Sorption Kinetics - Transport and Fate of Chemicals in Soils: Principles and Applications - page 50

100

Nonlinear

80

200

100

60

Equil

50
40
30
20
10 hr

40

20

0

0 200 400 600 800 000

60

Adsorb
Desorb

50 hr

40

20

10 hr

0

0 200 400 600 800 000

Solution Concentration (μg/cm 3 )

FIGURE 2.15
Simulated adsorption-desorption using a nonlinear kinetic retention model. Desorption was
initiated after 10 and 50 hours for each successive sorption step.

hysteresis parameter based on the maximum difference between an adsorp-
tion and a desorption isotherm:

N
N

×

a

ω= − 1 100

(2.9)

d

where N a and N d are the exponent Freundlich parameter associated with
adsorption and desorption, respectively. Cox, Koskinen, and Yen (1997)
proposed another desorption hysteresis coefficient H , based on the ratio of
desorption and adsorption isotherm parameters:

N
N

a

H =× 100

(2.10)

d

Both coefficients ω and H are simple and easy to calculate. Zhu and Selim
(2000) derived another formula to quantify the extent of hysteresis based
on the area under each adsorption and desorption curve. If A a represents