Effect of Aluminum Substitution in Goethite on Phosphorus Adsorption: II. Rate of Adsorption

Abstract

AbstractThe effects of initial pH, P concentration, Al substitution and method of synthesis on the rate of phosphate adsorption by a series of α‐FeOOH samples containing up to 30 mol % Al were investigated. The results, plotted as first‐order reactions with respect to phosphate disappearance, were characterized by an initial fast phase followed by a pseudo‐first‐order reaction. An approximation of the magnitude of the fast phase was made by extrapolating the first‐order line back to zero time. The difference between the initial and zero time first‐order concentration was then considered to be the magnitude of the rapid phase of the reaction. Phosphate concentration, initial pH, and method of synthesis influenced this parameter. Al substitution had little effect. However, Al substitution did affect the pseudo‐first‐order rate constant at all pH levels and lower P concentrations. It is postulated that Al substitution may sterically hinder the sorption of phosphate. The various synthesis methods affected the magnitude of the fast phase and the pseudo‐first‐order rate. This may be due to the apparent change in the number of active sites related to changes in synthesis as discussed in part 1.