Growth, Stratification, and Liberation of Phosphorus-Rich C(2)S in Modified BOF Steel Slag

Basic oxygen furnace (BOF) slag was modified by adding 3.5% SiO(2) and holding at 1673 K for 0, 5, 40, 90, 240, or 360 min. Kilo-scale modification was also carried out. The growth, stratification, and liberation of P-rich C(2)S in the modified slag were investigated. The optimum holding time was 240 min, and 90% of C(2)S grains were above 30 μm in size. The phosphorus content increased with holding time, and after modification, the phosphorus content in C(2)S was nearly three times higher than that in the original slag (2.23%). Obvious stratification of C(2)S was observed in the kilo-scale modification. Upper C(2)S particles with a relatively larger size of 20–110 μm was independent of RO (FeO-MgO-MnO solid solution) and spinel, which is favorable for liberation. Lower C(2)S was less than 3 μm and was embedded in spinel, which is not conducive to liberation. The content of phosphorus in upper C(2)S (6.60%) was about twice that of the lower (3.80%). After grinding, most of the upper C(2)S existed as free particles and as locked particles in the lower. The liberation degree of C(2)S in the upper increased with grinding time, from 86.02% to 95.92% in the range of 30–300 s, and the optimum grinding time was 180 s. For the lower slag grinding for 300 s, the liberation degree of C(2)S was 40.07%.