3. Results and discussion
Langmuir equation was derived from adsorption rate
equation, assuming a first order equilibrium kinetics
K. Chojnacka et al. / Chemosphere 59 (2005) 75–84 77
pattern. According to the model assumptions, sorbate
occupies one place, and the equation describing reaction
rate allows simultaneous occurrence of adsorption and
desorption processes. The model used is expressed as
Eq. (1),
dh
dt
¼ kadð1 hÞ kdeh ð1Þ
where h—states for the degree of surface coverage that
is, qq1
max. When sorption is in equilibrium, dh
dt ¼ 0, metal
biosorption isotherm can be expressed by Langmuir
equation, shown below,
q ¼
qmaxbCeq
1 þ bCeq
ð2Þ
where b is the ratio of adsorption and desorption rate
constants b ¼ kadk1
de .
In the present study, the parameter b was determined
from kinetic experiments and the parameter qmax from
isotherm studies. This approach enabled to evaluate a
single model parameter at a time.