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With the development of industrial activities and the agricultural and mining industries, farmland soils are facing serious problems related to heavy metal contamination, especially cadmium (Cd) and arsenic (As) contamination. In this study, two industrial by-products, phosphogypsum (PG) and red mud (RM), were modified by lanthanum (La) impregnation to form a new composite (L-PR) to investigate the adsorption performance of Cd(II)/As(V) in both single and binary systems. The adsorption mechanisms of Cd(II)/As(V) on L-PR were analyzed using SEM, XRD, FTIR, and XPS. The passivation effect of L-PR on the Cd-As composite contaminated soil was confirmed through a soil cultivation experiment. The adsorption experiments revealed that L-PR showed superior adsorption capabilities for Cd(II) and As(V) compared to PG and RM. Additionally, L-PR was found to be less affected by changes in pH. The kinetic studies indicated that Cd(II) and As(V) adsorption by L-PR followed the second-order kinetic model most accurately. Isothermal adsorption experiments revealed that the adsorption of Cd(II) by L-PR was more in accordance with the Freundlich model, while As(V) was more in accordance with the Langmuir model. The mechanisms of Cd(II) and As(V) adsorption on L-PR involved electrostatic attraction, ion exchange, complexation, and precipitation. The adsorption of Cd(II) is dominated by complexation and precipitation, and the adsorption of As(V) is dominated by ion exchange and complexation. Soil cultivation experiments showed that L-PR significantly reduced the available Cd and As concentrations in soil by 86.01% and 27.80%, respectively, and it could induce the transformation of non-stable Cd(II)/As(V) to the more stable residual. In summary, L-PR exhibits facile preparation, excellent adsorption performance, and is capable of simultaneously removing Cd(II) and As(V) from aqueous solutions while immobilizing these contaminants in soil. These remarkable attributes made it a highly promising alternative for the simultaneous treatment of various toxic metal contaminants. [ABSTRACT FROM AUTHOR]

Purpose: As one of the most critical sources of pollution from detrimental elements, smelting slags pose a huge threat to the surrounding environment. A comprehensive environmental risk evaluation of slag is beneficial to propose more rational suggestions on their management and treatment. Therefore, the aim of this study was to assess the potential environmental hazard of toxic elements in non-ferrous metal slags from Guangxi (GX) and Yunnan (YN) by comparing the leaching behavior and geochemical characteristics. Methods: The pHstat and semi-dynamic leaching tests were used to study the leaching behavior of metal(loid)s at different pH and simulate local rainfall, respectively. The potential mobility, bioavailability, and bioaccessibility of metal(loid)s were determined through a series of extraction experiments. In addition, a combination of leachability, mobility, bioavailability, and bioaccessibility is used to explore the potential environmental risk implications of slags. Results: The release of metal(loid)s showed a strong dependence on pH. Most metal(loid)s release decreased with increasing pH, while some metal(loid)s release increased under alkaline conditions. Variation in metal(loid)s concentrations induced by pH changes is due to the dissolution/precipitation and the adsorption/desorption processes of minerals. The results of the simulated rainfall indicate different trends in metal(loid)s release due to the differences in slag composition, rainfall, and pH between the two regions. The leaching of metal(loid)s decreases with increasing rainfall, which is due to the depletion of the slag surface. The mobility, bioavailability, and bioaccessibility of Cd, Cu, and Zn in GX were higher than in YN, while As and Pb were lower than in YN. These metal(loid)s are more likely to enter the environment and pose a greater threat to plants and humans. The correlation analysis showed that the exchange and carbonate-bound fractions of metal(loid)s have a positive effect on their bioavailability and bioaccessibility. Conclusion: The results show that among the elements studied, the potential environmental risks of Cd, Cu, and Zn in GX are greater than those of YN, while As and Pb are less than those of YN. The toxic elements in the slags may pose a potential risk to the surrounding environment. [ABSTRACT FROM AUTHOR]

Constructed wetlands are an environmentally friendly and economically efficient sewage treatment technology, with fillers playing an important role in treatment processes. However, traditional wetland fillers (e.g. zeolite) are known to be imperfect because of their low adsorption capacity. In this paper, the adsorbent sodium titanate nano fillers (T3-F) was synthesized as an alternative to traditional filler with sodium titanate nanofibers (T3) as the raw material, epoxy adhesive as the adhesive agent and NH 4 HCO 3 as the pore-making agent. The properties of T3-F were characterized by powder X-ray diffraction (XRD), scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX), porosity. The effect of different parameters such as pH, co-existing ions, contact time, initial metal ion concentrations and temperature was investigated for heavy metal adsorption. The results showed that the adsorption of heavy metal by T3-F followed the pseudo-second-order kinetic and Langmuir isotherm models. The maximum adsorption capacities for Cu2+, Pb2+, Zn2+, Cd2+ were about 1.5–1.98 mmol/g, which were 4–5 times that of zeolite, the traditional commonly used filler. Moreover, T3-F could entrap toxic ions irreversibly and maintain structural stability in the adsorption process, which solved the issue of secondary pollution. In the presence of competing ions, the adsorption efficiency for Pb2+ was not reduced significantly. Adsorption was strongest at high pH. From the results and characterization, an adsorption mechanism was suggested. This study lays a foundation for the practical application of T3-F as a constructed wetland filler in the future. Image 1 • A new constructed wetland fillers was prepared by sodium titanate nanofibers. • Fillers show excellent adsorption ability towards Cu2+, Pb2+, Zn2+, Cd2+ ions. • Adsorption occurs through ion exchange mechanism. • Fillers could entrap toxic ions irreversibly. The filler can effectively adsorb heavy metal ions and permanently trap toxic cations in the fiber. [ABSTRACT FROM AUTHOR]

