The Effect of Cation Species on the Sulfide Capacity in CaO-FeO-Al 2 O 3 -SiO 2 Melts

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1 The Effect of Cation Species on the Sulfide Capacity in CaO-FeO-Al 2 Melts Joon Sung Choi*, Youngjoo Park, Sunghee Lee and Dong Joon Min Department of Materials Science and Engineering

2 Contents

3 Introduction Slag Formation in Iron- and Steelmaking Process Ores: Δ 0.016% (P, Al 2 )/yr Coals : Δ 0.015% S/yr, Δ 0.08% Ash/yr, Continuous Casting EAF Coals (Carbon + Ash) (Al 2,, S) Iron Ores (Al 2, FeO X, P) Blast Furnace Al 2 Inclusions (Ca Aluminate, Spinel) Converter CaO Limestone (CaC ) Fe t O Ladle Increase in FeO,Al 2 & S Contents in Material Desulfurization in High-FeO, Al 2 Bearing Slags?

Literature Review T 3+ Ionic Characteristics (T = Al, Fe) B.O. Mysen (1980) peraluminous peralkaline CCCC 0.

Wagner (1976) Cationic Effect on CC SS 2 Y.J. Park and D.J.Min (2016) Y.B. Kang and J.H.

N) OO 2 S OO SS 2 CC SS 22 = ff (aa OO 22 ) Slag Basicity Si Si Si Si Ca 2+ Free M 2+ S 2- Ca 2+ Free Ca 2+ S 2- Free M 2+ T 3+ ions

4 Literature Review T 3+ Ionic Characteristics (T = Al, Fe) B.O. Mysen (1980) peraluminous peralkaline CCCC 0.5 NNNNNN + AAAA XXXX 44 AAAA CCCC D.B.Dingwell (1987) Sulfide Capacity & Basicity C.J.B. Fincham (1954) CC SS 22 = (wwwwwww) ( pp OO2) 1/2 pp SS 2 = Slag Property C. Wagner (1976) Cationic Effect on CC SS 2 Y.J. Park and D.J.Min (2016) Y.B. Kang and J.H.Park (2011) CC SS 22 = ff (aa OO 2, γγ SS 22 ) Low CaO Cation Structure Ca 2+ Increases High CaO Fe Network Former (4 C.N) OO 2 S OO SS 2 CC SS 22 = ff (aa OO 22 ) Slag Basicity Si Si Si Si Ca 2+ Free M 2+ S 2- Ca 2+ Free Ca 2+ S 2- Free M 2+ T 3+ ions form anionic structural unit TO 4 5- CC SS 22 = aa OO22 KK γγ SS 22 CC SS 22 = aa OO22 KK γγ SS 22 Study on the Relationship Between Sulfide Capacity and the Structure of High-FeO,Al 2 Bearing Slags

T 3+ Ionic Interaction Sulfide Capacity Slag Structure Partially Covalent Spectra Analysis γγ SS 22 (Stability of Sulfur) CC SS 22

5 Objective Pauling s Principles for Molten Slag Electronegativity & Neutrality Ionic Bonding Covalent Bonding Basic Oxide Amphoteric Oxide Acidic Oxide Ionic Interaction of M 2+ with S 2- M 2+ M 2+ S 2- vs. T 3+ Ionic Interaction Sulfide Capacity Slag Structure Partially Covalent Spectra Analysis γγ SS 22 (Stability of Sulfur) CC SS 22 = aa OO 22 KK γγ SS 22 NBO/T, Al C.N Thermodynamic & Structural Approach to Figure Out the preference of M 2+ Figure out the Cationic Effect of M 2+ (M : Fe,Ca) on the Sulfide Capacity

Theoretical Background T 3+ 1 Charge Compensation Effect 2 Partially Covalent Ionic Interaction of M 2+ with S 2- M 2+ M 2+ M + interacts with TO 4 5- prior to S 2- charge balancing join (Ca 2+ +Fe

