Preparation Of High Purity V₂O₅ And Study On Crystalline Mechanism Of Ammonium Vanadate

With the development of science and technology, the large application of vanadium in industry requires vanadium products with much higher purity. It is necessary to study how to remove the impurities in vanadium product. P and Si is the main impurity in vanadium production In this paper, the complete removals of phosphorous and silicon from sodium vanadate solution which is obtained from loaded strip liquor of ion exchange in the extraction of vanadium from stone coal by magnesium salt precipitation was studied. The effects of addtion amount of magnesium salt, pH, temperature and time on the removal of P and Si were investigated, and the mechanism for the removal of P and Si was also proposed. The results showed that the removals of P and Si reached 95% and 96% under weak base condition, respectively, while the recovery of V2O5 reached 94%. The other impurities such as Fe and As were also effectively removed. The optimum conditions of P and Si removal are as follows:12% feed solution of magnesium salt addtion amount at 45℃and pH 9.5 for 40 mins. The ammonium salt was then added into filtrate at 50℃after filtration, the obtained ammonium vanadate was calcined in Muffle furnace at 500℃for 2 hour. The purity of final product V2O5 reached 99.91%.The crystallization is an important step in the process of V2O5 preparation. In order to obtain the V2O5 product with different morphology and high purity, the process of vanadium precipitation by adding ammonium salt was further investigated. The effects of molar ratio of ammonium salt to vanadate, vanadium concentration in loaded strip liquor, pH, stirring intensity, temperature and time on the V precipitation and morphology of ammonium vanadate crystal were studied. The results showed that the optimum conditions of V precipitation were as follows: molar ratio of ammonium salt to vanadate was 1.3, concentration of V 80 g/L at pH 9.5 and 40℃for 30 mins with stirring speed of 300 r/min. The ammonium salt was added at twice. The precipitate was directly filtrated without stewing and was then washed using 2% NH4Cl solution after cooling. The SEM study of ammonium vanadate crystal revealed that the surface of crystal was intact and smooth with rhombic structure and without impurity contamination. After calcination in Muffle furnace at 500℃for 2 h, the purity of obtained V2O5 product reached 99.95% and the SEM analysis showed the product was also with intact and smooth rhombic structure and without impurity contamination.