Environmental Engineering Reference
In-Depth Information
Adsorption Isotherm and Adsorption Capacities
ApplicationoftheempiricalFreundlichisotherm(Freundlich
1906
) (Eq.
5
) and its
linearized form (Eq.
6
), given by
qkC
e
=
n
(5)
f
e
log
qnC
=
log
+
log
K
(6)
e
e
f
showed that the plots of log
q
e
vs. log
C
e
were linear (
r
from+0.96to+0.98forluoride
and + 0.95 to + 1.00 for arsenite). The values of the adsorption coefficient '
n
' obtained
fromtheplotsare0.76,0.76,0.65and0.67forluorideadsorptionand0.88,0.80,0.94
and0.76forarseniterespectivelyforB1,B2,B3andB4.Theadsorptionintensityis
n
< 1 for both the cases and indicates favourable adsorption on the adsorbents.
The values of the Freundlich adsorption capacity,
K
f
, on untreated and acid
treated bamboo dust are in the order of B1 (0.39 mg
1-1/n
L
1/n
g
−1
) < B2 (1.56 mg
1-1/n
L
1/n
g
−1
)<B4(2.26mg
1-1/n
L
1/n
g
−1
) < B3 (2.32 mg
1-1/n
L
1/n
g
−1
) for fluoride adsorption,
and B1 (0.66 ʼg
1-1/n
L
1/n
g
−1
) < B3 (3.13 ʼg
1-1/n
L
1/n
g
−1
) < B2 (3.23 ʼg
1-1/n
L
1/n
g
−1
)<B4
(9.09 ʼg
1-1/n
L
1/n
g
−1
) for arsenite adsorption.
Langmuir adsorption isotherm models the monolayer coverage of the sorption
surfaces and assumes that sorption take places on a structurally homogeneous sur-
face of the adsorbent. This isotherm (Langmuir
1916
) is given by the equation:
(
)
+
(
)
Cq bq
/
=
1
/
1
/
qC
(7)
e
e
m
m
e
The Langmuir plots of
C
e
/
q
e
vs.
C
e
are also linear (
r
from + 0.99 to + 1.00 in fluo-
ride adsorption and+0.98 to+1.00 in arsenite adsorption). Langmuir equilibrium
coefficient,
b
,hasvaluesof0.04-0.11Lg
−1
for fluoride and 0.005-0.070 L g
−1
for
arsenite adsorption. Langmuir monolayer adsorption capacity, q
m
, has the values
8.70mgg
−1
(B1),17.24mgg
−1
(B2),20.41mgg
−1
(B3)and20.41mgg
−1
(B4)for
luoride adsorption and 111.23 ʼg g
−1
(B1),112.74 ʼg g
−1
(B2), 123.00 ʼg g
−1
(B3)
and 123.92 ʼg g
−1
(B4)forarseniteadsorption.
Acidactivationhasapositiveinluenceonthemonolayeradsorptioncapacityofthe
adsorbent materials as it has been found that
q
m
values increase on acid activation.
Conclusions
Alltheadsorbentswereeffectiveintheadsorptionofluorideaswellasarsenite.
The amount adsorbed per unit mass of the adsorbent also increases on acid activa-
tion.Acid activation increases the adsorption capacity compared to the untreated
bamboo dust, which is due to the increase in surface area and anion exchange
capacity.
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