Abstract
In ex-situ washing, HCl, EDTA and H2O2 solutions can effectively extract heavy metals in river sediment. Nevertheless they often target different sediment components, possibly transforming metal species into more bioavailable and hence toxic ones. This study, in batch settings, investigated the influences of different types of washing agents (i.e. HCl, EDTA and H2O2) on metal (i.e. Cu and Zn) removal from contaminated river sediment, destroy or dissolution of sediment components, and transformation of metal fractions during chemical washing treatment. Additionally, bioavailability of these metals left in the washed sediment was assessed. Results showed that HCl obtained the highest Cu and Zn removal through destroying the reducible, oxidizable and residual sediment components. Meanwhile, it transformed metal fractions to acid extractable one, resulting in an increase in metal bioavailability. Thus, the feasibility of washing with HCl for sediment remediation shall be reconsidered due to the caused high metal bioavailability. EDTA was capable of removing metals via direct complexation of labile metal species and indirect dissolution of reducible and oxidizable sediment components, where the transformation of corresponding metal binding fraction may occur. H2O2 obtained the lowest total Cu and Zn removal, but it preferentially removed the oxidizable metal species by oxidizing sulfides in the sediment. The bioavailable levels of Cu and Zn in the sediment washed by EDTA or H2O2 seemed not increase. To maintain a good balance between labile metal species removal and avoiding increase of metal bioavailability, EDTA and H2O2 are promising additives for metal removal by sediment washing.
Highlights
Heavy metal contaminated sediment in rivers those are subject to anthropogenic discharges is a major problem from environmental perspective
To further investigate the performance of these washing agents (i.e. HCl, EDTA and H2O2) on different sediment components, with which metal species were associated, the collected sediment was pretreated to remove some metal fractions based on the modified European Community Bureau of Reference (BCR) three step sequential extraction procedure [24]
This study investigated Cu and Zn removal performance in river sediment by ex situ washing with three types of agents, i.e. HCl, EDTA, and H2O2
Summary
To provide more information for facilitating better engineering design of sediment washing treatment, the objective of this study is to investigate the influences of different often used types of washing agents (i.e. HCl, EDTA and H2O2) on the metal removal, destroy or dissolution of sediment components, as well as the transformation of metal fractions in sediment during chemical washing treatment
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