A wide variety of metals of considerable relevance to the European high-tech industry, and therefore also for our society, are supplied by the nonferrous metal industry. As the technologies became rapidly more complex in the last decades, the number and kind of metals and alloys utilized were getting more specialized and unique. With this technological innovation, the demand for minor elements increases steadily. Since their primary production, in most cases, can only be achieved economically as a by-product, it is difficult to respond to peaks in demand for minor elements. This, in turn, underlines the great need for recycling to compensate for these gaps. 
In this context, together with the industry partners of the Christian Doppler Laboratory, methods for determining the distribution of metals in the phases and compounds that occur in industrial intermediates, by-products, and residues are developed and applied, and the possibilities of influencing the behavior in hydro- and pyrometallurgical processes are investigated. This subsequently enables the development of extraction methods for selected elements.
Since residual industrial materials can differ significantly in their behaviour, various innovative processes using chemical and physical properties for separation are used. These include, for example, chlorination of valuables or artificial mineral production by targeted crystallization during the cooling of slags. The paper gives an overview of the activities of the Christian Doppler Laboratory and will then focus on the area of artificial mineral growth to enrich chromium in special spinel phases. 

In consideration of the growing production of stainless steel, which averaged at about 6 %/year between 2012 and 2021 and reached 58.3 Mio t/year in 2021, the accumulation of the corresponding residues such as dust increases as well [1]. During the production of stainless steel via electrical arc furnace (EAF), which is the most commonly applied production route, approximately between 10-20 kg of dust accrue per ton of steel [2]. This dust contains a quite significant amount of Cr and Ni. If no recycling of those dusts is carried out, these metals are lost for further operations and potentially interact in a harmful way with the environment in case of present leachable components, such as Cr^VI+. This would lead to economic loss as well as ecological harm. All of todays in industry applied processes to recover valuable metals from such dusts are of pyrometallurgical nature, which are carbon based and quite energy intensive. 

Hydrometallurgical operations for the recovery of metals from Cr-Ni-rich AOD and EAFD have been examined by Aromaa et all. and Stefanova et all. but with the goal to selectively extract Zn [3, 4]. Therefore, after thoroughly charactering the dust including X‑Ray diffraction (XRD), scanning electron microscope-energy dispersive X‑ray (SEM‑EDX), Elemental analysis with inductively coupled plasma‑optical emission spectroscopy (ICP‑OES) and thermogravimetric analysis (TGA), five different acids (hydrochloric, sulphuric, nitric, vinegar and citric acid) were investigated in their potential to leach Cr and Ni. Out of the five acids used, hydrochloric acid was the most promising candidate to conduct a parameter variation with. In the conducted follow-up experiments, a clear trend of increased extraction rates can be observed for higher temperatures and longer leaching times. To counter specific problems observed in previous experiments, a double walled reaction vessel including a lid with four openings for stirrer, reflux condenser, acid addition and pH‑electrode was used. Through applying these methods, the FeCr₂O₄ and NiFe₂O₄ spinel phases, which contain the metals of interest, were able to be leached in a satisfactory amount. The paper summarizes the results of the characterization in conjunction with the obtained extraction rates and conclusions on the mineralogical phases and their leachabilities under different conditions.