Dissolution Kinetics Of Vanadium Trioxide At Oxygen Pressure In Sodium Hydroxide Solution

The major materials for vanadium extraction are titanomagnetite, slags from the ferrous industry, vanadium-bearing stone coal, spent catalyst, petroleum residues and asphalt residues. Industrial processes for vanadium extraction differ from each other according to the species, properties and vanadium content of materials. In all these processes, alkaline leaching is promising because of its advantages including high recovery of vanadium, high purity of production, less production equipment, low production costs and less erosion. Theoretical researches of extraction of vanadium from vanadium-bearing materials in alkaline leaching process are few. The poverty of theoretical research seriously restricts the technology development of extraction of vanadium. Besides, existing studies are mostly aimed at solvent system that follows roasting process, and few studies are aimed at leaching system with oxygen pressure. Based on the research results of previous literatures, through lots of modem testing technologies such as chemical analysis and SEM-EDS, the paper studied the isothermal and non-isothermal dissolution mechanism of vanadium trioxide in NaOH-02 system. The purpose is to demonstrate the alkaline-leaching mechanism of vanadium trioxide in under oxygen pressure and to supply data for determination of parameters to industry.The main conclusions are as follows:In experiments of isothermal dissolution kinetics, the effects of temperature (80～130℃), partial pressure of oxygen (200～700 kPa), initial sodium hydroxide concentration (0.1-2 M) and stirring speed (200～1000 rpm) on the dissolution rate of vanadium were studied, respectively. Experimental data shows that the vanadium dissolution rate increases with increasing temperature and partial pressure of oxygen, and stirring speed over 800 rpm and sodium hydroxide concentration over 1.0 M had very little effect on the dissolution rate. The kinetic analysis of the experimental data for various experimental conditions indicated that the the dissolution process fits the shrinking-core model well. Initial dissolution process was controlled by the chemical reaction during the early stage of dissolution with activation energy of 45.32 kJ/mol, and then was controlled by liquid film diffusion with activation energy of 11.57 kJ/mol. In initial stage of dissolution, reaction orders related to sodium hydroxide concentration and oxygen concentration were 0 and 0.75, respectively.In experiments of non-isothermal kinetics, the effects of agitation speed (200～1000 rpm), partial pressure of oxygen (400～1200 kPa), initial sodium hydroxide concentration (0.1-2 M), and heating rate (1.31～4.01 K/min) on vanadium dissolution were determined. Experimental data shows that the vanadium dissolution rate increases with increasing heating rate. It also confirm the conclusions that dissolution rate increases with increasing partial pressure of oxygen and that stirring speed over 800 rpm and sodium hydroxide concentration over 0.5 M had very little effect on the dissolution rate. A non-isothermal kinetics model was applied to describe the dissolution of vanadium trioxide. It was found that the mean apparent activation energy of the kinetics process were 36.62～37.52kJ/mol between surrounding temperature and 423K, and dissolution process is controlled by both of chemical reaction and liquid film diffusion.The analysis result of SEM-EDS indicates that the V2O3 particles particles present the very dense surface with cylindrical geometry and present unchanged surface and shrinking size during the dissolution process. Therefore, the shrinking core model can be used to discribe the dissolution process.