MXenes are considered as an emerging class of two-dimensional (2D) adsorbent for various environmental applications. In this work, two different morphologies of Ti 3 C 2 T x MXene (multilayer (ML-Ti 3 C 2 T x) and delaminated titanium carbide (DL-Ti 3 C 2 T x)) were prepared through mild in situ HF etching and further delamination. The structural differences between the two were explored with a focus on their effects on the performance and mechanism of removing heavy metals from water. In comparison to ML-Ti 3 C 2 T x , DL-Ti 3 C 2 T x had more oxygen-containing functional groups, higher specific surface area (19.713 vs. 8.243 m2/g), larger pore volume (0.135 vs. 0.040 cm3/g), higher maximum Pb(II) adsorption capacity (77.0 vs. 56.68 mg/g), but lower maximum Cu(II) adsorption capacity (23.08 vs. 55.46 mg/g). Further investigation revealed that the removal of Pb(II) by the MXenes was mainly controlled through electrostatic attraction and surface complexation mechanisms, while Cu(II) was removed mainly through surface reduction by Ti-related groups. Because delamination of ML-Ti 3 C 2 T x increased the surface area and surface functional groups, DL-Ti 3 C 2 T x became a better sorbent for Pb(II) in water. During sonication, however, delamination inevitably led to partial oxidation of Ti 3 C 2 T x nanosheets and thus weakened the reducing ability of DL-Ti 3 C 2 T x for Cu(II) in water. Nevertheless, both ML- and DL-Ti 3 C 2 T x not only exhibited excellent heavy metal adsorption capacity under different solution conditions, but also showed good reusability. Findings of this study indicate that Ti 3 C 2 T x MXenes are promising adsorbents for treating heavy metal pollutants in water. [Display omitted] • Multilayer and delaminated Ti 3 C 2 T x showd great potential in removing heavy metals. • Delamination raised the surface area of Ti 3 C 2 T x , enhancing Pb(II) adsorption. • Delamination oxidized Ti 3 C 2 T x nanosheets, reducing their Cu(II) reduction ability. [ABSTRACT FROM AUTHOR]

Solving the increasing contamination from toxic heavy metal ions in wastewater is an imperative issue in photocatalysis research area. In this study, three-dimensional (3D) porous SrTiO 3 microspheres have been fabricated by a sol–gel-templating method using the agarose gel bead containing SrCO 3 granules as the template. The resultant SrTiO 3 microspheres, several tens of micrometers in diameter, exhibit a bimodal pore structure, in which the macropore about 70–150 nm in size stems from SrCO 3 granules and the mesopore about 3 nm is formed via removing the agarose fiber embedded in the composite microspheres. The porous framework of SrTiO 3 microspheres is assembled by regular single-crystalline SrTiO 3 nanocubes with an edge length of 100 ± 10 nm. The highly interconnected porous network renders numerous pathways for the rapid mass transport, strong adsorption of reactants and multi-reflection of incident light. Moreover, the as-prepared SrTiO 3 microspheres exhibit excellent photocatalytic performance for the Cr(VI) reduction under simulated sunlight, which can reduce nearly 100% Cr(VI) at pH 2 within 2 h and retain a relatively high reduction ability after six recycles. [ABSTRACT FROM AUTHOR]

