A Thermodynamic Model of Phosphate Capacity for CaO-SiO2-MgO-FeO-Fe2O3-MnO-Al2O3-P2O5 Slags Equilibrated with Molten Steel during a Top–Bottom Combined Blown Converter Steelmaking Process Based on the Ion and Molecule Coexistence Theory

A thermodynamic model for predicting the phosphate capacity of CaO-SiO₂-MgO-FeO-Fe₂O₃-MnO-Al₂O₃-P₂O₅ slags at the steelmaking endpoint during an 80-ton top–bottom combined blown converter steelmaking process has been developed based on the ion and molecule coexistence theory (IMCT). The phosphate capacity has a close relationship with the phosphate capacity index, whereas the logarithm of phosphate capacity is 12.724 greater than that of phosphate capacity index at 1873 K (1600 °C). The developed phosphate capacity prediction model can be also used to predict the phosphate capacity index with reliable accuracy compared with the measured and the predicted phosphate capacity index of the slags by other models in literatures. The results from the IMCT phosphate capacity prediction model show that the comprehensive effects of iron oxides and basic components control the dephosphorization reaction with an optimal ratio of (pct FeO)/(pct Fe₂O₃) as 0.62. The determined contribution ratio of Fe _t O, CaO + Fe _t O, MgO + Fe _t O, and MnO + Fe _t O to the phosphate capacity or phosphate capacity index of the slags is approximately 0.0 pct, 99.996 pct, 0.0 pct, and 0.0 pct, respectively. The generated 2CaO·P₂O₅, 3CaO·P₂O₅, and 4CaO·P₂O₅ as products of dephosphorization reactions accounts for 0.016 pct, 96.01 pct, and 3.97 pct of the phosphate capacity or phosphate capacity index of the slags, respectively.     

The apparent solubility of aluminum in cryolite melts

The apparent solubility of aluminum in cryolite melts saturated with A1₂O₃ has been determined by titration with electrolytically generated O₂. The results may be expressed by wt pct Al = − 0.2877 + 0.0268 (NaF/AlF₃ wt ratio) + 2.992 × 10⁻⁴ (temp °C) − 0.00192 (% CaF₂) −0.00174 (% Li₃AlF₆) −0.00288 (% NaCl) with a standard deviation of ±0.017. Ranges covered were ratio 0.8 to 2.3, temperatures 969° to 1054°C, CaF₂ ≤ 14 pct, Li₃AlF₆ ≤ 20 pct, and NaCl ≤ 10 pct. There was no significant effect of adding 0 to 38. pct K₃A1F₆ or 0 to 10 pct MgF₂. It was found that solubility was approximately proportional to activity of aluminum when Al-Cu alloys were used. Possible mechanisms of solution are discussed. Monovalent aluminum is ruled out on the basis of the variation of solubility with NaF/AlF₃ ratio and a_Al. The favored, but not proven, mechanism involves formation of both sodium atoms and a colloidal dispersion of aluminum.     

Solubility of oxygen and sulfur in copper-iron mattes

The concentrations of oxygen and sulfur in unsaturated and magnetite-saturated Cu-Fe mattes were measured as a function of oxygen and sulfur pressures and iron metal weight fraction of the matte (W _Fe = wt Fe/(wt Fe + wt Cu)). The liquid matte samples were equilibrated with streams of gas of known pressures of S₂ and O₂ at 1468 K. Empirical correlation equations were developed to describe the experimental results. The correlation for oxygen in unsaturated matte is wt pct O = 2.50P _{O 2} ^0.200 P _{S 2} ^-0.142 (1 + 9.0W _Fe ^2.19, and in magnetite-saturated matte it is wt pct O = 0.14 + 2.39W _Fe + 12.0W _Fe ² for 0.001 <P _{S 2} ≤ 0.01 atm and it is wt pct O = −3.06 + 2.39W _Fe + 12.0W _Fe ² − 1.60 logP _{S 2} for 0.01 <P _{S 2} < 0.023 atm. A single complex equation ofP _{O 2},P _{S 2}, andW _Fe describes the sulfur concentrations in both unsaturated and magnetite-saturated mattes. An erratum to this article is available at .     

