Die Verdampfung des Eisens und seiner Begleitelemente Kupfer und Mangan beim Schwebeschmelzen unter vermindertem Druck

Beschreibung einer Schwebeschmelzanlage für das tiegelfreie Schmelzen von Metallen unter kontrollierter Gasatmosphäre. Untersuchung der Verdampfung des Eisens und der Begleitelemente Kupfer und Mangan aus Proben des Stahles X 5 CrNi 18 9 in eine Argonatmosphäre bei Drücken zwischen 760 und 5 · 10^?2 Torr und Schmelztemperaturen zwischen 1760 und 1930 °C. Deutung der Versuchsergebnisse anhand eines Ansatzes von E. T. Turkdogan für die Diffusion von Metalldampf durch eine laminare Strömungsgrenzschicht. Vergleich der Ergebnisse für die Verdampfung unter vermindertem Druck in der Schwebeschmelzanlage und im Vakuuminduktionsofen und Schlußfolgerungen für die Einstellung optimaler Bedingungen zur Entfernung von Kupfer aus Stahlschmelzen.     

Margules behavior in binary metal solutions

By rearranging the Margules equations and postulating that the coefficients of these are inversely proportional to absolute temperature, it is shown that these equations may be used to deduce the relation established by Turkdogan and Darken (T.M.S.-AIME, 1968, vol. 242, pp. 1997–2005) between the parameters of terminal solution behavior, according to their quadratic formalism, for about thirty binary metal systems.     

Thermodynamic data of the formation of titanium nitride in iron

The solubility of titanium nitride in liquid iron is described by the solubility product log([%Ti][%N])₁ = ?17040/T + 6.40 reported by Turkdogan. The solubility in δ ferrite measured by Kunze is log<[%Ti][%N])_δ = ?17205/T + 5.56. Combining the solubilities in both phases and the solubilities of nitrogen the distribution equilibrium of titanium can be derived. It is characterized by the thermodynamic distribution coefficient k^δ/I_o,Ti = [%Ti]_δ/[%Ti] = 0.40. By zone melting and secondary ion mass spectrometry of the titanium distribution k^δ/I_Ti = 0.53 was measured. An analysis of all known data led to k^δ/I_o,Ti = 0.40…0.50. Measurements of the TiN solubility in austenite by heat treatment were not significant. They led to distribution coefficients between 0.07 and > 1. By zone melting in a carburizing atmosphere a distribution coefficient k^γ/I_Ti = 0.12 was measured. From a thermodynamic analysis performed by Ohtani et al., from the TiN solubility in the melt, and from the solubilities of nitrogen k^γ/I_o,Ti = 0.13 was deduced. Basing on the distribution equilibria of titanium and nitrogen and on the measured temperature dependence the solubility product log([%Ti][%N])_γ = ?15000/T + 4.06 was obtained.     

Kinetics of vapourization and oxidation of liquid iron levitated in flowing helium-oxygen

Abstract

Drops of iron, levitated and heated to about 1750° C, were oxidized in helium which contained up to 1.46% O₂ at flow rates up to 0.13 litre · sec^?1 Measured quantities were rates of oxidation and vapourization and the degree of oxidation of the fume. It was concluded that the formation of both FeO and Fe₃O₄ contributed to enhanced vapourization. A modified fonn of Turkdogan's expression describes the effect of partial pressure of oxygen on enhancement.

Résumé

Des gouttelettes de fer, lévitées et chauffées à environ 1750°C, ont ete oxydées sous hélium contenant jusqu'à 1.46% O₂ a un débit atteignant 0.13 litre·sec^?1. Les valeurs mesurées étaientles taux d'oxydation et de vaporisation et le degré d'oxydation des vapeurs. Il a été conclu que la formation de FeO et de Fe₃O₄ accélérait la vaporisation. Une forme modifiée de la relation de Turkdogan decrit l'effet de la pression partielle d'oxygène sur cette accéléra tion.     

