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322 4. Adsorption and Ion Exchange

and thus, from eq. (4.176),

ka
f u 15.61
ka
s u
where (eq. (4.177))

3 1
)
a u ( 1 44.31 cm
r o

The parameter X T is (eq. (4.173))

ka su Z
X T 3.528
1+1 / u
s
For Fr = 0.113, 0.8297 (eq. (4.169)), I A 1.7 and I B 1.08 (Figure 4.25). for Then,
C / C 0 X 0.1, and for eq. (4.165), we ha e v – X T 1.217 ( X i 0.066). Finally ,
T
from eq. (4.172),

ka  Z 
su  t  t 225 h
T
(1 1/ )  u s 
b
This is only a difference of 0.45% from the experimental value. Constant pattern approx-
v
imation does not neely affect the final result. For solid diffusion control, gati ζ→∞ and
for this case, from eq. (4.184), – X T = –1.277 ( X i = 0.1) and t 227 h or a dif ference
T
alue. of 0.25% from the experimental v
It is interesting to check the Peclet number of the fed bed. The Reynolds number is ix
alue,
0.154, and for this low v the most appropriate correlation is that of Chung (eq.
(3.314)). The resulting particle Peclet number is 0.39 and thus, the bed Peclet number is
151.98, which is fairly high, and we can assume that the plug-flow condition is assured.

A f e w comments on dibr omostyr ene : Known also as brominated styrene, it has been
used as a flame retardant in the manufacture of thermoplastics. Although it does not
seem to be toxic for the amounts present in the environment, it might have a teratogenic
potential if large amounts of it are orally administered, as de elopmental studies in rats v
e sho and rabbits ha wn. v

Example 6
Rivero et al . (2004) studied the remoal of HCrO v 4 (Cr 6 ) from polluted groundwater in
a fixed bed at 24 °C. The dimensions of the bed were D = 1.64 cm and Z = 13.25 cm. An