Scielo RSS <![CDATA[Journal of the Southern African Institute of Mining and Metallurgy]]> http://www.scielo.org.za/rss.php?pid=0038-223X20090002&lang=en vol. 109 num. 2 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Design of optimum roof support systems in South African collieries using a probabilistic design approach</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2009000200001&lng=en&nrm=iso&tlng=en When designing coal mine roof support, it is necessary to account for the uncertainties and variability that inherently exist within the rock mass and support elements. The performance of a support system is affected by these uncertainties, which are not taken into account in the current deterministic design methodologies used in South Africa. The key to the design of a roof support system is a better understanding of roof behaviour and uncertainties that can be encountered during extraction. This paper sets out to develop a method that takes all uncertainties that exist within the rock mass and the mining process into account and provides a quantitative risk-based design methodology. <![CDATA[<b>Incorporation of rehabilitation cost into the optimum cut-off grade determination</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2009000200002&lng=en&nrm=iso&tlng=en Determination of the optimum cut-off grades is one of the most important aspects of mine production planning. A cut-off is a grade below which we choose not to process material. This material is treated as waste and dumped. Dumping waste is accompanied by the rehabilitation cost which will affect the overall cost of final production and also the optimum cut-off grade. Rehabilitation cost is the cost per ton of rehabilitating material of a particular type of rock after it has been dumped as waste. One of the most popular algorithms for determination of the optimum cut-off grade is Lane's method. Lane formulated the cut-off grade ptimization, but he did not consider rehabilitation cost during the optimization process. This cost item should be evaluated first, and then considered during the cut-off grade optimization process. In this paper the rehabilitation cost is inserted directly into the cut-off grade optimization process using Lane's theory. The cut-off grades obtained using the suggested method will be more realistic than ones using the original form of Lane's formulations. <![CDATA[<b>Rock bolt condition monitoring using ultrasonic guided waves</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2009000200003&lng=en&nrm=iso&tlng=en Rock bolt integrity is a critical issue for the mining industry because of its influence on the safety of mining operations. Guided ultrasonic wave testing of the defects associated with resinanchored rock bolts was investigated. Axisymmetrical and threedimensional finite element models were built, one of a partially encapsulated bolt and the other of a bolt with a simulated local corrosion crack. Experimental bolts were then installed in a testing block and typical responses were compared to finite element models of different defect scenarios. Encouraging results were obtained for the smaller axisymmetrical and three-dimensional finite element models, as well as during the experimental investigation. It is recommended that software with energy-absorbing elements should be utilized to consider higher frequencies and longer bolts. Once the integrity of models such as these has been established, the models could in principle be used to train neural networks for use in commercial equipment to determine the integrity of the installed bolt. <![CDATA[<b>CFB technology provides solutions for reducing CO<sub>2</sub> emissions</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2009000200004&lng=en&nrm=iso&tlng=en The scheduled power cuts of early 2008 were a disturbing reminder that South Africa needs to expand its power-generating capacity. Low-grade and discard coals, of which South Africa has much, are a source of energy and amenable to combustion in circulating fluidized beds (CFBs). Foster Wheeler (FW) has a long ecord in developing this technology in boilers. The technology is flexible in burning a variety of fuels; low-grade, high-ash coals, good quality bituminous and anthracite coals, and biomass and waste fuels have all been used. CFB boilers are efficient, reliable and can be designed to meet tight emission standards. In recent years once-through supercritical (OTSC) CFB technology has been developed. It enables the next stage in CFB development to proceed to a medium-scale (500 MWe) utility in such projects as Łagisza, which runs at a net efficiency of nearly 44%. Scaling the technology up to 800 MWe with a net efficiency of >45% is planned to be commercial during 2009. CFB technology can reduce CO2 emissions in the repowering of coal-fired and greenfield power plants. It does so through greater efficiencies and by co-combusting coal with biomass. FW has also developed CFB technology for the gasification of biomass, as, for example, in a pressurized gasifier to produce syngas, which can be used for the production of biodiesel, thereby reducing CO2 emissions from vehicles. Carbon capture and storage (CCS) can potentially cut CO2 emissions in the generation of power from fossil fuels in the short term, provided that it gains public acceptance, that the required regulatory framework is created, and that emission-trading mechanisms or other incentives provide a solid return on the major investments required. Oxyfuel combustion is an option in CCS; Foster Wheeler is adapting its CFB combustion