The Effect of Silica, Alumina, Calcia and Magnesia on the Activity Coefficient of Cobalt Oxide in Iron Silicate Slags

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1 highlight significant inconsistencies in the pblished data. The Effect of Silica, Almina, Calcia and Magnesia on the Activity Coefficient of Cobalt Oxide in Iron Silicate Slags Xliang Li* and Eric J. Grimsey** * G.K. Williams CRC for Extractive Metallrgy, Dept. of Chemical Engineering, The University of Melborne, Vic 352, Astralia. Ph: (613) ** Dept. of Minerals Engineering and Extractive Metallrgy, Western Astralia School of Mines, Kalgoorlie, WA. 643, Astralia. Ph: (619) ABSTRACT Iron silicate slags with varying contents of silica (14 wt% to 43 wt%), or almina (p to 16 wt%), or calcia (p to 13 wt%) or magnesia (p to 11 wt%) were eqilibrated with solid-iron alloys or liqid cobalt-gold-iron alloys in cobalt, almina, or silica crcibles at oxygen pressres of either 1-9 or 1-1 atm (1 atrn. = 1.13 x 1 5 Pa) at 1573 K. The solbility of cobalt oxide was measred in the slags and the activity coefficient calclated relative to pre solid cobalt oxide as standard state. The activity coefficient of cobalt oxide was fond to increase with an increase in either almina, or calcia or magnesia in the slag and decrease with an increase in the silica content of slag. 1. INTRODUCTION Cobalt is often a by-prodct from nickel and copper smelting operations 1 The recovery depends on the distribtion of cobalt between matte and discard slag in the smelting stage and an important factor affecting this distribtion is the activity coefficient of cobalt oxide in slag. The athors have previosly measred the activity coefficient for silica satrated slags at 1573 K, and report a constant vale of.91 ±.9 relative to pre solid cobalt oxide, for slags containing p to 1 percent cobalt oxide 2. This vale is significantly lower than reported by others 3-5 for silica satrated iron silicate slags, althogh similar to that reported for almina satrated slags 6. These comparisons, dealt with in some detail previosly2, In indstrial practice, iron silicate slags are not silica satrated and the Fe/Si 2 ratio is an important variable. At the WMC Kalgoorlie Nickel Smelter, for example, the Fe/Si 2 ratio in the flash frnace was increased from 1. to 1.7 over a ten year period, in order to decrease the slag mass and to increase its flidity 7. The distribtion of cobalt from matte to slag ((%Co in slag)/[%co in matte]) increased by abot 35 percent as a reslt7. Zakharov and Tikhonov 8 reported a similar trend, with the distribtion of cobalt to iron silicate slags eqilibrated with mattes nder argon, being dobled as the percent silica in slag decreased from 4 to 13 percent. Takeda et al. 9 measred the oxygen pressre of liqid C-Ni-Fe alloys eqilibrated at 1573 K with iron satrated slag with between 2 and 36 percent s.ilica. The distribtion of cobalt from alloy to slag was reported to increase arond 4 percent as the silica in slag was increased over this range. These reslts imply that the activity coefficient of cobalt oxide decreases with an increase in silica content of slag, since the alloys contained essentially content amonts of cobalt (.28-.3%) over a narrow range of oxygen pressres. Fontana et al. 1 reported the solbilities of cobalt in iron silicate slags containing lime and eqilibrated with C-Co alloys by levitation at 1623 K, and at oxygen pressres of between 1-7 and 1-1 atrn. Althogh no activity coefficients were calclated, the solbility of cobalt reported for slags of constant Ca/Si ratio increased with increase in Fe/Si ratio, bt the effects of silica and calcia cold not be isolated. Katyal and J effes 11 eqilibrated iron silicate and ferrite slags with liqid Co-C alloys at temperatre between 1523 and 1623 K by the levitation techniqe. The activity coefficient of cobalt oxide in silica nsatrated iron silicate slag increased slightly with increase of silica content in slag. In addition to being nsatrated with silica, indstrial slags also contain oxide contaminants sch as magnesia, calcia and almina. No data are MOLTEN SLAGS, FLUXES AND SALTS '97 CONFERENCE - 79

