Influence of CaO/SiO₂ on the reduction behavior of sintered Fe₂O₃-CaO-SiO₂-Al₂O₃ tablets at the softening and melting temperatures

Reduction experiments were conducted with sintered Fe₂O₃-CaO-SiO₂-Al₂O₃ tablets at (mass%CaO)/ (mass%SiO₂) (C/S) of 1.5, 2.0, and 2.5 at 1 000, 1 050, 1 100, 1 150, and 1 200°C. From the reduction behaviors, we investigated the relationship between the reduction rate and C/S at the softening and melting zone temperatures of blast furnaces. The reduction rates at C/S = 2.0 and 2.5 increased with temperature in the range of 1 000 to 1 200°C. The reduction rate at C/S = 1.5 increased with temperature in the range of 1 000 to 1 150°C; however, at 1 200°C, it decreased to the same value obtained at 1 000°C. The microstructures of these samples, after sintering at 1 270°C, pre-reduction at 900°C, and reduction at 1 200°C, were analyzed through SEM-EDS. Fe₂O₃ particles, SFCA, slag, and pores among Fe₂O₃ particles existed in the samples after sintering. The matrix components in the pre-reduced sample were suggested to be calcium silicate slag containing FeO_x and Al₂O₃ at C/S = 1.5, and to be 'FeO_x' originated from SFCA at C/S = 2.0 and 2.5. The porosity of the open pores at C/S = 1.5 decreased to 16%. It was found that the reduction rate at 1 200°C decreased due to this lower porosity. By contrast, the porosity of the open pores after reduction at C/S = 2.0 and 2.5 was much higher than that after pre-reduction. The reduction rates of these samples at 1 200°C were found to not decrease as a result of maintaining a higher porosity.