Thermodynamic considerations of the corrosion of nickel ferrite refractory by Na3AlF6-AlF3-CaF2-Al 2O3 bath

Thermodynamic analysis was carried out to interpret the results of corrosion testing of nickel ferrite samples in cryolite-based baths. The equilibrium between cryolite-based baths and nickel ferrite was considered. Isopleths between cryolite-based baths and nickel ferrite confirmed that for the temperature range of interest (1223-1273 K) there was limited solubility of nickel ferrite in the bath. To better understand the formation of the metal from nickel ferrite, the effect of reducing potentials on nickel ferrite and nickel ferrite-cryolite-based bath systems were considered. The formation of a metal phase was predicted at relatively high pO2. The metal phase was nickel-rich at higher pO2, becoming enriched in iron as the pO 2 decreased. The oxide phases seen in corroded nickel ferrite samples corresponded to the spinel phase in the thermodynamic calculations. Penetration of aluminium oxides into the spinel phase seen in the experimental samples occurred only under a reducing potential

The effect of calcium aluminates on the coke analogue gasification

The gasification rate in CO2 of the coke analogue containing calcium oxide was studied using analogues doped with alumina (corundum), calcium aluminates (CA6, CA, C3A) and lime minerals. The coke analogue is a laboratory material with simplified carbon structure that has a mineral component with a particle size, size distribution and mineral dispersion that can be controlled. The main focus of this study was to quantitatively assess the effect of calcium in the mineral on the analogue’s reactivity. The analogues were reacted with CO2 isothermally in the temperature range of 1173–1623 K. It was found that the reaction rate increased with increasing CaO activity/number of moles of Ca in the mineral. The relative reaction rates (from lowest to highest) of the analogues doped were alumina, CA6, CA, C3A and lime. The relative apparent activation energies of the gasification from lowest to highest was lime, C3A, CA, CA6 and alumina

Sintering of Iron Ores in a Millipot in Comparison with Tablet Testing and Industrial Process

To explore the feasibility of small-scale sintering pot testing, a \u27millipot\u27 facility (diameter of 53 mm and height of 400 mm) was established and used to examine the sintering performance of iron ores and other non-traditional ferrous materials. The sintering performance of a millipot was examined across a range of different operational conditions (coke rate and suction pressure) and compared with an industrial sinter strand operation. Tablet tests were also performed to assist in the design of the millipot experiments and identify conditions for achieving mineral composition similar to the industrial sinter. For the millipot experiments, the materials used need to be compacted to increase the bulk density, and a higher coke rate is required to compensate the high heat loss caused by wall effects. A higher suction pressure is also necessary to maintain an oxidizing atmosphere in the sinter bed. As expected, it was not possible to eliminate the wall effect, which resulted in more primary hematite at edges of the sintered column. However, the sintered material from the center of column simulates industrial sinter reasonably well. As such, millipot provides a practical way to evaluate the sintering process and material performance at laboratory scale, helping to bridge the gap between tablet sintering and large scale pot sintering, or full scale plant trial. The results of millipot testing can be used for designing larger scale experiments or commercial sintering trials

Stability of Cementite formed from Hematite and Titanomagnetite Ore

The stability of cementite formed during the reduction of hematite and preoxidized titanomagnetite ores in a methane-hydrogen gas mixture was examined in the temperature interval 500oC to 900oC for the hematite ore and 300oC to 1100oC for titanomagnetite. Cementite formed from hematite ore was most stable at temperatures between 750oC to 770oC. Its decomposition rate increased with decreasing temperature between 750oC and 600oC and with increasing temperature above 770oC. Cementite formed from preoxidized titanomagnetite was most stable in the temperature range 700oC to 900oC. The rate of cementite decomposition increased with decreasing temperature between 700oC and 400oC and with increasing temperature above 900oC. Cementite formed from titanomagnetite ore was more stable than cementite formed from hematite under all conditions examined

Iron Ore Reduction with CO and H2 Gas Mixtures – Thermodynamic and Kinetic Modelling

The reduction of iron ore pellets has been studied using different techniques. Thermodynamic studies, experi-mental investigations and mathematical modelling have all been undertaken to better understand the behaviour of different pellet types in the new direct reduction process. The mathematical pellet model gives a good fit to most of the experimental conditions used in this work. There are some discrepancies between the experimental and calculated results under certain conditions, which are thought to be due to limitations in the experimental set up rather than fundamental issues in the model. The micromodel indicates that the hematite within the pellets is reduced to magnetite quickly, which in turn is reduced fairly quickly to wüstite. The reduction of wüstite to metallic iron seems to be the limiting stage in the reduction of the pellets, which is in line with what would be expected

