Abstract

Annals of Environmental Science
Volume 1, February 2007, Pages 35-44

Effects of pH and Temperature on the Interaction of Pb(II) with Azraq Humic Acid Studied with Schubert's Ion Exchange Method

H. Baker and F. Khalili, Department of Chemistry, Al Al-Bayt University, Mafraq, and Department of Chemistry, University of Jordan, Amman, Jordan.

Received August 23, 2006; in final form November 30, 2006; Accepted January 2, 2007

The binding of Pb(II) to humic acid extracted from the Azraq Oasis was studied. The influence of temp-erature and pH was investigated at a constant ionic strength of 0.1. This analysis was done using Schubert's ion-exchange equilibrium method and its modified version. The data showed temperature and pH dependence. The derived conditional stability constants (log βn) for 1:1 and 1:2 lead-humate complexes were determined. It was noticed that the conditional stability constant (log β1) increased with increasing pH and temperature. The derived constants and their temperature dependences were used to calculate the corresponding thermodynamic parameters ΔG, ΔH and ΔS. The results indicate that the stability of these complexes derives from a very favorable entropy increase.