2 iron silicate slag to 2 percent calcia in slag, it nearly dobled from 2 percent to 3 percent calcia in slag MOLTEN SLAGS, FLUXES AND SALTS '97 CONFERENCE Reddy 6 eqilibrated almina satrated fayalite slags (Fe/Si2 of 1.34) with liqid Co-C alloys at temperatres of 1473 and 1573 K and reported an activity coefficient for cobalt oxide very similar to that reported by Grimsey and Li 2 for almina-free silica satrated slags. This comparison implies that almina in slag has little effect on the solbility of cobalt oxide. In contrast, the addition of almina to iron silicate slags in contact with nickel mattes 12, may have sbstantially increased the activity coefficient of cobalt oxide, as evidenced by the reported enhancement in the matte/slag distribtion for cobalt. In the present work, solid Fe-Co alloys have been eqilibrated with silica nsatrated iron silicate slags at an oxygen pressre of 1-1 atrn. to evalate the effect of Fe/Si 2 ratio on cobalt oxide activity coefficient. Frther, liqid Co-Fe-A alloys have been eqilibrated with silica satrated slags containing almina, calcia or magnesia, as well as almina satrated slags, at 1-9 or 1-1 atrn. oxygen pressre, to evalate the effect of either almina, calcia or magnesia on the activity coefficient of cobalt oxide in the slags. 2. EXPERIMENT AL When eqilibrim is reached between an alloy of Co-Fe or Co-Fe-A, an iron silicate slag containing cobalt oxide and a C2/CO gas which sets a specific oxygen pressre, the relevant eqilibria are: [Co]+ C2 = (CoO) +CO [Fe]+ C2 = (FeO) +CO CO + 1/2 2 = C2 (1) (2) (3) where [ ] and ( ) represent the metal and the slag phase respectively. Iron is transferred from slag to alloy, and cobalt from alloy to slag, when eqilibrim is achieved sing initially iron free alloys and iron silicate slags. Eqilibrations with liqid Co-Fe-A alloys were carried ot by containing two grams of initially Co A alloy and two grams of slag mainly in pre recrystallised almina crcibles or silica crcibles; one experiment was carried ot with a magnesia crcible. The Co-A alloys were prepared in an indction frnace from 99.9 wt percent cobalt and wt percent gold, where the latter lowered the melting point of the alloy and also allowed the cobalt activity to be varied. Slags of the reqired composition were made from mixtres of two master slags of low ferric iron content, containing 38 and 12 percent silica respectively, which were prepared by melting iron, silica and ferric oxide powders in an iron crcible at 1573 K. Additions of almina, calcia and magnesia powder were made as necessary. The crcible, containing the alloy and iron silicate slag, was held at 1573 Kin a vertical, silicon carbide tbe frnace and nder a stream of prified and dried C 2 - CO gas, controlled at set ratios by capillary flow meters, and at a total flow of 2 cm 3 /min. The temperatre was measred by an almina-sheathed Pt/Pt-13% Rh thermocople placed directly nder the crcible, while the oxygen pressre was monitored by a stabilized zirconia solid electrolyte cell placed jst above the srface of molten slag. After eqilibration times of between 36 and 48 hors the crcible with the alloy and slag was qenched into an argon filled, water-cooled, copper chamber. The solidified slag was plverized nder ethanol to minimize secondary oxidation, and analysed for Co, ferros Fe, total Fe and Si2. The alloy was analyzed for Co and Fe by atomic absorption 16. A frstrating aspect of the work was the high percentage of the experiments which failed when sing cobalt crcibles, especially when the eqilibrim iron content of the alloy exceeded 2 percent. This occrred when the silica in the slag fell below 3 percent. The combination of a high level available for the effect of magnesia on activity coefficient of cobalt oxide. The work of Katyal and Jeffes 11 showed that while the activity coefficient of cobalt oxide increased slightly from calcia-free The experimental techniqe has been described in detail previosly Eqilibrations with solid Co-Fe were carried ot by containing approximately two grams of pre iron silicate slag within an 8 mm diameter by 25 mm high crcible of welded.1 mm thick (99.5 wt % Co) foil. A sheet of foil ( 4 mm x 15 mm) also was placed within the slag, to monitor the composition of the alloy at eqilibrim.

