Environmental Engineering Reference
In-Depth Information
9.5.1.2 Adsorption Kinetics
For adsorption kinetic studies, 0.1 g -Fe
2
O
3
nanoparticles were added into 40
mL of 50 mg/L Cr(VI), Cu(II) and Ni(II) single-solute individually. Other magnetic
nanoparticles were only mixed with 40 mL of 50 or 100 mg/L Cr(VI) solution. The pH
of the suspension for Cr(VI), Cu(II) and Ni(II) systems was adjusted to 2.5, 6.5 and 8.5,
respectively. Volumes of 3 mL of samples were taken for metal measurements at
specific time intervals of 1, 2, 2, 5, 10, 10, 15, 15 minutes.
Effect of pH.
Since Cr(VI) exists as oxyanions (CrO
4
2-
, Cr
2
O
7
2-
and HCrO
4
-
) in
the solution, acidic to basic pH was tested to find the optimal Cr(VI) adsorption. 0.1 M
HNO
3
and 0.1 M NaOH solutions were used for the pH adjustment. 20 mL of 100 mg/L
Cr(VI) solutions with pH ranging from 2.0 to 9.0 were prepared by dissolving a stock
solution of potassium chromate (1000 mg/L) in ultrapure water. The above solutions at
different pH were mixed with 0.1 g magnetic nanoparticles (e.g., Fe
3
O
4
, MeFe
2
O
4
) for 1
h to reach equilibrium.
Synthetic solutions were prepared by dissolving K
2
CrO
4
, Cu(NO
3
)
2
and
Ni(NO
3
)
2
into ultrapure water. Adsorption studies were performed by rotating 0.1 g
magnetic nanoparticles with 20 mL metal solution in a 25 mL glass vial at room
temperature of 22.5
o
C. To investigate the effect of pH, 20 mL of 50 mg/L Cr(VI), Cu(II)
and Ni(II) ternary component systems with pH at 2.0-9.0 were prepared by dissolving
desired metal salts in ultrapure water. The above solutions at different pH were mixed
with 0.1 g nanoparticles until equilibrium was reached.
Effect of Temperature.
To investigate the effect of temperature on the removal
of Cr(VI), batch tests were conducted by shaking the Cr(VI)-magnetic nanoparticle
mixture at temperatures of 10, 22.5 and 35
o
C for 10 minutes to reach equilibrium. 0.1 g
magnetic nanoparticles (e.g., -Fe
2
O
3
) and 20 mL of 100 mg/L Cr(VI) solution were
mixed at pH 2.5 in different temperatures, individually. At desired time intervals, 3 mL
of samples were taken using a syringe. After separation of particles, the Cr(VI) content
in the supernatant was measured by the ICP.
Effect of Shaking Speed.
Since the shaking speed affects mass transfer in the
system, the mixing rates ranging from 100 to 800 rpm were tested to establish the value
when mass transfer effect was insignificant. The effect of the mixing rate was conducted
at ambient temperature (22.5
o
C) at pH 2.5 by shaking the solution at various mixing
rates. Likewise, samples were taken using a syringe at desired time intervals. After
separation of particles, the Cr(VI) content in the supernatant was measured.
Effect of Common Ions and Ligands.
To explore the competitive effect of
various coexisting cations (Cu
2+
, Ni
2+
, Na
+
, Ca
2+
and Mg
2+
) and anions (NO
3
-
, Cl
-
, SO
4
2-
,
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