Preliminary trials on decontamination of Tributyltin (TBT) in a dredged sediment using combination of mechanochemical and electrokinetic techniques

Abstract

Purpose The objective of this research was to assess the effectiveness of a combined remediation strategy - electrokinetic treatment coupled with mechanochemical processes (ultrasound and grinding) and fluid recirculation - for the removal of tributyltin (TBT) from marine sediments. TBT is a persistent and highly toxic compound that resists most conventional remediation methods. The study aimed to validate the synergistic enhancement achieved by integrating these processes and to explore potential relationships between the removal of TBT, heavy metals, and other organic contaminants. Materials and methods A real marine sediment collected from a harbor in Spain was used in the study. The material was muddy (67% ≤ 63 μm; 30% ≤ 2 μm, and TOC 2.1%) and contained elevated concentrations of heavy metals. The total content of organotin compounds (OTs) was 21.1 µg kg -1 . The experimental design included several configurations with different parameters, combining mechanochemical treatments with Two‑Compartment Concentric Cells (TC) and One‑Compartment Flux Cells (FOC). TBT and its degradation products, dibutyltin (DBT) and monobutyltin (MBT), were quantified by gas chromatography coupled to a triple‑quadrupole mass spectrometer. Additionally, after each test, pH was measured, heavy metal concentrations were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES), and thermogravimetric analyses were performed. Results Ball milling of the real sediment did not significantly enhance TBT removal, whereas sonication achieved a 10–15% reduction in total organotin species. Overall, flow‑through experiments using FOC performed better than the two‑compartment cell (TC) trials. The treatment combining recirculation, electrical current, and ultrasound in the presence of citric acid as electrolyte (FOC‑1) achieved complete TBT removal. All electrochemical treatments promoted debutylation, converting TBT into DBT and MBT. The results also confirmed that near‑neutral pH conditions were the least effective for TBT removal. Interestingly, near neutral pH conditions resulted in higher retention of recalcitrant organic matter (OM), suggesting that TBT predominantly adsorbs onto these organic fractions. Conclusions Combining mechanochemical and electrokinetics techniques creates a strong synergy for the effective decontamination of marine sediments. The choice of electrolyte and the energy input are critical factors for achieving optimal results. Although the trials were preliminary, the findings indicate substantial potential for refining the conditions of these coupled technologies to improve the removal of both organotin compounds and heavy metals from contaminated environmental matrices.

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