Environmental Engineering Reference
In-Depth Information
continued to investigate the adsorption of radioactive metals (e.g., Rh, Sr, Ru) which
illustrated selective and efficient adsorption of radioactive pertechnetate ion onto iron
sulfide nanoparticles. The supported nanoscale zero-valent iron rapidly separated and
immobilized Cr(VI) and Pb(II) from aqueous solution (Ponder et al., 2000). This
technology used extra-small superparamagnetic composite particles, which were
embedded with iron oxide nanoparticles that did not lose their magnetic properties in the
presence of a magnetic field. Removal rates of Cr(VI) and Pb(II) were up to 30 times
higher for nanoscale iron than for iron filings or iron powder. Besides, reduction of
Cr(VI) was 4.8 times greater for nanoscale iron than for an equal weight of commercial
iron filings.
Recently, Moeser and Adhoum (2002) prepared the magnetic fluids consisting of
a suspension of 7.5 nm Fe 3 O 4 nanoparticles coated with a bifunctional polymer layer,
which comprised of an outer hydrophilic poly(ethylene oxide) (PEO) region for colloidal
stability and an inner hydrophobic poly(propylene oxide) (PPO) region. Bench-scale
experiments showed that these magnetic fluids exhibit a high capacity for organic
solutes (e.g., naphthalene, phelanthrene) and the used nanoparticles could be recovered
with 98% efficiency. Mak and Chen (2004) studied the adsorption of methylene blue
(MB) by polyacrylic acid-bound iron oxide magnetic nanoparticles. They found that the
adsorption and desorption of MB were quite fast and could be completely finished
within 2 minutes due to the absence of internal diffusion resistance. The adsorption of
pollutants by nanoparticles occurred via an external adsorption, resulting in a very short
adsorption time as compared to other pore-structured adsorbents. Chang and Chen (2005)
reported that the monodisperse chitosan-bound magnetite nanoparticles could be applied
effectively and rapidly for removal of Cu(II) ions at pH > 2, that is, the maximum
adsorption capacity is 21.5 mg/g and the equilibrium is only 1 minute.
Apparently, the magnetic nanoparticles possess the advantages of a large surface
area, high number of surface active sites, and high magnetic properties, which lead to
high adsorption efficiency, high removal rate of contaminants, and easy and rapid
separation of adsorbent from solution via the magnetic field. In addition, it is possible
that after magnetic separation by the external magnetic field, the harmful components
can be removed from the magnetic particles, which can be reused (Oliveira et al., 2003).
However, on the subject of the regeneration of spent nanoparticles and recovery of
adsorbates from these nanoparticles, little information except recent publications is
available. To make magnetic nanoparticles more economically or politically attractive,
our efforts have been focused on the recovery and reuse of these adsorbents as well as
the recovery of adsorbates. Four types of magnetic nanoparticles (-Fe 2 O 3 , MeFe 2 O 4 ,
surface-coated and metal-doped -Fe 2 O 3 ) were synthesized in our study.
 
 
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