Remediation of Cd-contaminated soil by electrokinetics coupled with the permeable reactive barrier from immobilized yeast

Decoding the divalent cation effect on sulfidation of zero-valent iron: Phase evolution and FeSx assembly

The decontamination ability of sulfidated zero-valent iron (S-ZVI) can be enhanced by the effective assembly of iron sulfides (FeSx) on neglected heterogeneous surfaces by liquid-phase precipitation. However, S-ZVI preparation with the usual pickling is detrimental to orderly interfacial assembly and leads to an imbalance between electron transfer optimization and electron storage. In this work, S-ZVI was prepared in solutions containing trace divalent cation, and it removed Cr(VI) up to 323.25 times higher than ZVI. This result is achieved by surface sites protonation of divalent cations regulating the phase evolution on the ZVI surface and inducing FeSx chemical assembly. Regulation of divalent cation and S(-II) content further promotes FeSx targeted assembly and reduces electron storage consumption as much as possible. The barrier for FeSx assembly is found to lie at the ZVI interface rather than in the deposition between FeSx. Chemical assembly at heterogeneous interfaces is a prerequisite for the ordered assembly of FeSx. In addition, S-ZVI prepared in simulated groundwater showed extensive preparation pH and universality for remediation scenarios. These findings provide new insights into the development of in-situ sulfidation mechanisms with particular implications for S-ZVI applied to soil and groundwater remediation by the regulation of heterogeneous interfacial assembly.

New-style electrokinetic-adsorption remediation of cadmium-contaminated soil using double-group electrodes coupled with chitosan-activated carbon composite membranes

Global soil cadmium (Cd(II)) contamination threatens the soil environment, food safety, and human health. Conventional electrokinetic remediation (EKR) and enhancement methods usually operate in strong electric fields, leading to strong side reactions and uneven removal. In this work, to remove Cd(II) from soil effectively in a low-voltage electric field, a new-style electrokinetic-adsorption remediation using double-group electrodes coupled with chitosan-activated carbon composite membranes (DE-EKR-CAC) was developed. Chitosan-activated carbon (CAC) composite membranes were synthesized for easy recovery and reuse of adsorbents. The effects of pH, contact time, initial concentration, and foreign ions on the removal of Cd(II) by the CAC composite membranes were determined. The CAC composite membranes performed well except in a strongly acidic environment (pH = 2.0). The soil pH varied between 3.4 and 5.0 in DE-EKR-CAC, where the CAC composite membranes were applicable. High concentrations of Ca2+ interfered with the adsorption of Cd(II), which means that the selectivity of CAC composite membranes for Cd(II) is not high enough. The Langmuir (R2 = 0.999) and pseudo-second-order kinetic (R2 = 1.0) models revealed the monolayer coverage and chemisorption mechanism, and the maximum adsorption capacity was 40.81 mg/g. Furthermore, SEM, FTIR, and XPS analyses suggest that physical adsorption, complexation of oxygen-containing functional groups, chelation of amino groups, and ion exchange are potential mechanisms for the adsorption of Cd(II) on CAC. DE-EKR-CAC performed better than the group remediated with one set of electrodes, with higher removal efficiencies and more uniform removal. The lowest energy consumption was 3.33 kWh/m3, which is lower than other enhancement methods. Separation of CAC composite membranes from soil is easy, and reuse performance is good. DE-EKR-CAC provides a potential option for Cd(II) removal from soil because of its better performance using low-voltage direct current, low energy consumption, and ease of recycling the adsorbent.