With the direct utilization of coal to produce hot metal, impurities i
n the coal, such as sulfur, enter into the process. The amount of sulf
ur in each phase (metal, slag and gas) depends on the operating condit
ions. Trials at American Iron Steel Institute (AISI) Direct Steelmakin
g and Japan (DIOS) indicate that much of the sulfur enters the gas pha
se and the thermodynamics indicate that H2S will be the predominant sp
ecie. The sulfur can enter the gas phase by a reaction of the smelting
gas with the slag or during the devolatilization and combustion of th
e coal. The rate of formation of H2S by the reaction of an Ar-H-2-H2O
gas with the slag was measured. It was found that the initial rate is
dependent on P(H2O) and the sulfur content of the slag. Under present
experimental conditions the rate is controlled by liquid phase mass tr
ansport. The diffusion coefficient of the sulfur in liquid slag, assum
ing mass transfer control, is estimated to be 6.65 x 10(-7) cm2/s at 1
723 K which is in agreement with published values. The rate of H2S fo
rmation was also measured when gas was bubbled through the slag. A rat
e expression was derived for desulfurization with a foamy slag. The su
lfur content of the slag as a function of time was calculated from the
derived rate expressions for different circulation rates of slag from
bulk to foam. The sulfur content of the bath smelting gas was estimat
ed based on experimental results. Some coal samples were devolitilized
and partially combusted with simulated bath smelting gas. The experim
ental results indicate that a large portion of the sulfur enters the g
as phase during devolatilization and combustion of the coal.