Browsing by Author "Maidza, Teboho"

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    Development of a rapid laboratory predictive test method using fluidised bed techniques for the determination of oxidisability of residual CR (III) present in slags
    (2006) Maidza, Teboho; Von Blottnitz, Harro
    Slag arising from smelting in the production of ferrochrome alloys, stainless steel andPlatinum group metals (PGM) is known to contain residual chromium in variousphases within the slag matrix. Although the bulk of slag ends up on landfills, slag isused in the construction, agriculture and marine industry among others. Applicationsfor slag include as an aggregate in road construction and paving, buttressing, and as asource of lime in agriculture. Previous studies have shown that about 0.1-1 % of residual Cr(III) in slags with CaO/Si02 ratios greater than 2 can be slowly converted to a toxic and water-soluble hexavalent species in the presence of atmospheric oxygen, at ambient temperaturesalbeit at very slow rates. The produced Cr(VI) is potentially able to leach intounderground waterways and terrestrial water bodies, thus posing an environmentalhazard. In a landfill scenario, the oxidation kinetics are likely to be limited by the externaldiffusion resistance of the bulk of the landfill and the internal diffusion limitations tothe reactive phases within individual particles where CaO and Cr20 3 phases are inintimate contact. Earlier studies have also shown that the conversion of Cr(Ill) toCr(VI) in an ambient atmosphere increases, as the particle size decreases, with an increase in CaO and in the presence of moisture.