**3. Application of cation exchangers in concentration and removal process of platinum metals**

There are numerous reports in the literature about cation exchangers application in concen‐ tration and separation of trace amounts of platinum metal ions. Ion exchange is widely applied also for control of bound and free platinum contents in the serum added in the cis-platinum form. After ultrafiltration, ethylenediamine was added to form complexes which are sorbed on cation exchange disks. Platinum ions were desorbed from the disks by means of 5 M HCl and determined using the AAS method. The detection limit was 35 μg/dm3 [6].

Besides the above-described procedures, there are separation methods using cation exchang‐ ers. As commonly known platinum metals tend to form anion complexes in the chloride systems, therefore partition coefficient values should not be high [7–9]. Much higher values of partition coefficients of platinum metal ions can be obtained by the addition of thiourea which results in cation complexes formation [9].

The polystyrenesulfone cation exchanger Dowex 50Wx8 in the hydrogen form was used for the determination of metals from the platinum group in ores and concentrates. Before ion exchange stage, noble metals in metallic copper were collected. The obtained alloy was digested in *aqua regia*. The pH of the solution was made 1 using hydrochloric acid. Ions of metals such as Cu(II), Ni(II) and Fe(III) were sorbed on the cation exchangers, whereas noble metals were not retained. The deposit was washed in HCl solution of pH = 1. The separated noble metals were determined gravimetrically and spectrophotometrically [10–14]. A similar technique was applied for the determination of noble metals and for the collection of Cu-Ni-Fe and ferronickel alloys [15–24]. Also the cation exchanger Dowex 50Wx8 was used for noble metal ions removal. Before the ion exchange stage, collection was made using fused tin. The obtained alloy was digested in the HCl-H2O2 solution. Tin(IV) was removed by evaporation from the HCl-HBr solution, and the obtained solution was evaporated dry several times in the presence of 12 M HCl [25]. The removal of noble metals from ores, the cation exchange followed by anion exchange method was applied. Cu(II), Ni(II) and Fe(III) ions are adsorbed at pH = 1.5 on the cation exchanger Dowex 50Wx8, whereas the noble metal ions pass on the column filled with the strongly basic anion exchanger in the chloride form Amberlite IRA-400. Before sorption on the anion exchange column, the solution is evaporated dry in the presence of sodium chloride, then it is dissolved in 12 M HCl and diluted to weakly acidic reaction. Under such conditions, rhodium(III) ions pass through the column, and the ions of other noble metals are retained on the anion exchanger bed [26]. A similar method was applied for the determi‐ nation of iridium in the flotation concentrate [27]. The application of cation exchange for the determination of platinum metals on the meteorites is quite interesting. In this method, twostage adsorption on the cation exchanger was used. Non-noble metal ions were adsorbed at pH 1.5 on the first column. Then they were desorbed by means of 3 M HCl. The obtained eluant was evaporated dry and the residue was dissolved in diluted HCl and the pH value was brought to 1.5. The other stage of non-noble metal ions adsorption was conducted in the same way as the first one. Application of the second stage allows avoiding errors connected with co-adsorption of noble metal ions [28, 29]. For determination of platinum and palladium in the copper and nickel stone, there were used two ion exchangers: the cation exchanger Dowex 50 in the hydrogen form and the anion exchanger Amberlite IRA-400 in the chloride form. Before the ion exchange process, the sample was melted with SnO2 to collect noble metals. Tin(IV) was evaporated from the mixture of HCl and HBr acids. After bringing the solution to pH 1.5, Cu(II), Ni(II) and Fe(III) cation were adsorbed on the cation exchanger bed. The obtained eluant containing Pt(IV) and Pd(II) was evaporated from NaCl and dissolved in HCl, next it was passed through the anion exchanger bed. At first, there were eluted Pd(II) ions by means of 12 M HCl and then Pt(IV) ions using 2.4 M HClO4. Both elements were determined using the spectrophotometric method [30]. The residue in the copper-nickel stone was determined using the cation exchanger Bio-Rad AG50W-x8 and the chromatographic column Porasil C impreg‐ nated by means of TBP (tri-n-butyl phosphate). The sample was melted with Na2O2, then digested in HCl and the acid concentration was brought to 0.1 M. Non-noble metal ions were separated on the cation exchanger and platinum metals were sorbed on the chromatographic column. Pt(IV) and Pd(II) ions were eluted by means of TBP in toluene but Rh(III) and Ir(IV) ions using water. Noble metals were determined gravimetrically and by means of AAS [31, 32]. Platinum alloys were determined in a two-stage separation process of noble metal ions. The sample was digested in *aqua regia*, next it was evaporated dry and the residue was diluted with HCl up to concentration about 0.1 M. The weakly acidic cation exchanger Amberlite IRC-50 of carboxylic groups in the sodium form was used in the first column. Palladium(II) ions were sorbed (probably precipitated in the hydrated oxide form [33]) on this ion exchanger, whereas Rh(III) and Pt(IV) passed to the eluant which was next put through the column with the strongly basic anion exchanger Dowex 2 in the chloride form. The adsorbed Rh(III) and Pt(IV) ions were eluted with 2 M HCl and 7 M HCl, respectively. The ion exchange technique was also applied for the determination of trace amounts of noble metals in common metals of high purity such as Fe, Ni, Cu, Mn and Al. The sample can be digested or melted with alkalis depending on its kind. The two-column cation–anion exchanger system was used for separa‐ tion of noble metal ions. On the cation exchanger Dowex 50x8, there were adsorbed ions of metals such as Fe(III), Ni(II), Mn(II), Cu(II) and Al(III) from the 90% v/v ethanol + 10% v/v 1 M HCl solution. Then by evaporation, the medium changed from chloride to nitrate(V) one. In the other column on the anion exchanger Dowex 1x 8 in the nitrate form, there were sorbed noble metal ions from the aqueous solution of pH 6. Noble metals were analyzed in the resin phase by means of the radioisotope technique [34]. The similar method was used for the determination of noble metals in atmospheric dusts melting them with Na2O2 [35]. The cation exchanger Dowex 50x8 was used for the separation of copper(II) from the 0.03 M hydrochloric acid solution from the noble metal ions such as Pt(IV), Pd(II), Au(III) and Rh(III) [36, 37]. Ion exchange combined with extraction was applied for the determination of noble metals present in uranium alloys which can be uncoupled. Uranium can be separated from rhodium by extraction with 30% solution of TBP in CCl4. Then after complete removal of chlorides, fluorides and nitrates by evaporation with chloric acid, rhodium(III) cations were sorbed by cation exchanger Dowex 50Wx8 from 0.3–0.9 % HClO4 solution. Rhodium(III) was eluted form the cation exchanger by washing the column with 6 M hydrochloric acid solution and then determined spectrophotometrically using the method with SnCl2 [38].

