**9. Chelating ion exchangers with the phosphonic and aminophosphonic functional groups**

Among various types of ion exchangers with the acidic ligands, those having phosphonate functionality are of particular interest since they are selective towards heavy metal cations. Development of this type of ion exchangers started in the late 1940s with phosphorylation of poly(vinyl alcohol) using various phosphorylating agents (Trochimczuk & Streat, 1999; Trochimczuk 2000). Besides phosphate, phosphinic and phosphonic resins, containing – OPO(OH)2, –PO(OH) and -PO(OH)2 functional groups, respectively, they also contain methylenediphosphonate, ethylenediphosphonate and carboxyethyl phosphonate ones (Marhol et al. 1974;

210 Ion Exchange Technologies

al. 1997).

found: Ni(II) > Co(II) > Mn(II) > Mg(II).

commercially available iminodiacetic acid resins.

**functional groups** 

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

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

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

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

**9. Chelating ion exchangers with the phosphonic and aminophosphonic** 

Among various types of ion exchangers with the acidic ligands, those having phosphonate functionality are of particular interest since they are selective towards heavy metal cations.

water the application of this resin is economical (Gode & Pehlivan, 2003)

Kabay, 1998a; Ogata et al. 2006). In all cases they display good selectivity towards metal ions even at very low pH (except for ethylenediphosphonate and carboxyl containing resins, being less acidic, more selective at the pH value from 1 to 2).

Chelating ion exchangers with the phosphonic functional groups are characterized by extremely high selectivity towards Th(IV) and U(IV,VI) as well as Cu(II), Cd(II), Zn(II), Ni(II), Ag(I), Au(III) and Fe(III) ions. Commercially available resins containing the phosphonic groups are Diaion CRP200 and Diphonix Resin. In the case of Diphonix Resin besides the diphosphonic functional groups in the structure of the ion exchanger, there are also carboxylic and sulphonic functional groups whose presence determines better hydrophilic properties. Diphonix Resin as well as Diphonix A with the functional phopshonic and ammonium (type 1) or pyridyne (type 2) groups have been of significant interest lately (Chiarizia et al. 1993; Horwitz et al. 1993; Chiarizia et al. 1994; Chiarizia et al. 1996, Alexandratos, 2009). Diphonix Resin was developed by the Argonne National Laboratory and University of Tennessee. It is synthesized by a patented process involving copolymerization of tetraalkylvinylidene diphosphonate with styrene, divinylbenzene, and acrylonitrile followed by sulphonation with concentrated sulphuric acid. Finding a method for effective copolymerization of vinylidene-1,1-diphosphonate (VDPA) ester was a major achievement because of the steric hindrance imposed on the vinylidene group by the diphosphonate group. This difficulty was overcome by using another relatively small monomer, acrylonitrile, as a carrier to induce polymerization of vinylidene-1,1 diphosphonate (Horwitz et al. 1994; Horwitz, et al. 1995). The protonation constants of Diphonix Resin® which are pK1 and pK2 < 2.5 pK3=7.24 and pK4=10.46 appear almost equal to the protonation constants of the starting material VDPA which are pK1=1.27, pK2 = 2.41, pK3=6.67 and pK4=10.04 (Nash et al. 1994).

