With the increasing global demand for raw materials and the consequent depletion of the global natural resource base, the possible utilisation of secondary raw material sources is receiving more attention. Slags are often touted as a raw material type of particular promise. Many slags are currently either landfilled - or alternatively downcycled into low value applications. This is despite the fact that some slags are known to contain elevated concentrations of critical raw materials (CRM). Most studies aimed at recovering CRM from slags have considered them as being a simple bulk material, ignoring the inherently complex and variable phase composition. In the present study, results are presented from a detailed deportment study for vanadium as a CRM in three large bulk samples of basic oxygen furnace slag (BOFS). Complementary analytical methods were used to quantify the abundance and composition of V-containing phases, including scanning electron microscope - energy dispersive X-ray spectroscopy (SEM-EDS)-based automated mineralogy, X- ray fluorescence spectrometry X-ray powder diffraction as well as electron probe microanalysis. The vanadium deportment was quantified using Monte-Carlo simulations of the data obtained from automated mineralogy and electron microprobe analysis. The total V concentrations in the three slag samples range between 1.7 and 2.2 wt per cent V. The most important hosts of vanadium are larnite-, brownmillerite- and portlandite-solid solutions. In two samples Ca carbonates also significantly contribute to the V deportment, while wuestite, lime, and native iron do not have significant V concentrations. a thorough consistency check identifies considerable uncertainties in the density of the V-bearing phases as the most likely reason to explain remaining discrepancies between measured and calculated V contents. Results suggest that enrichment of vanadium by mechanical beneficiation will not be possible. Instead, the slag will either have to be metallurgically treated, either by re-smelting or by (near) complete dissolution/leaching. Both these approaches do not appear economically nor ecologically feasible.