Manganese Equilibrium between Molten Iron and MgO-saturated. CaO-FeO-SiO-MnO t2slags* By Hideaki SUITO** and Ryo INOUE

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1 Manganese Equilibrium between Molten Iron and MgO-saturated CaO-FeO-SiO-MnO t2slags* By Hideaki SUITO** and Ryo INOUE Synopsis Manganese distribution between liquid iron and Mg0-saturated Ca0- FetO-Si02 Mn0 slaps containing P205 or S has been obtained in the temperature range to G by use of magnesia crucibles. The manganese distribution ratio was found to increase with increase in Si02 content and decrease in temperature. The good relationship between activity coefficient of Mn0 or equilibrium quotient kmn (= (%Mn0)/ {[%Mn]. (%Fet0)}) and the slag basicity B (= [(%Ca0)+0.3 (%Mg0)] [(%Si02)+(%P205)]) value was observed. I. Introduction Recently the combined process of hot metal pretreatment and top and bottom blown converter has become the important refining technique in steelmaking process. As compared with the conventional top blown process, it has been observed in this top and bottom blown process that the temperature difference between slag and metal becomes less and the degree of slagging improves as a consequence of the decrease of slag volume as well as the increase of bath agitations. This indicates that slag-metal reactions in BOF are considered to be nearly in equilibrium state. The present authors have previously investigated phosphorus1) or vanadium2~ distribution equilibrium between molten iron and Mg0-saturated Ca0-FetO- Si02 slags in the temperature range 1550 to 1650 C. Consequently, the Fee+/Fe3+ ratios and the solubilities of Mg0 were found to be significantly different from those obtained by Winkler and Chipman.3~ In view of controlling the slag-metal reactions in BOF, the manganese distribution ratios together with the activities of Fet0 are supposed to be one of the most important parameters. The objective of this investigation is to obtain the manganese distribution ratio between molten iron and Mg0-saturated Ca0- FetO-Si02-P205(<3wt%)-MnO(2N5wt%) slaps in the temperature range to 1650 C by use of the same experimental method described previously.1) II. Experimental The experimental apparatus and method are the same as those described in detail elsewhere.1'2~ A reagent grade of Mn02 was added to obtain 5 wt% Mn0 or 10 wt% Mn0 in slaps after experiments. In the present experiment, however, the phosphorus or sulfur distribution has been also measured along with the manganese distribution. Then the yield of manganese was found to be about 8O' 100 % in the case of approaching the equilibrium of phosphorus from the metal side, while it was about 30 to 50 % in the case of approaching the phosphorus equilibrium from the slag side and approaching the sulfur equilibrium from the metal side. The methods for the analysis in slag and metal compositions were the same as those described elsewhere.l,2~ Manganese contents in the metal and slag samples were determined by the sodium periodate oxidation absorptiometry, (JIS-G-1213) and (JIS-M- 8215), respectively. III, Results The slag and metal compositions after experiments at 1550, and C are summarized in Table 1. Slags in some experiments at 1600 C contained O.4.-'O.08 wt% S. The slag and metal compositions in these experiments will be reported in the paper on the sulfur distribution equilibria. In other experiments, slags contained P205 ranging from 0.1 to 3 wt%. With respect to the manganese content in slags, 3N4 wt% Mn0 was present in some experiments at C, but wt% Mn0 was present in the experiments where the equilibrium of phosphorus approached from metal side. In other experiments, the manganese content was 2-.3 wt%. The manganese content in metal was less than 0.05 wt% in all experiments. Figure 1 shows the manganese