In the past few years there were many publications on the separation of lanthanides and actinides on the chelating resins with the phosphonic groups. Lanthanides in minerals occur in small amounts, usually in the form of mixtures, often isomorphic, so that their extraction and separation create many problems. To this end also Diphonix Resin can be used especially at low pH. It is characterized by high affinity for U(VI), Pu(IV), Np(IV), Th(IV), Am(III) and Eu(III). It was found that from 1 M HNO3 solutions the distribution coefficient of Diphonix Resin for U(VI) ions is 70,000 compared to 900 for sulphinic acid resin (Alexandratos, 2007) and the recovery coefficient for Eu(III) under the same conditions is 98.3, whereas for the sulphonic acid resin 44.9 (Ripperger & Alexandratos, 1999). In the paper by Phillips et al. it was demonstrated that Diphonix Resin® can be successfully used for removal of uranium from the solutions of pH > 5 including high concentration of NO3 ions as it is less sensitive to interference by such ions as carbonates, nitrates(V), sulphates(VI), Fe(III), Ca(II) and Na(I) (Philips et al. 2008). It can be also used for removal of V(V), Cr(III), Mn(II), Co(II), Ni(II), Zn(II), Cd(II), Hg(II) and Pb(II) form waters and waste waters; V(V), Cr(III), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hg(II) and Pb(II) from drinking water; Mn(II), Co(II) and Ni(II) from waste waters of the oil industry; Cr(III) from acidic solutions, Fe(III) from the solutions containing complexing agents in the process of removing scale and radionuclides from radioactive waste waters. Smolik et al. (2009) investigated separation of zirconium(IV) from hafnium(IV) sulphuric acid solutions on Diphonix Resin®. It was found that the best medium for separation of hafnium(IV) and zirconium(IV) is 0.5 M sulphuric acid. A decrease in temperature lowers the degree of metals separation, while lower flow rates through the column increases zirconium(IV) from hafnium(IV) separation. Recent studies have shown that Diphonix Resin® can also be used for removal of Cd(II) and Cr(III) from the phosphoric acid solutions through column tests. Kabay et al. (1998b) found that the acid concentration strongly determines the resin behaviour with respect to the sorption/elution of Cd(II) and Cr(III). In the paper by Cavaco et al. it was pointed but that Diphonix Resin® has strong affinity for Cr(III) ions and high selectivity towards Fe(III) and Ni(II) (Cavaco et al. 2009). The mechanism of sorption on Diphonix Resin® can be written as (Hajiev et al. 1989):

$$\text{R} \text{--} (\text{PO} \text{\&} \text{H} \text{\&}) \text{\$2^{2}\$ + M\${}^{2+}} \rightleftharpoons \text{R} \text{--} (\text{PO} \text{\&} \text{H} \text{\&})^{2-} \text{\&} \text{M}^{2+} $$

where: R is the resin matrix.

However, according to the literature, Diphonix Resin® has the best selectivity for transition metals such as Fe(III), Cu(II) and Ni(II) over Cr(III). High affinity of Diphonix Resin® for Fe(III) compared to the mono- and divalent ions e.g. Ca(II) was reported in several papers. Owing to its very good separation capability, Diphonix Resin® was also applied in the project FENIX Iron Control System to remove iron from the spent copper electrolyte in Western Metals Copper Ltd. (Queensland, Australia). In this plant, copper(I) sulphate(VI) was used as a reducing agent at the reaction temperature of 85 °C to increase the elution of Fe(III):

> Fe2(SO4)3 + 6HR ⇄ 2Fe(R)3 + 3H2SO4 CuSO4 + Cu ⇄ Cu2SO4 2Fe(R)3 + 3H2SO4 + Cu2SO4 ⇄ 2FeSO4 + 2CuSO4 + 6HR

where: R is the resin matrix.

In the paper by Lee & Nicol (2007) it was proved that sorption capacities of Diphonix Resin® for Fe(III) and Co(II) ions in the sulphate(VI) system at pH 2 are equal to 130 mg/g and 90 mg/g, respectively.

The obvious disadvantage of this ion exchanger is therefore the fact that it is difficult to remove Fe(III) ions. To this end 1-hydroxyethane-1,1-diphosphonic acid (HEDP) is used. In the case of Cr(III), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hg(II), Sn(II) and Pb(II) ions 2M H2SO4 can be also applied.

