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A novel granular Fe–Mn (GFM) binary oxide sorbent, with a diameter of approximate 2.0 mm and a length of 2.0–3.0 mm, was successfully prepared using extrusion granulation method in this study. The GFM sorbent is highly porous with a BET-specific surface area of 210.3 m2/g. It shows high effectiveness in simultaneously adsorbing As(V) and As(III). The maximal sorption capacities for As(V) and As(III) are 33.2 and 50.7 mg/g at pH 7.0 ± 0.1, respectively, which are superior to most of granular sorbents reported in the literature. The present Ca2+, Mg2+, humic acids and fulvic acids do not have obvious influence on the arsenic sorption. But, coexisting anions affect negatively arsenic sorption in the following order: H2PO4− > SiO32− > HCO3− > SO42−. NaOH solution is an effective eluent for regeneration of the arsenic-loaded GFM. The GFM packed in the fixed-bed column can treat approximately 3400 and 6500 bed volumes of simulated groundwater containing 233 μg/L As(V) and As(III), respectively, before the arsenic concentration in the effluent reached a drinking water limit of 10 μg/L. The features of high effectiveness, selectivity and reusability make the GFM a potential alternative to remove simultaneously As(V) and As(III) from groundwater. [ABSTRACT FROM AUTHOR]

A novel sorbent of Fe–Mn binary oxide impregnated chitosan bead (FMCB) was fabricated through impregnating Fe–Mn binary oxide into chitosan matrix. The FMCB is sphere-like with a diameter of 1.6–1.8 mm, which is effective for both As(V) and As(III) sorption. The maximal sorption capacities are 39.1 and 54.2 mg/g, respectively, outperforming most of reported granular sorbents. The arsenic was mainly removed by adsorbing onto the Fe–Mn oxide component. The coexisting SO 4 2− , HCO 3 − and SiO 3 2− have no great influence on arsenic sorption, whereas, the HPO 4 2− shows negative effects. The arsenic-loaded FMCB could be effectively regenerated using NaOH solution and repeatedly used. In column tests, about 1500 and 3200 bed volumes of simulated groundwater containing 233 μg/L As(V) and As(III) were respectively treated before breakthrough. These results demonstrate the superiority of the FMCB in removing As(V) and As(III), indicating that it is a promising candidate for arsenic removal from real drinking water. [ABSTRACT FROM AUTHOR]

Abstract: To obtain a highly efficient and low-cost adsorbent for arsenic removal from water, a novel nanostructured Fe–Cu binary oxide was synthesized via a facile co-precipitation method. Various techniques including BET surface area measurement, powder XRD, SEM, and XPS were used to characterize the synthetic Fe–Cu binary oxide. It showed that the oxide was poorly crystalline, 2-line ferrihydrite-like and was aggregated with many nanosized particles. Laboratory experiments were performed to investigate adsorption kinetics, adsorption isotherms, pH adsorption edge and regeneration of spent adsorbent. The results indicated that the Fe–Cu binary oxide with a Cu: Fe molar ratio of 1:2 had excellent performance in removing both As(V) and As(III) from water, and the maximal adsorption capacities for As(V) and As(III) were 82.7 and 122.3 mg/g at pH 7.0, respectively. The values are favorable, compared to those reported in the literature using other adsorbents. The coexisting sulfate and carbonate had no significant effect on arsenic removal. However, the presence of phosphate obviously inhibited the arsenic removal, especially at high concentrations. Moreover, the Fe–Cu binary oxide could be readily regenerated using NaOH solution and be repeatedly used. The Fe–Cu binary oxide could be a promising adsorbent for both As(V) and As(III) removal because of its excellent performance, facile and low-cost synthesis process, and easy regeneration. [Copyright &y& Elsevier]

