3.15. SOLUBILIZATION OF LEAD ION FROM SOLIDS BY
NTA
A major concern regarding the widespread introduction of strong chelating agents
such as NTA into aquatic ecosystems from sources such as detergents or electroplating
wastes is that of possible solubilization of toxic heavy metals from solids
through the action of chelating agents. Experimentation is required to determine
whether this may be a problem, but calculations are helpful in predicting probable
effects. The extent of solubilization of heavy metals depends upon a number of
factors, including the stability of the metal chelates, the concentration of the
complexing agent in the water, pH, and the nature of the insoluble metal deposit.
Several example calculations are given here.
Consider first the solubilization of lead from solid Pb(OH)2 by NTA at pH 8.00.
As illustrated in Figure 3.11, essentially all uncomplexed NTA is present as HT2- ion
at pH 8.00. Therefore, the solubilization reaction is