Faculty of Engineering, Built Environment and Information Technology
School of Engineering
Department of Materials Science and Metallurgical Engineering
Selected Highlights from Research Findings
Research in hydrometallurgy continued to concentrate on chloride hydrometallurgy, solvent extraction, metal recovery from electronic waste materials, iron precipitation, and gold hydrometallurgy. The doctoral work of Johann Claassen focused on the removal of iron from zinc solutions by precipitation of the iron as oxyhydroxides.
It was found that close control of the neutralization step as well as seed recirculation was were necessary to promote the growth rather than nucleation of new precipitates. However, it was found that the growth of the precipitates occurred mainly by agglomeration i.e. the cementing of particles into larger conglomerates.
Claassen identified and optimised the process conditions which most strongly affect precipitate quality, and thus liquid-solid separation
Contact person: Prof RF Sandenbergh.
Cyanide is a dangerous, but useful reagent that is widely used in the extraction of gold from ores. It follows that the process residues will contain some residual cyanide that must be controlled to limit harmful interaction with the environment.
Nadia Lötter investigated and quantified the volatilisation of hydrogen cyanide from cyanide solutions and pulps in gold mining circuits as part of her master’s research.
The combined measurement of mass transfer conditions with on-site measurements, provided a quantitive tool for the prediction of cyanide transfer and attenuation of the cyanide present in such process streams, and as such will be useful in safety and environmental studies
Contact person: Prof RF Sandenbergh.
It has been known for some time that the recrystallisation behaviour of low carbon hot rolled strip steel from the Mittal Steel Vanderbijlpark plant after cold rolling may differ significantly from the corresponding behaviour of nominally identical strip steel from the Saldanha plant.
The long-standing question of why this might be the case (a question that has been a cause of concern for customers) has finally been resolved through two research projects conducted within the Department of Materials Science and Metallurgical Engineering.
Although it had long been suspected that the difference between the two steels might be associated with differences in the size and distribution of AlN (Aluminium nitride) precipitates caused by discrepant nitrogen content (with Saldanha originally running at lower nitrogen contents than its counterpart), researchers had not been able to establish a direct link between these variables.
One project therefore focused on the austenite-to-ferrite transformation behaviour of the two sets of steels, while the other investigated the recrystallisation behaviour after cold work.
The results of these projects have proven that the link between recrystallisation behaviour and AlN is a very indirect one, and that the fundamental difference can be traced to the presence or absence of MnS in either steel.
It was shown that the AlN preferentially nucleates heterogeneously on the coarse MnS (if it is present) and thereby becomes ineffective in pinning the dislocations, grain boundaries or moving transformation fronts.
If the sulphur content of the steel is very low (as in the earlier Saldanha steel production) the AlN is forced to nucleate homogeneously within the grains and adopts a very fine size distribution.
Such fine particles are highly effective in pinning dislocations and boundaries, thereby making the steel somewhat difficult to recrystallise after cold work.
Based on the results of these studies, it was possible to identify appropriate solutions for the problem experienced at the Saldanha plant
Contact person: Prof WE Stumpf.
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