**22. Amphoteric ion exchangers and anion exchangers**

**19. Ion exchangers of cyclic ligands**

16 Ion Exchange - Studies and Applications

recovery, respectively.

PdCl4

2- and PtCl6

**21. Chelating fibres**

recovery was not quantitative (>57%, 0.5M thiourea in 0.1M HCl).

**20. PAN-ATAL, PS-BMT ion exchangers**

Kałędowski and Trochimczuk [110, 111] synthesized polymers containing calixpyroles preparing among others the resin B4 (covalently bonded thiophene kalix[4]pyrol[2] with the vinylbenzene chloride and divinylbenzene (VBC-DV, 0.5% DVB) of the expanded gel struc‐ ture) selective towards noble metal ions. The maximal sorption capacity values determined from the Langmuir adsorption isotherms are 0.26 mmol/g; 0.55 mmol/g; 0.6 mmol/g; 0.61 mmol/g and about 1.7 mmol/g for Ag(I), Pt(II), Pt(IV), Pd(II) and Au(III), respectively. The resin B4 can be applied for the selective removal of Au(III) from the solutions originating from processing of ores, galvanic sludges containing other noble metals. The metals adsorbed on the resin are quantitatively washed out using 2 M solution of HCl or 2 M HNO3-Pt(IV), 0.5 M thiourea + 0.1 M HCl-Ag(I) and 5% solution of KCN-Au(III). In the case of palladium(II), the

Garcia et al. [112] used the polystyrene-based resin of 15-membered triolefinic azamacrocycle rings in Pd(II) and Pt(IV) ions sorption from aqueous and aqueous dioxane solutions. The addition of dioxane (10% v/v) results in increasing polymer swelling and effectiveness of palladium(II) ions sorption from 48% to 73%. The total sorption capacities for Pd(II) and Pt(IV) ions were 0.36 mmol/g and 0.28 mmol/g of the resin, respectively. The presence of Cu(II) and Ni(II) ions affects insignificantly the selectivity of the resin towards noble metals. 0.5 M thiourea in 0.1 M HCl was used as an eluent of Pd(II) and Pt(IV) ions with 100% and 79%

Chen and Zhao [113] prepared the chelating resin PAN-ATAL by immobilization of crosslinked polyacrylnitrile (PAN) (7% DVB) with 2-amino-2-thiazole (ATAL) selective towards noble metals, i.e Pd(II), Ru(II), Ir(IV) and Rh(III) ions, for which the sorption capacity values were 230.7 mg Pd(II)/g, 147.1 mg Ir(IV)/g, 137.6 mg Ru(IV)/g and 72.1 mg Rh(III)/g of the resin. The affinity of chelating macroporous resin PS-BMT (where PS – the cross-linked chlorome‐ tylated polystyrene (10% DVB), BMT – 2,5-dimercapto-1,3,4-thiadiazole) for Pd(II), Au(III) and Pt(IV) ions from chloride solutions was studied by Qu et al. [114]. The sorption capacity for Au(III) ions 5.8 mmol/g is much higher than for Pd(II) ions 0.19 mmol/g and Pt(IV) ions 0.033 mmol/g which is associated with gold(III) chlorocomplexes coordination by two donor N and S atoms of the resin and reduction of gold(III) to a metallic form. However, in the case of

2- complexes, only one donor atom – sulfur atom takes part in bonding.

It is worth presenting also the studies of using chelating fibres for the removal of platinum elements, for example, those Gong [115] and Li et al. [116] on application of fibres of functional Of a large group of ion exchangers, anion exchangers of different basicity (strong, average and weak basic) of functional groups are applied in ion exchange chromatography of noble metal ions. Strongly basic anion exchangers possessing well-dissociated functional groups capable of anion exchange of even weak acids, e.g. quaternary ammonium groups, are widely applied in the whole pH range. This group includes types 1 and 2 strongly basic anion exchangers of functional trimethylammonium groups (type 1) and dimethylhydroxyethylammonium groups (type 2). Weakly basic anion exchangers possess poorly dissociated functional groups i.e. primary-, secondary- and tertiary amine groups. There is also a group of amphoteric ion exchangers which, depending on solution pH, are able to exchange anions or cations. They are polyacids and polybases so-called polyampholites, e.g. of COO and –N+ (CH3)3 groups (snake in cage polymers).

