Faculty of Engineering, Built Environment and Information Technology
School of Engineering
Department of Materials Science and Metallurgical Engineering
Selected Highlights from Research Findings
Material footprints, which can be defined as the quantity (mass) of material used for an application, such as the total mass of concrete and brick in a house, together with the carbon footprint, form components of the ecological footprint. The material footprint emphasises material resources, whereas the carbon footprint focuses on energy consumption. Use of the material footprint helps decision-making when resource conservation is desirable, but should not be viewed in isolation. Material footprint calculations have been carried out for some illustrative examples such as personal computer equipment and home appliances. While the material footprint compares resource usage among various types of equipment as an aid in determining environmental impact, it does not indicate what quantities of material are being used or recycled. It is essentially a per unit approach. In order to obtain a more holistic perspective involving quantities of materials, material flow analysis is generally used. From such an analysis, it is possible to obtain a better understanding of how materials flow and reside in the market. That again makes it possible to determine where there are bottlenecks in the flow, and also whether recycling is financially feasible. Treatment of secondary materials can be complex and is often purpose designed. However, in general, it seems that physical separation methods should preferably be used to their fullest extent, as their environmental impact is generally lower than chemical separation processes. Clean metallic fractions could be suitable feeds to pyrometallurgical or hydrometallurgical processing. Mixed materials are probably best treated by hydrometallurgical techniques. For local processors, the cost of establishing refineries to treat secondary materials only is probably prohibitive. With an extensive South African industry dealing with primary feed materials, it would seem advantageous to process suitably cleaned secondary materials together with the primary feed materials. For instance, a fairly clean copper fraction could probably be accommodated in the anode casting step at the Palabora Mining Company. Clean zinc metal or oxide could possibly be used by Zincor instead of calcine as neutralising material. Precious metal fractions should be accommodated at the Rand Refinery and Platinum Group Metals (PGM) refineries. Platinum and palladium are used in catalytic converters and such fractions might, with suitable alloy adjustment, be suitable for use in this application without further refining and separation. E-waste has, over the last number of years, received greater attention and several recyclers are dealing with this material mainly by size reduction and metal fraction separation. Volumes are still small and the cleaned metal fractions are generally exported for refining. The associated plastics generally contain brominated flame retardants (BFRs), which makes them unacceptable for normal plastic recycling. As a result, they are exported to China or dumped into a landfill. Local companies have developed uses for these plastics. More attention should be given locally to these secondary feed materials. If present, primary producers could accommodate cleaned metallic fractions. Environmentally certified processors could probably import e-waste to increase volumes. This should be beneficial in terms of capital utilisation, work creation and to the economy, as well as to the environment, if the energy consumption is not weighed too heavily
Contact person: Dr DR Groot.
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