3 of iron diffsing into the alloy, and of cobalt dissolving from the alloy into slag, pitted the metal and allowed the slag to leak from the crcible. This problem was not encontered to the same extent when sing nickel crcibles in similar experiments 14, presmably since nickel has a lesser tendency to dissolve into slag and corrosion is less severe. 3. RESULTS The composition of eqilibrated slags and alloys are listed in Table I where all compositions have been smoothed to 1 percent except for the Co-Fe-A alloys, where the gold content was obtained by difference. The alloy compositions for solid Co-Fe alloys at a given temperatre, oxygen pressre, percent silica in the slag and a total pressre of one atm. are niqe since the system has for degrees of freedom. In contrast, the addition of gold to provide for liqid Co-Fe-A alloys, increases the degrees of freedom by one, and allows the cobalt content of the alloy to be varied when the for previos variable are defined. Cobalt is assmed to be present in the slag as CoO, in agreement with previos stdies The activity coefficient can be calclated from the eqilibrim Co = CoO (s) (4) where for the metal-slag-gas system: (5) Xco is the mole fraction of cobalt oxide in slag, p2 is the oxygen pressre in atmospheres, Yco and ac are the activity coefficient of cobalt oxide in slag and activity of cobalt in alloy respectively. The vale of the eqilibrim constant Ki is taken as 1.29 x 1 4 at 1573 K 5 when the solid cobalt standard is sed for solid Co-Fe alloy and as x 1 4 when the liqid cobalt standard is sed for liqid A-Co-Fe alloy 13. Oxygen pressre is calclated from the COi/CO ratio in the gas throgh the eqilibrim constant for (3), which is taken as 6.981x1 4 at 1573 K 17. The activity of cobalt in solid Co-Fe alloys at 1573 K, with atom fraction of cobalt greater than.7 is essentially ideal 18, while the activity of cobalt in liqid Co-Fe-A alloys can be calclated 19 sing the for sffix Margles eqation 2 with interaction parameters based on the binary systems Co-A 2 A Fe21 and Co-Fe 22. The activity coefficient of cobalt oxide relative to pre solid cobalt oxide was calclated from eqation (5) and is listed in table II, along with data associated with the calclation. The activity coefficient of cobalt oxide for silica nsatrated, almina-free slags is plotted against percent silica in Figre 1. The figre shows that the activity coefficient decreases with an increase the concentration of silica in the slag for the range of 28 to 38 weight percent silica. A description of the behavior of "(coo verss percent silica or mole fraction of silica in the almina-free slag is given by the least-sqare fitted eqation: or "(coo= Si2 (wt%) (6) "(coo = Xsi2 (7) The fitted lines inclde the previos data for silica satrated slags 2 containing 37 to 41 percent silica and apply for the range of 3 to 4 percent silica in slag i::: Q) 1.6 ~ ~. <+:: Q).8 ;;.-. ;;:..4 <::. ~-----'-~-'-~~~"------'-----'-~-'-~~_., U ~ ~ TI ~ ~ ~ ~ ~ Silica content (wt%) in slag Fig. 1: The activity coefficient of cobalt oxide at 1573 K as a fnction of silica content in almina-free slag. MOLTEN SLAGS, FLUXES AND SALTS '97 CONFERENCE - 711

4 p2 Slag Compositions (wt%) Alloy Compositions (atm.) (wt%) Si2 FeO Fe23 Coo Ah3 Cao MgO Co Fe A MOLTEN SLAGS, FLUXES AND SALTS '97 CONFERENCE Table I: Composition of iron silicate slags and eqilibrated solid Co-Fe and liqid Co-Fe-A alloys at 1573 K.

5 p2 Alloy Slag mole fraction Activity (atm.) coefficient Xco aco Si2 Alz3 Cao MgO coo 'YCoO MOLTEN SLAGS, FLUXES AND SALTS '97 CONFERENCE Table II: Activity coefficient of cobalt oxide in iron silicate slag at 1573 Kand data associated with the calclation.

