Environmental Engineering Reference
In-Depth Information
PO
4
3-
, CN
-
and F
-
) in electroplating wastewater on the removal of Cr(VI), the binary
solutions containing Cr(VI) and each of the above ions were prepared individually. For
the competitive studies concerning cations, 20 mL of 80 mg/L Cr(VI) solutions
containing each of various cations (80 or 160 mg/L) and 0.1 g -Fe
2
O
3
nanoparticles
produced via the sol-gel method were shaken for 1 h at pH 2.5. For the competitive
studies concerning anions, 20 mL of 0.5 mM Cr(VI) as CrO
4
2-
was shaken with 0.5 mM
or 1 mM of various anions for 1 h at pH 2.5. After equilibrium, the supernatants were
collected for measurement.
For adsorption of Cr(VI) onto modified MnFe
2
O
4
nanoparticles, all of the Cr(VI)
solutions had a matrix of 0.1 M NaNO
3
to keep the ionic strength constant, except for
one set of experiments where 0.01 M NaNO
3
solution was used to determine the
possible effect of the ionic strength on Cr(VI) adsorption. The conditions affecting
Cr(VI) adsorption onto modified MnFe
2
O
4
nanoparticles were studied by systematically
varying the total Cr(VI) concentrations, pHs, ionic strengths, and various ligands. The
pH of the suspensions was adjusted using 0.1 M HNO
3
and 0.1 M NaOH solutions. To
explore the competitive effect of various coexisting ligands (e.g., EDTA, NH
4
+
and
SO
4
2-
) in industrial wastewater on the removal of Cr(VI), the binary solutions containing
Cr(VI) and each of the above ligands were prepared. Twenty milliliters of 100 mg/L
Cr(VI) solutions containing each of the ligands with the same molar ratio as Cr(VI) and
0.1 g modified MnFe
2
O
4
nanoparticles were shaken at a pH ranging between 2 and 10
until equilibrium reached. After equilibrium, the supernatants were collected for metal
analysis.
9.5.1.3 Desorption and Regeneration Tests
Since heavy metal adsorption onto magnetic nanoparticles is a reversible process,
it is possible to regenerate or activate the adsorbents upon the completion of the
adsorption process. The primary objective of regeneration is to restore the adsorption
capacity of exhausted adsorbent, while the secondary objective is to recover valuable
components present in the adsorbed phase, if any.
Desorption Process.
For desorption studies, metal-adsorbed magnetic
nanoparticles were first washed by ultrapure water to remove the metals loosely attached
to the vial and the adsorbents. To find a more effective eluent for desorption of
adsorbed-Cr(VI), magnetic nanoparticles were subjected to Cr(VI) recovery experiments
using 0.01 N of different alkaline solutions, including Na
3
PO
4
, NaOH, NaAC, Na
2
CO
3
and NaHCO
3
. For determining the optimal concentration for desorption, different
concentrations (i.e., 0.01-1.0 M) of the potential eluents were examined. For Cr(VI)
desorption experiments, 0.1 g Cr-adsorbed magnetic nanoparticles were shaken with 5
mL of 0.01 M NaOH for 30 minutes to reach equilibrium. For Cu/Ni-adsorbed
nanoparticles, 0.1 g metal-adsorbed -Fe
2
O
3
nanoparticles were submerged in 5 mL of
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