Application of amphoteric ion exchangers for removal of trace amounts of Pd(II), Pt(IV) and Au(III) ions, among others, geological materials was studied by Chajduk-Maleszewska and Dybczyński [123], Dybczyński et al. [124] and Samczyński et al. [125] and Hubicki et al. [104]. Duolite ES 346 containing the functional amidoxime groups was successfully applied for recovery and separation of noble metal ions. There was proved high selectivity of amphoteric ion exchange Duolite ES 346 in Pd(II) ions sorption from the chloride (0.1–6M HCl–0.0011M Pd(II) and chloride-nitrate(V) (0.1–0.9 M HCl–0.9–0.1M HNO3–0.0011M Pd(II)) systems.The total sorption capacity towards Pd(II) ions is 1.099 mmol/g (0.1 M HCl) and 1.545 mmol/g (0.1M HCl–0.9M HNO3). The processes of sorption and separation of trace amounts of Pd(II), Au(III) and Pt(IV) from ammonium and aqueous-non-aqueous solutions on Duolite ES 346 were also conducted [123, 124]. Also high selectivity of this ion exchanger towards noble metal ions was proved. Ions desorption was achieved using the solutions: 2 M HCl (elution of Pt and other metal ions, 8 M NH4OH–0.01 M NH4Cl-CH3OH (1:5), desorption temperature 323 K (elution of Au(III) and 0.3 M CS(NH2)2 in 2 M HNO3 (elution of Pd(II)).

The amphoteric vinylpiridine ion exchangers VP-14K, ANKF-5 and the anion exchanger AN-251M were used for recovery of Pd(II) ions from spent car exhaust gas convertors subjected to extraction with the NaCl (2–2.3 M) solution acidified with hydrochloric acid (0.5–2 M) at 353 K, the extraction time was 4h. These ion exchangers were characterized by high affinity towards palladium(II) ions and their recovery was 98–99%. The sorption capacity of the anion exchanger AN-251M towards Pd(II) ions and the aminophosphonic ion exchanger ANKF-5 was comparable (2.4-2.5 mmol/g) and much larger than that of the ion exchanger VP-14K (1.4 mmol/g) so the ion exchangers AN-251M and ANKF-5 can be recommended for this type of application.

The strongly basic gel anion exchanger Dowex 1x10 (Cl form, grain size 100-200 mesh) was successfully applied for removal of Pd(II) and Pt(IV) ions from the dust collected in Germany from street and fast traffic roads (Saarbrücken, motorway A-1, A-61, road B-262). Quantitative desorption of sorbed metal ions took place using the 0.1 M thiourea solution in 0.1 M HCl at the increased temperature 333 K enabling reduction of the eluent volume by half. The matrix ions, i.e. Cd, Cu and Fe, were not retained on the anion exchanger but Ni, Pb and Zn sorbed at 8–15 %. Elimination of interferences during noble metals determination was achieved by using the reagents masking the matrix ions even before the sorption process, e.g. xylene orange (C31H32N2Na4O13S) [126]. Application of ion exchange technique for the determination of platinum(II) ions in biological tissues gives interesting results. The tissues with the cisdichloro-diamineplatinum(II) were irradiated with neutron in the reactor. The sample irradiation was mineralized by means of HNO3-H2SO4-H2O2 mixture. Then platinum ions were sorbed on the anion exchanger Dowex 1x8 in the chloride form with 6 M hydrochloric acid solution. Platinum was determined using the radiometric method [127]. Platinum and rhodium contained in ores were determined after separation on the anion exchanger Dowex 1x8 in the chloride form. The ore was digested in *aqua regia.* Next the solution was passed through two columns. In the first one, platinum ions were sorbed from 9 M HCl solution. In the other one, rhodium was sorbed in the form of a complex with zinc(II) chloride from 0.5 M HCl solution. 104Rh was determined directly in the ion exchange phase using the radiometric method [128].

For removal and determination of platinum from geological materials, a technique using the anion exchanger Rexyn 201 was proposed. Sorption was performed from 0.5 M of hydrochloric acid solution containing Ir(IV), Pt(IV), Pd(II) and Au(III) ions. Elution was carried out by means of 0.1 M solution of thiourea in 0.1 M HCl. Ir(III) was eluted using 6 M HCl. Platinum metals and gold were determined radiometrically [129]. The same methods were applied for the determination of platinum in carbons [130]. Somewhat modified technique was used for the determination of platinum metals in meteorites. Modification consisted in the change of the anion exchanger Rexyn 201 on Deacidite FF in the chloride form [131].

