Scielo RSS <![CDATA[Journal of the Southern African Institute of Mining and Metallurgy]]> vol. 109 num. 1 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[<b>The use of borehole radar in detecting disruptions in platiniferous horizons in the Bushveld Complex, South Africa - the financial implication</b>]]> Robust borehole radar tools were developed for application in South Africa's gold mines in the late 1990s. These tools are needed to operate under extreme underground mining conditions characterized by high temperature, high humidity and corrosiveness. Once borehole radar was proved as a delineation tool for the flat tabular gold reefs, the technology was tested on similarly orientated platinum reefs. Due to the extremely favourable dielectric contrast of these platinum orebodies with their host rocks, borehole radar has been successful in identifying small-scale disruptions in these reefs that may affect mining them. Slim-line borehole radar tools are deployed in boreholes drilled parallel to sub-parallel to the platinum reefs to delineate disruptive structures such as dykes, faults, slumps (called potholes) and iron-rich ultramafic pegmatites (IRUPs), which change the normal reef composition. Advance knowledge of how the reef is displaced affects how the orebody is mined. Mine planning can be adapted to mine the ore body more economically and potential hazardous situations can be negated. This paper presents examples of where borehole radar was used to delineate disruptions to the reef plane in two platinum mines. It is shown that applying borehole radar prior to mining has a significant financial benefit. Finally, development directions for future borehole radar technology are recommended. <![CDATA[<b>Nonlinear rock behaviour and its implications for deeper level platinum mining</b>]]> Uniaxial tests performed on core from instrumented sites at Amandelbult 1 shaft, Impala 10 shaft and Union Section Spud shaft showed a nonlinear elastic relationship between applied load and induced deformation. This nonlinear behaviour does not appear to be dependent on borehole orientation but in the case of the Amandelbult and Union sites appears to have been influenced by the stress condition of the rock mass at the time of drilling. Cores drilled at these two sites under destressed conditions, such as over a stope, showed a linear elastic response to the applied load whereas most of the cores drilled under relatively high radial stresses were nonlinear. The Impala 10 shaft tests, however, all showed strong nonlinear behaviour irrespective of the stress condition of the rock mass at the time of drilling, although high stress conditions may have influenced the severity of the nonlinearity. A comparison between underground stress change measurements and an elastic model indicated that the rock mass became nonlinear when the virgin stress condition was relaxed to about 10 MPa. The cores for laboratory testing were retrieved from vertical boreholes drilled up from the centre of a stope and from horizontal boreholes drilled over pillars and stopes at about 600 m, 1 100 m and 1 400 m below surface for the three sites respectively. The k-ratios under virgin conditions were estimated from sockets, modelling and stress measurements to be 1.0, 1.3, and 0.5 for the Amandelbult, Impala and Union sites respectively. Of the three sites, therefore, Impala 10 shaft appears to have had the highest virgin stress state. Tests performed on similar rocks from shallower depths at Impala Platinum essentially showed a linear relationship between stress and strain. From the small Impala Platinum rock test database available to the project, it appears that the nonlinear elastic behaviour initiates at this mine from about 1 000 m below surface and seems to become progressively more nonlinear below this depth. In addition, the nonlinear elastic rocks are weaker, have a lower Young's modulus and a higher Poisson's ratio than their linear elastic equivalents. Interestingly the tangential Poisson's ratios of the nonlinear elastic materials are often greater than 0.5 at 50% of the failure stress, suggesting an early failure initiation. The paper describes the microscope and modelling work done to determine the causes of the nonlinear behaviour and discusses some implications of the behaviour for deep-level mining. <![CDATA[<b>AziSA: Improving mining decisions with real-time data</b>]]> South African underground hard rock mines are typically managed using measurements made daily, weekly or even monthly of key parameters such as face advance, readiness to blast, blast success, temperature or dust levels. Health, safety and productivity can all be greatly improved if a real-time measurement system can inform decision making. To enable this vision of widespread sensing, communication and decision support, CSIR has developed an open standard architecture for communication of sensor data, and a reference implementation using that standard. The standard, called AziSA, meaning 'to inform' in isiZulu, will allow any device that complies with it to join any network that supports it. The standard is designed for South African gold and platinum mines. To be practical in a typical Bushveld platinum mine, a real-time sensor system needs to be robust, reliable and cheap: • Sensors are equipped with power sources that will last as long as the sensor is required.In effect, sensors need to be disposable: cheap enough not to warrant repair if they break. • Communication in the stope is wireless, to avoid the reliability problems associated with wire connections. For example, wires to sensors in the face area are unlikely to survive blasting. • To get information out of the stope, the power line to the scraper winch is used as a communications link. Unlike a separate communications link, the power line will be repaired if damaged, because of its importance to production. • Outside the stope, communications are transferred onto the mine communication infrastructure. To succeed as a management system, the next key element is the use of software decision support tools that will analyse masses of real-time data to extract key parameters and trends for decision makers. A range of sensors has been developed, including commercial sensors that have had wireless adapters added to make them AziSA compliant, and bespoke sensors that provide low cost sensing of typical mining parameters. An important parameter in any sensor network is the location of the sensor. This has to be easy and cheap to establish, so a tool has been developed to locate sensors in the confines of a stope, using ultrasonic and radio techniques. Once sensors are installed and located, they associate their location to all data that they produce. All the data from the system are captured at surface in a flexible database that can be queried by any application that requires data of any kind. It is simple to program alerts, and for actions to be associated with alerts. The use of wireless in stope also allows for communication from surface to the stope, or from stope to stope. The first implementation of an AziSA compliant system is being installed as part of the Mine Health and Safety Council funded rockfall elimination project. The design is discussed, and a future application for a platinum mine is considered. <![CDATA[<b>HPGR - revolution in platinum?