**8. Chelating ion exchangers with the iminodiacetic functional groups**

Recently the attention has been paid to the ion exchangers with the amino- or iminoacids groups. The presence of two carboxyl groups and the tertiary nitrogen atom provides strong preference for chromium(III) and copper(II) (Marhol & Cheng, 1974). Therefore, for the commercial chelating ion exchangers such as Chelex 100, Dowex A 1, CR-20, Lewatit TP 207, Lewatit TP 208, Purolite S 930, Amberlite IRC 748 (formely Amberlite IRC 718) or Wofatit MC-50 the sorption process of metal ions proceeds according to the order: **Cr3+ > Cu2+ > Ni2+ > Zn2+ > Co2+ > Cd2+ > Fe2+ > Mn2+ > Ca2+ >> Na+**. This type of ion exchangers also exhibis high affinity for Hg(II) and Sb(V) ions. It should be noted that depending on the pH value they may occur in the following forms (Zainol & Nicol. 2009a):

At pH <2.0 the nitrogen atom and the two carboxylic groups are protonated. In this case the chelating ion exchanger with the iminodiacetic functional groups behaves as a weakly basic anion exchanger. At pH ~ 12, the nitrogen atom and the two carboxylic groups undergo deprotonation – the ion exchanger behaves as a typical weakly acidic cation exchanger. For pH medium values, the iminodiacetic resin behaves as an amphoteric ion exchanger. The iminodiacetate groups provide electron pairs so that the binding force for the alkaline earth metals is 5000 times as large as that for alkali metals like Ca(II), which react with divalent metals to form a stable coordination covalent bond. Therefore, the affinity series determined for the iminodiacetic ion exchanger can be presented in the order: **Hg2+ > UO22+ > Cu2+ > Pb2+ > Ni2+ > Cd2+ > Zn2+ > Co2+ > Fe2+ >Mn2+ > Ca2+ > Mg2+ > Ba2+ > Sr2+ >> Li+ > Na+ > K+.** 

208 Ion Exchange Technologies

**groups** 

Cr(III) from sea water (Pyell & Stork, 1992).

may occur in the following forms (Zainol & Nicol. 2009a):

RCH2HN+

RCH2HN+

concentration of Mn(II), Pb(II), Cd(II), Cu(II) , Fe(III) and Zn(II) from complex matrices (Yebra-Biurrun et al. 1992). The copolymer of poly(iminoethylo)dithiocarbamate was used

A simple method for immobilization of 8-hydroxyquinoline in a silica matrix is described by Lührmann (1985). The sorbent was used in the sorption of Cu(II), Ni(II), Co(II), Fe(III), Cr(III) , Mn(II), Zn(II), Cd(II), Pb(II) and Hg(II) at pH from 4 to 6. It was shown that the sorption capacity varies in the range from 0.2 to 0.7 mM /g, and the partition coefficients from 1103 to 9104. Ryan and Weber showed (1985) that this type of sorbent has better sorption properties with respect to Cu(II) than Chelex 100 with the iminodiacetate functional groups. Th sorbents based on 8-hydroxyquinoline can be used, e.g. for concentration of the trace metal ions Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pb(II) and

for sorption of VO2+, Fe(II), Fe(III), Co(II), Ni(II) and Cu(II) (Kantipuly et al. 1990)

**7. Chelating ion exchangers with the 8-hydroxyquinoline functional** 

**8. Chelating ion exchangers with the iminodiacetic functional groups** 

Recently the attention has been paid to the ion exchangers with the amino- or iminoacids groups. The presence of two carboxyl groups and the tertiary nitrogen atom provides strong preference for chromium(III) and copper(II) (Marhol & Cheng, 1974). Therefore, for the commercial chelating ion exchangers such as Chelex 100, Dowex A 1, CR-20, Lewatit TP 207, Lewatit TP 208, Purolite S 930, Amberlite IRC 748 (formely Amberlite IRC 718) or Wofatit MC-50 the sorption process of metal ions proceeds according to the order: **Cr3+ > Cu2+ > Ni2+ > Zn2+ > Co2+ > Cd2+ > Fe2+ > Mn2+ > Ca2+ >> Na+**. This type of ion exchangers also exhibis high affinity for Hg(II) and Sb(V) ions. It should be noted that depending on the pH value they

At pH <2.0 the nitrogen atom and the two carboxylic groups are protonated. In this case the chelating ion exchanger with the iminodiacetic functional groups behaves as a weakly basic anion exchanger. At pH ~ 12, the nitrogen atom and the two carboxylic groups undergo deprotonation – the ion exchanger behaves as a typical weakly acidic cation exchanger. For pH medium values, the iminodiacetic resin behaves as an amphoteric ion exchanger. The iminodiacetate groups provide electron pairs so that the binding force for the alkaline earth