Bio-Rad AG1x8 (100–200 mesh) was characterized by high selectivity for Pd(II), Pt(IV) and Au(III) ions (the partition coefficient values were 106 , 104 , 103 for Au(III), Pt(IV) and Pd(II) ions, respectively), and therefore it could be applied for removal of noble metal ions from the environmental and geological samples, among others, from rocks, ores as well as dust and road dust [132].

Similar studies of application of anion exchangers Amberlite IRA-900 (macroporous, poly‐ styrene, strongly basic anion exchanger of type 1, 16–50 mesh) [133–135] and Amberlite IRA-410 (gel, polystyrene, strongly basic of type 2, 16–50 mesh) [135] for recovery and removal of trace amounts of Pd(II), Pt(II), Ru(III), Rh(III), Au(III) and Ir(IV) ions from chloride and radioactive nitrate waste waters were carried out by the Els et al. [133, 134] and El-Said et al. [135]. Selectivity of the anion exchanger Amberlite IRA–900 for Pd(II) ions depends on the concentration of Clˉ ions in the solution. Quantitative sorption of palladium(II) ions from the chloride solutions is obtained at [Clˉ < 0.25 M. Sorption capacity of the anion exchanger Amberlite IRA-900 for Pd(II) ions in 0.2 M HCl solution was 0.0017 mmol/dm3 ([Pd2+] 350 ppm) [133]. Selectivity of the anion exchanger Amberlite IRA-900 towards noble metal ions changes in the series: *Au(III) > Pt(II) > Pd(II) > Ru(III) > Ir(IV) > Rh(III)* [134].

Satisfactory results were obtained using the above-mentioned anion exchanger for separation of Pd(II) and Ni(II), Sr(II), Rh(III), Eu(III), Ce(III), Ru(III), U(VI), Fe(III), Cr(III), Al(III), Ca(II) and Cs(I) from the radioactive nitrate waste waters [135].

The anion exchangers of quaternary ammonium groups: Purolite A-850 and Amberlite IRA-958 of polyacrylate skeleton, Lewatit MP 500A of polystyrene-divinylbenzene skeleton as well as Varion AP of functional pyridine groups and polystyrene-divinylbenzene skeleton exhibit high selectivity for Pd(II) ions from chloride and chloride-nitrate(V) solutions. Sorption capacities towards Pd(II) ions are 0.0282 g/cm3 (in 0.1 M HCl) and 0.0005 g/cm3 (in 6 M HCl) for Amberlite IRA-958 as well as 0.0408 g/cm3 (in 0.1 M HCl) and 0.005 g/cm3 (in 6 M HCl) for Purolite A-850. The addition of Zn(II) and Al(III) to the solution largely decreases selectivity of most anion exchangers for Pd(II) ions. The exception is Varion AP, whose selectivity changes insignificantly despite the presence of Al(III) ions [136, 137].

Due to modification of the macroporous polystyrene-divinylbenzene resin Amberlite XAD-1, the ion exchanger containing functional tertiary amine groups was obtained. This ion ex‐ changer was used for separation of noble metal ions. Separation of Rh(III), Pd(II) and Pt(IV) ions mixture was achieved using suitable eluents:

Rh(III) – 1M HCl or 1M NaCl in 0.1 M HCl

exchanger AN-251M towards Pd(II) ions and the aminophosphonic ion exchanger ANKF-5 was comparable (2.4-2.5 mmol/g) and much larger than that of the ion exchanger VP-14K (1.4 mmol/g) so the ion exchangers AN-251M and ANKF-5 can be recommended for this type of

successfully applied for removal of Pd(II) and Pt(IV) ions from the dust collected in Germany from street and fast traffic roads (Saarbrücken, motorway A-1, A-61, road B-262). Quantitative desorption of sorbed metal ions took place using the 0.1 M thiourea solution in 0.1 M HCl at the increased temperature 333 K enabling reduction of the eluent volume by half. The matrix ions, i.e. Cd, Cu and Fe, were not retained on the anion exchanger but Ni, Pb and Zn sorbed at 8–15 %. Elimination of interferences during noble metals determination was achieved by using the reagents masking the matrix ions even before the sorption process, e.g. xylene orange (C31H32N2Na4O13S) [126]. Application of ion exchange technique for the determination of platinum(II) ions in biological tissues gives interesting results. The tissues with the cisdichloro-diamineplatinum(II) were irradiated with neutron in the reactor. The sample irradiation was mineralized by means of HNO3-H2SO4-H2O2 mixture. Then platinum ions were sorbed on the anion exchanger Dowex 1x8 in the chloride form with 6 M hydrochloric acid solution. Platinum was determined using the radiometric method [127]. Platinum and rhodium contained in ores were determined after separation on the anion exchanger Dowex 1x8 in the chloride form. The ore was digested in *aqua regia.* Next the solution was passed through two columns. In the first one, platinum ions were sorbed from 9 M HCl solution. In the other one, rhodium was sorbed in the form of a complex with zinc(II) chloride from 0.5 M HCl solution. 104Rh was determined directly in the ion exchange phase using the radiometric

