Formation Behavior of Phosphorous Compounds at the Interface between Solid 2CaO SiO2 and FeOx-CaO-SiO2-P2O5 Slag at 1673K

Abstract

The role of 2CaO · SiO 2 phase on the formation of P 2 O 5 condensed phase should be clarified to elucidate the microscopic dephosphorization mechanisms and to improve the hot metal dephosphorization efficiency by using CaO-based FeO x -CaO-SiO 2 -P 2 O 5 multi phase flux. In the present study, solid 2CaO · SiO 2 piece was reacted with molten FeO x -CaO-SiO 2 -P 2 O 5 slag for 1 to 60 s at 1673K, and the reaction interface between solid 2CaO · SiO 2 and molten FeO x -CaO-SiO 2 -P 2 O 5 slag was observed and analyzed by SEM and EDS. The dissolution of 2CaO · SiO 2 into the molten slag and the penetration of molten slag into solid 2CaO · SiO 2 simultaneously occurred. The 2CaO · SiO 2 -3CaO · P 2 O 5 was formed from solid 2CaO · SiO 2 and P 2 O 5 in the slag. On the other hand, during the penetration of slag, the P 2 O 5 in the slag reacted with 2CaO · SiO 2 to form 2CaO · SiO 2 -3CaO · P 2 O 5 phase. The P 2 O 5 content of 2CaO · SiO 2 -3CaO · P 2 O 5 phase existing in solid 2CaO · SiO 2 region was lower than that observed at the 2CaO · SiO 2 saturated liquid phase region because of the lower P 2 O 5 content of penetrating slag than that of 2CaO · SiO 2 saturated liquid slag. The 2CaO · SiO 2 saturated liquid slag region and the region where P 2 O 5 condensed phase was observed at the interface expanded with time.

Reaction Behavior of P2O5 at the Interface between Solid 2CaO·SiO2 and Liquid CaO–SiO2–FeOx–P2O5 Slags Saturated with Solid 5CaO·SiO2·P2O5 at 1 573 K

“…Comparing the present results with the previous ones, 11,12) the region with P 2 O 5 condensed phases at the interface between 2CaO · SiO 2 and the heterogeneous slag is much wider than that at the interface between 2CaO · SiO 2 and the homogeneous slag. Such difference indicates that the formation of P 2 O 5 condensed phases is enhanced and the back dissolution of P 2 O 5 condensed phases into the surrounding slag is restrained by adjusting the liquid slag to be saturated with 5CaO · SiO 2 · P 2 O 5 .…”

“…The existence of high P 2 O 5 content positions was revealed through EDS analysis. As mentioned in previous studies, 11,12) the precipitated P 2 O 5 condensed phase was smaller than the electron beam size and thus the obtained compositions by EDS were the average composition between P 2 O 5 condensed phase and surrounding liquid phase. Therefore, in the present study the positions where the FeO content is less than 16.0 mass%, CaO/SiO 2 molar ratio is larger than The solid line is drawn from the tendency of FeO content.…”

“…The composition points are mostly off the tie line between 2CaO · SiO 2 and 3CaO · P 2 O 5 , which is the same as reported in the previous study. 11,12) Such result indicates that the composition obtained by EDS analysis at the positions with the formation of P 2 O 5 condensed phases is the average composition of 2CaO · SiO 2 -3CaO · P 2 O 5 solid solution or compound and the surrounding liquid phase because the size of the formed solid P 2 O 5 rich particle is not large enough to be detected separately by the present analysis method. The ratio of solid P 2 O 5 condensed phases in certain area for slag C is larger than that for the other two cases on account of the fact that comparatively the composition points are closer to the tie line while far away from the liquid phase in the case of slag C. Thus it can be said that the formation of P 2 O 5 condensed phases is the most intense when using slag C.…”

“…Upon the unsolved problem, the reaction between solid 2CaO · SiO 2 and CaO-SiO 2 -FeO x -P 2 O 5 slag is investigated by the present authors. In the previous study, 11,12) the reaction between solid 2CaO · SiO 2 and homogeneous CaOSiO 2 -FeO x -P 2 O 5 slag was studied by dipping solid 2CaO · SiO 2 disc into the liquid slag for different time at 1 573 or 1 673 K. It is understood that the P 2 O 5 condensed phases (2CaO · SiO 2 -3CaO · P 2 O 5 solid solution or compounds) are formed at the 2CaO · SiO 2 /slag interface in less than 1 s. The occurrence of back dissolution of the solid P 2 O 5 rich phase soon after its formation was observed, indicating that the transfer of phosphorus in flux from liquid phase to solid phase is reversible. In the practical production, this property can be utilized to increase the concentration of phosphorus in the solid phase in hot metal dephos-phorization slag.…”

Effect of Al₂O₃ on Enrichment of Phosphorus in Hot Metal Dephosphorization Slag

“…Pahlevani et al 28) measured the distribution of P 2 O 5 between nC 2 S-C 3 P solid solution and liquid slags. Tsukihashi and co-workers et al [29][30][31][32] studied reaction behavior of P 2 O 5 at interface between solid C 2 S containing B 2 O 3 and CaO-SiO 2 -FeO x -P 2 O 5 slags saturated with nC 2 S-C 3 P solid solution.…”