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4.2 Design of Adsorption and Ion-Exchange Processes 303

el abo v liquid level, as a liquid v e the initial. x will result in an increase of the liquid le v orte
So, a vessel with a 60-cm height is selected.
The critical rotational speed of the impeller for complete suspension is approximately
541 rpm (9 rps) (eq. (3.114)). This rotational speed results in a Reynolds value of about 2.54
10 5 , and thus the floit has to be noted that the mass transfer coef ulent. Here, w is turb i- f
cient strongly depends on the rotational speed below the critical rotational speed needed for
complete suspension, and weakly depends on the rotational speed above its critical value at
which there are no particles remaining in rest for longer than 1–2 s in a fixed position.

Verification of the controlling mec hanism Zeolite particles are of irregular shape and a
value of
0.65 could be used (see Table 3.13). Furthermore, as a first approach, the
S
able 3.7
minimum mass transfer coeficient from T can be used. Thus, for density dif fer-
f
ence of 1 g/cm 3 this minimum value is k 0.005 cm/s. using Hand’ Then, s def inition (eq.
f
(4.105)), the minimum Biot number is 7.4 10 3 . This number is much higher than the
limit of 30 for solid diffusion control. Thus, we conclude safely that the controlling mech-
anism is solid dif een in the absence of agitation. Ho suficient agitation v we er f
,
fusion,
v
e ef should be provided to ay possible ne v oid an fect of liquid-f v ilm resistance. gati
Using the appropriate equations and correlations of Sections 3.3.5 and 3.3.6, we can cal-
culate the power consumption per unit volume of liquid and thus we can hae an approx- v
imation of the actual mass transfer coeficient in the liquid f f ilm. N P = 6 for this type of
impellers and thus k is about 0.1 cm/s. It is ob vious that k is about 20 times the minimum
f
f
v value used aboe for the Biot number .
A f e w comments on lead : The e e use of tetraethyl lead (TEL) as a gasoline addi- v xtensi
tive, for reducing engine knocking since 1922, constituted the greatest source of lead in
the environment. Despite the fact that manxperts were against its use and the ne y e ga-
tive effects on public health were known as early as the 1920s, the use of TEL contin-
ued till the decade of 1980 (Rosner and Mark 1985). witz, o
Lead is not an exception among heavy metals. It is very harmful een in very small v
amounts, since once absorbed into the body it blocks certain enzymes, causing se ere v
,
physiological or neurological consequences in the long term. The list of the hazardous
effects of lead on human health is quite long: anemia and other blood disorders, dam-
age to the nervous system and brain, kidney disease, and reproductie impairments in v
ere
men and women. Ovxposure to lead may cause birth defects, mental retardation,
behavioral disorders, and een death in fetuses and young children. v

Example 4
Choy and McKay (2005) studied the removal of Cu 2 from aqueous phase using bone char
in a batch reactor. The volume of the liquid was 1.7 L, the volume of the tank 2 L, and its
diameter 0.13 m. A six-bladed flat impeller with a diameter of 0.065 m and a blade height
of 0.013 m was used. Absorbent particles of 605- m diameter were used for the adsorp-
tion e xperiments.
The adsorption isotherm at 20 °C was found to obey the Langmuir equation with K 69.2
L/mmol and Q M 0.709 mmol/g. F xperiments, or the kinetics e Cu 2 solutions of 3.21-mM