Activities of Fe_xO in complex slags used during the final stages of external dephosphorization of hot metal

Abstract

Measurements of the activities of FexO in complex slags during the final stages of external dephosphorization by using a disposable electrochemical oxygen probe. Positive deviations of the FexO activities from the Raoult law. Iso‐activity curves drawn on the “ternary” diagram, (CaO + MgO + MnO + CaF2) + FexO + (SiO2 + P2O5) at 1673 K. Calculations of the activities of P2O5 in complex slags with an assumption of thermodynamic equilibrium between slags and hot metal. Beneficial effect of CaF2 in the slags with respect to lowering of the P2O5 activity.

Activities of FexO in Industrial Slags Used for External Removal of Phosphorous from Hot Metal

“…The activity coefficients of FexO of the present slags are not more than 3. Turkdogan and Pearson [4] has provided isoactivity curves for FexO in the pseudoternary system of (CaO + MgO + MnO)FexO(SiO 2 + P 2 O 5 ) at 1873 K. Iwase et al [1] also drew such diagram for (CaO + MgO + MnO + CaF 2 ) FexO(SiO 2 + P 2 O 5 ) at 1673 K. Yamada et al [18] gave the relation between γ FexO and (mass%CaO)/(mass%SiO 2 ) based on industrial data at open hearth furnace and BOF. By making use of these information, values of FexO activ ities for the present slags can be derived.…”

“…Such thermochemical information about the effect of CaF 2 on FexO activities for complex slags has been reported by several researchers [1,[3][4][5][6]. The research by Turkdogan and Pearson [2,3] concerned temperatures above 1800K.…”

“…This implies that the key to better control of the phosphorus levels in hot metal is a knowledge of the activities of FexO in slag. In spite of the industrial need for improved phosphorus removal, the physicochemistry of slags utilized for exter nal dephosphorization has not been studied sufficiently, except for research by Iwase et al [1], who investigated relatively high CaF 2 containing slags at 1673 K.…”

“…The research by Turkdogan and Pearson [2,3] concerned temperatures above 1800K. Iwase et al [1] mainly studied homogeneous liquid slag. Iwase et al [6] also reported the FexO activities of a CaOCaF 2 SiO 2 FeO quaternary system in which some slags comprised liquid and solid phases.…”

Thermodynamic Properties of Solid Solutions between Di-calcium Silicate and Tri-calcium Phosphate

“…By solving equation (51) under the condition that log a CaO = 0, this composition could be estimated as Y = 0.131 (at point c, T = 1573 K) (57) Inserting equation (57) to equations (52) and (53), the SiO 2 and P 2 O 5 activities in the threephase assemblage of 〈C 2 S-C 3 P 〉ss + CaO + Ca 3 SiO 5 (triangle cCaOCa 3 SiO 5 ) were obtained as log a SiO 2 = −4.80 (at point c; Y = 0.131, T = 1573 K) (58) log a P 2 O 5 = −26.27 (at point c; Y = 0.131, T = 1573 K) (59)The CaO activity in the regions including CaO should be unity. Thus, equations(12) and(16), respectively, could be rewritten as log a SiO 2 = log a Ca 2 SiO 4 − log K(10) (60) log a P 2 O 5 = log a Ca 3 P 2 O 8 − log K(14) (61) Combining equations (45), (46), (60) and (61), the SiO 2 and P 2 O 5 activities within the twophase resion of 〈C 2 S-C 3 P 〉ss + CaO (regions cdCaO and ghCaO) were given as log a SiO 2 = −4.74 + log(1 − Y ) + 1.91 × 10 −1 × Y 2 (62) log a P 2 O 5 = −24.79 + 2 log Y + 3.81 × 10 −1 × (1 − Y ) 2 (63)…”