Abstract: Arsenate retention, arsenite sorption and oxidation on the surfaces of Fe–Mn binary oxides may play an important role in the mobilization and transformation of arsenic, due to the common occurrence of these oxides in the environment. However, no sufficient information on the sorption behaviors of arsenic on Fe–Mn binary oxides is available. This study investigated the influences of Mn/Fe molar ratio, solution pH, coexisting calcium ions, and humic acids have on arsenic sorption by Fe–Mn binary oxides. To create Fe–Mn binary oxides, simultaneous oxidation and co-precipitation methods were employed. The Fe–Mn binary oxides exhibited a porous crystalline structure similar to 2-line ferrihydrite at Mn/Fe ratios 1:3 and below, whereas exhibited similar structures to δ-MnO2 at higher ratios. The As(V) sorption maximum was observed at a Mn/Fe ratio of 1:6, but As(III) uptake maximum was at Mn/Fe ratio 1:3. However, As(III) adsorption capacity was much higher than that of As(V) at each Mn/Fe ratio. As(V) sorption was found to decrease with increasing pH, while As(III) sorption edge was different, depending on the content of MnO2 in the binary oxides. The presence of Ca2+ enhanced the As(V) uptake under alkaline pH, but did not significantly influence the As(III) sorption by 1:9 Fe–Mn binary oxide; whereas the presence of humic acid slightly reduced both As(V) and As(III) uptake. These results indicate that As(III) is more easily immobilized than As(V) in the environment, where Fe–Mn binary oxides are available as sorbents and they represent attractive adsorbents for both As(V) and As(III) removal from water and groundwater. [Copyright &y& Elsevier]

Phosphorus is an essential nutrient for biological growth, but its excessive presence in water can lead to eutrophication. Reducing phosphorus concentrations is an important way to prevent eutrophication of surface water bodies. In this study, a novel zero-valent manganese (ZVM) Mn0@Mn 2 O 3 sorbent was synthesized via a facile one-step reduction method at ambient temperature. The morphology and surface properties of the Mn0@Mn 2 O 3 were analyzed by Scanning electron microscopy (SEM), X-ray diffraction (XRD), Zeta potential analyzer, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The obtained amorphous sample consists of many small tremella-like particles. The as-prepared sorbent shows exceptional phosphate removal performance and has a maximum adsorption capacity of 113.7 mg-P/g at pH 7.0, superior to many reported adsorbents. The removal of phosphate is obviously pH-dependent and is favorable under near-neutral and weak-alkaline conditions (pH 6.5–8.5). The kinetics data fit well to the pseudo-second-order model. The coexisting SO 4 2-, CO 3 2- and Cl- have no great influence on phosphate sorption, whereas, the SiO 3 2- shows negative effect at high concentration. The sorbent is effective for phosphate removal from real municipal wastewater. The results of ionic strength effect experiment, SEM, XRD, FTIR and XPS analyses reveal that the phosphate was mainly removed through surface precipitation and formation of inner-sphere surface complexes. The Mn0@Mn 2 O 3 is a promising sorbent for phosphate removal from surface water and wastewater, owning to its exceptional performance, high selectivity, environmental friendliness and easy preparation. "Facile synthesis of novel tremella-like Mn0@Mn 2 O 3 and its exceptional performance on removal of phosphate" by Wu et al. [Display omitted] • A novel tremella-like Mn0@Mn 2 O 3 sorbent was synthesized. • The sorbent has a high maximal sorption capacity of 113.7 mg-P/g at pH 7.0. • The sorbent is highly effective for phosphate removal at low concentration. • The sorbent possesses high selectivity towards phosphate. • Surface precipitation and specific sorption are the main removal mechanisms. [ABSTRACT FROM AUTHOR]

