An environmentally friendly hydrothermal method of vanadium precipitation with the application of oxalic acid

During the traditional metallurgical process of vanadium (V), an ammonium salt is often employed as the precipitator to form an ammonium vanadate, which converted into V2O5 in the subsequent calcination. Due to the restriction of ammonia emissions by the Chinese government, the vanadium-bearing shale industry in China urgently needs to find out a new environmentally friendly vanadium precipitation method. As the widely used method in the synthesis of VO2, hydrothermal reduction with oxalic acid was firstly introduced into vanadium precipitation in this study. Several factors that affect the vanadium precipitation were studied in the batch tests, such as initial reaction pH, temperature, time, and n(H2C2O4 center dot 2H(2)O)/n(V(V)). A product with 99.53% purity of VO2 (B) and 99.47% extent of vanadium precipitation was obtained under the optimized reaction conditions: initial reaction pH of 0.80, time of 8 h, temperature of 493 K, and n(H2C2O4 center dot 2H(2)O)/n(V(V)) of 1.00. Raman spectroscopy, inductively coupled plasma with optical emission spectrometry (ICP-OES) and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) were also carried out to characterize the product and the results indicated that the product was pure VO2(B) in the form of nanorods. The reaction mechanism of VO2 prepared from stripped vanadium solution is put forward and the transformation of V from stripped vanadium solution to VO2 is proposed as: VO2+ -> VO2(C2O4) -> VOC2O4 -> VO2. Overall, the present hydrothermal method of vanadium precipitation with the application of oxalic acid has the characteristics of environmentally friendly, short process, simple and efficient.