Effect of redox potential on heavy metals and As behavior in dredged sediments

Abstract

The effect of redox changes with respect to mobility of Cr, Cu, Pb, Zn, and As in five dredged sediments originating from disposal sites in the Netherlands was studied in the paper. An extraction procedure with a neutral unbuffered salt solution (0.01M CaCl2) was used to investigate the behavior of heavy metals and As in laboratory-based batch experiments conducted under oxidized and reduced redox conditions and carried out for 21 d. An increase in the redox potential (above +400 mV up to +503 mV) resulted in a rise of solubility of heavy metals in all sediments. However, at low redox potentials, an increase in As concentration was observed in the highly As-contaminated sediment. Mass balances were performed to follow the use of oxygen and the production of CO2, NO3-, SO42- and PO43-. An increase in redox potential has a large effect (40–80%) on the oxidation of reduced sulfur compounds to SO42-. Such increase in redox potential led to a solubilization of only about 1% of Cr, Cu, Pb, and Zn. Still, such low solubilization of these heavy metals leads to an increase of significance of the issue concerning ground and surface water quality.