Environmental assessment of contaminated marine sediments treated with solidification agents: Directions for improving environmental assessment guidelines

Remediation of sediments contaminated by harmful heavy metals using aluminum sulfate: Sustainable approach for practical applications

Chemical washing could be suitable for the remediation of marine sediments contaminated with harmful heavy metals. Considering green and sustainable remediation (GSR), the application of aluminum sulfate (AS) is intended to reduce the costs and environmental impacts. We extracted harmful heavy metals from manganese nodules using an ion exchange mechanism that occurs when AS dissociates in water. AS in the range from 2 % to 5 % was used. The remediation efficiencies using 5 % AS were found to be the highest, at 91.8 % for Ni and ≥ 100 % for other harmful heavy metals. The Pearson's coefficient evaluation showed that increasing elapsed time did not significantly affect the extraction of harmful heavy metals. Pollutants in post-processing products may not cause secondary pollutions if solidification/stabilization and additional treatments are used. Our results can serve as fundamental data for the actual remediation processes using AS not only for deep-sea mining tailings but also contaminated marine sediments.

Solid waste material reuse analysis: filling the road subgrade with riverway silt and sediment

This study proposes to explore solid waste material (SWM) reuse of the riverway silt and sediment, and examines the impacts of chemical composition on road construction through sensitivity analysis. Considering the characteristics of silt mixture, it is necessary to investigate the modified materials to improve the mechanical feasibility for subgrade filling. In this study, the water content of riverway silt and sediments was found to be important to determine the selection and content of modified materials. Specifically, the riverway silt and sediment with low water content could be improved effectively with 6 to 8% lime. Compared to the original sludge, the improved mixture had better particle size and permeability, and the carrying capacity also grew 2 to 3 times. On the other hand, the reuse of riverway silt and sediment with high water content over 40% was provided with multiple schemes. Among them, the modification scheme of construction waste or garbage slag showed well mechanical properties and environmental benefits in the sensitivity analysis, especially for the high water content sludge modified by the mixture of garbage slag and lime. The California bearing ratio (CBR_2.5) was 2 to 5 times higher than the original silt, which would promote the reuse of multiple solid wastes in road construction. Finally, this study puts forward engineering measures to prevent heavy metals from polluting the water and soil environment by silt-improved soil roadbeds, and the improved riverway silt and sediment roadbeds were proved to be safe and reliable for the environment during service.

Physico-mechanical and microstructural behaviour of high-water content zinc-contaminated dredged sediment treated with integrated approach PHDVPSS

This paper uses a new integrated method, namely PHDVPSS, which utilizes vacuum pressure (VP) coupled with prefabricated horizontal drain along with solidification/stabilization (SS) for the effective treatment of high-water content dredged contaminated sediment (DCS). This study sought to evaluate the physico-mechanical and microstructural behaviour of high-water content DCS treated with MgO-GGBS (MG) and Portland cement (PC) as PHDVPSS binders and compared to the traditional Portland cement solidification/stabilization (SS-PC) method. Physico-mechanical and microstructural characteristics of the DCS treated with the PHDVPSS method were evaluated by performing a number of tests such as unconfined compressive strength (UCS), toxicity characteristics of the leaching process (TCLP), pH, X-ray diffraction (XRD) and scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDS). Treatment results showed that the DCS treated with the MG binder in the PHDVPSS method showed superior performance in terms of a significant reduction in the water content and leachability of zinc (Zn) along with higher mechanical strength and dry density of the samples compared to the traditional SS-PC method. After 56-day curing time, VP-MG cases showed 17.6 % and 50 % higher dry density values, resulting in 2.5 and 17.3 times higher UCS values than VP-PC and SS-PC cases, respectively. In contrast, VP-MG cases showed lower pH values than those of VP-PC and SS-PC cases. Moreover, VP-MG cases exhibited 37.5 % and 44.3 % lower leached Zn concentration during a TCLP test than VP-PC cases and SS-PC cases, respectively. XRD and SEM-EDS tests showed that more voluminous hydration products were produced in the VP-MG cases, which in turn produced a dense stabilized matrix and significantly reduced the leachability of zinc.

Evaluation of the Anthropogenic Metal Pollution at Osisko Lake: Sediments Characterization for Reclamation Purposes

The anthropogenic pollution of lake ecosystems by human activities (e.g., mining industries) is recognized as a serious issue. The Osisko urban lake located in Rouyn-Noranda (Quebec, Canada) was used partially as a waste disposal facility for many decades, causing a heavy pollution. The main undertakings of this study are (i) assessing the mineralogical and geochemical properties of lake Osisko sediments, and (ii) studying the pollution that occurred within lake water due to the sediments’ reactivity. Water and sediments across the lake were collected in different sensitive locations. Within the sediment samples, two parts were distinguished: a small layer of black vase over grey sediments. The black vase resembled organic matter while the gray sediment seemed close to clean lake sediments. The collected samples were characterized for their physical (particle size distribution, specific gravity and specific surface area), chemical (minor and major elements as well as total sulfur and carbon) and mineralogical (X-ray diffraction and scanning electron microscope) properties. Additionally, the reactivity of sediments was studied using weathering cells to quantify chemical species leaching and their releasing rates. The results showed that the vase was the only contaminated part with high concentrations of sulfur and metals such as copper, zinc and iron. Geochemical data showed that the composite sample and the vase potentially cause contaminated acid drainage if they are exposed to atmospheric conditions. Indeed, the pH values of the leachates from both samples were between 4 and 6, while those corresponding to sediments remained around circumneutral values. Quantitatively, the contaminant release from the tested samples was variable. Indeed, the Fe cumulative concentrations were around 200, 80 and 20 mg/kg for the vase, composite and sediment samples, respectively. Similarly, the Zn cumulative concentrations were around 4500, 4200, and below the detection limit for vase, composite and sediment samples, respectively. The same tendency was observed for Cu, S, and Fe. Thus, sediments within Osisko lake present a risk for water contamination if they are resuspended or dredged out of the lake. Consequently, they should be stabilized before their disposal. The samples’ high Cu contents also offer the possibility of their reprocessing.

An Ex-Situ Immobilization Experiment with Zn, Pb, and Cu in Dredged Marine Sediments from Bohai Bay, China

The remediation of dredged marine sediments contaminated by metals has drawn increasing attention globally. Immobilization was regarded as a promising method for reducing adverse impacts on marine ecosystems. In this study, kaolinite and limestone were used as amendments to immobilize Zn, Pb, and Cu in dredged marine sediments, which were collected from the coastal zone adjacent to Tianjin Port in Bohai Bay. The sequential extraction procedure was applied to identify the mobility of metals and, further, to evaluate the immobilization effect of the amendments. The physical–chemical properties of the sediments, such as the pH, electrical conductivity (EC), salinity, and total organic carbon (TOC), were also measured to better understand their influence on the three metals’ mobility. The results of the sequential extraction procedure indicated that the mobile fractions of the metals were converted into relatively stable fractions because of the two amendments. In addition, the EC, salinity, and TOC decreased moderately, while no obvious variations in the pH of the sediments were observed with the addition of kaolinite and limestone. It was confirmed that both kaolinite and limestone can effectively reduce the mobility and bioavailability of metals, particularly Zn, and limestone generally has a better immobilization effect, compared with kaolinite.