The Influence of Ash Impurities on Interfacial Reactions between Carbonaceous Materials and EAF Slag at 1550°C

Abstract

Carbon/slag interactions have been investigated between two carbonaceous materials, metallurgical coke (18.3 % ash) and natural graphite (2.1 % ash), and an EAF slag (34.8 % Fe 2 O 3 ) using a sessile drop arrangement at 1 550°C to determine the role played by carbonaceous materials in carbon/slag interactions and interfacial phenomena. Gaseous emissions from metallurgical coke in the presence of slag were much higher than those from coke alone indicating significant carbon/slag interactions with the system exhibiting extensive/rapid iron oxide reduction, very high rates of gas generation but poor gas entrapment within the slag phase. High levels of gas generation led to a strong likelihood of convective transport of reactants and products across the metallurgical coke/slag interface with oxides present in coke ash partially dissolving in molten slag and modifying slag composition. Natural graphite on the other hand showed slow rates of gas generation, slow reduction of iron oxide and excellent gas entrapment. Gases generated from graphite alone were comparable to those generated in the presence of slag and were an order of magnitude lower than the corresponding emissions from metallurgical coke/slag system. Slag interactions with metallurgical coke resulted in lower surface tension due to pickup of silica from coke ash and small droplet volumes; slag interactions with natural graphite gave rise to minor changes in slag properties due to low ash levels and increases in droplet volumes. The rate of gas generation was found to be an important parameter in carbon/slag interactions and needs to be maintained at optimum levels for sustaining gas entrapment within slag over extended periods. This study highlights significant differences in the carbon/slag interactions of two carbonaceous materials with an EAF slag, and the important role played by ash impurities.