Coupling relationship between dephosphorisation and desulphurisation abilities or potentials for CaO–FeO–Fe₂O₃–Al₂O₃–P₂O₅slags over a large variation range of slag oxidisation ability during secondary refining process of molten steel

Abstract

t O of iron oxides based on the ion and molecule coexistence theory (IMCT). The proposed coupling relationships between dephosphorisation and desulphurisation abilities or potentials of the slags have been verified to be valid using reported data of oxygen, phosphorus and sulphur distribution equilibria between the slags and liquid iron over a temperature range from 1811 to 1927 K (1538-1654 °C) and predicted results of dephosphorisation and desulphurisation abilities or potentials. Not only the proposed coupling relationships between dephosphorisation and desulphurisation potentials but also the correlated coupling relationships between dephosphorisation and desulphurisation abilities for the slags in reducing and oxidising zones have been verified to be indeed independent of slag oxidisation ability.

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

“…It should be specially mentioned that the linkage between phosphate capacity C PO 3− 4 and sulfide capacity C S 2− for slags was first correlated by Sano et al [19] in 1990 as log C which is also derived in details by Yang et al [2] However, Ban-ya et al [20,21] clearly proved and argued that the ratio of the activity coefficient to the standard equilibrium constant, i.e., f %, i /K Θ i or γ i /K Θ i , of dephosphorization and desulfurization products cannot hold constant in multi-components solutions like molten slags, fluxes and salts. Thus, the assumption of the term on the right-hand side of the relationship between C PO 3− 4 and C S 2− by Sano et al [19] being constant is not a theoretically correct conclusion.…”

“…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.…”

“…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.…”

“…Thus, the assumption of the term on the right-hand side of the relationship between C PO 3− 4 and C S 2− by Sano et al [19] being constant is not a theoretically correct conclusion. Furthermore, the intrinsic relationship between the phosphorus distribution ratio L P = (% P 2 O 5 )/[% P] 2 and sulfur distribution ratio L S = (% S)/[% S] for slags with fixed chemical compositions has scarcely been investigated.…”

“…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.…”