Abstract: Since the activity of each component of the blast furnace slag has great effects on blast furnace smelting and product quality， a model was built to predict Al₂O₃ activity in CaO-SiO₂-Al₂O₃-MgO quaternary slag system， based on the molecule and ion coexistence theory. After the prediction model was validated by the experimental results， the effects of the R(w(CaO)/w(SiO₂))，w(MgO)/w(Al₂O₃) and w(Al₂O₃) on Al₂O₃ activity were explored. The results indicate that the model can predict the Al₂O₃ activity of molten slag accurately. When the w(Al₂O₃) was 20% and w(MgO)/w(Al₂O₃) was 0.40， the Al₂O₃ activity decreased with the increasing R. When the w(Al₂O₃) was 20% and R was 1.25， the Al₂O₃ activity decreased with the increasing w(MgO)/w(Al₂O₃). With the R=1.25 and w(MgO)/w(Al₂O₃) =0.40， the Al₂O₃ activity increased with the increasing w(Al₂O₃).

Key words: molecule and ion coexistence theory; mass concentration; blast furnace slag; prediction model; Al₂O₃ activity