| Vanadium is an important strategic resource for a modern industrial country,and it mainly exists in the form of vanadium-titanium magnetite(VTM).At present in China,the vanadium is extracted into convertor slag by oxidizing the vanadium-bearing hot metal that is formed by reducing VTM in a blast furnace.However,the physicochemical properties of vanadium slag becomes more complex since the high grade vanadium resource gradually decreases and the low grade chromium-rich vanadium resource is widely used.In this study,the melting properties of vanadium slag with FeO-V2O3-SiO2-Cr2O3-TiO2 as the main components,which is according to the composition of actual chromium-bearing vanadium slag in China,was investigated by using the rotating cylinder method and melting-point measuring instrument,and the structure characteristics of molten slag were studied by Raman spectroscopy.In addition,the viscosity model and the nucleation growth model of spinel were established to reveal the mechanism of the melting properties,to provide theoretical basis in order to optimize the process of vanadium extraction and improve the yield of vanadium.The conclusions are as follows.(1)The composition of vanadium slag has great effect on the viscosity.The results showed that the viscosity reduces from 2.9 Pa-s to 1.3 Pa·s when w(FeO)increases from 20%to 30%at 1350 ?.The viscosity reduces from 2.4 Pa-s to 0.79 Pa·s when w(SiO2)increases from 10%to 15%.However,the viscosity increases from 0.79Pa·s to 1.8 Pa·s when w(SiO2)increases from 15%to 20%,which indicates the viscosity reaches the minimum when w(SiO2)is 15%.The viscosity increases from 0.76Pa·s to 1.2 Pa-s when w(Cr2O3)increases from 5%to 10%.(2)Cr2O3 could significantly lower the melting properties and increase the viscosity of the slag.In the FeO-V2O3-SiO2-Cr2O3 system,the melting temperature increases from 1330 ? to 1545 ? when w(Cr2O3)increases from 0%to 10%.at 1500?,the viscosity increases from 0.24 Pa·s to 8.2 Pa·s correspondingly.(3)The viscosity approaches high level with high content of spinel(FeCr2O4).The nucleation rate and nucleation growth model were established for the possibly existed spinel.The results showed that in the range of 1300 to 1400?,the nucleation rate and growth rate of FeV2O4 are about 0.08 cm-3·s-1 and 1.85×10-24cm·s-1 respectively.Meanwhile,the nucleation rate of FeCr2O4 is between10.0 cm·s-1 and 2.1 cm-3·s-1 and the growth rate is between 3.7×10-24 cm·s-1 and 4.3×10-24cm·s-1.In addition,both the nucleation rate and the growth rate of Fe2TiO4 are close to zero if the temperature is above 1350?.This suggests that the amount of FeCr2O4 in slag is much higher than the one of FeV2O4 under the condition of vanadium extraction in convertor.(4)The slag composition has significant effect on polymerization degree of silicate.In FeO-V2O3-SiO2-Cr2O3-TiO2 systerm,n(NOB/T)decreases from 3.87 to 2.70 when w(Cr2O3)increases from 0%to 5%,which indicates that increasing w(Cr2O3)can improve the polymerization degree of molten slag.Furthermore,with a specific w(Cr2O3),n(NOB/T)increases from 2.70 to 2.84 when w(TiO2)increases from 0%to 13%,which suggests the polymerization degree of molten slag is lowered by increasing w(Cr2O3).(5)V3+ mainly exists in the form of V-O-V.The viscosity of vanadium slag becomes higher than ordinary steelmaking slag if the amount of the structure slightly increases.Cr2O3 and FeO can form spinel(FeCr2O4)in the slag,which leads to a considerable increase in the relative concentration of silicate ion,higher polymerization and slag viscosity.Ti4+ can break the chain structure of silicate ion and reduce the polymerization degree.As a result,the melting properties are improved and the slag viscosity is lowered. |
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