Environmental Engineering Reference
In-Depth Information
As can be seen from Figure 9.27, the adsorption capacity for Cr(VI), Cu(II) and
Ni(II) is respectively calculated to be 17.5 mg/g, 27.3 mg/g, 24.1 mg/g. Undergoing five
cycles of adsorption/desorption experiments, -Fe
2
O
3
almost kept the same adsorption
capacity for these three heavy metals, indicating that there were no irreversible sites on
the surface of the adsorbent. Thus, -Fe
2
O
3
nanoparticles could retain original metal
removal capacity after several successive adsorption-desorption processes. Meanwhile,
the desorbed heavy metals were highly concentrated and could be considered for
recycling application. Reuse of the adsorbent through regeneration of its adsorption
capacity is an economic necessity for industrialization.
9.5.3 Metal Ferrite (MeFe
2
O
4
) for Cr(VI) Removal and Recovery
9.5.3.1 Parameters Affecting Cr(VI) Adsorption
Effect of Contact Time.
The Cr(VI) removal as a function of contact time was
studied under the optimum conditions (i.e., pH of 2.0, the shaking speed of 400 rpm, see
below). The results are presented in Figure 9.28.
100
90
80
MnFe2O4
MgFe2O4
ZnFe 2O4
CuFe 2O4
NiFe 2O4
CoFe 2O4
70
60
50
40
30
20
10
0
0
10
20
30
40
50
60
70
80
Time (min)
Figure 9.28
Cr(VI) removal by various MeFe
2
O
4
at various contact times (Hu et al.,
2007a).
It was observed that the percentage adsorption of Cr(VI) increased with an
increase in contact time and gradually reached constant within less than 1 h. The Cr(VI)
removal efficiencies followed the descending order: MnFe
2
O
4
> MgFe
2
O
4
> ZnFe
2
O
4
>
CuFe
2
O
4
> NiFe
2
O
4
> CoFe
2
O
4
. The equilibrium time for Cr uptake by MnFe
2
O
4
,
MgFe
2
O
4
, ZnFe
2
O
4
, CuFe
2
O
4
, NiFe
2
O
4
and CoFe
2
O
4
nanoparticles is 5, 45, 30, 20, 15
and 60 minutes, respectively. It is evident that Cr(VI) adsorption onto MnFe
2
O
4
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