Interaction of lead(II) with sediment particles: a mercury microelectrode study

The usefulness of microelectrodes for trace metal speciation in the presence of particles is tested using anodic stripping voltammetry (ASV) at a mercury microelectrode. Discrimination between dissolved and particulate Pb(II) concentrations is carried out in the presence of particles from a freeze-dried sediment sample from Tejo (Portugal) estuary (zone not influenced by fresh water) as well as in the presence of SiO2 particles, chosen to mimic the major component of the sediment. Different sets of experiments were done with the sediment samples: before and after decomposition of organic matter and in the presence and absence of the dissolved major macroconstituents such as calcium, magnesium and chloride in order to assess the influence of organic matter and the competition of those ions for lead complexation with the sediment surface. In all situations, the ionic strength was kept constant at 0.70M and the pH=7.4±0.1. For the different experimental conditions used complexometric capacities for Pb(II) and average conditional surface complex formation constants were estimated from ASV voltammetric titration curves