The removal of arsenite [As(III)] has attracted increasing attentions because it is higher toxic and more difficult to be removed from water than arsenate [As(V)]. For efficient As(III) uptake, a nanostructured iron-copper-manganese trimetal oxide (ICM) was therefore synthesized using a simultaneous oxidation and co-precipitation approach at room temperature. The as-prepared ICM exhibits multifunctional properties, which can not only oxidize effectively As(III) but also sorb the produced As(V). The maximal sorption capacity of As(III) reaches up to 131 mg/g under neutral conditions, which outperforms the majority of adsorbents reported in the literature. The As(III) sorption drops gradually as solution pH increases. However, it is not significantly influenced by ionic strength and present anions except for PO 4 3−, implying a relatively high selectivity. The active sorption sites of spent ICM can be easily restored through NaOH solution treatment. The removal of As(III) is a complicated process involving in both oxidation and adsorption, in which inner-sphere surface complexes are formed. The oxidation of As(III) to As(V) is mainly ascribed to the Mn oxide content in composite, whereas the adsorption of formed As(V) is predominately attributed to the Fe oxide and Cu oxide. The ICM might act as a promising alternative to remove arsenic from groundwater and wastewater, due to its good performance, low cost, facile synthesis and high reusability. Unlabelled Image • A novel nanostructured Fe-Cu-Mn trimetal oxide sorbent was fabricated. • The sorbent has a high sorption capacity for As(V) and As(III). • The sorbent is highly effective for As(III) removal at trace concentration. • As(III) uptake is mainly achieved by adsorption coupled with oxidation. • The spent sorbent can be easily regenerated and repeatedly used. [ABSTRACT FROM AUTHOR]

Arsenite [As(III)] is more toxic and more difficult to remove from water than arsenate [As(V)]. For enhanced As(III) removal from water, a new nanostructured Ce-Mn binary oxide with a Ce/Mn molar ratio of 3:1 was fabricated via a facile one-step oxidation-coprecipitation method at ambient temperature. The synthetic Ce-Mn binary oxide is amorphous with a high surface area of 157 m 2 /g. Cerium (Ce) and manganese (Mn) in this oxide exist mainly in the oxidation state of Ce(IV) and Mn(IV), respectively. It can effectively oxidize As(III) to As(V) and efficently adsorb the formed As(V). Moreover, this sorbent exhibits an obviously synergistic effect. The maximal sorption capacity of As(III) is 97.7 mg/g, which is competitive with most of reported sorbents. The As(III) uptake is rapid and slightly affected by tested solution pH, ionic strength, dissolved organic matters and coexisting anions except for phosphate, indicating the high selectivity toward arsenic. The arsenic-loaded Ce-Mn binary oxide could be readily regenerated and repeatedly used. Both Mn and Ce oxides in sorbent are responsible for As(III) oxidation, and the Ce oxide is dominant for adsorbing formed As(V) during As(III) removal. The oxide could be used as an attractive sorbent for As(III) removal from contaminated water, because of its facile and low-cost synthesis process, good As(III) sorption performance, and reusability. [ABSTRACT FROM AUTHOR]

[Display omitted] • SZVMn is prepared using sulfidation with freshly formed S0 as sulfidizing agent. • Efficient removal of Cr(VI) by SZVMn: maximum capacity of 190.8 mg/g. • SZVMn surpasses nZVMn in terms of matrix resistance and long-term storage ability. • Low S/Mn molar ratio at 0.1 in material synthesis is beneficial to Cr(VI) removal. • Cr(VI) is rapidly reduced by Mn0 and later by dissolved/surface-bound Mn2+. Both zero-valent manganese (ZVMn) and sulfide possess high reducibility and strong affinity towards heavy metals in high oxidation states. The feasibility and behavior of combining these two components to create sulfidated zero-valent manganese (SZVMn) for hexavalent chromium (Cr(VI)) removal, however, remain largely uninvestigated. This study aims to explore the behaviors and mechanisms of Cr(VI) removal utilizing SZVMn, which was synthesized by borohydrides reduction of divalent manganese salt, followed by sulfidation using freshly generated elemental sulfur. SZVMn comprised a mixture of low-crystallinity Mn0, MnO x , and MnS x , with the fraction of MnS x increasing with higher S/Mn molar ([S/Mn]) ratio. The optimal [S/Mn] ratio was determined to be 0.1, achieving the highest Cr(VI) removal capacity of 190.8 mg/g. At [S/Mn] ratio exceeding 0.1, Cr(VI) removal declined due to higher consumption of Mn0 as a result of increased S dosing during material formation. SZVMn outperformed bare ZVMn in terms of preservation and resistance to coexisting ions. The removal of Cr(VI) occurred primarily through the rapid reduction of Cr(VI) to Cr(III) via Mn0 and MnS x initially, followed by slow reduction via dissolved/surface-bound Mn2+, along with precipitation of Cr(III) as Cr(OH) 3. This study provides a deep understanding of the interactions between Cr(VI) and SZVMn derived from freshly-generated elemental sulfur, offering new insights into Cr(VI) removal processes. [ABSTRACT FROM AUTHOR]