6 "/Feo + XFe1.5 dln "{Fe1.5 =, which is identical to that for silica nsatrated, almina-free slags MOLTEN SLAGS, FLUXES AND SALTS '97 CONFERENCE Fig. 2: The activity coefficient of cobalt oxide as a fnction of percent silica in almina satrated slag with between 13 and 16 percent Alz 3 at 1573 K. almina-free silica satrated slag at the oxygen pressre of either 1-9 or 1-1 atmospheres. The Figre shows that activity coefficient of cobalt oxide in the slag increases from.9 to abot 2. as the concentration of almina increases from to abot satrated slag is plotted against percent almina in the Figre 3, which incldes the data 2 for The activity coefficient of cobalt oxide in silica 16 weight percent, which indicates that almina has a Fig. 3: The activity coefficient of cobalt oxide as a fnction of percent almina in silica satrated slag, for all slags of this stdy, as well as twenty silica satrated slags 2 at 1573 K. Figre 4 shows the activity coefficient of cobalt oxide as a fnction of concentration of calcia in weight percent in slag. As can be seen, the activity coefficient increases slightly as the concentration of calcia increases. The trend can be qantified by following least sqare regression eqations: I'.:: <!) l--- [ 3 2. <!)...» ~ <.,~...i._._~c..~'-'-..l~~l.._~_j_, ~.. L_~_,_j Silica content (wt%) in slag I'.:: <!) <+: <!) c 1. ()... > < ().5. ~~~~~~~-'---'~-'-~"'--'~--'--' Almina content (wt%) in slag Figre 2 shows the activity coefficient of cobalt oxide for almina satrated slags containing similar levels of almina within the range of percent, verss percent silica in the slag. The activity coefficient appears to decrease with an increase in silica content, in agreement with the trend observed for almina-free slag (Figre 1). 4., ~ The effect of silica on the activity coefficient of cobalt oxide for almina satrated slags can be evalated for slags of approximately constant almina content, since in this case the form of the Gibbs Dhem eqation for slags containing silica, cobalt oxide, ferros oxide, ferric oxide, and almina becomes Xsioz dln Ysioz + Xco dln Yco + XFeo dln The relationship between activity coefficient of cobalt oxide and percent almina in slag which incldes all slags containing almina from this stdy, as well as the data for twenty silica satrated slags containing no almina 2 is given as: or Ycoo = Alz3 (wt%) (8) 'Ycoo = XA123 (9) The fitted lines inclde the previos data for silica satrated slags 2 containing 37 to 41 percent silica and apply for the range of p to 16 percent almina in slag. strong effect on the activity coefficient of cobalt oxide. This reslt is consistent with a previos report 12 that almina may redce the solbility of cobalt oxide in slag.

7 Yco = Xcao (11) The fitted lines inclde the previos data for silica satrated slags 2 containing 37 to 41 percent and apply for the range ofp to 13 percent calcia in slag. 2. ~ ~ l.6 4-< ~ s 8 2 I ;;.. p < o~~~~'~-~~'~-~~'-~~ MOLTEN SLAGS, FLUXES AND SALTS '97 CONFERENCE < l.2 i:: <1) tt:: <1).8 ()» ;;.::: < ().4. ~~~~~~~~~~~~~~~~ Calcim oxide content (wt%) in slag Fig. 4: The activity coefficient of cobalt oxide as a fnction of percent calcia in silica satrated slag, for all slags of this stdy, as well as twenty silica satrated slags 2 at 1573 K. Figre 5 shows that the activity coefficient ~ppears to increase as the mole fraction of magnesia increases. The relationship between activity coefficient of cobalt oxide and concentration of magnesia as weight percent in slag can be qantified by following least sqare regression eqations: or Yco = MgO (wt%) (12) Ycoo = XMgO (13) The fitted lines inclde the previos data for silica satrated slags 2 containing 37 to 41 percent and apply for the range of p to 11 percent magnesia in slag Magnesia content (wt%) in slag Fig. 5: The activity coefficient of cobalt oxide as a fnction of percent magnesia in silica satrated slag, for all slags of this stdy, as well as twenty silica satrated slags 2 at 1573 K. The experimental reslts can be combined to provide a general eqation to estimate the solbility of cobalt in slag. Eqation (5) can be rewritten as: K4p~.5 a co X coo =~~~~ Ycoo (14) Since the solbility, expressed as cobalt (wt %) is approximately proportional to its mole fraction, rearrangement of eqation (14) shows that a plot of cobalt (wt%) verss p2 5 acjyco shold be linear with a zero intercept at the origin. This leads to a relationship between cobalt (wt % ) in slag, cobalt activity, activity coefficient of cobalt oxide and oxygen pressre, namely: 1.13 X 1 6 p~.5 ac wt o/o Co=----~~ Ycoo (15) p2 represents oxygen pressre in atmospheres, and Yco and aco represent the activity coefficient of cobalt oxide and activity of cobalt respectively. Eqation (15) qantifies the increase in solbility of cobalt which occrs in slag with either an increase in oxygen pressre or cobalt activity in L.