The sustained release-direct precipitation preparation of vanadium pentoxide for energy utilisation from vanadium solution with high concentration of Fe and Al

Abstract

The direct preparation of energy-grade vanadium pentoxide from vanadium-rich solutions is hindered by the variety and high levels of impurities. To address this issue, this study utilized carbamide as a sustained release-direct precipitant to explore the parameters and mechanisms involved in vanadium precipitation. The findings indicate that with an initial pH of 0, a reaction temperature of 98 °C, a reaction duration of 6 h, and a carbamide addition ratio of 20, the vanadium precipitation efficiency reached 95.84%, and the purity of the V₂O₅ product achieved 99.87%. This method significantly improves the purity of V₂O₅ from the conventional ammonium salt precipitation process, which typically yields around 95%, to over 99%. Analyses of crystal phase, chemical bonding, and thermal decomposition reveal that the vanadium phase transitions from VO²⁺ to (NH₄)_2y-5xV_xO_y, ultimately forming (NH₄)₂V₆O₁₆. The gradual release of the ammonium ion circumvents the issue of local overconcentration. The impurity ions did not significantly adsorb onto the surface of the precipitated crystals within a brief period. Crystals of ammonium polyvanadate can develop in perfect order without coprecipitation. The resulting ammonium polyvanadate exhibits a favourable crystal structure and smooth morphology; the purity of vanadium pentoxide exceeds 99.5%.