METAL(II) ION BINDING ONTO CHELATING EXCHANGERS WITH NITROGEN DONOR ATOMS - SOME NEW OBSERVATIONS AND RELATED IMPLICATIONS

Chelating exchangers with only nitrogen donor atoms exhibit some unusual properties in relation to metal ion uptake from the aqueous phase. Specifically, for these chelating exchangers, (a) the metal ion uptake increases with an increase in competing Ca2+ and Na+ ion concentrations; (b) metal removal capacities remain almost unaffected at pH as low as 1.0; (c) regeneration or desorption of metal ions with ammonia is very efficient while acid regeneration is ineffective; and (d) both metal cations and other anions can be removed simultaneously from the aqueous phase. The foregoing behaviors are not observed at all for other commonly used chelating exchangers with carboxylate, iminodiacetate, or aminophosphonate functionalities. A molar-exchange model, where the individual nitrogen donor atoms bind metal ions independently on molar basis, can explain the anomalous characteristics of these specialty chelating exchangers. Because of their unusual properties, these chelating exchangers with only nitrogen donor atoms offer new application opportunities for heavy-metals removal unattainable through other exchangers.