Implication of hydrolysis on vanadium precipitation with acidic ammonium salt from high concentration of alkaline vanadium solution

摘要

Vanadium precipitation with acidic ammonium salt is widely applied in industrial practice of vanadium pentoxide production. However, the ammonia wastewater produced in the precipitation process and resultant environmental issues have been paid increasing attention. With the intention of reducing wastewater and extra cost, an enhancement in the vanadium content of basic qualified solution is the most directly effective method. Unfortunately, high vanadium concentration brings about a low precipitation rate and a high Na content in ammonium polyvana-date, as a result of hydrolysis existence in the precipitation process. The effect of hydrolytic vanadium reaction on acidic ammonium salt precipitation has rarely been reported. Therefore, the whole precipitation process, including the effect of pH value, reaction temperature and vanadium concentration on precipitation result were clarified by analyzing the thermodynamic form of vanadate radicals in this work. Simultaneously, a study on technological parameters was inquired based on the theoretical analysis. The phase composition and crystal morphology of precipitates were also inspected using XRD and SEM-EDS. The results show the negative reaction of vanadium hydrolysis cannot be eliminated in the process of vanadium precipitation with acidic ammonia salt. When vanadium content is higher than 35 g/L, Na in APV is easy to exceed 0.6. Na mainly precipitates in V_2O_5·H_2O in the formation of amorphous body or chemical absorption. The results in this work provide a fundamental guide for the application of high concentration vanadium precipitation technology.