Phosphorus redistribution during iron ore sintering and BOF slags leaching

• Main Authors: Tung-Hsin Su, 蘇同新
• Other Authors: Huai-Jen Yang
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/41775225057297844316

碩士 === 國立成功大學 === 地球科學系碩博士班 === 96 === The basic oxygen steel-making process removes sulfur, phosphorous, carbon, and silicon impurities from molten iron into “slag”, which makes up 10% of the total weight during steel-making, and the recycling of the so-called “BOF” slag has been an important issue for the operation of a steel-making plant. The coarse-grained BOF slag can be used as road building materials and raw material for cement. The fine-grained BOF slag, however, has not been efficiently recycled. The BOF slag is composed of 40~50％ CaO, 15％ Fe2O3, 10％ SiO2, 6~7％ MgO, < 1% sulfur, and ~1% phosphorous. The high CaO and MgO contents of the BOF slag make it a possible candidate replacing fluxes, such as marble, serpentine, and dolomite, in iron-ore sintering. However, phosphorous has to be removed prior recycling to the sintering process as it reduces the ductility and corrosiveness-resistance of steel. In order to found a basis for recycling BOF slag to iron-ore sintering, this research investigates the distribution of phosphorous during iron-ore sintering and leaching of BOF slag. In an attempt to remove phosphorous, hydrogen peroxide, carbamide, and coke were added into the raw materials for sintering. The results show that glass derived from partial melting of sintered materials is the major host of phosphorous. Calcium ferrite and some crystals of a dendritic phase might contain less than 0.4% of phosphorous. There is no significant variation in phosphorous concentration prior and post the sintering process, implying that insufficient hydrogen peroxide and carbamide was added or that this approach is not appropriate. Interaction between BOF slag and coke at 1350 ℃ did not resulted in phosphorous removal, either, possibly because the temperature did not reach that for thermal equilibration between these two phases. Leaching BOF slag with water and HCl did dissolve small amounts of dicalcium silicate with the formation of Ca(OH)2. Phosphorous is concentrated in dicalcium silicate. However, the phosphorous content of the residues after acid and water leaching increases because of decreasing the weight of the residues. It is inferred that leaching the BOF slag with large amount of running water could completely dissolve the dicalcium silicate in BOF-slag. Dephosphorization can therefore be achieved. It is concluded that phosphorous is an incompatible element during iron-ore sintering and prefers to enter melts, which form glass after quenching. Dicalcium silicate is the dominant phosphorous-hosting phase in the water and acid-leached residues. Phosphorous concentration will not decrease until completely dissolution of dicalcium silicate from leaching residues.