6 Theoretical Background T 3+ 1 Charge Compensation Effect 2 Partially Covalent Ionic Interaction of M 2+ with S 2- M 2+ M 2+ M + interacts with TO 4 5- prior to S 2- charge balancing join (Ca 2+ +Fe 2+ )/(Fe 3+ +Al 2 )=1 S 2- Proportion of T-O-T Linkage T-O-T Linkage CaO-Al 2 system ( /X Al2 =1.0) Proportion of T-O-T Linkage (S.K.Lee model) Al-O-Al Al-O-Si Si-O-Si Al-O-Al Al-O-Si X SiO2 Thermodynamic Property (C.H.P. Lupis model) Stability function Si-O-Si Ψ(Stability) Charge compensation effect on CC SS 22 (= aa OO 22/γγ SS 22 ) Slag dominant structure (Matrix) Figure out the Charge Compensation Effect of M 2+ (M : Fe,Ca) on the Sulfide Capacity

+ 2CO (g) = CO 2 (g) + ½ S 2 (g) ΔG = 258.5 KJ/mol Slag Compositions Sulfur Contents Fe 2+ /T.Fe Content Temp.

7 Experimental Slag Compositions CaO- FeO -Al 2 system 1 Charge Compensation (FeO Al 2 ) Experimental Apparatus Al 2 CaO 2 Cationic Substitution (FeO CaO) Experimental Analysis XRF CS Analyzer FeO K 2 Cr 2 O7 Titration -Sulfur potential controlled by mixture gas SO 2 (g) + 2CO (g) = CO 2 (g) + ½ S 2 (g) ΔG = KJ/mol Slag Compositions Sulfur Contents Fe 2+ /T.Fe Content Temp. Partial Pressure (atm) Ar CO CO 2 SO 2 pp SS22 pp OO22 (pp SS22 /pp OO22 ) 11/22 Slag Structure with Micro-Raman Spectroscopy 1873K

8 Results & Discussion (MO-Al 2 Ternary System) Effect of Al 2 / on Charge Balancing Join (MO/Al 2 =1) (Ca)Anorthite /(Fe)Cordierite Congruent Point CaO FeO Peralkaline (excess M 2+ ) -rich (Si-O-Si) (Si-O-Al) Al 2 -rich (Al-O-Al) (Si-O-Al) Peraluminous (deficient M 2+ ) 1) Silicate Dominant Structure (A/S 0.5) - Si-O-Si, Al-O-Si dominant ( stability Increase) - M 2+ -SiO 4 4- interaction, Fe-O-Si bonding - M 2+ -S 2- attraction increases (lower γγ SS 22 ) Si Free M 2+ Al Al M 2+ Al Fe 2 Al X SiO2 2) Aluminate Dominant Structure (A/S 0.5) - Al-O-Al, Al-O-Si dominant ( stability decrease) - M 2+ - AlO 4 5- interaction, Fe-O-Al bonding - M 2+ -S 2- attraction decreases (larger γγ SS 22 ) The Charge Compensation Domain Determined by Al 2 / (T-O-T Dominant Structure) logc S (CaO-Al 2 system) /X Al2 =1.0 log C S 2-- log a CaO (Al-O-Al) (Si-O-Al) Dominant T-O-T Structure Change (FeO-Al 2 system) X Fe 2+/(X Fe 3++X Al2 )=1.0 log C S 2- log a FeO (Si-O-Si) (Si-O-Al) loga MO (M : Ca, Fe)

9 Results & Discussion (MO-Al 2 Ternary System) Effect of M 2+ on Charge Compensation of AlO 4 5- and CC SS 22 (MO/Al 2 ) CaO-Al 2 Ca 2+ M 2+ Fe 2+ FeO-Al 2 CaO-Al 2 system (1873K) X Al2 /X O SiO CaO-Al 2 system (1873K) Solid Charge Balancing Join (Ca 2+ +Fe 2+ )/(Fe 3+ +Al 2 )=1 0 FeO-Al2 system (1873K) -1-2 X Al2 /X O SiO Satd. Al 2 log C S logc S Solid Free M 2+ S 2- peralkaline peraluminous -4 Solid /X Al X Fe 2+/(X Fe 3++X Al2 ) 1) Charge Compensation Effect of Ca 2+ - CC SS 22 is independent as basicity changes below meta-aluminous join ( XX CCCCCC XX AAAA22 O3 )=1) in high- Al 2 region (A/S > 0.7) CaO, FeO Fe 2, Al 2 2) Charge Compensation Effect of Fe 2+ - CC SS 22 is independent as basicity changes below charge balancing join ( XX FFFF 22+ (XX FFFF XX AAAA22 O3 )=1) The Charge Compensation Effect on the Sulfide Capacity (Deficit or Excess of M 2+ )

