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Vereeniging, South Africa

Nyoka M.,Vereeniging Refractories Pty Ltd | Nyoka M.,University of Pretoria | Garbers-Craig A.M.,University of Pretoria
Proceedings UNITECR 2011 Congress: 12th Biennial Worldwide Conference on Refractories - Refractories-Technology to Sustain the Global Environment | Year: 2011

In this study the formation of hexavalent chromium in refractory materials was examined. This included a complete characterisation of virgin and postmortem refractory samples, understanding the conditions under which hexavalent chromium forms and determining when it forms during the life cycle of a given refractory material. The study also determined the extent to which hexavalent chromium formation is associated with the manufacturing of these refractory materials. The presence of alkali oxides (specifically lime in the case of the castables) plays a significant role in the formation of hexavalent chromium under oxidising conditions. The formation of hexavalent chromium was found to be a time-temperature dependent reaction under oxidising conditions. Higher concentrations of hexavalent chromium formed with increasing temperatures up to a maximum at 800°C, after which the concentration of hexavalent chromium decreased with a further increase in temperature. Increasing the holding time at a specific temperature was found to result in a decrease in hexavalent chromium content. Source

Nyoka M.,Vereeniging Refractories Pty Ltd | Brazier D.,Vereeniging Refractories Pty Ltd | Courtney T.,Vereeniging Refractories Pty Ltd | Parry R.A.,Vereeniging Refractories Pty Ltd
Journal of the Southern African Institute of Mining and Metallurgy | Year: 2013

Historically bauxite-based refractories have been used in applications where andalusite-based refractories could work. Bauxite-based refractories were chosen over andalusite-based refractories mainly because of the availability of low-cost Chinese bauxite and also because many furnaces were designed by international companies that cannot easily access high-quality products. Currently, the availability of low-cost bauxite is under threat as a result of high export duties and tariffs as well as restrictions on the amount of material that China allows to be exported. South Africa is a major producer of andalusite, and this guarantees stability with respect to both availability and price. Refractories based on andalusite have an added economic advantage over bauxite-based refractories in that unlike bauxite, which requires high-temperature calcination before use, andalusite is used in its raw state. This paper constitutes a literature study of the merits, both technical and economic, of using refractories based on andalusite compared to bauxite-based refractories. Source

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