In the group of chelating ion exchangers containing phosphonic and aminophosphonic functionalities the resins with aminoalkylphosphonic functional groups, such as Duolite C-467, Duolite ES-467, Lewatit OC 1060, Purolite S 940, Purolite S 950 and Chelite P occupy a significant position. In the sorption of heavy metal ions on this kind of chelating ion exchangers the following affinity series is obtained: Pb2+ > Cu2+ > UO22+, Zn2+, Al3+ >Mg2+ > Sr2+ > Ca2+ > Cd2+ > Ni2+ > Co2+ > Na+ > Ba2+. These ion exchangers as well as the previously mentioned phosphonic ones exhibit poor affinity for Ca(II) and Mg(II). The effectiveness of sorption of the above mentioned metal ions, however, decreases with the decreasing pH. It is worth mentioning that depending on pH value, the aminoalkylphosphonic groups may occur in the following forms:

212 Ion Exchange Technologies

sulphates(VI), Fe(III), Ca(II) and Na(I) (Philips et al. 2008). It can be also used for removal of V(V), Cr(III), Mn(II), Co(II), Ni(II), Zn(II), Cd(II), Hg(II) and Pb(II) form waters and waste waters; V(V), Cr(III), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hg(II) and Pb(II) from drinking water; Mn(II), Co(II) and Ni(II) from waste waters of the oil industry; Cr(III) from acidic solutions, Fe(III) from the solutions containing complexing agents in the process of removing scale and radionuclides from radioactive waste waters. Smolik et al. (2009) investigated separation of zirconium(IV) from hafnium(IV) sulphuric acid solutions on Diphonix Resin®. It was found that the best medium for separation of hafnium(IV) and zirconium(IV) is 0.5 M sulphuric acid. A decrease in temperature lowers the degree of metals separation, while lower flow rates through the column increases zirconium(IV) from hafnium(IV) separation. Recent studies have shown that Diphonix Resin® can also be used for removal of Cd(II) and Cr(III) from the phosphoric acid solutions through column tests. Kabay et al. (1998b) found that the acid concentration strongly determines the resin behaviour with respect to the sorption/elution of Cd(II) and Cr(III). In the paper by Cavaco et al. it was pointed but that Diphonix Resin® has strong affinity for Cr(III) ions and high selectivity towards Fe(III) and Ni(II) (Cavaco et al. 2009). The mechanism of sorption on

R(PO3H2)22- + M2+ ⇄ R(PO3H2)2-→M2+

However, according to the literature, Diphonix Resin® has the best selectivity for transition metals such as Fe(III), Cu(II) and Ni(II) over Cr(III). High affinity of Diphonix Resin® for Fe(III) compared to the mono- and divalent ions e.g. Ca(II) was reported in several papers. Owing to its very good separation capability, Diphonix Resin® was also applied in the project FENIX Iron Control System to remove iron from the spent copper electrolyte in Western Metals Copper Ltd. (Queensland, Australia). In this plant, copper(I) sulphate(VI) was used as a

Fe2(SO4)3 + 6HR ⇄ 2Fe(R)3 + 3H2SO4

CuSO4 + Cu ⇄ Cu2SO4

2Fe(R)3 + 3H2SO4 + Cu2SO4 ⇄ 2FeSO4 + 2CuSO4 + 6HR

In the paper by Lee & Nicol (2007) it was proved that sorption capacities of Diphonix Resin® for Fe(III) and Co(II) ions in the sulphate(VI) system at pH 2 are equal to 130 mg/g

The obvious disadvantage of this ion exchanger is therefore the fact that it is difficult to remove Fe(III) ions. To this end 1-hydroxyethane-1,1-diphosphonic acid (HEDP) is used. In the case of Cr(III), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hg(II), Sn(II) and Pb(II) ions

reducing agent at the reaction temperature of 85 °C to increase the elution of Fe(III):

Diphonix Resin® can be written as (Hajiev et al. 1989):

where: R is the resin matrix.

where: R is the resin matrix.

and 90 mg/g, respectively.

2M H2SO4 can be also applied.

and therefore the selectivity of metal ions sorption depends on the degree of ionization of phosphonic groups. In the case of acidic solutions due to protonation of the nitrogen atom of aminophosphonic group there are formed combinations with the following structure:

One of the most favourable modes of chelation of the phosphonic acid group is the formation of a four-membered ring through determination of two P-OH groups.

