The kinetics of dephosphorization of carbon-saturated iron by oxidizing slags were studied at 1330 ЊC. Nine slag compositions were investigated in the systems CaO-Fe 2 O 3 -SiO 2 -CaF 2 and CaO-Fe 2 O 3 -SiO 2 -CaCl 2 . Increasing Fe 2 O 3 up to 50 pct was found to increase the rate and extent of dephosphorization, whereas further increases were found to decrease the rate and extent of dephosphorization. This was explained in terms of two competing effects on the driving force, where increased levels of iron oxide increase the oxygen potential for dephosphorization, hence the driving force, but simultaneously dilute the basic components in the slag, lowering the driving force for dephosphorization. CaF 2 and CaCl 2 were found to decrease the rate and extent of dephosphorization at levels higher than 12 pct. The rate of dephosphorization was found to be first order with respect to phosphorous in the metal and was controlled by mass transport in the slag. The oxygen potential at the 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, Fe 2 O 3 , CaF 2 and CaCl 2 were all found to increase the mass transfer coefficient of phosphorous in the slag, and a quantitative relationship has been demonstrated between these mass transfer coefficients and the slag viscosity for each system studied.

Fig. 8. Plots of MTDATA results case of (a) 56.9 mass% SiO 2 , (b) 42.8 mass% SiO 2 , (c) 27.2 mass% SiO 2 , (d) 0 mass% SiO 2 (normalised silica masses in the calculated oxide system).

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The rate of MgAl 2 O 4 spinel inclusion dissolution in CaO-SiO 2 -Al 2 O 3 slags at 1504uC has been measured using a laser scanning confocal microscope. It was found that the mechanism of spinel inclusion dissolution was at least in part controlled by mass transfer in the slag phase for the slag compositions used. Evidence in support of this finding was that the calculated diffusion coefficient was inversely proportional to the slag viscosity and that the diffusion coefficients were in reasonable agreement with those obtained in a separate study on alumina dissolution. The diffusion coefficients obtained were in the range of 0 . 76-2 . 2610 210 m 2 s 21 .