| The reserves of V-Ti-bearing magnetite are huge in China,which mainly distributed in Panzhihua area and Chengde area.The total reserves in Panzhihua area are more than 10 billion tons,and the reserves of vanadium and titanium rank the third and first in the world,respectively.The value of comprehensive utilization of the ores is very high.So far,the main method of utilization of the resource in Panzhihua is of Blast Furnace-Converter Smelting Process,which was mainly used for producing steel and recovering V.However,the utilization rate of vanadium resource is low.In fact,the content of TiO2 is only about 22%in blast furnace titaniferous slag.Due to its low content,it is very difficult to recover TiO2 from the slag,leading to a good deal loss of titanium resources.Therefore,in order to improve the grade of TiO2 in the slag,reduction-melting process was conducted by Panzhihua Iron and Steel Group.In this process,the reduction of vanadium V-Ti-bearing magnetite concentrate(assaying 54%Fe)was achieved by rotary kiln or rotary hearth furnace,then the metallized pellets was melted in electric arc furnace for producing vanadium-bearing hot metal and melting slag,the obtained melting slag containing about 45%TiO2,in which the content of TiO2 was twice as high as that of blast furnace slag.However,the content of impurities was still high.Thus,extraction of TiO2 from the melting slag was also difficult.In fact,nearly half of the titanium reserve is distributed in V-Ti-bearing magnetite concentrate of Panzhihua area.Therefore,preparation of high-grade titanium slag from V-Ti-bearing magnetite concentrate concentrate and could be used for production of titanium sulphate hydrolysis,which was significant to increase the amount of available titanium resources and improve the comprehensive utilization rate of titanium resources in Panzhihua area.This paper focused on solvation of the difficulty in making use of titanium resources in V-Ti-bearing magnetite concentrate in Panzhihua area,based on this,the novel academic idea of further removal of impurities from V-Ti-bearing magnetite concentrate of Panzhihua by mineral processing,followed by metallurgical process to prepare medium-grade titanium slag was put forward.The present study might provide technical support for derceasing the content of impurities and preparing titanium dioxide by sulfuric acid process.The main research work and achievements of this paper were as followed:(1)The purity of V-Ti-bearing magnetite concentrate from panzhihua was low,the grade of TFe was only 54%.By fineness grinding and concentrated process,impuritiy was decreased and the grade of Fe and TiO2 were increased,which was beneficial for getting high-grade titanium slag.The MLA(mineral liberation analysis)study of the high-grade vanadium-titanium magnetite concentrate showed that the content of the titanium magnetite concentrate after the purification was more than 95%,and the impurities were mostly embedded in the titanium magnetite particles as ultra-fine slice crystal,which is difficult to get further liberation and thus could not be purified more deeply by traditional mineral processing technology.Meanwhile,in order to reduce the loss of the resources,by using low intensity magnetic separation to recycle an iron concentrate from the selected tailings,the recycled iron with 54.06%Fe could be used as blast furnace smelting raw materials.Loss of both Fe and TiO2 in the final tailings was less than 10%,reducing the loss of resources effectively.(2)In order to prevent foreign impurities getting into slag and reduce the TiO2 grade of slag,organic binder pelletizing and external coal reduction was performed.Experimental results showed that the metallization rate was increased with the increase of reduction temperature.When metallization rate exceeded 90%,it was difficult to further increase the metallization rate.The XRD of metallized pellets results showed that the reduction of V-Ti-bearing magnetite concentrate was accomplished step by step.Firstly,Fe2.75Tio.25O4 was reduced to Fe2.5Ti0.5O4.Secondly,Fe2.5Ti0.5O4 was reduced to FeTiO3 and metallic iron,then the FeTiO3 was reduced to FeTi2O5 and metallic iron,and the reduction of FeTi2O5 was difficult.On the other hand,SEM-EDS results of metallized pellet under different reduction temperatures showed that with the increase of temperature the metallic iron grains grow more and more in pellets,and migration and aggregation behavior of elements became more obvious.Reduction kinetics results showed that the activation energy increased with the increase of percent conversion during the reduction process.At the 1250?reduction,when the percent conversion below 0.7,the reduction process was controlled by phase boundary reaction,when the percent conversion exceed 0.7,the reduction process was controlled by random nucleation and random growth.(3)The thermodynamic calculation of the melting of metallized pellets shows that the formation of metallic Fe,metallic V,metallic Ti and metallic Si was doable,and the Fe,Si and Ti in the molten iron would react with the FeO at the interfacial interface between molten iron and slag,the FeO content in the slag had the greatest effect on the reduction behavior of vanadium oxide.Addition of CaO when melting metallized pellets was beneficial to the reduction of FeO and decrease the content of FeO in slag,which was beneficial to increase the content of TiO2 in slag and vanadium content in molten iron,achieving better separation of slag and molten iron and efficient recovery of valuable elements.The reaction of reduction of titanium oxide to TiC in the process of melting was easy occurring.So in order to inhibit the formation of TiC,it was necessary to control the amount of carbon in the melting process.Calculation results of Factsage 7.0 showed that the melting temperature and viscosity of the slag between 0.8 and 1.2 was low.(4)Melting test results showed that the melting temperature was high in slag phase because of the initial alkalinity of metallized pellets was low,and as a result,separation of molten iron and slag could not be achieved.Conversely,a small quantity of CaO addition could effectively promote the separation of slag and iron.In facy,under the optimum melting condition of slag basicity 0.8,carbon content 4%,melting temperature 1550? and melting time 30min,effective separation of slag and molten iron was obtained.The content of V,Ti and Si was 0.56%,0.43%and 0.12%in the molten iron,respectively.The grade of TiO2 in the melting slag was 56.32%with the content of Fe was 6.34%.Besides,Fe mainly existed as fine metallic iron particles,which could be effectively removed from the melting slag by fine grinding and low intensity magnetic separation process and thereby improve the grade of TiO2 in slag.The non-magnetic production with TiO2 content of 60.38%and Fe content of only 0.62%.Because the grade of TiO2 in this slag was higher than the conventional melting slag and lower than high titanium slag of ilmenite smelting,this slag was called as medium titanium slag,which could be used as qualified raw materials for preparing titanium white by sulfuric acid process.The magnetic product should be returned into the next melting process,thus forming a closed-circuit process for the maximum utilizing resource of Ti and Fe. |
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