Additionally, in the case of the aminoalkylphosphonic groups, due to the fact that between the aromatic ring of the matrix and the nitrogen atom there is also presented the alkyl group, the increase of the electron density on the nitrogen atom of the amino group is expected. It affects the growth of its protonation. Therefore, this preferred zwitterion form can be as follows:

However, the possibility of coordination of the secondary nitrogen atom at lower pH seems to be impossible with respect to its protonated nature and also for steric reasons. Therefore the only potential donor and binding sites of Duolite ES-467 are the oxygen atoms of the phosphonic groups at lower pH values. The chelating, aminomethylphosphonic functional group is also potentially a tridentate ligand having two bonding sites at a phosphonic acid groups and one coordination site at the secondary nitrogen atom (Kertman, 1997; Nesterenko et al. 1999). Formation of a four membered ring through bonding of one of the OH groups and coordination of the oxygen atom has also been reported. These structures are presented below:

Chelating ion exchangers with the aminoalkylphosphonic functional groups, like picolylamine resins - Dowex M 4195 exhibits moderate selectivity for Cu(II) over Fe(III) in the acidic sulphate(VI) solutions compared to the iminodiacetic acid resins which show no or limited selectivity depending on pH. The stability constants for divalent metal ions with aminomethylphosphonic acid have been found in the order: Ca2+ < Mg2+ < Co2+ < Ni2+ < Cu2+ > Zn2+ (Sahni et al. 1985). In the paper by Milling and West (1984), it was found that Duolite ES-467 possesses a higher capacity for copper(II) ions compared to nickel(II) and iron(III) and that the capacity decreases with the decreasing pH and metal ion concentration in the solution.

Besides Duolite ES-467, Purolite S 950 has been proved to have a high affinity for various heavy metal ions and it is successfully applied in metallurgical and wastewater treatment processes. In the paper by Koivula et al. (2000) Purolite S-950 was used for purification of effluents from metal plating industry containing Zn(II), Ni(II), Cu(II) and Cd(II) ions. Among others, it was stated that Purolite S-950 showed lower sorption capacity equal to 1.2 eq/dm3 for zinc chloride compared to zinc solutions containing KCl and NH4Cl (1.3 eq/dm3). Under analogous conditions the sorption capacity for Cd(II) was 1.1 eq/dm3. Recovery of Ni(II) and Co(II) from organic acid complexes using Purolite S 950 was also studied by Deepatana & Valix (2006). They found that sorption capacities for nickel sulphate(VI) for Dowex M4195 (94.51 mg/g), Amberlite IRC 748 (125.03 mg/g) and Ionac SR-5 (79.26 mg/g) are much higher than those for Purolite S-950 in the case of sorption of Ni(II) complexes with citric acid (18.42 mg/g), malic acid (14.45 mg/g) and lactic acid (19.42 mg/g) mainly due to the steric hindrance. For Co(II) ions analogous results were obtained (citric (5.39 mg/g for citric acid; 7.54 mg/g for malic acid and 10.48 mg/g for lactic acid). The elution efficiencies of these complexes from Purolite S-950 resins were high (82–98%) therefore it would appear that the adsorption process involves weak interactions. However, in the case of the sorption of Cu(II) and Zn(II) ions from the sulphate solutions at pH 1.9 on the aminomethylphosphonic resin Lewatit R 252K and the iminodiacetic resin Lewatit TP 207 it was found that separation factors were much lower for Lewatit R 252K (83.0 at 10 oC and 30.0 at 80 oC) than for Lewatit TP 207 (1.67 at 10 oC and 1.4 at 80 oC) (Muraviev et al. 1995).

### **10. Chelating ion exchangers with the methylglucamine functional groups**

Selective ion exchange resins also include chelating ion exchangers containing N-methyl (polyhydroxohexyl)amine functional groups also called methylglucamine. Commercially available ion exchangers of this type are: Amberlite IRA 743, Duolite ES-371, Diaion CRB 02, Dowex BSR 1, Purolite S 108 and Purolite S110.

