**4. Application of chelating ion exchangers for concentration and removal of platinum metal ions**

Chelating ion exchangers also called complexing ion exchangers are formed by building organic reagents containing organic groups into the ion exchange resin skeleton. Owing to that they possess active chemical groups capable of selective/specific interactions with metal ions in the solution forming chelating complexes when a metal ion can bind with two or a larger number of donor atoms of their functional groups. These ion exchangers are characterized by high selectivity and their sorption capacities depend, among others, on the kind of functional groups, their reciprocal position and spatial configuration (steric effects) and also on physi‐ cochemical properties of the polymer matrix [42, 43].

On the huge number of chelating ion exchangers, on a large laboratory and industrial scale, there are produced ion exchangers of functional dithizone, thiourea, isothiourea, aminophos‐ phonic, phosphonic, thiol, amidooxime, aminoacetate, dithiocarbamate, iminodiacetate, thiosemicarbamate groups as well as chelating ion exchangers containing triisobutylphos‐ phine sulfides [44-64].
