Oxidation‐reduction equilibria of ferrous/ferric ions in oxide melts

Oxidation‐reduction equilibrium experiments were conducted with oxide melts containing CaO, Li₂O, Al₂O₃, ZnO, B₂O₃, SiO₂ and small concentrations of iron oxide. The results indicated that for compositions within the acidic regime, the ratio {(Fe³⁺)/(Fe²⁺) P_O2^1/4} decreased with an increase in basicity while for relatively basic melts, the ratio increased with an increase in basicity. This variation of {(Fe³⁺)/(Fe²⁺) P_O2^1/4} could be interpreted in terms of the optical basicity of the glass melts and is consistent with the following expressions for the red‐ox equilibria within acidic and relatively basic melts, respectively: In an acidic melt, the temperature dependence of the reaction yielded an enthalpy value which was in excellent agreement with the enthalpy change for the reaction: For a relatively basic melt, the enthalpy value for the corresponding reaction was about half of that found for the acidic melt.     

Oxidation-reduction equilibrium of Cu2+/Cu+ in binary alkaline sulfate melts

Oxidation-reduction equilibria for a Cu²⁺/Cu⁺ couple in binary alkaline sulfate melts, Li₂SO₄ + R₂SO₄ (R = Na, K, Rb, Cs), were determined at temperatures of 973, 1023, and 1073 K by equilibrating these melts with gas mixtures of Ar + O₂ + SO₂. RedOx equilibria are well interpreted by the average ionic radii of alkaline metals: r(average) = X(Li₂SO₄) r(Li) + X(R₂SO₄) r(R), wherer andX denote, respectively, mole fraction and the ionic radii of alkaline metal. The oxygen anion activities would increase with an increase in R₂SO₄ mole fractions of binary sulfates Li₂SO₄ + R₂SO₄.     

Application of UV/VIS‐Reflection Spectroscopy for Determination of the Oxidation State of Liquid Slags with High Fe3+‐Contents

This work considers the reflectivity of liquid oxides (silicates and phosphates) in the ultraviolet and visible spectral range using a reflection angle of 0°. We have developed a spectroscopic reflection method (impulse‐flash‐technique) and have investigated CaO‐FeO_n‐SiO₂ and CaO‐FeO_n‐P₂O₅ with Fe₂O₃‐contents above 32 mol‐% (FeO_1.5) at a temperature of 1400°C applying oxygen partial pressures of p_o2 = 0.001 bar up to p_o2 = 0.21 bar. The increased reflectivity in the ultraviolet spectral range is based on the very intensive electron transfer (charge transfer bands, CT) from the oxide ion (bound to the respective matrix) to the Fe³⁺‐ion. The increased reflectivities in the visible spectral range are due to d‐d‐transitions in the Fe³⁺‐ion located in Fe³⁺‐O^2? ‐complexes. This can be proven in the following way. The reflection bands in the visible range are much less pronounced than the CT‐bands in the UV range. In the slag melts, complexes with the coordination number 4, Fe³⁺(O^2?)₄, have been found predominantly. The relation between the redox state of liquid slags and their UV‐reflectance has been evaluated quantitatively. The basic investigations for recording the redox state of liquid silicates and phosphates during a running metallurgic process are part of this work. Liquid silicates and phosphates are the most important slag systems in this context.     

Structure and Properties of Ferrites Based on CuFe2O4

We have studied the magnetic and structural properties of the solid solutions M _x ²⁺ Cu _1?x ²⁺ Fe ₂ ³⁺ O₄, where M = Mg, Ni, Co, Zn, Mn, Me _0.5x ⁺ Cu _1?x ²⁺ Fe _2+0.5x ³⁺ O₄, were Me = Li, Cu, and (Mn₃O₄)_x(CuFe₂O₄)_1?x. We have developed a new method for detecting a tetragonal phase and have used this method to determine the range of existence for solutions with a tetragonal structure. We explain the dependence of these ranges on the nature of M and Me.     