distribution ratios, LMn= (wt%mn0)[%mn] plotted in the (Ca0+ Mg0)-(FeO + Fe203 + Mn0)-(Si02 + P205) pseudoternary systems at 1 550, and C on a weight percent basis. It can be seen from Fig. 1 that the iso-lmn lines tend to increase with approaching to the (FeO+Fe203+Mn0)-(Si02+P205) pseudobinary system and that the value for LMn at a given slag composition decreases with increase of temperature. Activity coefficients of MnO, TMno(s) with respect to solid standard state have been obtained from the standard free energy change, 4G 4) for the reaction given by Eq. (1) and the experimental results listed in Table 1. The following interaction parameters) were used for the calculation: e= -1750/ T'+0.734, eo n' = , e' = 0.07, eo' = , emil = , emnn' = 0, epn = and emn = Received July 1, ISIJ. Institute of M ineral Dressing and Metallurgy, Tohoku University, Katahira Sendai 980. ( 257)

2 (258) Transactions ISIT, Vol. 24, 1984 Table 1. Equilibrium slag and metal compositons. (Wt%)

3 Transactions ISIJ, Vol. 24, 1984 (259) Table 1. Continued. Fig. 1. Manganese distribution ratio LMn=(%Mn0)/ [%Mn] for (Ca0+Mg0)-(Fe0+Fe203+Mn0)- (S102+P205) system at (a) 1650 C, (b) 1600 C, and (c) C plotted on a weight percent basis. Fig. 2. Logarithms of activity coefficient YMno cs) for (Ca0 + Mg0)-(Fe0 + Fe203 + Mn0)-(Si02 + P205) system at (a) C, (b) C, and (c) C plotted on a weight percent basis. The results are shown in Fig, 2, Mn+O = Mn0 (s)...(1) 4G = T4~ (cal)...(2) Since the values for LMn are supposed to be proportional to those for 7Mno cs~ under the present experimental conditions, i.e., amn=, [%Mn] and ao=[%0], the trend of iso- IMno(s) lines is expected to be identical to that of iso-lmn lines shown in Fig. 1. That is, the values for TMno(s) decrease with approaching to the (Fe0+Fe203+Mn0)-(Si02+P205) pseudo-binary system and increase with increasing temperature at a given slag composition.

4 (2'60) Transactions ISIJ, Vol. 24, 1984 The equilibrium quotients, kmn, for the following reaction are given by Eq. (4). (FetO)+Mn = (MnO)+Fe...(3) kmn = (wt%mno)/{[%mn]. (wt%feto)}...(4) wt% FetO is an FeO content calculated assuming all the iron in the slag to be present in the ferrous condition. The iso-kmn lines shown in Fig. 3 increase with approaching to the (FeO+Fe203+MnO)-(Si02+ P205) pseudo-binary system and increase with decreasing temperature at a given slag composition. This trend is similar to that found in Figs. 1 and 2. Iv. Discussion 1. Comparison between Present and Previous Results The activity coefficients of MnO, rmno (1) with respect to liquid standard state were calculated from the value of the free energy of fusion for MnO, 4G f= T (cal)6) and the free energy change dg (Eq. (2)) for the reaction given by Eq. (1). Figure 4 indicates the values for rmno (1) plotted against the [(%CaO)+0.3(%MgO)]/[(%Si02)+(%P205)] ratio defined by B, in which the coefficient of MgO, 0.3 was determined from the results') of the previous dephosphorization studies. Furthermore a comparatively good relationship was observed in the plot of log kmn vs. B value, when 0.3 was chosen for the coefficient of MgO. In this paper, the value of B was used for representing the slag basicity ratio. The symbols 0, ~, D represent the results containing phosphorus at 1550, and C, respectively. The data points represented by A refer to the sulfurcontaining slags at 1 ~ 600 C. Those represented by th e symbols -0; -D, -e; -0- correspond to the results for MgO-saturated CaO-FetO-MnO slags with higher B values, and these slags contain a high FetO and a low Si02 (<3.lwt%). Those represented by the symbols,~~ ;0, correspond to the results for MgO-saturated FetO-MnO slaps [(%CaO) <0.42, (%Si02)<2.5]. As is seen in Fig. 4, the values for rmno (1) except for the data!'points described above increase with