Various metallurgical dust contains Fe2O3 and CaO, which catalyze the carbon–oxygen reaction and exhibit variable distributions and relative contents. Herein, we probe the interactions between Fe2O3 and CaO in a typical dust collection in the steelmaking process [basic oxygen furnace dust (BOF dust)] and their effects on BOF dust-catalyzed graphite combustion. Evaluation of composite catalysts with several Fe2O3 to CaO ratios and three types of BOF dust shows that high levels of Fe2O3 significantly inhibit the combustion process. These catalysts with variable Fe2O3 to CaO ratios undergo two sintering reactions at carbon–oxygen combustion temperatures of 650–900 °C to afford calcium ferrite (CaO·Fe2O3) or dicalcium ferrite (2CaO·Fe2O3). The former compound features a lower formation temperature and a faster reaction rate than the latter. Analysis of the Fe2O3–CaO binary phase diagram demonstrates that combustion is inhibited in the range of CaO·Fe2O3 formation, whereas increased catalytic activity is observed in the range of 2CaO·Fe2O3 formation, implying that catalyst sintering results in deactivation, and first-principles calculations suggest that the diffusion of carbon in CaO·Fe2O3 is most likely to be the limiting factor for the catalytic reaction. The formation of CaO·Fe2O3 can be suppressed (and hence, catalytic activity can be increased) by reducing the catalyst operating temperature and modulating the distribution ratio.

Hydrogen as the main cause of the gas porosity in aluminium alloys should be removed before casting. The degassing process with intensive melt shearing shows a high efficiency. In the present work, the water simulation was used to study the high shear degassing process and the effect of rotation speed on the size and distribution of inert gas bubbles. The results show that with the increase of rotation speed, the bubble size decreases and the affected region becomes larger. The proper rotation speed of the rotor for the rotor-stator high shear degassing process is 5000-6000 RPM.

The composition of fluoride‐containing mold fluxes changes when their melting point or viscosity are measured because the fluoride in the mold fluxes evaporates at high temperatures. Therefore, the measured melting points and viscosities are not those of the original fluxes, and thus, the results are not accurate. Therefore, evaluating the effects of evaporation is essential to accurately investigate the relevant properties. Herein, the chemical composition of the slag is determined using thermogravimetric analysis (TGA), roasting tests, and evaporation mechanism after the physical properties of the slag are measured using conventional methods. The measured melting point and viscosity are then matched with the modified slag composition instead of the original composition. This method is applied to different fluoride‐containing mold fluxes. The weight of the mold fluxes is reduced by more than 10% during the measurements, indicating that a large amount of the volatiles react and evaporate. The actual flux compositions corresponding to the observed melting point or viscosity of the mold fluxes are obtained through roasting test and TGA; therefore, one can easily match the measured mold flux properties to the flux composition. This study will help in determining other physical properties of slag and other melts containing volatiles.

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The spent carbon cathode (SCC) produced in the aluminum electrolysis process has been listed as hazardous waste due to excessive soluble fluoride and cyanide. In a high-temperature vacuum environment, the soluble fluoride and cyanide in SCC can be evaporated and decomposed, respectively. As a result, its impact on the environment can be eliminated. The remains and volatiles can be collected for resource use. Based on the analysis of SCC chemical composition and phase structure, thermodynamic parameters of evaporation reactions were calculated by FactSage. The effects of treatment temperature and particle size of SCC on the removal of soluble fluoride and cyanide were further investigated by experiment. A suitable treatment condition, in which SCC particle size is 1.000-3.000 mm, at 1000 ºC for 2 h at vacuum conditions of 10 Pa, was obtained. The removal rate of soluble fluoride and cyanide in treated SCC reached 91.10% and 99.33%, and carbon content reached 89.89%. Combined with the analysis of TG-DSC and particle profile scan, the evaporation reaction mechanism by high-temperature vacuum treatment (HTVT) was analyzed. The work will be helpful for the development of new SCC treatment process.The contributing editor for this article was Mansoor Barati.