A. Gineika / / Lithuania
ANDRIUS GINEIKA / KAUNAS UNIVERSITY OF TECHNOLOGY / LITHUANIA
TADAS DAMBRAUSKAS / KAUNAS UNIVERSITY OF TECHNOLOGY / LITHUANIA
KESTUTIS BALTAKYS / KAUNAS UNIVERSITY OF TECHNOLOGY / LITHUANIA
In this study, the formation of wollastonite (CaSiO3) using two-step synthesis from CaO and AlF3-rich silica gel waste was investigated. The molar ratio of calcium oxide and silica+alumina+fluoride in the initial mixture was equal to 1. The first step – hydrothermal synthesis was carried out in stirred suspension at 200 °C for 12 h where water to solid material ratio W/S was equal to 20. It was determined that tobermorite was dominant compound with admixtures of katoite and cuspidine in the synthesis product. In addition, under these synthesis conditions portlandite and aluminium fluoride were fully reacted. The second step – calcination was carried out at 900 °C for 1 h. It was found that during calcination tobermorite and other calcium silicates hydrates recrystalized to wollastonite and larnite, while cuspidine remained stable.
Keywords: wollastonite, AlF3, calcium silicate, two-step synthesis