Nano zero-valent manganese (nZVMn) is theoretically expected to exhibit high reducibility and adsorption capacity, yet its feasibility, performance, and mechanism for reducing and adsorbing hexavalent uranium (U(VI)) from wastewater remain unclear. In this study, nZVMn was prepared via borohydride reduction, and its behaviors about reduction and adsorption of U(VI), as well as the underlying mechanism, were investigated. Results indicated that nZVMn exhibited a maximum U(VI) adsorption capacity of 625.3 mg/g at a pH of 6 and an adsorbent dosage of 1 g/L, and the co-existing ions (K+, Na+, Mg2+, Cd2+, Pb2+, Tl+, Cl−) at studied range had little interference on U(VI) adsorption. Furthermore, nZVMn effectively removed U(VI) from rare-earth ore leachate at a dosage of 1.5 g/L, resulting in a U(VI) concentration of lower than 0.017 mg/L in the effluent. Comparative tests demonstrated the superiority of nZVMn over other manganese oxides (Mn 2 O 3 and Mn 3 O 4). Characterization analyses, including X-ray diffraction and depth profiling X-ray photoelectron spectroscopy, combined with density functional theory calculation revealed that the reaction mechanism of U(VI) using nZVMn involved reduction, surface complexation, hydrolysis precipitation, and electrostatic attraction. This study provides a new alternative for efficient removal of U(VI) from wastewater and improves the understanding of the interaction between nZVMn and U(VI). [Display omitted] • Efficient removal of U(VI) by nZVMn: maximum sorption capacity of 625.3 mg/g. • Excellent U(VI) removal in synthetic (99.9%) and real U-bearing wastewater (95.4%). • Rapid removal within 2 h and high resistance to interference by K+, Na+, Mg2+. • Main mechanisms include reduction, precipitation and surface complexation. • Experimental findings are consistent with the results from DFT calculation. [ABSTRACT FROM AUTHOR]

Owing to the high toxicity and mobility, the removal of arsenite (As(III)) is significantly more difficult than arsenate (As(V)), thus representing a major challenge in arsenite-contaminated water treatment. For efficient elimination of As(III), we successfully fabricated a novel Ti-Mn binary oxide via a simultaneous oxidation and coprecipitation process. The amorphous oxide was aggregated from nanosized particles with a high specific surface area of 349.5 m 2 /g. It could effectively oxidize As(III) to As(V) and had a high As(III) sorption capacity of 107.0 mg/g. As(III) sorption occurred rapidly and equilibrium was achieved within 24 h. The kinetic data was well fitted by the pseudo-second-order equation, indicating a chemical sorption process. The material was almost independent upon the presence of competitive ions. The As(III) removal by the sorbent is a combined process coupled oxidation with sorption, where the MnO 2 content is mainly responsible for oxidizing As(III) to As(V) and the formed As(V) is then adsorbed onto the surface of amorphous TiO 2 content, through replacing the surface hydroxyl group or the adsorbed As(III) and forming inner-sphere surface complexes. Furthermore, the arsenic-containing oxide could be effectively regenerated and reused. The bi-functional sorbent could be used as a potentially attractive sorbent for As(III) removal in drinking water treatment and environmental remediation. [ABSTRACT FROM AUTHOR]