Prepublication Version DOI: 10.1007/s11663-017-1070-1 1 Dephosphorization Kinetics between Bloated Metal Droplets and Slag Containing FeO: The Influence of CO Bubbles on the Mass Transfer of Phosphorus in the Metal Kezhuan Gu, Neslihan Dogan and Kenneth S. Coley McMaster Steel Research Centre Department of Materials Science and Engineering McMaster University 1280 Main Street West, Hamilton, Ontario, Canada, L8S 4L7 Email: guk3@mcmaster.ca and coleyk@mcmaster.ca Keywords: Bloated Metal Droplets, Dephosphorization Kinetics, CO bubble, Surface Renewal, Mass Transfer ABSTRACT Dephosphorization kinetics of bloated metal droplets was investigated in the temperature range from 1813K (1540 o C) to 1913K (1640 o C). The experimental results showed that the overall mass transfer coefficient,  , decreased with increasing temperature because of decreasing phosphorus partition ratio,   . It was also found that the mass transfer coefficient for phosphorus in the metal,   , had the highest value at the lowest temperature (i.e., 1813K (1540 o C)) because the formation of smaller CO bubbles increased the rate of surface renewal, leading to faster mass transport. Meanwhile, metal droplets without carbon were also employed to study the effect of decarburization on dephosphorization. The results show that although decarburization lowers the driving force significantly,   (6.2×10 -2 cm/s) for a carbon containing droplet is two orders of magnitude higher than that for carbon free droplets (5.3×10 -4 cm/s) because of the stirring effect provided by CO bubbles. This stirring offers a faster surface renewal rate, which surpasses the loss of driving force and then leads to a faster dephosphorization rate. I. INTRODUCTION In basic oxygen steelmaking, metal droplets created by the impact of the oxygen jet are ejected into the slag, where they are decarburized and dephosphorized by reaction with iron oxide. Those droplets which swell because of internal nucleation of CO bubbles are termed bloated droplets.The behavior of bloated droplets in terms of decarburization has been studied extensively, [1-7] although several of these studies predate the coining of the term “bloated droplet” which was first used by researchers in the authors’ laboratory. [8] Models for predicting residence time in the emulsion zone of the BOF based on droplet bloating behavior have also been developed. [8, 9] Workers at Swinburne University in Australia [10, 11] have developed an overall BOF model considering the behavior of bloated droplets. The development of the bloated droplet concept and its influence on BOF modeling has recently been reviewed in detail by Brooks et al. [12] All of these studies were focused on decarburization kinetics and the causes of droplet swelling. There are very few studies on bloated droplet refining kinetics related to elements other than carbon. One example of this is dephosphorization, which occurs in competition with decarburization in the emulsion zone of the BOF. Based on pilot plant data, Hewage et al. [13] attempted to model dephosphorization in the