~e system or a decrease in activity coefficient of cobalt oxide. 12 or Yco = CaO (wt%) (1)

8 However, this does not necessarily imply that the activity coefficient of cobalt oxide in slag increases with an increase in silica content (which wold be contrary to the reslts from this work). As explained by Grirnsey, the cobalt distribtion between matte and slag depends on the activity coefficient ratio of ferros oxide to cobalt oxide MOLTEN SLAGS, FLUXES AND SALTS '97 CONFERENCE or 12) are incorporated into eqation (15) the solbility of cobalt in slag can be calclated at different conditions. Figre 6 smmarises the present experimental vales, and those from a previos work 2, as a plot of the cobalt wt percent in slag, calclated by sing eqation (15). The predicted vales are in reasonable agreement with the experimental data; the slope of the best fit for the calclated vales verss measred vales is only 3 percent from nity. - "' OJ).. ~.s 9 '"O - 6 Q) ~ -::l ~..,-., ~. ::::. '-' ea,, ) 3 ~.'-' Q><-~~----'---~~~-'-----~~_L~~~ Cobalt (wt%) measred in slag Fig. 6: The relationship between the predicted ' solbility of cobalt in slag and that measred by experiments at 1573 K. 4.1 Effect of Silica 4. DISCUSSION The observed decrease in the act:j.v1ty coefficient of cobalt oxide with increase in the silica content of silica nsatrated, iron silicate slags, and those satrated in almina, can be interpreted thermodynamically by considering that cobalt oxide forms a relatively stable orthosilicate, compared say, to ferros oxide; The standard free energy of formation of cobalt and iron orthosilicates are respectively -1 kj/mol 23 and -4 kj/mol 24 at 1573 K. It is therefore reasonable to expect that the activity coefficient of cobalt oxide wold decrease with an increase in the silica content of iron silicate slags. # ("(Feol'Yco) as well as the percent iron in slag, and does not depend simply on the activity coefficient of cobalt oxide. When the percent silica in slag increases, the cobalt solbility will decrease mainly as a conseqence of the related decrease in the iron content of slag, since the activity coefficient ratio ("(Feo/'Yco) wold be expected to remain relatively constant for these chemically similar oxides. Ths the indstrial observations are not inconsistent with the present experimental reslts. 4.2 Effect of Almina A comparison of Figres 1 and 2 shows that the activity coefficient of cobalt oxide in almina satrated slag is virtally dobled compared to that in almina free slag. Almina is amphoteric and may be expected to act as acid relative to both cobalt and iron oxides in silica nsatrated slags. Ths the strong effect of almina on the activity coefficient is nexpected. If almina were to simltaneosly act as acidic oxide relative to ferros oxide and cobalt oxide, this might explain its effect in increasing the activity coefficient of CoO, since ferros alminate is chemically more stable than cobalt alrninate; the respective free energies of formation from the constitent oxides are -51 kj for FeO A}i 3 and -28 kj for CoO A12 3 at 1573 K 26. Ths cobalt oxide may be rejected from the melt, relative to ferros oxide, in the presence of almina, reslting in an increase in its activity coefficient as observed. However, the two fold magnitde of the observed increase is difficlt to explain. 4.3 Effect of Calcia An increase in calcia in slag was shown to increase the activity coefficient of cobalt oxide bt to a lesser extent than almina. Calcia is a stronger When the activity coefficient eqations (8, 1, The reslt is consistent with the evidence from a previos experimental stdy 9 1.

