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

Abstract

In-situ observations of metal-slag separation behaviors between CaO-Al2O3 based slag, iron and graphite powder mixed pellets by a confocal laser-scanning microscope (CLSM) have been carried out to find the effective way to use high Al2O3 iron ore in CCA reduction processes. Since a particular type of high Al2O3 iron ore such as laterite contains small amount of NiO and Cr2O3, the effect of NiO and Cr2O3 on the metal-slag separation behaviors were also studied. The observed metal-slag separation behaviors were analyzed based on the equilibrium phase fractions calculated by FactSage and carbon diffusion simulation in an iron sphere particle with a spot carbon source condition. Based on these in-situ observations and carbon diffusion results, starting temperature of metal-slag separation was found to correspond to the eutectic temperature of CaO-Al2O3 based slag. The iron carburization was initiated by slag melting and most of iron particles were melted within about 20 s after slag melting. The rapid carburization after slag melting was introduced by the good wettability between solid iron and molten slag. NiO and Cr2O3 additions did not change the fundamental behaviors of metal-slag separation at least up to about 3 mass%. Based on these results, it was confirmed that high Al2O3 content iron ore can be used in CCA reduction process by using CaO-Al2O3 based slag.KEY WORDS: metal-slag separation; high Al2O3 iron ore; iron carburization; spot source diffusion; CaOAl2O3 based slag.

Metal/Slag Separation Behavior of CCA with Various Slag Systems and Effect of Slag Composition on the Content of Sulfur and Phosphorus in Iron Nugget

“…4, it can be known that the carburization degrees of reduced iron (Fe) in CCA_Slag C and CCA_Slag D are relatively low and are not enough to form Fe-C melt at 1 673 K. Therefore, the current results show that the slag melting temperatures could be nicely correlated with the carburization of iron followed by the separation of metal and slag as discussed in the previous study. 6) Nevertheless, the separation temperature of CCA comprised of ore and coke is higher than that of Fe-C-slag system. 6) This is because the slag in Fe-C-slag system does not include FeO that should appear in the reduction progress of CCA containing the slag systems being considered in the present study.…”

“…6) Nevertheless, the separation temperature of CCA comprised of ore and coke is higher than that of Fe-C-slag system. 6) This is because the slag in Fe-C-slag system does not include FeO that should appear in the reduction progress of CCA containing the slag systems being considered in the present study. As demonstrated in the previous works, 6,9) the surface tension of the liquid slag initially formed in CCA would exert attraction force on Fe and carbon in a way that Fe can quickly be carburized in close touch with carbon, which results in the formation of liquid Fe-C melt.…”

“…It is clearly indicated that the introduction of low melting slag systems (CCA_Slag A-CCA_Slag D) clearly promoted the separation of metal and slag while CCA_no Slag showed very poor separation behavior even at 1 773 K. Among them, CCA_Slag C and CCA_Slag D showed relatively poor separation at 1 673 K than the others. As discussed in the previous study, 6) it is more difficult to develop the direct carburization and melting of solid iron (Fe) in the case of CaOAl2O3-based slag of high melting temperature compared with CaO-SiO2-based slag. In Fig.…”

“…In examining the feasibility of using CCA containing high basicity slag, the effect of CaO-Al2O3 slag of high basicity on the reduction of CCA and separation of metal and slag were previously investigated. 5,6) It is generally understood that the molten slag of high basicity is beneficial for both desulfurization and dephosphorization. 7) Therefore, high basicity slag can be utilized in the direct smelting reduction of CCA such as ITmk3 or Hi-QIP process to decrease the content of sulfur and phosphorus contained in the final iron nugget product.…”

Carburization Degree of the Iron Nugget Produced by High Al₂O₃ Iron Ore

“…Consequently, some researchers believe DRI process, especially the iron nugget process, will be one of the possible choices to effectively use high Al 2 O 3 iron ore resource. [2][3][4] The iron nugget process is an environmentally friendlier, economical alternative to the traditional blast furnace process. [5][6][7] It aims to produce pig iron nugget which has similar chemical and physical properties to blast furnace pig iron using fine iron ores and noncoking coals.…”