Extracting Vanadium From Vanadium Slag With High-calcium Content By Roasting And Soda Leaching

Vanadium is an important strategic material that is widely used in many fields such as steel industry, aerospace industry and chemical industry, ect. Leaching vanadium from titaniferous magnetite by the technological process: reduced in blast furnace-oxidized in LD converter-roasting and leaching the vanadium slag. For recovery of vanadium from vanadium titanium magnetite, the blast furnace reduction and converter oxidizing technology is used in Pan-Xi area. Traditional, calcium compounds cannot be used in vanadium extraction processing due to the limitation of sodium roasting technology, which results in unsatisfied dephosphorization for vanadium-containing hot metal in converter and thus increasing the dephosphorization burden for subsequent steelmaking. The calcium roasting technology is an alternative for vanadium extraction and allows adding lime into vanadium slag in converter. In this study, leaching vanadium from the vanadium slag that derives from adding CaO into the converter vanadium recover by direct roasting and soda leaching. This could let most vanadium and less phosphorus get into the solution and could promote the industry practice of adding CaO into the converter vanadium recover.The direct roasting process of vanadium slag was investigated. The Phase transition, optimal roasting condition and the kinetics of vanadium slag were studied. The results show that ①The major phase in the slag are iron-vanadium spinel, olivine phase, pyroxene phase and Fe3O4 and vanadium mainly exists in iron-vanadium spinel. After roasting, the main phase were Fe2O3 and Fe2TiO5 and little Ca(VO3)2, CaV2O7 was found. The morphology of vanadium slag is almost invariant when temperature rises 300 ℃ from 600 ℃.When temperature reaches above 800 ℃,the vanadium-rich phases could be observed. But when temperature reaches above 1000 ℃,the vanadium slag sintered. ② Roasting temperature and time have a significant effect on leaching rate of vanadium. The optimal roasting condition is 950 ℃ and 2.5 h. When temperature is too low, the vanadium slag cannot be oxidized. Otherwise, the vanadium slag sintered. And the roasting time has the similar effect. ③Oxidation process of vanadium slag is gas-solid reaction and could be described by shrinking core model. The oxidation rate is fast in the 0-30 min and slows down in the 30-90 min. In the initial stage(0-30 min), the oxidation was controlled by chemical reaction mechanics and the apparent activation energy is 59.53 kJ/mol. And later stage(30-90 min) was controlled by mixing diffusion, the apparent activation energy is18.96 k J/mol.The process of roasted slag leached by soda was investigated. The optimum leaching condition, phase transition, leaching of phosphorus and leaching kinetics were studied. The results show that ①The roasted slag which roasted at 950 ℃ for 2.5 h is leached by 160 g/L Na2CO3 for 2 h at 95 ℃ with the liquid to solid ratio is 10:1 m L/g, the leaching rate of vanadium could reach up 94.13%, while the phosphorus is 10.41%. ②According to the SEM、XRD and XRF analysis, most of vanadium gets into the solution and Ca CO3、Phosphorus get into the residue. ③When temperature rises 300 ℃ from 600 ℃, the leaching rate of phosphorus has no obvious change. When temperature rises 600 ℃ from 1000 ℃, the leaching rate of phosphorus increased. At 1000 ℃, the leaching rate of phosphorus is 10.23%. ④Leaching process could be described shrinking core model. 0-30 min, the leaching rate of vanadium explode and the process is controlled by reaction mechanics, the apparent activation energy is 67.74 k J/mol; 30-120 min, the leaching rate of vanadium increases slowly and the process is controlled by internal diffusion, the apparent activation energy is 8.58 k J/mol.