Magnetic Separation of Iron Ion from Leaching Solution …
851
The microtopography of the concentrates and tailings with the two MNPs is
shown in the SEM images (Fig. 2b–e). In the concentrates, the goethite particles
with α-Fe 3 O 4 as the crystal nuclei were dispersive and less than 1 μm in diameter,
while the goethite particles with γ-Fe 2 O 3 as the crystal nuclei aggregated into large
particles. The newly formed goethite precipitates on the surface of the MNPs have low
crystallinity and can be used as the flocculants between different goethite precipitates.
Hence, it is hard for the α-Fe 3 O 4 particles with a small amount of goethite attached
on the surface to aggregate with each other. As can be seen from the SEM image of
tailing for α-Fe 3 O 4 , there were many goethite particles on the surface of the gypsum
particles. These goethite particles, which were formed in the solution rather than
on the α-Fe 3 O 4 surface, were non-magnetic and therefore could not be collected
during magnetic separation. Instead, those non-magnetic goethite particles entered
the tailings with gypsum particles. Only gypsum particles appeared in the tailing for
γ-Fe 2 O 3 , which suggested that almost all the goethite particles were collected into
the concentrate for γ-Fe 2 O 3 .
In order to reduce the cost of the magnetic nanoparticles, the recovery of the two
magnetic nanoparticles from the concentrates and the cycle use efficiency of the
MNPs as the magnetic seeds in the goethite process was investigated. Figure 3a, b
shows the magnetic collection yield of the concentrates for α-Fe 3 O 4 and γ-Fe 2 O 3
under different milling time and magnetic fields. 5 min of the milling time and 750
Gs of the magnetic field intensity were optimum for collecting the magnetic nanoparticles from the concentrates. The obtained magnetic nanoparticles were reused as the
magnetic seeds for a new iron removal process and their performance was investigated. The recovery of Fe and loss of Ca in the multiple cycle use of the α-Fe 3 O 4
or γ-Fe 2 O 3 are shown in Fig. 3c and 3d, respectively. For γ-Fe 2 O 3 , the recovery of
Fe was around 99% during the 5 cycles, which is much higher than that of α-Fe 3 O 4
(around 60%), while the loss of Ca for both magnetic nanoparticles maintained at
around 15–20%. These results indicated the feasibility of recycling magnetic seeds
in the iron removal process, which would effectively reduce the cost of magnetic
seeds in the industrial application.
Conclusion
The residues of the goethite process in the zinc oxide dust hydrometallurgy contain toxic and heavy metallic elements. Impounding these residues in tailings ponds
causes serious environmental concerns. In this study, a novel and robust method
based on the addition of maghemite fine particles as the crystal nucleus of goethite
precipitates in the goethite process was proposed and tested. The goethite precipitates
formed on the surface of maghemite particles became magnetic that can be separated
into goethite concentrate and calcium sulfate tailings by magnetic separation. The
calcium sulfate (gypsum) tailings generated with a small quantity of goethite can be
used in cement and building materials production. The technology developed in this
851
The microtopography of the concentrates and tailings with the two MNPs is
shown in the SEM images (Fig. 2b–e). In the concentrates, the goethite particles
with α-Fe 3 O 4 as the crystal nuclei were dispersive and less than 1 μm in diameter,
while the goethite particles with γ-Fe 2 O 3 as the crystal nuclei aggregated into large
particles. The newly formed goethite precipitates on the surface of the MNPs have low
crystallinity and can be used as the flocculants between different goethite precipitates.
Hence, it is hard for the α-Fe 3 O 4 particles with a small amount of goethite attached
on the surface to aggregate with each other. As can be seen from the SEM image of
tailing for α-Fe 3 O 4 , there were many goethite particles on the surface of the gypsum
particles. These goethite particles, which were formed in the solution rather than
on the α-Fe 3 O 4 surface, were non-magnetic and therefore could not be collected
during magnetic separation. Instead, those non-magnetic goethite particles entered
the tailings with gypsum particles. Only gypsum particles appeared in the tailing for
γ-Fe 2 O 3 , which suggested that almost all the goethite particles were collected into
the concentrate for γ-Fe 2 O 3 .
In order to reduce the cost of the magnetic nanoparticles, the recovery of the two
magnetic nanoparticles from the concentrates and the cycle use efficiency of the
MNPs as the magnetic seeds in the goethite process was investigated. Figure 3a, b
shows the magnetic collection yield of the concentrates for α-Fe 3 O 4 and γ-Fe 2 O 3
under different milling time and magnetic fields. 5 min of the milling time and 750
Gs of the magnetic field intensity were optimum for collecting the magnetic nanoparticles from the concentrates. The obtained magnetic nanoparticles were reused as the
magnetic seeds for a new iron removal process and their performance was investigated. The recovery of Fe and loss of Ca in the multiple cycle use of the α-Fe 3 O 4
or γ-Fe 2 O 3 are shown in Fig. 3c and 3d, respectively. For γ-Fe 2 O 3 , the recovery of
Fe was around 99% during the 5 cycles, which is much higher than that of α-Fe 3 O 4
(around 60%), while the loss of Ca for both magnetic nanoparticles maintained at
around 15–20%. These results indicated the feasibility of recycling magnetic seeds
in the iron removal process, which would effectively reduce the cost of magnetic
seeds in the industrial application.
Conclusion
The residues of the goethite process in the zinc oxide dust hydrometallurgy contain toxic and heavy metallic elements. Impounding these residues in tailings ponds
causes serious environmental concerns. In this study, a novel and robust method
based on the addition of maghemite fine particles as the crystal nucleus of goethite
precipitates in the goethite process was proposed and tested. The goethite precipitates
formed on the surface of maghemite particles became magnetic that can be separated
into goethite concentrate and calcium sulfate tailings by magnetic separation. The
calcium sulfate (gypsum) tailings generated with a small quantity of goethite can be
used in cement and building materials production. The technology developed in this