Precipitation of vanadium from Bayer liquor with lime

Based on the thermodynamic calculation for the precipitation of vanadium from Bayer liquor by lime, experiments were carried out to investigate the influence of temperature and CaO dosage on the vanadium precipitation rate when lime was added into Bayer liquor to precipitate vanadium directly. The results indicate that more than 80% of the vanadium can be precipitated directly from Bayer liquor by lime. Unfortunately, the obtained precipitation residues mainly consist of 3CaO•Al2O3•6H2O with very little vanadium content (V2O5, about 0.45%). An improved process, during which precipitation residues were used cyclically as precipitants for vanadium at high temperature (> 150 °C), was proposed after careful analysis on thermodynamic calculation and former experimental results. The improved process was proven completely feasible by experiments for the precipitation of vanadium from Bayer liquor to prepare vanadium-bearing residues with high vanadium content. With precipitation residues recycled, the V2O5 content increased to almost 3%. The appropriate conditions for the cyclical precipitation of vanadium include the C/A rate 0.4 for the first vanadium precipitation, cycle numbers 4–5, temperature 180 °C–220 °C, reaction time 1 h and stirring speed 200 rpm.