Removal of Chromium(VI) from Groundwater Using Oil Shale Ash Supported Nanoscaled Zero-valent Iron

Two-Dimensional Modeling of Nano Zero-Valent Iron Transport and Retention before and after Phosphate Adsorption

The mobility of nano zero-valent iron (nZVI) will greatly affect its practical application as a remediation material for contaminated groundwater. One-dimensional (1D) column tests are commonly used in previous work to study its migration behavior, but the two-dimensional (2D) test is still very limited. This study reports a novel research system to study the 2D transport and retention behavior of colloids and solutes, which includes a 2D model test setup and the corresponding image analysis method. The transport behaviors of methyl orange (MO), nZVI, and phosphate-loaded nZVI (PnZVI) are studied using this system. The results show that the research system can reasonably describe the tempo-spatial concentration distribution of colloids and solutes. After phosphate adsorption, the mobility of nZVI is enhanced due to the increase in negative surface charge, which implies a potential environmental risk of nZVI to facilitate contaminant transport. The migration of PnZVI is not significantly influenced by its density, which is faster than MO in the longitudinal direction. The range of the plume of PnZVI in the longitudinal direction is larger than that of MO, which implies that PnZVI has a stronger longitudinal dispersion than MO.

Advances in metal(loid) oxyanion removal by zerovalent iron: Kinetics, pathways, and mechanisms

Metal(loid) oxyanions in groundwater, surface water, and wastewater can have harmful effects on human or ecological health due to their high toxicity, mobility, and lack of degradation. In recent years, the removal of metal(loid) oxyanions using zerovalent iron (ZVI) has been the subject of many studies, but the full scope of this literature has not been systematically reviewed. The main elements that form metal(loid) oxyanions under environmental conditions are Cr(VI), As(V and III), Sb(V and III), Tc(VII), Re(VII), Mo(VI), V(V), etc. The removal mechanisms of metal(loid) oxyanions by ZVI may involve redox reactions, adsorption, precipitation, and coprecipitation, usually with one of these mechanisms being the main reaction pathway and the other playing auxiliary roles. However, the removal mechanisms are coupled to the reactions involved in corrosion of Fe(0) and reaction conditions. The layer of iron oxyhydroxides that forms on ZVI during corrosion mediates the sequestration of metal(loid) oxyanions. This review summarizes most of the currently available data on mechanisms and performance (e.g., kinetics) of removal of the most widely studies metal(loid) oxyanion contaminants (Cr, As, Sb) by different types of ZVI typically used in wastewater treatment, as well as ZVI that has been sulfidated or combination with catalytic bimetals.

Nanoscale Zero Valent Iron Supported by Biomass-Activated Carbon for Highly Efficient Total Chromium Removal from Electroplating Wastewater

The application potential of nanoscale zero valent iron (nZVI) in wastewater treatment is huge and has attracted a lot of attention. In this study, the composite material BC-nZVI was prepared by emulsion of nZVI and biomass-activated carbon (BC) under the mechanical agitation condition, and was characterized by SEM-EDX, XRD, XPS, and FTIR. The decontamination abilities of BC-nZVI were tested by the removal of total chromium (Cr) from electroplating wastewater. The results showed that the removal efficiencies of Cr in the electroplating wastewater by nZVI particles can be effectively improved when supported with BC, but cannot be improved in its storage capacity. The chemical adsorption process between the Cr and BC-nZVI is the main rate-limiting step in the removal of total Cr from wastewater, and multiple parameters such as dosage, pH, and initial concentration of Cr was found to affect the rate.