Thermochemical Activation of Carbon Steel EAF and FeCr Slags for Chromium and Vanadium Leaching

This study presents a novel, low-temperature thermochemical activation process for the selective extraction of Cr and V from carbon steel EAF (CH1) and FeCr (CH2) slags at temperatures of up to 600 °C. Of the twelve reagents tested, NaOH was identified as the optimal alkaline agent for Cr activation at 500 °C, achieving extraction yields of 61.6% for CH1 (slag-to-reagent ratio of 12:8 g) and 80.6% for CH2 (ratio of 12:16 g). KOH at 400 °C was the most effective reagent for V extraction, yielding 89.4% for CH1 and 54.5% for CH2. Maximum metal concentrations were achieved after only five minutes of leaching at 60 °C. The process exhibits high selectivity; primary matrix components (Fe, Si, Al, Ca, Mg) either do not leach or only leach in negligible amounts. Iron forms insoluble oxides, and calcium converts into stable calcite, while magnesium is bound in the form of hydrotalcite specifically in the CH2 slag leaching residue. The CaCO₃ content was proven to be a crucial parameter determining the activation efficiency and effective transformation of Fe-Cr-V phases. This procedure enables the recovery of clean Cr and V leachates, while the residual mineral-rich fraction offers potential for various industrial applications in a closed-loop slag recycling process.