A solid state emf study of the pyrrhotite-magnetite equilibrium in the temperature interval 850 to 1275 K

The equilibrium 3/(1 −x)Fe_1−x S(s) + (5 − 2x)/(1 −x)O₂(g) Fe₃O₄(s) + 3/(1 −x)SO₂(g) was studied in the temperature interval 850 to 1275 K by measuring oxygen potentials in a galvanic cell containing calcia stabilized zirconia as solid electrolyte. The SO₂ activity was controlled by equilibrating the solid phases pyrrhotite and magnetite with a continuously flowing SO₂-Ar gas mixture of known composition. Formation of S₂ gas was taken into account and a recently published thermodynamic model for the pyrrhotite phase⁴ was used to derive the Gibbs energy change for the pyrrhotite-magnetite equilibrium and for the formation of Fe_1−x S as a function of the variables temperature and pyrrhotite composition.     

Investigation of the phase composition of accretions formed into WHB under flash smelting of copper concentrate

The phase composition of the depositions formed in the radiation section of the waste heat boiler utilizer (RS of WHB) after injecting sulphatizing flow in the volume of the off-gases from the uptake of flash smelting furnace for copper sulphide concentrate smelting was studied. With the help of X-ray diffraction (XRD), Reflected-light microscopy and Electron probe microanalysis (EPMA) of samples from the accretions, it was established that the main crystalline phases in the accretions were spinel, delafossite, cuprite and tenorite. The results from EPMA have shown that the spinel phase is with variable composition from cuprospinel to solid solution into the system Fe₃O₄-CuFe₂O₄-ZnFe₂O₄ (magnetite-cuprospinel-franklinite). Calculated on the basis of XRD and EPMA approximate formulae for the phases, identified in the samples from the accretions were the following: of the cuprospinel-(Cu_0.85²⁺Zn_0.09²⁺Fe_0.06²⁺)(Fe_1.87³⁺Al_0.10³⁺Si_0.03⁴⁺)O₄; of the spinel solid solution—(Cu_0.32²⁺Zn_0.36²⁺Fe_0.32²⁺)(Fe_1.81³⁺Al_0.19³⁺)O₄; Delafossite—Cu_1.07Fe_0.93O₂; cuprite—Cu_1.99Fe_0.02Si_0.01O and tenorite—Cu_0.993Fe_0.008O. The influence of the temperature on the sulphate formation processes of copper and iron oxides in the dust-gas flow was evaluated, based on experimental data and thermodynamic analysis of phase equilibriums in the systems Cu-S-O and Fe-S-O for the conditions, typical of the radiation section of the waste heat boiler (RS of WHB).     

Crystal structure determination by high resolution electron microscopy for (Sr0.86Nd0.14)3Cu2O5 intergrown with infinite-layer compound

A new phase (Sr_0.86Nd_0.14)₃Cu₂O₅ is found to be intergrown with the infinite-layer (IL) superconducting compound (Sr, Nd)CuO₂ prepared under high pressure, with the annealing temperature lower than usual. It belongs to the homologous series of (Sr, Nd) _n+1Cu _n O_2n+1 (n=1, 2, 3, …). The crystal structure has been determined by high resolution electron microscopy (HREM). The structure relationship between this phase and the IL phase is discussed.     

Thermodynamics of iron oxide in Fe x O-dilute CaO+Al2O3+Fe x O fluxes at 1873 K

The distribution of iron between Fe _x O-dilute CaO+Al₂O₃+Fe _x O fluxes and Pt+Fe alloys, as well as the redox equilibrium of iron ions in these fluxes, was experimentally investigated in pressure-controlled CO₂/CO gas at 1873 K. Total iron content in flux (pct Fe ^T ) and the ratio of (pct Fe²⁺) to (pct Fe ^T ) in fluxes with constant can be related to the activity of iron, α _Fe, and the partial pressure of oxygen, a _Fe, using the following equation:

Stability of silico-ferrite of calcium and aluminum (SFCA) in air-solid solution limits between 1240 °C and 1390 °C and phase relationships within the Fe2O3-CaO-Al2O3-SiO2 (FCAS) system

