Environmental Engineering Reference
In-Depth Information
exhibits a linear relation with the line passing through the origin of the coordi-
nate and a slope of 1, indicating the complete detaching of loaded copper ions.
The mechanism of copper detachment by acid washing seems similar to that in
the regeneration of exhausted ion-exchange resins often used in wastewater
management. The detachment is most likely accomplished by ion exchange due
to the high chemical potential of hydrogen ions in acidic solutions, which
compete with copper ions for amino groups on magnetic sorbents.
After stripping off metal ions, the recycled magnetic carriers were character-
ized by XPS, DRIFTS, zeta-potential measurements, and the copper loading
test to determine the density and reactivity of silanized films remained on
magnetic sorbents. The results from the analysis all indicate a partial detach-
ment of immobilized silanes from the surface after acid stripping. Moreover, in
DRIFTS the band at 1,580 cm
1
for amino groups on magnetic sorbents shifted
to 1,615 cm
1
after copper loading, indicating the amino groups reacted with
copper ions. However, after detachment a new band at 1,711 cm
1
appeared,
which is attributed to oxidization of amines, possibly imides which have little
affinity to copper [132], thus reducing the reactivity of magnetic sorbents with
copper in the following reloading test.
Considering that amino groups are susceptible to oxidation [133], using
EDTA to extract loaded copper from magnetic sorbents may be beneficial.
The minimal breakage of siloxane bonds, and hence the detachment of APTES
films from the magnetic sorbents are anticipated. Therefore, using EDTA or
similar complexing reagent to detach metal ions from loaded magnetic sorbents
is worth exploring.
6.5.3 Poly(1-vinylimidazole)-Grafting on Magnetic Nanoparticles
Grafting of silane-terminated polymers on silica via chemical siloxane bonds
has been reported in a number of studies [134, 135, 136]. In this study [137],
a newly synthesized poly(1-vinylimidazole) with trimethoxysilyl terminal
groups is chemically anchored (grafted) on nanosize maghemite particles.
Poly(1-vinylimidazole) is chosen to graft on nanosize magnetic particles, as the
resultant organic-inorganic hybrid magnetic materials are anticipated to expand
the sorbent-based separation technology to a multiphase complex system, ranging
from biological cell sorting to industrial effluent detoxification and recovery
of valuables. Poly(1-vinylimidazole) can form complexes with such metal ions as
Cu-(II) [138], Zn(II) [139], Cd(II) [140], Ag(I) [141], and Hg(II) [142].
Figure 6.17 shows schematically the preparation procedure and the
resulting configuration of grafted polymers (thick lines) with bond metals
(M). Compared with the polymer-coating method, the polymer-grafting (direct
silanation) method offers a number of distinct advantages. First, particle size
shows little effect on polymer immobilization. Polymer chains immobilized on
magnetic particles would remain flexible. Polymer-grafted magnetic particles
