Study On Preparation Of High Purity V₂O₅

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 were the main impurities affecting the quality of refined vanadium in the process of vanadium extraction from vanadium slag. The aluminum salt precipitation method for complete removing phosphorous and silicon from sodium vanadate solution which was obtained from vanadium slag treated with the process of sodium roasting-water leaching by was proposed in this paper. The effects of various factors in the process of vanadium precipitation and APV washing on the vanadium precipitation rate and quality of APV were investigated, and then the high purity V2O5was obtained.The effects of addition amount of aluminum salt, pH, temperature, reacting time and standing time on the removal of P and Si were investigated, and the mechanism for the removals of P and Si was also proposed. The results showed that the removals of P and Si reached98%and99%under weak base condition, respectively, while the recovery of V2O5reached98%. The optimum conditions of P and Si removal were as follows:volume ratio for20%aluminum salt solution and the liquid was0.12:1; reacting temperature was85℃; pH was10.0; reacting time was15minutes and standing time was60-70min.As addition amount of aluminum salt was in excess in the process of P and Si removal, aluminum remaining in the solution would affect the quality of V2O5. It is necessary to remove the aluminum remaining before precipitating vanadium. The optimum conditions of Al removal were as follows:pH was8.0～8.5; reacting temperature was30℃; reaction time was10minutes and standing time was20～30minutes. Under these conditions, the removals of Al reached98%, while the recovery of V2O5reached98%.The crystallization is an important step in the preparations of V2O5. In order to obtain high purity V2O5, the process of vanadium precipitation by adding ammonium salt was further investigated. The effects of molar ratio of ammonium salt to vanadate, pH, stirring intensity, temperature and time on the vanadium precipitation, morphology of ammonium vanadate crystal and temperature for adding acid and ammonium were studied. The result showed that the optimum conditions of vanadium precipitation were as follows:(NH4)2SO4was the precipitating agent; molar ratio of ammonium salt to vanadate was1.3; adding acid and ammonium was at room temperature; pH for vanadium precipitation was2.0-2.5; reacting temperature was95℃; reacting time was60minutes; stirring speed was300r/min.It is effective to remove Na and K from APV by washing. The results showed that the optimum conditions for washing APV were as follows:washing water was1%(NH4)2SO4; solution liquid to solid ratio was40:1and washing time was40-50minutes. After calcined at550℃for2h in a Muffle furnace, the final product of V2O5with a purity more than99.8%.