Prediction model of sulphur distribution ratio between CaO–FeO–Fe₂O₃–Al₂O₃–P₂O₅slags and liquid iron over large variation range of oxygen potential during secondary refining process of molten steel based on ion and molecule coexistence theory

Abstract

A thermodynamic model for predicting sulphur distribution ratio L S between CaO-FeO-Fe 2 O 3 -Al O -P O slags and liquid iron, i.e. the ion and molecule coexistence theory (IMCT)-2 3 2 5 L S model, has been developed for slags in a large variation range of slag oxidisation ability based on the IMCT. The developed IMCT-L S model has been verified with measured data of oxygen, pho-The results indicate that the desulphurisation reaction is mainly controlled by reactionthe reducing zone with the optimised standard molar Gibbs free energy change of D r G H m;CaS ¼ 147 023:63 2 27:94T ðJ mol 21 Þ; the desulphurisation reaction is dominated by reactionthe oxidising zone with the reported standard molar Gibbs free energy change of D r G H m;FeS ¼ 115 526 2 33:35T ðJ mol 21 Þ. The influence of CaO on the desulphurisation ability of the slags can be counteracted by that of Fe O because higher CaO content corresponds to lower Fe O content in the slags. An asymmetric V type relationship between sulphur distribution ratio L S and the mass action concentration ratio N FeO =N CaO or N Fe 2 O 3 =N CaO or N FeO•Fe 2 O 3 =N CaO or N Fe t O =N CaO , or the mass percentage ratio (%FeO)/(%CaO) or (%Fe 2 O 3 )/(%CaO) or (%Fe O)/(%CaO) or the simplified complex basicity ð%CaOÞ=½ð%Al 2 O 3 Þ þ ð%P 2 O 5 Þ or optical basicity can be established for the slags equilibrated with liquid iron in a temperature range from 1811 to 1927 K (1538 to 16548C). The abovementioned mass action concentration ratios or mass percentage ratios of various iron oxides to basic oxide CaO can be recommended to represent the comprehensive effect of iron oxides Fe O and basic oxide CaO on desulphurisation ability of the slags.

Titanium Distribution Ratio Model of Ladle Furnace Slags for Tire Cord Steel Production Based on the Ion–Molecule Coexistence Theory at 1853 K

“…It is quite essential to establish a thermodynamic model for calculating the titanium distribution ratio between steel and slag. The ion-molecule coexistence theory (IMCT) has been efficaciously applied to describe phosphate capacity, manganese distribution, sulfide capacity, and so on, as shown in Table 1 [10][11][12][13][14][15][16][17][18][19][20][21][22][23]. In the IMCT, the defined mass action-concentration (MAC) is consistent with the classical concept of activity in the slag.…”

A Further Evaluation of the Coupling Relationship between Dephosphorization and Desulfurization Abilities or Potentials for CaO-based Slags: Influence of Slag Chemical Composition

“…The chemical compositions of CaO-FeO-Fe 2 O 3 -Al 2 O 3 -P 2 O 5 slags equilibrated with liquid iron by Ban-ya et al [1] and three parameters for representing slag oxidization ability as the mass percentage of Fe t O through (% Fe t O) = (% FeO) + 0.9(% Fe 2 O 3 ); calculated [3] comprehensive mass action concentration N Fe t O of Fe t O and oxygen potential p O 2 of the CaO-based slags over a temperature range from 1811 to 1927 K (1538 to 1654 • C) are summarized in Table 1. In addition, the determined [2] and calculated [2] coupling relationship terms as log L P + 5 log L S or log C zone based on measured log L P, measured or measured log L S, measured by Ban-ya et al [1], predicted log L IMCT P, calculated [3] or log L IMCT S, calculated [4] by the IMCT models, determined log C PO 3− 4 , determined [3] or determined log C S 2− , determined [5] after Ban-ya et al [1], and predicted log C IMCT PO 3− 4 , calculated [3] or log C IMCT S 2− , calculated [5] by the IMCT models are also tabulated in Table 2 for comparison. Thus, the effects of chemical composition of slags described by three group parameters including the reaction abilities of components represented by the mass action concentrations N i , two kinds of slag basicity as simplified complex basicity (% CaO)/[(% P 2 O 5 ) + (% Al 2 O 3 )] and optical basicity Λ, and the comprehensive effect of iron oxides Fe t O and basic oxide CaO on proposed coupling relationships [2] for the CaO-based slags are further evaluated in the next section.…”

“…Comparison between determined and calculated coupling relationship terms between dephosphorization and desulfurization abilities or potentials for CaO-FeO-Fe 2 O 3 -Al 2 O 3 -P 2 O 5 slags over a large range of slag oxidization ability equilibrated with liquid iron during the secondary refining process of molten steel based on measured log L P, measured or log L S, measured by Ban-ya et al [1], predicted log L IMCT P, calculated [3] or log L IMCT S, calculated [4] by the IMCT models, determined log C PO 3− 4 , determined [3] or determined log C S 2− , determined [5] after Ban-ya et al [1], and predicted log C IMCT PO 3− 4 , calculated [3] or log C IMCT S 2− , calculated [5] It was verified [3] that good corresponding relationships between mass percentages of components and calculated [3] mass action concentrations N i of CaO, FeO, Fe 2 O 3 , and Al 2 O 3 as components are established for the CaO-based slags. Thus, the calculated [3] mass action concentrations N i of components based on the IMCT [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] can be applied to the representation of the chemical composition of the CaO-based slags, like the mass percentage (% i) of components. As a newly-formed structural unit FeO • Fe 2 O 3 , according to the IMCT [2][3][4][5][6][7][8][9][10][11]…”

“…Nevertheless, no conclusions or results on the linkage between dephosphorization and desulfurization abilities or potentials of the slags were provided by Ban-ya et al [1]. The coupling relationships between dephosphorization and desulfurization abilities or potentials for CaO-FeO-Fe 2 O 3 -Al 2 O 3 -P 2 O 5 slags [1] over a large range of slag oxidization ability during the secondary refining process of molten steel have been recently proposed by Yang et al [2] as log L P + 5 log L S or log C [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The proposed coupling relationships [2] for the CaO-based slags have been verified to be independent of slag oxidization ability as expected.…”

“…The ultimate objectives of this study can be summarized as (1) to further verify the linkage between dephosphorization and desulfurization abilities or potentials for a fixed flux or slags not only regardless of slag oxidization ability as expected but also independent of slag chemical composition; (2) to provide fundamental information for optimizing the chemical composition of slags or fluxes with the aim of enhancing simultaneous dephosphorization and desulfurization abilities or potentials of iron-based melts by a fixed flux or slags; (3) to enrich the foundations of the reaction mechanism during the simultaneous dephosphorization and desulfurization process of iron-based melts by a fixed flux or slags over a large variation range of slag oxidization ability; (4) moreover, to open new application fields of the IMCT [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] for metallurgical slags.…”