**6. Ion exchangers of functional thiourea and phosphonic groups and their derivatives**

Of significant importance are the results of studies on the application of commercial ion exchangers Tulsion of the functional isothiourea and phosphonic groups for removal of Pd(II) ions from nitric(V) acid solutions (0.1–4 M). High values of partition coefficients (particularly in diluted HNO3 (0.1 M) solutions) decreased with the increasing concentration of nitric(V) acid for the ion exchangers Tulsion CH-95, Tulsion CH-96 and Tulsion CH-97. The values of partition coefficients (particularly in diluted HNO3 (0.1 M) solutions) which were >10 000 cm3 / g, 1650 cm3 /g, 5210 cm3 /g for Tulsion CH-95, Tulsion CH-96 and Tulsion CH-97, respectively, decreased with the increasing nitric acid(V) concentration. The selectivity series of the Tulsion ion exchangers towards Pd(II) ions is as follows: *Tulsion CH-95 > Tulsion CH-97 > Tulsion CH-96.*

The ion exchangers of the functional thiourea and isothiourea groups, commercially known as Srafion NMRR, Lewatit TP-214 and Purolite S-920, are widely used for the concentration of platinum metal ions [53-61]. Srafion NMRR (Ionac SR-3) exhibits great affinity for Au(III) and Ag(I) as well as Pd(II), Pt(IV), Rh(III), Ru(III), Ir(III) and Os(VI) ions [53-61]. It is applied in the separation of noble metal ions [57], similar to the ion exchangers Monivex which develop high sorption capacity values particularly in the largely acidic solutions (2–6 M HCl) [67]. Lewatit TP-214 was used for the removal Pd(II) ions from two component Pd(II)–Zn(II); Pd(II)–Cu(II)) and multicomponent (Pd(II)–Cu(II)–Zn(II)) chloride solutions [61] and for the removal of Pd(II) ions from chloride solutions (0.1–8.0 – 0,001 M Pd(II)) and chloride–nitrate ones (0.1÷0.9 M HCl – 0.9÷0.1 M HNO3– 0,0011 M Pd(II)) ) [55]. The total ion exchange capacity of Lewatit TP-214 towards Pd(II) ions was from 0.97 mmol/g–3 M HCl to 1.16 mmol/g–0.1 M HCl [55].

Zuo and Muhammed prepared a large number of ion exchangers of the functional thiourea groups by modification of macroporous polystyrene matrices of Bonopore, Amberlite XAD-2, Amberlite XAD-4 as well as the weakly basic anion exchanger Amberlite IR-45 [62]. Newly prepared ion exchangers were used in sorption of Au(III), Ag(I), Cu(II) and Fe(III) ions from one-component chlorides solutions (2 M HCl) and their mixtures (Au(III), Ag(I), Fe(III), Cu(II)), as well as in sorption of platinum metal ions e.g. Pd(II), Pt(IV), Rh(III), etc. The studied ion exchangers are characterized by high selectivity towards noble metal ion, particularly gold and silver in the presence of Cu(II) and Fe(III).

Separation of Pd(II), Cu(II) and Zn(II) ions using the melamine-formaldehyde-thiourea (MFT) resin was presented in [63]. There was proved high selectivity of this resin towards Pd(II) ions, and the obtained values of sorption capacity were 15.29 mg Pd(II)/g (static method) and 1580 μg Pd(II)/g resin (dynamic method). Desorption of ions with studied resin was conducted using 0.5 M thiourea, 0.5 M HCl solutions and the acidified thiourea (0.5 M (NH2)2CS–0.5 M HCl).
