Effect of Aluminum Substitution in Goethite on Phosphorus Adsorption: I. Adsorption and Isotopic Exchange

Abstract

AbstractThree sets of goethite samples, pure (α‐FeOOH) and aluminum substituted (α‐[Fe,Al]OOH), were made using different synthesis techniques. Specific surface area ranged from 6.8 to 28.4 × 104 m2 kg−1. Adsorption isotherms were carried out on a surface area basis at pH values ranging from 2.6 to 7.6 for up to 120 h. The specific surface area (determined by Brunauer, Emmett, and Teller N2 adsorption [BET]) depended on the method of synthesis. Phosphate adsorption and isotopic exchange rates were dependent upon mode of synthesis, aluminum substitution, and pH. These results and the accompanying transmission electron micrographs indicate that the chemico‐physical environment during synthesis is a prime determinant of goethite's phosphate adsorption capacity. Aluminum substitution affects specific surface area and extent of phosphate adsorption as greatly as does the synthesis process. The Al samples had faster isotopic exchange rates than their pure counterparts. The rate of exchange increased with increasing surface area (smaller crystal size).