Crystallization control mechanism of molten vanadium slag for effective vanadium transformation and extraction
The vanadium extraction efficiency fluctuates greatly during sodium roasting-water leaching process caused by cooling methods of molten vanadium slag.In this paper,the effects of vanadium precipitation from molten vanadium slag and vanadium spinel crystallization characteristics on vanadium extraction rate were studied by using optical microscopy(OM),X-ray diffraction(XRD),scanning electron microscopy(SEM+EDS)and electron probe(EPMA).The mechanism of efficient vanadium extraction controlled by vanadium-spinel crystallization was further discussed.The results show that the water quenching temperature of molten vanadium slag has a significant effect on the precipitation rate of vanadium from molten vanadium slag,the crystallization size of vanadium spinel,and the vanadium phase conversion and leaching rate of vanadium slag during the sodic roasting-water leaching process.During the cooling process of molten vanadium slag,the rapid nucleation growth period of spinel occurs at 1400-900℃,the migration of vanadium from molten liquid phase to solid phase spinel completes at 900℃,and the crystalline phase is dominated by vanadium spinel,in which vanadium is uniformly dispersed.After 900℃,spinel growth slows down,and ferro-titanium spinel grows along the edge of vanadium spinel,and the"central-aggregation effect"of vanadium presents in spinel.Sodium roasting-water leaching experiments were carried out on the water-quenching slag at 1400℃,900℃and 400℃,respectively.The particle size of water-quenching vanadium slag(WQVS)is less than 0.15 mm,and m(Na2CO3)∶m(NaCl)∶m(WQVS)= 10∶3∶100,the roasting temperature is 780℃,and the roasting time is 200 min.When the roasted products are ground with size less than 0.18 mm,and then arebleached in water at 80℃for 45 min,the vanadium leaching rates are 75.15%,95.09%and 78.78%,respectively.The extraction efficiency of vanadium and production efficiency can be improved by temperature-controlled crystallization of vanadium slag,that is,molten vanadium slag is firstly air slow-cooled to 900℃and then water-quenched.
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