Heavy metal / polyacid interaction : an electrochemical study of the binding of Cd(II), Pb(II) and Zn(II) to polycarboxylic and humic acids

Polyelectrolyte effects in the interaction of heavy metal ions with model polycarboxylic acids have been described, in order to establish the relevance of these effects in the interaction of heavy metal ions with naturally occurring humic and fulvic acids. The model systems consisted of Cd(II), Pb(II) or Zn(II) nitrates in combination with partially neutralized poly(acrylic acid), poly(methacrylic acid) or partially esterified poly(methacrylic acid). Metal binding characteristics have been investigated as a function of the metal/polyion ratio, the degree of neutralization, and the concentration of added 1:1 salt, and have been determined applying normal pulse polarography, conductometry and potentiometry. Covalent and electrostatic contributions to the binding have been disentangled, and discussed in terms of intrinsic binding constants and effective polyion charge densities. It is concluded that polyelectrolyte effects play an important role in heavy metal/humic acid systems at natural pH levels.