Residual Vanadium Mechanism Of Extracted Vanadium Tailings By Calcified Roasting And Their Vanadium Re-extraction Process

Vanadium tailings,as a by-product of vanadium extraction from vanadium slag after many times of leaching,have a huge output each year,not only occupying a huge area,but also containing a large number of metal ions in the tailings.If it is not dealt with effectively,the pollution of the environment is immeasurable,and it is also a waste of resources for today's increasingly scarce resources.Therefore,it is necessary to comprehensively utilize vanadium tailings and recover metal elements.In this paper,the tailings from calcified roasting and acid leaching of Panzhihua Iron and Steel Company were used as raw materials,and some vanadium was found to exist in the tailings by XRF,XRD and SEM,and in the form of high-valence vanadium and low-valence vanadium.Based on the method of sub-molten salt leaching of vanadium tailings after sodium roasting in Chengde Steel,the method of normal pressure alkaline leaching is proposed to leach vanadium tailings after calcified roasting in Panzhihua Iron and Steel Company in order to achieve the purpose of vanadium extraction.Firstly,the chemical composition,phase composition and microstructure of vanadium tailings are analyzed to explain the mechanism of vanadium residues.Then,the effects of leaching temperature,alkali concentration,leaching time,stirring rate and solid-liquid ratio on vanadium leaching rate were studied scientifically through compound experiment,orthogonal experiment and single factor experiment under normal pressure,and the optimal leaching conditions for vanadium leaching from vanadium tailings under normal pressure were obtained.Finally,the kinetics experiment and the phase and microstructure study of leaching residue were carried out to analyze the mechanism of vanadium extraction from calcified roasted vanadium tailings by alkaline leaching.The main conclusions and results are as follows:(1)The vanadium content in vanadium tailings is about w[V]=3.8%,and the main phases of vanadium tailings are R₂O₃ phase,titanite Fe₂TiO₅ phase,ferromagnetic phase Fe₃O₄,CaSO₄·2H₂O phase,silicate phase Ca₂SiO₄,Ca₃Fe₂(SiO₄)₃,SiO₂ phase,and vanadiumcontaining phases CaV₂O₅ and FeV₂O₄;(2)The main reasons for vanadium residue in vanadium tailings include incomplete oxidation of vanadium spinel and formation of intermediate transition phase,solid dissolution of vanadium in hematite phase and titanite phase,influence of silicate on oxidation degree of spinel,interaction with vanadium and competition for calcium source,formation of vanadium bronze,different optimal acid-soluble pH value of calcium vanadate and obstruction of vanadium liquid filtration by a large number of CaSO₄ particles.(3)High valence vanadium can react with NaOH to generate various kinds of high valence sodium vanadate;Low valence vanadium is not completely oxidized in NaOH-H₂O-O₂ system to form various high valence sodium vanadate and Fe₃O₄,and is completely oxidized to form various high valence sodium vanadate and Fe₂O₃.SiO₂ and silicate can react with NaOH to form soluble sodium silicate and other products.(4)Under the conditions of leaching time 2 h,stirring rate 520 r/min and liquid-solid ratio 3:1,the composite experiment of leaching temperature and alkali concentration showed that the leaching temperature of 200? and 80%NaOH were the best leaching conditions.The orthogonal test of vanadium tailings leaching process was carried out at 200? and 80%NaOH concentration.The results showed that the main factors affecting vanadium leaching rate were leaching time>stirring rate>liquid-solid ratio.The optimum leaching conditions were as follows:leaching temperature 200?,NaOH concentration 80%,leaching time 3 h,stirring rate 780 r/min,liquid-solid ratio 5:1,and leaching rate 81.98%under these conditions.(5)The main phases of vanadium leaching residue are solid solution R₂O₃ phase,irontitanium phase Fe₂TiO₅,Fe₃O₄ phase,SiO₂ phase and CaSO₄ phase,without obvious vanadate phase,the leaching of vanadium tailings is basically complete,the residual vanadium is mainly dissolved in Fe₂TiO₅ phase,and a small amount remains in R₂O₃ phase;(6)The control step of the alkali leaching process of vanadium tailings is mixed control.It is controlled by both chemical reaction and diffusion The apparent activation energy EH of the alkali leaching process is 27.22 kJ·mol-1,and the value of the pre-exponential factor A is 26.32,with the expression of k=26.32exp[-27220/(RT)].