To overcome the inexpressive recycling rate (<1%) of critical raw materials (CRM) such as Ta from slags originating from the Cu industry, the enrichment of these metals in targeted minerals under specific conditions may facilitate the recycling. Based on that, our study investigated the mineralogy of Ta-rich phases in a synthetic fayalitic slag at different holding times in a specific transformation temperature, which was defined by thermochemical modeling. Laboratory scale samples of fayalitic slags mixed with Ta2O5 were smelted in an electric resistance furnace under argon atmosphere. Subsequently, the crystallization was achieved through cooling at a fixed rate of 25 °C/h to a specific temperature and held for different hold times. The samples were then removed from the furnace into air atmosphere and room temperature. The thermochemical modeling indicates that the oxidation of fayalite generates mainly magnetite (spinel) and silica, but also several other phases, such as pyroxene. The analysis performed on the samples was electron probe microanalysis (EPMA) and X-ray diffractometer (XRD), which showed that as the hold time increased, the individual crystals became larger and were distributed evenly throughout the sample. Moreover, the analyzed spinel phases were not directly associated with Ta-containing solidified phases. Rather, the metal exhibited preferential interaction with Ca-Si phases. In addition, the dissolution of Ta was observed in the last liquid phases, which were mainly Ca-Al-Si oxides. Prolonged hold times do not promote targeted Ta crystals nor control Ta mobility, but concentrate it in specific mineral phases which can allow further segregation.