A molten salt process for producing neodymium and neodymium-iron alloys

The production of low-cost neodymium metal in a stirred tank reactor by the reduction of Nd₂O₃ with sodium in the presence of CaCl₂−KCl−NaCl melts by the overall reaction Nd₂O₃+3CaCl₂+6Na→2Nd+3CaO+6NaCl at ∼750 °C is described. The metal produced is recovered from the salt medium by dissolving it in a Nd−Zn or Nd−Fe alloy pool. In the case of Nd−Zn alloy pools, product yields (percentages of theoretical neodymium produced) in excess of 94 pct are obtained when using salt ratios,i.e., the amounts of salt per gram of neodymium produced, ≥3.5 and excess reductant ≥10 pct. The alloy produced is of high quality, and following vacuum distillation of the zinc, can be used in producing General Motors’ MAGNEQUENCH alloy for permanent magnets. In the case of Nd−Fe pools, the yield is also ∼95 pct with a salt ratio as low as 3.5. The yield is found to depend on the salt composition and salt ratio, and to decrease at salt ratios below 3.25. Stirrer position has little effect on yield, while increasing the temperature and placing fins in the reactor increase the yield. The Nd−Fe alloy produced is of as good quality as that produced using Ca reductant and is suitable for direct use in preparing the MAGNEQUENCH alloy.     

A Sulfide Capacity Prediction Model of CaO-SiO2-MgO-FeO-MnO-Al2O3 Slags during the LF Refining Process Based on the Ion and Molecule Coexistence Theory

A sulfide capacity prediction model of CaO-SiO₂-MgO-FeO-MnO-Al₂O₃ ladle furnace (LF) refining slags has been developed based on the ion and molecule coexistence theory (IMCT). The predicted sulfide capacity of the LF refining slags has better accuracy than the measured sulfide capacity of the slags at the middle and final stages during the LF refining process. Increasing slag binary basicity, optical basicity, and the Mannesmann index can lead to an increase of the predicted sulfide capacity for the LF refining slags as well as to an increase of the sulfur distribution ratio between the slags and molten steel at the middle and final stages during the LF refining process. The calculated equilibrium mole numbers, mass action concentrations of structural units or ion couples, rather than mass percentages of components, are recommended to represent the slag composition for correlating with the sulfide capacity of the slags. The developed sulfide capacity IMCT model can calculate not only the total sulfide capacity of the slags but also the respective sulfide capacity of free CaO, MgO, FeO, and MnO in the slags. The comprehensive contribution of the combined ion couples (Ca²⁺ + O²⁻) and (Mn²⁺ + O²⁻) on the desulfurization reactions accounts for 96.23 pct; meanwhile, the average contribution of the ion couple (Fe²⁺ + O²⁻) and (Mg²⁺ + O²⁻) only has a negligible contribution as 3.13 pct and 0.25 pct during the LF refining process, respectively. The oxygen activity of bulk molten steel in LF is controlled by the [Al]–[O] equilibrium, and the oxygen activity of molten steel at the slag–metal interface is controlled by the (FeO)–[O] equilibrium. The ratio of the oxygen activity of molten steel at the slag–metal interface to the oxygen activity of bulk molten steel will decrease from 37 to 5 at the initial stage, and further decrease from 28 to 4 at the middle stage, but will maintain at a reliable constant as 5 to 14 at the final stage during the LF refining process. The proposed high-oxygen potential layer of molten steel beneath the slag–metal interface can be quantitatively verified.     

