The specific reactive surface area of granular zero-valent iron in metal contaminant removal: Column experiments and modelling

Antarctic heavy metal pollution and remediation efforts: state of the art of research and scientific publications

In Antarctica, human activities have been reported to be the major cause of the accumulation of heavy metal contaminants. A comprehensive bibliometric analysis of publications on heavy metal contamination in Antarctica from year 2000 to 2020 was performed to obtain an overview of the current landscape in this line of research. A total of 106 documents were obtained from Scopus, the largest citation database. Extracted data were analysed, and VOSviewer software was used to visualise trends. The result showed an increase in publications and citations in the past 20 years indicating the rising interest on heavy metal contamination in the Antarctic region. Based on the analysis of keywords, the publications largely discuss various types of heavy metals found in the Antarctic water and sediment. The analysis on subject areas detects multiple disciplines involved, wherein the environmental science was well-represented. The top countries and authors producing the most publication in this field were from Australia, China, Brazil and Chile. Numerous efforts have been exercised to investigate heavy metal pollution and its mitigation approaches in the region in the past decades. This paper not only is relevant for scholars to understand the development status and trends in this field but also offers clear insights on the future direction of Antarctic heavy metal contamination and remediation research.

Selenium (Se) recovery for technological applications from environmental matrices based on biotic and abiotic mechanisms

Selenium (Se) is an essential element with application in manufacturing from food to medical industries. Water contamination by Se is of concern due to anthropogenic activities. Recently, Se remediation has received increasing attention. Hence, different types of remediation techniques are listed in this work, and their potential for Se recovery is evaluated. Sorption, co-precipitation, coagulation and precipitation are effective for low-cost Se removal. In photocatalytic, zero-valent iron and electrochemical systems, the above mechanisms occur with reduction as an immobilization and detoxification process. In combination with magnetic separation, the above techniques are promising for Se recovery. Biological Se oxyanions reduction has been widely recognized as a cost-effective method for Se remediation, simultaneously generating biosynthetic Se nanoparticles (BioSeNPs). Increasing the extracellular production of BioSeNPs and controlling their morphology will benefit its recovery. However, the mechanism of the microbial production of BioSeNPs is not well understood. Se containing products from both microbial reduction and abiotic methods need to be refined to obtain pure Se. Eco-friendly and cost-effective Se refinery methods need to be developed. Overall, this review offers insight into the necessity of shifting attention from Se remediation to Se recovery.

Characterization methods of zerovalent iron for water treatment and remediation

Appropriately selecting methods for characterizing the reaction system of zerovalent iron (ZVI) favors its application for water treatment and remediation. Hence, a survey of the available ZVI characterization techniques used in laboratory and field studies are presented in this review for clarifying the characteristic properties, (in-situ) corrosion processes, and corrosion products of ZVI system. The methods are generally classified into four broad categories: morphology characterization techniques, (sub-)surface and bulk analysis mainly via the spectral protocols, along with the (physio)electrochemical alternatives. Moreover, this paper provides a critical review on the scopes and applications of ZVI characterization methodologies from several perspectives including their suitable occasions, availability, (semi-)quantitative/qualitative evaluations, in/ex-situ reaction information, advantages, limitations and challenges, as well as economic and technical remarks. In particular, the characteristic spectroscopic peak locations of typical iron (oxyhydr)oxides are also systematically summarized. In view of the complexity and variety of ZVI system, this review further addresses that different characterization methods should be employed together for better assessing the performance and mechanisms of ZVI-involved systems and thereby facilitating the deployment of ZVI-based installations in real practice.

Combined Effect of Weak Magnetic Fields and Anions on Arsenite Sequestration by Zerovalent Iron: Kinetics and Mechanisms

In this study, the effects of major anions (e.g., ClO₄^-, NO₃^-, Cl^-, and SO₄^2-) in water on the reactivity of zerovalent iron (ZVI) toward As(III) sequestration were evaluated with and without a weak magnetic field (WMF). Without WMF, ClO₄^- and NO₃^- had negligible influence on As(III) removal by ZVI, but Cl^- and SO₄^2- could improve As(III) sequestration by ZVI. Moreover, the WMF-enhancing effect on As(III) removal by ZVI was minor in ultrapure water. A synergetic effect of WMF and individual anion on improving As(III) removal by ZVI was observed for each of the investigated anion, which became more pronounced as the concentration of anion increased. Based on the extent of enhancing effects, these anions were ranked in the order of SO₄^2- > Cl^- > NO₃^- ≈ ClO₄^- (from most- to least-enhanced). Furthermore, the inhibitory effect of HSiO₃^-, HCO₃^-, and H₂PO₄^- on ZVI corrosion could be alleviated taking advantage of the combined effect of WMF and SO₄^2-. The coupled influence of anions and WMF was associated with the simultaneous movement of anions with paramagnetic Fe²⁺ to keep local electroneutrality in solution. Our findings suggest that the presence of anions is quite essential to maintaining or stimulating the WMF effect.

A permeable reactive barrier (PRB) media sequence for the remediation of heavy metal and hydrocarbon contaminated water: A field assessment at Casey Station, Antarctica

A field trial was conducted at Casey Station, Antarctica to assess the suitability of a permeable reactive barrier (PRB) media sequence for the remediation of sites containing both hydrocarbon and heavy metal contamination. An existing PRB was modified to assess a sequence consisting of three sections: (i) Nutrient release/hydrocarbon sorption using ZeoPro™ and granular activated carbon; (ii) Phosphorus and heavy metal capture by granular iron and sand; (iii) Nutrient and excess iron capture by zeolite. The media sequence achieved a greater phosphorus removal capacity than previous Antarctic PRB configurations installed on site. Phosphorus concentrations were reduced during flow through the iron/sand section and iron concentrations were reduced within the zeolite section. However, non-ideal flow was detected during a tracer test and supported by analysis of media and liquid samples from the second summer of operation. Results indicate that the PRB media sequence trialled might be appropriate for other locations, especially less environmentally challenging contaminated sites.

Metallic iron for environmental remediation: A review of reviews

This article critically evaluates recent review articles on using metallic iron (Fe(0)) for environmental remediation in order to provide insight for more efficient Fe(0)-based systems. The presentation is limited to peer-reviewed articles published during 2014 and 2015, excluding own contributions, dealing mostly with granular Fe(0). A literature search was conducted up to June 15th 2015 using Science Direct, SCOPUS, Springer and Web of Science databases. The search yielded eight articles that met the final inclusion criteria. The evaluation clearly shows that seven articles provide a narrative description of processes occurring in the Fe(0)/H20 system according to the concept that Fe(0) is a reducing agent. Only one article clearly follows a different path, presenting Fe(0) as a generator of adsorbing (hydroxides, oxides) and reducing (Fe(II), H/H2) agents. The apparent discrepancies between the two schools are identified and extensively discussed based on the chemistry of the Fe(0)/H20 system. The results of this evaluation indicate clearly that research on 'Fe(0) for environmental remediation' is in its infancy. Despite the current paucity of reliable data for the design of efficient Fe(0)-based systems, this review demonstrates that sensible progress could be achieved within a short period of time, specific recommendations to help guide future research are suggested.