Activity Of FeS Research Articles

Molecular orbital calculations for iron catalysts

To elucidate the possible catalytic action of iron-based direct coal liquefaction (DCL) catalysts, we model various surfaces of FeS and Fe (1−x) S y clusters with a molecular orbital approach. We have studied the adsorption of toluene and 1-methylnaphthalene at various sites on FeS and related defect clusters and have calculated bond-breaking energies of the aromatic-aliphatic linkage. A preliminary explanation of the catalytic activity of FeS is the donation of electrons to the iron surface by the adsorbate, followed by a subsequent decrease in the bond-breaking energies as compared to the nonchemisorbed species

Activities in Cu2S-FeS-SnS melts at 1200 °C

The dew-point technique was used to measure the vapor pressures of SnS over liquid sulfides of the system Cu2S-FeS-SnS at 1200 °C. Activities of SnS were generated from the measured vapor pressures of SnS. Activities of Cu2S and FeS were evaluated both in binary and ternary melts by Gibbs-Duhem calculations from the known SnS activity data. The systems Cu2S-SnS and Cu2S-FeS exhibit negative departures from ideal behavior, while FeS-SnS melts exhibit positive deviations.

Ｃｕ２Ｓ‐ＦｅＳ‐ＰｂＳ系融体の熱力学的研究

The vapour Pressures of PbS in the moltem Cu2S-FeS-PbS system have been measured by means of the transportation method at 1150°C The activity of PbS exhibited nearly negative behavior and the data obtained was used to calculate the activities of other components and slight negative deviations of acu2s and aFes from Raoult's law were observed in the molten Cu2S-FeS-PbS system.The activities of Cu2S and FeS of Cu2S-FeS melts were calculated by Darken's method extrapolated from Cu2S-FeS-PbS system to Cu2S-FeS system, and they showed negative deviation from ideality.Furthermore, the distribution behavior of Pb between matte and slag was explained by thermodynamic analysis.

Overexpression and purification of ferric enterobactin esterase from Escherichia coli. Demonstration of enzymatic hydrolysis of enterobactin and its iron complex.

The Escherichia coli ferric enterobactin esterase gene (fes) was cloned into the vector pGEM3Z under the control of the T7 gene 10 promoter and overexpressed to approximately 15% of the total cellular protein. The ferric enterobactin esterase (Fes) enzyme was purified as a 43-kDa monomer by gel filtration chromatography. Purified Fes preparations were examined for esterase activity on enterobactin and its metal complexes and for iron reduction from ferric complexes of enterobactin and 1,3,5-tris(N,N',N"-2,3-dihydroxybenzoyl)aminomethylbenzene (MECAM), a structural analog lacking ester linkages. Fes effectively catalyzed the hydrolysis of both enterobactin and its ferric complex, exhibiting a 4-fold greater activity on the free ligand. It also cleaved the aluminum (III) complex at a rate similar to the ferric complex, suggesting that ester hydrolysis of the ligand backbone is independent of any reductive process associated with the bound metal. Ferrous iron was released from the enterobactin complex at a rate similar to ligand cleavage indicating that hydrolysis and iron reduction are tightly associated. However, no detectable release of ferrous iron from the MECAM complex implies that, with these in vitro preparations, metal reduction depends upon, and is subsequent to, the esterase activity of Fes. These observations are discussed in relation to studies which show that such enterobactin analogs can supply growth-promoting iron concentrations to E. coli.

