Properties of poly（1-naphthylamine）/Fe3O4 composites and arsenic adsorption capacity in wastewater

The research results of poly（1-naphthylamine）lFe3O4 （PNA/Fe3O4） nanocomposites synthesized by a chemical method for As（Ⅲ） wastewater treatment are presented in this paper. XRD patterns and TEM images showed that the Fe3O4 grain size varied from 13 to 20 nm. The results of Raman spectral analysis showed that PNA participated in part of the PNA/Fe3O4 composite samples. The grain size of PNA/Fe3O4 composite samples is about 25-30 nm measured by SEM. The results of vibrating sample magnetometer measurements at room temperature showed that the saturation magnetic moment of PNA/Fe3O4 samples decreased from 63.13 to 43.43 emu/g, while the PNA concentration increased from 5% to 15%. The nitrogen adsorption-desorption isotherm of samples at 77 K at a relative pressure PIPo of about 1 was studied in order to investigate the surface and porous structure of nanoparticles by the BET method. Although the saturation magnetic moments of samples decreased with the polymer concentration increase, the arsenic adsorption capacity of the PNA/Fe3O4 sample with the PNA concentration of 5% is better than that of Fe3O4 in a solution with pH = 7. In the solution with pH 〉 14, the arsenic adsorption of magnetic nanoparticles is insignificant.

Effect of ionic strength on adsorption of As(Ⅲ) and As(V) on variable charge soils

The study was to investigate the adsorption behavior of arsenite （As（HI）） and arsenate （As（V）） on two variable charge soils, i.e., Haplic Acrisol and Rhodic Ferralsol at different ionic strengths and pH with batch methods. Results indicated that the amount of As（HI） adsorbed by these two soils increased with increasing solution pH, whereas it decreased with increasing ionic strength under the acidic condition. This suggested that As（Ⅲ） was mainly adsorbed on soil positive charge sites through electrostatic attraction under the acidic condition. Moreover, intersects of As（Ⅴ） adsorption-pH curves at different ionic strengths （a characteristic pH） are obtained for both soils. It was noted that above this pH, the adsorption of As（Ⅴ） was increased with increasing ionic strength, whereas below it the reverse trend was true. Precisely the intersect pH was 3.6 for Haplic Acrisol and 4.5 for Rhodic Ferralsol, which was near the values of PZSE （soil point of zero salt effect） of these soils. The effects of ionic strength and pH on arsenate adsorption by these soils were interpreted by the adsorption model. The results of zeta potential suggested that the potential in adsorption plane becomes less negative with increasing ionic strength above soil PZSE and decreases with increasing ionic strength below soil PZSE. These results further supported the hypothesis of the adsorption model that the potential in the adsorption plane changes with ionic strength with an opposite trend to surface charge of the soils. Therefore, the change of the potential in the adsorption plane was mainly responsible for the change of arsenate adsorption induced by ionic strength on variable charge soils.

Adsorption of arsenate on lanthanum-impregnated activated alumina:In situ ATR-FTIR and two-dimensional correlation analysis study

Lanthanum modified materials have been widely used for the removal of hazardous anions.In this study,in situ ATR-FTIR and two-dimensional correlation analysis were employed to investigate the adsorption mechanism of arsenate（As（V）） on lanthanum-impregnated activated alumina（LAA）.Our results showed that electrostatic interaction attracted As（V） anions to the LAA surface,and then As（V） could form monodentate configuration on the LAA surface at pH 5-9.The result of 2D-COS showed that two coexistent adsorbed As（V） species,H2AsO4^- and HAsO4^2-,were adsorbed on the LAA surface without specific sequence at different pH conditions,indicating a negligible role of the incorporated protons of As（V） on the adsorption affinity to LAA surface.The results of this study reveal insights into LAA surface complexes on the molecular scale and provide theoretical support to new metal oxides design for efficient arsenic removal.

