Germany has a long history in metal ore mining stretching over a period of more than 1000 years. Both small and large heaps or dumps remain in the mining districts typically without any safety measures (coverage, monitoring etc.). Often these sites are still a considerable point source for pollutants like metals, metalloids or processing chemicals. However, extraction technologies have been much less effective in the past and for certain elements (e.g. Ge) no technical application has been known. As such, mine waste including historic waste or ore dumps and tailings may represent a considerable and easily extractable future resource especially for technology critical elements.

We investigate the mineralogy, geochemistry and leaching behaviour of different types of mine residues in former mining districts of the Black Forest, Wiesloch and the Donnersberg area. With respect to the critical raw materials Ge, Sb, barite and fluorite, several of the investigated mine waste seem to be of potential economic interest. But elements like Pb, Zn (both in the wt% range) or Ag (>100 mg/kg) are also promising with regard to reprocessing in some of the investigated districts. From an environmental point of view, Pb, Zn, As, Cd, Sb und Tl are of concern regarding their concentration and leachability. Both, the content and potential mobility largely depend on the ore type, the period of extraction and the processing technique applied. We think that extracting raw materials from mine residues has the advantage of gaining metals locally and giving back space to nature and society at the same time.

Due to the Green Deal proposed by the European Union, several industry sectors in Europe are forced to change the production techniques towards a zero-carbon dioxide emission until 2050. For the steel industry the substitution of fossil fuel, used in the blast furnace (BF), by hydrogen as reduction agent relates to the introduction of new technologies and aggregates. Nowadays, only a small amount of shaft furnaces using natural gas for reduction of iron ores to produce direct reduced iron (DRI). However, this combination is one of the favoured future hydrogen operated routes of alternative steel making in the European Union. The crude steel is, thereby, produced from solid DRI together with scrap molten within the electric arc furnace (EAF). Thus, the minor and trace element composition of the produced EAF slags is directly inherited from the input materials because no density driven phases separation takes place in the DRI which is one major difference to the traditional BF route.

Here we present the results of mineralogical, chemical as well as construction technological investigations carried out on one exemplary slag from the EAF route were app. 2/3 of the input material was sponge iron. The main emphasis of the presented study lies on the ongoing applicability of the EAF slags produced in the future as secondary product in the context of steel industry feature the planned reduction of carbon dioxide emissions.

Basic oxygen furnace slag (BOFS) is a by-product of steelmaking of which about 10.4 Mt are produced annually in the EU. BOFS is mostly used in road construction, earthwork and hydraulic engineering. However, in this use, the iron bound in BOFS is lost and the opportunity to produce higher value products from BOFS is forgone.

In recent decades, many researchers have investigated the production of both Portland cement clinker and crude iron from BOFS via a thermochemical reductive treatment. The reductive treatment of liquid BOFS causes a reduction of iron oxides to metallic iron, which separates from the mineral phase due to its higher density and can be recovered. An advantage of this process is that simultaneously the chemical composition of the reduced BOFS is adapted to that of Portland cement clinker and the hydraulic reactive mineral alite (Ca₃SiO₅) is formed.

In this study, German BOFS was reduced in a small-scale electric arc furnace and a low-iron mineral product rich in alite was produced. Despite a chemical and mineralogical composition similar to that of Portland cement clinker, the reduced BOFS produced less heat of hydration, and its reaction was delayed compared to Portland cement. However, adding gypsum accelerated the hydration rate of the reduced BOFS.

Further research to improve the hydraulic properties of the reduced BOFS is essential. If successful, the production of a hydraulic material and crude iron from BOFS could have economic and ecological benefits for both the cement and steel industry.

In the processing of construction and demolition waste (CDW), the sorting of the delivered mixtures is one of the decisive process steps in order to produce pure recyclates, which can be used, for example, as a cement substitute or as a raw material component for the brick production. A previously unused method for the separation of fine brick particles as sand utilises rare-earth magnets. This method is based on differences in magnetic susceptibility, which have been confirmed by measurements on bricks and concretes. Sorting tests carried out using a roll magnetic separator with a field strength of 1,4 Tesla at a belt thickness of 0,7 mm confirmed the separability of brick-concrete-mixtures and provided insights into the most important influencing variables. In addition to manual sorting the quantification of the contents of concrete or brick in the magnetic and non-magnetic fractions was determined with laser-induced breakdown spectroscopy (LIBS) and artificial intelligence-based optical quality assurance. Thus, in addition to the proof of seperability, a first step to faster ways for quality control has been accomplished.