scholarly journals A Thermodynamic Analysis on the Roasting of Pyrite

Minerals ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 220 ◽  
Author(s):  
Yan Zhang ◽  
Qian Li ◽  
Xiaoliang Liu ◽  
Bin Xu ◽  
Yongbin Yang ◽  
...  
Keyword(s):  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Iron Oxides ◽  
Thermodynamic Analysis ◽  
Inert Atmosphere ◽  
Thermodynamic Calculations ◽  
Oxidizing Atmosphere ◽  
Low Levels ◽  
Iron Sulphates ◽  
The Relationship

A series of thermodynamic calculations are performed for the roasting of pyrite in changing temperatures and atmospheres. The relationship between ΔrGθ and temperature in the range of T = 300–1200 K shows that, depending on the atmosphere it is in, reactions of pyrolysis, oxidation or reduction can occur. Both the pyrolysis of pyrite in an inert atmosphere and its oxidation by oxygen can form pyrrhotite (mainly Fe0.875S and FeS), but the temperature required for oxidation is much lower than that for pyrolysis. In an oxygen-containing atmosphere, the isothermal predominance areas for the Fe–S–O system indicate that a change in temperature and oxygen partial pressure can lead the pyrite to undergo desulphurization to pyrrhotite (FeS2 → Fe0.875S/FeS) or iron oxides (FeS2 → Fe3O4/Fe2O3), or sulphation to iron sulphates (FeS2 → FeSO4/Fe2(SO4)3). The presence of carbon is beneficial to the desulphurization of pyrite under an oxidizing atmosphere since iron sulphates can be converted to iron oxides at very low levels of PCO/PCO2. Results presented in this paper offer theoretical guidance for the optimization of roasting of pyrite for different purposes.

Oxygen potentials of PuO2-x

2012 ◽  
Vol 1444 ◽  
Author(s):  
Akira Komeno ◽  
Masato Kato ◽  
Shun Hirooka ◽  
Takeo Sunaoshi
Keyword(s):  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Measurement Data ◽  
Approximate Equation ◽  
Defect Chemistry ◽  
Thermo Gravimetry ◽  
Metal Ratio ◽  
The Relationship

ABSTRACTOxygen potentials of PuO2-x were measured at temperatures of 1473 - 1873 K by thermo-gravimetry. The oxygen potentials were determined by in situ analysis as functions of oxygen-to-metal ratio and temperature. The measurement data were analyzed on the basis of defect chemistry and an approximate equation was derived to represent the relationship among temperature, oxygen partial pressure, and deviation x in PuO2-x.

Undergraduate students' misconceptions about respiratory physiology.

1999 ◽  
Vol 277 (6) ◽  
pp. S127 ◽  
Author(s):  
J A Michael ◽  
D Richardson ◽  
A Rovick ◽  
H Modell ◽  
D Bruce ◽  
...  
Keyword(s):  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Undergraduate Students ◽  
Liberal Arts ◽  
Minute Ventilation ◽  
Respiratory Physiology ◽  
Carbon Dioxide Partial Pressure ◽  
Arterial Oxygen ◽  
Physiological Variables ◽  
The Relationship

Approximately 700 undergraduates studying physiology at community colleges, a liberal arts college, and universities were surveyed to determine the prevalence of our misconceptions about respiratory phenomena. A misconception about the changes in breathing frequency and tidal volume (physiological variables whose changes can be directly sensed) that result in increased minute ventilation was found to be present in this population with comparable prevalence (approximately 60%) to that seen in a previous study. Three other misconceptions involving phenomena that cannot be experienced directly and therefore were most likely learned in some educational setting were found to be of varying prevalence. Nearly 90% of the students exhibited a misconception about the relationship between arterial oxygen partial pressure and hemoglobin saturation. Sixty-six percent of the students believed that increasing alveolar oxygen partial pressure leads to a decrease in alveolar carbon dioxide partial pressure. Nearly 33% of the population misunderstood the relationship between metabolism and ventilation. The possible origins of these respiratory misconceptions are discussed and suggestions for how to prevent and/or remediate them are proposed.

