Recovery of vanadium with urea in acidic medium

Classical hydrometallurgy methods such as chemical precipitation, ion exchange, solvent extraction and adsorption have been used to recover vanadium from aqueous solutions, but the last step of these methods involves precipitation with ammonium salts, which are harmful to the environment at high concentration. Therefore, here we tested urea as a new precipitant to replace ammonium salts. We studied the effect of various parameters on the precipitation efficiency of vanadium. Results showed that urea is hydrolyzed to form NH4+ in acidic medium at 90 degrees C. Then, NH4+ reacts with V6O162- and precipitates as (NH4)(2)V6O16. Nearly 95% of the vanadium was precipitated within 120 min in the system containing 2.8 g/L vanadium and n(CON2H4)/n(V) of 0.6. The Avrami model was used to describe crystallization kinetics and analysis of the dimensions of crystal growth. Model results show that the crystalline growth was one-dimensional and that the crystals were shaped in columns. Overall, this study introduced a new way for urea utilization as a new precipitant to recover vanadium.