Page 275 - Adsorption, Ion Exchange & Catalysis- 2007, Elsevier - Copy

Else_AIEC-INGLE_cH004.qxd 7/1/2006 6:53 PM Page 271
4.1 Basic Principles of Adsorption and Ion Exchange 271

with

q
Y i (4.26)
i
q max
C i
X i (4.27)
C o

where i is A or B. Here, q max is the MEL in equialents per unit solid mass, which only in v
the case of complete exchange is equal to the REC. The REC is the “ceiling” of the solid-
phase capacity. Furthermore, C o is the initial concentration (normality) of the solution
phase in equivalents per unit liquid volume, which is, in the case of ion e constant xchange,
throughout the exchanging process. If ion A is preferred, the separation factor is larger than
unity, whereas if ion B is preferred, it is smaller than unityThe numerical value of the .
dimensionless separation factor is not affected by the choice of concentration units.
alents, Expressing all concentrations in equi v

X A X B X 1 B X 1
A
Y Y Y 1 Y 1
A B B A

Then,

Y (1 X )
AB A A (4.28)
X A (1 Y A )

Then, the relationship between A B and the Langmuir equilibrium parameter ( La ) is

1
AB (4.29)
La

”
That is why La is also called the “separation fFurthermore, it is clear that the con-
actor
.
stant separation f actor A-B in an ion-exchange system means that in practice, this system
obeys a Langmuiran equilibrium isotherm, in which La is of course constant.
Another important equilibrium parameter is the distribution coeficient ( f ) defined as i
q
i (4.30)
i
C i

f
icient,
In practice, for the specific case of the distribution coef mg/g units are used for q
and mg/L for C . Thus, the units of are L/g.