A desulfurization slag is difficult to recycle, since there is a possibility to elute a sulfur containing solution. To promote the recycle of the desulfurization slags, it is important to know the physicochemical properties of the slag. In addition, desulfurization process could be modified, when the sulfur behavior in the slag was understood.
In this study, the effect of sulfur and oxygen partial pressure on the crystallization behavior was investigated using Hot Thermocouple Technique. Three different atmospheres were established in the electric furnace through the modification of experimental apparatus. One was an argon without deoxidation, the second was an argon with Ti plate (Ar+Ti) which was located in the electric furnace for deoxidation of argon gas, and the third was an argon with CaS pellet located on the Ti plate (Ar+Ti+CaS) in which the partial pressure of SO₂ increased with the decrease of the oxygen partial pressure.
The nose position of TTT diagram of CaO–Al₂O₃ eutectic composition under Ar atmosphere was 7 s at 1100°C, while the nose positions under Ar+Ti and Ar+Ti+CaS were 7 s at 1150°C. TTT diagrams under Ar+Ti and Ar+Ti+CaS, which are lower oxygen potential and higher SO₂ potential, showed the earlier crystallization behavior in the higher temperature region than the nose position. From the results of XRD analysis, the sulfur added to the slag existed in the monocalcium aluminate (CaO·Al₂O₃) primary crystal. When the content of CaS increased, a formation of CaO through oxidation increased and the tricalcium aluminate (3CaO·Al₂O₃) was formed as a primary crystal, in which the sulfur content was higher than the eutectic structure in the matrix.