Function And Mechanism Of Coal Slimes And Blast Furnace Dust In Direct Reduction Roasting Process Of High-phosphorus Oolitic Hematite

High-phosphorus oolitic hematite ore is recognized as one of the difficult separation of iron ore at home and abroad. In recent years, studies shown that the coal-based direct reduction roasting-magnetic separation process can be effective for the ore. Coal slime is a by-product generated in coal separation process, because it has many disadvantages of high water-content, strong viscosity, high ash-content, which makes it difficult to use. Blast furnace dust is a by-product of steel industry which is produced about 15 million T per year in China, which has the characteristics of containing fixed carbon and containing iron oxide, because there is no effective method of use. Almost of the blast furnace is stored at outdoors, which has resulted in environmental pollution and waste of iron resources.This paper studies the feasibility of coal slime and BF dust used as reductants in direct reduction roasting on the high phosphorus oolitic hematite. The effects of different types coal slimes on the high phosphorus oolitic hematite of direct reduction process were investigated, and the optimum process conditions were obtained. The results showed that T slime is best suitable to be used as reductant. With the T slime dosage of 20 mass%, the DRI ?Direct Reduced Iron? of 91.35% iron grade,81.13% iron recovery and phosphorus content 0.076% can be obtained. The study has achieved the purpose of coreduction roasting of blast furnace dust and high phosphorus oolitic hematite, which not only recovered iron comprehensively from blast furnace dust and high-phosphorus oolitic hematite, but also utilized fixed carbon of blast furnace dust. A systematic research on the effect of blast furnace dust dosages, reduction roasting temperature, and reduction roasting time in coreduction roasting process is done, which has achieved optimum process conditions. The results showed, with the roasting condition of 30 mass% blast furnace dust, being roasted for 60min at 1150?, that a DRI of 92.16% iron grade,87.89% iron recovery and 0.072% P content can be obtained in the optimum process conditions. CaCO₃ can decrease the P content of direct reduced iron ?DRI?, and Na₂CO₃ can promote hematite reduction and improves the iron recovery. This study found that the blast furnace dust and high phosphorus oolitic hematite can complete coreduction when the C/Fe ratio is 1.04. It is found, with BF dust as reductant, that the coreduction has better roasting effect than coal.The functions of Coal slimes and BF dust during the coreduction roasting process were investigated by XRD and SEM-EDS analyses. The results showed the quartz existed in coal slime ash had accelerated the reduction of fluorapatite to phosphorus when the reduction system has a sufficient reduction atmosphere, which will increase phosphorus content of DRI. The concept of C/Fe ratio was introduced to find out the mechanism of blast furnace dust in coreduction roasting process. The results showed that volatile component in coal slime was conducive to the increase of iron recovery while adverseed to the decrease of phosphorus. The results also showed that solid-solid state reaction occurs easily with the blast furnace dust as reductant during the coreduction, while gas-solid state reaction occurs easily with the coal as reductant at the same roasting condition. Solid-solid state reaction is conducive to get a high iron recovery and the decrease of P content of DRI, but gas-solid state reaction is detrimental to decrease of P content of DRI.