A New Process To Prepare Vanadium Oxides By Hydrogen Reduction Of Na VO₃

Vanadium is an important strategic resource, mainly used in metallurgy industry. Many vanadium products were widely used in all of kind industries. To avoid the generation of high concentration ammonia nitrogen wasterwater containing vanadium and chromium in the existing industrial vanadium precipitation process of vanadium metallurgy, the key material obtained before the industrial vanadium precipitation process, NaVO3, was chosed as the raw material and a cleaner process for the production of vanadium oxide by hydrogen reduction was proposed. Consequently, the vanadium precipitation step in the traditional process was replaced, and no high concentration ammonia nitrogen wasterwater would be discharged.The valence, strucuture and chemical composition changes of reduction products during hydrogen reduction of NaVO3 were investigated. The removal of Na and valence change of vanadium in the hydrolysis process was studied. The reaction process in the reduction of NaVO3 to NaVO2 was elucidated. The strengthening hydrolysis mechanism in the oxidation hydrolysis or mechanical activation-pressurized hydrolysis were revealed, V2O5 and V2O3 were prepared by this cleaner process, and NaOH solution containing vanadium could be recycled.The following innovative progresses were achieved in this work:1) NaVO2 was prepared using the method of hydrogen reduction. The effect of several parameters, such as reaction temperature(450~700℃), time(3~4 h) and material thickness(1.5~2 cm), on the conversion rate and the phase of product was investigated. The results show that the reduction of NaVO3 hardly occur before 400℃, whereas the NaVO3 is gradually reduced at the temperature range 450 to 700℃. Product with a single phase of NaVO2 were obtained when NaVO3 was reduced at 700℃ for 3 h with the material thickness of 1.5 cm.2) The hydrolysis experments of Na VO2 were carried out using the reduction product obtained under the optimal conditions. The effect of hydrolysis temperature, time and liquid-solid ratio on the removing of sodium during the hydrolysis was studied. It turned out that the removal rate of sodium can reach 98% with the relative conditions that the temperature is 200℃, reaction time is 3 h and the liquid-solid ratio is 13:1. The intermediate contains V2O5, V2O3 and some kinds of vanadium acid. The by-product of NaOH solution can be recycled to the water leaching process.3) The preparation of vanadium oxides from the intermediate was also investigated using the method of calcination. The calcination temperature, time and atmosphere were the main factors which were examined in the experiments. It was found that regularly layered V2O5 with a granular size less than 0.1 μm was obtained by calcining the intermediate product in air at 550℃ for 3 h. By contrast, regularly flaked V2O3 with an average size of 70 μm was obtained in hydrogen at 550℃ for 3 h. And yet, when the intermediates were calcined with oxalic acid in nitrogen under the same conditions, regularly spherical V2O3 with an average size of 10 μm was obtained.