increase of the B value and tend to increase with temperature at a fixed B value. Bishop et al.7) plot the activity coefficients of MnO with respect to liquid standard state in the (CaO + MgO)-(FetO+MnO)-(Si02+A1203+P02.5) pseudoternary diagram on a molar basis. The MnO content in their slags is 1 N 10 wt% and the temperature range is from to C. As a result, the value of 7Mno(1) increases as the (CaO+MgO)/(Si02+ A1203+P02,5) ratio on a molar basis increases to a value of about 2.3; however, the values of 7Mno(1) then decrease above a value of 2.3. Elliott and Luerssen8) also plot the values of rmno (1) obtained from operational data as well as the previous laboratory data3) as a function of the (CaO +MgO +MnO ) (Si02+P205+A1203) ratio on a molar basis and then found that the maximum value of rmno (1)(- 3 ) was obtained at this basicity ratio=2.5. It cannot Fig. 3. Logarithms of kmn(= (%MnO)/({ %Mn]. (%FetO) }) for (CaO+MgO)-(FeO+Fe203+MnO)-(Si02+ P205) system at (a) C (b) 1600 C, and (c) C plotted on a weight percent basis. Fig. 4. Activity coefficients of MnO with respect to liquid standard state plotted against B values. be concluded from their plot, however, that the maximum value of IMnou) is present at a certain basicity ratio, since the data points shown by them are scattered to a great extent. The values for rmno (1) obtained from the present experiments increase with increase of B value, but do not indicate

5 Transactions IsIJ, Vol. 24, 1984 (261) the tendency to have a maximum value, when the B value is about 2 as shown in Fig. 4. The relationship between the values for log kd7n calculated from the data in Table 1 and the B value is given in Fig. 5, where the symbols are the same as those in Fig. 4. The values for log kmn corresponding to respective temperatures decrease with increasing the B value. Moreover at a certain B value, they increase with decreasing temperature in spite of considerable scatterings. The values for log kmn obtained from the data for B>4 are considerably scattered, indicating a different trend from that in the range of B<3. The fact that the values for log kmn decrease with increase of the B value is due to that the values of log (rfeto/rmno) decrease with increasing B value. Thus, this can be explained by the increase of activity coefficient of MnO and/or the decrease of activity coefficient of FetO with increase of B value since MnO is a more basic oxide than FetO, as generally accepted. The previous results of the manganese distribution between FetO-MnO-MOx (MOx=PO2.5, SiO2, AlO1.5, MgO, CaO) ternary slaps and molten iron have been discussed in some detail in the previous report.4) Figure 6 shows the relationship between values of B and log kmn calculated from the results for MgOsaturated SiO2 FetO-MnO slags by Bell et a1.,9'10> for MgO-saturated CaO-SiO2 FetO-MnO slags by Chipman et a1.,3'11) for CaO-saturated FetO-P2O5 MnO slags12-14) and for CaO-FetO-MgO-SiO2-MnO saturated with dolomite by Harders et a1.'5 The three lines corresponding to respective temperatures obtained in Fig. 5 are also illustrated in Fig. 6 for comparison. The considerable scatter in the data points was observed in the slags (a, ~, ) containing a high MgO and no CaO at the low value of B9-11) and also was observed in the slags (E, (], ) containing a high P2Q ) Gorl et a1.16~ obtain the manganese distribution between molten iron and 9 % or 15 % MnO-containing CaO-FetO-SiO2 slaps saturated with CaO, 2CaO SiO2 and 3CaO SiO2 at C. From their results for the slaps containing 9 wt% MnO, the values for log kmn were calculated and were plotted against the B values by a dotted line, indicating a higher value of log kmn as compared with the present results. In the plot of log kmn Us. B value, the results obtained by other investigators are considerably scattered as compared with the present results. The reason for this is not clear; however, it is due to either the experimental error or the different behavior in log kmn for the different slag compositions. 