A novel approach to mineral effects on coke reactivity

A coke analogue has been developed to evaluate mineral effects on coke reactivity. Elucidation of the effects of minerals on coke reactivity has proved difficult due to the complex and heterogeneous nature of industrial coke and the potential non-additive effects of minerals on coke reactivity. The coke analogue addresses this complexity and heterogeneity through control of its mineralogy, porosity and carbon structures. Recent studies have shown the analogue is capable of discriminating individual mineral effects on coke reactivity. In this paper the reaction mechanism of the analogues reactivity in CO2 is assessed and compared with that of industrial coke

The Kinetics of the reactivity of a coke analogue with carbon dioxide

In this study the suitability of a laboratory analogue for coke for studying the reactivity of coke was evaluated. Coke reactivity and strength are closely related, as such, an improved understanding of the kinetics of blast furnace coke reactions can be used to enhance blast furnace performance. However, coke is a complex composite material, with an inherent heterogeneity with respect to oxide phase composition and phase dispersion. The complexity and heterogeneity of coke makes it difficult to isolate the effects of a specific component on coke reactivity. The coke analogue has been developed to address these issues and was used for controlled testing of specific mineral, and to some degree maceral, effects on reactivity. The reaction of coke analogue with CO2 was studied using thermogravimetric analysis to measure the kinetics at temperatures from 850 to 1350°C. The reaction rate behaviour of the analogue is similar to that reported for industrial coke. The gasification rate increased with increasing temperature and three reaction zones corresponding to different kinetic control regimes, as found in industrial coke, have been identified. These findings show that the coke analogue demonstrates similar reaction kinetics to industrial coke indicating its suitability for use in coke kinetic studies

Nickel Ferrite - Does it have potential as a sidewall material?

A great deal of work has been done on evaluation of nickel ferrite as a material for fabrication of inert anodes, usually as a component in a metal-ceramic composite. Its relatively good resistance to corrosion by cryolite rich baths has led to the suggestion that it might be feasible to use nickel ferrite as a sidewall material. This is a very attractive option, as elimination of the frozen ledge has significant benefits in terms of energy savings and increased productivity. However, very little work has been done to assess its suitability as a refractory material Benchmark testing of the properties of nickel ferrite as a refractory have been conducted as part of a project funded by the CSIRO Flagship Cluster “Breakthrough Technology for Primary Aluminium”. Results of initial work confirm that the nickel ferrite spinel does have a relatively high resistance to attack by cryolite based baths, but the corrosion mechanism is complex, and is not yet understood. However, design of a corrosion resistant grain boundary phase may be the key to development of a successful spinel based refractory

Development of a metallurgical coke analogue to Investigate the effects of coke mineralogy on coke reactivity

In this study the suitability of a laboratory analogue for coke for studying the effects of minerals on the reactivity of coke was evaluated. In addition to this, the effects of different physical properties and production conditions on the reactivity of the coke analogue were also tested. The coke analogue was used for control testing of specific mineral, and to some degree maceral, effects on reactivity. Such information would improve our fundamental understanding of coke reactivity behaviour and could be used to develop more accurate predictive models of coke strength after reaction (CSR) or associated indices and coke properties. The effect on reactivity of the addition of different simple minerals to the coke analogue was evaluated by conducting pseudo-coke reactivity index (CRI) tests. It was found that the addition of minerals to the coke analogue had an effect on its reactivity. While the addition of minerals also affected physical properties such as porosity, it was found that the minerals themselves played a role in determining the reactivity of the coke analogue. The principal conclusion of this study though is that the coke analogue has been identified as having potential to be a suitable tool for studying the effects of mineralogy on coke reactivity in a CSR/CRI like test

Using inert hot-spots to induce ignition within industrial stockpiles

The potential for materials undergoing oxidation reactions to spontaneously combust when they are stored in large stockpiles is well known. We consider an application in which such self-heating is desirable and investigate the use of inert hotspots as a means to promote thermal runaway. The size and location of the hotspot are found to have the largest effects on self-heating. Less pronounced are effects due a periodic ambient temperature. The advection velocity through the stockpile can have large effects