Phase Equilibria in the System “Mno”–Cao–Mgo–Sio2–Al2o3 with Al2o3/Sio2 Weight Ratio of 0.17 and Mgo/Cao Weight Ratio of 0.25 at Mn–Si Alloy Saturation

ISIJ International, Vol. 46 (2006), No. 11, pp. 1594–1602

Phase Equilibria in the System “MnO”–CaO–MgO–SiO2–Al2O3 with Al2O3/SiO2 Weight Ratio of 0.17 and MgO/CaO Weight Ratio of 0.25 at Mn–Si Alloy Saturation

Baojun ZHAO, Eugene JAK and Peter C. HAYES

Pyrometallurgy Research Centre, School of Engineering, The University of Queensland, Brisbane, Queensland, 4072, Australia. E-mail: [email protected] (Received on July 14, 2006; accepted on September 5, 2006)

Liquidus isotherms and phase equilibria have been determined experimentally for a pseudo-ternary section of the form “MnO”–(CaO MgO)–(SiO2 Al2O3) with a ﬁxed Al2O3/SiO2 weight ratio of 0.17 and MgO/CaO weight ratio of 0.25 for temperatures in the range 1 393–1 673 K. The primary phase ﬁelds found in the investigated section include manganosite (Mn, Mg, Ca)O; dicalcium

silicate a-2(Ca, Mg, Mn)O · SiO2; merwinite 3CaO · (Mg, Mn)O · 2SiO2; melilite [2CaO · (MgO, MnO, Al2O3)· 2(SiO2,Al2O3)]; wollastonite [(Ca, Mg, Mn)O · SiO2]; diopside [(CaO, MgO, MnO, Al2O3)·SiO2]; tridymite (SiO2); rhodonite [(Mn, Mg, Ca)O · SiO2]; anorthite (CaO · Al2O3 · 2SiO2) and tephroite [2(Mn, Mg, Ca)O · SiO2]. The liquidus temperatures and primary phase ﬁelds are signiﬁcantly different to those in the ternary sys-

tem “MnO”–CaO–SiO2, but are close to those previously reported pseudo-ternary section “MnO”– (CaO MgO)–(SiO2 Al2O3) for Al2O3/SiO2 weight ratio of 0.17 and MgO/CaO weight ratio of 0.17. The partitioning of CaO, MgO and MnO between liquid and solid phases was measured using EPMA, and the extents of solid solutions for a range of bulk compositions and temperatures were characterised.

KEY WORDS: slag; equilibria; “MnO”–CaO–MgO–SiO2–Al2O3; liquidus.

1. Introduction 2. Experimental Procedure In a recent study by the authors1) the liquidus temper- The experimental method used in the present study is atures and phase equilibria in the quinary system identical to that reported by the authors in Part 1 of a series 1) “MnO”–CaO–MgO–SiO2–Al2O3 at Mn–Si alloy saturation of papers describing this investigation. The method essen- were reported for Al2O3/SiO2 0.17 and MgO/CaO 0.17. tially involves the preparation of mixtures from high purity That study demonstrated that the liquidus temperatures and oxide powders with excess of the Mn–Si alloy, high temper- primary phase fields in the quinary system are markedly ature equilibration in Ar gas atmosphere, rapid quenching different from those observed in the ternary system of the samples into cool water, and examination and analy- 2) “MnO”–CaO–SiO2 under reducing conditions. The liq- sis of the resulting microstructures and phase compositions uidus temperatures were shown to be principally dependent using electron probe X-ray microanalysis (EPMA). on the modified basicity weight ratio (CaO MgO)/(SiO2 The metal oxide powders used in the study are 99 % Al2O3) at low “MnO” concentrations, and dependent on the MnO, CaCO3, SiO2 and Al2O3. The Mn–Si alloy was pre- mole ratio (CaO MgO “MnO”)/(SiO2 Al2O3) at higher pared by mixing Mn and Si powders with mole ratio of “MnO” concentrations. Mn : Si3:1 and heating under an argon gas atmosphere in In commercial ferro-manganese and silico-manganese a carbon crucible at 1 473 K for 2 h. Approximately 0.3 g of smelting practice the MgO/CaO ratio in the final slag is sig- powdered oxide/alloy mixture was placed in an envelope nificantly influenced by the MgO present in the feed to the made from 0.025 mm thick Mo metal foil, and suspended in furnace. High MgO slags are formed during pyrometallur- flowing stream of high purity Ar gas in the equilibration gical processing of South African manganese ore concen- furnace. The oxygen was removed from the alumina reac- trates. The present paper provides additional experimentally tion tube by flushing with the Ar, prior to lifting the sam- determined data on the phase equilibria and liquidus tem- ples suspended by Mo wire into the hot zone of the furnace. peratures for the quinary system “MnO”–CaO–MgO–SiO2– The presence of Mn–Si alloy particles distributed through- A12O3 for Al2O3/SiO2 0.17 and MgO/CaO 0.25, no data out the samples ensured that local equilibrium between slag in this composition range are available from the previous and metal was attained, and that the manganese in the slag studies on this system.3–8) was present principally as Mn2. The quenched samples were mounted and polished for

