Experimental study of phase equilibria in the PbO-ZnO-“Fe2O3”-CaO-SiO2 system in air for high lead smelting slags (CaO/SiO2=0.35 and PbO/(CaO + SiO2)=5.0 by weight)

Experimental studies on phase equilibria in the multicomponent system PbO-ZnO-CaO-SiO₂-FeO-Fe₂O₃ in air have been conducted to characterize the phase relations of a complex slag system used in commercial lead oxidation smelting. The liquidus in the pseudo-ternary section ZnO-“Fe₂O₃”-(PbO + CaO + SiO₂) with the CaO/SiO₂ weight ratio of 0.35 and the PbO/(CaO + SiO₂) weight ratio of 5.0 has been constructed using results of over 100 high-temperature equilibration and quenching experiments followed by electron probe X-ray microanalysis. The liquidus in this pseudoternary section contains primary phase fields of spinel (zinc ferrite) Zn _x Fe_3−x O_4+y , zincite Zn _u Fe_1−u O, melilite Pb _v Ca_2−v Zn _w Fe_1−w Si₂O₇, hematite Fe₂O₃, magneto-plumbite PbFe₁₀O₁₆, and dicalcium silicate Ca_2−t Pb _t SiO₄. The laboratory results are compared with the slags obtained from an industrial reactor.     

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     

Cryoscopic studies in fluoride-Oxide-Silica systems: Part II. systems containing Mg2+, Ca2+, Ba2+ and Pb2+

The depressions of the freezing temperatures of MgF₂, CaF₂, and BaF₂ by adding 2MO · SiO₂, 3MO · 2SiO₂, MO · SiO₂, 2MO · 3SiO₂, and MO · 2SiO₂ where M = Mg, Ca and Ba, have been measured, as have the depressions of the freezing temperature of PbF₂ resulting from additions of 2Pb · SiO₂, 3PbO · 2SiO₂ and PbO · SiO₂. The variations of the activities of the fluorides with liquidus composition have been calculated. These are shown to be in good agreement with a proposed theoretical model of the constitutions of these melts. In the alkaline earth systems with MO/SiO₂ > 1.5 linear chain silicate ions and free F⁻ ions are postulated and in melts of MO/SiO₂ < 1.5 reaction between F⁻ and silicate ions to form polyfluorosilicate anions is postulated. These conclusions are in agreement with those drawn from infrared absorption studies of CaF₂-CaO-SiO₂ glasses. The activity behavior in the reciprocal systems MF₂-M′O · SiO₂ and M′F₂-MO · SiO₂ is explained in terms of polymerization and preferred ionic association effects within the melts. In the lead fluoride-silicate systems fluorination of the silicate ions occurs at PbO/SiO₂ = 2 and, in contrast with the alkali and alkaline earth systems, it appears that polyfluorosilicate anions and free O²⁻ anions can coexist in lead fluorosilicate melts.     

Standard enthalpy of formation of Sc5Si3

The standard enthalpy of formation of Sc₅Si₃ has been determined by solute-solvent drop calorimetry at (1473±2) K. The following value is reported: ΔH _f ^o (mean)=−(719.1±34.0) kJ mol⁻¹. This result is compared with corresponding published values for the enthalpies of formation of Me₅Si₃, with Me=Mn, Cr, V, Ti. This comparison shows regularly increasing negative enthalpies of formation from Mn₅Si₃ to Sc₅Si₃. LETTTIA TOPOR, formerly Senior Research Associate, The James Franck Institute, The University of Chicago,     

Standard gibbs energy of formation of Mg<Subscript>48</Subscript>Zn<Subscript>52</Subscript> determined by solution calorimetry and measurement of heat capacity from near absolute zero kelvin