Quenching experiments were used to investigate the solid solution range, thermal stability, and selected phase relationships of silico-ferrite of calcium and aluminum (SFCA) within the Fe₂O₃-CaO-Al₂O₃-SiO₂ (FCAS) system. SFCA was found to be stable within a plane that connects the end members CF₃ (CaO·3Fe₂O₃), CA₃ (CaO·3Al₂O₃), and C₄S₃ (4CaO·3SiO₂). Chemical substitution in the four component system follows the coupled substitution mechanism 2(Fe³⁺, Al³⁺)↔(Ca²⁺, Fe²⁺)+Si⁴⁺ with the greatest range in chemical substitution occurring in the direction of the Al³⁺↔Fe³⁺ exchange (ranging from 0 wt pct Al₂O₃ to ∼31.5 wt pct Al₂O₃). The extent of Al³⁺↔Fe³⁺ substitution decreases with increasing temperature, and it was estimated that SFCA completely decomposes by ∼1480 °C. Coupled substitution involving Ca²⁺ and Si⁴⁺ for 2M³⁺ is not as extensive as the Al³⁺↔Fe³⁺ exchange, having a maximum range between 3 and 11 wt pct C₄S₃ component. Additional phases encountered in the experimental program included hematite; magnetite; quench liquid; dicalcium silicate; Fe-bearing gehlenite; calcium alumino-ferrite solid solutions, C(A, F)₆ and C(A, F)₂, plus an unidentified phase, possibly representing a solid substitution between SFCA-I and C(A, F)₃. Schematic phase diagrams have been constructed to show the relationship of SFCA with these surrounding phases.     

UV/VIS-spectroscopy of liquid slags

UV/VIS-spectroscopical methods have been applied to investigate the absorption behaviour of CaO-Al₂O₃-SiO₂-slags in a wide temperature range from 20 to 1655°C. The observations reveal a strong temperature dependence of the absorption bands, which can be explained by means of a newly developed theoretical model. The model also correlates the observed long-frequency UV cutoff-wavelength with the optical basicity. The definition of the optical basicity has been corrected for higher temperatures, since there are remarkable deviations between the solid and the liquid state, which have not been taken in consideration yet. Further investigations on a CaO-Al₂O₃-slag containing CaF₂ at 1500°C show that no Fe³⁺… F-complexes like Fe³⁺(F^?)₄ or Fe³⁺(F^?)₆ are formed. F^? reacts with Al³⁺ forming Al-O-F-complexes. The F^?-ions displace the O^2--ions from the Al³⁺. This causes the basicity to increase.     

Activities in the spinel solid solution Fe X Mg1−X Al2O4

Activities in the spinel solid solution Fe _X Mg_1−X Al₂O₄ saturated with α-Al₂O₃ have been measured for the compositional range 0<X<1 between 1100 and 1350 K using a bielectrolyte solid-state galvanic cell, which may be represented as Pt, Fe + Fe _X Mg_1−X Al₂O₄+α-Al₂O₃//(Y₂O₃)ThO₂/(CaO)ZrO₂//Fe + FeAl₂O₄+α-Al₂O₃, Pt Activities of ferrous and magnesium aluminates exhibit small negative deviations from Raoult’s law. The excess free energy of mixing of the solid solution is a symmetric function of composition and is independent of temperature: ΔG ^E=−1990 X(1−X) J/mol. Theoretical analysis of cation distribution in spinel solid solution also suggests mild negative deviations from ideality. The lattice parameter varies linearly with composition in samples quenched from 1300 K. Phase relations in the FeO-MgO-Al₂O₃ system at 1300 K are deduced from the results of this study and auxiliary thermodynamic data from the literature. The calculation demonstrates the influence of intracrystalline ion exchange equilibrium between nonequivalent crystallographic sites in the spinel structure on intercrystalline ion exchange equilibrium between the monoxide and spinel solid solutions (tie-lines). The composition dependence of oxygen partial pressure at 1300 K is evaluated for three-phase equilibria involving the solid solutions Fe + Fe _X Mg_1−X Al₂O₄+α-Al₂O₃ and Fe + Fe _y Mg_1−Y O+Fe _X Mg_1−X Al₂O₄. Dependence of X, denoting the composition of the spinel solid solution, on parameter Y, characterizing the composition of the monoxide solid solution with rock salt structure, in phase fields involving the two solid solutions is elucidated. The tie-lines are slightly skewed toward the MgAl₂O₄ corner.     