</b>]]> High pressure grinding rolls (HPGR) technology has come a long way in its application for comminution duty in hard rock mineral processing in the last three years. Several major projects in copper, nickel, gold, molybdenum, platinum, and iron ore have opted for this technology. Advances in wear abatement technology have established the HPGR as a reliable machine with the required high utilization and availability. The HPGR captures the imagination as the next step change improvement in ore processing, based on the following benefits: • Energy efficiency (potentially 10-30% more efficient)-very topical in an increasingly 'green' society, and in times of rapidly increasing energy costs and availability concerns. 2008 has shown this to be especially important in Southern Africa • High (and stable) throughput with a relatively small footprint • Lower operation cost • Liberation benefits • Creative 'mine-to-metal' system improvements made possible by HPGR. The platinum industry, renowned for its historically conservative approach, has not been left behind with two significant new HPGR installations, one in Platreef application and one in UG2 application, commissioned in 2008. While the decision for the Platreef application was driven primarily by comminution circuit capacity and design imperatives, the UG2 application seeks to develop a flowsheet that will have a significant recovery benefit in addition to capacity increase and reduced operating cost. The Platreef application of HPGR also provides the opportunity to introduce a novel comminution flowsheet and to demonstrate exceptionally low wear rates treating very hard, abrasive and variable ore types. The HPGR lends itself for inclusion in existing SABC circuits to increase the capacity of the plant and mills. With current PGM prices many operations are attracted to the HPGR technology benefits. The HPGR clearly has the potential to transform entrenched opinion and provide decision makers with significant alternative comminution options. This paper aims to provide an overview of the current applications and to speculate on the transforming stimulus that the HPGR exerts on industry. <![CDATA[<b>The significance of grinding environment on the flotation of UG2 ores</b>]]> A large body of work exists discussing the impact of grinding media on mineral flotation. Generally, the work indicates that a change to a less electrochemically active grinding environment has positive benefits on downstream processing. There is a fear, however, that these benefits may not be realized when treating low sulphide containing ores, typified by UG2 style deposits. A series of experiments was developed to test the flotation response of UG2 ores using the Magotteaux MillĀ® to determine if measurable differences in the pulp chemistry could be discerned using a range of grinding media types. Further, the flotation responses of the contained sulphides (chalcopyrite, pentlandite and pyrrhotite) were determined. The data collected provided strong evidence that the grinding environment can significantly influence the pulp chemistry and flotation characteristics of all sulphide minerals, even when the ore contains less than 0.5 per cent total sulphide. The results show that the change to an inert media type produced a substantial improvement in the flotation rate of all sulphide minerals, as well as the PGMs. <![CDATA[<b>Energy considerations in the current PGM processing flowsheet utilizing new technologies</b>]]> 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. <![CDATA[<b>Furnace energy efficiency at Polokwane Smelter</b>]]> Anglo Platinum's Polokwane Smelter is situated outside Polokwane, in the Limpopo Province in South Africa. A single 168 MVA six-inline rectangular furnace smelts dry concentrates containing platinum group metals (PGMs). Furnace energy consumption since commissioning is presented, showing that energy efficiency improves as capacity utilization increases. An energy balance for the furnace is outlined, indicating the measured or calculated energy losses from the hearth and sidewall cooling, the copper coolers, the upper furnace walls and roof, and the energy losses in off-gas, matte, and slag. From the energy balance, the potential to improve energy efficiency by controlling the slag temperature, the slag level, and the off-gas volume is derived. Furthermore, the impact on the energy balance of different concentrate types is discussed, as well as the potential impact of replacing all upper waffle coolers by plate cooler panels. <![CDATA[<b>Towards electrode immersion control on Lonmin's no. 1 circular furnace</b>]]> A control philosophy to be applied by Lonmin to maintain constant electrode immersion in their no. 1 circular smelting furnace is put forward. This control philosophy is facilitated though a combination of thermodynamic models used to predict the slag composition and empirical correlations to estimate the furnace eometric factor as well as the slag conductivity. The model can determine the operating resistance setpoint required in order to maintain a desired electrode immersion as a function of the feeds to the furnace, slag level and temperature. If modifying the resistance setpoint cannot maintain the desired immersion without moving out of the furnace P-V-I operating envelope, the model can be used to determine the amount of slag modifiers (silica or lime) required to shift the slag chemistry back into a region where the immersion can be controlled though resistance setpoint manipulation. <![CDATA[<b>Development of roasting parameters for the ConRoast process with low-sulphur feedstock</b>]]> The ConRoast process for the production of platinum group metals involves the use of a fluidized bed reactor for the removal of sulphur from ore concentrates by roasting prior to smelting in a DC-arc furnace. Test work was carried out in 2007 at Hazen Research in Golden, Colorado to provide the data necessary for a commercial roaster to be designed by Technip. This paper discusses the rationale behind the test work, the goals for calcine composition to be used as smelting furnace feed, the results of various roaster operating parameters in terms of calcine composition (particularly residual sulphur and the fate of trace elements), and the impact of the results in terms of a commercial roaster design.