The thermodynamic properties of Mg₄₈Zn₅₂ were investigated by calorimetry. The standard entropy of formation at 298 K, Δ_f S ₂₉₈ ^o , was determined from measuring the heat capacity, C _p , from near absolute zero (2 K) to 300 K by the relaxation method. The standard enthalpy of formation at 298 K, Δ_f H ₂₉₈ ^o , was determined by solution calorimetry in hydrochloric acid solution. The standard Gibbs energy of formation at 298 K, Δ_f G ₂₉₈ ^o , was determined from these data. The obtained results were as follows: Δ_f H ₂₉₈ ^o (Mg₄₈Zn₅₂)=(−1214±(300) kJ · mol⁻¹;Δ_fS ₂₉₈ ^o (Mg₄₈Zn₅₂)=(−123±0.36) J · K⁻¹ · mol⁻¹; and Δ_f G ₂₉₈ ^o (Mg₄₈Zn₅₂)=(−1177±(300) kJ · mol⁻¹. The electronic contribution to the heat capacity of Mg₄₈Zn₅₂ was found to be approximately equal to pure magnesium, indicating that the density of states in the vicinity of the Fermi level follows the free electron parabolic law.     

Occlusion and ion exchange in the molten (lithium chloride-potassium chloride-alkali metal chloride) salt + zeolite 4A system with alkali metal chlorides of sodium, rubidium, and cesium

Interaction between molten salts of the type LiCl-KCl-MeCl (Me = Na, Rb, Cs, x _MeCl = 0 to 0.5, x _KCl/x _LiCl = 0.69) and zeolite 4A have been studied at 823 K. The main interactions between these salts and zeolite are molten salt occlusion to form salt-loaded zeolite and ion exchange between the molten salt and salt-loaded zeolite. No chemical reaction has been observed. The extent of occlusion is a function of the concentration of MeCl in the zeolite and is equal to 11±1 Cl⁻ per zeolite unit cell, (AlSiO₄)₁₂, at infinite MeCl dilution. The ion-exchange mole fraction equilibrium constants (separation factors) with respect to Li are decreasing functions of concentration of MeCl in the zeolite. At infinite MeCl dilution, they are equal to 0.84, 0.87, and 2.31 for NaCl, RbCl, and CsCl, respectively, and increase in the order Na<Rb<Cs at identical MeCl concentrations. The standard ion-exchange chemical potentials are equal to −(0.0±0.5) kJ·mol⁻¹, −(0.4±0.3) kJ·mol⁻¹, and −(6.5±0.5) kJ·mol⁻¹ for Na⁻, Rb⁻¹, and Cs⁺, respectively.     

Standard enthalpies of formation of TiSi2 and VSi2 by high-temperature calorimetry

The standard enthalpies of formation of TiSi₂ and VSi₂ have been measured by a new calorimetric method. The following results are reported: ΔH _f ^° (TiSi₂) = −(170.9 ± 8.3) kJ mol⁻¹ and ΔH _{f ^°} (VSi₂) = −(112.4 ± 6.0) kJ mol⁻¹. These results are compared with experimental, assessed, and predicted values reported in the literature and with our own data for the corresponding borides. Estimates are given for the enthalpies of formation of the silicides of scandium and chromium.     

Thermodynamic properties of PbO-SiO2 slags by emf measurements

Abstract

The thermodynamic properties of PbO-SiO₂ liquid slags have been investigated by measuring the emfs of the following cell:

Pt, O₂(1 atm)/0.90 ZrO₂ + 0.10 CaO/(PbO-SiO₂)_liq.sol'n Pb_(l)

From the results, the activities and the other partial molar properties of the system have been calculated for compositions between 40 and 85 mole % PbO in the temperature range 720 to 110°C.

Résumé

Les propriétés thermodynamiques des scories liquids PbO-SiO₂ ont été recherchees en mesurant la f.e.m. de la pile suivante:

Pt,O₂(1 atm.)/0.90 ZrO₂ + 0.10 CaO/(PbO-SiO₂)_liq.sol'nPb_(l)

A partir des résultats, les activités et les autres propriétés molales partielles de ce système ont été calculées pour des compositions molales variant de 40 à 85% en PbO, sur un intelvalle de température s'etendant de 720 a 1100°C.     

