Effect of Calcium Fluoride on Phosphorus Distribution between MgO Saturated Slags of the System CaO-MgO-FeOx-SiO2 and Liquid Iron

Abstract

SynopsisExperiments have been made to study the phosphorus distribution between liquid iron and Mg0 saturated Ca0-Mg0-Fe0x-Si02 slags containing 1 to 4 % CaF2 in the temperature range 1 550 to 1 650 °C. The effect of CaF2 on the equilibrium quotient k5(= (%P205) f ([%P]2(%FeO)5}) was found to be nearly equal to that of Ca0 on the weight percentage base. The equilibrium quotient kp is expressed as The effect of CaF2 on the activity coefficient o f P205 was also studied by the Turkdogan and Pearson's treatment. The following expression for the activity coefficient of P205 is given for the slaps containing CaF2.log TP2o5 = -1.01(23NCao+21NcaF2+l7WMgo+BNFeo) -26300/T+ 11.24It was found from the plot of the activity coefficient of FeO vs. the mole fraction of Si02 that the activity of FeO increases with the addition of CaF2. I. IntroductionThe beneficial effect of fluorspar addition to steelmaking slags has been traditionally recognized. Laboratory and plant scale investigations on fluorspar substitutes have been made on account of the short supply and rising cost of metallurgical fluorspar as well as the environmental problem. The addition of fluorspar to steelmaking slags increases the degree of dephosphorization and desulfurization; it is not clear, however, whether fluorspar affects the slag-metal equilibrium ratios, or whether it simply causes the increase of the fluidity of slags and, consequently, faster approach to the equilibrium. The fundamental study on the influence of CaF2 on the phosphorus partitions between slaps and metal has been first made by Winkler and Chipman,1 who have reported the partitions between liquid iron and Mg0 saturated Ca0--Mg0-FeOx Si02-P205 slags with 4 to 18 % CaF2 in the temperature range of 1 530 to 1 640 °C. The contents of P205 in the slags are between 6 wt% and 19 wt%. Their conclusion is that the addition of fluorspar have no adverse effect on the dephosphorizing power of the slag. However, the small number of melts (7 melts) investigated by Winkler and Chipman have not allowed the quantitative deductions for the exact effect of CaF2 on the slag-metal equilibrium. The further systematic works are necessary to the de-

Effect of Fluorine on the Minerals Phase and Citric Acid Solubility of CaO&ndash;SiO₂&ndash;Fe_<i>t</i>O&ndash;P₂O₅&ndash;CaF₂ System

“…Due to the complex composition, the XRD result gives a high probability of several phases. Phosphorus is found to be distributed in (C 2 S-C 3 P)ss (both Ca 15 (PO 4 ) 2 (SiO 4 ) 6 and Ca 5 (PO 4 ) 2 SiO 4 ) and Fe 4 (PO 4 ) 2 O. Figure 2 shows the X-ray diffraction patterns of the fluorine-containing slags (Nos.…”

“…1,2) There exists extensive literature on effect of CaF 2 on dephosphorization of hot metal. It has been found that in slags with CaF 2 additions between 1-4 wt%, the phosphate capacity could be increased up to a factor of three.…”

“…[4][5][6] Sen indicated that CaF 2 was the twice as effective as CaO for dephosphorization of steel in an induction furnace by using CaO-FeO-SiO 2 -CaF 2 slag. 7) Kitamura et al indicated that the higher CaF 2 /(CaOϩCaF 2 ) concentration ratio in flux were effective for the dephosphorization without the oxidization of chromium in chromium containing hot metal pretreatment.…”

Phosphate Capacity of CaO–SiO2–MnO–FeO Slag Saturated with MgO

“…slags at 1 823 K increases and is followed by a constant value within some experimental scatters. 5,6) However, the phosphate capacity of the Na 2 O-SiO 2 -Fe t O-5(Ϯ1)mass%MnO-MgO satd. system, which can be considered to be more basic than lime-based slags, linearly increases with increasing basicity index at 1 873 K. 8) Based on a definition of phosphate capacity given in Eq.…”

“…The phosphate capacity of various MgO-saturated slags measured by several authors was also shown for comparison. [5][6][7][8][9][10][11][12] Here, the phosphate capacity of the slag was calculated from Eqs. (2) and (4).…”