Selective nitridation-corrosion process to recover vanadium, titanium, chromium, and iron from vanadium slag

Vanadium slag (V-slag) is an important secondary V source, but other valuable elements are discarded in the tailings in industry. Herein, a green nitridation-corrosion process is proposed for the comprehensive recovery of valuable elements (V, Ti, Cr, Fe) from V-slag without producing hazardous waste. Thermodynamic results indicate that ammonia gas (NH₃) can selectively reduce Fe and nitride V, Cr, and Ti. The main phase composition of the nitrided V-slag included metallic Fe, nitrides, and diopside under optimal conditions, and their relative contents were 42.5, 26.2, and 31.3%, respectively, after roasting at 1000 °C for 6 h. The effects of the main parameters on corrosion test were investigated, and the highest weight-gain ratio attained was 19.6%. FeOOH crystallizes on the surface of the nitrided V-slag due to the oxidization of metallic Fe. The phase evolution during the entire process is spinel/olivine/diopside → Fe/nitrides/diopside → FeOOH/nitrides/diopside. Owing to finer particle sizes, most FeOOH is separated by wet sieving (<1400 mesh). The purity of the enriched nitrides attained was 43% after pickling to remove excess Fe. The total recovery rates of Fe, V, Ti, Cr were 87.76%, 95.92%, 92.92%, 92.11%, respectively. This paper provides a sustainable strategy for the comprehensive utilization of V-slag, and guides the cleaner treatment of other similar minerals.