Equilibrium formation and thermodynamic properties of gaseous silicon monosulfide

The formation of gaseous silicon monosulfide according to the reaction 1/2 SiS_2(s + 1/2 Si_(s) = SiS_(g) has been studied by the Knudsen effusion-gravimetric technique over the temperature range 863 to 1161 K. The equilibrium SiS pressure may be expressed by the equation logP _SiS(atm) = 7.205 -12,600T ⁻¹+ 0.4677 logT -4.508 × 10⁻⁴ T + 29.88T ^−1/2 The experimental free energy of the reaction may be represented by the two-term expression ΔF _{863-1161 K} ⁰ = 54,270 -38.34T Combination of these results and recent experimental data provide the standard free energy of formation of gaseous silicon monosulfide as expressed by ΔF _{863-1686 K} ⁰ = 12,740 -19.18T Si_{(s )} + 1/2 S_2(g) = SiS_(g) ΔF _{1686-2953 K} ⁰ = 640 -12.02T Si_(l) + 1/2 S_2(g) = SiS_(g)     

The thermal capacity and enthalpy of gadolinium sesquiselenide over a wide temperature range

Measurements have been made on the thermal capacity of γ-Gd₂Se₃ at 58.88–298.34 K. Values have been obtained for the thermal capacity, entropy, reduced Gibbs energy, and enthalpy under standard conditions: C°_p = 125.87 ± 0.5 J· mole⁻¹ · K⁻¹; S°(298.15 K) = 196.5 · 1.6 J · mole⁻¹ · K⁻¹; Φ°(298.15 K) = 103.6 ± 1.6 J · mole⁻¹ · K⁻¹; H°(298.15 K)-H°(0) = 27681 ± 138 J · mole⁻¹. The enthalpy of Gd₂Se₃ has been measured and the major thermodynamic functions have been calculated for the solid and liquid states over the temperature range 450–2300 K. The temperature dependence of the enthalpy in the ranges 300–1800 K and 2000–2300 K are represented: H°(T)-H°(298.15 K) = = 1.1949 · 10⁻² · T² + 122.38 · T + 347402 · T⁻¹ − 38716 and H°(T)-H°(298.15 K) = 262.81 · T-− 196047, respectively. The calculated temperature, enthalpy, and entropy of melting for Gd₂Se₃ are: T_m = 1925 ± 40 K, Δ_mH° (Gd₂Se₃) = 68.5 kJ · mole^-1, Δ_mS°(Gd₂Se₃) = 35.6 J · mole⁻¹ · K⁻¹. __________ Translated from Poroshkovaya Metallurgiya, Nos. 3–4(448), pp. 56–61, March–April, 2006.     

Enthalpies of formation of liquid and solid (palladium + indium) alloys

Enthalpies of formation of (Pd + In) alloys have been obtained by direct reaction calorimetry using a very high temperature calorimeter between 1425 and 1679 K in the concentration range 0 <x _Pd < 0.66. They are very negative with a minimum Δ_mix H _o ^m, = -59.6 /2.5 kJ · mol^-1 atx _Pd = 0.59 and independent of temperature within the experimental error. The integral molar enthalpy of mixing is given by Δ_mixΔH _m ^o /· mol^-1 =x(1 -x)·- (-126.94 - 92.653x-83.231.x ₂ - 734.49.x ₃ + 949.07x ⁴), wherex = x _Pd. The limiting partial molar enthalpy of palladium in indium was calculated as Δh _m(Pd liquid in ∞ liquid In) = -127 ± 5 kJ·mol^-1. The results are discussed and compared with the enthalpies of formation of solid alloys. The anomalous behavior of the partial enthalpy of Pd is assumed to be due to the charge transfer of, at most, two electrons of In to Pd. Formerly Ph.D. Student, Université de Provence.     