© 2006 ISIJ 1594 ISIJ International, Vol. 46 (2006), No. 11 examination following high temperature equilibration. A the primary phase ﬁelds, with increasing (CaOMgO), ap- JEOL 8800L Electron Probe Microanalyser (EPMA) with pear in the sequence of cristobalite, tridymite, diopside,

Wave Length Dispersive detectors was used for measure- melilite, merwinite, a-Ca2SiO4 and manganosite. ments of the phase compositions. The standards used for The primary phase ﬁelds observed in the section de-

EPMA include alumina (Al2O3) for Al, magnesia (MgO) scribed in the present paper are the same as those observed for Mg, spessartine (Mn3Al2Si3O12) for Mn and wollas- for the section with Al2O3/SiO2 0.17 and MgO/CaO 0.17 tonite (CaSiO3) for Ca and Si. These standards were pro- but also include the anorthite primary phase field. vided by Charles M Taylor Co., Stanford, California, USA. The analysis was conducted at an accelerating voltage of 3.2. Comparison with Other Systems 15 kV and a probe current of 15 nA. The ZAF correction The experimental data on the liquidus obtained in the procedure supplied with the electron probe was applied. present study in the joins (CaO MgO)–(SiO2 Al2O3) with The average accuracy of the EPMA measurements is within fixed Al2O3/SiO2 weight ratio of 0.17 and MgO/CaO weight 1 wt%. The phase compositions were recalculated to ox- ratio of 0.25 in the liquid are in good agreement with those ides on the assumption that all manganese is present as interpolated from the system CaO–MgO–SiO2–Al2O3 re- Mn2. Although it is possible to measure the compositions ported by Osborn9) and Cavalier and Sandreo-Dendon.10) of the oxide phase unfortunately it has not been possible to Comparison of the phase diagram of the system 2) determine the corresponding compositions of the fine dis- “MnO”–CaO–SiO2 with the sections of the quinary sys- persed alloy in the quenched samples. tem containing MgO and Al2O3 determined in the present study indicates that, whilst the general position of the liquidus valley is similar in the ternary system, there are im- 3. Experimental Results portant differences in the primary phase fields and shape of 3.1. Description of the Pseudo-ternary Section the liquidus surface. The rankinite, a-dicalcium silicate The compositions of the phases identified in the sam- and pseudo-wollastonite primary phase fields in the ternary 2) ples following equilibration of the oxide/alloy mixtures, system “MnO”–CaO–SiO2 are replaced by melilite, mer- measured using EPMA, are presented in Table 1. These winite, diopside, tephroite and anorthite in the sections of data have been used to construct liquidus isotherms on the quinary system. At the same time most importantly the the pseudo-ternary section “MnO”–(CaO MgO)–(SiO2 liquidus temperatures in the quinary system are signifi- Al2O3) with a fixed Al2O3/SiO2 weight ratio of 0.17 and cantly different from those in the ternary system. MgO/CaO weight ratio of 0.25. Figure 1 shows the experi- To assist in the comparison of the liquidus temperatures 2) mentally determined liquidus points for compositions hav- between the system ternary “MnO”–CaO–SiO2 and the ing the appropriate Al2O3/SiO2 and MgO/CaO ratios in the pseudo-ternary system “MnO”–(CaO MgO)–(SiO2 1) liquid phase. From these data the liquidus isotherms at Al2O3) determined in the present and previous studies, the 1 473, 1 523, 1 573, 1 623 and 1 673 K have been deter- liquidus for sections at 20 wt% “MnO” are shown in Fig. 3. mined. The remaining data with different Al2O3/SiO2 and In the ternary system primary phase fields of wollastonite, MgO/CaO ratios are also provided in Table 1 for subse- rankinite and dicalcium silicate are present in the composi- quent thermodynamic modelling of this system. The liq- tion range compared. In the two pseudo-ternary sections uidus surface of the pseudo-ternary section for the quinary melilite and tephroite are stable at low (CaOMgO) con- system is shown in Fig. 2. centrations and manganosite primary phase field is located The experimentally determined phase boundaries are at high (CaOMgO) concentrations. Between the tephroite marked with thick full lines. The boundaries marked with and manganosite primary phase fields, merwinite is present dashed lines indicate the approximate positions. Experi- in the section with Al2O3/SiO2 0.17 and MgO/CaO 0.25 mental data were obtained in all primary phase fields in and dicalcium silicate is present in the section with the pseudo-ternary section and the pseudo-binary joins Al2O3/SiO2 0.17 and MgO/CaO 0.17. (CaO MgO)–(SiO2 Al2O3) and “MnO”–(SiO2 Al2O3). It can be seen from Fig. 3 that at low (CaO MgO) con- The pseudo-ternary section is characterised by the centrations the liquidus temperatures in the quinary system presence of the following primary phase fields (see Fig. are significantly lower than those in the ternary in the com- 2): Manganosite (Mn, Mg, Ca)O; a-dicalcium silicate position range investigated. Between 37 and 43 wt% 2(Ca, Mg, Mn)O·SiO2; merwinite 3CaO·(Mg, Mn)O·2SiO2; (CaO MgO) the liquidus temperatures in the quinary sys- melilite [2CaO·(MgO, MnO, Al2O3)·2(SiO2,Al2O3)]; wol- tem are slightly higher than those in the ternary. lastonite [(Ca, Mg, Mn)O·SiO2]; diopside [(CaO, MgO, In the quinary system the liquidus temperatures in the MnO, Al2O3)·SiO2]; tridymite (SiO2); rhodonite [(Mn, Mg, silicates primary phase fields gradually increase with in- Ca)O·SiO2]; anorthite (CaO·Al2O3·2SiO2) and tephroite creasing (CaO MgO) concentrations. In the low (CaO [2(Mn, Mg, Ca)O·SiO2]. MgO) concentration region, where melilite and tephroite At high “MnO” concentrations the liquidus surface of are the primary phases, high MgO slags (MgO/CaO0.25) the manganosite primary phase field extends across the have slightly higher liquidus temperatures. In the high whole width of the diagram from the “MnO”–(SiO2 (CaO MgO) concentration region, where manganosite is Al2O3) join to the (CaO MgO)–(SiO2 Al2O3) join. At the primary phase, the manganosite is stabilised with addi- higher (SiO2 Al2O3) concentrations the tephroite primary tion of MgO. The manganosite starts to be stable at phase field extends across the diagram, such that this phase 44.6 wt% (CaOMgO) with MgO/CaO0.25 and starts to is encountered for all compositions with (CaOMgO)/ be stable at 48 wt% (CaOMgO) with MgO/CaO0.17. In (SiO2 Al2O3) less than 1.0. At low “MnO” concentrations the manganosite primary phase field the liquidus tempera-