溶融ＦｅＳ‐ＰｂＳおよびＣｕ２Ｓ‐ＰｂＳ系の熱力学的研究

Vapour pressures of PbS in the pure PbS, FeS-PbS and Cu2S-PbS systems were measured by the transportation method within a temperature range from 1115 to 1170°C, and the activities of the components in the two binary systems were calculated. Also, the phase diagrams of the FeS-PbS and Cu2S-PbS systems were determined by the DTA method to compare with the experimental date of activities.The experimental results obtained are summarized as follows:(1) The vapour pressure of PbS in the range of 1115-117°C was given as: log PPbS/atm=-9193/T+5.69and the boiling point and heat of vaporization of PbS calculated from the equation of vapour pressure were 1341°C and 42. 0kcal/mol, respectively.(2) The activities of FeS and PbS in the FeS-PbS system at 1150°C exhibited nearly the ideal behavior, and the calculated activities from the phase diagram supposing a regular solution agreed with the experimental results.(3) The activities of Cu2S and PbS in the Cu2S-PbS system in the range of 1130-1170°C showed negative deviation from the Raoult's law, and they were little changed by differences in temperature. The activity coefficients at the infinite dilution of the components in the system were estimated 0.04 and 0.22 for Cu2S and PbS at 1150°C, respectivery.

Ｃｕ‐Ｆｅ‐Ｓ系マットの１４７３Ｋにおける活量

The chemical compositions of iron-saturated mattes have been measured at 1473 K. The vapor pressures of sulfur have been determined experimentally over the Cu-Fe-S mattes by equilibrating them under the H2-H2S gas mixtures. Based on the present work and also literature data, a single equation has been established which provides excellent descriptions of sulfur partial pressures over the entire Cu-Fe-S matte compositions including the Fe-S and Cu-S binary systems as well. This simple function facilitates the ternary Gibbs-Duhem integrations for determining the Cu and Fe activities in mattes. The Fe and Cu activities in the matte-saturated alloys, which are required as initial conditions for the Gibbs-Duhem integrations, have been established by using quasichemical solution models. The Raoultian activities of FeS and CuS0.5 have been presented for the metal-saturated mattes as well as the pseudobinary FeS-CuS0.5 mattes.

Sphalerite and hexagonal pyrrhotite geobarometer; experimental calibration and application to the metamorphosed sulfide ores of Broken Hill, Australia

Sphalerite (sp) and hexagonal pyrrhotite (po) were recrystallized in a eutectic LiCl-KCl salt flux at 450 degrees to 750 degrees C and 1 to 6 kbars. The activity of FeS (a Fes ), controlled by the composition of excess pyrrhotite, varied from 0.5 to 1.0. Our data show that FeS activity-sphalerite composition relationships for any pressure are independent of temperature, i.e., the sphalerite composition (X sp Fes is a function of the FeS activity only, consistent with results of earlier investigations at low pressure.Plots of FeS activity vs. X sp Fes show that da Fes /dX sp Fes is a constant (defined as gamma sp Fes ), which increases with pressure and is also independent of temperature for the conditions of our experiments. The pressure dependence of gamma sp Fes as given by the expression: P(kbars) = 15.040 log gamma sp Fes - 2.672 (+ or -0.5 kbars) constitutes a geobarometer for rocks containing the trivariant assemblage sphalerite + hexagonal pyrrhotite. Although gamma sp Fes is independent of temperature for the range of a Fes = 0.5 to 1.0, a rough estimate of temperature is necessary to permit calculation of a Fes and hence gamma sp Fes . For example, sulfide ores of the North mine, Broken Hill, Australia, where N po Fes = 0.966 and X sp Fes = 0.201: at 650 degrees C, P = 6.6 kbars; and at 800 degrees C, P = 6.7 kbars. Pressures calculated from coexisting sphalerite and hexagonal pyrrhotite, at 650 degrees C, from the New Broken Hill Consolidated mine; the C lode and the Zinc Corporation mine; and the Pinnacles mine (12 km southwest of the main Broken Hill lode), indicate pressures of 6.8, 5.5, 6.2, and 6.3 kbars, respectively. These pressures are in excellent agreement with estimates based on silicate assemblages in adjacent host rocks.

Characterization of the Fe-S cluster in aconitase using low temperature magnetic circular dichroism spectroscopy.