10 Results & Discussion (CaO-FeO-Al 2 Quaternary System) Slag Structural Analysis (CaO FeO) Raman Spectroscopy Deconvolution of Raman Spectra (Q 2 ) (CaO-FeO-Al 2 sytem) +X FeO = 0.4, X Al2 /X SiO2 = 0.1 A9 =0.4 CaO Al (CaO-FeO-Al 2 sytem) +X FeO = 0.4 X Al2 /X SiO Fe 2 T-O-T Q n CF3-1 =0.3 CF2-1 =0.2 CF1-1 =0.1 F1-6 = Raman Shift (cm -1 ) 1) Interpretation of Raman Spectra - XX AAAA2 O + XX AAAA2 O = 0.6, Q n unit (Q 1, Q 2, Q 3 ) - Increases FeO : 400~600cm -1 Fe 2 peak decreases, 600~700cm -1 T-O-T peak Increases, 800~1200cm -1 Q n peak left chemical shift FeO ) Q 2 Unit : Fe 2+ --Q 2 -Increases FeO : Prefer Fe 2+ -Q 2 unit -Role of Fe 2+ : Fe 2+ -O-Al 3+ (-41000J/mol), Fe 2+ -O- Fe 3+ (-18660J/mol) Fe 2+ -O-Si 4+ (-41840J/mol) -FeS dominant Fe-O-Si prefer & CaS dominant Q 2 Increases (F/(C+F) >0.5) Fe 2+ - Q 2 Increases Proportion of Q 2 (%) Q 1 +Q 3 =2Q 2 (NBO/T=1~2) Fe 2+ -Q 2 >> Ca 2+ -Q X FeO /(X FeO + ) Fe 2+ / (Fe 3+ + Al 2 ) >1 Fe-O-Si increase Fe 2+ /(Fe 3+ +Al 2 )

11 log {(a FeO * a CaS ) / (a FeS * a CaO )} Results & Discussion (CaO-FeO-Al 2 Quaternary System) Thermodynamic Facotrs (CaO FeO) Stability Function & CaS/FeS Preference (CaO-FeO-Al 2 sytem) +X FeO = 0.4 X Al2 /X SiO CaO+FeS=CaS+FeO, K= aa CCCCCC aa FFFFFF aa CCCCCC aa FFFFFF X FeO /(X FeO + ) 10 CaO 8 1) Stability Function & CaS/FeS 6 4 Ψ(Stability function) - Stability Function : Upward concave as FeO increases (Low Al 2 ), Linearly decreases (High Al 2 ) - CaS/FeS : Increases CaS preferncy rather than FeS as FeO increases Q 1 +Q 3 =2Q 2 FeO Sulfide Capacity (CC SS 22 ) Al 2 O Fe 2+ -Q 2 >> Ca 2+ -Q X FeO /(X FeO + ) 2) FeO CaO Substitution Effect - Ionic Interaction (F/(C+F) 0.5) : ε Ca S 2 <ε Fe S 2, γ MS,C S 2 (γ FeS ) as FeO Increases - Fe-Q 2 effect (F/(C+F) 0.5) : γ MS,C S 2 (γ CaS ) as FeO Increases (F/(C+F) <0.5) : Fe 2+ -S 2- Ionic Interaction (γγ FFFFFF ), (F/(C+F) >0.5) : Fe-Q 2 Effect (γγ CCCCCC ) logc S (CaO-FeO-Al 2 sytem) +X FeO = 0.4 X Al2 /X SiO Ca 2+ Si Al Free Fe 2+ S 2- Excess Ca 2+ Fe 2+ -S 2- (Ionic Interaction) CaO -FeO at T=1773K, X SiO2 =0.48~0.5 After M.M.Nzotta et al. CaO -FeO at T=1776K, X SiO2 =0.45 After A.Bronson and G.R.St.Pierre CaO -MgO at T=1923K, X SiO2 =0.5 After K.P. Abraham et al. CaO -MnO at T=1873K, X SiO2 =0.47~0.54 After K.P. Abraham et al. MnO -FeO at T=1773K, X SiO2 =0.47~0.54 After M.M.Nzotta et al. Si Fe 2+ Al Free Ca 2+ S 2- Excess Fe 2+ Fe 2+ -Q 2 (Covalent Bonds)

