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Study on the effect of process on phosphorus behavior activity of components in reduction of high ph

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Tutor: WangHua
School: Kunming University of Science and Technology
Course: Non-ferrous metallurgy
Keywords: High phosphorus iron ore,Smelting reduction,Activity in melting slag,Phosphorus
CLC: TF533
Type: Master's thesis
Year:  2013
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High-phosphorus iron ore, which widely distributes in Inner Mongolia, Jiangxi, Si chuan, Chongqing, Hunan, Yunnan and Guizhou in China, is a kind of typically low grade complex refractory iron ore. High-phosphorus iron ore is abundant in Huimin, Yunnan. However, as the ore grade is low, particle size is fine, composition is complex and the phosphorus content is high, it has not been exploited yet. Presently, the main researched methods used to extract iron and remove phosphorus from High-phosphorus iron ore are benefication, leaching by microbiological or chemical way and metallurgy. But it is hard to make progress in this area, because these methods are not economical by now. Therefore, it is significant for the development of iron and steel industry in China to utilize High-phosphorus iron ore effectively by decreasing phosphorus economically.High attention has been payed to Reduction smelting ironmaking for its unique advantages. Hismelt reduction smelting pilot plant in Kwinana, Australia produced high quality molten iron with0.04%phosphorus from iron ore with0.12%phosphorus. Thus this metallurgical technology showed strong dephosphorization ability. In this paper, Hismelt oxygen-enriched top-blowing reduction smelting technology was stimulated to smelt Huimin high-phosphorus iron ore. Affects of influencing factors, which were particularly slag basicity, mole ratio of carbon and oxygen, smelting temperature, oxygen (purity was99%) blowing time and rate of oxygen (purity was99%) flow, on the formation and migration of phosphorus phase in the molten iron bath were studied. The phosphorus distribution coefficient formula was deduced on the base of slag ionic theory, and the main influencing factors in the formula, particularly, ferrous oxide activity, phosphorus capacity of slag and phosphorus distribution coefficient in molten iron were theoretically analysed, so that influence rule on phosphorus distribution ratio of slag component activity during oxygen-enriched top-blowing reduction smelting was revealed.Through analyzing experimental data obtained from high-phosphorus iron ore smelting and thermomechanical analysis on phosphorus distribution ratio between slag and molten iron, we can come to the following conclusions:(1)X-ray diffraction analysis of Hui Min high-phosphorus iron ore showed:ferric content in the ore was41.02%and the main iron phase was hematite and ferrihydrite; most of the phosphorus was aluminium phosphate and a small part of phosphorus was flake calcium phosphate with a fine mosaic size and acicular structure; main components of the gangue were compound of silicon, aluminium and calcium, among which silicon content (17.98%) was the highest.(2) Temperature had a significant impact on dephosphorizing effect.When the temperature was1400-1600℃, the dephosphorizing effect was relatively remarkable and when the temperature was1550℃, the dephosphorizing rate was highest. Besides, when the temperature was higher than1550℃, phosphorus content in the molten iron increased. Phosphorus content in the molten iron was low when the basicity was1.1to1.2. When the oxygen blowing time was20min and rate of oxygen flow was250L/h, oxidability of slag could be significantly improved and ferrous oxide content was high about15%in slag, which was typical high-ferrous oxide slag with low basicity. Carbon oxygen atom rate, which affected dephosphorization insignificantly, was controlled at1.0. In conclusion, the optimum condition were:temperature was1550℃, carbon oxygen atom rate was1.0, basicity was1.1, oxygen blowing time was20min and oxygen flow rate was250L/h. Under the optimum condition, molten iron with0.068%phosphorus was produced, while the dephosphorizing rate reached up to93.2%.(3) Phosphorus distribution rate in slag increased with the increasing of ferrous-oxide activity. Logarithm of ferrous-oxide activity is proportional to logarithm of phosphorus distribution ratio, and a straight line with a slope of1.65close to the theoretical value2.5was fixed according to experimental data.(4)Through optical basicity analysis of slag, it was found that oxygen ion activity increased with the increasing of slag basicity, which revealed that phosphorus capacity of slag increased. Dissolved oxygen and carbon in the molten iron could increase activity coefficient of phosphorus in the molten iron, so that transfer of phosphorus from molten iron to slag was improved and phosphorus distribution ratio between slag and molten iron was increased.
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