Preparation And Mechanism Of Vanadium Nitride Via Precursor Based On Vanadium-rich Solution During Vanadium Extraction From Black Shale

Vanadium nitride?VN?,the largest vanadium alloy additive in China,is widely used in high strength low alloy steel.The method of carbothermal reduction–nitridation is the only way to produce VN in industrial production,which take V₂O₅,V₂O₃ and other vanadium products as the vanadium source.However,the cost remains high due to the high reaction temperature and long reaction period.In China,most of the vanadium resources exist in the form of black shale,so the utilization and exploitation of black shale to obtain vanadium products has good prospects.Vanadium-rich solution,obtained in the process of vanadium extraction from black shale,can be used as vanadium source for the preparation of VN due to high concentration of vanadium.The extraction and nitriding of vanadium are combined for the purpose of shortening the process and promoting the preparation of VN.Vanadium-rich solution,simulated in the process of vanadium extraction from black shale,was the vanadium source to synthesize VN.Carbon black?C?was added to the vanadium-rich solution,the precursor formed gradually during the vanadium precipitation,then the precursor was reduced and nitrided to yield VN.The optimal conditions on the preparation of VN were confirmed,which was verified with the actual vanadium-rich solution.By analyzing the phase and microstructure of the precursor,investigating phase evolution and thermodynamics during the reaction process,the phase evolution of vanadium from the precursor to VN was acquired,which revealed the mechanism of advantages of precursor in the preparation of VN.The dynamical behavior and reaction mechanism of the process were also investigated in this study.VN product,with an N and V content of 16.38% and 79.25% respectively,was prepared under the optimal conditions: the C/V mass ratio of 0.55,vanadium precipitation p H of 1.8,briquetting pressure of 14 MPa,reduction and nitridation at 1150 °C for 1 h,N2 flow velocity of 300 m L/min.The apparent density of the product is 3.13 g/cm3,which showed that the VN16 in GB/T 20567-2006 was successfully obtained.Moreover,this process is feasible and effective for the actual vanadium-rich solution obtained during vanadium extraction from black shale.The vanadium-coated carbon structure of precursor enlarged the contact area between reactants significantly and provided a more homogeneous chemical composition,which significantly reduced the reaction temperature and shortened the reaction time.The phase evolution of vanadium was as follows:?NH₄?2V6O16·1.5H2 O ? V₂O₅ ? V₃O₇ ?V6O13 ? VO₂ ? V4O7 ? V₂O₃ ??VO ??VC ? VN.The pentavalent vanadium can be reduced to V6O13 by NH3,obtained by the decomposition of ammonium polyvanadate?APV?,indicating that the calcination of APV and pre-reduction of V₂O₅ in the traditional method can be omitted,meanwhile the emission of NH3 can be reduced.The transformation of V₂O₃ to VN at high temperature is the key to prepare VN.The reduction,carbonization and nitriding of V₂O₃ occurred simultaneously and promoted each other.The dynamical behavior of the complex reaction during the transformation of V₂O₃ to VN at 900-1200 °C was investigated by non-isothermal thermogravimetry.The restriction is third-order chemical reaction,reaction kinetic mechanism function is F3.The activation energy is 291.6152 k J/mol and the frequency factor is 3.9609×10¹³.