Phase Equilibrium And Structural Change Of Vanadium Extraction From Vanadium Slag

Vanadium slag is a sort of slag with high vanadium oxide and high iron oxide,which is obtained by blowing vanadium-containing molten iron through metallurgical equipment.The generally content of vanadium is about 10% in the vanadium slag.The vanadium content of vanadium-containing molten iron and the control of the process parameters in the metallurgical blowing process determine the vanadium content in the vanadium slag.It is known that the main phase in vanadium slag includes spinel phase?MeO·Me'2O3?,silicate phase?Me2SiO4?,and phase according to the present literature.But due to the changes of the temperature of vanadium slag roasting and the components,the main phase of vanadium slag will also taken place corresponding changes.Different vanadium slag phase plays a crucial role to the next step in the vanadium slag leaching.According to the extraction of V₂O₅ from vanadium slag is usually put sodium salt or calcium salt into the vanadium slag and roasting in a middle temperature [800?,900?).The study was aimed at analyzing the change of the roasting process at different temperatures in simulating the vanadium slag system?V₂O₅-SiO₂-FeO?.The mainly experiment results are:When the Vanadium content is constant,the simulation of vanadium slag A group of samples in the high temperature section,the A2 sample?V₂O₅-10.98 g,SiO₂-28.82 g,FeO-60.20g?appeared the highest vertex,to the two ends of the high temperature section of the inflection point temperature gradually lower;When the silicon content is constant,the simulation of vanadium slag D group of samples in the moderate and high temperature section,the D3 sample?V₂O₅-17.53 g,SiO₂-24.39 g,FeO-58.08g?appear at the lowest vertex temperature.There are roughly three vertex temperatures the composition of vanadium slag in the ternary phase diagram and the phase change law of the roasting process were roasting at 1000?.About 150?,the simulate of vanadium slag lose crystal water were completed;About 450?,the iron content of vanadium slag oxidized were completed;About 750?,the binding of silicon and iron components of the oxygenolysised were completed;Above 750 ?,vanadium components and iron components make compound reaction and pyroxene composition oxidation decomposition.The vanadium slag with a high-iron content had a significant endothermic peak at 1143?.In order to make sure the distribution of vanadium slag B and C groups analysised differential thermal analysis curve.Combined with the metallographic method to observe the different phase area of the sample.High vanadium and high silicon content of the slag type is mainly "gravel type" structure,and the melting point of roughly above 1300?.The slag with high iron content in the metallographic photos are mainly reflected in the dense into a large block of black structure.The influence factors of roasting and the process heat by contrast in the two processes of sodium vanadium slag/calcification and roasting.Analyze the changes from the additive in different proportions of sodium salt/calcium salt and the quality of the changes during the roasting process.In the case of sodium chloride as an additive,the increase of the add on amount of sodium chloride has little effect on the roasting temperature.In the case of sodium carbonate as the additive,the increase of the add on amount of sodium carbonate has a great influence on the roasting temperature.When V/Na = 1: 1,the lowest required roasting temperature is 686.9?;When V/Na = 1: 4,the highest required roasting temperature is up to 785.7oC.Due to the different content of sodium carbonate additives,the roasting temperature change interval [686.9?,785.7?].In the case of calcification roasting,it has a certain impact to the degree of roasting when calcium oxide or calcium carbonate as an additive.With the decrease of V/Ca ratio?the increase of calcium salt additive?,the roasting temperature increased,and the vanadium slag with the calcium oxide as the additive was relatively low in the roasting temperature,it is about 635.9-687.0?;And calcium carbonate as an additive in the roasting process,the temperature is high,at 752.2-801.4?.For the sodium vanadium slag roasting,at 600?,800?form sodium vanadate?Na3VO4?and Na Fe3V9O19 in varying degrees.When the roasting temperature increasing from 600? to 800 ?,the miscellaneous peak is relatively small in the material of XRD that it formed,we can see that improve temperature could make the formation of sodium vanadate more stable and the proportion increased.For calcification vanadium slag roasting,the main formation is calcium vanadate?CaV3O7?and calcium ferrite?CaFe2O4?.The peak of the characteristics of Fe2O3 in the vanadium slag that calcification roasted is obvious,so vanadium iron spinel was destroyed in the process of calcification roasting,and formed Fe2O3.Whether it is calcium oxide or calcium carbonate as an additive for vanadium slag.The results of roasting at 800°C produce almost the same material and structure by analyze in the characteristic peaks of the XRD pattern.The experiment make the element range of the ternary phase diagram of the metallurgical slag system reduced and to make it closer to the actual vanadium slag ingredient,and raise more credible theoretical guidance to the realization of the actual process.In the technical route,the use of the main components of the simulation analysis,could be better avoid other impurities affect the accuracy of the results and provide a reliable basis for chemical reactions for the roasting process.