Evaluation of Five Anion Exchange Resins for Assessing Soil Phosphorus Release

Abstract

ABSTRACT As a part of efforts to develop a laboratory soil-resin incubation technique to assess soil phosphorus (P) release by mixing resin beads directly with soil acting as a P sink to mimic plant root uptake, selecting a suitable type of anion exchange resin (AER) is essential. Thus, five types of strong basic AER in bicarbonate (HCO3)—form were evaluated for their ion exchange characteristics in salt solutions. The P adsorption study was conducted under four sulfate (SO4 2-) concentrations (0.1, 0.01, 0.001, and 0.0001 M) at each of three fixed concentrations (0.21, 0.62, and 2.06 mM) of potassium dihydrogen phosphate (K2HPO4). Results showed that adsorbed P was quantitatively extracted from the resins with dilute hydrochloric acid (1 M, HCl). Also, increasing the SO4 2- concentration dramatically decreased the adsorption of P by the resins, with little difference between a one- and seven-day equilibration period. All five resins behaved similarly at higher concentrations of SO4 2-, but at lower concentrations of SO4 2-, the HCO3—form Amberlite I-6766 resin had a higher affinity for P than other Dowex resins. There was much greater P adsorption to the resin at solution pH > 7.2, which suggests hydrogen phosphate (HPO4 2-) to be much more strongly adsorbed than dihydrogen phosphate (H2PO4 −). Also, the Amberlite resin has more favorable physical properties with a granular structure, lower density, and ease of handling and separation from soil, which was chosen for subsequent soil studies.