6 Recovery of Magnetic Particles
Although abundant experimental photographic results were reported for the prospect
of separation and recovery of magnetic nanoparticles from water or wastewater,
there is no successful industrial application of magnetic particles for water or
wastewater treatment that have been published. The discrete magnetic particles
which are prone to agglomerate due to the magnetism property were believed to
decrease the heavy metal removal capacity. The problem has become a prodigious
limitation for recovery and reuse of the magnetic particles. Several conditions are
manipulating the applicability of magnetic particles in a sustainable treatment
process.
Several studies have indicated that the nanoscale iron oxide, which behaves as
superparamagnetic material, can offer high accessibility and reusability for water or
wastewater treatment systems [21, 41–43]. Majority of the systems require centrifugation or filtration process to separate solid wastes. Magnetic nanoparticles,
however, can be separated and recovered easily with the aid of an external magnetic
field due to the inherent characteristic of the nanoparticles, magnetism [44].
Magnetic separation is a technique to collect or separate magnetic substances
from flowing streams. High-gradient magnetic separation (HGMS) device comprises
of a bed of magnetically susceptible filling placed inside an electromagnet usually
practiced in magnetic separations. Scientific literature has indicated that magnetic
field-enhanced process with magnetite and HGMS offers substantial improvement
for the removal of heavy metals from wastewater [45]. The generation of significant
magnetic field gradients, size and magnetic properties of particles, and the area of
magnetized surfaces are the crucial factors for effective particle collection. When the
particle suspension flows through the separation unit, the magnetic force attracting
particles must be on top of the gravitational, fluid drag, buoyancy, inertial, and
diffusion forces.
Separation of magnetic nanoparticles with a low-gradient magnetic field or a
handheld permanent magnet (usually made of Fe and Nd) from solution has been
regularly conveyed [46]. However, a higher magnetic force for a superconducting
magnet in HGMS instead of an electromagnet is required when the particle size is
reduced to the nanoscale. Complementary to this, aggregation due to strong magnetic dipole-dipole interactions between particles can either be coated with a surfactant to provide steric stability or particle surfaces be modified to produce a repulsive
electrostatic force [47, 48]. In short, an optimum particle size, synthesis methods of
magnetic nanoparticles, and fluid properties are the aspects needed to be considered
to design an effective recovery and high removal performance system.
10 Removal of Heavy Metal Ions Using Magnetic Materials
405
Although abundant experimental photographic results were reported for the prospect
of separation and recovery of magnetic nanoparticles from water or wastewater,
there is no successful industrial application of magnetic particles for water or
wastewater treatment that have been published. The discrete magnetic particles
which are prone to agglomerate due to the magnetism property were believed to
decrease the heavy metal removal capacity. The problem has become a prodigious
limitation for recovery and reuse of the magnetic particles. Several conditions are
manipulating the applicability of magnetic particles in a sustainable treatment
process.
Several studies have indicated that the nanoscale iron oxide, which behaves as
superparamagnetic material, can offer high accessibility and reusability for water or
wastewater treatment systems [21, 41–43]. Majority of the systems require centrifugation or filtration process to separate solid wastes. Magnetic nanoparticles,
however, can be separated and recovered easily with the aid of an external magnetic
field due to the inherent characteristic of the nanoparticles, magnetism [44].
Magnetic separation is a technique to collect or separate magnetic substances
from flowing streams. High-gradient magnetic separation (HGMS) device comprises
of a bed of magnetically susceptible filling placed inside an electromagnet usually
practiced in magnetic separations. Scientific literature has indicated that magnetic
field-enhanced process with magnetite and HGMS offers substantial improvement
for the removal of heavy metals from wastewater [45]. The generation of significant
magnetic field gradients, size and magnetic properties of particles, and the area of
magnetized surfaces are the crucial factors for effective particle collection. When the
particle suspension flows through the separation unit, the magnetic force attracting
particles must be on top of the gravitational, fluid drag, buoyancy, inertial, and
diffusion forces.
Separation of magnetic nanoparticles with a low-gradient magnetic field or a
handheld permanent magnet (usually made of Fe and Nd) from solution has been
regularly conveyed [46]. However, a higher magnetic force for a superconducting
magnet in HGMS instead of an electromagnet is required when the particle size is
reduced to the nanoscale. Complementary to this, aggregation due to strong magnetic dipole-dipole interactions between particles can either be coated with a surfactant to provide steric stability or particle surfaces be modified to produce a repulsive
electrostatic force [47, 48]. In short, an optimum particle size, synthesis methods of
magnetic nanoparticles, and fluid properties are the aspects needed to be considered
to design an effective recovery and high removal performance system.
10 Removal of Heavy Metal Ions Using Magnetic Materials
405