The polystyrenesulfone cation exchanger Dowex 50Wx8 in the hydrogen form was used for the determination of metals from the platinum group in ores and concentrates. Before ion exchange stage, noble metals in metallic copper were collected. The obtained alloy was digested in *aqua regia*. The pH of the solution was made 1 using hydrochloric acid. Ions of metals such as Cu(II), Ni(II) and Fe(III) were sorbed on the cation exchangers, whereas noble metals were not retained. The deposit was washed in HCl solution of pH = 1. The separated noble metals were determined gravimetrically and spectrophotometrically [10–14]. A similar technique was applied for the determination of noble metals and for the collection of Cu-Ni-Fe and ferronickel alloys [15–24]. Also the cation exchanger Dowex 50Wx8 was used for noble metal ions removal. Before the ion exchange stage, collection was made using fused tin. The obtained alloy was digested in the HCl-H2O2 solution. Tin(IV) was removed by evaporation from the HCl-HBr solution, and the obtained solution was evaporated dry several times in the presence of 12 M HCl [25]. The removal of noble metals from ores, the cation exchange followed by anion exchange method was applied. Cu(II), Ni(II) and Fe(III) ions are adsorbed at pH = 1.5 on the cation exchanger Dowex 50Wx8, whereas the noble metal ions pass on the column filled with the strongly basic anion exchanger in the chloride form Amberlite IRA-400. Before sorption on the anion exchange column, the solution is evaporated dry in the presence of sodium chloride, then it is dissolved in 12 M HCl and diluted to weakly acidic reaction. Under such conditions, rhodium(III) ions pass through the column, and the ions of other noble metals are retained on the anion exchanger bed [26]. A similar method was applied for the determi‐ nation of iridium in the flotation concentrate [27]. The application of cation exchange for the determination of platinum metals on the meteorites is quite interesting. In this method, twostage adsorption on the cation exchanger was used. Non-noble metal ions were adsorbed at pH 1.5 on the first column. Then they were desorbed by means of 3 M HCl. The obtained eluant was evaporated dry and the residue was dissolved in diluted HCl and the pH value was brought to 1.5. The other stage of non-noble metal ions adsorption was conducted in the same way as the first one. Application of the second stage allows avoiding errors connected with co-adsorption of noble metal ions [28, 29]. For determination of platinum and palladium in the copper and nickel stone, there were used two ion exchangers: the cation exchanger Dowex 50 in the hydrogen form and the anion exchanger Amberlite IRA-400 in the chloride form. Before the ion exchange process, the sample was melted with SnO2 to collect noble metals. Tin(IV) was evaporated from the mixture of HCl and HBr acids. After bringing the solution to pH 1.5, Cu(II), Ni(II) and Fe(III) cation were adsorbed on the cation exchanger bed. The obtained eluant containing Pt(IV) and Pd(II) was evaporated from NaCl and dissolved in HCl, next it was passed through the anion exchanger bed. At first, there were eluted Pd(II) ions by means of 12 M HCl and then Pt(IV) ions using 2.4 M HClO4. Both elements were determined using the spectrophotometric method [30]. The residue in the copper-nickel stone was determined using the cation exchanger Bio-Rad AG50W-x8 and the chromatographic column Porasil C impreg‐ nated by means of TBP (tri-n-butyl phosphate). The sample was melted with Na2O2, then digested in HCl and the acid concentration was brought to 0.1 M. Non-noble metal ions were separated on the cation exchanger and platinum metals were sorbed on the chromatographic column. Pt(IV) and Pd(II) ions were eluted by means of TBP in toluene but Rh(III) and Ir(IV)

