Influence of Ionic Strength and Lead Concentrations on the Adsorption of Aluminum by a Latosol

Abstract

A Latosol was used to examine the effect of ionic strength on the adsorption of aluminum (Al), as well as the competitive adsorption between Al and lead (Pb). The adsorption of Al shown very little ionic strength dependence on the change in supporting electrolyte concentrations (0.001 M, 0.01 M, and 0.1 M) of NaNO₃, which demonstrated that Al is adsorbed specifically by the soil. The observation that Al was adsorbed when the net surface charge is positive confirmed this opinion. The addition of 0.1 M Ca(NO₃)₂ resulted in a noticeable reduction of Al adsorption, a result of competition between Al and background salt, while this inhibitory effect gradually eliminated with the increase in pH. Competitive adsorption between Al and Pb at low concentration (0.1 mM) was noticeable at low pH and become less noticeable as pH increased from 3.5 to 5.5. Additionally, competition was enhanced throughout the pH range examined as the initial metal concentration was raised up to 1.0 mM. The observed affinity by the soil was Al>Pb consistent with the tendency of metal hydrolysis. The 0.1 mM Pb shown no influence on the 1.0 mM Al adsorption, and more important adsorption of Pb was not eliminated under the condition that the molar ratio of [Al]/[Pb] was as large as 10:1, which may reflect that some adsorption sites on surface of the soil show high selectivity for Pb.

Keywords:

• Adsorption
• Aluminum
• Lead
• Ionic strength
• Soil

Acknowledgments

The research was jointly supported by the National Natural Science Foundation of China (Project No. 40071046 and 49831005), and the China Ministry of Science and Technology (NKBRSF‐G1999011801‐3).