Study On Inadequate Roasting And Electro-catalytic Oxidation Leaching Of Converter Vanadium Slag

Vanadium is widely used in steel smelting,alloy materials,chemical batteries and catalysis for its high tensile strength,fine ductility,corrosion resistance and other excellent physical and chemical properties.In China,vanadium-titanium magnetite is the principal raw material for vanadium production,which is extracted by the method of"high temperature roasting-hydrometallurgical leaching".However,conventional high-temperature roasting technology for vanadium extraction has the bottlenecks of superheated temperature,large energy consumption,and partial sintering.Meanwhile,high temperature makes the silicon phase easily melt into the liquid,which encapsulates vanadium,reduces the mass transfer efficiency and oxidation efficiency of the reaction system,and seriously restricts the efficiency of vanadium extraction.Therefore,research on low temperature and high efficiency of vanadium extraction technology has risen to one of the key issues concerned by relevant academia.Based on electro-catalytic oxidation technology,chemical oxidation technology and chemical process intensification,this research focused the efficient vanadium extraction from converter vanadium slag under low temperature roasting.A novel method of"low-temperature sodium roasting-electro-catalytic oxidation leaching"was proposed,while the research on the inadequate sodium roasting of vanadium slag,electro-catalytic oxidation leaching and catalytic oxidation leaching kinetics were also carried out.The research conclusions are as follows:（1）The raw powder of converter vanadium slag was characterized by XRF,XRD,XPS,FESEM and TG-DTA.The results showed that the content of vanadium was 9.16wt.%,while the silicon was 10.67 wt.%,which belonged to"high silicon vanadium slag".Vanadium mainly existed of vanadium spinel and low-valent vanadate such as V₃O₄ and Mn V₂O₄,which were mostly trivalent.It needed to be roasted and oxidized to obtain extractable vanadium in high-valance.（2）Based on the principle of low-temperature roasting,the research on the inadequate sodium roasting of converter vanadium slag was carried out.It was found that roasting could destroy spinel structure,change the phase composition of the vanadium as well as chemical environment.In addition,it also caused the oxidation of low-valant vanadium in the raw material to form Na VO₃ or Na₃VO₄.The content of pentavalent vanadium in the roasting clinker was 48.06 wt.%while the roasting temperature,roasting time and molar ratio of sodium-to-vanadium were kept constant as650℃,2 h and 0.6,respectively.Few low-valant vanadium still existed in the clinker,which needed to be oxidized during leaching to achieve efficient extraction of vanadium.（3）Based on the theory of electro-catalytic oxidation and chemical catalytic oxidation,the electro-catalytic oxidation leaching by electric field coupling with sodium persulfate was studied.The results show that electric field,chemical field（sodium persulfate）and the coupling all promoted the directional oxidation of low-vanlant vanadium.The leaching efficiency of vanadium reached to 95.64%as the leaching temperature was 60℃,reaction time was 30 min,liquid-solid ratio was 2 m L:1 g,sodium persulfate dosage was 5 wt.%,current density was 1000 A/m²,which made the leaching efficiency increased by 26.94%,25.41%and 11.30%compaied with electro-catalytic oxidative leaching,chemical field（sodium persulfate）catalytic oxidative leaching and direct leaching.（4）Based on the basic theory of physical chemistry and process intensification,the research on the mechanism of electro-catalytic oxidation leaching was carried out.The results showed that hydroxyl radical intermediate（MAO（·OH））and trace O₂ produced by electric field system promoted the selective oxidation of VO₃^-.Meanwhile,electric field expedited the collision among the moving particles,therefore it facilitated the dissolution of wrapped vanadium.（5）Based on the basic principles of chemical kinetics,the research on kinetics of the reaction under different leaching systems were carried out.The results showed that chemical oxidation of vanadium during leaching process was the rate-controlling step,while it controlled by the surface chemical reaction under the shrinking core model.The apparent activation energy was calculated as 16.77 k J/mol in direct leaching,and it decreased with the application of electric field and oxidant.The apparent activation energy of electro-catalytic leaching and coupling catalytic leaching were 15.33 k J/mol and 11.95 k J/mol,respectively.