Scielo RSS <![CDATA[Journal of the Southern African Institute of Mining and Metallurgy]]> vol. 110 num. 11 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Ore Dressing</b>]]> <![CDATA[<b>Student Colloquium</b>]]> <![CDATA[<b>Case study: High capacity spiral concentrators</b>]]> Spiral concentrators are compact, cost-effective and generally efficient gravity concentration separators for a wide range of applications (for example: coal, beach sands, iron ore, chromite and tantalite). Large mineral processing plants consist of thousands of spiral concentrators resulting in large plant footprints (capital intensive) and the adjustment of splitters is time consuming, impractical and is in many cases neglected-high capacity (HC) spiral concentrators aim to address these shortcomings. As a result Exxaro Namakwa Sands is currently investigating high capacity spiral technology for the spiral circuit upgrade at the primary concentrator plants (PCPs). This article summarizes the rougher spiral performance evaluation that was conducted on different types of spiral concentrators (the traditional MG4 spiral concentrator and the high capacity (HC) spiral concentrator) under different feed conditions. In addition, the effect of slimes on the spiral concentrator performance was also investigated. Slimes rheology was linked to the poor concentrator performance at the higher slimes concentrations. The test campaign shows a sacrifice in recovery under design-feed conditions can be expected when using high capacity spiral concentrators in the rougher stage when compared to traditional spiral technology currently in use. Both spiral concentrators show a detrimental impact of slimes on the performance, but the high capacity spiral concentrator is more sensitive to the higher slimes conditions. <![CDATA[<b>Optimizing the performance of wet drum magnetic separators</b>]]> The difference in the magnetic properties of minerals is the basis for magnetic separation. All minerals can be generally classified as ferromagnetic (strongly magnetic), paramagnetic (weakly magnetic) or diamagnetic (non-magnetic). Magnetic separation can be conducted dry or wet. The majority of the applications of wet magnetic separation in the mining industry are based on the wet drum magnetic separator. The wet drum magnetic separator has been in use for over 50 years and its design is based on a rotating drum installed inside a tank. Inside the drum are stationary, permanent magnets arranged in an arc to provide the magnetic field. These magnets can be of the ceramic ferrite type providing a low intensity magnetic field or of the rare earth type providing a high intensity magnetic field. Wet drum magnetic separators are generally applied in three different ways, namely to recover and recycle the medium used in dense medium separation (DMS), to remove magnetic contaminants from ores and concentrates, and to recover valuable magnetic products. Wet drum magnetic separators are applied in the following commodity areas: coal, diamonds, iron ore, chrome, platinum, heavy mineral sands, industrial minerals, and base metals. Whereas the design and operation of wet drum magnetic separators is relatively straightforward, it is very often found that the performance of wet drum magnetic separators is far from optimum. The reason for this is generally a lack of understanding of how the different design and operating variables interact and how they affect performance. This paper examines these variables, describing their importance and impact for all applications of wet drum magnetic separators. It also provides clear guidelines on how to adjust and control these variables so that optimum performance is achieved. <![CDATA[<b>The influence of control and mechanical conditions of certain parameters on jigging</b>]]> Jigging is a process of particle stratification in which the particle rearrangement results from an alternate expansion and compaction of a bed of particles by a pulsating fluid flow. The rearrangement results in layers of particles that are arranged by increasing density from top to bottom of the bed. The particles, in addition to the vertically expanded and compacted bed motion, move continuously, horizontally across the supporting screen and helped and influenced by the feed material that is introduced at one end. Following the particle stratification, the particle bed is physically 'cut' at a desired horizontal particle density plane to separate the desired product from the less dense gangue material. The issue of correct pulse characteristics (shape, amplitude and frequency) for the optimal metallurgical stratification of air pulsating jigs has been the subject of much discussion over the years. The accuracy of the dissymmetric stratification depends on the control parameters and the mechanical condition of specific equipment used. This paper will touch on some of the control and mechanical parameters affecting the separation efficiency. <![CDATA[<b>Processing strategy for different coal types</b>]]> The metallurgical response of a difficult to treat coal and an easy to treat coal orebody were investigated in terms of the coal yield and the coal quality in a basic coal recovery flowsheet. The purpose of this paper is to show trends and derive principles for the treatment of different coal