THE KINETICS OF DEPHOSPHORIZATION OF CARBON-SATURATED IRON USING AN OXIDIZING SLAG

The kinetics of dephosphorization of carbon-saturated iron by oxidizin g slags were studied at 1330 degrees C. Nine slag compositions were in vestigated in the systems CaO-Fe2O3-SiO2-CaF2 and CaO-Fe2O3-SiO2-CaCl2 . Increasing Fe2O3 up to 50 pct was found to increase the rate and ext ent of dephosphorization, whereas further increases were found to decr ease the rate and extent of dephosphorization. This was explained in t erms of two competing effects on the driving force, where increased le vels of iron oxide increase the oxygen potential for dephosphorization , hence the driving force, but simultaneously dilute the basic compone nts in the slag, lowering the driving force for dephosphorization. CaF 2 and CaCl2 were found to decrease the rate and extent of dephosphoriz ation at levels higher than 12 pct. The rate of dephosphorization was found to be first order with respect to phosphorous in the metal and w as controlled by mass transport in the slag. The oxygen potential at t he slag/metal interface was controlled by the FeO activity in the slag . When the kinetic results were analyzed to take account of different driving forces, Fe2O3, CaF2 and CaCl2 were all found to increase the m ass transfer coefficient of phosphorous in the slag, and a quantitativ e relationship has been demonstrated between these mass transfer coeff icients and the slag viscosity for each system studied.