High Oxygen Potential Research Articles

Performance calculation of slag from vanadium titano-magnetite by full oxygen bath smelting process

Vanadium titano-magnetite is an important iron ore resource containing iron, vanadium and titanium. Although iron and vanadium can be recovered by the traditional blast furnace process, titanium can only be stored in the form of TiO2 bearing slag, which resulting in a great waste of titanium resources. In the full oxygen bath smelting process, thanks to high oxygen potential, low nitrogen content and no coke bed in the furnace, the reduction of TiO2 in the slag. This may lead to slag viscosity, inhibit the smelting of vanado-titano-magnetite, and obtain a slag with high TiO2 content. Based on slag coexistence theory, a multi system coexistence theoretical model of vanadium titano-magnetite smelting slag is established, and the influence of slag basicity on the concentration of slag components and the ratio of sulfur between slag and iron is calculated. The results show that with the increase of slag basicity, the interaction concentration of TiO2 in slag decreases gradually, which makes the reduction of TiO2 more difficult and is conducive to the smelting of vanadium–titanomagnetite. Under the optimum alkalinity and reduction temperature (R=1.1, melting temperature is 1500 °C), the distribution ratio of S element between slag and iron is 6.57, and the theoretical S concentration in molten iron is 0.073%. The molten iron can meet the steel-making requirements after pretreatment and desulfurization.

Direct-to-blister smelting of copper concentrate based on a calcium ferrite slag system

The direct-to-blister smelting process realizes single furnace smelting from chalcocite to blister copper. This process saves the matte transport process, avoids multiple feeding in the smelting process, and has the advantages of high productivity, a short production process, and less SO2 pollution. By comparing with the phase diagram of iron silicate slag system, it shows that calcium ferrite slag system is more suitable for direct-to-blister smelting under the condition of high oxygen potential. In this study, high-grade copper concentrate was used as the raw material and direct-to-blister smelting experiments were carried out at the laboratory scale. The variation of copper recovery with CaO/Fe ratio, smelting temperature and sedimentation time was studied. The phase composition of slag and the loss of copper in slag were analyzed by X-ray diffraction (XRD) and scanning electron microscopy with an energy spectrometer (SEM-EDS). The results showed that by adjusting process parameters, the copper recovery can reach 90.15 wt.% and the blister copper grade is more than 98.50 wt.%. It provides a theoretical basis for the industrial application of calcium ferrite slag in direct-to-blister smelting.

Effect of CO2 on the Desulfurization of Sintering Flue Gas with Hydrated Lime.

The effect of carbon dioxide (CO2) on the desulfurization of sintering flue gas with hydrate (Ca(OH)2) as an absorbent was investigated, and the formation of calcium carbonate (CaCO3) and its effect on the desulfurization was discussed. The competitive relationship between carbon dioxide (CO2) and sulfur dioxide (SO2) with the deacidification agent in sintering flue gas is discussed thermodynamically, showing that sulfates are more likely to be generated under high oxygen potential conditions and that SO2 reacts more preferentially than CO2 under a thermodynamic standard state. The amount of produced CaCO3 increases under the condition that the CO2 concentration is absolutely dominant to SO2 in the sintering flue gas atmosphere. The effect of temperature, humidity and CO2 concentration on the desulfurization of Ca(OH)2 are discussed experimentally. The increasing temperature is not conducive to desulfurization, and the humidity can promote desulfurization, while excessive humidity could inhibit desulfurization. The suitable relative humidity is 20%. In situ generated calcium carbonate has a certain desulfurization effect, but the desulfurization effect is not as good as Ca(OH)2. However, a large proportion of CaCO3 was produced in the desulfurization ash under the condition that CO2 concentration was absolutely dominant to SO2 in the sintering flue gas atmosphere.

Development of PGE-Bearing Silicate Glass Standards for Quantitative Trace Element Analysis in Silicate-Based Metallurgical Slags

Two batches of silicate glass doped with precious metals (PMs) (Pt, Rh, Pd, Os, Ir, Ru, Au, and Re) were prepared as analytical reference materials at very high oxygen potentials, which can be achieved only at elevated pressure. The high oxygen potentials allow the PMs to dissolve in the glasses as oxide components. The two glasses were examined and characterized using electron probe X-ray microanalyzer (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for their chemical composition and homogeneity. The glasses were found to be homogeneous on the micron scale or less to within analytical precision, and are well suited as standards for the rapid and accurate LA-ICP-MS analysis of PMs in silicate slags or similar materials.

