In order to study the effect of highly oxidizing dephosphorizing converter slag on the migration behaviour of phosphorus in molten steel, an industrial test was carried out on a 300t dephosphorizing converter in a steel plant by the duplex method. Theoretical analysis shows that when the temperature is low, the basicity is 1.5 and the FeO content is 25%-30%, the phosphorus capacity of slag is stable. The industrial test results show that when the temperature is 1630K-1665K, the basicity is 1.05-1.25, the FeO content is 35%-40%, and the dephosphorization efficiency of the converter can generally reach above 60%. XRD and SEM-EDS analysis results showed that phosphorus was mainly enriched in 2CaO•SiO 2 -3CaO•P 2 O 5 solid solution. Infrared analysis results show that under the condition of high FeO and low basicity, properly increasing of basicity is beneficial to reduce the degree of polymerization of dephosphorization slag.
The CaO-SiO 2 -FeO-P 2 O 5 slag was measured by Raman spectra, and the changes in the structure and behaviour of phosphorus were analysed under different slag components. The results proved that phosphorus exists in two enrichment behaviours in the slag, which can be judged according to the mole fractions of Q 1 (Si), Q 2 (Si), and Q 3 (Si). When the content of P 2 O 5 increases from 4.5% to 8.5%, the Q 0 (P) intensity changes most significantly. Since the Fe-O bond energy (390.4 kJ mol −1 ) is weaker than the P-O (410 kJ mol −1 ) bond energy, the silicon-oxygen network structure will show a behaviour change of depolymerization first and then polymerization. XRD analysis shows that with the increase of P 2 O 5 content, different calcium silicate phases are added and decreased in the slag, and the content of a small amount of calcium ferrite phase changes, Si x O z− y bonds or separates from each other, which is consistent with the change law of Raman analysis.
In order to make better use of converter dust to achieve effective predephosphorization of molten iron, the influence of the addition ratio of dedusting ash and oxide scale on dephosphorization of molten iron was compared, so as to reveal the reasons for the decrease of dephosphorization rate caused by dust. Through theoretical analysis, XRD, SEM-EDS, Raman and infrared spectroscopy, the influence of mineral phase structure, polymerization degree and phosphorus structure of pre-dephosphorization final slag on predephosphorization was studied. The results show that when the proportion of dedusting ash in the oxidant increases from 0 to 25%, the dephosphorization rate decreases from 50.8% to 38.71%, and the dephosphorization rate increases to 50% after adding fluorite. The increase in the proportion of dedusting ash will lead to the decrease of phosphorus-rich phase and the increase of RO phase and iron-rich phase, which will affect the dephosphorization effect. When the dedusting ash ratio increased from 0% to 25%, the proportion of Q 0 (Si), Q 0 (P), Q 1 (P) and [FeO 6 ] 9structures in the pre-dephosphorization final slag increased, which was beneficial to the diffusion in the slag, but unfavorable to the migration of phosphorus. In addition, by adding fluorite in the experiment with 25% dedusting ash, it was found that the molar fractions of Q 1 (Si), Q 3 (Si), Q 0 (P) and Q 2 (P) in the pre-dephosphorization final slag increased, and the phosphorus migrating into the silicon-oxygen network structure gradually increased. This study can provide reference for iron and steel enterprises to realize the secondary utilization of dedusting ash.
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