Experimental study of phase equilibria in the “FeO”-ZnO-(CaO + SiO2) system with the CaO/SiO2 weight ratio of 0.71 at metallic iron saturation

The pseudoternary section “FeO”-ZnO-(CaO + SiO₂) with a CaO/SiO₂ weight ratio of 0.71 in equilibrium with metallic iron has been experimentally investigated in the temperature range from 1000 °C to 1300 °C (1273 to 1573 K). The liquidus surface in this pseudoternary section has been determined in the composition range of 0 to 33 wt pct ZnO and 30 to 70 wt pct (CaO + SiO₂). The system contains primary-phase fields of wustite (Fe _x Zn_1−x O_1−y ), zincite (Zn _z Fe_1−z O), fayalite (Fe _w Zn_2−w SiO₄), melilite (Ca₂Zn _u Fe_1−u Si₂O₇), and pseudowollastonite (CaSiO₃). The phase equilibria involving the liquid phase and the solid solutions have also been measured.     

Activity of chromic oxide in the CaF2−CaO−Cr2O3 and the CaF2−Al2O3−Cr2O3 systems

The values of the activity of Cr₂O₃ in the slags based on the CaF₂−CaO−Cr₂O₃ and the CaF₂−Al₂O₃−Cr₂O₃ systems which may be used in the electroslag remelting (E.S.R.) process have been determined at 1450, 1500 and 1550°C by equilibrating the slags with Pt−Cr alloys of known chromium activity under known oxygen partial pressure and studying the equilibrium 2[Cr] alloy+3/2 O₂(g)=(Cr₂O₃)_slag. It was found that activity of Cr₂O₃ decreases with the addition of CaO and Al₂O₃ in the respective systems. In slags containing less than about 20 wt pct CaO and in the Al₂O₃ bearing slags, solutions of Cr₂O₃ showed a positive deviation from ideality and in slags containing more than 20 wt pct CaO, they showed a negative deviation. Both the authors were formerly with the Department of Metallurgy, University of Sheffield, England     

The diffusivity and solubility of oxygen in liquid tin and solid silver and the diffusivity

The diffusivity and solubility of oxygen in liquid tin and solid silver in the temperature range of about 750° to 950°C (1023 to 1223 K) and the diffusivity of oxygen in solid nickel at 1393°C (1666 K) were determined using the electrochemical cell arrangement of cylindrical geometry: Liquid or Solid Metal + O (dissolved) | ZrO₂ + (3 to 4%)CaO | Pt, air The diffusivity and solubility of oxygen in liquid tin are given by:D _O(Sn) = 9.9 × 10⁻⁴ exp(−6300/RT) cm²/s (9.9 × 10⁻⁸ exp − 6300/RT m²/s) andN _O ^S (Sn) = 1.3 × 10⁵ exp(−30,000/RT) at. pct The diffusivity and solubility of oxygen in solid silver follow the relations:D _O(Ag) = 4.9 × 10⁻³ exp (−11,600/RT) cm²/s ( 4.9 × 10⁻⁷ exp − 11,600/RT m²/s) andN _O ^S (Ag) = 7.2 exp (−11,500/RT) at. pct The experimental value for the preexponential in the expression forD _O(Ag) is lower than the value calculated according to Zener’s theory of interstitial diffusion by a factor of 11. The diffusivity of oxygen in solid nickel at 1393°C (1666 K) was found to be 1.3 × 10⁻⁶ cm²/s (1.3 × 10⁻¹⁰ m²/s). Formerly Graduate Student, Department Formerly Graduate Student, Department Formerly Graduate Student, Department This paper is based upon a This paper is based upon a This paper is based upon a This paper is based upon a     

The determination of oxygen in gas mixtures by electromotive force measurements using solid oxide electrolytes