Effect of the electrolyte composition on the electrochemical behavior of Nd fluoride complex in a LiF-NdF3-Nd2O3 molten salt

Abstract The electrochemical behavior of Nd fluoride complexes for Nd electrowinning has been investigated according to the electrolyte composition in the LiF-NdF3 system. The electrochemical characteristics of the LiF-NdF3 electrolyte at low oxygen potential under acidic conditions and the LiF-NdF3-Nd2O3 electrolyte at high oxygen potential under basic conditions were also studied. The Nd fluoride complex behavior in the electrolyte was investigated by cyclic voltammetry for a concentration change of NdF3 with LiF at 1100 °C from 10 wt% to 64.6 wt%. The experimental results indicated that NdF3 is reduced to Nd(0) via a multi-step process. NdF2 could be produced by the comproportionation reaction between NdF3 and Nd metal. Additionally, the rate equation for NdF2 generation was derived through a reactivity test between the metal and the Nd2O3-free electrolyte. However, NdF2 production was suppressed in LiF-NdF3-Nd2O3 electrolyte.

Infrared laser absorption and melting behaviour of nano-sized cerium dioxide: A laser heating study

The absorption of a 1064.5 nm Nd:YAG laser line and the consequent heating up to melting of nano-crystalline CeO2 has been studied in compressed air. The behaviour of crystallites ranging from 3.2 nm to 11 nm has been investigated and compared with micro-crystalline CeO2.A transparent / opaque transition occurs in CeO2 at lower heating laser power density in smaller crystallite sizes. Also the melting behaviour is strongly dependent on the crystallite size. If one manages to directly melt nano-crystals by optimising the heating conditions under a suited oxygen overpressure, the resulting melt has been observed to solidify at the highest temperature so far reported for CeO2 (3012 K), about 250 K higher than the temperature most commonly registered under oxidising conditions (2750 K). This is attributable to the large specific surface of nano-crystals, resulting, under a high oxygen potential, in their higher stability with respect to oxygen losses.

Study of stand-support sintering to achieve high oxygen potential in iron ore sintering to enhance productivity and reduce CO content in exhaust gas

Abstract Coarse coke particles, thick combustion zone, and poor thermal permeability during sintering have been widely reported to lead to incomplete solid fuel combustion and low oxygen potential, which induces the formation of harmful gas and decreases the energy efficiency. To solve these problems, stand-support sintering with an ultrathick 1000 mm bed was first proposed in this paper. The influences of the stand height and coke size on the process parameters and sinter quality were studied through a series of experiments. The results showed that the average gas flow velocity increased from 0.24 m/s to 0.32 m/s and the maximum combustion zone thickness decreased from 202 mm to 140 mm, which indicated that stand-support sintering could substantially improve the thermal permeability and enhance the oxidizing atmosphere. The fuel consumption was reduced by 1.28 kg/t (2.25%), the generated CO in exhaust gas was reduced, and the production efficiency increased by 17.4% when the stand height increased from 0 to 500 mm. Moreover, a 3D high-energy X-ray computerized tomography (CT) scanner was first used to quantitatively confirm the effect of the stand on the distribution and size of the pores in the whole sinter cake. Research findings showed that the porosity increased by 7.1% when the height of the stand increased from 0 to 500 mm, which further illustrated the effect of stand-support sintering. The present study provided an effective way to optimize the energy efficiency and reduce the CO content in exhaust gas.

Study on reaction of 15-15Ti with fission products under various oxygen potential

ABSTRACT The effect of oxygen potential on the Fuel-Cladding Chemical Interaction (FCCI) of 15-15Ti cladding material was studied in this paper. In the test, the materials have been exposed to simulated fission products at 600◦C for 120 h under the oxygen potential in equilibrium with Mo/MoO2 and Cr/Cr2O3.The general corroded depth was roughly 30 µm. Furthermore, the results also show that corroded depth on the cladding surface increase with the increase of oxygen potential. No intergranular attacks were observed, which might be caused by the absence of the high-temperature gradient. A single layer of CrTe is assumed to be formed under low oxygen potential, whereas cesium and oxygen may play an important role under high oxygen potential. Moreover, FCCI may impose a great threat to the integrity of China designed 15-15Ti material.

