(91c) Selective Ion Exchange for Removal of Inorganic Trace Contaminants from Water

Removal of undesirable trace contaminants like heavy metals and oxy anions from is achieved by means of weakly basic anion exchangers in their free base form: (i). Selective elimination of divalent cationic species is due to Lewis base – Lewis acid interactions from which the background composition of the water matrix is excluded. (ii) Traces of oxy anions can effectively be removed at neutral pH because they are preferred over sulphate and chloride ions. Slow kinetics because of the small concentrations can be overcome by applying magnetic weakly basic micro exchangers. Standard anion exchangers can be applied in usual packed beds while continuously stirred tank reactors have to be used with magnetic micro exchangers. Using different types of anion exchangers, the approaches have successfully been demonstrated in the laboratory and pilot scales for removal of cadmium (Cd2+), copper (Cu2+), mercury species, chromate (Cr(VI)) and natural uranium species from contaminated ground and surface waters. Regeneration depends on the system and is achieved by means of H2SO4, NaOH or citric acid.