Table 1. Experimental results in system “MnO”–CaO–MgO–SiO2–Al2O3 with nominal liquid phase Al2O3/SiO2 weight ratio of 0.17 and MgO/CaO weight ratio of 0.25 in equilibrium with Mn–Si alloy.

Fig. 1. Experimental data obtained on the liquidus of the system “MnO”–CaO–MgO–SiO2–Al2O3 with weight ratios of Al2O3/SiO2 0.17 and MgO/CaO0.25 in equilibrium with Mn–Si alloy, compositions in wt%, temperatures in K.

Fig. 2. Liquidus of the system “MnO”–CaO–MgO–SiO2–Al2O3 with weight ratios of Al2O3/SiO2 0.17 and MgO/CaO 0.25 in equilibrium with Mn–Si alloy, compositions in wt%, temperatures in K.

tures increase dramatically with increasing (CaO MgO) [(CaO MgO)/SiO2] of 0.8 and 1.1 the liquidus tempera- concentration, and with increasing MgO concentration at tures slightly increase with increasing MgO/CaO ratio. At ﬁxed (CaOMgO) concentration. higher basicity of 1.4 the liquidus temperatures signiﬁ- This is in good agreement with the trends reported by cantly increase with increasing MgO/CaO ratio. Eric et al.8) It was found in the study8) that at low basicities In Fig. 4 the change in liquidus temperature with chang-

Fig. 3. Slag liquidus temperatures for section for 20 wt% “MnO”. ------from section with Al2O3/SiO2 0.17 1) and MgO/CaO0.17, from section with Fig. 5. Liquidus temperatures as a function of “MnO” concentra- Al O /SiO 0.17 and MgO/CaO0.25, – · – · – · – from 2 3 2 tion at various B (CaO MgO)/(SiO2 Al2O3) weight system “MnO”–CaO–SiO .2) 2 ratios, Al2O3/SiO2 0.17, CaO/MgO 0.25.

