| Direct import of mineral has been a main way to utilize abroad mineral resources for quite a long time. The firm and area, where the resource is distributed unevenly and import superiority and urgent requirements are existed, import abroad mineral resources not only can ease off the domestic demand, but also can increase the special strategic resources and stimulate economic growth.High chromium vanadium-titanium magnetite is a special vanadium-titanium magnetite resource. The percent accounting for the total reserves of vanadium-titanium magnetite is little, but it has extremely high comprehensive utilization value for abundant symbiotic chromium resource. Chromium is one of severe shortage strategic resources which can be used to produce stainless steel, special steel and electro vacuum products. Compared with general vanadium-titanium magnetite, its mineral composition is more compicated. Agglomeration of raw material, blast furnace smelting and comprehensive utilization of vanadium, titanium and chromium are more difficult. Moreover related studies are little and system integration technique has not been formed. All these facters can lead to no industry practices of high chromium vanadium-titanium magnetite, and vanadium and chromium resource has not been utilized effectively. Therefore, how to utilize the high chromium vanadium-titanium magnetite reasonabley and effectively is becoming a key task about development and utilization of mineral resources for our country and the world. In this study, based on high chromium vanadium-titanium magnetite, the fundamental features of the mineral, sintering and pelletizing, reasonable burden structure and optimization of blast furnace slag system have been researched systematicly. Through this study, some theoretical foundations are supplied for smelting high chromium vanadium-titanium magnetite with blast furnace. And many reliable technical parameters are given to pratical production.The fundamental properties of high chromium vanadium-titanium magnetite and several iron ore fines used in pratical production were researched with micro sintering device. It was shown that many distinctions of fundamental properties were exsisted in different iron ore, and FeO, MgO, SiO2 and crystal water in iron ore had important effects on its fundamental properties. The high chromium vanadium-titanium magnetite had a high assimilation temperature, bad liquid liquidity, low grade of binding phase intensity and bad crystal consolidation strength, and it was difficult to be sintered. Base on those fundamental properties and practical raw material condition, high chromium vanadium-titanium magnetite, when used to be sintered, should be matched with homemade mixed powder as much as possible.The results of the sintering experiment were given that as high chromium vanadium-titanium magnetite ratio increasing, the vertical sintering speed and drum index were decreased, the finished ratio and the sintering cup utilization increased firstly and deceased then. When the ratio was below 20%, the comprehensive index was changed little. Phase analysis results indicated that high chromium vanadium-titanium sinter had complicated mineral compositions. Some magnetite, hematite, perovskite, calcium ferrite, dicalcium silicate and vitric were in it. With high chromium vanadium-titanium magnetite increasing, the number of liquid in sinter was quite a little, the content of dicalcium silicate was decresed, and much perovskite and vitric were come up which all resulted in bad indexes of sinter. In a word, usually the ratio of high chromium vanadium-titanium magnetite in sinter should be controlled at 10%～20%.Basicity and carbon ratio play important roles in metallurgical performance of sinter. Effects of basicity and carbon ratio on sinter’s metallurgical performance were investigated. Some results were obtained, when the carbon ratio was increased, the vertical sintering speed, the sintering ratio and drum index were decreased, he finished ratio and the sintering cup utilization were increased firstly and deceased then. Reduction disintegration property was improved, and RDI+3.15 was increased gradually. Comprehensive index was increased firstly and decreased then, when the carbon ratio is 5%, the index was the highest, the metallurgical performance was the best. As increasing with the basicity, the vertical sintering speed, the finished ratio, drum index and the sintering cup utilization were increased. The sintering ratio was decreased. Reduction disintegration property was improved, and RDI+3.15 were increased gradually. Comprehensive index was increased, when the basicity was 2.70, both the index and the metallurgical performance were the best.Based on high chromium vanadium-titanium magnetite, pelletizing research was proceeded. Some results