Environmental Engineering Reference
In-Depth Information
by all types of MeFe
2
O
4
nanoparticles reached equilibrium within 1 h. The
removal efficiency was highly pH-dependent and the optimal adsorption
occurred at pH 2. Cr(VI) adsorption efficiency increased with the shaking rates
from 100 to 400 rpm, but remained almost constant thereafter. Among all types
of MeFe
2
O
4
nanoparticles, MnFe
2
O
4
showed the highest adsorption efficiency
and the shortest adsorption time, while the lowest recovery efficiency due to a
redox reaction occurred between Cr(VI) and Mn(II).
7)
In order to enhance the adsorption of Cr(VI) onto nanoparticles, two methods for
adsorption enhancement, involving metal-dopant and surface coating, were
developed. During preparation of modified -Fe
2
O
3
nanoparticles, different kinds
of metal (e.g., Al, Ni, Cu, Zn, Mg) were substituted into the -Fe
2
O
3
; amorphous
-FeOOH was used as a surface coating material. The results from laboratory
batch adsorption experiments showed that doping small amounts of aluminum
into -Fe
2
O
3
significantly enhanced Cr(VI) adsorption compared to doping other
metals; coated -FeOOH increased the adsorption efficiency by improving
surface properties. Effects of aluminum dosage or coating mass on adsorption
efficiency, adsorption rate, and magnetic separation were investigated and
compared. Having considered these important parameters, the optimal Al-doped
or -FeOOH-coated -Fe
2
O
3
nanoparticles were verified and applied for the
equilibrium adsorption and mechanism studies. The data of Cr(VI) adsorption
were modeled and fit well with Langmuir isotherm. The Cr(VI) adsorption
capacity of Al-doped -Fe
2
O
3
(23.5 mg/g) or -FeOOH-coated -Fe
2
O
3
(26 mg/g)
is higher than that of pure -Fe
2
O
3
(19 mg/g).
9.7
References
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Ayuso, E. A., Sanchez, A. G., and Querol, X. (2003). “Purification of metal
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Wat. Res
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Blais, J. F., Shen, S., Meunier, N., and Tyagi, R. D. (2003). “Comparison of natural
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73-82.
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