basicity B at the same “MnO” concentration. For “MnO” concentrations greater than 30 wt% “MnO” the primary phases are always manganosite and tephroite. The maxi- mum extent of the manganosite primary phase field ex- pands from 53 wt% “MnO” to 28 wt% “MnO” when B increases from 0.40 to 1.0. At low “MnO” concentrations (30 wt% “MnO”) the primary phases change with basicity B. At B0.40 wollastonite and diopside are the primary phases. When B increases to 0.60 wollastonite and melilite are the primary phases. At B0.80 and 1.0 melilite is the primary phase. In manganosite primary phase field the liq- Fig. 4. Liquidus temperatures as a function of “MnO” concentra- uidus temperatures dramatically increase with increasing tion at a (CaO MgO)/(SiO2 Al2O3) weight ratio of “MnO” concentration regardless basicity B. In the tephroite 0.90. ------from section with Al2O3/SiO2 0.17 and primary phase field the liquidus temperatures generally in- 1) MgO/CaO0.17, from section with crease with increasing “MnO” concentration but the rate of Al O /SiO 0.17 and MgO/CaO0.25, – – – – from 2 3 2 · · · the increment decreases with increasing basicity so that at system “MnO”–CaO–SiO .2) 2 high basicities (B0.8) the effect of “MnO” concentration on liquidus temperature is relatively smaller. In other pri- ing “MnO” concentration is plotted for (CaOMgO)/ mary phase fields such as melilite, diopside and wollas- (SiO2 Al2O3) ratio of 0.90 to reflect how the liquidus tem- tonite the liquidus temperatures do not change significantly peratures change as manganese is reduced from the slags with “MnO” concentration. during the smelting operation. It can be seen that the liq- 3.3. The Relationships between Liquidus Temperature uidus profiles for the quinary slags with Al2O3/SiO2 0.17 and MgO/CaO0.25 and 0.17 are very close to each other. and Basicity The high-MgO slag has slightly higher liquidus tempera- In part I of this study1) the experimental data were used tures in the whole composition range shown in Fig. 4. For to determine the relationship between liquidus temperature these two sets of slags in the region where the “MnO” con- and basicity of the liquid phase for traditional basicity ratio centration is lower than 25 wt% the liquidus temperature in (CaO MgO)/SiO2 and modified basicity ratio (CaO the quinary slags does not significantly change with “MnO” MgO)/(SiO2 Al2O3). In Figs. 6 and 7 the liquidus temper- concentration. This behaviour reflects the shape of the liq- atures are plotted against the traditional and modified basic- uidus in Fig. 2 where the isotherms in the melilite and ities for Al2O3/SiO2 ratio of 0.16–0.20, MgO/CaO ratio of tephroite primary phase fields are nearly parallel to the 0.20–0.26 and “MnO” concentrations in the range of join “MnO”–[(CaO MgO) (SiO2 Al2O3)] with (CaO 0–30 wt%. In the melilite, merwinite, dicalcium silicate and MgO)/(SiO2 Al2O3) ratio of 0.90. The presence of MgO in tephroite primary phase fields the relationships between liq- the manganosite solid solution is shown to extend the pri- uidus and basicity ratios are approximately linear and are mary phase field of this phase to lower “MnO” concentra- described by the following equations: tions.  (wt%CaO wt%MgO)  The liquidus temperature as a function of “MnO” con- Tliq(K) 286 1302 ....(1) centration is also compared at various B (CaO MgO)/  wt%SiO  2 (SiO2 Al2O3) ratios. Figure 5 shows the results from the quinary system “MnO”–(CaOMgO)–(SiO Al O ) 2 2 3  (wt%CaO wt%MgO)  with Al O /SiO weight ratio of 0.17 and MgO/CaO weight T (K)342 1298 2 3 2 liq   ...(2) ratio of 0.25 (Fig. 1). It can be seen from Fig. 5 that the  (wt%Al23 O wt%SiO 2)  liquidus temperatures generally increase with increasing

Table 2. Composition range of the solid phases present in sys-

tem “MnO”–CaO–MgO–SiO2–Al2O3 with liquid phase Al2O3/SiO2 weight ratio of 0.17 and MgO/CaO weight ratio of 0.25 in equilibrium with Mn–Si alloy.

Fig. 6. Relationship between liquidus temperatures and traditional basicity (CaO MgO)/SiO2 of the liquid phase at 0–30 wt% “MnO” with Al2O3/SiO2 weight ratios of 0.16–0.20 and MgO/CaO weight ratios of 0.20–0.26.

this range of compositions.

