Recycling of waste aluminum scraps to fabricate sulfidated zero-valent iron-aluminum particles for enhanced chromate removal

Massive waste aluminum scraps produced from the spent aluminum products have high electron capacity and can be recycled as an attractive alternative to materials based on zero-valent iron (Fe0) for the removal of oxidative contaminants from wastewater. This study thus proposed an approach to fabricate micron-sized sulfidated zero-valent iron-aluminum particles (S-Al0@Fe0) with high reactivity, electron selectivity and capacity using recycled waste aluminum scraps. S-Al0@Fe0 with a three-layer structure contained zero-valent aluminum (Al0) core, Fe0 middle layer and iron sulfide (FeS) shell. The rates of chromate (Cr(VI)) removal by S-Al0@Fe0 at pH 5.0‒9.0 were 1.6‒5.9 times greater than that by sulfidated zero-valent iron (S-Fe0). The Cr(VI) removal capacity of S-Al0@Fe0 was 8.2-, 11.3- and 46.9-fold greater than those of S-Fe0, zero-valent iron-aluminum (Al0-Fe0) and Fe0, respectively. The chemical cost of S-Al0@Fe0 for the equivalent Cr(VI) removal was 78.5% lower than that of S-Fe0. Negligible release of soluble aluminum during the Cr(VI) removal was observed. The significant enhancement in the reactivity and capacity of S-Al0@Fe0 was partially ascribed to the higher reactivity and electron density of the Al0 core than Fe0. More importantly, S-Al0@Fe0 served as an electric cell to harness the persistent and selective electron transfer from the Al0-Fe0 core to Cr(VI) at the surface via coupling Fe0-Fe2+-Fe3+ redox cycles, resulting in a higher electron utilization efficiency. Therefore, S-Al0@Fe0 fabricated using recycled waste aluminum scraps can be a cost-effective and environmentally-friendly alternative to S-Fe0 for the enhanced removal of oxidative contaminants in industrial wastewater.

Occurrence of iodinated contrast media (ICM) in water environments and their control strategies with a particular focus on iodinated by-products formation: A comprehensive review

Iodinated contrast media (ICM), one of the pharmaceutical and personal care products (PPCPs), are frequently detected in various water bodies due to the strong biochemical stability and recalcitrance to conventional water treatment. Additionally, ICM pose a risk of forming iodinated by-products that can be detrimental to the aquatic ecosystem. Consequently, effectively removing ICM from aqueous environments is a significant concern for environmental researchers. This article provides a comprehensive review of the structural characteristics of ICM, their primary source (e.g., domestic and hospital wastewater), detected concentrations in water environments, and ecological health hazards associated with them. The current wastewater treatment technologies for ICM control are also reviewed in detail with the aim of providing a reference for future research. Prior researches have demonstrated that traditional treatment processes (such as physical adsorption, biochemical method and chemical oxidation method) have inadequate efficiencies in the removal of ICM. Currently, the application of advanced oxidation processes to remove ICM has become extensive, but there are some issues like poor deiodination efficiency and the risk of forming toxic intermediates or iodinated by-products. Conversely, reduction technologies have a high deiodination rate, enabling the targeted removal of ICM. But the subsequent treatment issues related to iodine (such as I- and OI-) are often underestimated, potentially generating iodinated by-products during the subsequent treatment processes. Hence, we proposed using combined reduction-oxidation technologies to remove ICM and achieved synchronous control of iodinated by-products. In the future, it is recommended to study the degradation efficiency of ICM and the control efficiency of iodinated by-products by combining different reduction and oxidation processes.

Bi/mZVI Combined with Citric Acid and Sodium Citrate to Mineralize Multiple Sulfa Antibiotics: Performance and Mechanism

The oxidative mineralization of sulfanilamide drugs (SAs) using micro-size zero-valent iron (mZVI) cooperated with a citric acid buffer solution was evaluated. In this study SM2, SMX, and SD could be removed at 66%, 89%, and 83%, respectively, in a 0.5% Bi/mZVI+CA+NaCA system within 2 h. Based on our analysis, the produced ·OH could be ascribed from the complexation between citrate iron (Fe(II)[Cit]⁻) and the generated H₂O₂ resulting from the activation of O₂ on the mZVI surface in the Bi/mZVI+CA+NaCA system, further inducing the mineralization of antibiotics. The related possible degradation pathways were proposed. Two similar degradation pathways of SM2, SMX, and SD in the mixed liquid, including hydroxylation and SO₂ extrusion, were solved. Meanwhile, there was an additional proposed degradation pathway for SMX to be degraded more effectively, as reflected in the opening of the N-O bond on the benzene ring. Therefore, this work provides an experimental basis and theoretical support for the efficient treatment of antibiotic wastewater in real industry by using an iron-based method.

Enhanced reductive reactivity of zero-valent iron (ZVI) for pollutant removal by natural organic matters (NOMs) under aerobic conditions: Correlation between NOM properties and ZVI activity

While ubiquitous natural organic matters (NOMs) are capable of enhancing zero-valent iron (ZVI) performance under aerobic conditions, there is limited understanding of how the properties of NOMs affect the reactivity of ZVI towards contaminants removal. Here, the corresponding activity of ZVI under aerobic conditions was investigated in the presence of humic acid (HA), fulvic acid (FA), bovine serum albumin (BSA). It was found that three models of NOMs were all effective in promoting diatrizoate (DTA) reduction via depassivating ZVI. Interestingly, fast adsorption of NOM onto ZVI surface initially caused inconspicuous impact or visible inhibition on hydrophilic DTA reduction depending on their hydrophobicity. However, subsequent exposure of more reactive sites with high hydrophilicity arising from the detachment of surfaced NOM-associated iron oxide finally contributed to the enhanced consumption of Fe⁰ with the ability: HA > FA ≈ BSA, and 1-2 times increase in DTA removal kinetic rate following the order: HA > FA > BSA. It further revealed that there were two key factors in determining DTA removal under aerobic conditions, including the ability of NOMs to boost Fe⁰ consumption as contributed by their aromaticity degree and amino groups, and the hydrophobicity of NOMs to initially affect the property of ZVI surfaces.

Aerobic removal of iodinated contrast medium by nano-sized zero-valent iron: A combination of oxidation and reduction

The removal performance and mechanisms of diatrizoate (DTA), a typical iodinated contrast medium, from water by nano-sized zero-valent iron (nZVI) under aerobic conditions were investigated in this study. Reactive oxygen species (ROS) and transformation products were detected with electron spin resonance and liquid chromatography electrospray ionization tandem mass spectrometry, respectively. Furthermore, the effects of several operational parameters on DTA removal were illustrated. The results showed that nZVI had a much higher DTA removal ability compared to microscale zero-valent iron (mZVI) in the presence of oxygen. Moreover, the detection of ROS and I^- as well as the analysis of intermediate products suggested a combination of oxidation and reduction pathways for DTA removal by nZVI under aerobic conditions. Additionally, a high dosage of nZVI and acidic conditions led to the enhancement of DTA removal, while nZVI aging, as well as chloride and nitrate ions in the solution, had negative effects on the degradation of DTA by nZVI in the presence of oxygen.

Visible-light-induced degradation of polybrominated diphenyl ethers with AgI–TiO2

Visible-light-induced multi-electron transfer in debromination of polybrominated diphenyl ethers by AgI–TiO₂.