Page 194 - Adsorbents fundamentals and applications

INTERACTIONS OF ADSORBATE WITH CATIONS 179

Clinoptilolite is a member of the heulandite group of natural zeolites. It has
been used for radioactive waste disposal and ammonia recovery from sewage
effluents (Vaughan, 1988). It has also been studied extensively in the separation
of N 2 /CH 4 for natural gas upgrading by molecular sieving or kinetic separation
(Ackley and Yang. 1991; see chapter for details). The cation sites in clinoptilolite
are shown in Figure 7.13.
The framework of clinoptilolite consists of three channels, A, B, and C, formed
by 10- and 6-oxygen rings, as shown in Figure 7.13. Channels A and B are
alternating and parallel, and channel C is on the same plane with A and B and

O O O M[3]
0.72 nm 0.47 nm z z
O K + O

B C
A
z = 0.14 nm
(a) M(3) site

M[4]
w w 0.47nm 0.55nm
Mg 2+
B C
A
w = 0.30nm
(b) M(4) site

M[1] M[2]
M[2]
Na + w Ca 2+ z
M[1]
B C
A x = 0.22nm z = 0.45 nm
w = 0.50nm
(c) M(1), M(2) sites
b b

a c
Figure 7.13. Cation sites in channel-type zeolite of clinoptilolite (heulandite), with dimensions
of channel blockage (Ackley and Yang, 1991).