2. Dependence of log kmn and log kmf,p on Slag Compositions Dependence of log kmn on slag compositions shown in Fig. 3 indicates the adverse trend in comparison with that of log kp [=log (wt%p2o5)/{[%p]2 (wt% FetO)5} ].1~ It has been reported that the value of log kp can be expressed as a linear function of slag compositions on a weight percent basis.17~ Fig. 5. Logarithms of kmn obtained from the present work plotted against B values. Fig. 6. Logarithms of kmn works plotted against obtained B values. from log kp = 0.145[(%CaO)+0.3(%MgO) -0.5(%P2O5)+0.6(%MnO)} /T The values of log kmn were analyzed the as a previous function (5)

6 (262) Transactions ISIT, Vol. 24, 1984 of CaO, FetO, MgO and Si02 content (wt%) by the method of a multiple regression. As a result, log kmn is found to be linearly correlated to the [(%CaO)+3.6 (%FetO)+4.2(%MgO)+8.4 (%Si02)] term. Since the present slags contain 2'.'5 wt% MnO and less than 3 wt% P205, the values for log kmn are plotted against the {(%CaO)+3.6 [(%FetO)+ (%MnO)] + 4.2(%MgO)+8.4[(%Si02) + (%P205)]} term in Fig. 7 assuming that the coefficients of MnO and P205 are identical to those of FetO and Si02, respectively. From the average values of slopes and intercepts of the lines for respective temperatures obtained by the method of a linear regression, log kmn can be expressed as a function of slag composition and temperature. log (%MnO)/ {[%Mn]. (%FetO)} = log kmn = {(%CaO)+3.6[(%FetO)+(%MnO)] +4.2(%MgO)+8.4[(%Si02)+(%P205)]} T (6) The lines for respective temperatures correspond to Eq. (6). Activity of manganese is considered to be equal to [%Mn], since manganese content in metal is less than 0.05 %. Actually, however, in the present experimental conditions, activity coefficient of manganese in metal decreases to 0.95, resulting in a change of log (%MnO)f [amn.(%feto)] by * The calculated values of [%Mn] from Eq. (6) are compared with the observed values in Fig. 8, indicating a good agreement. The exchange equilibrium between slag and metal with respect to phosphorus and manganese can be written by Eq. (8). Fig. 7. Logarithms of kmn plotted against the {(%CaO) + 3.6[(%FetO) + (%MnO)] + 4.2(%MgO) [(%Si02)+(%P205)]} term at 1 550, 1600 and 1650 C. 2P+5(MnO) _ (P205)+5Mn...(7) log kmf,p = log (%P205). {%Mn}5/{[%P]2 (%Mn0)5} = log k-5 log kmn...(8) where, kmf,p. the equilibrium quotient for the reaction given by Eq. (7). Substitution of Eqs. (5) and (6) into Eq. (8) gives the value of log kmn,p as a function of slag composition and temperature in the following. log kmf,p = 0.123[(%CaO)-0.40(%MgO).64(%FetO)--0.07(%MnO) (%Si02)-2.10(%P205)] /T (9) The values of log kmf,p calculated from the present results are plotted against the first term of the right hand side of Eq. (9) in Fig. 9, where the three lines for respective temperatures are obtained from Eq. (9). It is apparent that the values of log kmf,p are fairly well on the lines in the slag compositions where the first term of the right hand side of Eq. (9) is more Fig. 8. Comparison of calculated and observed manganese content in metal. than -50 wt%. The values of log kmf,p are plotted against the B values by the symbols 0, ~, 0 in Fig. 10. The comparatively good correlation is observed, since the value of log kmf,p is equivalent to the (log kp-5 log kmn) term in which log kmn is found to be more closely related to B than log kp. The values of log kmf,p increase with increase of B values, but their temperature dependence is not observed in this plot. The data points represented by the symbols, A, and U, a, LI correspond to the results for MgO- * The following equation was derived by the method similar to that used in log kmn : log (%MnO)/[aMn (%FetO)] {(%CaO)+3.6[(%FetO)+(%MnO)]+4.2(%MgO) +8.4[(%Si02)+(%P205)]} /T-4.923

