EFFECT OF ION-EXCHANGE RESIN STRUCTURE ON NITRATE SELECTIVITY

The nitrate/sulfate selectivity of a range of anion-exchange resins with backbones consisting of crosslinked polystyrene, polyepichlorohydrin or polydiallylamine derivatives and containing different nitrogen substituents is discussed. It is shown that the preference of an anion-exchange resin for nitrate over sulfate increases as the resin becomes more hydrophobic (less polar). It appears not to matter whether the increase in the hydrophobic character is caused by the nature of the polymer backbone or the nature of the nitrogen substituents. The most nitrate-selective resins found were those with a polystyrene backbone and large trialkyl substituents on the amino-nitrogen atom. Nitrate-selective resins are more difficult to regenerate with sodium chloride solution than sulfate-selective resins. Experiments designed to overcome the difficulty of regeneration of nitrate-selective resins by regeneration at higher temperatures and also regeneration of weak-base resins using stoichiometric amounts of sodium hydroxide solution are described. © 1990.