Fundamental Investigation On Cr-bearing Vanadium And Titanium Magnetite Ore In Sintering And Iron-making Process

Cr-bearing vanadium and titanium magnetite(V-Ti-Cr) is a complex iron ore and it is classified as a polymetallic paragenic resource,but it has a higher utilization value for it contains various valuable metal elements such as iron, vanadium, titanium and chromium.The main route for utilizing Cr-bearing vanadium and titanium magnetite is a blast furnace (BF)? basic oxygen furnace (BOF). Its utilization is significance to ensure the sustainable development of steel industry in China. Mean-while,it could change the strategic situation of "lack of chromium"and has a extra-ordinary significance for our national security.In the present study,fundamental research on V-Ti-Cr ore in sintering and iron-making process for its high-efficiency utilization was conducted systematically.Raw materials properties, high temperature characteristics, mixing granulation, Sinter pre-paration and optimization, the optimization of BF burden structure were researched combining with actual production, as well as, from the perspective of the theory of rheological to evaluate the influence of Cr2O3 on Ti-bearing BF slag.Chemical composition, size distribution and particle morphology of 5 kinds of V-Ti-Cr ores were measured and observed firstly.The results indicated that the 5 kinds of V-Ti-Cr ores are all high Fe and low silicon ores and they all have poor properties in granulation.Different ores have different high temperature physical-chemistry performances (HTPCP) and the single iron ore is difficult to meet the requirements that all of the HTPCPs are excellent.Thus 9the ores with different HTPCPs could match with each other to optimize the mixture HTPCPs based on the theory of complementarity. The results showed that the HTPCPs of V-Ti-Cr ores that come from Chengde, are good except liquid phase fluidity, which is the reason that V-Ti sinter with a poor sinter strength, for the insufficient liquid phase,less bonding phase and large pores.The V-Ti-Cr ore that provided by ARICOM,it has a poor ability of assimilation,so it needs the ores with a good assimilation ability to match with. On the basis of the HTPCPs and the theory of complementarity, the ores with poor properties could become the excellent ores.The optimization of granulation process is very important for V-Ti-Cr mixture with a poor granulating efficiency,and it could make the V-Ti-Cr mixture meet the requirement of production.The amount of calcium ferrite was increased and the mineral composition and structure of V-Ti-Cr sinter were improved, which was achieved by improving the permeability of the mixture for the optimization of granulation process, resulting in higher yield and quality.In addition,the optimization of granulation process is beneficial to the development of low temperature and high material layer sintering.The consolidation mechanism of V-Ti-Cr sinter using V-Ti-Cr ore provided by ARICOM indicated that a V-Ti-Cr sinter requires an approximately 14% calcium ferrite liquid-state consolidation and an approximately 15% silicate liquid-state, supp-lemented by a solid-state reaction and recrystallization of magnetite. Compared to an ordinary sinter, the calcium ferrite content in V-Ti-Cr sinter is relatively low and the perovskite content high, resulting in poor sinter results. In order to obtain a high quality V-Ti-Cr sinter, the amount of calcium ferrite should be increased and the content of perovskite decreased, and the effects of solid-state recrystallization should also be considered.On the basis of the aim to improve the production and quality, the influence of MgO,fuel level, boron oxide and basicity on the V-Ti-Cr sintering was studied via a sintering pot tests.melting tests and mineralogical analysis using metallographic micr-oscopy, XRD and SEM-EDS. The results showed that the optimal MgO content was 2.63wt%,the optimal fuel level was 4.0wt% and the boron-bearing iron concentrate additive was 5.0wt%.In addition, the optimal basicity was 2.55.To solve the problem of insufficient production capacity of acid pellet,which brought by using of (ultra)high basicity V-Ti-Cr sinter with a good quality,to maintain the balance of basicity of the slag at R=1.10,the new burden structure of BF "(ultra)High basicity sinter+Acid pellet+Acid sinter"in smelting V-Ti-Cr was proposed.And the softening and dripping properties were determined, analyzed and compared.The results showed that the new burden structure has some advantages.The influence of Cr2O3 on the high temperature viscosity of Ti-bearing molten slag was researched in a view of rheological.The results indicated that,the content of Cr2O3 and V2O5 have little influence on the viscosity of slag at a high temperature, the influence of Cr2O3 on the melting temperature of the slag is not obvious as that of V2O5; the shear thickening phenomenon would appear in the cooling process of the molten slag adding Cr2O3 or V2O5,and when the temperature changes, the shear thickening phenomenon would disappear.Therefore, V-Ti-Cr ore was smelted through BF was feasible from the above perspective.In conclusion,some key problems in the sintering and iron-making for V-Ti-Cr ores were researched,and the results would be beneficial to the high efficiency utilization of V-Ti-Cr and it could provide some references for the production.Some results had been used in the plant,and got a good application.