7 Transactions ISIJ, Vol. 24, 1984 (263) Fig. 9. Logarithms of kmf,p plotted against the (%CaO)- 0.4(%MgO)-0.64(%FetO)-0.07(%MnO)-1.50(%- Si02)-2.10(%P205) term at 1550, and 1650 C. Fig. 10. Variations of log kmf,r with B values. saturated CaO-FetO-MnO ((%Si02)<_3.1) and MgOsaturated FetO-MnO ((%CaO)<0.42 and (%Si02) <2.5), respectively. These points exhibit a different behavior. Figure 11 shows the relationship between log Lp and log LMn obtained in the present work as a function of temperature. The symbols indicated in Fig. 11 are the same as those used in Fig. 10. The values of log Lp obtained in the MgO-saturated FetO-MnO slags are almost zero, whereas those of log LMn are Fig. 11. Relationship between log LP andd log LM at and C. around 2.5. The values of log LMn tend to increase slightly and thereafter decrease with increase of log Lp. It is clear from Fig. 11 that the temperature dependence in the relation between log Lp and log LMn are hardly found in MgO-saturated FetO-MnO system (c:,, A, CI), but the extent of their dependence increases with increase of L~. The two data points represented by the mark k, which refer to the slags (Nos. 381 and 382 in Table 1) containing a high Si02 (2931 wt%) and a low FetO (l4'-'17 wt%), deviate greatly from the curve at 1600 C. 3. Comparison between Present and Plant Data The log (%MnO)J {[%Mn].(%T.Fe)} (=log k ~) is plotted against the B value in order to compare the present laboratory data with the reported plant data. The values of log kmn calculated from the present results except for the data for MgO-saturated CaO-FetO- MnO((%Si02)<3.1) slags are shown in Fig. 12, in which the axis of ordinates is different by 0.11 in comparison with log kbzn in Fig. 5. It has been reported by Plockinger18) and Tesche19~ that the values of log kmn (or log kmn) decrease as the CaO/Si02 values increase up to 2 and thereafter become constant. The results obtained by Plockinger18~ and Tesche19~ are also shown in Fig. 12. The value of log kmn obtained by Tesche at 1 550N C (in average 1675 C) is represented to be 0.18 in the range of (%CaO)f (%Si02)>2, while that by Plockinger at C is 0.3. Recently, Kai et al.20~ have reported in the studies on metallurgical characteristics in top and bottom blown converter (LD-AB) that the values of log kin decrease with increase of bath agitation intensity and approach to the same value as Q-BOP when the bottom gas flow rate increase more than 400 Nm3f h. Their data are also included in Fig. 12. Koch et al.21 plot the value of log

8 (264) Transactions ISIJ, Vol. 24, 1984 Fig. 12. Logarithms of kmn obtained from the plant data plotted against B values. previous Fig. 13. Values for LMn plotted a function of B values. against T. Fe content as obtained from the plant data in BOF against the effective basicity, Bw=(%CaO)w/(%S1O2) in which (%CaO)w denotes the lime content excluding the undissolved lime (free CaO) from total lime. The considerable scatter is observed in the values of log kmn obtained from the plant data, but these data are expected to be on the line extrapolated from the present results for MgO-saturated CaO-FetO-Si02 MnO slags. The values of LMn= (%MnO)/[%Mn] obtained from the present results at 1600 C are plotted against (%T.Fe) in Fig. 13, where the symbols--, --and:a', denote the results for MgO-saturated CaO-FetO- MnO slaps ((%Si02(<3.1) and those for MgO-saturated FetO-MnO slaps ((% CaO) ~ 0.42, (%Si02) < 2.5), respectively and the symbol A denotes the results for sulfur-containing slaps. The figure on each experimental point corresponds to the B value. The values of LMn decrease with increase of B value at a given T.Fe