Study On Roasting - Leaching Behavior And Technology Of Vanadium Residue

Vanadium is an important strategic metal resource in China, it plays an important role in chemical, military, aerospace and other fields. At present, vanadium slag generated in the steelmaking process is the main raw material, sodium salt roasting and calcium salt roasting are the most commonly used technology for the treatment of vanadium slag. It is very easy to generate harmful gases in the sodium roasting process, causing environmental pollution problems, while calcium roasting can avoid harmful gases but still needs high-temperature roasting, which faces mass transfer barriers and low recovery of vanadium. Therefore, it is urgent to develop new method to improve vanadium resource utilization and solve the environmental pollution. This paper took Chenggang vanadium slag as experimental materials, studied extraction of vanadium from vanadium slag by roasting-hydrothermal alkali leaching, secondary roasting-hydrothermal leaching and oxygen-enriched air roasting-hydrothermal alkali leaching, the three methods provided new approaches for cleaner and effective conversion of vanadium.According to the assay of mineralogy, it indicates that the metal of V is at a grade of10.45%, exists in the vanadium slag in the form of vanadium iron spinel(FeV2O4), the valence of vanadium is+3, only the vanadium is oxided to the valence of+5, the effective recovery of vanadium can be achieved by the way of leaching. The vanadium iron spinel, olivine and chrome spinel iron coexistence together closely, difficult separation. Therefore, only after the oxidative decomposition of olivine and chrome spinel iron, the vanadium iron spinel could be oxided successfully.This paper took the method of roasting-leaching, the phase transformation of vanadium slag in different roasting conditions was systematically studied, providing theory basis for choosing the best roasting conditions. In the leaching process, effects of leaching temperature, leaching time, ratio of liquid-solid, concentration of NaOH, stirring speed on the leaching rate of vanadium were studied, and the optimal process parameters were obtained, the following conclusions were achieved: (1)Blank roasting-hydrothermal alkali leaching:after blank roasting, the oxidation and decomposition of vanadium slag were completed, the low valence of vanadium was oxidized to the high valence, with the increase of roasting temperature, the extension of roasting time, the decrease of particle size of raw material, the leaching rate of vanadium gradually increased. Under the optimal roasting conditions of leaching temperature180℃, leaching time2.Oh, alkali concentration30%, ratio of liquid to solid5:1, stirring speed500r/min, the leaching rate of vanadium could arrive95.09%.(2)Secondary roasting-hydrothermal leaching:the vanadium after roasting once was chosen for experimental material. Na2CO3was the additive, the process achieved at a relatively low roasting temperature (600～700℃), the process produced no low melting silicates, under the optimal roasting conditions of roasting temperature680℃, roasting time1.5h, particle size of vanadium slag<48μm (-300mesh), vanadium slag phase conversion rate reached the maximum, and the vanadate was generated. After roasting the vanadium slag was leached in the water, under the leaching conditions of the reaction temperature80℃, extraction time1.5h, ratio of liquid to solid5:1, the leaching rate of vanadium reached94.12%.(3)Oxygen-enriched air roasting-hydrothermal alkali leaching:the vanadium slag was used for the raw material; blank roasting was completed at the oxygen atmosphere, the vanadium slag after roasting was leached by hydrothermal alkali. Under the optimum roasting conditions of roasting temperature800℃, roasting time1.0h, particle size<74μm (-200mesh), and the oxidative decomposition of vanadium iron spinel was achieved, the leaching rate of vanadium could arrive96.05%.Compared of the three methods of roasting-leaching, by oxygen-enriched roasting-hydrothermal alkali leaching, the leaching rate of vanadium could reach the maximum, followed by blank roasting-hydrothermal alkali leaching, the secondary roasting-hydrothermal leaching was the worst. The oxide decomposition conditions of vanadium iron spinel were optimized by oxygen-enriched roasting:the roasting temperature could be lowered, the roasting time could be shortened, the particle size of vanadium slag could be reduced, therefore the oxygen-enriched air roasting-hydrothermal alkali leaching was recommended as the optimal method of extraction of vanadium from vanadium slag.