Beef heart aconitase has been studied by low temperature magnetic circular dichroism (MCD) spectroscopy in the wavelength region 300 to 1900 nm. Together with parallel electron paramagnetic resonance and activity measurements, these data enable correlations between Fe-S cluster-type and enzymic activity in aconitase. In samples not exposed to extraneous Fe, the Fe-S cluster in aconitase exhibits the characteristic properties of a 3Fe center in both the as isolated and dithionite-reduced states. On the basis of the detailed form of the low temperature MCD spectra, three types of 3Fe center can be distinguished in biological samples. These are typified by the 3Fe centers in aconitase, Desulfovibrio gigas FdII, and Azotobacter crooccocum Fd. In aconitase, maximal enzymic activity is found to be associated with the build-up of [4Fe-4S]2+ clusters in good agreement with the Mössbauer studies of Kent et al. (Kent, T. A., Dreyer, J. L., Kennedy, M. C., Huynh, B. H., Emptage, M. H., Beinert, H., and Münck, E. (1982) Proc. Natl. Acad. Sci. U. S. A. 79, 1096-1100). However, significant catalytic activity (approximately 60%) was obtained by reduction of the 3Fe center with dithionite in the absence of added Fe. The form and intensity of the resultant MCD spectrum are consistent with the majority of the Fe being in the form of reduced 3Fe clusters. The possibility that a reduced 3Fe cluster is capable of promoting partial catalytic activity in aconitase is discussed in light of these results.

Activities of CoS and FeS in copper mattes and the behavior of cobalt in copper smelting

The distributions of cobalt and iron between metallic copper and high copper mattes were measured at 1400 and 1500 K. A value of 0.40 ±0.02 was found as the Raoultian activity coefficient of CoS at infinite dilution in the Cu2S-FeS-CoS mattes. The present activities of FeS in the Cu-saturated Cu2S-FeS mattes were found to deviate more positively than those reported by Krivsky and Schuhmann at 1623 K, and the positive deviation from the Temkin’s ideality was greater at 1400 K than at 1500 K. Using the activity coefficient of CoS, the partitions of cobalt between copper mattes and fayalitic slags were calculated for various conditions of copper smelting. It was found that cobalt exhibits, in the matte-slag equilibria, chemical properties intermediate between nickel and iron, but much closer to iron than to nickel. The overall recovery of cobalt in blister copper depends on matte grade, and is as low as 3 pct at best. When a high cobalt recovery is desired, therefore, a copper concentrate rich in cobalt must not be processed by conventional pyrometallurgical technology in view of the inevitably high loss to slag.

Activities in Cu2S-FeS-PbS melts at 1200 °C

The dew-point method was used to determine the vapor pressures of PbS over liquid sulfides of the system Cu2S-FeS-PbS at 1200 °C. From the PbS activity data, activities of Cu2S and FeS were evaluated both in binary and ternary melts by Gibbs-Duhem calculations. The systems Cu2S-PbS and Cu2S-FeS exhibit negative departures from ideal behavior, while the FeS-PbS melts are ideal solutions at 1200 °C.

Reconnaissance of the Cu-Fe-Zn-S system; sphalerite phase relationships

A reconnaissance study of the phase relations involving sphalerite, pyrite, pyrrhotite, intermediate solid solution, and coexisting phases in the central portion of the Cu-Fe-Zn-S system was conducted for the interval 800 degrees to 500 degrees C. This report discusses sphalerite relationships in this interval. The copper content of sphalerite, which is dependent upon temperature and the activity of FeS, may exceed 5 wt percent when coexisting with pyrrhotite and intermediate solid solution and 7 wt percent when in equilibrium with bornite. The exsolution of the copper and iron as a sulfide or sulfides does not appear to alter significantly the utility of the sphalerite geobarometer. The solid solution of CuS in iron-bearing sphalerite slightly reduces the unit cell dimension. Natural sphalerites, though, after initial equilibration with copper and iron sulfides, have reequilibrated by exsolution and now invariably contain less than 0.5 wt percent CuS.

Thermodynamics of the system Fe-Mn-S: Part I. activities in Iron sulfide-manganese Sulfide Solid Solutions in the Temperature Range 1100 to 1400°C

The equilibrium ratios pH2S/ pH2 of a gas phase coexisting with (Fe, Mn)S solid solutions of the system Fe-Mn-S and metallic iron have been determined in the temperature range 1100 to 1400°C. The activity of FeS in the sulfide solid solutions is proportional to pH2S/ pH2. The activity of MnS is obtained by a Gibbs-Duhem integration. The α-formalism is used to derive the analytical relationships between pH2S/ pH2 ora Mns, and composition of the solid solution.