These ion exchangers show high selectivity for boron (in the form of trioxyboric acid H3BO3) (Alexandratos, 2007; Alexandratos, 2009). The boron sorption process proceeds according to the scheme:

214 Ion Exchange Technologies

are presented below:

R NH

OH groups and coordination of the oxygen atom has also been reported. These structures

Chelating ion exchangers with the aminoalkylphosphonic functional groups, like picolylamine resins - Dowex M 4195 exhibits moderate selectivity for Cu(II) over Fe(III) in the acidic sulphate(VI) solutions compared to the iminodiacetic acid resins which show no or limited selectivity depending on pH. The stability constants for divalent metal ions with aminomethylphosphonic acid have been found in the order: Ca2+ < Mg2+ < Co2+ < Ni2+ < Cu2+ > Zn2+ (Sahni et al. 1985). In the paper by Milling and West (1984), it was found that Duolite ES-467 possesses a higher capacity for copper(II) ions compared to nickel(II) and iron(III) and that the capacity decreases with the decreasing pH and metal ion concentration in the solution.

P R NH

+ Cu2+ + 2H+

P

Cu O

O

O

OH

O

OH

Besides Duolite ES-467, Purolite S 950 has been proved to have a high affinity for various heavy metal ions and it is successfully applied in metallurgical and wastewater treatment processes. In the paper by Koivula et al. (2000) Purolite S-950 was used for purification of effluents from metal plating industry containing Zn(II), Ni(II), Cu(II) and Cd(II) ions. Among others, it was stated that Purolite S-950 showed lower sorption capacity equal to 1.2 eq/dm3 for zinc chloride compared to zinc solutions containing KCl and NH4Cl (1.3 eq/dm3). Under analogous conditions the sorption capacity for Cd(II) was 1.1 eq/dm3. Recovery of Ni(II) and Co(II) from organic acid complexes using Purolite S 950 was also studied by Deepatana & Valix (2006). They found that sorption capacities for nickel sulphate(VI) for Dowex M4195 (94.51 mg/g), Amberlite IRC 748 (125.03 mg/g) and Ionac SR-5 (79.26 mg/g) are much higher than those for Purolite S-950 in the case of sorption of Ni(II) complexes with citric acid (18.42 mg/g), malic acid (14.45 mg/g) and lactic acid (19.42 mg/g) mainly due to the steric hindrance. For Co(II) ions analogous results were obtained (citric (5.39 mg/g for citric acid; 7.54 mg/g for malic acid and 10.48 mg/g for lactic acid). The elution efficiencies of these complexes from Purolite S-950 resins were high (82–98%) therefore it would appear that the adsorption process involves weak interactions. However, in the case of the sorption of Cu(II) and Zn(II) ions from the sulphate solutions at pH 1.9 on the aminomethylphosphonic resin Lewatit R 252K and the iminodiacetic resin Lewatit TP 207 it was found that separation factors were much lower for Lewatit R 252K (83.0 at 10 oC and 30.0 at 80 oC) than for Lewatit TP 207 (1.67 at 10 oC and 1.4 at 80 oC) (Muraviev et al. 1995).

**10. Chelating ion exchangers with the methylglucamine functional groups** 

Selective ion exchange resins also include chelating ion exchangers containing N-methyl (polyhydroxohexyl)amine functional groups also called methylglucamine. Commercially available ion exchangers of this type are: Amberlite IRA 743, Duolite ES-371, Diaion CRB 02,

Dowex BSR 1, Purolite S 108 and Purolite S110.

Besides boron the following components of waste water should be also taken into account: Na(I), K(I), Ca(II), Mg(II), Cl- , SO42-, HCO3- , CO32- and effects should be also considered. Ion exchangers of this type can be used in the removal of Cr(VI) and As(V) (Dambies et al. 2004; Gandhi et al. 2010) although the mechanism of sorption of chromate ions(VI) involves both electrostatic interactions with the protonate amino group and the reduction of Cr(Vl) to Cr(III):

As for arsenate removal the process should be conducted from aqueous solutions at neutral pH. The percent removal of arsenate from the aqueous solution of 100 mg/ dm3 arsenate and 560 mg/dm3 sulphate on NMDG resin is 99% and the reaction is unaffected by the presence of phosphate ions and the solution pH above 9.0, indicating that it can be regenerated with the alkaline solution. It was determined that the key variable in its selectivity is that the resin has to be protonated prior to contact with the aqueous solution (Alexandratos, 2007).