The behavior of impervious ZrO₂+ 10 mole pct CaO electrolyte tubes was studied at 500∮ to 1100° in oxygen concentration cells of the type (−) Ar-O₂or CO-CO₂/ZrO₂-CaO/O₂(+) The equilibrium oxygen pressures imposed by Ar-O₂(1 to 10⁻⁶atm) and CO-CO₂ (10⁻⁶to 10⁻¹⁸ atm at 1000°) mixtures of known compositions were determined from electromotive force measurements. The measured and theoretical electromotive forces were compared. For Ar-O₂ mixtures, the oxygen pressures can be measured with accuracies of ±0.4 pct at 1 to 10⁻² atm and ±4 pet at 10⁻⁴ to 10⁻⁵ atm. An accuracy of ±11 pct can be achieved with CO-CO₂ mixtures. The electromotive force of the above cell increases as the gas flow rate at the anode increases at low flow rates and becomes independent of flow rate at high flow rates. The minimum flow rates required to eliminate any significant flow rate dependence are presented as a function of oxygen pressure. Formerly Graduate Student, Department of Metallurgy and Materials Science, University of Toronto, Toronto, Ontario, Canada     

Nitrogen solubility and nitride formation in austenitic Fe-Ti alloys

The equilibrium nitrogen solubility and nitride formation in austenitic Fe and Fe-Ti alloys were measured in the temperature range from 1273 to 1563 K. Specimens 0.5 mm thick were equilibrated with four different nitrogen-argon gas mixtures containing 1 pct hydrogen. The nitrogen solubility in austenitic iron obeys Sieverts' law. The equilibrium nitrogen content was determined to be log (wt pct N)_γ-Fe, P_{N2=1 atm} = (539 ± 17)/T − (2.00 ± 0.01). The precipitated titanium nitride was identified as cubic TiN, and the solubility product was determined to be log(wt pct Ti) (wt pct N) = −14,400/T + 4.94.     

Activities of chromium in molten copper at dilute concentrations by solid-state electrochemical cell

In order to obtain the activities of chromium in molten copper at dilute concentrations (<0.008 chromium mole fractions), liquid copper was brought to equilibrium with molten CaCl₂ + Cr₂O₃ slag saturated with Cr₂O₃ (s), at temperatures between 1423 and 1573 K, and the equilibrium oxygen partial pressures were measured by means of solid-oxide galvanic cells of the type Mo/Mo + MoO₂/ZrO₂(MgO)/(Cu + Cr))alloy + Cr₂O₃ + (CaCl₂ + Cr₂O₃)_slag/Mo. The free energy changes for the dissolution of solid chromium in molten copper at infinite dilution referred to 1 wt pct were determined as Cr (s) = Cr(1 wt pct, in Cu) and ΔG° = + 97,000 + 73.3(T/K) ± 2,000 J mol⁻¹.     

The effects of silicon on the reaction between solid iron and liquid 55 wt pct Al−Zn baths

The effect of various silicon levels on the reaction between iron panels and Al-Zn-Si liquid baths during hot dipping at 610°C was studied. Five different baths were used: 55Al−0.7Si−Zn, 55Al−1.7Si−Zn, 55Al−3.0Si−Zn, 55Al−5.0Si−Zn, and 55Al−6.88Si−Zn (in wt pct). The phases which formed as a result of this reaction were identified as Fe₂Al5 and FeAl3 (binary Fe−Al phases with less than 2 wt pct Si and Zn in solution),T1, T2, T4, T8, andT _5H (ternary Fe−Al−Si phases), andT _5C (a quaternary Fe−Al−Si−Zn phase). Compositional variations through the reaction zone were determined. The phase sequence in the reaction zone of the panel dipped for 3600 seconds in the 1.7 wt pct Si bath was iron panel/(Fe₂Al₅+T ₁)/FeAl₃/(T _5H+T _5C)/overlay. In the panel dipped for 1800 seconds in the 3.0 wt pct Si bath the reaction zone consisted of iron panel/Fe₂Al₅/(Fe₂Al₅+T ₁)/T ₁/FeAl₃/(FeAl₃+T ₂)/T _5H/overlay. In the panel dipped for 3600 seconds in the 6.88 wt pct Si bath the phase sequence was iron panel/Fe₂Al₅/(Fe₂Al₅+T1)/(T1+FeAl3)/(T1+T2)/T2/T8/T4/overlay. The growth kinetics of the reaction zone were also studied. A minimum growth rate for the reaction zone which formed from a reaction between the iron panel and molten Al−Zn−Si bath was found in the 3.0 wt pct Si bath. The growth kinetics of the reaction layers were found to be diffusion controlled in the 0.7, 1.7, and 6.88 wt pct Si baths, and interface controlled in the 3.0 and 5.0 wt pct Si baths. The presence of the interface between theT2/T5H, Fe2Al5/T ₁, orT ₁/FeAl₃ phases is believed responsible for the interface controlled growth kinetics exhibited in the 3.0 and 5.0 wt pct Si baths.     