Enthalpies of formation of chromium carbides

Adiabatic oxygen combustion calorimetry has been used to determine the enthalpies of combustion of the chromium carbides Cr₂₃C₆, Cr₇C₃ and Cr₃C₂ to be—15,057.6±12.4 kJ ·mole⁻¹,—4985.3±3.8 kJ ·mole⁻¹ and—2400.5±0.9 kJ ·mole⁻¹ respectively. The products of combustion in all cases were Cr₂O₃ and CO₂. Using standard data for Cr₂O₃ and CO₂, the enthalpies of formation of the carbides have been calculated to be:fΔH ₂₉₈ ^o Cr₂₃C₆=−290.0±27.6 kJ·mole⁻¹ fΔH ₂₉₈ ^o Cr₇C₃=−149.2±8.5 kJ·mole⁻¹ fΔH ₂₉₈ ^o Cr₃C₂=−81.1±2.9 kJ·mole⁻¹     

Experimental liquidus in the PbO-ZnO-“Fe2O3”-(CaO + SiO2) System in Air,with CaO/SiO2 = 0.35 and PbO/(CaO + SiO2) = 3.2

Experimental studies on phase equilibria in the multicomponent system PbO-ZnO-CaO-SiO₂-FeO-Fe₂O₃ in air have been conducted to characterize the phase relations of a complex slag system used in lead and zinc smelting. The liquidus in the pseudoternary section ZnO-“Fe₂O₃”-(PbO + CaO + SiO₂) with a CaO/SiO₂ weight ratio of 0.35 and a PbO/(CaO + SiO₂) weight ratio of 3.2 has been constructed to describe liquidus temperatures as a function of composition in the range of commercial operating conditions employed by the Lead Isasmelt smelting process. The section contains the primary phase fields of spinel (zinc ferrite, Zn _x Fe_3−y O_4+z ), zincite (Zn _u Fe_1−u O), melilite (Pb _v Ca_2−v Zn _w Fe_1−w -Si₂O₇), hematite (Fe₂O₃), magnetoplumbite (PbFe₁₀O₁₆), and wollastonite (CaSiO₃).     

Standard enthalpies of formation for some samarium alloys, Sm + Me (Me = Ni, Rh, Pd, Pt), determined by high-temperature direct synthesis calorimetry

The standard enthalpies of formation of eight samarium alloys with late transition metals have been determined by direct synthesis calorimetry at 1273±2 K. The following values of ΔH _f ⁰, in kJ·(mole atom)⁻, are reported: SmNi₅, −27.4±0.5; Sm₅Rh₄, −66.5±1.0; SmRh₂, −65.5±1.2; SmPd, −82.4±2.0; Sm₃Pd₄, −87.2±2.5; SmPd₃, −82.9±2.5; SmPt, −108.7±3.5; and SmPt₂, −100.2±2.6. The results are compared with predicted values from the Miedema model, with available literature data for SmNi₅, SmPd, and SmPt, and with earlier values for similar compounds formed by other lanthanide metals reported by this laboratory. The observed relationships between the enthalpies of formation and the number of f-electrons in the considered binary alloys RE _n Me _m (RE=lanthanide elements; and Me=Group VIII elements) are discussed.     

Quantitative differential thermal analysis of polymorphic transformations in LaGe1.8 and SmSi2

The possibility of using quantitative differential thermal analysis to investigate phase transformations is examined. The temperature, enthalpy, and entropy of polymorphic transformations in LaGe_1.8 and SmSi₂ are determined: T_tr = 724 K, Δ_trH = 1635 ± 79 J · mole⁻¹, Δ_trS = 2.3 ± 0.1 J · mole⁻¹ · K⁻¹ (LaGe_1.8); T_tr = 658 K, Δ_trH = 1384 ± 69 J · mole⁻¹, Δ_trS = 2.1 ± 0.1 J · mole⁻¹ · K⁻¹ (SmSi₂). __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 3–4 (454), pp. 72–78, 2007.     

