In industrialized countries, the recycling of different materials has become a focal point in industry and science. Nowadays, the field of metallurgy is characterized by a continuous increase in metal demand and a decrease in available primary resources. In addition to this, due to stricter environmental legislation, waste dumping is being restricted; however, the recycling of these residues, and therefore the recovery of the metals, will make these processes essential in the near future. Thus, nowadays, beside scraps, metal bearing slags, dusts and sludges are considered secondary raw materials, and not simple waste.
Nevertheless, most of the existing and upcoming recycling processes are energy-intensive and require high amounts of reducing agents. Both requirements are mostly covered by the use of fossil carbon and electrical energy leading to high CO2 emissions and elevated energy costs. These reasons are a serious drawback for the implementation of the above-mentioned recycling processes. Especially heavy metal containing wastes including zinc, lead, copper and iron are characterized by processes based on carbothermal reduction at high temperatures.
Therefore, the main points in the research of potential complex materials recycling can be summarized as follows: A primary objective is to investigate the potential of biomass (or biomass derived products) as a substitute for fossil carbon used as a reducing agent. Although these materials may act as an energy carrier, the focus lies on their behavior as reducing agents, which is most important for the metallurgical process itself.
The detailed characterization of typical metal-containing wastes concerning morphology and phase distribution is another main goal prior to the reduction and melting behavior study. This builds the base for the estimation of a possible simultaneous recovery of valuable metals from the residue. Furthermore, this study can lead to the development of a more effective process from the energy point of view, as well. Together with the characterization, the effect of problematical impurities of the secondary raw materials such as halogens, arsenic, cadmium and their behavior during the recycling process should be investigated. The presence of these impurities may interfere in the upgrade of product qualities. Due to the fact that the products of such processes are still used as a feed for primary metallurgy, again the whole amount of energy for primary winning beside that of the preceding recycling process is consumed. Performing a selective separation of impurities, an upgrade of the products should be possible, which enables their direct use in several technical applications. This leads to an explicit higher value as well as a high potential for energy conservation.
A superior task is the modeling and balancing of the concerned metallurgical processes. On the one hand, it is essential to locate the potential for an optimization regarding the above-described aims, and on the other hand, it allows considerations on how the generated knowledge could be successfully implemented.
The investigated residues originate from metallurgical processes and can be summarized as follows: