Adsorption of inorganic and organic phosphorus by amorphous aluminum hydroxide

Abstract

The adsorption of inorganic ? (Pi) and organic ? (Po) compounds by amorphous aluminum hydroxide was studied over the equilibrium ? concentration range of 8 × 10^‐7 to 1 × 10^‐4 M under normal lake pH conditions using the Langmuir adsorption isotherm. The isotherms for Pi and Po adsorption plotted according to a modified Langmuir equation generally exhibited multiphasic behavior indicative of more than one population of sorption sites differing in their affinity for P. Adsorption maxima and binding energy constants for the adsorption of inorganic and organic phosphorus compounds are reported. Cations, anions, and chelating agents typical of natural waters greatly affected Po adsorption. In general, Po adsorption increased with anionic charge, number of reactive phosphate groups, decreasing steric hindrance and decreasing molecular size. Results indicate that a significant fraction of the native Po in lakes differs from the model Po compounds studied.