3.4. Solid Solutions Not only the liquid but also solid phase compositions have been determined by EPMA measurements in present study. The stoichiometric and measured compositions of the solid phases present in the system investigated are pre- Fig. 7. Relationship between liquidus temperatures and modiﬁed sented in Table 2. The extents of the solid solutions (in basicity (CaOMgO)/(Al O SiO ) of the liquid phase 2 3 2 mol) measured in this study are illustrated by projections at 0–30 wt% “MnO” with Al2O3/SiO2 weight ratios of 0.16–0.20 and MgO/CaO weight ratios of 0.20–0.26. onto the plane CaO–MgO–MnO (Fig. 8) and the plane “MnO”–(CaO MgO)–(SiO2 Al2O3) (Fig. 9) respectively. where: Tliq is liquidus temperature in K. The squares of the The data on solid solutions present in multiphase equilibria correlation coefﬁcient (R2) are 0.96 and 0.97 respectively will be valuable for development of thermodynamic model- for Eqs. (1) and (2). ling. In industrial ferro-manganese smelting practice a mole Some phases exhibit only limited ranges of solid solu- ratio of (CaO MgO “MnO”)/(SiO2 Al2O3) can be used bility, i.e., anorthite (CaO·Al2O3·2SiO2) and diopside to evaluate the relationship between liquidus temperature [(CaO, MgO, MnO, Al2O3)·SiO2] (see Figs. 8 and 9). Some and slag composition. It was found from the present study phases have moderate extents of solid solutions such that for slags in the composition range of Al2O3/SiO2 ratio as merwinite 3CaO·(Mg, Mn)O·2SiO2, melilite [2CaO· of 0.14–0.20, MgO/CaO ratio of 0.13–0.26 and “MnO” (MgO, MnO, Al2O3)·2(SiO2,Al2O3)] and rhodonite [(Mn, concentrations 20–53 wt%, liquidus temperature is de- Mg, Ca)O·SiO2]. Extensive solid solutions are exhibited by scribed by following equation: manganosite (Mn, Mg, Ca)O, tephroite [2(Mn, Mg, Ca)O·

SiO2] and wollastonite [(Ca, Mg, Mn)O·SiO2].  (mol%CaO mol%MgO mol%MnO)  The principal species that are variable within these solid T (K) 342  liq solutions are Ca2 , Mg2 and Mn2 . It can be seen from  (mol%Al23 O mol%SiO 2)  Fig. 9 that the SiO /(CaOMgOMnO) mole ratios re- 2 1267 main constant for the ranges of compositions describing the ...... (3) various silicates. In this multicomponent system the compositions of the The square of the correlation coefficient is 0.88 for Eq. (3). solid and liquid phases do not lie on in the same section in The experimental data used in these correlations are in the compositional space; it is not possible therefore to present tephroite and manganosite primary phase fields. The pa- the true tie-lines between liquid and solid compositions on rameters in this relationship are, within experimental uncer- a single plane. However, the “tie-lines” can be projected tainty, the same as those determined for MgO/CaO0.17 in onto a plane to show general trends in solid solutions as part I of the study.1) This clearly indicates that in molar functions of temperature and liquid composition. The major terms MgO and CaO have similar effects on the liquidus in solid silicate phases in the system exhibiting significant

Fig. 8. Ranges of the solid compositions (in mol%) measured in this study, projected onto the plane CaO–MgO–MnO.

Fig. 9. Ranges of the solid compositions (in mol%) measured in this study, projected onto the plane “MnO”– (CaO MgO)–(SiO2 Al2O3).

solid solution are tephroite [2(Mn, Mg, Ca)O·SiO2], The partitioning of CaO, MgO and MnO between liquid, melilite [2CaO·(MgO, MnO, Al2O3)·2(SiO2,Al2O3)] and tephroite, melilite and wollastonite phases at different wollastonite [(Ca, Mg, Mn)O·SiO2]. As pointed out above temperatures presented as projections onto the plane the mol% of (SiO2 Al2O3) in each of these phases are al- CaO–MgO–MnO (in mol) is shown in Fig. 10. It can be most constant in each case, with Ca2, Mg2 and Mn2 seen from Fig. 10 that the MgO/CaO ratios in tephroite are cation concentrations variable. in all cases higher than those in the liquid phase, and tend

Fig. 10. Trends in the equilibrium partitioning of Ca–Mg–Mn between liquid and solid oxide phases observed in the study presented as projections onto the CaO–MgO–“MnO” surface. Liquid phase: ; melilite [2CaO·(MgO, MnO, Al2O3)·2(SiO2,Al2O3)]: ; tephroite [2(Mn, Mg, Ca)O·SiO2]: .

