**5. Chelating ion exchangers with the hydroxamic and amidoxime functional groups**

The choice of hydroxamic acids is based on their application in mineral processing as collectors in flotation of haematite, pyrolusite or bastnaesite ores. The copolymer of malonic acid dihydroximate with styrene-divinylbenzene was used for uranium(VI) removal from sea water (Park & Suh, 1996). In the paper by Ahuja (1996) it was found that glycin hydroximate resin shows maximum adsorption for Fe(III), Cu(II) and Zn(II) at pH 5.5; for W(VI), U(VI), Co(II) and Ni(II) at pH 6.0 as well as for Cd(II) at pH 6.5. It can be recommended for separation of Cu(II) from Co(II) and Ni(II) at pH 5.5. However, the iminodiacetic– dihydroximate resin can be applied for U(VI), Fe(II), Cu(II) separation according to the affinity series: **UO22+ > Fe3+ > Cu2+ > Zn2+ > Co2+ > Cd2+ > Ni2+ > Zn2+**. Hydroxamic acids exist in the two tautomeric forms:

and metal ions are coordianated by the hydroxamide functional group (a).

Chelating resins with the amidoxime functional groups such as Duolite ES-346, and Chelite N can be applied for the concentration of solutions containing Ag(I), Al(III), Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Hg(II), Mn(II), Ni(II), Mo(VI), Pb(II), Ti(IV), U(VI), V(V) and Zn(II) in the presence of alkali and alkaline earth metal ions (Samczyński & Dybczyński, 1997; Dybczyński et al. 1988). Alkali and alkaline earth metal ions are poorly retained by these resins. Duolite ES-346 is commonly used to extract uranium(VI) from seawater and As(III) from aqueous solutions. It can be also applied for Pd(II) removal (Chajduk-Maleszewska & Dybczyński, 2004). It is characterized by high selectivity towards Cu(II) ions due to the presence of amidoxime groups and small quantities of hydroxamic acid (RCONHOH):

where: R is the resin matrix.

It was found that for the amidoxime resins the selectivity series can be as follows: **Cu(II) > Fe(III) > As(III) > Zn(II) > Ni(II) > Cd(II) > Co(II) > Cr(III) > Pb(II).** Interesting results were obtained by observing the impact of acidity on the behaviour of this ion exchanger. At low pH values (<3) there was a decrease in the chelating ability of Duolite ES 346 for heavy metal ions as well as degradation of its functional groups according to the reactions (Ferriera et al. 1998):

**functional groups** 

where: R is the resin matrix.

1998):

Hydroxamic acids exist in the two tautomeric forms:

R

C

N H OH

O

and metal ions are coordianated by the hydroxamide functional group (a).

**(a) (b)** 

Chelating resins with the amidoxime functional groups such as Duolite ES-346, and Chelite N can be applied for the concentration of solutions containing Ag(I), Al(III), Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Hg(II), Mn(II), Ni(II), Mo(VI), Pb(II), Ti(IV), U(VI), V(V) and Zn(II) in the presence of alkali and alkaline earth metal ions (Samczyński & Dybczyński, 1997; Dybczyński et al. 1988). Alkali and alkaline earth metal ions are poorly retained by these resins. Duolite ES-346 is commonly used to extract uranium(VI) from seawater and As(III) from aqueous solutions. It can be also applied for Pd(II) removal (Chajduk-Maleszewska & Dybczyński, 2004). It is characterized by high selectivity towards Cu(II) ions due to the presence of amidoxime groups and small quantities of hydroxamic acid (RCONHOH):

R

C

OH

OH

N

It was found that for the amidoxime resins the selectivity series can be as follows: **Cu(II) > Fe(III) > As(III) > Zn(II) > Ni(II) > Cd(II) > Co(II) > Cr(III) > Pb(II).** Interesting results were obtained by observing the impact of acidity on the behaviour of this ion exchanger. At low pH values (<3) there was a decrease in the chelating ability of Duolite ES 346 for heavy metal ions as well as degradation of its functional groups according to the reactions (Ferriera et al.

NOH

NH2

R C

**5. Chelating ion exchangers with the hydroxamic and amidoxime** 

The choice of hydroxamic acids is based on their application in mineral processing as collectors in flotation of haematite, pyrolusite or bastnaesite ores. The copolymer of malonic acid dihydroximate with styrene-divinylbenzene was used for uranium(VI) removal from sea water (Park & Suh, 1996). In the paper by Ahuja (1996) it was found that glycin hydroximate resin shows maximum adsorption for Fe(III), Cu(II) and Zn(II) at pH 5.5; for W(VI), U(VI), Co(II) and Ni(II) at pH 6.0 as well as for Cd(II) at pH 6.5. It can be recommended for separation of Cu(II) from Co(II) and Ni(II) at pH 5.5. However, the iminodiacetic– dihydroximate resin can be applied for U(VI), Fe(II), Cu(II) separation according to the affinity series: **UO22+ > Fe3+ > Cu2+ > Zn2+ > Co2+ > Cd2+ > Ni2+ > Zn2+**.

However, the second reaction is the representative of the degradation of amidoxime groups under less acidic conditions (pH < 3.0). The increase in pH causes the weakening of the hydrogen ions competition for active sides resulting in an increase in the complexation of metal ions such as Cu(II). The fact that the degradation of the functional groups of Duolite ES-346 occurs under the influence of strong mineral acids is a serious problem which can significantly reduce the chelating capacity of the resin. However, this effect was made use of the recovery of adsorbed ions on the resin ion exchange. Corella et al. (1984) demonstrated that poly(acrylamidoxime) can be successfully used for the preconcentration of trace metals from aqueous solutions.

Also salicylic acid is a ligand which can selectively complex with Zn(II), Pb(II), Fe(III). Using the salicylic acid loaded resin for preconcentration of Zn(II) and Pb(II), it was proved that the preconcentration factors are much higher than those for bis(2 hydroxyethyl)dithiocarbamate (Saxena et al. 1995). However, the phenol-formaldehyde resin with the salicylaldoxime and salicylaldehyde functional chelating groups shows high selectivity for Cu(II) ions (Ebraheem & Hamdi, 1997).

The affinity order of metal complexes of salicylaldoxime is as follows: Fe3+ > Cu2+ > Ni2+ > Zn2+ > Co2+.

#### **6. Chelating ion exchangers with the dithiocarbamate functional groups**

The high affinity for transition metal ions is also exhibited by the classes of ion exchangers with the dithiocarbamate functional groups (including commercially available Nisso ALM 125), in which sulphur is the donor atom. Ion exchangers of this type have high affinity for the Hg(II), Pb(II), Cd(II) ions as well as precious metal ions, however, they do not adsorb alkali and alkaline earth metals. It was shown that dithiocarbamates obtained with the share of primary amines are less stable than those obtained with the share of secondary amines, and the binding of metal ions to the functional group of the donor atom increases in the number of Fe2+ < Ni2+ < Cu2+. The sorption efficiency is dependent on the presence of ions in the solution such as SCN-. In the paper by McClain and Hsieh (2004) the selective removal of Hg(II), Cd(II) and Pb(II) was presented. This resin is also effective for separation and 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 for sorption of VO2+, Fe(II), Fe(III), Co(II), Ni(II) and Cu(II) (Kantipuly et al. 1990)
