Speciation of cadmium mixed ligand complexes in salt water lakes

  • John L. Kituyi Moi University, Department of Chemistry, Box 1125, Eldoret, Kenya
  • Henry M. Thairu Jomo Kenyatta University of Agriculture and Technology, Box 62000, Nairobi, Kenya
  • Justin Irina Commission for Higher Education, Box 48823, Nairobi, Kenya
  • Knut H. Schroder University of Trondheim, Department of Chemistry, N-7055 Trondheim, Norway
Keywords: Heavy metals, Hanging drop electrode, Amalgam voltammetry, Speciation, Cadmium mixed ligand complexes

Abstract

Amalgam voltammetry has been used to study heavy metal interaction in model lake water in KNO3 at 23 oC at concentration levels of genuine lake water. The hanging drop amalgam electrode was prepared in situ before exchanging the medium for the sample solution. Half-wave potentials at two metal ion concentrations were measured, one at the actual concentration in the lake while the other at a much lower one. The experimentally determined shifts in half-wave potentials are used to compute several formation constants.

At the natural [CO32-] of 0.5 M in the lake, the main contributor to the speciation of cadmium is [Cd(CO3Cl2)]2-. At high [Cd2+], the DPASV detects the presence of free Cd2+ ions, hence, potential polluting effect, while the amalgam reports [Cd(CO3)2Cl)]3- to be dominant above [CO32-] = 0.8 M. There is a variation in the number of complexes detected, their stabilities and percentage distribution in the two methods. Cd2+ ion concentration also affects the number of complexes formed and their stabilities.

 

KEY WORDS: Heavy metals, Hanging drop electrode, Amalgam voltammetry, Speciation, Cadmium mixed ligand complexes

 

 

Bull. Chem. Soc. Ethiop. 2003, 17(1), 85-94.

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eISSN: 1726-801X
print ISSN: 1011-3924