Thermodynamics of iron oxide in Fe x O-dilute CaO + Al2O3 + MgO + Fe x O slags at 1873 K

In order to determine the ferrous and ferric ion capacities: 3

Er3+/Yb3+/Li+/Zn2+: Gd2(MoO4)3 upconverting nanophosphors in optical thermometry

Er~(3+)-Yb~(3+)-Li~+:Gd_2(MoO_4)_3 and Er~(3+)-Yb~(3+)-Zn~(2+):Gd_2(MoO_4)_3 nanophosphors, synthesized by chemical co-precipitation technique were characterized through XRD,FESEM,dynamic light scattering(DLS),diffuse reflectance, photoluminescence, photometric and decay time analysis. The enhancement of about～28, ～149 and ～351 times in the green upconversion emission band is observed for the optimized Er~(3+)-Yb~(3+),Er~(3+)-Yb~(3+)-Li~+ and Er~(3+)-Yb~(3+)-Zn~(2+):Gd_2(MoO_4)_3 nanophosphors in comparison to the singly Er~(3+) doped nanophosphors. The electric dipole-dipole interaction is found to be responsible for the concentration quenching. The temperature dependent behaviour of the two green thermally coupled levels of the Er~(3+) ions based on the fluorescence intensity ratio technique was studied. The maximum sensor sensitivity ～38.7 × 10~(-3) K~(-1) at 473 K for optimized Er~(3+)-Yb~(3+)-Zn~(2+) codoped Gd_2(MoO_4)_3 nanophosphors is reported with maximum population redistribution ability～88% among the ~2H_(11/2) and ~4S_(3/2) levels.     

Chemical potentials of oxygen for three-phase assemblages of CaSiO3(s) + Ca3Si2O7(s) + {CaO + SiO2 + FexO} melt and Ca3Si2O7(s) + Ca2SiO4(s) + {CaO + SiO2 + FexO} melt

By employing an electrochemical technique involving stabilized zirconia as solid electrolyte and Mo + MoO₂ mixture as reference electrode, the equilibrium oxygen partial pressures for three-phase assemblages of CaSiO₃(s) + Ca₃Si₂O₇(s) + {CaO + SiO₂ + Fe_xO} melt and Ca₃Si₂O₇(s) + Ca₂SiO₄(s) + {CaO + SiO₂ + Fe_xO} melt were determined as: - log {P_O2 (CS + C₃S₂ + L)/bar} = - 3.22 13000/(T/K) ± 0.05 - log {P_O2 (C₃S₂ + C₂S + L)/bar} = - 0.92 16400/ (T/K) ± 0.04. respectively, where CS, C₃S₂ and C₂S indicate CaSiO₃(s), Ca₃Si₂O₇(s). and Ca₂SiO₄(s), respectively.     

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.     

Thermodynamics of iron oxide in FexO‐dilute CaO + Al2O3 + SiO2 + FexO slags at 1873 K

The ferrous and ferric ion capacities, and , for the slag of CaO + Al₂O₃ + SiO₂ are determined at 1873 K by means of the distribution equilibrium of iron between Fe_xO dilute slags of the system and Pt + Fe alloys under a controlled atmosphere. Compared with the values of for CaO + Al₂O₃ binary slag at a constant ratio of Al₂O₃ to decreases with an increase in SiO₂ content. Nearly linear relationships are observed between the logarithm of the ferrous and ferric ion capacities and the optical basicity. Applying these capacities, the relationship between (%Fe^T) and PO₂ under iron saturation, as well as the iron redox equilibrium in slag in relation to the optical basicity were discussed.     

Oxygen potentials in Ni + NiO and Ni + Cr2O3 + NiCr2O4 systems

The chemical potential of O for the coexistence of Ni + NiO and Ni + Cr₂O₃ + NiCr₂O₄ equilibria has been measured employing solid-state galvanic cells, (+) Pt, Cu + Cu₂O // (Y₂O₃)ZrO₂ // Ni + NiO, Pt (-) and (+) Pt, Ni + NiO // (Y₂O₃)ZrO₂ // Ni + Cr₂O₃ + NiCr₂O₄, Pt (-) in the temperature range of 800 to 1300 K and 1100 to 1460 K, respectively. The electromotive force (emf) of both the cells was reversible, reproducible on thermal cycling, and varied linearly with temperature. For the coexistence of the two-phase mixture of Ni + NiO, δΜ_{O 2}(Ni + NiO) = −470,768 + 171.77T (±20) J mol⁻¹ (800 ≤T ≤ 1300 K) and for the coexistence of Ni + Cr₂O₃ + NiCr₂O₄, δΜ_{O 2}(Ni + Cr₂O₃ + NiCr₂O₄) = −523,190 + 191.07T (±100) J mol⁻¹ (1100≤ T≤ 1460 K) The “third-law” analysis of the present results for Ni + NiO gives the value of ‡H ₂₉₈ ^o = -239.8 (±0.05) kJ mol⁻¹, which is independent of temperature, for the formation of one mole of NiO from its elements. This is in excellent agreement with the calorimetric enthalpy of formation of NiO reported in the literature.     