were given that with the increasing ratio of high chromium vanadium-titanium magnetite, the properties of green pellet had little changes, but the compressive strength of oxidized pellet was decreased, when the ratio was more than 20%, the compressive strength couldn’t meet the requirement of blast furnace production. On the other hand, increasing the ratio of high chromium vanadium-titanium leaded to lower reduction swelling of pellet. When the ratio was increased from 0 to 20%, the reduction swelling was decreased from 32.1% to 21.1% accordingly. The agglomerating mechanisms of high chromium vanadium-titanium magnetite pellet were mainly included microcrystalline key connection of Fe2O3, recrystallization connection of Fe2O3, recrystallization agglomerating of Fe3O4 and connection of slag, among which, recrystallization connection of Fe2O3 was shown the best. As the increasing ratio of high chromium vanadium-titanium magnetite, the number of liquid was decreased when agglomerating, the cementing action was waken, the strength of pellet was worse.Through the two optimization measures including fine grinding high chromium vanadium-titanium magnetite and replacing the practical production iron ore with cheap finer Oukong powder, the incremental utilization of high chromium vanadium-titanium magnetite could be achieved. When the ratio of high chromium vanadium-titanium magnetite was 40%, the compressive strength was 2475 N per one and 2005 N per one respectively, while the reduction expansion ratio was 19.2% and 16% correspondently. These paramaters all met the requirements of the practical blast furnace production.When the content of MgO in sinter was increased from 1.95% to 2.63%, the vertical sintering speed was decreased, the sintering cup utilization changed a little, the finished ratio, and drum index, comprehensive index and reduction disintegration property were all improved. When the content of MgO in pellet was increased from 1.95% to 2.63%, the compression strength of green pellet was improved slightly, while the compression strength of oxidized pellet was decreased significantly, shown as from 1985 N per one to 1479 N per one. The reduction swelling was decreased from 15.2% to 8.6%. Because of obvious decreasing of the compression strength of oxidized pellet for increasing content of MgO, the requirement of concentrate burden wasn’t arrived; therefore, MgO wasn’t favorable to added in pellet. Comprehensively considering of the influences of MgO on the metallurgical properties of sinter and pellet, the sinter with high MgO matching with the pellet with low MgO should be the reasonable burden structure of smelting high chromium vanadium-titanium magnetite in blast furnace.With the increase of basicity of sinter and the ratio of pellet added into blast furnace, temperatures of softening start, softening end, melting start and end were all decreased. Melting zone was thinned and narrowed. Differential pressure of dropping and the highest differential pressure were both decreased. The permeability of comprehensive burden was improved. In a word, the burden structure of high basicity sinter matching with high ratio acid pellet was good for smelting high chromium vanadium-titanium magnetite in blast furnace.By means of orthogonal test synthetic weighted score method and single factor test, optimization of blast furnace slag for high chromium vanadium-titanium magnetite was researched. It was shown that the optimal slag for high chromium vanadium-titanium magnetite was obtainded as follows:Binary basicity is 1.15, content of MgO, TiO2 and Al2O3 is 10%,8% and 15% respectively.In order to clarify the slag system of high chromium vanadium-titanium magnetite smelting in BF (blast furnace), the melting properties of slag samples prepared by analytically pure reagents were measured. By means of orthogonal test synthetic weighted score method, the optimal slag for high chromium vanadium-titanium magnetite was obtainded as follows:binary basicity was 1.15, content of MgO, TiO2 and Al2O3 was 10%,8% and 15% respectively. With the increasing basicity, melting temperature(Tm) was increased; initial viscosity (η0) and high-temperature viscosity (ηh) were decreased in general. With the increasing MgO content, Tm was decreased firstly and increased then.η0 and ηh increased firstly and decreased then. With the increasing Al2O3 content, Tm was increased,η0 and ηh are decreased firstly and increased then. With the increasing TiO2 content, Tm was increased,η0 and ηh were decreased. The content of V2O5 in slag was increased from 1% to 3%, Tm and η0 was decreased,ηh was changed little. As for the content of Cr2O3 in slag increasing from 1% to 3%, Tm was decreased slightly, while η0 was increased,ηh was changed little. |
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