Study On Direct Preparation Of Vanadium Nitrate From Ammonium Metavanadate

Vanadium nitride is a kind of important alloy additive in steelmaking,which can significantly improve the comprehensive performance of steel.80 ~ 90% of vanadium were used in steel industry,and it had the effect on refining grain size and precipitation strengthening.Compared with other vanadium-based alloys,the addition of vanadium nitride in steelmaking can effectively use the strong affinity between vanadium and nitrogen,which not only improves the strength of steel,but also reduces the adding amount of vanadium production costs.China is a magor country for the production and application of the steel,and the demand for vanadium nitride is increasing year by year.At present,the industrial production of vanadium nitride has been widely used by the reduction of vanadium pentoxide,which is a long process with high energy consumption and environmental pollution.Based on thermal decomposition process of NH4VO3(as the precursor of V2O5),direct preparation of vanadium nitrate by NH4VO3 have been studied in this paper.The vanadium nitride was made by one-step carbon thermal reduction technology in the paper,in which NH4VO3 was used as raw material,based on relevant literatures.The effects of pre-reduction temperature,pre-reduction time,carbon ratio,nitriding temperature and nitriding time and nitrogen flow rate on the composition and content of nitrided products were studied.The thermodynamic conditions of the relevant reaction were analyzed.The kinetic mechanism of the main reaction was analyzed combined with thermogravimetric test.The content of nitrogen and vanadium in the nitrided products were determined by chemical method.The carbon content in the nitridedproducts was determined by C/S analyzer.The nitriding products were further characterized by XRD.The thermodynamic analysis show that NH4VO3 can be easily decomposed into V2O5,and the carbon thermal reduction of the decomposition product V2O5 is a stepwise process.V2O5 can be completely reduced to vanadium oxide with high melting point under the melting point temperature of V2O5,and VC is preferentially generated by the four-step reduction reaction.The transition temperature of the reduction reaction is affected by the partial pressure of carbon monoxide,which is not conducive to the reduction reaction.The transition temperature of the nitriding reaction is also affected by the partial pressure of nitrogen and the nitriding reaction can be promoted by increasing the partial pressure of nitrogen.When the temperature was higher than 910?,the vanadium carbide is produced by carbonation reaction and further nitrided under the effect of nitrogen,namely a simultaneous reduction and nitridation.When the temperature was higher than 1272?,vanadium nitride can be transformed into vanadium carbide under the action of excessive carbon.The reaction kinetics during the process was analyzed by thermogravimetric analysis.The results show that the decomposition of NH4VO3 and the pre-reduction of V2O5 mainly emerge in the low temperature stage,and nitrogen was not the reaction gas.While the nitriding process mainly occurs in the high temperature stage.The linearity of the straight line fitted by the first-order reaction kinetic function according to non-isothermal thermal analysis is good and the correlation coefficient is high.The kinetic calculation results of the reaction process show that the activation energy of the reduction reaction is 19.12 KJ/mol and the frequency factor is 1.64×104 at the temperature of 1002~1120?.The activation energy of nitridation reaction is131.19KJ/mol and the frequency factor is 6.26×108 at the temperature of 1310~1420?.The nitridation reaction is a limiting part of one-step preparation of vanadium nitride by carbon thermal reduction of NH4VO3.V2O5 can be completely reduced to low-valence vanadium oxide when the pre-reduction was carried out at 650? for 4h.The nitrogen content of nitrided products increases first and then decreases with the increase of carbon ratio,and the nitrogen content is highest in the theoretical ratio.When the nitriding temperature was higherthan 1300?,the nitrogen contents of the nitriding products all excess 10%.The nitrogen content reaches highest when the temperature was at 1400? and the substance phase is vanadium nitride.The temperature continued to increase,the nitrogen content of nitriding products was stable as a whole.The nitriding effect is the best when preserving at the same temperature for 4h and the optimum nitrogen flow rate for nitridation is 240 ml/min.Therefore,the optimum reaction conditions were determined and then semi-industrial tests were carried out.In this study,the technology on directly preparing vanadium nitride by VH4VO3 was set up.The volume of as-prepared vanadium nitride was contracted and its apparent density reaches 4.75g/cm3,in accordance with the national standard.