Solubility of metals in an anoxic sediment during prolonged aeration

This work was conducted to study the evolution of the solubility of selected metals during the aeration of an anoxic sediment. Batch experiments were carried out for 76 days with a metal-polluted dredged sediment. The pH, Eh and concentration of Al, Cu, Fe, Hg, Pb and Zn were periodically recorded. Results showed that during the early stages of aeration, the solubility of metals increased rapidly but was then followed by fast re-adsorption. As a consequence, after 14 days most of the metals excepted Cu and Zn were present at low or undetectable concentrations in solution. Re-adsorption of Zn was observed to be much slower during the first two weeks, whereas solubilisation of Cu increased gradually during months after land disposal. According to speciation calculations, Cu solubilisation was in part due to complexation in solution by carbonates. In the case of Hg, although complexation by dissolved organic matter (DOM) could be expected, re-adsorption was the dominant process. However, more knowledge about the behaviour of the DOM present in anoxic sediments is needed in order to make more quantitative statements about the mobility of heavy metals contained in dredged material.