Enthalpies of formation of liquid (copper + manganese) alloys

The enthalpies of formation of liquid (Cu + Mn) alloys were measured in the isoperibolic heat-flux calorimeter at 1573 K in the entire range of compositions. The integral molar enthalpy of mixing was found to be negative in the range of molar fractions 0 < x _Mn < 0.31, with ΔH(min) = −0.69 ± 0.27 kJ mol⁻¹ at x _Mn = 0.12, and positive in the range 0.31 < x _Mn < 1, with ΔH(max) = 3.67 ± 0.36 kJ mol⁻¹ at x _Mn = 0.75. Limiting partial molar enthalpies of manganese and copper were calculated as = −18.0 ± 6.6 kJ mol⁻¹ and = 29.1 ± 4.9 kJ mol⁻¹, respectively. The results are discussed in comparison with the thermodynamic data available in the literature and the equilibrium phase diagram.     

Oxidation of Fe (II) in sulfuric acid solutions with dissolved molecular oxygen

The oxidation of Fe(II) with dissolved molecular oxygen was studied in sulfuric acid solutions containing 0.2 mol · dm⁻³ FeSO₄ at temperatures ranging from 343 to 363 K. In solutions of sulfuric acid above 0.4 mol · dm⁻³, the oxidation of Fe (II) was found to proceed through two parallel paths. In one path the reaction rate was proportional to both [Fe⁻²⁺]² andp _{o 2} exhibiting an activation energy of 51.6 · kJ mol⁻¹. In another path the reaction rate was proportional to [Fe²⁺]², [SO ₄ ^{2 −}], andp _{o 2} with an activation energy of 144.6 kJ · mol⁻¹. A reaction mechanism in which the SO ₄ ^{2 −} ions play an important role was proposed for the oxidation of Fe(II). In dilute solutions of sulfuric acid below 0.4 mol · dm⁻³, the rate of the oxidation reaction was found to be proportional to both [Fe(II)]² andp _{o 2}, and was also affected by [H⁺] and [SO ₄ ^{2 −}]. The decrease in [H⁺] resulted in the increase of reaction rate. The discussion was further extended to the effect of Fe (III) on the oxidation reaction of Fe (II).     

Calculation of equilibrium species for the aqueous solution systems of UO2SO4−U(SO4)2−H2SO4−HF and UO2Cl2−UCl4−HCl−HF at 298 K

Speciation models for aqueous solutions of UO₂SO₄−U(SO₄)₂−H₂SO₄−HF and UO₂Cl₂−UCl₄−HCl−HF were proposed based on chemical reaction equilibria, mass balances, charge balance, and stoichiometry of UF₄(s). The equilibrium concentrations of uranium and fluoride species in these solutions were calculated at 298 K, and are of relevance to the electrolytic reduction of U(VI), followed by the precipitation of UF₄(s). In these calculations, the reduction ratios of U(VI) were set at 25, 50, 75, and 100 pct. In the sulfate system the stable domains of U⁴⁺, U(SO₄) _n ⁴⁻²ⁿ , UF _n ⁴⁻ⁿ , and UF₄(s) as U(IV) species and UO ₂ ²⁺ , UO₂(SO₄) _n ²⁻²ⁿ , and UO₂F _n ²⁻ⁿ , as U(VI) species are strongly dependent on theC _T(F)/C _T(U(IV)) value. On the other hand, the stable domains of U⁴⁺ UCl³⁺, UF _n ^/4−n , and UF₄(s) as U(IV) species and UO ₂ ²⁺ , UO₂Cl⁺, and UO₂F _n ²⁻ⁿ as U(VI) species are also strongly affected by theC _T(F)/C _T(U(IV)) ratio in the chloride system. The initiation and precipitation of UF₄(s) in both the sulfate and chloride systems are a function of the reduction ratio of U(VI). The higher the reduction ratio, the lower theC _T(F)/C _T(U(IV)) values required. Compared to the chloride system, UF₄(s) precipitation in the sulfate system starts at a lower value ofC _T(F)/C _T(U(IV)). The addition of an excess amount of HF does not cause the dissolution of UF₄(s) precipitates because HF is a weak acid. KOJI SATO, formerly Graduate Student, Department of Metallurgy, Kyoto University, Kyoto, Japan