Environmental Engineering Reference
In-Depth Information
ochroleuca
and
Pelvetia caniculata
were 74, 95, 79, 64 and 75 mg g
-1
,
respectively.
Seven species of brown, green, and red seaweeds were examined for their
abilities to remove Cd
2+
from aqueous solution by Hashim and Chu [130].
Kinetic studies revealed that cadmium ions uptake was fast with 90% or more
of uptake occurring within 30-40 min of the contact time. Maximum cadmium
ions uptake capacities at pH 5 ranged from the highest value of 83.18 mg g
-1
for the brown seaweed
Sargassum baccularia
to the lowest value of 17.99 mg
g
-1
for the red seaweed
Gracilaria salicornia
, representing a difference of
363%. In general, brown seaweeds were found to exhibit the best overall
cadmium ion removal.
The monolayer adsorption capacity of cadmium ions onto macro alga
Hypnea valentiae
increased from 15.79 to 28.65 mg g
-1
when the temperature
was raised from 30 to 60 ºC, which indicated a spontaneous endothermic
physisorption process [131].
The Cd
2+
adsorption capacity of peat was evaluated by Liu
et al.
[132].
The results show that the adsorption rates are fast: the thermodynamic
equilibrium is reached in 20min. The adsorption kinetics can be described by
the Elovich kinetic equation. The total amount adsorbed in the single-
component system (Cd
2+
=5.16 mg g
-1
) is higher than in the double-component
system (Cd
2+
plus Ni
2+
=4.57 mg g
-1
and Cd
2+
plus Cu
2+
=3.83 mg g
-1
) which is
higher than in the tri-component system (Cd
2+
plus Ni
2+
plus Cu
2+
=3.35 mg g
-
1
). This is due to the limited number of adsorption sites for nickel, copper and
cadmium in the peat. Nickel, copper and cadmium occupied the same sites
during the competitive adsorption process. However, they occupied only one
adsorption site per ion during the non-competitive adsorption.
The removal of cadmium by chitosan was studied by Erosa
et al.
[133].
Chitosan is a very efficient cadmium ion adsorbent and it adsorbs through a
chelation mechanism, involving the amine groups. The sorption capacity of a
chitosan adsorbent exceeds 150 mg g
-1
.
The Cd
2+
adsorption onto chitin was evaluated by Benguella and Benaissa
[134]. The sorption performances are strongly affected by several parameters,
such as: initial concentration of cadmium ion and particle size. The amount of
cadmium removed by the chitin adsorbent increased with the increase of these
parameters at a specific time. The removal capacity of cadmium ion is about
14.7 mg g
-1
of chitin at 25ºC.
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