New insight in adsorption of Sb(III)/Sb(V) from waters using magnetic nanoferrites: X-ray absorption spectroscopy investigation

Mechanism for the simultaneous removal of Sb(III) and Sb(V) from mining wastewater by phytosynthesized iron nanoparticles

Since antimony (Sb) is a toxic metalloid cost-effective method for the simultaneous removal of the two major Sb species from mining wastewater has attracted much attention. In this study, phytosynthesized iron nanoparticles (nFe) prepared using a eucalyptus leaf extract were successfully used to simultaneously remove Sb(III) and Sb(V) via an adsorption and oxidation mechanism with removal efficiencies of 100 and 97.7% for Sb(III) and Sb(V), respectively. Advanced analysis using X-ray photoelectron spectroscopy (XPS), ion chromatography-atomic fluorescence spectroscopy (IC-AFS), and electrochemical analysis confirmed that Sb(III) was oxidized to Sb(V) by Fe(III) on the nFe surface while Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) indicated that both Sb(III) and Sb(V) were adsorbed onto nFe. Adsorption of both Sb(III) and Sb(V) best fit the Langmuir adsorption model with R² of 0.999 and 0.989, respectively and both followed pseudo-second-order kinetics with R² of 0.999 and 0.981, respectively. Furthermore, the adsorption rate of Sb(III) was faster than that of Sb(V) due to inner-sphere complex formation, and the Fe-O bonds in the asymmetric tetrahedron structure of Sb(III) were easier to break due to a lower energy barrier (0.863 eV). Consequently, a simultaneous removal mechanism of Sb(III) and Sb(V) was proposed. Finally, nFe was used practically to remove Sb in mining wastewater with a removal efficiency of 93.5%, demonstrating that nFe have significant potential to remove Sb in contaminated mining wastewaters.

Adsorptive behavior of thallium using Fe3O4-kaolin composite synthesized by a room temperature ferrite process

Thallium (Tl) contaminants pose serious threats to the ecological environment and human health due to its acute/chronic poisoning on the health of most organisms even at low concentrations. To find a rapid and efficient technology in removing Tl from waters thus becomes a crucial issue. A magnetic Fe₃O₄-kaolin composite (denoted by FKC) with high specific surface area (133.7 m²/g) was successfully synthesized via a simple and low-cost technique for Tl(I) removing from various water media. The HRTEM images confirmed the existence of lattice fingers Fe₃O₄ and displayed that a large number of Fe₃O₄ nanoparticles dispersed on the surface of kaolin sheets. Compared with kaolin or Fe₃O₄ alone, FKC enhanced obviously the adsorption rate and capacity of Tl(I) over a wide pH range (4.5-9.0). The maximum adsorption capacity of FKC for Tl(I) was 19,347 mg/kg (calculated by Langmuir model), which was almost one hundred times and two times higher than those of kaolin and Fe₃O₄, respectively. Importantly, FKC was observed to have a great potential in removing Tl(I) from surface water, groundwater, and tap water in more alkaline conditions. By applying the external magnetic field, FKC could be recovered efficiently (99%) and rapidly (20 s). Moreover, Tl L₃-edge XANES spectra revealed that Tl(I) was adsorbed on the FKC and would not be converted to more toxic Tl(III). The cations (CaCl₂, NaCl, and KCl) and the ionic strength with concentrations of 0.001-1.0 mol/L showed a great influence on the adsorption of Tl(I) by FKC, implying that this adsorption was dominated by outer-sphere surface complexation at investigated pH values. The information provided is essential for designing a rapid and effective scavenger for removing Tl in various natural waters.

Sustainable and efficient technologies for removal and recovery of toxic and valuable metals from wastewater: Recent progress, challenges, and future perspectives

Due to their numerous effects on human health and the natural environment, water contamination with heavy metals and metalloids, caused by their extensive use in various technologies and industrial applications, continues to be a huge ecological issue that needs to be urgently tackled. Additionally, within the circular economy management framework, the recovery and recycling of metals-based waste as high value-added products (VAPs) is of great interest, owing to their high cost and the continuous depletion of their reserves and natural sources. This paper reviews the state-of-the-art technologies developed for the removal and recovery of metal pollutants from wastewater by providing an in-depth understanding of their remediation mechanisms, while analyzing and critically discussing the recent key advances regarding these treatment methods, their practical implementation and integration, as well as evaluating their advantages and remaining limitations. Herein, various treatment techniques are covered, including adsorption, reduction/oxidation, ion exchange, membrane separation technologies, solvents extraction, chemical precipitation/co-precipitation, coagulation-flocculation, flotation, and bioremediation. A particular emphasis is placed on full recovery of the captured metal pollutants in various reusable forms as metal-based VAPs, mainly as solid precipitates, which is a powerful tool that offers substantial enhancement of the remediation processes' sustainability and cost-effectiveness. At the end, we have identified some prospective research directions for future work on this topic, while presenting some recommendations that can promote sustainability and economic feasibility of the existing treatment technologies.