9 4.4 Effect of Magnesia MOLTEN SLAGS, FLUXES AND SALTS '97 CONFERENCE (3) The level of enhancement of the activity coefficient in the presence of almina was significantly greater than in the presence of calcia. This was nexpected from a thermodynamic standpoint. The magnitde of the effect of magnesia reqires frther experimental confirmation. 7. M.E. Reed and BJ. Elliot, "The Distribtion of Cobalt in the Kalgoorlie Nickel Smelter," Non Ferros Smelting Symposim (As. I. M. M.), Port Pirie, Soth Astralia, Sept. 1989, pp V.N. Zakharov and A.I. Tikhonov, "Co Distribtion between Matte and Slag," Tsvetyne (2) The activity coefficient of cobalt oxide increased with the addition of either almina (p to 16 wt%), calcia (p to 13 wt%) or magnesia (p to 11 wt%) into the slag. 6. R.G. Reddy, "Solbility of Cobalt in Copper Smelting and Refining Slags," Second Congress Cobalt Metallrgy and Uses, (Cobalt Development Inst.), Venice, Italy, 3 Sept.-3 Oct. 1985, pp (1) The activity coefficient of cobalt oxide decreases with an increase in silica content over the range of 15 to 41 percent silica in slag. 5. E.J. Grimsey and J.M. Togri, "The Solbility of Nickel and Cobalt in Iron Silicate Slags," Can. Metall. Q., Vol. 27, 1988, pp CONCLUSIONS The activity coefficient of cobalt oxide relative to pre solid cobalt oxide was measred in iron silicate slags over a range of silica, almina, calcia and magnesia contents throgh the eqilibrim of slags with either solid Co-Fe or liqid Co-A-Fe alloys at oxygen pressre of either 1-1 or 1-9 atm. at 1573 K. It was fond that: 3. S.S. Wang, A.J. Krtis and J.M. Togri, "Distribtion of Copper-Nickel and Copper-Cobalt between Copper-Nickel and Copper-Cobalt Alloys and Silica Satrated Fayalite Slags, " Can. Metall. Q., Vol. 12, 1973, pp S.S. Wang, N.H. Santander and J.M. Togri, "The Solbility of Nickel and cobalt in Iron Silicate Slags," Metall. Trans, Vol. 5, 1974, pp Since only three data points were observed for the effect of magnesia on cobalt oxide in slag, the magnitde of the increase in the activity coefficient with magnesia addition needs frther investigation. However, the observed increase was expected since magnesim silicate is more stable than either iron or cobalt silicate, that is, MgO is a mch stronger base relative to silica than either FeO or CoO, and preferentially interacts with it. REFERENCES 1. J.W. Matosek, "The Pyrometallrgical Winning of Cobalt," CIM Blletin. Vol. 76, Dec 1982,pp E.J. Grimsey and X. Li, "The Activity Coefficient of Cobalt Oxide in Silica-Satrated iron Silicate Slags, " Metall. Mater. Trans. B, Vol. 26B, 1995, pp base, relative _ to silica, than almina and shold preferentially interact with silica to strongly reject cobalt oxide and ferros oxide 27. The cobalt oxide activity coefficient may be expected to increase significantly therefore as calcia is added to the slag, with the effect greater than for almina addition. However, the relative stability of FeO Ah3 may have to be considered also, sch that the present observations cannot be interpreted based on a comparison of oxide-silica interactions alone. ACKNOWLEDGEMENTS The athors wish to thank the Mineral and Energy Research Institte of Western Astralia and Western Mining Corporation for sponsorship of this work, and Mr. Barry Elliot, Technical Sperintendent of the WMC Kalgoorlie Nickel smelter for his enthsiastic spport and helpfl comments. One of athors (X. Li) also wishes to thank Mrdoch University for the provision of a Postgradate Research Scholarship.

