Characteristics of Iron Entrainment into Slag Due to Rising Gas Bubbles

Abstract

Iron droplets can be entrained into the slag phase when gas bubbles pass through the molten iron/slag interface. The entrainment phenomena occurring during passage of single bubbles through the interface were investigated by using in-situ X-ray transmission (fluoroscopic) techniques and by collecting and measuring the entrained iron droplets. The effects of bubble size, interfacial tension and viscosity of the slag on the iron droplets entrainment were investigated. The results showed that the mass of the entrainment increased with the increasing bubble size, but decreased with increasing interfacial tension and slag viscosity. A dimensionless equation was proposed to describe the relation between the entrainment of metal into slag and the above-mentioned parameters. This information can be used to optimize heat and mass transfer processes e.g. in ladle metallurgy and to reduce the financial loss due to metal discard within the slag.KEY WORDS: entrainment; gas bubble; iron droplet; iron/slag interface. a bubble (typically 10-14 mm). The sharp edge of the hole on the downward side was ground smoothly by a diamond tool.In each typical experiment the furnace was preheated to 1 580°C, then an alumina crucible-capillary system and a graphite crucible were introduced into the furnace tube from the bottom and the top, respectively. The alumina crucible with 35 mm I.D. and 60 mm height contained 135 g iron sample. Four different alumina capillaries were used to produce bubbles with different size, their I.D./O.D. were 2/4, 1.6/3, 1/2 and 0.7/1.3 mm, respectively, all their length was 550 mm. The alumina plate was located inside the crucible above the iron charge. The graphite crucible with 35 mm I.D. and 65 mm height was filled with 55 g slag.After the furnace tube was purged by pure argon about 2 min, 90 % Ar plus 10 % H 2 mixture gas was introduced as protective atmosphere. The alumina crucible was moved upwards slowly to the high temperature zone, while the graphite crucible was moved gradually downwards to the furnace center. After the iron was partly melted and covered the mouth of the alumina capillary (the pressure curve appeared on the monitor screen), the graphite crucible was quickly moved downwards to be seated on the alumina crucible to melt the slag and allow it to flow onto the iron melt. The whole period of the crucible moving and materials melting took about one hour; during this period the gas flow rate from the capillary was very low (ϳ0.2 mL/min). After the iron and slag samples were totally melted, the alumina plate, with a density (about 3.8 g/cm 3 ) greater than the density of the slag (about 2.6-2.8 g/cm 3 ) but lower than that of liquid iron (about 7.1 g/cm 3 ), floated on the surface of the iron melt submerged in the liquid slag. When experiments with gas bubbles passing through the iron/slag interface were conducted both with and without the alumina plate, no significant differences were observed. When the gas flow rate was set to the proper value (normally, 1.7-5.0 mL/min), observation of the ...

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