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Cape Town, South Africa

Neizel B.W.,North West University South Africa | Beukes J.P.,North West University South Africa | Van Zyl P.G.,North West University South Africa | Dawson N.F.,Xstrata Alloys
Minerals Engineering | Year: 2013

The production of ferrochrome is an energy intensive process. At present, the pelletised chromite pre-reduction process is most likely the ferrochrome production process with the lowest specific energy consumption, i.e. MW h/t ferrochrome produced. Higher chromite pre-reduction levels correspond to lower specific energy consumptions. It was previously proven that various compounds could enhance the level of chromite pre-reduction. In this paper the effect of CaCO3 addition on pelletised chromite pre-reduction is presented. CaCO3 (as limestone) is already used as a flux in some FeCr production processes, hence its use does not constitute the addition of an extra raw material. Results indicated that CaCO3 addition enhance the level of chromite pre-reduction achieved significantly, which could results in substantial specific energy consumption improvements. However, CaCO3 addition caused severe decreases in both compressive and abrasion strengths of pre-reduced pellets, which is unlikely to be negated by mitigation measures. The addition of CaCO3 in the pelletised chromite pre-reduction process is therefore likely to result in the formation of excessively fine feed materials. In practise, this reduces the usefulness of this technique for submerged arc furnace ferrochrome production significantly, since excessive fines in the feed material are likely to result in increased operational instabilities, equipment damage and safety risks. TGA and thermochemical calculations also indicated that CO2 released from the CaCO 3 will result in in situ carbon and energy consumption, which is an additional negative associated with its use as an additive during pre-reduction of composite chromite pellets. Although this paper was not specifically aimed at obtaining mechanistic information, thermo-mechanical analysis indicated that especially iron pre-reduction rates were enhanced by CaCO3 addition. © 2013 Elsevier Ltd. All rights reserved. Source


Beukes J.P.,North West University South Africa | Dawson N.F.,Xstrata Alloys | Van Zyl P.G.,North West University South Africa
Journal of the Southern African Institute of Mining and Metallurgy | Year: 2010

The production of ferrochrome alloy from chromium bearing chromite ores is conducted at high temperature under highly reducing conditions. However, albeit completely unintended, it is impossible to completely exclude oxygen from all high temperature process steps, with the corresponding possibility arising for the generation of small amounts of Cr(VI) species. Certain Cr(VI) species are regarded as a carcinogenic, with specifically airborne exposure to these Cr(VI) species being associated with cancer of the respiratory system. With approximately three-quarters of the world's viable chromite ore reserves located in South Africa, and annual ferrochrome production approaching almost half of total annual global output, aspects of Cr(VI) generation and control are of particular relevance and importance to the local industry, and naturally to the global industry at large. This paper seeks to examine theoretical and practical aspects associated with Cr(VI) generation (based largely on experience within the local South African industry, but considered to be generally encountered in the broader global industry context), together with mitigating measures that can be applied within the context of the production processes. From the discussions it is clear that significant improvements in various Cr(VI)-related aspects have been made by the South African ferrochrome industry. However, it is also evident that several areas of uncertainty still exist, which require further research in order to better quantify risks and enhance the efficacy of mitigating steps. © The Southern African Institute of Mining and Metallurgy, 2010. Source


Glastonbury R.I.,North West University South Africa | van der Merwe W.,North West University South Africa | Beukes J.P.,North West University South Africa | van Zyl P.G.,North West University South Africa | And 4 more authors.
Water SA | Year: 2010

South Africa holds more than 70% of the world's viable chromite ore reserves and produces ~46.2% of the world's high carbon ferrochrome. It was recently reported that beneficiated South African chromite ores contained significant amounts of Cr(VI). If this is true, it could have serious consequences for South African chromite mines and the local environment. Currently none of these mines make any provision for Cr(VI) leaching from their mined ores. The data obtained in this study proved that the Cr(VI) content of chromite samples is influenced by the sample preparation technique employed prior to chemical analysis, more specifically, that pulverising of chromite samples in a normal atmospheric environment resulted in Cr(VI) formation. No Cr(VI) was liberated when pulverising was conducted in an inert atmosphere. The presence of Cr(VI) in South African chromite ores therefore seems unlikely. The results also suggest that the perceived threat of Cr(VI) contamination of groundwater and surface water, originating from chromite ore stockpiles, is improbable. Source


Mhlongo S.E.,University of Venda | Amponsah-Dacosta F.,University of Venda | Mphephu N.F.,Xstrata Alloys
Journal of African Earth Sciences | Year: 2013

The issue of abandoned mine sites is a major environmental and social problem for the mining industry, communities and governments. Historical mine sites are characterized by significant environmental, health and safety problems. The aim of this study was to develop hazard maps that can assist in the prioritization of rehabilitation at Nyala Mine. The approach used involved site examination and characterization to establish the environmental conditions of the mine. Hazards at the mine were identified, scored, and rated using modified Historic Mine Site Scoring System. The scoring focused on source and exposure pathways. The developed hazard maps showed that the best approach of effectively reducing the physical and environmental hazards at Nyala Mine was to give priority to extremely and moderately hazardous pits; surface infrastructure and spoil dumps, and then to tailings dumps characterized with less physical hazards but extremely high environmental hazards. Pits and spoil materials which were found to be relatively less problematic in terms of physical hazards were to receive least attention. The use of this hazard-scoring and risk-ranking methodology coupled with the hazard maps would provide a more robust scientific basis for making sound decisions and prioritize actions that need to be taken to minimize or manage risks associated with various areas of the mine site. © 2013. Source

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