A criticism of the Flood-Grjotheim ionic treatment of slag-equilibria

The analysis by Flood and Grjotheim¹ of the equilibria between a metal and a fused slag utilizes the ionic behavior of the slag or salt, and it employs a reversible thermodynamic cycle. However, in the original analysis there appears to be an error in the use of free energy. A corrected treatment has been developed which involves a modest change and simplification in the original formulation. The revised analysis shows the importance of the thermodynamic behavior of ionic species in the slag, which may be nonideal. Data from the literature on slag-metal equilibria, for example: $$\left[ {Fe^{2 + } } \right] + \underline {Mn} = Fe\left( l \right) + \left[ {Mn^{2 + } } \right]$$ , are analyzed by the new formulation to obtain expressions for ratios of activity coefficients such as (γS^2?/γO^2?), (γMn²⁺/γFe²⁺) and [(γPO ₄ ^3? )²/(γO^2?)³] in terms of slag composition, the last two having been found to depend strongly on the oxygen-ion content of the slag.     

Leaching kinetics of ionic rare-earth in ammonia-nitrogen wastewater system added with impurity inhibitors

Ammonia-nitrogen wastewater is produced during the dressing and smelting process of rare-earth ores.Such wastewater includes a very high concentration of NH4＋, as well as other ions（e.g., NH4＋, RE3＋, Al3＋, Fe3＋, Ca2＋, Cl–, and Si O32–） with a p H of 5.4–5.6.Its direct discharge will pollute, yet it can be recycled and used as a leaching reagent for ionic rare-earth ores.In this study, leaching kinetics studies of both rare earth ions and impurity ion Al3＋ were conducted in the ammonia-nitrogen wastewater system with the aid of impurity inhibitors.Results showed that the leaching process of rare-earth followed the internal diffusion kinetic model.When the temperature was 298 K and the concentration of NH4＋ was 0.3 mol/L, the leaching reaction rate constant of ionic rare-earth was 1.72 and the apparent activation energy was 9.619 k J/mol.The leaching rate was higher than that of conventional leaching system with ammonium sulfate, which indicated that ammonia-nitrogen wastewater system and the addition of impurity inhibitors could promote ionic rare-earth leaching.The leaching kinetic process of impurity Al3＋ did not follow either internal diffusion kinetic model or chemical reaction control, but the hybrid control model which was affected by a number of process factors.Thus, during the industrial production the leaching of impurity ions could be reduced by increasing the concentration of impurity inhibitors, reducing the leaching temperature to a proper range, accelerating the seepage velocity of leaching solution, or increasing the leaching rate of rare earths.     

Kinetics of the dissolution of scheelite in aqueous Na4EDTA solutions

The reaction kinetics of the dissolution of pure scheelite (CaWO₄) particles in aqueous Na₄EDTA solutions were studied at atmospheric pressure. As expected, the dissolution rate increased with decreasing initial particle size and with increasing temperature and Na₄EDTA concentration. Further, the dissolution rate decreased as the initial solid-liquid ratio and the ionic strength of the solution were increased. The experimental results do not support the conventional shrinking-core model for a single irreversible reaction. A new shrinking-core model for multiple reactions, composed of a noninstantaneous reversible reaction (scheelite dissociation into the ions Ca²⁺ and WO ₄ ²⁻ ) and an instantaneous irreversible reaction (formation of Ca-EDTA complex), was presented. The observed dependency of the dissolution rate on the relevant operating variables was the same a the theoretical predictions based on the present shrinking-core model. The activation energy was 49800 J mol⁻¹. These findings justify the validity of the assumed kinetic model with the multiple reactions as the rate-controlling step. The dissolution rate expression was obtained as a function of the initial particle size, initial solid-liquid ratio, Na₄EDTA concentration, temperature, and ionic strength of the solution.     

Electrical and electronic conductivity of CaO-SiO2-FeOx slags at various oxygen potentials: Part II. Mechanism and a model of electronic conduction

The experimental results obtained for ionic and electronic conductivity of ‘FeO’-CaO-SiO₂ melts have been analyzed considering the mechanism of each conduction process. The Nernst-Einstein equation was employed to calculate diffusion coefficients of Fe²⁺ and Ca²⁺ cations from ionic conductance. A “diffusion-assisted charge transfer” model was developed to explain the dependence of the electronic conductivity on the oxidation state of iron in the slag. The model considers the electronic conduction as a two-step process: in one step, ferrous ions diffuse from their initial position to a proper distance from ferric ions; in the next step, an electron is transferred between Fe²⁺ and Fe³⁺. The optimum distance of the iron ions for electron hopping was found to be approximately 4 Å, in great consistency with the values reported for electron transfer between Fe²⁺ and Fe³⁺ in aqueous solutions and solid glasses.     