Solid Solutions in the System Cu-Fe-S, Part I; The Cu-S and CuFe-S Joins

The data of Rau (1967) on the H 2 S/H 2 ratios of gas in equilibrium with high digenite solid solutions permit the calculation of the activity of Cu 2 S as a function of temperature and composition. The activity of Cu 2 S falls to 0.5 when the mole fraction (in the system Cu 2 S-S) drops only to 0.87. These calculations also permit the estimation of the activity of S 2 -temperature curve for the hexagonal chalcocite-high digenite reaction and a revised standard free energy for covellite.New data on the variation of the activity of S 2 in equilibrium with various metal/sulfur ratios for Cu = Fe in the intermediate solid solution permit the calculation of the activity of CuFeS 2 and show that it may drop as low as 0.2 at a mole fraction of 0.90 (system CuFeS 2 -Cu 2 Fe 2 S 2 ). The behavior of the copper-bearing solid solutions closely parallels that of pyrrhotite (Toulmin and Barton, 1964) in which the activity of FeS falls to 0.4 at a mole fraction of 0.9. A phase diagram is given for the CuFe-S join between 400 degrees and 700 degrees C.

Thermodynamics of the Fe-Ni-S system at 1250°C

The activity of sulfur in the Fe-S and Ni-S binary and the Fe-Ni-S ternary systems was investigated at 1250°C by equilibrating molten mattes with gaseous mixtures of H2S and H2. From the sulfur activity data the activities of iron and nickel in the Fe-S and Ni-S binary systems as well as the activities of FeS and Ni3S2 in the ternary system were calculated. Isoactivity diagrams are presented for S, FeS, and Ni3S2 in the Fe-Ni-S ternary system. Some comments are offered on the industrial problems of nickel slag loss and ferronickel separation.

Pyrrhotite (FeS<SUB>1+X</SUB>)の800°∼1100°Cにおける熱力学的研究

In order to establish the relations between the sulphur activities and the compositions of pyrrhotite (FeS1+x), the equilibrium measurements were carried out with the aid of the gaseous mixture of H2-H2S. The equations that relate the gas composition at room temperature to that at high temperature were derived thermodynamically by considering the species of S2 and HS besides H2 and H2S. The experimental results permit to calculate the activities of sulphur, iron and FeS, ΔGT0 of the formation of stoichiometric FeS, the heat and the entropy of mixing in pyrrhotite. The statistical thermodynamics of imperfect crystals was then applied tentatively to the system for interpreting the activity-composition relations in pyrrhotite.

A thermodynamic study of pyrite and pyrrhotite

Through the use of the electrum-tarnish method the following equation has been found to interrelate the composition of pyrrhotite, fugacity of sulfur, and temperature: In this equation f s 2 is the fugacity of sulfur relative to the ideal diatomic gas at 1 atm, N is the mol fraction of FeS in pyrrhotite (in the system FeS-S 2), and T the absolute temperature. The experimental uncertainty in the equation is 0–003 in N. The activity of FeS ( a FeS ) in pyrrhotite relative to the pure substance at the temperature of consideration follows from the above equation by virtue of the Gibbs-Duhem relation; it is given by: The electrum-tarnish method has permitted us to determine the f s 2 vs. T curve for the univariant assemblage pyrrhotite-pyrite-vapor from 743 to 325°C. Our determinations of the composition of pyrrhotite are in excellent agreement with the results of Arnold. The activity of FeS in pyrite-saturated pyrrhotite is very different from unity, a fact that greatly influences the interpretation of some other phase equilibrium studies involving pyrrhotite and their application to sulfide mineral assemblages, but has little effect on the more general calculations of composition of hydrothermal or magmatic fluids. Pressure effects calculated from available volumetric data on the phases are small.