Study of continuous corrosion on astm a335 p91 steel in an environment of co2-o2-n2-h2o derived from the theoretical combustion products of a mixture of refining gases at high temperatures

The current energy production processes go hand in hand with corrosive phenomena; which is the case of combustion process in a refinery, where the presence of compounds such as CO2 and H2O, result in alloys catastrophic carburization and oxidation respectively. In this research work was evaluated the corrosive effect that can be generated in a real combustion environment, for which, it was necessary to select a model mixture of refinery gases and to simulate its theoretical combustions products. The main results showed the formation of a semi-protective duplex oxide layer; whose inner layer was composed mainly of chromium, while the outer layer was much richer in iron. On the other hand, the carburizing effect of CO2 was suppressed by the high oxygen potential in the combustion environment; leading to the conclusion that in real conditions, at 750 oC and after 200 h of testing, steels such as ferritic alloy ASTM A335 P91, could not present appreciable damages during their operation in refinery boilers and furnaces.

Evaluation of Corrosion Damage Obtained During the Combustion Process in a Boiler. Case Study: Ferritic Steel ASTM A335 P91

The corrosive effects developed on Fe-9Cr-1Mo steel in a typical combustion environment were evaluated. For this, steel samples were submitted in a pirotubular horizontal boiler, through the design of a coupon holder. With the experimental conditions characterized, the theoretical corrosion products were simulated; which showed similarity with SEM-EDS and DRX analysis, in the formation of hematite, magnetite and chromite. On the other hand, the oxide layers morphology deposited on the substrate, indicated the appearance of multiple efforts in them: cracks, pores, voids and detachments were observed. To complement these observations, the kinetic study was carried out, which allowed to determine a semi-protective behaviour from the oxide layers formed on Fe-9Cr-1Mo steel; where the diffusive processes are partially reduced. Finally, only oxidation and some localized nitridation could be identified. Carburization could not be identified due to the high oxygen potentials in the environment, and to the short-selected exposure times.

Coupling of Redox Conditions of Mantle Melting and Copper and Sulfur Contents in Primary Magmas of the Tolbachinsky Dol (Kamchatka) and Juan de Fuca Ridge (Pacific Ocean)

The compositions of parental melts of Tolbachinsky Dol (Kamchatka) basalts were estimated from the compositions of olivine-hosted (Fo90.5-83.1) primitive melt inclusions in the rocks of the Northern breakthrough of the Great Tolbachik Fissure Eruption (1975 A.C.) and of the late-Holocene cone “1004”. The parental melts contain 100–150 ppm Cu and 0.16–0.30 wt % S. These concentrations are much higher than those determined for the initial magmas of mid-ocean ridge basalts (MORB), for example of the Juan de Fuca ridge (Cu = 55–105 ppm, S=0.09–0.12 wt %). Modeling of mantle melting under variable redox conditions demonstrated that the high Cu and S contents in the Tolbachinsky Dol melts can be obtained by 6–12% melting of DMM-like source under oxidized conditions (ΔQFM = +1.2 ± 0.1) and do not require a significant (>30–35% for S) subduction-related influx of these elements to the mantle source. The high contents of Cu and S in the Tolbachinsky Dol melts are largely explained by the increase of sulfide solubility in a silicate melt under oxidized conditions. In contrast, relatively reduced (ΔQFM ∼ 0) conditions of MORB generation result in low contents of Cu and S in their initial magmas. The estimated ΔQFM values agree well with the data obtained using the Cr-spinel–olivine oxybarometer. The high oxygen potential of Tolbachinsky Dol primary magmas is inherited by more evolved magmas, thus favouring Cu enrichment up to 270 ppm during magma fractionation, approaching maximum copper contents in the global systematics of island-arc rocks.

Control of Low Melting Point Mno-Sio2-Al2o3 Inclusions in Low Carbon Thin-Strip Continuous Casting Steel

There is a significant difference in the demand for molten steel quality between thin-strip continuous casting and traditional continuous casting. In order to make sure the better surface quality of the thin strips, to generate an oxidation film on the surface of cooling roller is required. This will require that the higher oxygen potential in molten steel and inclusions with low melting point. In this article, the possibility of producing low-melting inclusions which is mainly consisted of SiO2 and MnO is studied by controlling the initial oxygen potential and addition order of deoxidizing alloys. The interaction activity between each component in the ternary system of Al2O3-SiO2-MnO is obtained by Action Concentration model. The equal [Mn], [Si], [O], [Al] curve under the temperature of 1823K and equilibrium condition in ternary system of Al2O3-SiO2-MnO is obtained by relative thermodynamic calculation as well. The control method for getting the low-melting point inclusion is as below. While the weight percentage of Si is 0.35% and the one of Mn is 0.90%, in order to maintain the melting point of inclusion around 1200°C, the free oxygen potential in melted steel F[O] should be maintained between 0.002% ∼ 0.004%. On the contrary, the requirement for acid dissolved [Al] content in melted steel is as low as 0.0001% ∼ 0.0005%.

