USE OF SELECTED MINERALS AS SECONDARY RAW MATERIALS IN CEMENT INDUSTRY. PT.2. EFFECT ON CLINKER STRUCTURE

It is known that certain foreign elements exert a considerable effect on the cement raw mix burnability and clinker structure, even at low concentration. The minerals, iron rich wolframite, stibnite and a wolframite-stibnite assemblage, were selected in order to introduce W, Sb and S into the cement raw mix. One reference and twelve modified mixtures were prepared by mixing the reference sample with 0.5, 1.0, 1.5 and 2.0 wt% of the above minerals and their effect on the structure of the produced clinker studied. XRD, performed in samples that were burned at 1450 C, showed that the diffraction patterns correspond to a structure of a typical clinker, obtained at the above temperatures. In addition, samples sintered at lower temperature (1200-1400 C) were examined in order to investigate the effect of the additives on the intermediate products. It is concluded that the added compounds affect mainly the structure of calcium aluminate and calcium aluminoferrite phases, due to their dissolution in the melt formed during the sintering. SEM was used in order to examine the structure of the clinker and the distribution of the foreign elements in its main phases. It is shown that W and Sb were mainly concentrated in the solidified melt. In addition, bigger and more roundish alite crystals were found in these samples. These modifications are attributed to the effect of the added elements on the properties of the melt. 4 refs.