DEVELOPMENT OF HIGHLY REACTIVE METAKAOLIN FROM PAPER SLUDGE

The paper industry in Western Europe generates around 6 million tons/y ear of sludges, which contain about 60% dry matter mainly composed of cellulose fibers, kaolinite, and calcite. The present study deals with an original way of utilizing such wastes: the production of metakaoli n by calcining paper sludge in the temperature range of 700 degrees C to 800 degrees C. After calcination, pastes containing 50% calcium hyd roxide and 50% burnt sludge were hydrated and the lime consumption inv estigated by differential thermal analysis. The results show that a ve ry reactive pozzolan is produced by calcining paper sludge at 700 degr ees C or 750 degrees C for 2 or 5 hours. Despite a smaller kaolinite c ontent, the burnt paper sludge exhibits move pozzolanic activity than commercially available metakaolins, especially at early ages. Thermode sorption analyses show that this higher activity is due to the presenc e of superficial defects that occur during the sludge calcination. (C) 1998 Elsevier Science Ltd.