Zinc is one of the most important metals in human society. Especially its application as corrosion protection of steel makes it an omnipresent element in daily life showing an increasing demand in future. In addition to corrosion protection, other important applications of zinc can be found in the rubber, ceramics, and fertilizer industry, and in different casting products, pharmaceuticals and nutritional supplements.
The European zinc demand ranges from 2.4 to 2.7 Mio. t/a. Unfortunately, Europe is weak in primary zinc resources. Only a small part of approximately 27 % can be supplied by European mines. As a result, the dependency on imports from Asia and South America is quite high. Furthermore, zinc concentrates show strongly decreasing zinc values with a rising iron contamination. This contaminant leads to problems as huge amounts of residues are generated which are difficult to dispose of.
One way out of this situation is to utilise zinc from end-of-life products. Nevertheless, the remelting of such scraps only contributes to about 6 %. However, due to its volatile character, zinc is often found as oxide in the dust of steel recycling facilities. Furthermore, slags from the lead industry also contain interesting amounts of zinc. Such by-products have the potential to contribute much more to the European demand. Taking high zinc containing dust from the steel industry and slags from the lead industry into account, about 20 % of the demand could easily be covered. Unfortunately, present technologies show essential disadvantages which start to become a big obstacle for future metal recovery efforts, such as:
- Only zinc is recovered, even though further metals like iron and lead are available.
- Huge amounts of new residues, up to 80 % of the input material, are generated.
- Currently applied processes are based on reduction with fossil carbon carriers resulting in a significant carbon footprint.
One option to overcome the CO2-emissions problem is the utilization of hydrogen. However, for the moment hydrogen is still quite expensive. Moreover, there are currently no technologies available that allow the use of hydrogen. An alternative is the implementation of bio-coke which shows a similar behaviour to currently used fossil carbon carriers in many aspects and would allow an application in existing recycling technologies. The influence on the process caused by the much higher reactivity and different impurities must be studied, and whether and how existing treatment procedures have to be optimized needs to be defined. With this in mind, process optimization has to aim for the option of slag conditioning that allows for utilization in the building and construction industry, achieving a zero-waste concept.
Considering the current state of the art, for both aims – CO2-neutrality and zero-waste – short- to mid-term and long-term solutions are investigated in this project. Based on long-term experience in research and development in the field of zinc recycling possible solutions will be defined, modeled and tested on laboratory and pilot scale. Discussions with the relevant industry sectors which are part of the consortium should guarantee the applicability of the concepts developed and form the basis for pilot scale.
Converting zinc recycling processes towards CO2 neutrality and zero-waste hugely influences the applied energy carriers and their demand. Novel recycling processes also allow new heat integration concepts for enhancing energy efficiency by using waste heat. Some of them also enable on-site hydrogen production and demand-side management. This may help couple the processes closer to electricity markets and to use time frames with low electricity prices. In the general approach, those energy-related topics are addressed at an early stage since, in this phase of design, they can be solved more easily and more comprehensively compared to energy system optimizations with already given process chains.