This review paper presents an overview of the available technologies used nowadays for the removal of arsenic species from water. Conventionally applied techniques to remove arsenic species include oxidation, coagulation-flocculation, and membrane techniques. Besides, progress has recently been made on the utility of various nanoparticles for the remediation of contaminated water. A critical analysis of the most widely investigated nanoparticles is presented and promising future research on novel porous materials, such as metal organic frameworks, is suggested.

The covalent triazine framework, CTF-1, served as host material for the in situ synthesis of FeO nanoparticles. The composite material consisted of 20 ± 2 m% iron, mainly in γ-FeO phase. The resulting γ-FeO@CTF-1 was examined for the adsorption of As, As and Hg from synthetic solutions and real surface-, ground- and wastewater. The material shows excellent removal efficiencies, independent from the presence of Ca, Mg or natural organic matter and only limited dependency on the presence of phosphate ions. Its adsorption capacity towards arsenite (198.0 mg g), arsenate (102.3 mg g) and divalent mercury (165.8 mg g) belongs amongst the best-known adsorbents, including many other iron-based materials. Regeneration of the adsorbent can be achieved for use over multiple cycles without a decrease in performance by elution at 70 °C with 0.1 M NaOH, followed by a stirring step in a 5 m% HO solution for As or 0.1 M thiourea and 0.001 M HCl for Hg. In highly contaminated water (100 μg L), the adsorbent polishes the water quality to well below the current WHO limits.

Abstract:The chromium-based metal-organic framework MIL-101(Cr) served as a host for the in situ synthesis of Fe 3 O 4 nanoparticles. This hybrid nanomaterial was tested as an adsorbent for arsenite and arsenate species in groundwater and surface water and showed excellent affinity towards As III and As V species. The adsorption capacities of 121.5 and 80.0 mg g -1 for arsenite and arsenate species, respectively, are unprecedented.

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Highlights• Chitosan effectively adsorbed Ni from a real Ni/Ca/SO4 2bearing leachate • Sulfate had a positive effect on Ni adsorption while Ca did not have any effect• Formation of NiSO4 0 species contributed to the enhanced Ni adsorption onto chitosan • Chitosan has a Ni qmax of 1.49 mmol/g even with 500 mM SO4 2and 10 mM Ca present • Chitosan was selective for Ni over Ca as validated in a column setup ABSTRACT Nickel (Ni) is an economically important metal characterized by its mechanical strength and anticorrosion properties. With the increasing industrial demand for Ni and the depleting accessible Ni primary ores, sustainable technologies are required for the recovery of this metal from alternative resources. In this study, adsorption using chitosan was investigated as a sustainable technique to recover Ni from sulfate (SO4 2-) and calcium (Ca) rich secondary resources. The effects of pH, contact time, and the presence of SO4 2and Ca on Ni adsorption were investigated in batch experiments. Chemical speciation modeling was performed to analyze how the predominant Ni species present under different conditions may affect the efficiency of the adsorption process. The comparison of chitosan's maximum Ni adsorption capacities in the absence (1.00 mmol/g) and presence (1.49 mmol/g) of 500 mM SO4 2and 10 mM Ca indicated the positive effect of these ions on Ni adsorption. The predominance of the neutrally charged NiSO4 0 species in Ni/SO4 2system has contributed to the enhanced Ni adsorption on chitosan as verified by X-ray photoelectron spectroscopy (XPS) analysis.However, kinetic studies confirmed that the Ni adsorption rate decreased by 4.5 times when SO4 2was present. The subsequent continuous Ni adsorption from a real SO4 2--rich leachate in a column setup revealed that chitosan is selective for Ni over Ca and Cr with selectivity quotients of 9.6 (KNi/Ca) and 3.0 (KNi/Cr). Overall, this study indicated that Ni complexation with SO4 2enhances the Ni adsorption capacity of chitosan, but slows down the adsorption process.

Unmodified microalgal biomass grown on wastewater works as an effective and selective indium biosorbent even at low pH values.

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