10 Metally (Non-Ferros Metals) Vol. 16, Sept. 1975, pp Y. Takeda, S. Kanesaka and A. Yazawa, "Eqilibria between FeOx-CaO-Si2 Slag and Liqid C-Ni-Fe Alloy," Proceedings of CIM 25th. Annal Conference of Metallrgists, 1986, pp A. Fontana, et al., "Properties of Ferros Silicate _ Slags Associated with Copper Flash Smelting and Electric Frnace Processes," Extractive Metallrgy 89. IMM, London, 1989, pp A. Katyal and J.H.E. Jeffes, "Activities of Cobalt and Copper Oxides in Silicate and Ferrite Slags," The 3rd International Conference on Molten Slags and Flxes, Jne RS. Cehner and J.M. Togri, "Cobalt and Gold Distribtion in Nickel-Copper Matte Smelting," Proceedings of CIM 25th. Annal Conference of Metallrgists, 1986, pp X. Li, "Ph.D. Thesis: The Solibility of Cobalt in Iron Silicate Slags at 1573 K," Mrdoch University, Western Astralia, October (1992). 14. E.J. Grimsey and A.K. Biswas, "Solbility of Nickel in Iron-Silicate Slags both Lime-free and Containing Lime at 1573 K," Trans. Instn. Min. Metall. (Sect. C: Mineral Process. Extractive Metallrgy). Vol. 86C, 1977, pp. Cl-C RF. Farrell, S.A. Matthes and A.J. Mackie, "A Simple, Low-Cost Method for the Dissoltion of Metal and Mineral Samples in Plastic Pressre Vessels," U.S. Brea of Mines, RI 848, 198, pp RF. Farrell, A.J. Mackie and W.R. Lessick, "Analysis of Steelmaking Slags by Atomic Absorption Spectroscopy Using Pressre Dissoltion," U.S. Brea of Mines, 8336, 1979, pp E.J. Grimsey and A.K. Biswas, "Solbility of Nickel in Silica-Satrated Iron Silicate Slags at 1573 K," Trans. Instn. Min. Metall. (Sect. C: Mineral Process. Extractive Metallrgy). Vol. 85C, 1976, pp. C A.F. Gillermet, "Critical Evalation of the Thermodynamic Properties of the Iron-Cobalt System," High Temp.-High Press. Vol. 19, 1987, pp A.E. Morris, et al., "Stepsol - An IBM based Thermodynamic Modelling Program for Pyrometallrgical Processes, Version 3.," Generic Mineral Technology Center of Pyrometallrgy, Rolla, MO, USA, Teppo and P. Taskinen, "Critical Evalation of the Thermodynamic Properties of Cobalt-Gold Alloys," Scand. J. ofmetall. Vol. 16, 1987, pp M. Nagamori and M. Kameda, "Thermodynamics of Liqid A-Fe Alloys between 11 C and 13 C," J. Jap. Inst. Met., Vol. 29, 1965, pp N.A. Gokcen and M.R. Baren, "Thermodynamic Properties of S-Fe-Co-Ni and Fe-Co-Ni Systems", Metall. Trans. A. Vol. 16A, 1985, pp G.M. Kale and K.T. Jacob, "Gibbs Energy of Formation of Co2Si4 and Phase Relations in the System Co-Si-," Trans. Instn. Min. Metall. (Sect. C: Mineral Process. Extractive Metallrgy. Vol. 98, 1989, C Kbaschewski and "Metallrgical Thermochemstry," Pergamon Press, New York C.B. 5th Alcock, edition, 25 E.J. Grimsey, "The Behavior of Cobalt Dring Nickel Smelting and Converting," Proc. Astralas. Inst. Min. Metall., Vol. 299 (2), 1994, pp Kbaschewski, "The Thermodynamic Properties of Doble Oxides (A Review)," High Temp.-HighPress. Vol. 4, 1972, pp D.R. Gaskell, "Thermodynamic Models of Liqid Silicates," Can. Metall. Q. Vol. 2, 1981, pp MOLTEN SLAGS, FLUXES AND SALTS '97 CONFERENCE