types. This investigation entailed using the LIMN simulator to simulate the metallurgical response by varying the plant operational parameters. The controllable plant variables investigated were: e Cyclone size e Screen and hydrocyclone cut points e Medium cut density e Feed particle size distribution. The following general principles can be derived from the work: e Crushing finer can significantly improve the overall metallurgical performance, especially for a difficult to treat ore e The strategy of crushing finer works better when there is a flotation stage in the circuit as it minimizes losses to fine discard e Smaller cyclones result in slightly better performance because of the greater centrifugal force generated giving a smaller breakaway size. <![CDATA[<b>Leeuwpan fine coal dense medium plant</b>]]> Exxaro installed their first ultra fines treatment plant at Leeuwpan Coal mine. The plant is now fully operational and results already show that the plant has great potential. The plant was designed and installed by DRA. Several challenges were faced during the installation due to the space constraints in the Leeuwpan plant. Efficiency tests were conducted on both modules after commissioning and showed very promising results. A lower ash product with a higher yield can be produced with the fine coal dense medium cyclones compared to the spirals previously employed. <![CDATA[<b>The efficiency of Wemco drums at Kleinkopje coal washing plant over 30 years</b>]]> Kleinkopje Colliery has five Wemco drums that were installed and commissioned in 1978. Over the years, there have been remarkable changes in mining and geological conditions at the colliery. First, an increase in the percentage of fines was recorded, which resulted in an uneven split or an imbalance in silo levels between material feeding the cyclone (-12 mm) and Wemco drum (+12 mm) sections respectively. This problem was solved by doing modifications around the banana screens to allow finer material to the drums. The imbalance challenge was then followed by spontaneous combustion that takes place in situ and results in low product yield. The results obtained from efficiency tests indicate that although there is a limit in the percentage of -6 mm material in the feed, Wemco drums are still very efficient and applicable to the current mining conditions. These results also suggest that it is essential to lower the throughput when the drums are treating low yielding coal. <![CDATA[<b>Experiences in the production of metallurgical and chemical grade UG2 chromite concentrates from PGM tailings streams</b>]]> Recovery of a chromite concentrate from UG2 flotation tailings streams, of a grade suitable for further pyrometallurgical treatment for the production of ferrochrome, has certain specific challenges not only by virtue of the decoupled nature of the primary PGM recovery process and secondary gravity based chromite recovery circuits, but also because of intrinsic variations in the nature of the ore and its mineral composition. Variability in the ore, together with upstream process dynamics, creates a challenging environment in which to achieve optimal recovery of a gravity concentrate with accurate grade control. This paper examines certain interrelational aspects between the ore gangue and chromite mineral types, the influence of the primary PGM extraction circuit and secondary chromite extraction activity as applied specifically to UG2 ore against a background of actual plant experiences and circuit configurations applied in order achieve a suitable quality of chromite concentrate. <![CDATA[<b>The potential of electrostatic separation in the upgrading of South African fine coal prior to utilization - a review</b>]]> Coal is a complex mixture of organic and mineral constituents and is the most abundant resource of fossil energy in the world. In recent years, significant research into dry coal beneficiation has gained much attention, primarily due to the need to improve grades and reduce the environmental contaminants in coal without the use of water, and to achieve this in as cost-effective manner as possible, relative to wet beneficiation processes. This paper seeks to review the application of various electrostatic separators with their process principles, to draw comparisons between different dry beneficiation techniques with specific emphasis on the triboelectrostatic separation method, and finally to report the results of triboelectrostatic separation conducted on various South African coals. Previous research conducted on Indian, European and American coals has indicated that this technique is likely to lead to significant economic benefit through the reduction of ash content, NOx and more specifically SOx by separating out the liberated Fe-S-bearing minerals prior to utilization. The removal of the latter suite of minerals is also likely to significantly reduce or eliminate the emissions of associated trace elements, including mercury and arsenic. The research results reported in this paper indicate that the rotary triboelectrostatic process has the potential for significant upgrading of high ash pulverized South African coal. The impact of various operational parameters was investigated and key factors established for the optimum recovery of low ash and low sulphur fine coal.