Cationic Effect of Ferrous Ions on Sulfide Capacity of CaO-Fe t O-Al 2 O 3 -SiO 2 Slag System
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O-Al2O3-SiO2 quaternary system is a fundamental slag system in pyrometallurgy and is present in geological system,[1,2] coal ash,[3] and sintered ore.[4] Numerous studies on the properties and structure of high-temperature melts have been reported.[5] Many researchers have investigated the physico-chemical properties of high-temperature slag melts, and studies on the effects of FeO and Al2O3 on the physical[6,7] and chemical properties of the melts[8–10] have been performed in accordance with industrial objectives. The thermodynamic properties of FeO[11–13] in pyrometallurgical processes are considered to indicate the basic behavior of Fe2+ ions. Ban-Ya derived an integrated empirical model based on a regular solution model,[13] and Park et al. reported the maximum value of FeO activity due to the enhancement by stoichiometric stabilization[14] of orthosilicate, i.e., (Ca, Mg, Mn)2SiO4, at (CaO + MgO + MnO)/(SiO2 + P2O5 + Al2O3) = 2.0.[11] FeO in slags was considered to be a strongly basic oxide and the properties of slags have
JOON SUNG CHOI and DONG JOON MIN are with the Department of Materials Science and Engineering, Yonsei University, 50, Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea. Contact e-mail: [email protected] Manuscript submitted May 7, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
been underestimated.[8,9,11,12] However, it has been reported that the oxidized states (FeO and Fe2O3) of iron oxide affect the optical properties of glass[15,16] as well as interfacial reactions in the steelmaking process. In several geological studies, the viscosity of melts increased with the Fe3+/(Fe2+ + Fe3+) ratio.[7,17] The redox equilibria of FeO can be expressed by Eqs. [1] and [2]. Many researchers have reported that the Fe3+/Fe2+ ratio increases by a factor of 1/4 with the increase of the oxygen partial pressure (pO2 )[18,19] and decreases with the increase of the slag basicity.[20] The Fe2+/(Fe2+ + Fe3+) ratio increases and converges to a constant value with the increase of the total Fe content, according to an analysis based on a mathematical interpretation of the redox equilibria.[20] 1 1 Fe2þ þ O2 ðgÞ ¼ Fe3þ þ O2 ðacidic slagsÞ 4 2
½1
1 7 Fe2þ þ O2 ðgÞ þ O2 ¼ FeO5 4 ðbasic slagsÞ 4 2
½2
Fe2O3 is known as an amphoteric oxide similar to Al2O3, and has been reported to act as both a network modifier (Fe3+, Al3+) and network former (FeO45, AlO45) depending on the basicity (aO2 ) and concentration of cations (Ca2+ and Na+).[2] The electrical neutrality rule according to Pauling’s principle[21] suggests that silicon tetrahedral structures ([IV]Si;SiO44) satisfy electrical neutrality with the oxygen anion, but 5-
and 6-coordinated aluminum structures ([V]Al, [VI]Al; Al3+) form aluminum tetrahedra ([IV]Al; AlO45) that satisfy the electrical neutrality from the charge compensation of cations (Ca2+ and Fe2+). Recently, Toplis et al.[22] reported that the charge-compensation behavior described by Eq. [3] was due to the excess or absence of Ca2+ according to the CaO/Al2O3 ratio; ðCaÞ0:5 N
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