57Fe Mossbauer study of iron distribution in a kaolin raw material:: influence of the temperature and the heating rate

The thermal transformation of a kaolin raw material results from individual contributions of kaolinite and mica minerals, and from the complex nature of their mixture. In addition, it appears that the iron sites are subject to changes with the firing temperature and the heating rate, which influence the thermal transformations. Mossbauer spectroscopy provides information about iron site geometry and iron valence, and the resolution of this technique is high. For the kaolin studied, we determined the relative quantity of structural Fe-III and hematite as a function of temperature, up to 1100 degreesC and for two heating rates, 3 and 50 degreesC/min. Results indicate the loss of hematite above 900 degreesC and a subsequent increase of Fe-III in the structure of silico-aluminate phases. This trend is accentuated for a higher heating rate. (C) 2002 Elsevier Science Ltd. All rights reserved.