Influence of manganese on vanadium precipitation and V₂O₅ purity based on different roasting methods of vanadium slag

Manganese is a major impurity in acidic vanadium-bearing leaching solutions, but its effects on vanadium precipitation via hydrolysis and acidic ammonium salts remain unclear. In this study, vanadium-bearing leachates with varying manganese concentrations (VL-cMn) were prepared through calcium, a calcium–manganese composite, and manganese-based roasting of vanadium slag (VS) to investigate the influence of manganese on vanadium precipitation behavior during hydrolysis precipitation (HP) and ammonium salt precipitation (AP), as well as the microscopic characteristics and purity of the resulting V₂O₅ products. The results showed that increasing the pH mitigated the negative effects of Mn on the V precipitation rate during HP. However, as the manganese concentration increased from 5.69 to 15.38 g/L, the V precipitation rate gradually declined at higher temperatures and longer reaction times. The precipitates exhibited increased microstructural density, which might had contributed to the formation of Mn-bearing phases. Additionally, the average grain size of V₂O₅ was reduced and the particles were increasingly agglomerated, leading to a 2.55% decrease in product purity. For AP, as manganese concentration increased, raising the pH counteracted the negative impact of Mn on the V precipitation rate and reduced the required amount of ammonium sulfate. Moreover, Mn was unevenly adsorbed on the surface of the precipitates. Although V₂O₅ grains gradually shrank and became denser, there was no significant effect on the final product purity, which remained above 99.3%. In conclusion, roasting with added manganese salts influenced the hydrolysis of vanadium but had no significant effect on acidic ammonium salt precipitation.