Mineralogical and morphological changes of calcined paper sludge at different temperatures and retention in furnace

This work reports the project of thermal effects in mineralogy and texture of the paper sludge to employ them as pozzolanic material. For this reason, the chemistry and mineralogical composition has been studied, as well as its morphology by XRD, SEM and EDX. The initial sludge has been treated to 700, 750 and 800 °C during 2 and 5 h being observed that initial kaolinite becomes metakaolinite and that its pozzolanic activity with a paper sludge treated to 700 °C for 2 h is comparable to that of a commercial metakaolinite. The transformation of kaolinite after the dehydroxylation is to convert in amorphous metakaolinite. At the temperature mentioned above, calcite from the initial sludge is maintained active. It is concluded that the pozzolanic activity of metakaolinite is strongly related to the crystallinity of the original kaolinite. Well-ordered kaolinite is transformed into more reactive metakaolinite.