Dephosphorization Kinetics between Bloated Metal Droplets and Slag Containing FeO: The Influence of CO Bubbles on the Mass Transfer of Phosphorus in the Metal

Dephosphorization kinetics of bloated metal droplets was investigated in the temperature range from 1813 K to 1913 K (1540 °C to 1640 °C). The experimental results showed that the overall mass transfer coefficient, $k_{\text{o}}$, decreased with increasing temperature because of decreasing phosphorus partition ratio, $L_{\text{P}}$. It was also found that the mass transfer coefficient for phosphorus in the metal, $k_{\text{m}}$, had the highest value at the lowest temperature [i.e., 1813 K (1540 °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, $k_{\text{m}}$ (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.