## 3 Results
### Characterization of Sorbent
#### 3.1.2 Chemical Characterization--FTIR spectroscopy  
Characterization of synthesized materials: The comparison of FTIR spectra confirms the incorporation of magnetite nanoparticles with the appearance of a peak at ~560 cm\({}^{-1}\) (Fe-O-Fe stretching in Fe\({}_{3}\)O\({}_{4}\)) (Figure 2). Figure 1: SEM micrograph of G@MChs. Figure 2: FTIR spectra of glycine, chitosan, and G@MChs sorbents (and intermediary compounds: MCh, magnetic chitosan; MChs, crosslinked magnetic chitosan; MChs*, and activated crosslinked magnetic chitosan with spacer arms) in the wavenumber range: 2000–400 cm\({}^{-1}\). Table S3a-e report the assignments of the FTIR main peaks of reagents (glycine and chitosan), intermediary compounds, and the sorbent. All the intermediary products show an FTIR fingerprint close to the reference spectrum of chitosan, with the exception of the double band appearing in the range 1700-1500 cm\({}^{-1}\). Indeed, for raw chitosan, two bands are observed at 1648 and 1578 cm\({}^{-1}\): C=O stretching (amide I) and -NH bending, respectively. With the incorporation of magnetite (MCh), the amide I band apparently disappears and the absorbance of amine groups largely predominates (at 1558 cm\({}^{-1}\)). After epichlorohydrin crosslinking (MChs) and activation with spacer arms (MChs*), on the other hand, the predominating peak is shifted toward higher wavenumbers (i.e., 1624 and 1653 cm\({}^{-1}\), respectively). Epichlorohydrin is supposed to graft (or crosslink) polymer units on hydroxyl groups of chitosan backbone [46] (formation of C-O-C bonds in case of interchain bonding and/or formation of C-Cl bonds in case of free ending grafting). The C-O-C bond is supposed to appear in the range 1150-1050 cm\({}^{-1}\)[47]; herein, this is hidden by the contribution of the carbohydrate ring. The C-Cl bond is usually detected in the range 800-700 cm\({}^{-1}\); this vibration is not detected on MChs and MChs* spectra. After the immobilization of glycine onto the activated composite, two main differences are observed: (a) the appearance of a peak at \(\sim\)796 cm\({}^{-1}\), and (b) the widening of the broad band 1700-1500 cm\({}^{-1}\) (probably due to the contribution of the carboxylate functional group of glycine, at 1574 cm\({}^{-1}\)). These successive changes demonstrate the incorporation of magnetite nanoparticles and the grafting of glycine on the chitosan backbone (through two successive steps of reaction with epichlorohydrin to crosslink and activate the support, respectively). Characterization of metal ion interactions with G@MChs: here, the sorption of metal ions hardly changes the FTIR fingerprints (Figure 3). The most significant changes are observed at around 1600 cm\({}^{-1}\). The band is relatively large, probably due to the FTIR contribution of different reactive groups (amine, carboxylate). With metal sorption, the width of the band is modified, because the binding on these reactive groups shifts the wavenumber and/or modify the intensity of the relative contributions. In the case of Ni(II) and Hg(II), the group contributing at \(\sim\)1595 cm\({}^{-1}\) ap  
Figure 3: FTIR spectra of G@MChs sorbent before and after Ni(II), Zn(II), Hg(II) and after treatment of ore leachate, in the wavenumber range: 2000–400 cm\({}^{-1}\). pears to be reinforced. On the contrary, for Zn(II), the width of the band is considerably reduced and the peak is centered around -1632 cm\({}^{-1}\) (reduction of the contribution of the FTIR component at lower wavenumber). The other significant change is identified at low wavenumber (below 850 cm\({}^{-1}\)). The FTIR spectra are very similar for the sorbent before and after sorption of either Ni(II) and Hg(II), while for Zn(II) a much greater absorbance is observed between 600 and 850 cm\({}^{-1}\): the well-resolved peak at -795 cm\({}^{-1}\) is masked by a broad band of absorption. These results tend to confirm that the binding of the three metal ions does not follow the same mechanism, with Zn(II) being differentiated from Ni(II) and Hg(II).