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radioactive ions (e.g., Rh, Sr, Ru) from solutions. The uptake of these metals was rapid
(30 min) and the loading on the adsorbent was high (Watson et al., 2001).
With the potential applications of nanoparticles in the wastewater treatment, the
separation of the fine particles, however, becomes a challenge. Generally, nanoparticles
are anchored onto a solid matrix such as carbon, zeolite, or membrane for
water/wastewater treatment applications, which undoubtedly results in higher cost.
Although the superior performance of nanoparticles on the removal of heavy metals and
organics has sufficiently demonstrated, previous research revealed very little insight into
the regeneration capabilities for recycling or recovery purposes. Because of the high
regeneration cost, recovery of these adsorbents becomes uneconomical, and
consequently, the spent adsorbent nanoparticles may form a secondary pollution to the
environment (Schmidt and Kodukula, 1985). Therefore, it deserves more attention in the
exploration of the new adsorbents with high external surface area and low regeneration
cost as well as significant improvement on the adsorption system.
In this chapter, the focus would be more on the removal efficiency and
mechanisms of heavy metals from industrial wastewater using iron-based magnetic
nanoparticles as well as the recovery of the spent nanoparticles.
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Magnetic nanoparticles ensure an easy and cheap separation using a strong
magnetic field. Due to its magnetic property, a magnetic adsorbent acts not only as an
adsorbent for removing toxic metals from solution, but also as a magnetically
energizable element for attracting and retaining paramagnetic nanoparticles, which can
be removed from solution.
The advantage of this separation technology is that the
harmful ingredients together with the magnetic particles can be eliminated from the
treatment system by a simple magnetic field (Raven et al., 1998). After magnetic
separation in the external magnetic field, the harmful components can often be removed
from the magnetic particles, and the magnetic particles can be used again. Easier
operation and lower cost in the regenerating process render the magnetic adsorption
process more economical with a possibility of replacing the common filtration and
centrifuge separation technologies (Kaminski, 1997).
Generally, the magnetic behavior of particles can be classified into five major
groups: diamagnetism, paramagnetism, ferromagnetism, ferrimagnetism, and antiferro-
magnetism (Viswanathan and Murthy, 1996). Diamagnetism is a fundamental property
of all matter, although it is usually very weak. It is due to the non-cooperative behavior
of orbiting electrons when exposed to an applied magnetic field. For paramagnetism,
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