Shouyi Sun

CSIRO’s multiphase reaction models and their industrial applications

The status and ongoing work on a multiphase reaction model developed at the Commonwealth Scientific & Industrial Research Organization are outlined in this article. The package enables metallurgists to simulate reactions in pyrometallurgical processes with respect to equilibrium between various phases and to calculate slag viscosity at elevated temperatures. The models have been validated against measurements on physico-chemical properties of melts and solid phases produced in industrial processes. A number of examples of the application of the package to ferrous and non-ferrous smelting and refining processes are presented.

Determination of the chemical diffusion of oxygen in liquid iron oxide at 1615 °c

The chemical diffusion of oxygen in liquid iron oxide has been studied by the oxidation of a melt in a long capillary at 1615 °C. When pure oxygen was used as the oxidizing agent, the surface composition of the slag was found to be in close agreement with the expected gas-slag equilibrium, suggesting that diffusion is the controlling step. This was not the case when air, 5 pct oxygen in argon or pure CO2 was used to oxidize the slag. The deviation of the surface composition from the expected equilibrium was in accordance with a mechanism of mixed control by both the gas-slag reaction and diffusion in the bulk. The average value of the chemical diffusivity of oxygen (or iron) in liquid iron oxide with Fe2+/FeT between 0.25 and 0.77 was established to be 3(±1) × 10-7 m2/s. This value is one to two orders of magnitude higher than those from earlier studies. There seems to be a reasonable correlation between the chemical and the ionic self-diffusivities through the Darken equation. A quantitative analysis in this respect and on the role of electron hole migration depends on the availability of data on the ionic conductivity and the tracer diffusivities.

REVIEW AND APPLICATIONS OF THERMAL CONDUCTIVITY MODELS TO ALUMINUM CELL SIDEWALL REFRACTORIES

Silicon nitride bonded silicon carbide (Si3N4-SiC) refractories are commonly used as the sidewall of aluminum electrolysis cells. They have to withstand an extremely corrosive molten electrolyte bath for long periods. The sidewall is normally protected with a layer of solidified electrolyte (called frozen ledge), which is sensitive to the thermal conductivity of the sidewall. In this work, through review of the literature on modeling methods for predicting the effective thermal conductivity of dense composites and porous materials, some selected methods were applied to calculate the effective thermal conductivity of Si3N4-SiC refractories. The model predictions were compared with the thermal conductivity of a commercial Si3N4-SiC refractory measured by using laser flash technique. The present study showed that, due to multi-phase nature and complex microstructure of Si3N4-SiC refractories, most of the selected modeling methods individually do not give satisfactory predictions in one step. Recursive applications of one method or combinations of different methods are capable of giving satisfactory predictions.

Activity of Lead in Copper Matte at Very Low Lead Concentration

Abstract The thermodynamic behavior of lead in Cu-Fe matte was investigated using a transportation technique where argon gas was bubbled into a bath of copper matte containing approximately 100 ppm lead at temperatures between 1300 and 1400 °C. The effect of flow rate, temperature and matte grade were investigated on the lead transport from a bath containing 100 grams of synthetic copper matte to the gas phase. The concentration of lead in the bath was followed with time. At argon flow rates between 3 l h1 and 18 l h−1, it was observed that the concentration change of lead in the matte was found to follow a first order relationship where the calculated concentration at time t, is of the form [Pb] = a.e−b.t, where a is equal to the initial lead content in ppm, [Pb]i, and b is an exponential term and t is time in minutes. The partial pressure of lead species in the gas phase was calculated from the concentration changes in the matte and from the bubbling gas rate. At gas flow rates between 3 and 9 l h−1, the lead removal appeared to be under equilibrium conditions. At higher gas flow rates, the apparent rate decreased, mainly due to splashing of matte into the cold zone of the furnace. In these experiments with Ar as the carrier gas, the sulphur and oxygen partial pressures of the melt were not controlled. Chemical analysis of the major components in the matte showed only random variation with bubbling time, and so a thermodynamic solution model for copper matte was used to calculate the equilibrium sulphur pressure expected. From this approach the proportion of Pb, PbS and Pb2 species in the gas could be calculated knowing the relevant reaction constants, e.g., PbS(g) = Pb(g) + ½S2(g). From the proportions of the lead species in the gas, the value of the lead activity coefficient with respect to the gas state could be determined. For a 50% copper matte, it was found that the activity coefficient increased with temperature, from a value of 0.8 at 1300 °C to 1.4 at 1400 °C. At the white metal composition, this value was 0.28 at 1300 °C. These results are compared with other relevant studies in the literature.

Semiconductivity and physicochemical properties of iron oxide-containing slags

Solid and liquid iron oxides exhibit characteristics of semiconductors. The semiconductive behavior also features in some slags containing iron oxide. This paper aims at highlighting some of the experimental indications of the role of semiconductivity in electrical conduction, the chemical diffusion and in reaction kinetics at slag surfaces. It is not a thorough review of the subject matter but an attempt at shedding some light on the connection between these properties.