Study on the intrinsic defects in ZnO by combing first-principle and thermodynamic calculations

2015 ◽  
Vol 29 (31) ◽  
pp. 1550194 ◽  
Author(s):  
Changmin Ma ◽  
Tingyu Liu ◽  
Qiuxiang Chang
Keyword(s):  
High Temperature ◽  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Fermi Level ◽  
Thermodynamic Calculations ◽  
Vibrational Entropy ◽  
Low Oxygen ◽  
Text Type ◽  
Zno Crystal ◽  
Formation Energies

In this paper, the intrinsic point defects in ZnO crystal have been studied by the approach that integrates first-principles, thermodynamic calculations and the contributions of vibrational entropy. With temperature increasing and oxygen partial pressure decreasing, the formation energies of oxygen vacancy [Formula: see text], zinc interstitial [Formula: see text] and zinc anti-site [Formula: see text] are decreasing, while it increases for zinc vacancy [Formula: see text], oxygen interstitial [Formula: see text] and oxygen anti-site [Formula: see text]. They are more sensitive to temperature than oxygen partial pressure. There are two interesting phenomena. First, [Formula: see text] or [Formula: see text] have the lowest formation energies for whole Fermi level at special environment condition (such as at [Formula: see text], about [Formula: see text] or [Formula: see text], about [Formula: see text]) and intrinsic [Formula: see text]-type doping of ZnO is possible by [Formula: see text] at these special conditions. Second, [Formula: see text] as donors have lowest formation energy for all Fermi level at high temperature and low oxygen partial pressure [Formula: see text], [Formula: see text]. According to our analysis, the [Formula: see text] could produce [Formula: see text]-type doping in ZnO at these special conditions and change [Formula: see text]-type ZnO to [Formula: see text]-type ZnO at condition from low temperature and high oxygen partial pressure to high temperature and low oxygen partial pressure.

scholarly journals Transport Properties of Film and Bulk Sr0.98Zr0.95Y0.05O3−δ Membranes

2020 ◽  
Vol 10 (7) ◽  
pp. 2229 ◽  
Author(s):  
Adelya Khaliullina ◽  
Liliya Dunyushkina ◽  
Alexander Pankratov
Keyword(s):  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Transport Properties ◽  
Effective Conductivity ◽  
Ionic Transport ◽  
Transport Numbers ◽  
Pressure Gradients ◽  
Solution Deposition ◽  
Bulk Membrane ◽  
The Relationship

In electrode-supported solid oxide fuel cells (SOFCs) with a thin electrolyte, the electrolyte performance can be affected by its interaction with the electrode, therefore, it is particularly important to study the charge transport properties of thin electrode-supported electrolytes. The transport numbers of charged species in Ni-cermet supported Sr0.98Zr0.95Y0.05O3−δ (SZY) membranes were studied and compared to those of the bulk membrane. SZY films of 2.5 μm thickness were fabricated by the chemical solution deposition technique. It was shown that the surface layer of the films contained 1.5–2 at.% Ni due to Ni diffusion from the substrate. The Ni-cermet supported 2.5 μm-thick membrane operating in the fuel cell mode was found to possess the effective transport number of oxygen ions of 0.97 at 550 °C, close to that for the bulk SZY membrane (0.99). The high ionic transport numbers indicate that diffusional interaction between SZY films and Ni-cermet supporting electrodes does not entail electrolyte degradation. The relationship between SZY conductivity and oxygen partial pressure was derived from the data on effective conductivity and ionic transport numbers for the membrane operating under two different oxygen partial pressure gradients—in air/argon and air/hydrogen concentration cells.

scholarly journals Prereduction of Nchwaning Ore in CO/CO2/H2 Gas Mixtures

Minerals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1097
Author(s):  
Trygve Schanche ◽  
Merete Tangstad
Keyword(s):  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Iron Oxides ◽  
Reduction Rate ◽  
Gas Mixtures ◽  
X Ray Diffraction ◽  
Co2 Gas ◽  
X Ray ◽  
Reduction Of Iron ◽  
Partial Pressures

