Leaching And Separation Process Of Vanadium And Chromium From Residue

Vanadium and chromium are important strategic metal widely used in the manufacturing of ion and steel,metallurgy,aerospace and petrochemical,et al.The main hydrometallurgical technology for vanadium and chromium extraction was roasting-leaching,including sodium-roasting,calcium-roasting,without salt roasting.It was needed to utilize and improve the technology as with high energy consumption,low vanadium oxidation efficiency and heavy pollution during the roasting process.Many hydrometallurgical processes have been proposed to recover vanadium and chromium,while the suitable technology for leaching of vanadium and chromium should be based on the source and characteristics of the vanadium and chromium residue.This paper focused on the utilization of the vanadium and chromium residue collected from Panzhihua city.The leaching process,kinetic behavior of vanadium,and also the technology for separation of vanadium and chromium were investigated.The following conclusions were obtained:（1）Leaching process enhanced by electric field.The vanadium and chromium was hard to leach out as it was presented as Fe（Cr,V）2O4,VOSO4,Cr2（SO4）3 in the residue.During the leaching process,H2 O and OH-around the metal anode would lose electron formed ·OH,which had high oxidation,under the effecting of electric field.The vanadium oxides in low valence,V（III）,V（IV）,might be oxidized to vanadium in high valence,V（V）,which had high solubility.The leaching efficiency of vanadium was increased from 62.6% to 91.7% enhanced with electric filed.Chromium was not easy to oxidize and hard to leach out,the leaching efficiency of chromium was below 7%.（2）Leaching of vanadium and chromium with H₂O₂.The thermodynamic analysis showed that the oxidation of vanadium and chromium with H₂O₂ were practicable,and vanadium was more easily to be oxidized.The dosage of H₂O₂ and Na OH had big influence on the leaching efficiency of vanadium and chromium,lower of reaction temperature and reaction time.The leaching efficiency of vanadium and chromium was 98.6% and 86.5% under optimal conditions.（3）Leaching kinetic of vanadium and chromium.The leaching kinetics of vanadium from residue with electro-oxidation and H₂O₂ in alkaline medium was investigated.The leaching kinetic of vanadium was followed the shrinking core model and the controlling step was the surface chemical reaction.The leaching efficiency increased from 62.6% to 91.7% enhanced by electric field and the apparent energy decreased from 16.58 kJ/mol to 8.10 kJ/mol.H₂O₂ acted as oxidant not only enhanced the leaching process of vanadium,but also made chromium easily leaching out and the leaching efficiency was up to 86.49%.The couple of electric and H₂O₂ was the best efficient way to enhance the leaching process and decreased the apparent energy.（4）Adsorption process of vanadium with melamine.Melamine,possessing three free amino groups and three aromatic nitrogen atoms in its molecule,showed a fast adsorptive rate,and was easy to achive the saturated adsorption capacity.The adsorption efficiency was affected mainly with pH of tinitial solution and dosage of melamine.The adsorption kinetics could be accurately described by the pseudo-second-order kinetic model.The isotherm of vanadium adsorption with melamine was found to follow both the Langmuir and Freundlich models,but it has slightly better fitting on Langmuir model.（5）Precipition of chromate with lead sulfate.The conversion of lead sulfate to lead chromate was based on the difference between lead sulfate and lead chromate.The thermodynamic analysis showed that the reaction was workable.The experiment results showed that lead sulfate was easy to precipitate chromate and the precipitation efficiency was nearly 100%.The pH of initial solution and dosage of lead sulfate were the main parameters affected the reaction.