## 4 Conclusions  
The conducted experiments presented in this study support the hypothesis that the release of Cr and especially V can be minimized by decreasing the FeO/SiO\({}_{2}\) ratio in EAF slags. In contrast to the original sample, the leached V concentrations of the samples modified with quartz sand were 10 to 100 times below the limit value for the use of recycling building materials in Austria. Although the original samples already showed leachate concentrations of Cr below the limit values in Austria, Cr leaching was reduced even further in some samples, which is promising for possibly stricter limit values in future. Furthermore, the experiments provided information on the influence of the chemical composition of the melt and the cooling rate on spinel formation and the associated Cr leaching. By adding quartz sand to the molten slag, the wuestite formation was suppressed and the formation of spinel, which is characterized by a lower solubility, fostered. Additionally, a transformation from highly soluble larnite to less soluble calcium silicate phases was achieved. Both effects led to a decrease in V and Cr leaching at natural pH compared to the original samples in the laboratory experiments. Investigation of the pH-dependent leaching behavior of the samples derived from pilot scale experiments demonstrated that the release of V was minimized over a pH range from 8 to 12. The performed FactSageTM calculations were in good agreement with the obtained experimental data and served as a basis for the melting experiments. The described up scaling from the laboratory scale to the pilot plant scale was also successful. However, since the presented results showed preliminary results on two EAF slags only, the experiments need to be repeated for further up scaling with a statistically more significant number of samples. Further research will also consider how the economic and ecologic feasibility can be improved by reducing the amount of quartz sand or replacing it with alternative materials as the source of SiO\({}_{2}\) (e.g., residuals from the recycling of building materials). The following are available online at [[http://www.mdpi.com/2076-3417/10/7/2549/s1](http://www.mdpi.com/2076-3417/10/7/2549/s1)]([http://www.mdpi.com/2076-3417/10/7/2549/s1](http://www.mdpi.com/2076-3417/10/7/2549/s1)). Table S1: Input data and selected base phases with end members for the performed FactSageTM calculations; Tables S2-S22: Results of the performed chemical mineral EMPA analyses; Table S23: Chemical composition of original samples A, B and C; Figure S1: BSE images and element mappings of samples derived from the laboratory experiments; Figure S2: XRD patterns of all described samples; Figure S3: BSE image and element mapping of sample BC3; Figure S4: BSE images of MgO inclusions and EDS analyses for sample BC1. Conceptualization, S.N., D.A., P.D., B.A., P.P., K.P.S., J.S., J.G.R., R.P., and D.V. ; Methodology, S.N., D.A., P.D., B.A., P.P., K.P.S., J.S., J.G.R., R.P., and D.V. ; Software, S.N., P.P., and J.S. ; Investigation, S.N., D.A., P.D., B.A., P.D., B.A., P.P., J.S., and J.G.R. ; Writing--original draft preparation, S.N., Writing--review and editing, S.N., D.A., P.D., B.A., P.P., K.P.S., J.S., J.G.R., R.P., and D.V. ; Visualization, S.N. and K.P.S. ; Supervision, S.N., J.G.R., R.P., and D.V. ; Project administration, S.N. and D.V. ; Funding acquisition, R.P. and D.V. All authors have read and agreed to the published version of the manuscript. This research was funded by the Austrian Research Promotion Agency (FFG) (grant number 851210, program \"Bridge Early Stage\", project MiLeSlag (Mineralogy and Leachability of Steel Slags)). The authors thank all participating project partners, Chair of Resource Mineralogy, Chair of Ferrous Metallurgy, Federal Institute for Materials Research and Testing, FEB Building Materials Institute, ECN part of TNO, Max Aicher Umwelt GmbH, PORR Umweltechnik GmbH, Scholz Austria GmbH and Stahl- und Walzwerk Marienhatte GmbH for their contributions throughout the project.