For removal and determination of platinum from geological materials, a technique using the anion exchanger Rexyn 201 was proposed. Sorption was performed from 0.5 M of hydrochloric acid solution containing Ir(IV), Pt(IV), Pd(II) and Au(III) ions. Elution was carried out by means of 0.1 M solution of thiourea in 0.1 M HCl. Ir(III) was eluted using 6 M HCl. Platinum metals and gold were determined radiometrically [129]. The same methods were applied for the determination of platinum in carbons [130]. Somewhat modified technique was used for the determination of platinum metals in meteorites. Modification consisted in the change of the

Bio-Rad AG1x8 (100–200 mesh) was characterized by high selectivity for Pd(II), Pt(IV) and

respectively), and therefore it could be applied for removal of noble metal ions from the environmental and geological samples, among others, from rocks, ores as well as dust and

Similar studies of application of anion exchangers Amberlite IRA-900 (macroporous, poly‐ styrene, strongly basic anion exchanger of type 1, 16–50 mesh) [133–135] and Amberlite IRA-410 (gel, polystyrene, strongly basic of type 2, 16–50 mesh) [135] for recovery and removal of trace amounts of Pd(II), Pt(II), Ru(III), Rh(III), Au(III) and Ir(IV) ions from chloride and radioactive nitrate waste waters were carried out by the Els et al. [133, 134] and El-Said et al.

, 104 , 103

anion exchanger Rexyn 201 on Deacidite FF in the chloride form [131].

Au(III) ions (the partition coefficient values were 106

form, grain size 100-200 mesh) was

for Au(III), Pt(IV) and Pd(II) ions,

The strongly basic gel anion exchanger Dowex 1x10 (Cl-

application.

18 Ion Exchange - Studies and Applications

method [128].

road dust [132].

Pd(II) – 0.05 M NaClO4 in 1 M HCl or 1 M NaCl + 0.025 M NaClO4

Pt(IV) – 0.1 M NaClO4 in 1 M HCl or 1 M NaCl + 0.15 M NaClO4.

The method is quick (about 30–40 minutes) and allows separation of 1.18–11.8 μg amounts of noble metal ions [138].

Among weakly basic anion exchangers of special interest is the macroporous polystyrenedivinylbenzene anion exchanger of functional dimethylamine groups Amberlite-93 used for recovery of Pd(II), Pt(II) and Rh(III) ions from spent car exhaust gas convertors. Rhodium(III) was desorbed from the anion exchanger as the first using 6 M hydrochloric acid solution, then palladium(II) was desorbed using 1% ammonia solution at room temperature. Platinum(II) was washed out with the ammonia solution of the concentration 5% (at increased temperature). Separation of palladium from platinum from the eluant solution can be achieved reducing to the metallic form or precipitating (NH4)2PdCl4 and (NH4)2PtCl6 using hydrochloric acid. The presented method of selective removal of platinum metals using Amberlite IRA-93 can be regarded as an effective technique for separation of these ions on a laboratory and commercial scale [139].

The weakly basic Amberlite IRA 67 is applied for selective removal of microquantities of platinum(IV) ions from the acid solution containing CuCl2, FeCl3, NiCl2, AlCl3 and ZnCl2. In chloride solutions, the above components can partly form anions, which reduces the sorption capacity of weakly basic anion exchangers. The effect of the above-mentioned macrocompo‐ nents on decrease of sorption capacity towards platinum(IV) ions can be presented in the series: CuCl2 ≈ FeCl3 ≈ NiCl2 < AlCl3 < ZnCl2 [140, 141]. A similar series can be determined for the anion exchanger Duolite S 37, which contains secondary and tertiary functional groups added to the phenol-formaldehyde skeleton [142].