Diffusion of managenese and silicon in liquid iron over the whole range of composition

The measurement of the diffusivities of manganese and silicon in molten binary ferroalloys over the whole range of composition was undertaken to clarify existing but conflicting data at lower concentrations, to present new data at higher concentrations and to indirectly confirm the behavior of both systems observed in thermodynamic studies. The experiments were carried out under argon atmosphere in a Tammann furnace. The diffusion couples were held in 5 mm ID alumina tubes (98 pct Al₂O₃). Electron probe microanalysis of the samples led to a diffusion-penetration curve for the system under consideration. Results obtained over the whole range of composition showed a slight negative deviation for the Fe−Mn system and a very large positive deviation for the Fe−Si system. At lower concentrations (0 to 4 pct Mn), the temperature dependence of managanese diffusivity for the Fe−Mn binary alloy in the temperature range 1550° to 1700°C is as follows:D _Fe−Mn=1.8×10⁻³ exp (−13,000/RT) cm²/sec The concentration dependence of manganese diffusivity for the same system at 1600°C may be expressed asD _Fe−Mn={5.48−0.0137 (%Mn)+0.000276 (%Mn)²}×10⁻⁵ cm²/sec The temperature dependence of silicon diffusivity for the Fe−Si binary system in the temperature range 1550° to 1725°C at various concentrations is as follows:D _Fe−Si=2.8×10⁻³ exp (−11,900/RT) cm²/sec at 20 pct SiD _Fe−Si=2.1×10⁻³ exp (−13,200/RT) cm²/sec at 12.5 pct SiD _Fe−Si=5.1×10⁻⁴ exp (−9,150/RT) cm²/sec at 2.2 pct Si FELIPE P. CALDERON, formerly Graduate Student. University of Tokyo, Tokyo, Japan. This paper is based on a portion of a thesis submitted by FELIPE P. CALDERON in partial fulfillment of the requirements for the degree of Doctor of Engineering at University of Tokyo.     

Experimental study of phase equilibria in the “FeO”-ZnO-(CaO + SiO2) system with CaO/SiO2 weight ratios of 0.33, 0.93, and 1.2 in equilibrium with metallic iron

The pseudoternary sections “FeO”-ZnO-(CaO + SiO₂) with CaO/SiO₂ weight ratios of 0.33, 0.93, and 1.2 in equilibrium with metallic iron have been experimentally investigated in the temperature range from 1000 °C to 1300 °C (1273 to 1573 K). The liquidus surfaces in these pseudoternary sections have been experimentally determined in the composition range from 0 to 33 wt pct ZnO and 30 to 70 wt pct (CaO + SiO₂). The sections contain primary-phase fields of wustite (Fe _x Zn_1−x O_1+y ), zincite (Zn _z Fe_1−z O), fayalite (Fe _w Zn_2−w SiO₄), melilite (Ca₂Zn _u Fe_1−u Si₂O₇), willemite (Zn _v Fe_2−v SiO₄), dicalcium silicate (Ca₂SiO₄), pseudowollastonite and wollastonite (CaSiO₃), and tridymite (SiO₂). The phase equilibria involving the liquid phase and the solid solutions have also been measured.     

