the global hedge book contracted by 352 t; contraction amounted to 158.6 t in first quarter of 2006. The objectives and benefits of hedging include continuity and stability of cash flows, stability in price achieved, reduction of frictional costs, and creating an effective management tool. The importance of a defined hedging strategy in reducing uncertainty about the hedging objectives is essential to a successful hedging policy. Historical patterns in hedging revenues at an industry level indicate five distinct periods during which the fortunes of hedgers have fluctuated. Finally, since 2001 the rising gold price and reduced price volatility through the consolidation in the global price means that the need to stabilize revenue flows is less urgent. This has meant that hedging is becoming progressively less important for the mining industry at large.

Jan 1, 2007

By Arun Vathavooran, Adrian Singh, Michael Fletcher, Rainer Imhof

The Imhoflot G-Cell, a new development in the pneumatic flotation technology (which incorporates centrifugal forces in the separating vessel) is a recent innovation in the mineral processing world. The G-Cell was invented by Dr Rainer Imhof and commercialised by Maelgwyn Mineral Services Ltd. In a short time span a number of plants and units have been successfully commissioned in the mineral processing industry. In addition, a number of industrial G-Cell flotation plants are in the process of construction for the purpose of coal preparation and environmental remediation. In this paper two industrial installations have been highlighted together with a pilot plant test programme investigating ultra fine flotation recovery for a base metal operation.

Jan 1, 2007

By S. Frimpong

Cable shovels are used for primary excavation in in-situ and/or pre-fragmented formations in surface mining operations. Poorly fragmented hard rock formations and random occurrence of hard boulders in soft formations cause extreme variability of material diggability, resulting in varying shovel stress loading. The stress loading of a shovel’s front-end assembly could result in fatigue failure. Conventional design process, which uses physical shovel simulation studies, is very costly and time consuming for achieving statistically significant results. In this paper, rigid and flexible multi-body dynamic theories are used to develop component stress loading and deformation models of the cable shovel, and solved in the ADAMS/NASTRAN/FLEX environments. Detailed simulation experiments are carried out to examine the performance, reliability, durability and efficiency of the P&H 4100A under varying in-situ formation conditions. The results show areas of high stress fields with a maximum stress of 313.31 MPa at node 441 within the hoist rope. The reliability of the results is confirmed by comparing existing test data. The study is significant because it provides a solid foundation for further study of failure life analysis of the cable shovel components.

Jan 1, 2007

Mine site rehabilitation is the repair of the disturbance caused by mining on the immediate mining area and also on the surrounding environment. The long-term objectives of rehabilitation can vary from simply returning an area to a safe and stable condition, to restoring the mined land to a state as close as possible to its pre-mining condition, capable of being self-supporting and having a beneficial final land use. This paper investigates the importance and benefits of environmental planning, in particular for rehabilitation, and how input into daily operations can allow mining to progress with limited impact on the surrounding environment. It will also identify some of the key mistakes currently made during mining which could be averted by implementing prior planning and incorporating environmental consideration into daily operations. A number of rehabilitation opportunities will also be detailed for the different stages of the life cycle of a coal mine.

Jan 1, 2007

By H. Aykul

The choice of which mining method to use at many large surface coal mines is often dicated by what machinery is available or what experience the mine management can offer. One of the most significant surface coal mines in Turkey is owned and operated by the Turkish National Coal Board, located to the west of the city of Kütahya. The Seyitömer Lignite Enterprise (SLE) extracts low quality coal, the majority of which is supplied to an adjacent power station. The coal seems at SLE contain bands of ash which under normal mining conditions are extracted with the coal. This increases the ash content of the run of mine coal and results in lower efficiency at the power station and financial penalties for SLE. In this paper, therefore, selection of the best possible equipment and production method was identified to achieve high selective mining at SLE. The research found that two different high selective mining methods were suitable for selective excavation of the B3 seam, which were hydraulic excavator and truck and surface miner and truck combinations. It was also found that high selective excavation could provide the desired coal quality at 52% lower costs when the whole process (excavation, transportation, processing, etc.) was considered. Keywords: coal mining, surface mining, selective mining.

Jan 1, 2007

By Mingju Liu

China has been suffering from coal and gas outbursts since 1950s. Nowadays, the situation has become worse than ever with the need to mine deeper coal deposits at higher production rates in a more complex underground mining environment. In the year 2006 alone, 37 outbursts occurred in underground coal mines with a death toll of 232. This paper describes a case study of an outburst event, which occurred in July 2006 during the shaft development of the Mengjin Coal Mine, Henan Province, China at a depth of 768m below surface. Detailed analysis of the possible causes that led to the occurrence of the outburst is reported. These include the study of complex geological features, gas storage conditions, possible improper technical management practice as well as incomplete prevention and control measures. Based on the case study and the observation of outburst occurrence in China in the year 2007, suggestions have been put forward to help prevent and control future coal and gas outbursts.