Results & Discussion Iso-Sulfide Capacity Line & Iso-aa MMMM Line (M : Ca,Fe) CaO-Al 2 System FeO-Al 2 System CaO-FeO-Al 2 System FeO - Al 2-1873 K, Iso-FeO activity, Iso-Sulfide Capacity

7 Grossite (CaAl 4 O 7 ) Iso-sulfide capacity line Iso-aa CCCCCC line Anorthite (CaAl 2 Si 2 O 8 ) Mullite (Al 6 Si 2 O 13 ) Hibonite (CaAl 12 O 19 ) Corrundum (Al 2 ) 0.9 0.8 0.7 Cristobalite ( ) 0.

$5 0.4 0.3 0.2 0.1 FeO Al 2 O mole fraction 3 Hercynite (FeAl 2 O 4 ) 2) CaO-FeO-Al 2 Quaternary System - CaO-rich (F/(C+F) 0.$

12 Results & Discussion Iso-Sulfide Capacity Line & Iso-aa MMMM Line (M : Ca,Fe) CaO-Al 2 System FeO-Al 2 System CaO-FeO-Al 2 System FeO - Al K, Iso-FeO activity, Iso-Sulfide Capacity Dicalciumsilicate (Ca 2 SiO 4 ) Lime (CaO) Cristobalite ( ) Grossite (CaAl 4 O 7 ) Iso-sulfide capacity line Iso-aa CCCCCC line Anorthite (CaAl 2 Si 2 O 8 ) Mullite (Al 6 Si 2 O 13 ) Hibonite (CaAl 12 O 19 ) Corrundum (Al 2 ) Cristobalite ( ) ) MO-Al 2 Ternary System (M:Ca,Fe) - CaO-Al 2 : Ca 2+ interact with AlO FeO-Al 2 : Fe 2+ interact with AlO 4 5-, FeO Not stabilize sulfur in peraluminous (γγ SS 22 ) Iso-sulfide capacity line Iso-aa FFFFFF line Cordierite (Fe 2 Al 4 Si 5 O 18 ) Mullite (Al 6 Si 2 O 13 ) Corrundum (Al 2 ) FeO Al 2 O mole fraction 3 Hercynite (FeAl 2 O 4 ) 2) CaO-FeO-Al 2 Quaternary System - CaO-rich (F/(C+F) 0.5) : Ionic Interaction dominant, FeO stabilize sulfur (γγ FFFFFF ) - FeO-rich (F/(C+F) 0.5) : Fe-Q 2 effect, CaO stabilize sulfur (γγ CCCCSS ) The Cationic Substitution Effect on the Sulfide Capacity (Maximum : F/(C+F) = 0.5) CaO FeO Al 2

Conclusion The effect of anionic slag structure and charge compensation behavior on sulfide capacity of CaO-FeO-Al 2 system is investigated by measurement of sulfide capacity and Micro-Raman

13 Conclusion The effect of anionic slag structure and charge compensation behavior on sulfide capacity of CaO-FeO-Al 2 system is investigated by measurement of sulfide capacity and Micro-Raman spectroscopy. From the results of present work, founding are summarized as followings: 01 The charge compensation of M2+ (M:Fe,Ca) : The Inflection Point of the sulfide capacity in the charge balancing join due to the deficit or excess charge compensator. 02 The cationic substitution (CaO FeO) : The Fe-Q 2 units increases as CaO FeO substitution (F/(C+F)>0.5) by figure out the deconvolution of raman spectra 03 The cationic substitution (CaO FeO) : The strong interaction between Fe 2+ and S 2- in the CaO-rich region. The weak interaction between Fe 2+ and S 2- in the FeO-rich region.

14 Thank you

Sulfide Capacity of CaO-SiO 2 -FeO-Al 2 O 3 -MgO satd. Slag

Sulfide Capacity of CaO-SiO 2 -FeO-Al 2 O 3 -MgO satd. Slag ISIJ International, Vol. 56 (06), ISIJ International, No. 4 Vol. 56 (06), No. 4, pp. 50 56 Sulfide Capacity of CaO-SiO -FeO-Al O 3 -MgO satd. Slag Youngjoo PARK and Dong Joon MIN* Department of Materials