technology for oxyfuel combustion to meet this challenge. It is developing Flexiburn ™, which enables a plant to be operated either with or without carbon capture. This paper describes the status of CFB technology in terms of boiler efficiency and fuel flexibility. It highlights the advantages of CFB technology for oxyfuel combustion, presents a development plan for Flexi-burn™, and discusses a pressurized gasifier for biodiesel applications. <![CDATA[<b>Fluidized-bed technology for the production of iron products for steelmaking</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2009000200005&lng=en&nrm=iso&tlng=en The dominating technologies for steelmaking are the basic oxygen furnace (BOF or LD process, Linz-Donawitz) and the electric-arc furnace (EAF). The main iron input materials for both are liquid iron as hot metal, or solid iron as pig iron, DRI (direct reduced iron), HBI (hot briquetted iron) and scrap. Hot metal, pig iron (i.e., solidified hot metal) and DRI/HBI are virgin iron materials, which have to be produced from iron ore by so-called ironmaking technologies. The family of ironmaking technologies includes three process routes: blast furnace, smelting reduction and direct reduction. Driven by steadily increasing costs of raw materials in the last two decades, the sector has seen a number of new developments in ironmaking technologies, developments based on fluidized-bed technology. The main advantage of a fluidized-bed technology is that fine iron ore can be directly charged to the process without prior treatment; it does away with agglomeration and its concomitant cost, a step practised in blast-furnace, COREX® and MIDREX® processes. With Posco of South Korea, Siemens VAI Metals Technologies has successfully developed the FINEX® process, a smelting reduction based on the direct use of iron ore fines to produce hot metal. The key technology is the four-stage, bubbling fluidized-bed-reactor system, in which fine iron ore is reduced to DRI fines in a countercurrent flow with a reducing gas generated by coal gasification. Beside surveying the current state of the art, this paper discusses the technological principles of smelting-reduction and direct-reduction processes. The status of FINEX® and the outlook for further developments are described. Crucial to the successful development of the new ironmaking technologies for the direct use of fine ore was the scaling up of the fluidized-bed reactor system, which demonstrated new design features. <![CDATA[<b>Simulation of titanium dioxide (TiO<sub>2</sub>) ore elutriation from chlorination fluidized bed reactors</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2009000200006&lng=en&nrm=iso&tlng=en Elutriation of solid reactants from fluidized bed reactors can affect their process performance and efficiency greatly. Chlorination fluidized bed reactors for selective conversion of solid metal oxides to metal chlorides are used widely these days. This study provides a platform for a proper understanding of reactant solid haracteristics and solid shrinkage interaction with elutriation rate constants using multi-sized particles, sand-like, 'Geldart B' chloridable materials. The study has found that actual elutriation rates of the reactive system are influenced by complex parameters' interaction including bed diameter, reactor freeboard height, bed minimum fluidization velocity, and reactant's physical properties. <![CDATA[<b>Development of flotation rate equations for Konkola primary mill cyclone overflow at various pulp densities and thickener underflow at 35% solids</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2009000200007&lng=en&nrm=iso&tlng=en Elutriation of solid reactants from fluidized bed reactors can affect their process performance and efficiency greatly. Chlorination fluidized bed reactors for selective conversion of solid metal oxides to metal chlorides are used widely these days. This study provides a platform for a proper understanding of reactant solid haracteristics and solid shrinkage interaction with elutriation rate constants using multi-sized particles, sand-like, 'Geldart B' chloridable materials. The study has found that actual elutriation rates of the reactive system are influenced by complex parameters' interaction including bed diameter, reactor freeboard height, bed minimum fluidization velocity, and reactant's physical properties. <![CDATA[<b>Application of magnetic separation technology for the processing of a colemanite ore</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2009000200008&lng=en&nrm=iso&tlng=en Application of magnetic separation was investigated for the enrichment of colemanite ores by removing the magnetic gangue fraction. The detailed XRD analysis of the ore has indicated that the gangue fraction is composed predominantly of the iron-bearing silicates such as smectite and, to a lesser extent, illite. Magnetic susceptibility measurements of the colemanite and gangue samples have proved that colemanite is diamagnetic in character whereas gangue fraction is weakly paramagnetic to allow the removal of this fraction by magnetic separation. Magnetic separation of the crushed and sized ore samples (-5 mm +75 μm) was erformed using a high intensity permanent magnetic separator. Under the test conditions a colemanite concentrate (41.29 wt.% B2O3) was found to be produced from the crushed ore (30.76 wt.% B2O3) at a recovery of 96.76%. These findings suggest that magnetic separation has great potential as an alternative process for the production of a concentrate of commercially sufficient grade.