Iron-Based Magnetic Nanoparticles for Removal of Heavy Metals from Electroplating and Metal-Finishing Wastewater - Nanotechnologies for Water Environment Applications - page 262

percentage and, as a result, the Cr(VI) adsorption efficiency is enhanced. Furthermore,
there is a linear relationship between the surface area and the Cr(VI) adsorption
efficiency of the Al-doped -Fe 2 O 3 , suggesting that the surface area is a predominant
factor affecting Cr(VI) adsorption.

As aforementioned, the magnetic properties of Al-doped -Fe 2 O 3 decreased with
increasing incorporation of the nonmagnetic aluminum. The decreased magnetic
properties of adsorbent particles will inevitably affect their magnetic separation from
solution. To directly investigate the separation of adsorbent particles from solutions, the
mixture of the Al-doped -Fe 2 O 3 and Cr(VI) was separated with a magnet after
adsorption. The times required for a complete separation of nanoparticles are listed in
Table 9.7. The Al-doped -Fe 2 O 3 nanoparticles containing 7.5, 9.3, 11, 13.1 mol% Al
could be separated completely from solution within 0.5, 1, 5, 10 minutes, respectively.
For the as-grown -Fe 2 O 3 nanoparticles, the magnetic separation was finished within 20
seconds. By analyzing and comparing the adsorption time, adsorption efficiency and
magnetic separation, an Al/(Al + Fe) of 9.3 was finally determined to be the optimal Al
dosage for the enhanced Cr(VI) adsorption.

Table 9.7 Summary of the effects of Al-doped -Fe 2 O 3 nanoparticles on Cr(VI)
adsorption and magnetic separation.
Al/(Al + Fe)
(mol %)

Adsorption
Efficiency (%)

Equilibrium
time (min)

Separation
Time (min)

0 79.8 10 0.1

7.5 84.3 25 0.5

9.3 86.7 30 1

11.0 87.5 60 5

13.1 88.9 90 10

Table 9.8 Magnetization and surface area for various Al-doped -Fe 2 O 3 .
Al/(Al + Fe)
(mol %)

Surface
Area (m 2 /g)

Magnetic Properties
(emu)

0.0 162 3.48

7.5 182 2.26

9.3 191 1.65

11.0 198 1.14

13.1 210 /