A kinetic study of phosphate adsorption by boehmite

Rates of phosphate adsorption to PT-A (a new type of aluminum oxide hydroxide) and ALG (aluminum hydroxide gel) from a pH 3 phosphate solution 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 phosphate adsorption for ALG. The intraparticle diffusivities (D-p's) of phosphate were evaluated from the time courses of adsorption using the model 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 values resembled those for porous inorganic ion exchangers. The adsorption rates are high enough for each of the samples to be utilized as a phosphate adsorbent to prevent hyperphosphatemia in patients on chronic dialysis. PT-A is favored as a phosphate adsorbent because of its high chemical stability against acid.