Environmental Engineering Reference
In-Depth Information
through a particle diffusion mechanism at 25 ºC, while film diffusion is the
adsorption mechanism at 40 ºC. Demirbas [15] studied the adsorption of Cd
2+
onto lignin from beech and poplar woods. They modified these lignins with
alkali glycerol delignification and observed that the adsorption capacity
increases with pH.
Harmita
et al.
[16] studied the Cd
2+
adsorption using kraft and organosolv
lignins. The sorption capacity of Cd
2+
onto all the lignin studied, increased
with the pH increase. The Cd
2+
sorption kinetic was very fast; the
thermodynamic equilibrium was reached in 80 min. The sorption capacity on
each material decreases in the following order: softwood organosolv lignin <
hardwood organosolv lignin < hardwood kraft lignin < softwood kraft lignin.
They noticed that the maximum sorption was lignin dependent and the
maximum sorption for softwood organosolv lignin, hardwood organosolv
lignin, hardwood kraft lignin, softwood kraft lignin were 0.9, 2.1, 2.8 and 3.2
mg g
-1
, respectively.
The adsorption of cadmium onto phosphogypsum, a byproduct from the
manufacture of phosphoric acid by the wet process, was studied by Balkaya
and Cesur [17]. Before the batch adsorption was studied, phosphogypsum was
pre-conditioned by a process that uses milk of lime. Maximum adsorption
capacity of lime-preconditioned phosphogypsum was found to be 131.58 mg
g
-1
.
Papandreou
et al.
[18] observed that fly ash, a byproduct from power
plants, have high adsorption capacity for cadmium (19 mg g
-1
), but the contact
time required for reaching equilibrium (72 h) is also very high. The bagasse fly
ash, an industrial solid byproduct of the sugar industry, was used to remove
cadmium and nickel from wastewater from metal containing effluents [19-20].
In about 60 min, under the batch test conditions, as much as 90% of cadmium
was removed. The adsorption Cd
2+
ions increased as the temperature
increased, indicating an endothermic nature of the adsorption process. The
monolayer adsorption capacity increased from 1.24 to 2 mg g
-1
when the
temperature was raised from 30 to 50 ºC.
Coal combustion ashes, an industrial waste, were studied as an adsorbent
material for Cd
2+
removal [21]. They found that the Cd
2+
uptake was 67 mg g
-
1
. Its physical-chemistry properties of ashes make them a good adsorbent.
Colemanite ore (CW) is a waste material originated from boron plants. The
Pb
2+
and Cd
2+
adsorptions onto CW waste were investigated [22] and they
found out that the adsorption capacity for Cd
2+
ions was 29.7 mg g
-1
. The
desorbability experiments using 1 M HCl were found to be 98%.
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