Environmental Engineering Reference
In-Depth Information
13.9 cm
3
resin.
Figure 8.11 is a schematic of the number of stages.
(b) To arrive at a graphical solution, Figure 8.12, use:
Plugging into contaminant balance,
S
=
.
=
.
+
.
Overall mass balance: 1
5(220)
1
5(11)
6
25
Y
1
cm
3
Y
1
=
50
.
2mg
/
.
Then, 1 plot equilibrium data using Langmuir isotherm;
2 plot operating line: (
X
n
,
Y
n
+
1
) and (
X
0
,
Y
1
);
3 determine the step off stages.
The number of stages required is three.
S
,
Y
1
L
= 1.5 L waste
L
= 1.5 L (assume dilute solution)
X
0
=220mg
/
L
X
1
=22mg
/
L
S
=?
Y
0
=0
Figure 8.10
Schematic for wastewater treatment, Example 8.2.
X
0
= 220,
L
=1.5
X
n
= 11,
L
=1.5
…
1
n
S
=6.25cm
3
,
Y
n
+1
= 0
S
= 6.25,
Y
1
=?
Figure 8.11
Number of countercurrent stages, Example 8.2.
8.8
Remember
Ion exchange is a UNIT OPERATION. Regardless of what chemicals are being sepa-
rated, the basic design principles for ion exchange are always similar.
An ion-exchange process will look much like an adsorption process, with a liquid phase
being contacted with a solid phase (the RESIN) where the ion exchange occurs.
Like adsorption, an ion-exchange process can be carried out in a fixed-bed column, or
in a batch process. Columns are more appropriate for industry and water or wastewater
applications, while batch processes are more likely to be used in a lab for analytical
purposes.
An ion-exchange process can remove anions or cations from solution, depending on the
charge of the functional group within the resin.
There are some naturally occurring ion-exchange resins as well as synthetic resins.
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