**19. Ion exchangers of cyclic ligands**

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

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% recovery, respectively.
