铬酸钠碱性液中加石灰除钒

Vanadate removal from alkaline sodium chromate solution by adding lime

通过计算反应Gibbs自由能和平衡溶解度对铬酸钠碱性液添加石灰除钒过程进行理论分析，结合红外光谱研究了含钒溶液的结构变化，研究添加石灰除钒时各因素的影响规律。结果表明：在298～373K的范围内，体系中各离子与氧化钙生成相应钙盐的反应自由能绝对值由大到小的顺序为VO3-、C032-、SO42-、VO43-、Cr042-；同时，各钙盐间可能存在相互转化，溶液中CO32-能分解CaCrO4和Ca3（vO4）2等钙盐，VO43-能分解CaCrO4。除钒过程中除生成Ca3（vO4）2和Ca2V2O7外，还能生成CaCO3、CaCrO4、CaSO4·nH2O等化合物，这是由于石灰加入量过多所致。溶液结构分析结果表明：随着pH值从13降到9左右，钒酸根由V043-转化成V043-和V2074-共存的结构。除钒实验结果表明：提高溶液pH值、增大n（CaO）／n（V205）或加入高活性石灰乳均可提高除钒率，而溶液中C032-的存在明显降低除钒率；加入理论用量3倍的石灰，溶液pH值降至10左右时，除钒率可达到85％，相对于工业除钒过程钒渣量减少88％左右。

The removal of vanadium from the alkaline sodium chromate solution with addition of lime was invesUgatea based on the calculation of reaction Gibbs free energy and equilibrium solubility, and the removal rule of vanadate, as well as the structure of vanadate, was also studied by experiments. The thermodynamic calculation indicates that VO3-, CO32-, SO42- , VO43- and CrO42- can sequentially be precipitated by formation of compound containing calcium at 298-373 K. Meanwhile, the mutual transformation occurs between calcium salts. Ca3（VO4）2 and CaCrO4 can react with CO32-, and CaCrO4 can convert to Ca3（VO4）2 in the existence of VO43-. In addition, the formation of CaCO3, CaCrO4, CaSOa·nH2O as well as Ca3（VO4）2, Ca2V207 may account for the excess lime in the removal of vanadium. The structural studies with IR spectra on the pure vanadate solution indicate that some VO43- convert to V2O74- at pH decreasing from about 13 to 9. Experiment results show that increasing the solution pH value and the n（CaO）/n（V205） or adding active lime slurry can improve the removal rate of vanadium, but the presence of CO32 is unfavorable to the vanadate removal. The vanadate removal rate can reach 85% and the vanadium residue can be reduced by 88% with 3 times the amount of the theoretical lime required at pH of 10.