THE ROLE OF CaF2 AND CaS04 IN CEMENT CLINKEHlNG

Abstract

2C2S-CaF2 can't be detected in the mix with F/SO3> 0.158 burned at 1,000 or 1,080 C. 3C3S-CaF2 can hardly form at 1,140 C even in the mix according to its stoichiometric composition, and can't form in the presence of SO3. 2C2S-CaSO4 occurs only in the mix with F/SO3<0.158 burned at 1,140 C. 3C2S.3CaSO4.CaF2 forms easily at 940 C owing to the melting of eutectic mix at 910 C. It begins to melt at 1,225 C and the corresponding endo-thermic peak is at 1,260 C. Its melting point may be reduced to 1,180 - 1,248 or 1,160-1,248 C when Al2O3+Fe2O3 or Al2O3 +Fe2O3+MgO is added. Both CaF2 and CaSO4 can depress the melting point of eutectic mix T2. The melting point of mix may be reduced to 850-900 C when large quantities of CaF2+CaSO4 are added. It seems probable that a small quantity of melt may be produced at some points in the raw meal with CaF2g+CaSO4 before 900 C, it promotes 3C2S3CaSO4-CaF2 forming. Both CaF2 and CaSO4 also increase the fluidity (or reduce the viscosity) of eutectic melt. Both CaF2 and CaF2+CaSO4 can promote the clinker formation at lower temperature. The ciin- keri'ng temperature of cement with CaF2+CaSO4 could be reduced to 1,300 - 1,350 C. The mix near the inner side of refractory in clinkering zone of shaft kiln could be well burned, and the industrial wastes such as coal gangue might be used when mineralizer is added.