Jan 1, 2007

By Kyle Kershaw

Micropiles are routinely used in the United States for foundation support and stabilization of slopes. In recent years, several retaining walls have been constructed using micropiles in an A-frame type configuration to support temporary and permanent excavations at sites with limited access and limited right-of-way. Typical A-frame micropile walls consist of a row of vertical micropiles at the face of the wall and a row of battered micropiles extending into the soil or rock to be retained. The two rows are then tied together with a pile cap such that the front pile acts primarily in bending and the back pile acts primarily in tension. Because of tight right-of-way constraints at a residential site in Aspen, Colorado, it was not possible to construct the wall using conventional shoring systems or micropiles in the typical A-frame configuration. Rather, the wall was designed such that the row of battered piles was installed at the wall face and the row of vertical piles was installed adjacent to the property line behind the wall. As a result of the reverse configuration of the A-frame wall, FLAC, a two-dimensional, finite difference software program, was used to model the soil-structure interaction. The final wall design consisted of both temporary and permanent retaining wall sections with maximum heights of 26 feet. Inclinometers were installed in several piles to monitor the behavior of the retaining walls during and after excavation. This paper presents an overview of the design method, a discussion of construction techniques, and a comparison between the FLAC model and the measured behavior of the wall in the field.

Jan 1, 2007

By X. Ndlovu

Underground observations in a coal mine have indicated failure oft he immediate roof above the bords. Careful observations and photographic recording of occurrences of these roof failures, termed ?roof guttering?, have been made. The occurrence of guttering results directly in roof instability, and indirectly, due to the interaction of the guttering with natural planes of weaknesses in the immediate roof rock. In this paper, relevant observations of roof guttering, possible mechanisms of formation of roof gutters, laboratory testing for determination of material strength and deformation properties, and numerical analyses to explain underground observations are described. Mapping of roof failures showed that these took place mainly towards the centre of the roadways. Roof guttering was observed often to occur violently and with little warning. Occurrence of roof guttering has a negative impact on production?some panels are abandoned, production times are increased and safety of workers is compromised. The numerical stress analyses showed that, although none of the constitutive behaviour criteria used predicted the observed underground failures correctly, the extension strain criterion gave the best agreement.

Jan 1, 2007

There are available today many various types of mixing systems, tank types and process liquors confronting the process designer of gold adsorption circuits. This short paper is to give the process designer an insight into the special mixing requirements for resin-in-leach and resin-in-pulp, plus the advantages and disadvantages of the various mixing systems that are available to agitate the required tank shapes. An understanding of the latest developments in this important process area of gold production is addressed and information given on the results of resin degradation in various tank sizes over long periods of mechanical agitation.

Jan 1, 2007

The Skorpion process comprises three processing steps, atmospheric leaching in sulphuric acid, zinc solvent extraction and electrowinning to produce special high grade zinc. The major mode of impurity transfer was attributed to crud runs in the solvent extraction circuit. Crud may be described as a heterogeneous, partly inorganic, partly organic mass of material which accumulates predominantly at the interface between organic and aqueous solutions. The paper describes the route causes of the crud formation in the solvent extraction circuit and optimisation strategies which are being followed to prevent impurity excursions in electrowinning. Keywords: zinc oxide, solvent extraction, crud formation, colloidal silica

Jan 1, 2007

By G. Plascencia, C. López, J. González, D. Jaramillo, M. A. Barrón

Air jet and molten matte interaction within a Peirce - Smith converter is analyzed during the first stages of blowing using Computational Fluid Dynamics (CFD), by means of the Large Eddy Simulation and Reynolds Stress turbulence models. Jet velocities ranging from 5 to 150 mis, which involve the bubbling and open jet regimes, were considered in 2 and in 3-D numerical simulations. As a result of the computer simulations, it was found that low velocities results in gas bubbling in the molten copper, whereas higher gas velocities results in well defined plumes. The consequence of such different behaviours results in an increment in the rate of refractory wear or in copper splashing respectively. The analysis of the results may lead to improve the design of the tuyeres currently used in copper converting. Bottom blowing of air is also explored in this work. Numerical results show a strong non-linear parabolic behaviour of the jet velocity on the average velocity of copper; which means that beyond certain jet velocity, the copper de-accelerates thus reducing its velocity. This may be due to the open nature of the jet, which prevents the momentum transfer from the injected gas to the molten copper.

Jan 1, 2007