wt%, although the considerable scatter in the data points was observed. Using the laboratory and plant data in the temperature range to C, Turkdogan22> plots kmn as a function of B'=[(%CaO)+1.4(%MgO)]/ [(%S102)+0.84(%P205)], resulting in the relationship kmn=6/b'.23) This indicates that LMn is proportional to (%FetO) for a given basicity B'. The values of LMn at B'= 1, 2, 3 and 4 are plotted against T. Fe wt% in Fig. 13. The values of LMn obtained from the data of BOP and Q; BOP are also plotted against T.Fe wt% in Fig. 13 by the shade area,23~ where the B value ranges from 2.5 to 4.0. One may see that these practical data lie within the B' values ranging from 2 to 4 obtained by Turkdogan. Furthermore, the relationship between LMn and T.Fe obtained from top and bottom blown process24> (STB) is also shown in Fig. 13 as a function of (%CaO)/(%S102) ratio= 3.5,,4 (C<0.12 %). V. Summary Manganese distribution between molten iron and MgO-saturated CaO-FetO-Si02 MnO slaps has been studied in a temperature range to C and the results obtained are summarized as follows : (1) Manganese distribution ratios LMn (= (%MnO)/[%Mn]) increase with approaching to the (FeO+Fe203+MnO)-(Si02+P205) pseudo-binary system and decrease with increasing temperature at a given slag composition. (2) The values of TMnow obtained increase with increase in the B value (= [(%CaO)+0.3 (%MgO)]/ [(%Si02)+(%P205)]), but the maximum value was not observed at B_, 2, which was reported in the previous work. The values of TMno (1) at a given B value increase with increasing temperature. (3) Logarithms of equilibrium quotient kmn (= (%MnO)/ {[%Mn]. (%FetO)} ) decrease with increasing B value and temperature. The previous results that the values of kmn remain constant in the slag composition of B>2 were not confirmed in the present work. The following equation was derived : 1) 2) log kmn = {(%CaO)+3.6[(%FetO) +(%MnO)] +4.2(%MgO)+8.4[(%Si02) +(%P205)]} /T REFERENCES H. Suito, R. Inoue and M. Takada : Trans. ISIJ, 21 (1981), 250. R. Inoue and H. Suito: Trans. ISIJ, 22 (1982), 705.

9 Transactions ISIJ, Vol. 24, 1984 (265) 3) 4) 5) 6) 7) 8) 9) 10) 11) 12) 13) T. B. Winkler and J. Chipman : Trans. AIME,167 (1946), 111. H. Suito and R. Inoue: Trans. ISIJ, 24 (1984), No. 4. G. K. Sigworth and J. F. Elliott: Metal Sci., 8 (1974), 298. I. Barin and 0. Knacke: Thermochemical Properties of Inorganic Substances, Springer-Verlag, Berlin, (1973). H. L. Bishop, Jr., N.J. Grant and J. Chipman: Trans. AIMS, 212 (1958), 890. J. F. Elliott and F. W. Luerssen: Open Hearth Proceedings, RIME, 37 (1954) 193; Trans. AIMS, 203 (1955), H. B. Bell, A. B. Murad and P. T. Carter: Trans. AIMS, 194 (1952), 718. H. B. Bell : JISI, 201 (1963), 116. J. Chipman, J. B. Gero and T. B. Winkler : Trans. RIME, 188 (1950), 341. G. Tromel and W. Fix: Arch. Eisenhi ttenw., 33 (1962), 745. H. Knuppel, F. Oeters and H. GruB : Arch. Eisenhuttenw., 30 (1959), ) 15) 16) 17) 18) 19) 20) 21) 22) 23) 24) H. Knuppel and F. Oeters : Stahl u. Eisen, 81 (1961), F. Harders, H. Grewe and W. Oelsen : Stahl u. Eisen, 71 (1951), 973. E. Gorl, R. Klages, R. Scheel and G. Tromel: Arch. Eisenhuttenw., 40 (1969), 959. H. Suito and R. Inoue : Trans. ISIJ, 24 (1984), 40. E. Plockinger : Arch. Eisenhuttenw., 22 (1951), 283. K. Tesche : Arch. Eisenhuttenw., 32 (1961), 503. T. Kai, K. Okohira, M. Hirai, S. Murakami and N. Sato : Tetsu-to-Hagane, 68 (1982), K. Koch, T. Kootz and H.-D. Pflipsen: Arch. Eisenhuttenw., 52 (1981), 103. E. T. Turkdogan: BOF Steelmaking, R. D. Pehlke, W. F. Porter, R. F. Urban and J. M. Gaines, eds., Iron Steel Soc. AIME, New York, (1975), 1. E. T. Turkdogan: Physical Chemistry of High Temperature Technology, Academic Press, New York, (1980). T. Ueda, M. Taga, K. Yoshida, K. Marukawa and S. Anezaki: Journees Siderurgiques ATS, Paris, (Dec. 1981).