EFFECT OF FLUOSILICATE ON CEMENT RAW MIX BURNABILITY AND KILN BUILDUP

Chemically and granulometrically identical cement raw mixes incorporating different limestones from a single deposit were reported to show different degrees of burnability. The limestone samples from the particular deposit were examined by XRD, DTA and microscope and then classified on the basis of the occurrence of fluosilicate in the form of phlogopite, KMg3 (Si3 AlO10) (F, OH)2. Fluorine contents of the examined limestone samples showed almost direct relationship with the XRD pulse counts for the fluosilicate (Phlogopite) at hkl (001), d = 9.96 angstrom. It is found that raw mixes containing limestone with phlogopite detectable by DTA, fired at 1400-degrees-C for one hour, are left with lower amounts of free CaO than the identically fired raw mixes, where phlogopite could not be detected by DTA. The kiln feed with the phlogopite bearing limestone occasionally shows build-up in the preburning zone which contains significant amounts of fluorine and the mineral spurrite.