INTERACTIONS BETWEEN PHOSPHATE SPECIES AND ALUMINUM HYDROXIDE GEL

JUE-CHEN LIU, Purdue University

Abstract

This study was undertaken to investigate the interactions between phosphate species and aluminum hydroxide gel. Phosphate adsorption is strongly affected by pH, time, particle size and concentration. The independence of the point of zero charge for phosphate adsorption gives evidence that phosphate is specifically adsorbed by aluminum hydroxide gel. The experimental observations demonstrate that there are three different sites, i.e. carbonate, hydroxyl and water sites, on the aluminum hydroxycarbonate surface that can be exchanged by phosphate species. The proportion of the sites exchanged varied with pH. The contribution of phosphate adsorption by each type of exchange site at constant pH remained the same in spite of the overall increase in phosphate adsorption with time and concentration which suggests that new surface, composed of the same proportion of exchange sites, is becoming available as phosphate adsorption occurs. It is proposed that a structure composed of 4 to 7 fused six-membered rings comprises the primary particles for aluminum hydroxide gel. The effect of the process of phosphate adsorption on the state of aggregation can be divided in three stages: Phosphate diffusion; Aggregate deaggregation; and Primary particle peeling. The point of zero charge is changed by phosphate adsorption. Phosphate adsorption also affects the rate of acid neutralization for aluminum hydroxide gel. It suggests the use of aluminum hydroxyphosphate gel to minimize phosphate depletion is not desirable if the antacid properties are important due to the slower acid neutralization activity of aluminum phosphate gel. On the other hand, an aluminum hydroxide with high surface area can be used to treat patient with hyperphosphatemia as associated with renal failure.

Degree

Ph.D.

Subject Area

Pharmaceuticals

COinS