Effects of iron and temperature on solubility of light rare earth sulfates in multicomponent system of Fe2(SO4)3-H3PO4-H2SO4 synthetic solution

Numerous light rare earth elements (LREE) minerals containing Fe and P were processed by sulfuric acid roasting method, and the leaching solution mainly comprises LREE sulfate, Fe₂(SO₄)₃, H₃PO₄, and H₂SO₄, however, the solubility data of LREE sulfates in this system is few. This work studies the solubility of LREE sulfates in independent LREE sulfate system RE₂(SO₄)₃-Fe₂(SO₄)₃-H₃PO₄-H₂SO₄ (RE = La, Ce, Pr or Nd) and mixed LREE sulfates system (La,Ce,Pr,Nd)₂(SO₄)₃-Fe₂(SO₄)₃-H₃PO₄-H₂SO₄ at different temperature (25–65 °C) and concentrations of Fe₂(SO₄)₃ (Fe₂O₃, 0–50.13 g/L), H₂SO₄ (0.5 mol/L), and H₃PO₄ (P₂O₅, 20.34 g/L) based on the industrial operating condition at low liquid and solid ratio 2:1. The solubility of each LREE sulfate in the independent system (La₂O₃, 12.25–20.88 g/L; CeO₂, 41.93–62.35 g/L; Pr₆O₁₁, 37.34–56.69 g/L; Nd₂O₃, 26.60–37.63 g/L) is much higher than that of the mixed system (La₂O₃, 6.95–11.03 g/L; CeO₂, 10.63–21.51 g/L; Pr₆O₁₁, 11.56–20.36 g/L; Nd₂O₃, 12.36–19.79 g/L) under the same other conditions. The results also indicate that, in the two systems, both Fe and the temperature have negative effects on the solubility of LREE sulfates. That may occur due to the complication reactions between the complexes of RESO₄⁺ and Fe(SO₄)₂^–. However, the influence degree of temperature and iron concentration on the LREE sulfates solubility varies in the two systems and among different LREE species. This research is of theoretical significance for optimizing the conditions of the sulfuric acid process for recovering the LREE from the mixed LREE bearing minerals as well as the single LREE containing secondary rare earth scraps.     

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).     

Characterization and alkaline decomposition–cyanidation kinetics of industrial ammonium jarosite in NaOH media

A complete characterization was carried out on a jarositic residue from the zinc industry. This residue consists of ammonium jarosite, with some contents of H₃O⁺, Ag⁺, Pb²⁺, Na⁺ and K⁺ in the alkaline “sites” and, Cu²⁺ and Zn²⁺ as a partial substitution of iron. The formula is: [Ag_0.001Na_0.07K_0.02Pb_0.007(NH₄)_0.59(H₃O)_0.31]Fe₃(SO₄)₂(OH)₆. Some contents of franklinite (ZnO^·Fe₂O₃), gunninguite (ZnSO₄·H₂O) and quartz were also detected. The jarosite is interconnected rhombohedral crystals of 1–2 μm, with a size distribution of particles of 2–100 μm, which could be described by the Rosin–Rammler model.The alkaline decomposition curves exhibit an induction period followed by a progressive conversion period; the experimental data are consistent with the spherical particle with shrinking core model for chemical control. The alkaline decomposition of the ammonium jarosite can be shown by the following stoichiometric formula:NH₄Fe₃(SO₄)₂(OH)_6(s)+3OH_(aq)⁻→(NH)_4(aq)⁺+3Fe(OH)_3(s)+2SO_4(aq)²⁻.The decomposition (NaOH) presents an order of reaction of 1.1 with respect to the [OH⁻] and an activation energy of 77 kJ mol⁻¹. In NaOH/CN⁻ media, the process is of 0.8 order with respect to the OH⁻ and 0.15 with respect to the CN⁻. The activation energy was 46 kJ mol⁻¹. Products obtained are amorphous. Franklinite was not affected during the decomposition process. The presence of this phase is indicative that the franklinite acted like a nucleus during the ammonium jarosite precipitation.