Experimental study on remediation of low permeability Cu-Zn contaminated clay by vacuum enhanced leaching combined with EDTA and hydrochloric acid

Insight into the electrochemical process of EDTA-assisted soil washing effluent under alternating current

EDTA has been widely utilized as a chelating agent in soil heavy metal remediation, due to its strong coordination capability. Electrochemical deposition is a promising avenue to treat soil washing effluent. However, the impact of advanced electrochemical techniques on EDTA remains incompletely understood. Herein, we present a pioneering approach, utilizing a dual-chamber electrolytic cell and alternating current (AC) power supply. This approach achieves concurrent removal of M-EDTA while efficiently recovering heavy metal and recycling EDTA. Results demonstrate AC displays superior heavy metal removal capability for Cu, Pb, and Cd compare to direct current (DC), with EDTA decomposition mainly occurring in the anolyte. Substituting DC with AC and employing the dual-chamber electrolytic cell significantly enhances EDTA recovery efficiency from 47% to an impressive 96.8%. XPS and Raman spectra reveal an enhanced oxidative surface of the graphite anode under AC, which diminishes the decomposition of EDTA. Long-term experiments validate that this strategy boosts EDTA cyclability to 20 cycles with an outstanding 84% recovery efficiency and negligible electrode corrosion, surpassing the 8 cycles under the traditional strategy. This study innovatively combines cell design and electrochemical techniques, remarkably improving the reusability of EDTA and anode, offering valuable insights for chelate-related applications.

Core-shell design of UiO66-Fe3O4 configured with EDTA-assisted washing for rapid adsorption and simple recovery of heavy metal pollutants from soil

The coupling of washing with adsorption process can be adopted for the treatment of soils contaminated with heavy metals pollution. However, the complex environment of soil and the competitive behavior of leaching chemicals considerably restrain adsorption capacity of adsorbent material during washing process, which demands a higher resistance of the adsorbents to interference. In this study, we synthesized strongly magnetic, high specific surface area (573.49 m2/g) UiO66 composites (i.e., UiO66-Fe3O4) using hydrothermal process. The UiO66-Fe3O4 was applied as an adsorbent during the ethylene diamine tetraacetic acid (EDTA)-assisted washing process of contaminated soil. The incorporation of UiO66-Fe3O4 results in rapid heavy metal removal and recovery from the soil under low concentrations of washing agent (0.001 mol/L) with reduced residual heavy metal mobility of soil after remediation. Furthermore, UiO66-Fe3O4 can quickly recollect by an external magnet, which offers a simple and inexpensive recovery method for heavy metals from contaminated soil. Overall, UiO66-Fe3O4 configuration with EDTA-assisted washing process showed opportunities for heavy metals contaminated sites.

Coupling electrokinetic remediation with flushing using green tea synthesized nano zero-valent iron/nickel to remediate Cr (VI)

This study focuses on a flushing-electrokinetic remediation technology of hexavalent chromium from the chromium slag dump site. A suspension of nanoscale zero-valent iron/nickel fabricated from green tea (GT-nZVI/Ni), was employed as an eluent to degrade Cr (VI) and enhance the remediation effectiveness of a single EK. The removal efficiency of Cr (VI) was compared under different voltages, electrode spacings and pH values of the anolyte. The results demonstrated that the combined flushing and EK achieved a removal rate of Cr (VI) in the soil throughout all the experiments ranging from 83.08 to 96.97% after 120 h. The optimal result was obtained when the voltage was 28 V, the pH value of anolyte was 3 and the electrode spacing was 15 cm. The removal of Cr (VI) reached 91.49% and the energy consumption was 0.32606 kW·h·g-1. The underlying mechanisms responsible for the removal of Cr (VI) by GT-nZVI/Ni flushing-EK primarily involved electromigration, reduction and adsorption co-precipitation processes. The fractionation analysis of Cr (VI) concentration in the soil after remediation showed that the presence of GT-nZVI/Ni facilitated the conversion of Cr (VI) into oxidizable and residual states with low mobility and toxicity. The results of toxicity characteristic leaching procedure (TCLP) indicated that the leaching concentration of Cr (VI) was below 1 mg·L-1, complying with the standards set by the Environmental Protection Agency. Additionally, the phytotoxicity testing revealed that the germination index (GI) of the remediated soil reached 54.75%, indicating no potential harm to plants.

Application of bovine bone meal and oyster shell meal to heavy metals polluted soil: Vegetable safety and bacterial community

The development of efficient, environmentally friendly soil amendments is necessary in order to minimize the risk of metal contaminants (Cd, Pb, Cu, and Zn) to the soil ecosystem. As soil amendments, bovine bone meal (BM) and oyster shell meal (OS) reduced the mobility and bioavailability of metals primarily by increasing soil pH. Soil geochemical properties (pH, EC, CEC, Ca, P, and K) after amendment supplementation were more likely to affect metal migration than enzyme activity. Furthermore, BM and OS were found to suppress the Cd and Pb uptake by water spinach, keeping them below international standards for safe utilization. The protein and sugar content and peroxidase (POD) activity showed a significant negative correlation with the amount of metal in water spinach, whereas superoxide dismutase (SOD), ascorbate peroxidase (APX) activities and malondialdehyde (MDA) content exhibited a positive correlation with metal content in water spinach. We also found that BM and OS had less perturbation to phylum-level and genus-level bacterial composition during the remediation of heavy metals contaminated soil. Based on the above, we assume that BM and OS are eco-friendly soil amendments, which could improve soil nutrients contents, stabilize heavy metals and regulate bacterial community structure. Our research contributes to resource utilization of waste and holds promise for widespread application in current agricultural systems.