On the langmuir phosphate adsorption maximum

Abstract

The use of the Langmuir isotherm equation to calculate phosphate (P) adsorption maximum was investigated by studying P adsorption by boehmite (a soil mineral) at pH 3.25, 4.00, and 5.50. This well‐defined simple system was designed to eliminate other influencing reactions and factors in an attempt to study only the adsorption process. The Langmuir adsorption maximum was compared to three other methods (K_d, “concentration null”, and graphical) for determining the value of this constant. There was generally good agreement between methods at the different pH's, except the “concentration null” at pH 3.25 and the Langmuir at pH 4.00. It appears that at least three of the methods (Langmuir included) can be used independently to develop the adsorption envelope, which peaked at pH 4.00. At maximum adsorption, approximately 20% of the surface was covered by P, suggesting monolayer adsorption at specific sites on the surface. Apparently the simple Langmuir isotherm equation, if used correctly, may give valid adsorption maximum values.