Determination of the chemical diffusion of oxygen in liquid iron oxide at 1615 °c

The chemical diffusion of oxygen in liquid iron oxide has been studied by the oxidation of a melt in a long capillary at 1615 °C. When pure oxygen was used as the oxidizing agent, the surface composition of the slag was found to be in close agreement with the expected gas-slag equilibrium, suggesting that diffusion is the controlling step. This was not the case when air, 5 pct oxygen in argon or pure CO₂ was used to oxidize the slag. The deviation of the surface composition from the expected equilibrium was in accordance with a mechanism of mixed control by both the gas-slag reaction and diffusion in the bulk. The average value of the chemical diffusivity of oxygen (or iron) in liquid iron oxide with Fe²⁺/Fe _T between 0.25 and 0.77 was established to be 3(±1) × 10^-7 m²/s. This value is one to two orders of magnitude higher than those from earlier studies. There seems to be a reasonable correlation between the chemical and the ionic self-diffusivities through the Darken equation. A quantitative analysis in this respect and on the role of electron hole migration depends on the availability of data on the ionic conductivity and the tracer diffusivities. Formerly Postgraduate Student     

Effects of ionic liquid additive [BMIM]HSO4 on copper electro-deposition from acidic sulfate electrolyte

The effect of a new ionic liquid additive 1-butyl-3-methylimidazolium hydrogen sulfate-[BMIM]HSO₄ on the kinetics of copper electro-deposition from acidic sulfate solution was investigated by cyclic voltammetry, polarization and electrochemical impedance measurements and compared with those exerted by the conventional additive, thiourea. Results from cyclic voltammetry and kinetic parameters such as Tafel slope, transfer coefficient and exchange current density obtained from Tafel plots, indicated that [BMIM]HSO₄ had a pronounced inhibiting effect on Cu²⁺ electro-reduction and led to more leveled and fine-grained cathodic deposits. In addition, [BMIM]HSO₄ was found to inhibit the charge transfer and slightly change the copper electro-deposition mechanism compared to the absence of additives. Data obtained from X-ray diffraction spectra revealed that the presence of these additives did not change the crystal structure of the electro-deposited copper but strongly affected the crystallographic orientation of the crystal planes.     

Dielectric relaxation studies in soft — matter like nanocomposite polymer electrolyte PPG4 — AgCF3SO3: MgO

We have designed a new class of soft — matter like nanocomposite polymer electrolyte with the incorporation of MgO nanoparticles into poly (propylene glycol) (PPG) 4000 — AgCF₃SO₃ and examined the segmental dynamics and structural relaxation processes in detail by the impedance data as a function of frequency at various temperatures. The ionic conductivity value of 3 wt% MgO nanoparticles embedded composite revealed the maximum of 5.2 × 10^?4 Scm^?1 at 298 K. The frequency — dependence of mobility and structural relaxations has been discussed in terms of real and imaginary parts of modulus and dielectric spectra which suggested the presence of two types of relaxation times appearing within the electrolyte: the low frequency side revealed the dispersion contributing the α-relaxation (dipole — segmental motion) and an almost plateau — like trend contributing β-relaxation that is visible at the high frequency end. The frequency response of the modulus plot showed an asymmetrical nature rather than the ideal Debye type of behaviour.     

Behavior of tannins in germanium recovery by tannin process

The behavior of tannins in complexation with various metal ions was investigated to understand the complexation process of germanium, to reduce tannins use, and to improve the germanium recovery as a byproduct in zinc metallurgy. The experimental results obtained show that metal ions with relatively high valence (e.g. Fe³⁺) and big ionic radius (e.g. Pb²⁺) bind strongly to tannins, and that utilization of the tannins can be improved greatly by re-use and multi-use.     