RCH2HN+

RCH2N

pH=3,99

pH=12,3 CH2COO-CH2COO-

CH2COOH CH2COO-

pH=2,21

pH=7,41 CH2COO-CH2COO-

CH2COOH CH2COOH

Amberlite IRC 748 in the K(I) form was also used for removal of Ca(II), Mg(II) from the potassium chromate solution (Yua et al. 2009). The optimum pH obtained for Ca(II) and Mg(II) adsorption onto Amberlite IRC 748 from the potassium chromate solution is 9.8 and 9.5, respectively. It was also noted that an increase of temperature and resin dosage resulted in their higher adsorption and the equilibrium conditions were attained within 480 min. The experimental data were relatively well interpreted by the Langmuir isotherm and the monolayer adsorption capacities of Ca(II) and Mg(II) were equal to 47.21 mg/g and 27.70 mg/g, respectively. This is of great importance because manufacturing of chromium trioxide by electrolyzing chromate salts, as a green process with the zero emission of waste, is studied widely now (Li et. al 2006). It should be also pointed out that separation factors between Mg(II) and Ca(II) and other divalent metal ions on an iminodiacetate resin are much smaller than those expected from the stability constants of their IDA complexes in solutions. Such phenomena were qualitatively described as the 'polymer effect' or operation of ion exchange as well as complexation reactions. Pesavento et al. (1993) gave a quantitative explanation for these anomalies on the basis of the Gibbs-Donnan model. Ca(II) and Mg(II) ions are adsorbed forming the R(Hida)2M complexes in acidic media and R(ida)M in neutral and alkaline systems whereas Ni(II) or Cu(II) etc. forms the R(ida)M complexes:

Commercially available chelating resins with the iminodiacetate functional group (Amberlite IRC 748, Lewatit TP 207, Lewatit TP 208, Purolite S 930, Lewatit MonoPlus TP 207) have been evaluated for their suitability for the adsorption of Ni(II) and other metal ions (Al(III), Ca(II), Co(II), Cr(III), Cu(II), Fe(II/III), Mg(II), Mn(II) and Zn(II)) from the tailings of a pressure acid leach process for nickel laterites. The Amberlite IRC 748 and TP MonoPlus 207 resins were found to be the most suitable in terms of loading capacity for nickel and kinetics of adsorption. Although all the five resins studied have the same functional groups their performance is not identical. The observed differences are possibly caused by variations in the synthesis procedure which results in variations in the structure of the matrix, degree of cross linking, density of functional groups, proportion of iminodiacetate groups and also the particle size (Zainol & Nicol, 2009a)

Additionally, the research carried out by Biesuz et al. (1998) shows that in the case of Ni(II) and Cd(II) sorption the structure of formed complexes is different. Ni(II) forms complexes of

R(ida)M type, whereas Cd(II) R(idaH)2M. However, in the paper by Zagorodni & Muhammed (1999) it was stated that the complexes R(Hida)2M should be extremely weak or even impossible. The adsorption equilibrium of Ni(II), Co(II), Mn(II) and Mg(II) on Amberlite IRC 748 has been discussed in (Zainol & Nicol, 2009b). The resin proves to have high selectivity for Ni(II) and Co(II) which suggests that these metals can be easily separated from Mg(II) and Mn(II) at pH 4 and 5. The following order of selectivity of the resin was also found: Ni(II) > Co(II) > Mn(II) > Mg(II).

The kinetics of Cd(II) sorption from separate solutions and from the mixtures with the nonionic surfactant Lutensol AO-10 (oxyethylated alkohols) in the hydrogen form of chelating iminodiacetic ion exchanger has also been investigated (Kaušpėdieniė et al. 2003). It was stated that the sorption of Cd(II) from separate solutions and from the mixture with AO-10 is controlled by the intraparticle diffusion in acidic (pH 5) and alkaline media (pH 7.6). The presence of AO-10 leads to a decrease in the rate of intraparticle diffusion. The iminodiacetate resin has a large collective adsorption with Cr(III) ion. The Cr(III) form bearing waste water can be removed at any pH in the range 3-6 at 2h of the phase contact time. Therefore for treatment of leather tanning, electroplating, textile and dyeing waste water the application of this resin is economical (Gode & Pehlivan, 2003)

Adsorption of trivalent metal ions on iminodiacetate resins was not studied as extensively as that of divalent metal ions. The known selectivity order of trivalent metal ions on an iminodiacetate resin can be presented as: Sc3+ > Ga3+ > In3+ > Fe3+ > Y3+ > La3+ > Al3+ (Yuchi et al. 1997).

Also since the end of the 1960s fibrous adsorbents with the iminodiacetic acid groups have been studied. For example, the capacity of a commercially available iminodiacetic acid fiber named Ionex IDA-Na was established to be 0.9-1.1 mmol/g for Cu(II). The fibrous materials containing iminodiacetate groups were developed by the group of Jyo et al. (2004) . Although the metal ion selectivity of the present fiber was close to that of iminodiacetic acid resins, the metal adsorption rate of chloromethylstyrene-grafted polyethylene coated polypropylene filamentary fiber is much higher than that of commercially available granular exchangers of this type having cross-linked polystyrene matrices. In the column mode adsorption of Cu(II), breakthrough capacities of Cu(II) were independent of the flow rates of feeds up to 200-300/h. The main reasons for the extremely fast adsorption rate of sorbent can be ascribed to the diameter of the fiber being much less than those of the resins as well as to the fact that the functional groups were introduced onto non cross linked grafted polymer chains. Their chemical and physical stabilities are comparable to those of commercially available iminodiacetic acid resins.
