Oxygen application to chloride leaching of complex sulfide ores

The study investigates leaching of complex sulfide ores with simultaneous regeneration of the leaching solution and removal of dissolved iron to balance the iron concentration in the leaching process. To minimize environmental pollution and obtain high metal extraction from the ores, leaching with a ferric chloride solution is adapted to treat Delta sulfide ores. The experimental results indicate that under high oxygen pressure leaching, oxidation of ferrous ion to ferric ion and partial precipitation of iron from solution can occur simultaneously. However, the findings also indicate that leaching the ores with simultaneous iron precipitation in one operation is difficult. It is better to precipitate excess iron in one stage; then leach the ores in another stage using the regenerated leaching solution

High-temperature relative enthalpies and related thermodynamic properties of CuI

"Relative enthalpies of cuprous iodide (cui) were measured at the Bureau of Mines to provide thermodynamic data for the advancement of mineral technology. Enthalpy measurements between 298.15 And 1,396.3 K were made with a copper-block drop calorimeter. The temperatures of transition were measured by differential scanning calorimetry. Reversible transitions were determined at 643 k with a standard enthalpy of transition = 0.74 Kcal/mol, at 679 k with a standard enthalpy of transition = 0.65 Kcal/mol, and at 868 k with a standard enthalpy of fusion = 1.895 Kcal/mol. Tabulated values are listed at selected temperature increments from 298.15 to 1,600 k for the standard relative enthalpy, heat capacity, entropy, and Gibbs energy function. The enthalpy data are also given in the form of equations and combined with thermodynamic data from other investigations to derive values of standard enthalpies of formation, Gibbs energies of formation, and logarithms of the equillibrium constants of formation (log kf)." - NIOSHTIC-2NIOSHTIC no. 1000564

Measurement of Gibbs energies of formation of CoF₂ and MnF₂ using a new composite dispersed solid electrolyte

Gibbs energies of formation of CoF2 and MnF2 have been measured in the temperature range from 700 to 1100 K using Al2O3-dispersed CaF2 solid electrolyte and Ni+NiF2 as the reference electrode. The dispersed solid electrolyte has higher conductivity than pure CaF2 thus permitting accurate measurements at lower temperatures. However, to prevent reaction between Al2O3 in the solid electrolyte and NiF2 (or CoF2) at the electrode, the dispersed solid electrolyte was coated with pure CaF2, thus creating a composite structure. The free energies of formation of CoF2 and MnF2 are (± 1700) J mol−1; ΔG°f(CoF2,s)=-664,010+134.38T(700-980K) ΔG°f(MnF2,s)=-848.270+129.59T(700-980K) =-850.200+131.56T(980-1100K) The third law analysis gives the enthalpy of formation of solid ΔG°f2 as ΔH° (298·15 K) = −672·69 (± 0·1) kJ mol−1, which compares with a value of −671·5 (± 4) kJ mol−1 given in Janaf tables. For solid MnF2, ΔH°(298·15 K) = − 854·97 (± 0·13) kJ mol−1, which is significantly different from a value of −803·3 kJ mol−1 given in the compilation by Barinet al

High-quality EuO thin films the easy way via topotactic transformation

Epitaxy is widely employed to create highly oriented crystalline films. A less appreciated, butnonetheless powerful means of creating such films is via topotactic transformation, in which achemical reaction transforms a single crystal of one phase into a single crystal of a differentphase, which inherits its orientation from the original crystal. Topotactic reactions may beapplied to epitactic films to substitute, add or remove ions to yield epitactic films of differentphases. Here we exploit a topotactic reduction reaction to provide a non-ultra-high vacuum(UHV) means of growing highly oriented single crystalline thin films of the easily overoxidizedhalf-metallic semiconductor europium monoxide (EuO) with a perfection rivallingthat of the best films of the same material grown by molecular-beam epitaxy or UHV pulsedlaserdeposition. As the technique only requires high-vacuum deposition equipment, it hasthe potential to drastically improve the accessibility of high-quality single crystalline films ofEuO as well as other difficult-to-synthesize compounds

Derivation of Internally-Consistent Thermodynamic Data by the Technique of Mathematical Programming: a Review with Application the System MgO-SiO2-H2O

The problem of deriving an optimal set of thermodynamic properties of minerals from a diverse experimental data base is reviewed and a preferred methodology proposed. Mathematical pro-gramming(MAP) methods extend the linear programming (LIP) approach first presented by Gordon (1973), and make it possible to account for the type of information conveyed, and the uncertainties attending both phase equilibrium data and direct measurements of phase properties. For phase equilibrium data which are (in most cases) characterized by non-normal error distributions across experimental brackets, the midpoint of a bracket is no more probable than other points, and the data are best treated by considering the inequality in the change in Gibbs free energy of reaction at each half-bracket. Direct measurements of phase properties can be assumed to have approximately normal error distributions, and the MAP technique optimizes agreement with these values by using the principles of least squares in the definition of an objective function. The structure of this problem, treatment of uncertainties in various types of experimental data, and method of optimizing final solutions are discussed in some detail. The method is applied to experimental data in the MgO-SiO2-H2O system, where inconsistencies among the data are resolved and an optimal set of thermodynamic properties is presented. The derived standard state entropies and volumes agree with all direct measurements (within their uncertainties), as do enthalpies of formation from the elements except for those of talc (+16 kJ mol−1), anthophyllite (+ 14 kJ mol−1), and brucite (−1 kJ mol−1). Stable phase relations in the system have the topology predicted by Greenwood (1963, 1971), with quartz- and forsterite-absent invariant points at 683 °C-6-4 kb and 797 °C-12 kb respectively, repeating at 552 °C-120 b and 550 °C-55 b. The thermodynamic analysis indicates little remaining flexibility in the phase relations, which, when combined with suitable activity models for solid solution, should allow for accurate determination of the conditions of metamorphism of ultramafic rock

