Precipitation of vanadium from leachate solutions by reduction with hydrazine

Vanadium is a 'critical metal' with wide reaching applications. Current methods to extract vanadium from ores and slags rely on generating a solution of pentavalent vanadium ions, which are then precipitated using ammonium salts to form a vanadium-bearing solid. However, this precipitation method generates large volumes of unrecyclable wastewater which must be discharged. Herein, we describe a cleaner method to precipitate vanadium from leachate solutions, by reduction with dilute aqueous solutions of hydrazine. This approach generates a nano-colloidal suspension that can be agglomerated to give precipitation efficiencies of up to 94%, and product purities of up to 99.5%. This is a zero-liquid-discharge method - after reduction, hydrazine is oxidised to volatile by-products which can be removed by simply heating. Therefore, this process outputs only solid material, whilst retaining all liquids within a closed-loop process.