REACTIONS OF PHOSPHATE IN ALUMINUM SYSTEMS.: I. ADSORPTION OF PHOSPHATE BY X-RAY AMORPHOUS "ALUMINUM HYDROXIDE"

Abstract

The initial fixation of phosphate by X-ray amorphous "aluminum hydroxide" at pH values of 7, 6, 5 and 3.8 and at initial phosphate concentrations ranging from 2 to 100 p.p.m. of P and in certain instances, up to molar concentration, was shown to be primarily a result of an adsorption reaction. This reaction occurred very rapidly and was practically completed within a half-hour, but was followed by a slow decomposition-precipitation process. The adsorption mechanism was suggested to be basically the same as the decomposition-precipitation reaction, except the latter requires the release of the aluminum ion into solution.The limitations of the Langmuir adsorption isotherm are discussed in light of the data obtained. A unified equation for adsorption and precipitation of phosphate in aluminum systems is presented.