Activities of oxygen in liquid Bi,Sn, and Ge from electrochemical measurements

Modified coulometric titrations on the galvanic cell: O in liquid Bi, Sn or Ge/ZrO₂( + CaO)/Air, Pt, were performed to determine the oxygen activities in liquid bismuth and tin at 973, 1073 and 1173 and in liquid germanium at 1233 and 1373 K. The standard Gibbs energy of solution of oxygen in liquid bismuth, tin and germanium for 1/2 O₂ (1 atm) →O (1 at. pct) were determined respectively to be ΔG° (in Bi) = −24450 + 3.42T (±200), cal· g-atom⁻¹ = − 102310 + 14.29T (±900), J·g-atom⁻¹, ΔG° (in Sn) = −42140 + 4.90T (±350), cal· g-aton⁻¹ = −176300 + 20.52T (± 1500), J-g-atom⁻¹, ΔG° (inGe) = −42310 + 5.31 7 (±300), cal·g-atom⁻¹ = −177020 + 22.21T(± 1300), J· g-atom⁻¹, where the reference state for dissolved oxygen was an infinitely dilute solution. It was reconfirmed that the modified coulometric titration method proposed previously by two of the present authors produced far more reliable results than those reported by other investigators. TOYOKAZU SANO, formerly a Graduate Student, Osaka University     

The rate of formation of intermetallic layers between aluminum and steel below 660°C

The rate of formation of intermetallic compounds between aluminum and three ferritic steels, one austenitic steel, and Inconel has been determined by an electrolytic method. The steel was held at zero potential with respect to aluminum in a NaCl-AlCl₃ melt, and the current measured. Comparison of measured thicknesses of intermetallic layers with those calculated from the integrated current gives an average deposition efficiency of 95 pct. For the Type 304 austenitic steel thickness (min), andk is given by logk= −6400/T(⁰K) +4.469. The ferritic steels show a linear rate of growth of Al₅Fe₂, with an initial higher rate such that extrapolation of the linear curve back to zero time gives an intercept of 16±7 μm. The rate constants (mm min⁻¹) may be represented by log (rate)=α/T+β, and the values of α and β are respectively −2650 and−0.788 for a plain carbon steel,−6580 and + 3.469 for a 1.3 pct Cr, 0.4 pct Mo steel, and−5950 and +2.466 for a 2.2 pct Cr, 0.9 pct Mo steel. The more highly alloyed steels are thus attacked, more slowly. Results for Inconel could not be fitted to any simple equation. With the ferritic steels growth is by aluminum diffusing inwards; with Inconel it is by nickel diffusing outward.     

Thermodynamics of MnO, FeO, and phosphorus in steelmaking slags with high MnO contents

The thermodynamics of managanese oxide and iron oxide and the phosphate capacity of CaO-SiO₂-MnO-Fe _t O-P₂O₅-MgO_sat slags with high MnO contents relevant to the smelting of MnO ores in steelmaking were investigated. Previous data were limited to about 5 pct MnO, whereas in this study MnO contents up to 25 pct were studied. The activity of MnO showed positive deviation from ideal behavior and increased with basicity, while that of Fe _t O decreased with basicity. This is reflected in that the manganese distribution ratio at a given Fe _t O content decreases with basicity and high Mn in the metal is favored by high basicity. CaF₂ additions up to 4 pct did not affect the activities of MnO and Fe _t O. The activity coefficient of P₂O₅ decreases and the phosphate capacity increases with basicity. There was not adverse effect of high MnO contents on the dephosphorizing abilities of the slags.     