Extraction of fission palladium by Aliquat 336 and electrochemical studies on direct recovery from ionic liquid phase

The wide electrochemical window and ion exchange properties of a room-temperature ionic liquid (RTIL) have been exploited for the extraction of palladium from nitric acid medium into ionic liquid phase — followed by direct electrodeposition of the metal from the organic phase. Extraction of palladium by commercial Aliquat 336 ionic liquids, tri-n-octylmethylammonium chloride (TOMAC) and tri-n-octylmethylammonium nitrate (TOMAN), was studied as a function of [HNO₃], [NO₃⁻] and [TOMAN]. The distribution ratio (D_Pd(II)) of palladium in TOMAN increased with an increase in the concentration of nitric acid and passed through a maximum at 1.0 M nitric acid. In contrast, the D_Pd(II) value of palladium in TOMAC decreased continuously with an increase in the concentration of nitric acid. Substantial amounts of water and nitric acid were also co-extracted into the organic phase with palladium.     

Electrical conductivity of individual molten rare-earth element chlorides: III. Structure of the melts and electricity transport mechanism

Reported data are analyzed, and the structure of individual molten rare earth metal chlorides is found to represent a loose ionic network with a local octahedral configuration of every cation. Electricity in such melts is carried by both Ln³⁺ cations and Cl_- anions. Electrotransport occurs via the following two main mechanisms: translational motion of individual ions and translational transfer in which several ions simultaneously hop into neighboring equilibrium positions.     

The kinetics of the dissolution of chalcocite in alkaline cyanide solution

A kinetic study of the dissolution of chalcocite in an alkaline cyanide solution indicates that the reaction is first order with respect to surface area and free cyanide ion concentration, and inversely proportional to the sulfide ion concentration to approximately the 0.1 power. The experimental rate constant is approximately 7.5 × 10⁻⁵ (mole Cu¹⁺/ min) ([S⁻²]^0.1/[CN¹⁻]/cm²/l at 25°C. The activation energy of 2.5 kcal/mole indicates rate control by diffusion through a limiting boundary layer. The concentrations of the important ions in the cyanide solutions are obtained by solving the ionic equilibria and mass balance equations for the system.     

Unique structural and magnetic traits of Nd3+-substituted Co–Zn nanoferrites

Because of the technological potential of magnetic spinel nanoferrites, we prepared neodymium ion (Nd³⁺)-substituted cobalt-zinc ferrites (CZFs) with the form Co_0.5Zn_0.5Nd_xFe_2–xO₄ (0.0 ≤ x ≤ 0.05) via a hydrothermal method. The as-prepared samples were thoroughly characterized using various analytical techniques. XRD, FTIR and FESEM analyses confirm the formation of a cubic spinel phase of the CZFNPs (CZF nanoparticles). A decrease in the lattice parameter due to the substitution of Fe³⁺ by Nd³⁺ in the lattice structures is manifested in the XRD refinement data. The magnetic properties of the proposed CZFNPs were evaluated in terms of the saturation magnetization, remanence, coercivity, squareness ratio and magnetic moment. These CZFNPs exhibit superparamagnetic behaviors at room temperature. Moreover, the Nd³⁺ inclusion does not significantly affect the measured magnetizations and coercivities of the CZFNPs. Samples containing 0.01 and 0.03 Nd³⁺ exhibit lower saturation magnetizations than that of the pristine product. The squareness ratios much less than 0.53 are ascribed to surface spin disordering. The unique magnetic traits of the synthesized CZFNPs are primarily attributed to the substitution of Fe³⁺ ions, with smaller ionic radii, by Nd³⁺ ions, with larger ionic radii. The proposed CZFNPs may be useful for diverse magneto-optic applications.     