Prereduction of Nchwaning manganese ore was investigated by isothermal reduction between 600 and 800 °C to optimize the conditions for industrial pretreatment of manganese ores. Experiments were conducted in CO/CO2 gas mixtures with and without hydrogen at two different oxygen partial pressures. Ore in the size fraction 9.52–15 mm was reduced in a thermogravimetric furnace, and the O/Mn ratio from the chemical analysis was used to determine the extent of prereduction. The samples were investigated by X-ray diffraction to investigate the evolution of phases under the course of reduction. The X-ray diffraction revealed that bixbyite and braunite (I and II) were reduced to manganosite with no or limited formation of hausmannite. Reduction of iron oxides subsided with wüstite, which is stabilized by manganese in the monoxide phase, and hydrogen was seen to improve the reduction of iron oxides. Modeling revealed that the reduction rate increased 2.8-fold upon increasing the CO content from 30% to 70% in a CO/CO2 gas mixture. The addition of hydrogen improved the reduction rate with factors of 1.3 and 2.6 for the low and the high oxygen partial pressures, respectively. Hence, the optimal conditions for pretreatment can be achieved by keeping the oxygen partial pressure as low as possible while adding hydrogen to the reducing gas and ensuring a high reduction temperature. Successful pretreatment limits the extent of the Boudouard reaction in the submerged arc furnace, reducing the amount of CO produced and, thus, reducing the CO available for pretreatment. Hydrogen is a useful addition to the pretreatment unit since it lowers the oxygen partial pressure and improves the kinetics of prereduction.

scholarly journals Changes in phase composition of soderites of the bakal deposit at heating

2018 ◽  
Vol 61 (11) ◽  
pp. 891-897
Author(s):  
O. Yu. Sheshukov ◽  
M. A. Mikheenkov ◽  
E. A. Vyaznikova ◽  
A. S. Bykov ◽  
L. B. Vedmid’
Keyword(s):  
Phase Composition ◽  
Iron Oxide ◽  
Iron Oxides ◽  
Inert Atmosphere ◽  
Degree Of Substitution ◽  
Oxide Content ◽  
Iron Oxide Content ◽  
Magnesium Ions ◽  
High Iron Content ◽  
Oxidizing Atmosphere

The article presents the results of a study of formation mechanism of magnesia-ferrite when heated siderites of the Bakal deposit with different iron oxide content in an inert and oxidizing atmosphere. It was established that in the case of firing in an inert atmosphere, the decomposition of siderite with high iron content begins at a lower temperature and the enthalpy of such decomposition is less. This effect can be explained by the different phase composition of the samples. The main phases formed under conditions of oxidative firing are hematite and magnesia-ferrite. The amount of hematite and magnesia-ferrite produced in the samples with different iron oxide content during firing in an oxidizing atmosphere is different. Siderite with high content of iron oxides contains more hematite in the firing products than magnesia-ferrite, and siderite with a low content of iron oxides contains more magnesia-ferrite in the firing products than hematite. Formed under conditions of oxidative firing magnesia-ferrites are solid solutions and differ in the degree of substitution of iron and magnesium ions. In siderites with high content of iron oxides, the degree of substitution of magnesium ions with iron ions is greater than in samples with a low content of iron oxides. Since the siderites of the Bakal deposit are poor ore formations, the considerable amount of magnesia-ferrite formed in them during firing makes it difficult to separate silicate and iron-oxide firing products by traditional enrichment methods. Wustite in the products of oxidative firing is not detected, because under these conditions it is in a metastable state and in the presence of a weakly oxidizing atmosphere is converted into magnetite. The scientific novelty is the explanation of the mechanism of siderite decomposition and the description of products of such decomposition. Understanding of the mechanism of decomposition of siderite from the Bakal deposit made it possible to develop the technology of reductive firing of siderite to facilitate separation of its products, and which consists in the regulation of the phase composition of silicate products of reductive firing, ensuring the collapse of magnesia-ferrite and output of iron oxide in a separate phase. The developed technology can be used to provide high-quality enrichment of siderite from the Bakal deposit.

What Does Human Development Index Rating Mean in Terms of Individualism/Collectivism?

2003 ◽  
Vol 8 (2) ◽  
pp. 97-100 ◽  
Author(s):  
Maria José Sotelo ◽  
Luis Gimeno
Keyword(s):  
Human Development ◽  
Human Development Index ◽  
Principal Component ◽  
General Idea ◽  
Development Index ◽  
Low Levels ◽  
The Relationship

The authors explore an alternative way of analyzing the relationship between human development and individualism. The method is based on the first principal component of Hofstede's individualism index in the Human Development Index rating domain. Results suggest that the general idea that greater wealth brings more individualism is only true for countries with high levels of development, while for middle or low levels of development the inverse is true.

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