The effects of electrochemical pretreatment and curing environment on strength and leaching of stabilized/solidified contaminated sediment

Abstract

Stabilization and solidification (S/S) is known to improve the structural properties of sediment and reduce contaminant mobility, enabling the utilization of dredged contaminated sediment. Further reduction of contaminants (e.g., tributyltin (TBT) and metals) can be done using electrochemical treatment prior to S/S and could potentially minimize contaminant leaching. This is the first study on how electrochemical pretreatment affects the strength and leaching properties of stabilized sediments. It also investigates how salinity and organic carbon in the curing liquid affect the stabilized sediment.The results showed that the electrolysis reduced the content of TBT by 22% and zinc by 44% in the sediment. The electrolyzed stabilized samples met the requirements for compression strength and had a reduced surface leaching of zinc. Curing in saline water was beneficial for strength development and reduced the leaching of TBT compared to curing in fresh water. The results indicate that pretreatment prior to stabilization could be beneficial in reducing contaminant leaching and recovering metals from the sediment. The conclusion is that a better understanding of the changes in the sediment caused by electrochemical treatment and how these changes interact with stabilization reactions is needed. In addition, it is recommended to investigate the strength and leaching behavior in environments similar to the intended in situ conditions.

Keywords: Compressive strength; Curing; Dissolved organic carbon; Leaching; Salinity; Stabilization and solidification; TBT; Zn.

Fig. 1

Overview of the testing procedure, steps 1 to 6. Sample names used are marked in italics in each box. The number in sample names denotes the age of the stabilized and solidified (S/S) test piece, U-P denotes samples being cured in ultra-pure water, and NaCl denotes samples being cured in saline conditions. Electro denotes electrochemically pretreated samples, while original denotes untreated samples

Fig. 2

Average compressive strength for electrochemically pretreated stabilized (Electro S/S) and untreated stabilized (Original S/S) samples cured in ultra-pure (U-P) and saline (NaCl) water. The black dashed line corresponds to the compressive strength requirement of 140 kPa (Göteborgs hamn 2019)

Fig. 3

TBT leaching from electrochemically pretreated (electro) and untreated (original) stabilized samples cured in ultra-pure water, saline water, and saline water with dissolved organic carbon (DOC) in the NEN7375 surface diffusion leaching test. The curve e*(n) displays the measured cumulative leaching, and e(n) displays the derived cumulative leaching. The slope 0.5 is marked as a reference for identifying diffusion-controlled leaching (Environment Agency (2005))

Fig. 4

Mg leaching from electrochemically pretreated (electro) and untreated (original) stabilized samples cured in ultra-pure water and saline water in the NEN7375 surface diffusion leaching test. The curve e*(n) displays the measured cumulative leaching, and e(n) displays the derived cumulative leaching. The slope 0.5 is marked as a reference for identifying diffusion-controlled leaching (Environment Agency, (2005))

Fig. 5

Zn leaching from electrochemically pretreated (electro) and untreated (original) stabilized samples cured in ultra-pure water, brackish water, and saline water, as well as ultra-pure water with dissolved organic carbon (DOC) and saline water with DOC in the NEN7375 surface diffusion leaching test. The curve e*(n) displays the measured cumulative leaching, and e(n) displays the derived cumulative leaching. The slope 0.5 is marked as a reference for identifying diffusion-controlled leaching (Environment Agency (2005))

Fig. 6

Cu leaching from electrochemically pretreated (electro) and untreated (original) stabilized samples cured in ultra-pure water, brackish water, and saline water, as well as ultra-pure water with dissolved organic carbon (DOC) and saline water with DOC in the NEN7375 surface diffusion leaching test. The curve e*(n) displays the measured cumulative leaching, and e(n) displays the derived cumulative leaching. The slope 0.5 is marked as a reference for identifying diffusion-controlled leaching (Environment Agency (2005))

Fig. 7

Metals released (µg/kg DW) during the granular waste compliance L/S10 leaching test, leached in either ultra-pure water or saline water. Each uniquely colored bar is corresponding to either untreated (original) or electrochemically pretreated (electro) stabilized samples cured in ultra-pure water or saline water. The number on the horizontal axis denotes the number of days the samples have been curing when the leaching test was conducted