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Sorption of trace metasl (Cu, Pb, Zn) by suspended lake particles in artificial (0.05 M NaNO3) and natural (Esthwaite Water) freshwaters.

Research output: Contribution to journalJournal article

Published

Journal publication date21/02/1997
JournalColloids and Surfaces A: Physicochemical and Engineering Aspects
Journal number1-3
Volume120
Number of pages15
Pages205-219
Original languageEnglish

Abstract

The sorption of Cu, Pb, and Zn onto natural lake particles, suspended in 0.005 M NaNO3 solution and in a natural lake water (Esthwaite Water, Cumbria, UK), was studied as a function of pH and time in a series of laboratory experiments, under environmentally realistic conditions. The sorption of all three metals increased with increasing pH and reaction time (2 h and 7 days). In 0.005 M NaNO3 solution, the well-defined sorption edges spanned 2–2.5 pH units for Cu and Pb, and ≈ 4 pH units for Zn. In the natural lake water, the Cu sorption edge was broader and both Cu and Zn were less strongly sorbed. The binding stability decreased in the order Pb>Cu>Zn. Competitive adsorption onto surface sites appeared to be the main factor determining the observed sorption behaviour. Application of a macroscopic metal exchange model to the 7 day NaNO3 results enabled the surface site concentration to be estimated as 0.79 ± 0.07 mmol g−1. The modelling exercise suggested that an observed shift in the sorption edge of Zn, in the presence of Pb and Cu, was due to competition for surface sites. The experimental data are in good general agreement with field observations of trace metal behaviour in Cumbrian lakes. The almost total sorption of Pb by lake particles throughout the in-situ pH range is compatible with previous field measurements including trace metal budgets and residence times. Dissolved Zn concentrations in the lake are lower than predicted by the sorption experiments, but the lower lake concentrations are consistent with the previously observed scavenging of Zn by planktonic algae. Both the decreased sorption of Cu in the experiments with natural lake water, compared to that in NaNO3 solution, and the relatively small-scale removal of dissolved Cu by particles in the lake itself can partially be explained by humic complexation.