Fig. 11. The equilibria between liquid phase () and tephroite (), and between liquid phase () and melilite () projected in the system “MnO”–CaO–MgO–SiO2–Al2O3 with liquid phase Al2O3/SiO2 0.17 and MgO/CaO 0.25 in equilibrium with Mn–Si alloy.

1601 © 2006 ISIJ ISIJ International, Vol. 46 (2006), No. 11 to increase with decreasing temperature. The CaO in the gated exhibit solid solutions with variable Ca2, Mg2 and melilite is approximately constant with some exchange Mn2 cation concentrations present. The partitioning of of Mg2 with Mn2 ions. The solubility of MnO in the these cations between solid and liquid phases have been melilite increases with increasing MnO in the liquid phase. measured for all of the temperatures investigated. Tie-lines between tephroite and liquid, and between melilite and liquid are projected onto the plane Acknowledgements “MnO”–(CaO MgO)–(SiO2 Al2O3) (in mol) as shown in The authors wish to thank: Samancor Mn, Meyerton for Fig. 11. providing the financial support necessary to undertake this project and Clem Smith for coordinating this project. Ms Ying Yu, who provided general laboratory assistance and 4. Conclusions undertook much of the careful sample preparation and The liquidus temperatures and phase relations in the sys- equilibration work. Mr Ron Rasch of the Centre for Mi- tem “MnO”–(CaO MgO)–(SiO2 Al2O3) with a fixed croscopy and Microanalysis at the University of Queens- Al2O3/SiO2 weight ratio of 0.17 and MgO/CaO weight ratio land, who provided support for the electron microprobe X- of 0.25 have been determined in equilibrium with Mn–Si ray analysis (EPMA) facilities. alloy in the temperature range 1 393–1 673 K. The phases present at the liquidus surfaces in this system REFERENCES include: Manganosite (Mn, Mg, Ca)O; dicalcium silicate a- 1) B. Zhao, E. Jak and P. C. Hayes: ISIJ Int., 45 (2005), 1019. 2(Ca, Mg, Mn)O·SiO2; merwinite 3CaO·(Mg, Mn)O·2SiO2; 2) F. P. Glasser: J. Am. Ceram. Soc., 45 (1962), 242. melilite [2CaO·(MgO, MnO, Al2O3)·2(SiO2,Al2O3)]; wol- 3) W. Ding and S. E. Olsen: Metall. Mater. Trans. B, 27B (1996), 5. 4) R. Rait and S. E. Olsen: Scand. J. Metall., 28 (1999), 53. lastonite [(Ca, Mg, Mn)O·SiO2]; diopside [(CaO, MgO, MnO, Al O )·SiO ]; tridymite (SiO ); rhodonite [(Mn, Mg, 5) R. Rait and S. E. Olsen: 6th Int. Conf. on Molten Slags, Fluxes and 2 3 2 2 Salts, Stockholm, Sweden, Helsinki, Finland (2000), paper 018. Ca)O·SiO2]; anorthite (CaO·Al2O3·2SiO2) and tephroite 6) G. Roghani, E. Jak and P. Hayes: Metall. Mater. Trans. B, 33B [2(Mn, Mg, Ca)O·SiO2]. (2002), 839. The liquidus temperatures and primary phase fields in 7) G. Roghani, E. Jak and P. Hayes: Metall. Mater. Trans. B, 34B the quinary system are markedly different from the system (2003), 173. 8) R. H. Eric, A. A. Hejja and W. Stange: Miner. Eng., 4 (1991), 1315. “MnO”–CaO–SiO2 under reducing conditions but close 9) E. F. Osborn, R. C. DeVries, K. H. Gee and H. M. Kraner: J. Met., 6 to those observed for the “MnO”–(CaO MgO)–(SiO2 (1954), 33. Al2O3) system for Al2O3/SiO2 0.17 and MgO/CaO 0.17. 10) G. Cavalier and M. Sandreo-Dendon: Rev. Metall., 57 (1960), 1143. Many of the silicate phases present in the system investi-