The anion-exchange properties of akaganeite (beta-FeOOH) with phosphite (H2PO3- and HPO32-) are reported herein. Uptake of phosphite by akaganeite followed the Freundlich isotherm model with exchange capacity of 1.0 mmol/g, and high distribution coefficients in multianion solution of 2.0 mmol/dm(3) concentration (7.0 x 10(3) cm(3)/g at pH 3.9). Akaganeite displayed nearly constant uptake of phosphite (0.9 mmol/g) at pH 2.5-6.0. The kinetics on uptake of phosphite rapidly reached an equilibrium in 4 h. Akaganeite was also found to be feasible for high uptake of phosphite (1.2 mmol/g) and low uptake of hypophosphite (<0.10 mmol/g) at pH 6.3 from a highly concentrated binary solution containing 0.70 mol/dm(3) phosphite, and 0.20 mol/dm(3) hypophosphite. Akaganeite can be regenerated and reused for uptake of phosphite with an exchange capacity equivalent to that of the original akaganeite.