Recycling is becoming more and more important due to the increasing scarcity of resources and the resulting increase in the price of raw materials. There is great potential as a future source of raw materials in the slags of steel and smelting works, but also in other branches of industry, which were previously hardly regarded as raw materials. The aim of this thesis is the chemical and mineralogical characterization of different slags of the Voestalpine Stahl Donawitz. The data obtained will then be used as a basis for subsequent work to assess the recyclability of the slag material. The investigations were limited to the slag fractions of pig iron desulphurization (REE), secondary metallurgy (CC) and recycling fraction (B-Fe). The main focus of the investigations was on the largest partial stream of the CC fraction, the ladle slag. For the investigation and characterization of the slags, stockpile samples were taken and 45 samples were scooped directly from the ladle furnace. The slags were then analyzed by X-ray fluorescence analysis (XRF), powder X-ray diffraction (XRD) as well as reflected light and scanning electron microscopy. The XRD spectra were evaluated both qualitatively and quantitatively by Rietveld analysis. As a first group, slagheap samples of the fractions REE, CC and B-Fe were investigated. No phase association systems could be concluded, as the samples have a very wide chemical composition range. The individual samples contain up to ten different phases. The presence of hydrate phases is untypical of slag, but can be explained by the stockpiling. The second slag group analyzed is the ladle slag, which was scooped liquid from the ladle furnace. The 45 samples could be assigned to 12 steel mill brands. The composition of the slag components of the samples was within the 4 phase system Al2O3-SiO2-MgO-CaO. On the basis of the analyses, the slags can be divided into three groups of different phase association. Group 1: C2S-C3A-M-Pleochroite, Group 2: C2S-C3MS2-M-Melilith, Group 3: CMS-C3MS2-M-Melilith, The chemical composition of Melilith varies and is either closer to the chemical composition of Akermanite or Gehlenite.