Oxide-Metal Ratio Dependence of Central Void Formation of Mixed Oxide Fuel Irradiated in Fast Reactors

Based on thermal computation results obtained using an irradiation behavior analysis code, we have evaluated the effect of oxide-metal ratio on fuel restructuring from the results of postirradiation examinations for the B14 irradiation test fuel, which was a mixed oxide fuel and was irradiated in the experimental reactor Joyo. The thermal computation results showed that fuel restructuring in the stoichiometric oxide fuel was accelerated, though the fuel temperature in the stoichiometric oxide fuel was evaluated as lower than that of the hypo-stoichiometric one. We explained this behavior as follows: first, the fuel temperature decreased due to the high thermal conductivity at stoichiometry; second, the pore migration velocity increased due to the increase in vapor pressure caused by the high vapor pressure of UO3, which was derived from the high oxygen potential at stoichiometry. In addition, our results indicated that the central void diameter strongly depended on not only fuel temperature, but also vapor pressure.

The structure of liquid UO2−x in reducing gas atmospheres

High energy X-ray diffraction experiments performed on hypostoichiometric UO2−x liquids in reducing gas mixtures of 95%Ar:5%CO and 95%Ar:5%H2 are compared to that conducted in a pure Ar atmosphere [Skinner et al., Science 346, 984 (2014)]. The measurements are pertinent to severe accident scenarios at nuclear reactors, where core melts can encounter reducing conditions and further shed light on the oxide chemistry of the low valence states of uranium, particularly U(III), which become stable only at very high temperatures and low oxygen potentials. The radioactive samples were melted by floating small spheres of material using an aerodynamic levitator and heating with a laser beam. In the more reducing environments, a 1.7% shift to lower Q-values is observed in the position of the principal peak of the measured X-ray structure factors, compared to the more oxidizing Ar environment. This corresponds to an equivalent elongation in the U-U nearest neighbor distances and the U-U periodicity. The U-O peak (modal) bond-length, as measured from the real-space total correlation functions, is also observed to expand by 0.9–1.6% under reducing conditions, consistent with the presence of 15–27% U3+ cations, assuming constant U-O coordination number. The slightly larger U-U elongation, as compared to the U-O elongation, is interpreted as a slight increase in U-O-U bond angles. Difficulties concerning the determination of the hypostoichiometry, x, are discussed, along with the future directions for related research.

Kinetic Study on Desulfurization of Hot Metal Using CaO and CaC2

The kinetics and reaction mechanisms of hot metal desulfurization using CaO and CaC2 were studied in a well-controlled atmosphere with a lab scale high temperature furnace. The growths of CaS around CaO and CaC2 were measured and compared at 1773 K (1500 °C). The parabolic rate constant was evaluated to be 5 × 10−7 (cm s−1) on CaO particles, and 2.4 × 10−7 (cm s−1) on CaC2. The bigger parabolic constant of CaO resulted in more efficient desulfurization. Agglomerates and big CaO particles led to 2CaO·SiO2 formation which hindered further utilization of CaO for desulfurization. The 2CaO·SiO2 formation was favoured by a high oxygen potential. Since the desulfurization reaction of CaO not only produced CaS but also oxygen, the local oxygen concentration around big CaO particles was higher than around small particles.

Oxidation effect on steel corrosion and thermal loads during corium melt in-vessel retention

During a severe accident with core meltdown, the in-vessel molten core retention is challenged by the vessel steel ablation due to thermal and physicochemical interaction of melt with steel. In accidents with oxidizing atmosphere above the melt surface, a low melting point UO2+x–ZrO2–FeOy corium pool can form. In this case ablation of the RPV steel interacting with the molten corium is a corrosion process.Experiments carried out within the International Scientific and Technology Center's (ISTC) METCOR Project have shown that the corrosion rate can vary and depends on both surface temperature of the RPV steel and oxygen potential of the melt. If the oxygen potential is low, the corrosion rate is controlled by the solid phase diffusion of Fe ions in the corrosion layer. At high oxygen potential and steel surface layer temperature of 1050°C and higher, the corrosion rate intensifies because of corrosion layer liquefaction and liquid phase diffusion of Fe ions.The paper analyzes conditions under which corrosion intensification occurs and can impact on in-vessel melt retention (IVR).

