The Role of Molten Slag in Iron Melting Process for the Direct Contact Carburization: Wetting and Separation

Abstract

Rapid iron melting initiation and molten slag separation which take place in carbon composite iron ores are quite interesting phenomena, but their mechanisms have not been established yet. Since the size of carbonaceous material and iron ore particles is tiny in carbon composite iron ores, molten slag can dynamically play a critical role in the iron melting initiation and the slag separation. The behavior of the molten slag was clarified by direct observation of phenomena occurring in a simplified carbon composite agglomerate sample (iron disk-slag particle-graphite or coke particle) via a confocal laser scanning microscope combined with an image furnace. It was found that the molten slag wetting induced the iron melting initiation by attracting graphite or coke to iron and the molten slag separation took place with iron melting propagation. However, the high content of coke ash could suppress the iron melting initiation. In addition, the mechanism of molten slag separation from Fe-C melt was verified by phase field modeling.KEY WORDS: iron melting initiation; slag wetting; slag separation; coke ash; carbon composite iron ore; confocal laser scanning microscope; phase field method. 1099© 2010 ISIJ ExperimentalIron disks (diameter: 1.0 mm, purity: 99.99%) were prepared by polishing sliced iron particles from an iron rod. Thickness of the iron disks was 0.5 mm. Graphite disks (diameter: 1 mm; high purity) were made by punching a graphite plate (thickness: 0.5 mm). Cokes fragments (mesh: Ͻ1.0 mm) were prepared by crushing the original cokes (mesh: Ͻ60 mm), whose composition is given in Table 1. In order to know the ash effect on the wetting behavior, higher ash content containing cokes were made by the reaction of the broken cokes particles with CO 2 gas at 1 273 K for 20 min. Slag was prepared by heating mixture of oxide powders (CaO: 22.2%, Al 2 O 3 : 15.1%, SiO 2 : 62.7%) up to 1 673 K in a platinum crucible by using a muffle furnace. According to a literature, 11) the melting temperature of the slag is around the eutectic temperature, 1 446 K, which was confirmed by direct observation via a confocal laser scanning microscope. A piece of, approximately, 0.8 mg slag was positioned between an iron disk and a graphite disk or a fragment of coke on an alumina plate as shown in Fig. 1(a). The plate was slightly coated with boron nitride by a BN spray in order to prevent the slag from reacting with the alumina crucible. "In-situ" observation of the phenomena within iron, slag and carbonaceous material was conducted. The sample was heated up to 1 523 K at the rate of 200 K/min under the atmosphere of purified Ar. The behavior of the particles and the slag were recorded in a personal computer at a frame rate of 15 frames/s.The present experiment consisted of two sub-experiments. The first one was designed that the wetting behaviors of CaO-Al 2 O 3 -SiO 2 slag would be compared for different types of carbonaceous material: graphite, coke and reacted coke. Since ash in coke plays a critical role in slag wetting at the in...

Reduction Behavior of Carbon Composite Pellets Including Alumina and Silica at 1273 K and 1373 K

“…10,11) In CCA system, iron oxide reduction and iron melting were much improved by Fe-C melt due to the faster mass transport according to Kim et al,12,13) The role of slag on melting and separation of iron was also clarified from the previous studies. 14,15) However, reduction behavior of carbon composite pellet specifically the influence of slag composition is not well understood yet. The influence of CaO-SiO2-Al2O3 ternary slag system on the reduction of carbon composite pellet was studied in terms of reaction kinetics 16) as well as morphological properties 17) at temperatures between 1 623 K (1 350°C) and 1 773 K (1 500°C).…”

Reduction Behavior of Dolomite-Fluxed Magnetite: Coke Composite Pellets at 1573 K (1300 °C)

“…[6][7][8] Several works on self-fluxed carbon composite agglomerates have been reported. [8][9][10][11] Kim et al reported the enhanced melting behavior of Fe-C from direct contact carburization in the presence of molten slag. [9] Increased melting rate of iron was also confirmed, when contacted to graphite and wu¨stite.…”

Metal-slag Separation Behaviors of Pellets Consisted of Iron, Graphite and CaO–Al2O3 Based Slag Powders

“…Consequently, the coal-based CCA reduction behaviors with the slag composition 'a', 'b' and 'c' have been well studied. [6][7][8][9][10] However, these slag compositions are not suitable © 2014 ISIJ for high Al2O3 iron ore due to the increase of slag volume. Thus, to effectively and extensively use high Al2O3-containing iron ores with CCA reduction process, alternative slag design must be developed.…”

“…These steps with the slag region 'a', 'b' and 'c' have been already studied. [6][7][8]12) Ohno et al 6) investigated the effect of metal-slag separation based on slag melting temperatures and viscosities with slag region 'b' and 'c'. Nogueira et al 7) also observed clear metal-slag separation behavior with slag 'a'.…”

“…Nogueira et al 7) also observed clear metal-slag separation behavior with slag 'a'. Kim et al 8,12) studied the role of liquid phase on the metal-slag wetting/ separation behavior in the slag composition 'a' based on insitu confocal laser-scanning microscope (CLSM) observation. But none of them focused on the metal-slag separation behavior of the slag region 'd' which can be practically important to use high Al2O3 ore for CCA reduction process.…”