Drop amalgam voltammetric study of lead complexation by natural inorganic ligands in a salt lake

Abstract

A study of inorganic complexation of lead using drop amalgam voltammetry is described. The study has been carried out in simulated salt lake water and at ionic strength of 7.35 M, the predetermined ionic strength of Lake Katwe. The complexation of lead with the simple ligands (Cl^-, CO₃^2-) created anodic waves and the shifts of the peak potentials of lead with the introduction of varying concentrations of each ligand measured. The analysis of these shifts furnished information about the stability constants of the lead complexes which was employed in the calculation of lead species distribution. These mathematical treatments revealed the existence of two lead chloride complexes with corresponding stability constants log b₁ = 0.88, log b₂ = 2.95; and two carbonate complexes with log b₁ = 8.50 and log b₂ = 9.62. The results obtained indicate that in Lake Katwe water (25 ^oC, carbonate alkalinity = 0.11 M, pH 11) approximately 0.00% of total inorganic lead exists as the free ion, and at chloride concentration of 1.8 M only 1.3% of lead exists as the free ion.

KEY WORDS: Drop amalgam, Lead speciation, Stability constants, Lake Katwe, Voltammetric complexation, Species distribution

Bull. Chem. Soc. Ethiop. 2004, 18(1), 91-100.