Antimony oxidation and adsorption by in-situ formed biogenic Mn oxide and Fe–Mn oxides

Antimony（Sb）, which can be toxic at relatively low concentrations, may co-exist with Mn（Ⅱ）and/or Fe（Ⅱ） in some groundwater and surface water bodies. Here we investigated the potential oxidation and adsorption pathways of Sb（Ⅲ and V） species in the presence of Mn（Ⅱ） and Mn-oxidizing bacteria, with or without Fe（Ⅱ）. Batch experiments were conducted to determine the oxidation and adsorption characteristics of Sb species in the presence of biogenic Mn oxides（BMOs）, which were formed in-situ via the oxidation of Mn（Ⅱ） by a Mn-oxidizing bacterium（Pseudomonas sp. QJX-1）. Results indicated that Sb（Ⅲ） ions could be oxidized to Sb（V） ions by BMO, but only Sb（V） originating from Sb（Ⅲ） oxidation was adsorbed effectively by BMO. Introduced Fe（Ⅱ） was chemically oxidized to Fe OOH, the precipitates of which mixed with BMO to form a new compound, biogenic Fe–Mn oxides（BFMO）. The BMO part of the BFMO mainly oxidized and the Fe OOH of the BFMO mainly adsorbed the Sb species. In aquatic solutions containing both As（Ⅲ） and Sb（Ⅲ）, the BFMO that formed in-situ preferentially oxidized Sb over As but adsorbed As more efficiently. Chemical analysis and reverse transcription real-time polymerase chain reaction revealed that the presence of Fe（Ⅱ）, As（Ⅲ） and Sb（Ⅲ） accelerated the oxidation of Mn（Ⅱ） but inhibited the activity of Mn-oxidizing bacteria. These results provide significant insights into the biogeochemical pathways of Sb, Mn（Ⅱ） in aquatic ecosystems, with or without Fe（Ⅱ）.

Effects of cobalt doping on the reactivity of hausmannite for As(Ⅲ)oxidation and As(Ⅴ)adsorption

Hausmannite is a common low valence Mn oxide mineral,with a distorted spinel structure,in surficial sediments.Although natural Mn oxides often contain various impurities of transitional metals(TMs),few studies have addressed the effect and related mechanism of TM doping on the reactivity of hausmannite with metal pollutants.Here,the reactivity of cobalt(Co)doped hausmannite with aqueous As(Ⅲ)and As(Ⅴ)was studied.Co doping decreased the point of zero charge of hausmannite and its adsorption capacity for As(Ⅴ).Despite a reduction of the initial As(Ⅲ)oxidation rate,Co-doped hausmannite could effectively oxidize As(Ⅲ)to As(Ⅴ),followed by the adsorption and fixation of a large amount of As(Ⅴ)on the mineral surface.Arsenic K-edge EXAFS analysis of the samples after As(Ⅴ)adsorption and As(Ⅲ)oxidation revealed that only As(Ⅴ)was adsorbed on the mineral surface,with an average As-Mn distance of 3.25–3.30 A,indicating the formation of bidentate binuclear complexes.These results provide new insights into the interaction mechanism between TMs and low valence Mn oxides and their effect on the geochemical behaviors of metal pollutants.

Removal of arsenate with hydrous ferric oxide coprecipitation: Effect of humic acid

Insights from the adverse effect of humic acid （HA） on arsenate removal with hydrous ferric oxide （HFO） coprecipitation can further our understanding of the fate of As（V） in water treatment process. The motivation of our study is to explore the competitive adsorption mechanisms of humic acid and As（V） on HFO on the molecular scale. Multiple complementary techniques were used including macroscopic adsorption experiments, surface enhanced Raman scattering （SERS）, extended X-ray absorption fine structure （EXAFS） spectroscopy, flow-cell attenuated total reflectance Fourier transform infrared （ATR-FTIR） measurement, and charge distribution multisite complexation （CD- MUSIC） modeling. The As（V） removal efficiency was reduced from over 95% to about 10% with the increasing HA concentration to 25 times of As（V） mass concentration. The SERS analysis excluded the HA-As（V） complex formation. The EXAFS results indicate that As（V） formed bidentate binuclear surface complexes in the presence of HA as evidenced by an As-Fe distance of 3.26--3.31 ,~. The in situ ATR-FTIR measurements show that As（V） replaces surface hydroxyl groups and forms inner- sphere complex. High concentrations of HA may physically block the surface sites and inhibit the As（V） access. The adsorption of As（V） and HA decreased the point of zero charge of HFO from 7.8 to 5.8 and 6.3, respectively. The CD-MUSIC model described the zeta potential curves and adsorption edges of As（V） and HA reasonably well.