High temperature relative enthalpies of CuBr

"Relative enthalpies of cubr from 298.15 to 1,301 k were measured at the Bureau of Mines to provide thermodynamic data needed for the advancement of mineral technology. The temperatures of transition were meaured by differential scanning calorimetry and the standard enthalpies of transition (ahtr deg) by drop calorimetry. The combined results gave reversible transitions at 657 k with ahtr deg = 1.10 Kcal/mol, at 741 k with ahtr deg = 0.51 Kcal/mol, and at 759 k with an enthalpy of fusion (ahm deg) of 1.22 Kcal/mol. An anomalous increase in heat capacity preceded the first crystal transition at 657 k. Tabulated values are listed for the standard relative enthalpy, heat capacity, entropy, and Gibbs energy function from 298.15 to 1,500 k. Standard relative enthalpies are also given in equation form and combined with thermodynamic data from the literature to derive values of standard enthalpies of formation and Gibbs energies of formation." - NIOSHTIC-2NIOSHTIC no. 10004150198

Vapor-phase reactions to prepare titanium nitride powder

"The U.S. Bureau of Mines conducted research on preparing submicrometer titanium nitride (TiN) powder as a substitute for tungsten carbide in cutting tools and wear-resistant parts. Earlier research on a small scale was expanded to include a larger reactor. The tin powder was produced by contacting titanium tetrachloride (TiCl4) with anhydrous ammonia (NH3) in the presence of mg at 1,100 deg c. The powder was collected in an electrostatic precipitator (ESP) filled with ultra-high-purity (UHP) Ar. All collected powder was thermal-vacuum-distilled to remove mg and magnesium chloride (MgCl2), leaving the purified TiN. Powder handling and purification procedures were conducted to assure low oxygen content in the powder product. Oxygen content in the distilled TiN powder product was as low as 0.40 wt pct. Nitrogen averaged near 22.0 wt pct with a high of 22.4 wt pct. The purified powder product had an average median particle diameter of 0.14 microm with a standard deviation of 0.09 microm." - NIOSHTIC-2NIOSHTIC no. 10011335199

Phase equilibria and thermochemistry of selected sulfide systems in the pyrometallurgy of Ni and Cu

A review of phase equilibria and thermodynamic data of Ni-(As, Se)-S and Cu-(As, Bi, Pb, Sb,Se, Te, Nb, Zn, Mo)-S systems was done. Particular emphases were given to the compilationand refine of the standard Gibbs energies of formations of equilibrium phases, which are ofinterest in the pyrometallurgical processes of copper and nickel production. Phase stabilities,phase relations and solubility limits of some equilibrium phases in the Ni-(As, Se)-S and Cu-Mo-Bi-Nb-S systems were also compiled and reviewed, based on the available literature.This work also reviews, updates, and extends the earlier reports. The Gibbs energies offormations and reactions are mostly presented as linear equations, in each temperature rangesof phase stabilities. List of thermal stabilities of some pure sulfides and sulfosalts were alsoreviewed and compiled (Appendix)

Thermodynamic properties of aegirine

"The thermodynamic properties of aegirine, of composition [(na0.869Fe3+0.7362Fe2+0.16Mn0.03Ca0.1121) (Al0.141Si1.9738) (O6)], were experimentally determined at the Bureau of Mines as part of its efforts to advance minerals technology. The standard enthalpy of formation was determined by hydrofluoric acid solution calorimetry. Low-temperature heat capacities were determined by adiabatic calorimetry from 19.1 to 304.6 K. The derived standard entropy was determined. The heat capacity was measured over the range 348 to 1,198 k by differential scanning calorimetry. These experimentally determined data were combined with data from the literature to calculate the Gibbs energies of formation and equilibrium constants of formation over the temperature range of the measurements. " - NIOSHTIC-2NIOSHTIC no. 1000402

Electrochemical determination of thermodynamic properties of bismuth sesquioxide and stannic oxide

"The Bureau of Mines investigated the thermodynamic properties of bi2o3 (bismuth sesquioxide) and sNO2 (stannic oxide). Equilibrium oxygen pressures of the bi-bi2o3-o2 systems were measured by a high- temperature electromotive force (emf) method using a solid electrolyte tube of stabilized zro2 (zirconia). The emf measurements yielded standard Gibbs energies of formation of bi2o3 and sNO2 from the elements. The enthalpy and temperatures for the a to g phase transformation of bi2o3 were determined. These data for bi203 and sNO2 were compared with previously reported measurements, and discrepancies were discussed. Standard enthalpies of formation of bi2o3 and sNO2 were derived by combining results from this investigation with auxiliary data from the literature." - NIOSHTIC-2NIOSHTIC no. 1000401