Adsorption of Free Lead (Pb2+) by Pedogenic Oxides, Ferrihydrite, and Leaf Compost

Abstract

Iron oxides and organic matter have a high capacity to adsorb Pb and concomitantly maintain a low free Pb2+ activity in solution. It is, therefore, important to assess the adsorption capacity of naturally occurring materials and evaluate their potential to reduce toxicity. The free Pb2+ activity was measured in the solution in equilibrium with ferrihydrite (a synthetic Fe oxide), two field‐collected pedogenic amorphous oxides, and leaf compost. The experiment used a factorial design varying total Pb loading and solution pH. The results show that ferrihydrite was more efficient in lowering Pb aqueous concentration than the two pedogenic oxides. Furthermore, of the two pedogenic oxides examined, a higher Pb2+ activity was maintained in solution at equilibrium with the most crystalline phase, which also has a lower surface area relative to the other adsorbents. Leaf compost maintained a significantly higher free Pb2+ activity, relative to the various oxides. The experimental data could be fitted to a semi‐mechanistic model predicting free Pb2+ activity as a function of total Pb loadings and pH, with R2 varying from 0.77 to 0.92.