6 Ion Exchange - Studies and Applications

Separation of noble metals can be conducted on the cation exchangers from the thiourea systems. Separation of microquantities of various pairs of noble metal ions was made using the polystyrene sulfone cation exchanger Bio-Rad AG 50Wx4 in the hydrogen form. Pd(II) and Au(I), Pd(II) and Pt(II) ions as well as the Rh(III), Au(I), Pt(II) and Ag(I) mixture were separated using the acetate-thiourea solutions in the hydrochloric or hydrobromic acid medium [39]. Platinum(II) and palladium(II) ions were separated from aluminium ions using also the cation exchanger Bio Rad AG50Wx4 in the hydrogen form. Aluminium ions as well as Fe, Zn, Pb, U, Ni, Co and Sr ones do not form cationic complexes under experimental conditions, therefore only noble metals are sorbed from 0.1 M thiourea solution in 1.5 M hydrochloric acid solution. 2% Br2 and 1.5 M HCl solution was used for elution of Pt(II) and Pd(II) ions. 0.87 M HBr–0.01 M thiourea solution in 90% acetone proved to be the best eluant towards Pt(II) ions. The presence of Cu(II) and Hg(II) ions is not recommended because of possible co-adsorption with noble metals [40]. It is relatively difficult to separate rhodium(III) ions from platinum(IV) ones in the chloride medium, therefore in some cases it is necessary to change the medium into the nitrate one. Before the separation of platinum(IV) and rhodium(III) ions on the polystyrenesulfone cation exchanger Varion KS in the hydrogen form, the chloride complexes were in contact with sodium hydroxide at pH 13 for four hours. Then the obtained solution was acidified with 4 M HNO3 to pH 2. Under such conditions, rhodium(III) ions occur in the cation form and platinum(IV) ions in the anion form. Platinum(IV) ions are not retained by the cation exchanger. Rhodium(III) ions can be eluted with 1 M hydrochloric acid from the cation exchanger [41].
