Metal removal and associated binding fraction transformation in contaminated river sediment washed by different types of agents

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.

The influence of sediment properties and experimental variables on the efficiency of electrodialytic removal of metals from sediment

“…Increasing removal efficiencies appear to depend on differences in binding to the reducible and oxidisable fractions, suggesting that Zn bound in the oxidisable fraction is released at this stage. The difference in trends of metal partitioning influence of Pb and Zn may indicate that removal occurs from all fractions of the sediment during EDR, as observed in previous studies [37,46]. For Cu the influence of metal partitioning clearly indicates that removal is easier from the exchangeable and reducible fractions and may be removed from the exchangeable, reducible, oxidisable and residual fractions in that order to a higher degree than is the case for Pb and Zn.…”

Content of nutrients, trace elements, and ecotoxicity of sediment cores from Rożnów reservoir (Southern Poland)

“…In the aquatic environment, there is evidence that eutrophication could have an influence on content of trace elements in the bottom sediments. Changes in pH and redox conditions in the water–sediment system lead to the release of metals bound to exchangeable carbonate and easily reducible phases in the sediment (Helios-Rybicka and Wilson 2000; Kumar et al 2015; Wang et al 2017). Moreover, the high content of organic matter and nitrogen are considered as important agents for the assessment of the eutrophication rate.…”

Recent Progress on Ex Situ Remediation Technology and Resource Utilization for Heavy Metal Contaminated Sediment

“…Moreover, the additives of chelators (e.g., EDDS, EDTA, organic acid (AA and CA)) have been extensively studied and applied to increase the solubility of heavy metals [ 7 ]. Particularly, EDTA is the most efficient extractant because it can form very stable complexes with metals [ 24 ] but a significant part of metal-EDTA complexes remain in the soil/sediment due to adsorption on the mineral surface [ 25 ]. In addition, surfactants (e.g., rhamnolipid, HS) can enhance the solubilization diffusion and desorption of metal contaminants in contaminated sediments [ 26 , 27 ]; the mechanism of heavy metal removal is that of biosurfactant molecules complex with metals and transfer to the solution phase in the form of aggregation into micelles (spherical bilayer with a diameter less than 50 nm) [ 28 ].…”