Fundamental Research On The Reduction-Melting Separation Process For Metalized Pellets Of Vanadium-bearing Titanomagnetite Concentrates

The vanadium-bearing titanomagnetite concentrates is the main ore dressing product of vanadium-titanium magnetite. The titanium resources can not be effective used by blast furnace smelting process, however the non-blast furnace smelting process is an effctive solution to solve it, which have been realized the comprehensive recovery and utilization of iron, vanadium and titanium resources. Due to the complexity of mineral structure, the non-blast furnace smelting process also has a series of problems, such as high energy consumption, product quality and the smelting separation process is difficult smooth operation.In this paper, according to the problems of the electric furnace smelting process, under the premise of good separation of slag and iron, the vanadium and chromium were promoted from slag into the hot metal, so that the high grade melting-seperation titanium slag and vanadium-chromium-bearing hot metal were obtained. Based on the analysis of theoretical research, the key technology of theory has been studied to obtain the optimization parameters of the process and the controlling mechanism of elements distribution ratio between slag and iron.First of all, the metallization rate and carbon content of metallized pellet as control index, the thermodynamics and experimentation of the carbothermal reduction process for vanadium-bearing titanomagnetite concentrates were analyzed and studied. The research results show that the metallization rate and carbon content of metallized pellet could be controlled by changing the carbon oxygen ratio, reduction temperature, reduction time and the MgO addition content, and the MgO addition content can promote the reduction process when the reduction temperature is less than 1225℃. The metallization rate of metallized pellet increase by 10 percentage with the 6% MgO addition content at 1150℃.The thermodynamics of element distribution between slag system (TiO2≈ 50%) and molten iron is calculated and analyzed theoretically by Congregated electron phase and Wagner model. The calculation results show that the melting temperature and the content of FeO in slag are the key control parameters for the distribution constants of vanadium and chromium between slag and iron. The vanadium and chromium could be greatly reduced into molten iron by increasing melting temperature and decreasing the FeO content in the slag.The viscosity and melting temperature of slag system (TiO2≈50%) were calculated and analyzed theoretically by FactSage thermodynamic software. The research suggests that the viscosity and melting temperature of melting-seperation titanium slag system were decreased with increasing the CaO and FeO content in the slag. When the basicity of slag was fixed at about 0.6 and the FeO content in slag was fixed at about 5%, the melting temperature of melting-seperation titanium slag is 1420℃ and the viscosity of melting-seperation titanium slag is about 0.2 Pa·s at 1550℃.The reduction-melting separation process for metalized pellet of vanadium-bearing titanomagnetite concentrates was investigated in laboratory, the effect of chemical composition of metallized pellet and the parameters of reduction-melting separation process on the slag-iron separation and element distribution behavior were discussed. The experimental results show that the suitable MgO/SiO2 of metallized pellet is 1.0, the suitable CaO/SiO2 of metallized pellet is 0.6 and the carbon content of metallized pellet should be less than 5% when the slag-iron good separation and the TiO2 content of slag is more than 47%. The FeO content of the final slag is the critical criterion for the vanadium and chromium distribution ratio between slag and iron, so that more than 80% of vanadium, chromium into hot metal which control the FeO content in the final slag is less than 3%. The reasonable process arrangement is as follow:melting temperature being 1550℃, melting time being 30min, the carbon content of metallized pellet being 3.59% and basicity of metallized pellet being 0.6, the slag and iron are effectively separated, the recovery rate of iron, vanadium and chromium is 93.13%,90.17% and 86.25% respectively, the slag TiO2 content is 47.98% in this condition.The acid soluble of melting-seperation titanium slag and the separation of vanadium and chromium from vanadium-chromium slag were investigated in laboratory. The experimental results show that the acid hydrolysis ratio of mixed ore is above 90% when the melting-seperation titanium slag and ilmenite mixing ratio is less than 30%. The two-step oxidizing and Na-activation roasting process can separate the vanadium and chromium from vanadium-chromium slag, the conversion ratio of vanadium and chromium are 88.6% and 1.28% respectively under the first oxidizing and Na-activation roasting step, the leaching conversion ratio of chromium is above 80% under the second oxidizing and Na-activation roasting step.