Fuel and fission product behaviour in early phases of a severe accident. Part II: Interpretation of the experimental results of the PHEBUS FPT2 test

One objective of the FPT2 test of the PHEBUS FP Program was to study the degradation of an irradiated UO2 fuel bundle and the fission product behaviour under conditions of low steam flow. The results of the post-irradiation examinations (PIE) at the upper levels (823mm and 900mm) of the test section previously reported are interpreted in the present paper. Solid state interactions between fuel and cladding have been compared with the characteristics of interaction identified in the previous separate-effect tests. Corium resulting from the interaction between fuel and cladding was formed. The uranium concentration in the corium is compared to analytical tests and a scenario for the corium formation is proposed. The analysis showed that, despite the rather low fuel burn up, the conditions of temperature and oxygen potential reached during the starvation phase are able to give an early very significant release fraction of caesium. A significant part (but not all) of the molybdenum was segregated at grain boundaries and trapped in metallic inclusions from which they were totally removed in the final part of the experiment. During the steam starvation phase, the conditions of oxygen potential were favourable for the formation of simple Ba and BaO chemical forms but the temperature was too low to provoke their volatility. This is one important difference with out-of-pile experiments such as VERCORS for which only a combination of high temperature and low oxygen potential induced a significant barium release. Finally another significant difference with analytical out-of-pile experiments comes from the formation of foamy zones due to the fission gas presence in FPT2-type experiments which give an additional possibility for the formation of stable fission product compounds.

The Origin and Archaeometallurgy of a Mixed Sulphide Ore for Copper Production on the Island of Kea, Aegean Sea, Greece

At the hill of Agios Symeon, on the island of Kea, Aegean Sea, Greece, ancient metallurgical slags with a high Pb–Zn–Cu content have been found. Thermodynamic simulations have been carried out, using the FactSage™ thermodynamic database computing system, with a view to understanding the ancient metallurgical processes that produced the observed slag compositions and morphologies. The simulations demonstrate that the slag samples resulted from Cu‐making processes. It would thus appear that mixed ores were used, containing Cu2S–FeS–PbS with significant amounts of sphalerite (ZnS) as impurity. The roasted ores were reduced at relatively high oxygen potentials at ∼1125°C to form Cu containing low levels of Pb, Fe and Zn.

DFT study on the electronic structure and chemical state of Americium in an (Am,U) mixed oxide

We investigated the electronic state of an (Am,U) mixed oxide with the fluorite structure using the all-electron full potential linear augmented plane wave method and compared it with those of Am2O3, AmO2, UO2, and La0.5U0.5O2. The valence of Am in the mixed oxide was close to that of Am2O3 and the valence of U in the mixed oxide was pentavalent. The electronic structure of AmO2 was different from that of Am2O3, particularly just above the Fermi level. In addition, the electronic states of Am and U in the mixed oxide were similar to those of trivalent Am and pentavalent U oxides. These electronic states reflected the high oxygen potential of AmO2 and the heightened oxygen potential resulting from the addition of Am to UO2 and also suggested the occurrence of charge transfer from Am to U in the solid solution process.

Water Vapour Effects on FeO Scale Growth: Differences Between Iron and Steel

High purity iron and a low carbon, low silicon steel were oxidised at temperatures of 800–1,200 °C, in atmospheres of N2–H2–H2O and N2–O2–H2O. Scales of wustite grew at low oxygen potentials, and of FeO/Fe3O4/Fe2O3 at high oxygen potentials, both according to parabolic kinetics after an initial transient period. The iron and steel behaved similarly in the O2/H2O gases, but not in H2/H2O, where the steel oxidised much more slowly than the iron. The rate for steel increased with $$ p_{{H_{2} O}} $$ at fixed $$ p_{{O_{2} }} , $$ but for iron was almost independent of $$ p_{{H_{2} O}} , $$ whilst rates for both metals increased with $$ p_{{O_{2} }} $$ at fixed $$ p_{{H_{2} O}} $$ . These results are discussed using point defect models involving hydroxyl anions and cation vacancies. Scaling rates in O2/H2O also increased with $$ p_{{H_{2} O}} , $$ a result attributed to gas phase transport within oxide pores which were present in the scales, but absent in wustite grown in H2/H2O.