The silica and alumina contained in clay minerals contributed to
observed increase of dissolved ions. In particular, the silica phase
contained in DE was slightly changed with heat treatment, while
kaolinite and montmorillonite could transform to metakaolin and
disrupted montmorillonite thereby providing more active surfaces.
Dissolution of silicate molecules at high pH (>10) resulted in the
formation of silicic acid; H3SiO4
−, H2SiO4
2−, HSiO4
3− and SiO4
4−,
dependent on pH of the system [11]. The measured pH of this
experiment was around 14. Thus, the stable silicic acid species of
geopolymeric system will normally be expected to be HSiO4
3− and
SiO4
4−. These species are likely to play an important role in silicate
polymeric condensation. To further investigation these effects,
the DE800 was screened through 325 mesh size sieve and used
as source material to prepare geopolymeric materials for furthetests.