Sustainable remediation of Cr(VI)-contaminated soil by soil washing and subsequent recovery of washing agents using biochar supported nanoscale zero-valent iron.

Soil contamination by Cr(VI) has attracted widespread attention globally in recent years, but it remains a significant challenge in developing an environmentally friendly and eco-sustainable technique for the disposal of Cr(VI)-contaminated soil. Herein, a sustainable cyclic soil washing system for Cr(VI)-polluted soil remediation and the recovery of washing agents using biochar supported nanoscale zero-valent iron (nZVI-BC) was established. Citric acid (CA) was initially screened to desorb Cr(VI) from contaminated soil, mobilizing Cr from the highly bioaccessible fractions. The nZVI-BC exhibited superior properties for Cr(VI) and Cr(total) removal from spent effluent, allowing effective recovery of the washing agents. The elimination mechanism of Cr(total) by nZVI-BC involved the coordinated actions of electrostatic adsorption, reduction, and co-precipitation. The contributions to Cr(VI) reduction by Fe0, surface-bound Fe(II), and soluble Fe(II) were 0.6 %, 39.8 %, and 59.6 %, respectively. Meanwhile, CA favored the activity of surface-bound Fe(II) and Fe0 in nZVI-BC, enhancing the production of soluble Fe(II) to strengthen Cr(VI) removal. Finally, the recovered washing agent was proven to be reused three times. This study showcases that the combined soil washing using biodegradable chelant CA and effluent treatment by nZVI-BC could be a sustainable and promising strategy for Cr(VI)-contaminated soil remediation.

Demulsification of oily wastewater using a nano carbon black modified with polyethyleneimine.

In this work, nano carbon black was modified with polyethyleneimine (CB-PEI) under an ultrasonic field. The obtained product was used as a demulsifier to break oily wastewater. Morphology, structure, and chemical composition of CB-PEI were systematically analyzed. Bottle test was carried out to evaluate the influence of dosage, pH value and salinity on the demulsification efficiency of the emulsion. The results showed that the light transmittance of water phase (TSW) after the demulsification was 79.1% and corresponding oil removal rate (ORR) could reach up to 99.4% with 60 mg/L of CB-PEI at ambient temperature for 30 min. In addition, the possible demulsification mechanism was explored by dynamic interface tension (IFT), elasticity modulus, wettability, self-assemble of interfacial membrane, zeta potential and micrograph analysis. It indicated that CB-PEI had an appropriate amphiphilicity and good interfacial activity, which could improve it quickly transfer to the oil-water interface and result in the oil-water separation. The current work provides a simple method to prepare a demulsifier with excellent performance, so it has a good application prospect for the treatment of oil-water emulsions.

Demulsification of water-in-crude oil emulsion driven by a carbonaceous demulsifier from natural rice husks.

Removing emulsified water from a water-in-crude oil (W/O) emulsion is critically required prior to downstream processing in the petroleum industry. In this work, environmentally friendly and amphipathic rice husk carbon (RHC) demulsifier was prepared by a simple carbonization process in a muffle furnace using rice husks as starting materials. RHC was characterized by field-emission scanning electron microscope, energy dispersive spectrometer, Fourier transform infrared spectrometer, ultraviolet-visible spectrometer, powder X-ray diffraction, zeta potential and synchronal thermal analyzer. The factors such as dosage, temperature, settling time, pH value and salinity were systematically investigated. The results indicated that the dehydration efficiency (DE) reached as high as 96.99% with 600 mg/L of RHC for 80 min at 70 °C. RHC exhibited an optimal DE under neutral condition, but it was also effective under acidic and alkaline conditions. Also, it had an excellent salt tolerance. The possible demulsification mechanism was explored by interfacial properties, different treatment methods for RHC and microexamination. The demulsification of RHC is attributed to its high interfacial activity, oxygen-containing groups and content of silica. It indicates that RHC is an effective demulsifier for the treatment of the W/O emulsion.

Nanoscale silica-coated graphene oxide and its demulsifying performance in water-in-oil and oil-in-water emulsions.

In current work, GO@SiO2 nanocomposite was prepared by coating nanoscale silica onto graphene oxide (GO). GO@SiO2 was characterized with scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (IF-IR). Additionally, the demulsifying performance of GO@SiO2 was investigated by bottle test. The results showed that GO@SiO2 had a good demulsifying performance in both oil-in-water (O/W) and water-in-oil (W/O) emulsions. When the concentration of GO@SiO2 was 200 ppm in the O/W emulsion, the optimal light transmittance of aqueous phase (LTA) and corresponding oil removal rate (ORR) at room temperature could reach 86.9% and 99.48%, respectively. Also, GO@SiO2 had an excellent salt tolerance under acidic condition. Furthermore, GO@SiO2 also could demulsify the W/O emulsion, and the efficiency at 70 °C could reach 80.5% when the concentration was 400 ppm.