Chitosan and Chitosan Derivatives as Chelating Agents - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 5

2009). The ability of these adsorbents to extract Cu(II) and Ni(II) ions from water by
a solid-liquid extraction process was studied. The effects of adsorbent amount, contact
time and pH on the adsorption of CTS-azacrown ethers were investigated. The extrac-
tion of metal ions by chitosan itself has been mostly found to be pH sensitive (Peng et al.,
1998; Roberts, 1992; Tang et al., 2002). Here, the adsorption of Cu(II) and Ni(II) ions
on CTS-azacrown ethers was observed at different pH values; results showed that
CTS-azacrown ethers had good sorption capacities for Cu(II) ions at 25 ± 1°C and
pH = 5.5. These newly prepared chitosan derivatives could be used in environmental
analysis and hazardous waste remediation as toxic-metal binding agents in aqueous
environments.
Recently, Alsarra and coworkers (Radwan et al., 2010) have employed micro-
wave irradiation in the synthesis of a N -Schiff base-type cross-linked chitosan crown
ether (CCdBE) via the reaction between the -NH 2 and -CHO groups in chitosan and
4,4′-diformyldibenzo-18-c-6, respectively; the adsorption capacity of the obtained
CCdBE was much higher for Hg 2+ than that for Pb 2+ . The reported cross-linking meth-
od could retain higher adsorption capacity of CTS and, at the same time, improve
the acidic resistance of CTS with a desirable selectivity towards mercury ions over
lead ions. The reusability tests for CCdBE for Pb 2+ adsorption showed that complete
recovery of the ion was possible with CCdBE after 10-multiple reuses while CTS had
no reusability in acidic solution because of its higher dissolution. The studied features
of CCdBE suggested that the material could be considered as a new adsorbent. It is
envisaged that the cross-linking of CTS into CCdBE would enhance practicality and
effectiveness of adsorption in ion separation and removal procedures.
metal ion adsorption studies of magnetic Chitosans
Donia and coworkers (Donia et al., 2008) have prepared magnetic chitosan resin mod-
ified by Schiff's base derived from thiourea and glutaraldehyde. The resin obtained
was applied for the separation of Hg(II) from aqueous solution and an uptake value of
2.8 mmol/g was reported. The nature of interaction between the metal ion and the resin
was found to be dependent upon the acidity of the medium. At pH 1, Hg(II) could be
selectively separated from Cu(II), Pb(II), Cd(II), Zn(II), Ca(II), and Mg(II). Kinetic
and thermodynamic studies indicated that the adsorption process is pseudo-second-
order exothermic spontaneous reaction and proceeds according to Langmuir isotherm.
The resin was regenerated effectively using 0.1 M potassium iodide. The studied resin
showed an efficient uptake behavior towards Hg(II) relative to the commercial resin
Dowex-D3303. Moreover, the same authors have recently reported on the use of dif-
ferent chelating resins with various functionalities for the selective separation of mer-
cury (Atia, 2005; Atia et al., 2003, 2005; Donia et al., 2005). They also reported on
the use of magnetic resins in removal of some metals from aqueous solutions. These
magnetic resins shown in Figure 4, are easily collected from aqueous media using an
external magnetic field and displayed higher uptake capacity compared to the mag-
netic particles-free resin (Donia et al., 2006a, b). These methods are also cheap and
often highly scalable. Moreover, techniques employing magnetism are more amenable
to automation (An et al., 2003).