Dynamic hydrothermal synthesis of xonotlite from acid-
extracting residues of circulating ﬂuidized bed ﬂy ash
Received: 23 January 2015 / Accepted: 30 March 2015 / Published online: 11 April 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract This investigation was made to examine how the conditions of hy-
drothermal synthesis inﬂuence the crystal structure of xonotlite and its morphology.
For synthesis, we used acid residues after extracting the alumina from circulating
ﬂuidized bed ﬂy ash as raw material, as far as we know, that no one used before.
Staring with Ca/Si = 1, hydrothermal temperatures were between 180 and 260 °C.
The samples were characterized in terms of mineralogical composition (XRD),
morphological analysis (SEM), and thermal gravimetric and differential thermal
analyses. During the 72 h synthesis at 240 °C, well formed xonotlite ﬁbers of
10–15 lm long were obtained. Under the same conditions, but at 200 °C, the ob-
tained xonotlite was poorly formed. The results indicated that the residue could be
used to prepare pure xonotlite. Different hydrothermal temperatures and holding
times have a great impact on crystallinity and morphology of xonotlite.
Keywords Circulating ﬂuidized bed ﬂy ash Á Xonotlite Á Hydrothermal synthesis Á
Thermal insulation material
Coal ﬂy ash is generated during high temperature combustion of coal in coal-ﬁred
power plants. Currently, about 800 million tons of coal ﬂy ash has been generated in
the world [1–3]. The annual ﬂy ash discharge is more than 4 9 10
tons in China [4,
5]. Because of the low utilization rate, coal ﬂy ash is generally dumped in land, after
which it poses a serious threat to the environment . The circulating ﬂuidized bed
& Yinshan Jiang
Key Laboratory of Automobile Materials, Ministry of Education, Department of Materials
Science and Engineering, Jilin University, 5988 People’s Avenue, Changchun 130025,
People’s Republic of China
Res Chem Intermed (2016) 42:519–530