of the modified samples all showthe typical diffraction peaks of the
clinoptilolite structure and are similar to that of natural clinoptilolite
with no additional peaks appear. The crystal structure of clinoptilolite
is not obviously damaged, which suggests that the
natural clinoptilolite has good alkali resistance.
The change about crystallinity and cell parameters of clinoptilolite
modified by NaOH showed in Table 4 indicated that the
crystallinity increased. The crystallinity of clinoptilolite modified by
3.00 mol L1 NaOH increased from 90.54% to 92.99% but cell parameters
changed little. Meanwhile, the ICP-OES results found that
there appeared more Si element in the solution when NaOH concentration
is higher, but no change in crystal. The results demonstrate
that alkalis would dissolve amorphous silicon in the surface
of clinoptilolite or poor crystallinity silicon in the clinoptilolite
framework [16].
The OH in alkali solution which is greatly influenced by the Si/
Al ratio can selective dissolution the amorphous silicon. As the
clinoptilolite is negatively charged, so is inert for the attack of OH,
and each of the four ligand aluminum will preserve the four
neighboring silicon atoms. For lower Si/Al ratio clinoptilolite which
protected by four ligand aluminum electric field, the OH will not
cause damage of silicon in the clinoptilolite framework, only selective
dissolution of amorphous silicon [17]. There is a slight increase
of the crystallinity and decline in Si/Al ratio, but no
significant alteration of the cell parameters