Predicting the cotransport of functional microorganisms and heavy metals in porous media is essential to both bioremediation and pollutant risk assessment. In this study, batch and column experiments were conducted to explore the cotransport behaviors of functional bacteria (FA1) and heavy metals (Pb2+/Cd2+) in saturated sand media under different conditions. The sorption capacity of heavy metals on FA1 was much greater than that of the sand, while both FA1 and sand showed stronger affinity to Pb2+ than Cd2+. The surface properties, especially zeta potential, of the bacteria and sand were altered by metal adsorption. As a result, the co-existence of Pb2+ decreased the transport of FA1 more significantly than that of Cd2+, and the influence was more significant with higher heavy metal concentration. On the other hand, the co-existence of FA1 inhibited the mobility of Pb2+ and Cd2+ in most scenarios, except when the cotransport concentration of Pb2+ was 5 mg L−1, and the inhibition was more pronounced for Pb2+ than Cd2+. Increase in metal concentrations decreased the FA1-associated Pb2+/Cd2+ in effluents due to the remarkable decrease in FA1 mobility, and free soluble Pb2+/Cd2+ became the major migration species. In addition, due to stronger attractive forces and affinity between Pb2+ and FA1, nearly all presorbed-Pb2+ by sand was remobilized by FA1 and transported mainly in FA1-associated form other than soluble Pb2+. Findings from this study indicated that the cotransport of biocolloids and heavy metals are highly sensitive to the ion type and concentration, and evaluation of their transport in the subsurface should be carefully carried out to avoid inaccurate estimations. Image 1 • The mobility of FA1 decreased with increasing Pb2+/Cd2+ concentration. • Co-existence of Pb2+ decreased bacteria FA1 mobility more significantly than Cd2+. • The migration of Pb2+ and Cd2+ was mostly impeded by bacteria FA1 in sand columns. • FA1 can remobilize pre-adsorbed Pb2+ from the quartz sand surface. [ABSTRACT FROM AUTHOR]

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With large specific surface area, abundant adsorption sites, flexible pore structure, and good water stability, Materials of Institute Lavoisier frameworks (MILs) have attracted increasing attention as effective environmental adsorbents. This review systematically analyzes and recapitulates recent progress in the synthesis and application of MIL-based adsorbents for the removal of aqueous heavy metal ions. Commonly used solvothermal, microwave, electrochemical, ultrasonic, and mechanochemical syntheses of MILs are first summarized and compared. Instead of focusing on adsorption process parameters, adsorption performances and governing mechanisms of virgin MILs, functional MILs, MIL-based composites, and carbonized MILs to representative metal(loid) ions (chromium, arsenic, lead, cadmium, and mercury) in water under various conditions are then systematically reviewed and discussed. In the end, this work also outlines prospects and future directions to promote the applications of MILs in treating heavy metal contaminated water. [Display omitted] • Advantages and limitations of synthesis methods of MILs are summarized and compared. • Adsorption performances of MILs to aqueous metal(loid) ions are reviewed and compared. • Adsorption mechanisms of MILs to aqueous metal(loid) ions are analyzed and recapitulated. • Future perspectives of MILs in wastewater treatment are proposed. [ABSTRACT FROM AUTHOR]

Abstract: The bioaccessibility and human health risks of As and heavy metals (Cu, Pb, Zn, Ni, Co, Cr, Cd and Mn) in total suspended particulates (TSP) and fine particulate matter (PM2.5) in Nanjing, China were investigated. The average mass concentration ratios of PM2.5 to TSP were 0.61 for Gulou sampling site and 0.50 for Pukou sampling site, respectively. Zn, Pb, Mn and Cu were the most abundant elements among the studied metal(loid)s in both TSP and PM2.5. The results of a simple bioaccessibility extraction test of the studied metal(loid)s varied among elements, with Cd, Zn, Mn, Pb and As showing the higher bioaccessibility. The carcinogenic risks of As, Cd, Co, Cr and Ni in both TSP and PM2.5 via dermal contact and inhalation exposure were within the acceptable level (<1 × 10−4) for both children and adults, but there was potential carcinogenic risk posed by Pb via ingestion to children and adults. The hazard index values for all of the studied elements suggested no non-carcinogenic health risks via ingestion and dermal contact, but a potential non-carcinogenic health risk via inhalation to adults. Values of hazard quotient and hazard index indicated the non-carcinogenic risks from the studied metal(loid)s to children via ingestion, dermal contact and inhalation pathways in Nanjing given the present air quality. [Copyright &y& Elsevier]

• Removal of heavy metal oxoanions by MOF adsorbents is comprehensively reviewed. • Adsorption mechanisms between target anions and MOFs are discussed in detail. • The strategies to enhance adsorption performance of MOF adsorbents are concluded. • The future direction of MOF adsorbents to capture metal oxoanions is proposed. Due to the serious threat of heavy metal oxoanions to human health and the natural environment, their efficient removal from water contaminants has become a vital issue. Currently, adsorptive removal is one of most promising approaches to purify contaminated water. Thus, the exploration of advanced adsorption materials has attracted widespread attention. Metal-organic frameworks (MOFs) with the advantages of tunable porosity, high surface area, and abundant functional groups are superior than conventional adsorbents. Herein, this review summarizes recent progress in different MOFs as outstanding adsorbents to remove heavy metal oxoanions from water, including typical SeO 3 2−/SeO 4 2−, HAsO 4 2−/H 2 AsO 4 −/H 3 AsO 3 , and CrO 4 2−/Cr 2 O 7 2−. In addition, their adsorption mechanisms are also involved, which is conducive to not only understand the adsorption process between MOFs and heavy metal oxoanion contaminants but also design new MOFs-based adsorbents with excellent performance for further research. [ABSTRACT FROM AUTHOR]