**13. Retardion 11A8**

218 Ion Exchange Technologies

R–M2+(2Cl-

R–M2+(HPO42-) + 2Cl-

R–M2+(HPO42-) + 2Cl- ⇄ R–M2+(2Cl-

**12. Chelating ion exchangers with the thiol, thiourea and isothiourea** 

In the group of ion exchangers with the thiol functional groups (Chelite S, Duolite ES-465, Imac GT 73) Imac TMR resin is very important. It is the macroporous ion exchanger with the PS-DVB matrix, which besides the thiol ones, also possesses the sulphone groups. Imac TMR is used for selective sorption of Hg(II) ions from the process solutions as well as Ag(I), Au(III), Pt(IV) and Pd(II). The sorption process of Hg(II) with the saline solution proceeds

Also ion exchangers with the isothiourea functional groups (Ionac SR 3, Lewatit TP 214, Purolite S 920, Srafion NMRR) exhibit high affinity for Hg(II) ions. They are also selective for noble metal ions. Depending on the pH, the isothiourea groups occur in the following

R SH + Hg2+ S)2 (R Hg2+ + 2H+ R SH + HgCl+ SHgCl + H+ R

For the first form, coordination bond formation is possible, whereas for the second one the

NH NH2 +HX R S C NH2 NH2

R

[HgCl4] <sup>X</sup> 2- + 2X-

NH2

+ + X-

NH2

2

sorption process proceeds in accordance with the anion exchange mechanism:

<sup>R</sup> <sup>S</sup> + [HgCl <sup>S</sup> <sup>+</sup> 4] 2 2- <sup>C</sup>

C +

R S C

NH2

NH2

Four chelating ion exchange polymeric resins were tested to remove Ni(II) and Co(II) from synthetic solutions on the commercially available ion exchangers Dowex M4195, Amberlite IRC 748, Ionac SR-5 and Purolite S930. Among the selected resins, Dowex M4195 showed the best results for Ni(II) and Co(II) selective sorption from acid liquors in the whole pH range and with small influence of other elements. Even at pH 1 Dowex M4195 was the most

The desorption process can be written as follows:

effective (Mendes & Martins, 2004).

**functional groups** 

according to the reaction:

forms:

) + HPO42- ⇄ R–M2+(HPO42-) + 2Cl-

+ H+ ⇄ R–M2+(2Cl-

) + H2PO4-

) + HPO42-

Dowex Retardion 11A8 is an example of a very interesting ion exchanger of the type 'snake in a cage' with the quaternary ammonium and carboxylic functional groups (amphotheric resin) (Dybczyński, 1987). It is produced by polymerizing acrylic acid monomer inside an anion exchange resin. Polyacrylic chains are (snake) alternate with the PS-DVB matrix (cage) and therefore they are trapped inside the cross linked ion exchange resin and cannot diffuse out. As a result, cationic and anionic sites are so closely associated that they partially neutralize their electric charges. Mobile ions, such as chlorides, nitrates(V) are attracted and retained on these unique sites until they are eluted with hot water.

Dowex Retardion 11A8 can be used for selective separation of Cd(II) ions in the presence of other heavy metal ions (Samczyński & Dybczyński, 2002). Cd(II) ions are sorbed from 2 M HCI and 2 M NH4OH with 0.1 M NH4Cl systems according to the reactions:

> (n-2)RCl + [CdCln] 2-n R([CdCln] 2-n) + (n-2)Cl-2RCOONH4 + [Cd(NH3)n] 2+ (RCOO)2[Cd(NH3)n-x] + 2NH4 + + nNH3

In the case of separation of Ga(III), In(III), Tl(III), Pt(II), Pd(II) and Na(I), Ni(II), Cu(II) and Zn(II) mixtures in acidic media the resin acts mainly as an anion exchanger. For the elements that can exist as both cations and anions in solution (e.g., Ni, Co, Cu and Zn), the amphoteric properties of Retardion11A8 permit more specific isolation of certain elements from complex mixtures than would be possible with the use of monofunctional ion exchangers (Dybczyński & Sterlińska, 1974).