A sintering study on the β-spodumene-based glass ceramics prepared from gel-derived precursor powders with LiF additive

Beta-spodumene (Li₂O·Al₂O₃·4SiO₂, LAS) powders were prepared by a sol-gel process using Si(OC₂H₅)₄, Al(OC₄H₉)₃, and LiNO₃ as precursors and LiF as a sintering aid agent. Dilatometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and electron diffraction (ED) were utilized to study the sintering, phase transformation, microstructure, and properties of the β-spodumene glass-ceramics prepared from the gel-derived precursor powders with and without LiF additives. For the LAS precursor powders containing no LiF, the only crystalline phase obtained was β-spodumene. For the pellets containing less than 4 wt pct LiF and sintered at 1050 °C for 5 hours the crystalline phases were β-spodumene and β-eucryptite (Li₂O·Al₂O₃·2SiO₂). When the LiF content was 5 wt pct and the sintering process was carried out at 1050 °C for 5 hours, the crystalline phases were β-spodumene, β-eucryptite (triclinic), and eucryptite (rhombohedral (hex.)) phases. With the LiF additive increased from 0.5 to 4 wt pct and sintering at 1050 °C for 5 hours, the open porosity of the sintered bodies decrease from 30 to 2.1 pct. The grains size is about to 4 to 5 μm when pellect LAS compact contains LiF 3 wt pct as sintered at 1050 °C for 5 hours. The grains size grew to 8 to 25 μm with a remarkable discontinuous grain growth for pellet LAS compact contain LiF 5 wt pct sintered at 1050 °C for 5 hours. Relative densities greater than 90 pct could be obtained for the LAS precursor powders with LiF > 2 wt pct when sintered at 1050 °C for 5 hours. The coefficient of thermal expansion of the sintered bodies decreased from 8.3 × 10⁻⁷ to 5.2 × 10⁻⁷/°C (25 °C to 900 °C) as the LiF addition increased from 0 to 5 wt pct.     

Loss of current efficiency in aluminum electrolysis cells

Consideration of the mechanism of loss of current efficiency (CE) leads to a form of equation which is simple, likely to give reasonable extrapolation beyond the range where experimental data are available, and convenient for responding to practical questions. With coefficients generated from plant experiments (performed by others), the equation is log (pct loss of efficiency) = 0.0095 (superheat) -−0.019 (pct A1F₂) − 0.060 (pct LiF) + const where superheat is the difference (in °C) between cell temperature and the pseudo-binary eutectic temperature with A1₂O₃, and pct A1F₃ is excess A1F₃. The coefficient for CaF₂ is zero. The constant is characteristic of the cell design. The question of reconciling the values of the coefficients with literature data on the solubility of Al in cryolite melts and current theories of loss of efficiency is discussed. Formerly Principal Scientist, Kingston Laboratory, Alcan International Ltd., Kingston, ON K7L 5L9, Canada, is retired.     

Effects of CaO, Al2O3, and MgO additions on the copper solubility, ferric/ferrous ratio, and minor-element behavior of iron-silicate slags

The effects of CaO, Al₂O₃, and MgO additions, singly or in combination, on the copper solubility, the Fe³⁺/Fe²⁺ ratio in slag, and on the minor-element behavior of silica-saturated iron silicate slags were examined at 1250 °C and a p _O2 of 10⁻¹² to 10⁻⁶ atm. The results indicated that copper solubility in slag was lowered with the addition of CaO, MgO, and Al₂O₃, in decreasing order. The Fe³⁺/Fe²⁺ ratio in the slag decreased with the additions, but this effect was smaller at lower oxygen potentials. The presence of small amounts (about 4 pct) of CaO, Al₂O₃, and MgO in the slag resulted in increased absorption of Bi and Sb into molten copper, but had a smaller effect at large additions (about 8 to 11 pct). The distribution behavior of Pb was a function of oxygen partial pressure, which indicates the oxidic dissolution of Pb in the slag as PbO, while the behavior of Bi, Sb, and As was found to be independent of oxygen potential, supporting the atomic (neutral) dissolution hypothesis of these elements in the slag. The distribution behavior of Pb and As was not significantly affected by the additions. The activity coefficients of Bi and Sb in the slags were determined to be as follows: (1) for no addition, γ _Bi=40 and γ _Sb=0.4; (2) for small additions (about 4.4 pct), γ _Bi=70 to 85 and γ _Sb=0.8; and (3) for large additions (about 8 to 11 pct), γ _Bi=60 to 75 and γ _Sb=0.5 to 0.7.