Effects of key impurities (Al, Fe, P, Si and Na) on the precipitation process of vanadium in the novel ultrasound-assisted precipitation system

The effects of Al, Fe, P, Si and Na on the precipitation characteristics of vanadium in the ultrasound precipitation (UP) system were firstly investigated to establish the applicable vanadium-rich solution system and reveal the relevant mechanisms. The experimental results indicate that NaAl8V10O38 center dot 30H(2)O generated at 3.0 g/L Al hinders the reaction between vanadium and NH4+ and hence decreases the precipitation efficiency and purity of the vanadium products. Iron barely affects vanadium precipitation efficiency. Nevertheless, it might integrate into the precipitates by superficial adsorption or formation of an iron-bearing phase at 0.2 g/L and 0.4 g/L, respectively, leading to a significant decrease of the purity of products. Sodium has a negative effect on the purity of products when the concentration exceeds 15 g/L, ascribing to the formation of NaV3O8 and Na2V6O16 center dot 3H(2)O. Phosphorous can unevenly adsorb on the crystals' surface when the concentration exceeds 0.02 g/L, and it would induce the generation of sodium vanadate salts, which further hinders the growth process of the crystals and deteriorates the crystallinity and structure of the precipitates. Silicon has no adverse effects on the precipitation of vanadium at the studied concentration ranges. Herein, the concentration upper limit of Al, Fe, P and Na is confirmed as 0.3 g/L, 0.05 g/L, 0.02 g/L and 15 g/L, respectively. The precipitation rate constant at corresponding upper limit of Al, Fe, P and Na is 0.092 min(-1), 0.118 min(-1), 0.209 min(-1) and 0.433 min(-1), respectively, implying that the magnitude of the negative influence of impurities on vanadium precipitation kinetics decreases in the order Al > Fe > P > Na. The present work may provide theoretical and technical support for the industrial application of the UP technology.