The present study contributes to the current worldwide activities aiming to replace fossil carbon in steel making processes with hydrogen causing considerable reduction of greenhouse gas emissions. Compacts prepared from iron oxide pellets fines were isothermally reduced in pure hydrogen gas and a mixture of hydrogen and argon in the temperatures range from 700 to 1100 °C. The total weight loss produced during the reduction process was continuously recorded using thermogravimetric analysis (TG) technique. The findings demonstrated that the temperature has a considerable impact on the conversion and reduction rates. At a given temperature, the reduction rate was accelerated as the amount of H2 increased in the reducing gas. The results indicated that H2 content does not have an effect on reduction behavior, when it is higher than 80%. The reduction reaction of samples was shown to takes place in a step wise manner from hematite to metallic iron. The reduction kinetic and mechanism were deduced from the application of mathematical models and the morphological structure of the reduced samples and correlated with the apparent activation energy (Ea) values. The Ea values at the early, intermediate and final stages were 16.36, 29.24 and 49.35 kJ/mole, respectively. The early stage of the reduction process was controlled by chemical reaction, whereas the gaseous diffusion was controlled the latter stage. At the intermediate stage, the reduction process was controlled by mixed mechanism of gaseous diffusion and chemical reaction. Graphical Abstract
Silicon nitride (Si3N4) and silicon powder (Si) are two kinds of harmful solid waste in industrial production. As an environmental and low-consumption method, the cold-bonding technique is a novel method to utilize the problem of powder resource cycling. In this experiment, mechanical and high-temperature properties of Si and Si3N4 briquettes were studied after cold bonding. The results are as follows: (1) The compressive strength of the Si and Si3N4 briquettes increased with the improvement of molding pressure. With the same binder (1 wt.%) and water (10 wt.%) addition, the compressive strength of the Si3N4 briquette arrived at 12,023.53 N under 40 Mpa molding pressure, which is much higher than that of the Si briquette (942.40 N). The Si particles are uneven and irregular, which leads to an intense arch bridge effect in the Si briquette and the compressive strength decrease. Compared with Si powder, the particle size and shape of Si3N4 is small, uniform, and regular. The influence of the arch bridge effect is smaller than that in the Si briquette. (2) After being treated at 1473 K for 1 h, the compressive strength of the Si briquette increased to 5049.83 N, and the compressive strength of the Si3N4 briquette had a slight change. The surface of the briquettes was contacted with oxygen and reacted to form an outer shell which mainly contains SiO2 in the high-temperature treatment. FT-IR results have shown there were no extra impurities in cold-bonded briquettes when using the organic binder. (3) The microstructure of the cross section of the Si and Si3N4 briquettes after high-temperature treatment presented that oxygen entered the briquette through the pores and continued to react with the Si and Si3N4. The outer shell of the Si briquette grew and thickened continuously with the oxygen spreading in the Si briquette. However, because of the smaller particle size and regular shape, little oxygen diffused in the Si3N4 briquette. The outer shell of the Si3N4 briquette is fairly thin, so the compressive strength did not change too much.
Ultrahigh-speed continuous casting is a critical element in achieving high-efficiency continuous casting. In the present work, a three-dimensional model of a 160 mm × 160 mm billet ultrahigh-speed continuous casting mold was developed for use in studying the influences of different casting parameters on molten steel flow. The results showed that the flow pattern in the mold was not associated with its casting speeds, submerged entry nozzle (SEN) immersion depths, or inner diameters. Variation in casting speeds significantly affected the liquid level of the steel–slag interface. Its liquid level fluctuation was reasonable at an SEN immersion depth of 80 mm. Its impact depth reached the shallowest point, which was conducive to upward movement within high-velocity and high-temperature regions, and accelerated the floating of non-metallic inclusions. Expanding the inner diameter of the SEN could effectively weaken the initial kinetic energy of the jet. However, it may cause a deeper impact depth and a degree of upward movement in the raceway, which exhibited the shallowest impact depth in the jet and the most reasonable behavior of molten steel at a liquid level for which the inner diameter of the SEN was 40 mm.
Electric arc furnace dust (EAFD) is a hazardous by-product of steel production. As global steel output increases, substantial amounts of EAFD are produced, which causes significant environmental issues. EAFD contains amounts of Fe and Zn, which could be reused as raw materials in the steelmaking process. However, zinc oxides can be reduced and vaporized during this process, forming zinc vapor that contaminates equipment surfaces and causes damage. Consequently, various pyrometallurgical methods have been proposed for zinc removal from EAFD. Due to the extensive usage of carbonaceous materials, these methods contribute to significant CO2, raising concerns about greenhouse gas emissions. Microwave heating offers an efficient, energy-saving, and environmentally friendly alternative to pyrometallurgical approaches. EAFD can generate heat under microwave irradiation without carbon addition, which means the CO2 emissions can be reduced by replacing the reductant in the microwave heating process. Furthermore, microwaves enhance zinc removal reactions to a certain extent, resulting in higher efficiency. Thus, employing microwave heating for EAFD processing has significant potential for future development. This paper reviews recent research on using microwave heating for zinc removal from EAFD, focusing on the heating behavior of EAFD in microwaves and the mechanisms of zinc removal. This review will be crucial for researchers working on processing EAFD using microwave heating and could help guide the development of more sustainable and efficient methods.
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