Solubility products of metal sulfides in molten salts: II. Measurements and calculations for lead sulfide in the LiCl-KCl and the LiCl-LiF eutectic compositions

The solubilities of lithium sulfide and the solubility products of lead sulfide in the LiCl-KCI and LiCI-LiF eutectic mixtures have been measured by an electrochemical titration method in the temperature range from 673 to 823 K. At 823 K, the solubility of Li₂S in the LiCI-LiF eutectic was much larger than in the LiCI-KCI eutectic (1.95 × 10⁻¹ compared with 3.50 × 10⁻³). The measured solubility product of PbS in the LiCI-KCI eutectic (1.0 × 10⁻¹⁰ at 823 K) did not differ greatly from that in the LiCI-LiF eutectic (6.8 × 10⁻¹¹ at 823 K).A priori calculations were made of the solubility products of PbS and several transition and heavy metal Sulfides in the molten LiCI-KCI eutectic at 723 K. Fundamental theories of reciprocal and additive ternary molten salt solutions are used to explain the influence of the solvent on the solubilities of Li₂S and on the solubility products of PbS. The correlation of experiments with theory illustrates the utility of known theories of ionic systems in making predictions of solubilities and solubility products in ionic systems.     

Comparative leaching of a sulfidic gold ore in ionic liquid and aqueous acid with thiourea and halides using Fe(III) or HSO5 oxidant

The leaching of gold, silver and base metals from a sulfidic gold ore in the presence of an oxidant (peroxomonosulfate (HSO₅⁻) or iron(III)) and leaching agent (thiourea, chloride, bromide or iodide) is compared in 1-butyl-3-methylimidazolium hydrogen sulfate (bmimHSO₄) and chloride (bmimCl) ionic liquids, as well as in aqueous saturated K₂SO₄ as the solvent medium. Over 85% of gold and silver was recovered in the presence of HSO₅⁻/ thiourea at 25–50 °C in both bmimHSO₄ and bmimCl, with silver recovery significantly enhanced compared with that from aqueous sulfate medium. The leaching efficiency with HSO₅⁻ was similar to that with Fe(III) as oxidant in bmimHSO₄ and was far superior in bmimCl. With HSO₅⁻ /halide ion (Cl⁻, Br⁻, I⁻) as leaching agent, gold and silver recovery in bmimHSO₄, bmimCl or saturated aqueous K₂SO₄ improved from Cl⁻ to Br⁻ to I⁻, but only I⁻ gave a high recovery in the bmimCl ionic liquid due to the particular stability of the iodo complex anion in this medium. However, recovery was significantly higher than in an aqueous medium. Negligible recovery of base metals occurred in the ionic liquid medium, making it highly selective for Au and Ag. Concentration dependence studies with respect to halide and oxidant have defined optimum conditions for gold and silver recovery.     

Structural and electronic properties of bastnaesite and implications for surface reactions in flotation

The structural and electronic properties of bastnaesite were studied by using the first-principles method based on the density functional theory(DFT).The geometry structure of bastnaesite was first optimized,and then the Mulliken populations,electron density and density of states were calculated and further analyzed in detail.The calculation results reveal that it mainly ruptures along the ionic Ce-O and Ce-F bonds during the cleavage of bastnaesite,leaving≡Ce~+,≡F~-and≡CO_3~-dangling bonds exposed on the cleavage surface of bastnaesite.Combined with contact angle measurement,surface complexation theory and XPS analysis,the implications of structural and electronic properties on bastnaesite flotation reactions were studied.The hydration of exposed strong ionic bond on cleavage surface results in hydrophilic surface.According to surface complexation theory,the formed surface groups are≡CeOH~0,≡CO_3 H~0 and≡FH~0 groups.The investigated metal ions and flotation reagents complex with surface≡CeOH~0 groups,while≡CO_3 H~0 and≡FH~0 groups are not involved in the complexation.The high activity of Ce atoms facilitates these surface reactions.     

Electrowinning of Copper in the Presence of Anodic Depolarisers - A Review

Abstract

Alternative anodic reactions have been investigated to reduce the cell voltage and hence energy consumption in the electrowinning of copper. It is necessary to avoid oxygen evolution reaction at the anode, which requires a high potential of 2 V in order to reduce the cell voltage. An extensive literature review reveals that the cell voltage can be reduced by using various ionic couples, such as Fe²⁺/Fe³⁺, Cu²⁺/Cu¹⁺. Addition of cobalt, soluble sulfites and sulfur dioxide to the electrolyte modifies the anodic reaction. Examination of several electrode materials for anodic oxidation confirms that graphite is the most suitable material. Some fundamental studies on the anodic oxidation of sulfur dioxide have also been reviewed.