A KINETIC-STUDY OF PHOSPHATE ADSORPTION BY BOEHMITE

Rates of phosphate adsorption to PT-A (a new type of aluminum oxide hy droxide) and ALG (aluminum hydroxide gel) from a pH 3 phosphate soluti on were measured by a batch method. Phosphate uptake progressed mainly by the adsorption mechanism for PT-A, but dissolution of aluminum and precipitation of aluminum phosphate took place in addition to phospha te adsorption for ALG. The intraparticle diffusivities (D-p's) of phos phate were evaluated from the time courses of adsorption using the mod el of pore diffusion with a Freundlich-type adsorption isotherm. The D -p values were similar to 7 x 10(-7) cm(2) s(-1) for PT-A and 1 x 10(- 6) cm(2) s(-1) for ALG. The tortuosity factors calculated from a model of parallel plate pore were 5.1 for PT-A and 6.7 for ALG; these value s resembled those for porous inorganic ion exchangers. The adsorption rates are high enough for each of the samples to be utilized as a phos phate adsorbent to prevent hyperphosphatemia in patients on chronic di alysis. PT-A is favored as a phosphate adsorbent because of its high c hemical stability against acid.