Influence of the structure and composition of Fe–Mn binary oxides on rGO on As(III) removal from aquifers

Fe–Mn binary oxide (FMBO) possesses high efficiency for As(III) abatement based on the good adsorption affinity of iron oxide and the oxidizing capacity of Mn(IV), and the composition and structure of FMBO play important roles in this process. To compare the removal performance and determine the optimum formula for FMBO, magnetic graphene oxide (MRGO)–FMBO and MRGO–MnO₂ were synthesized with MRGO as a carrier to improve the dispersity of the adsorbents in aquifers and achieve magnetic recycling. Results indicated that MRGO–FMBO had higher As(III) removal than that of MRGO–MnO₂, although the ratios of Fe and Mn were similar, because the binary oxide of Fe and Mn facilitated electron transfer from Mn(IV) to As(III), while the separation of Mn and Fe on MRGO–MnO₂ restricted the process. The optimal stoichiometry x for MRGO–FMBO (Mn_xFe_3-xO₄) was 0.46, and an extraordinary adsorption capacity of 24.38 mg/g for As(III) was achieved. MRGO–FMBO showed stable dispersive properties in aquifers, and exhibited excellent practicability and reusability, with a saturation magnetization of 7.6 emu/g and high conservation of magnetic properties after 5 cycles of regeneration and reuse. In addition, the presence of coexisting ions would not restrict the practical application of MRGO–FMBO in groundwater remediation. The redox reactions of As(III) and Mn(IV) on MRGO–FMBO were also described. The deprotonated aqueous As(III) on the surface of MRGO–FMBO transferred electrons to Mn(IV), and the formed As(V) oxyanions were bound to ferric oxide as inner-sphere complexes by coordinating their “–OH” groups with Mn(IV) oxides at the surface of MRGO–FMBO. This work could provide new insights into high-performance removal of As(III) in aquifers.     

Sodium citrate and biochar synergistic improvement of nanoscale zero-valent iron composite for the removal of chromium (Ⅵ) in aqueous solutions

Sodium citrate (SC) is a widely-used food and industrial additive with the properties of complexation and microbial degradation. In the present study, nano-zero-valent iron reaction system ([email protected]) was successfully established by modifying nanoscale zero-valent iron (nZVI) with SC and biochar (BC), and was employed to remove Cr(Ⅵ) from aqueous solutions. The nZVI, SC-nZVI and [email protected] were characterized and compared using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analyses (TGA), vibrating sample magnetometer (VSM), scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results showed that nZVI was successfully loaded on the biochar, and both the agglomeration and surface passivation problems of nanoparticles were well resolved. The dosage of SC, C:Fe, initial pH and Cr(Ⅵ) concentration demonstrated direct effects on the removal efficiency. The maximum Cr(Ⅵ) removal rate and the removal capacity within 60 min were 99.7% and 199.46 mg/g, respectively (C:Fe was 1:1, SC dosage was 1.12 mol.%, temperature was 25°C, pH = 7, and the original concentration of Cr(Ⅵ) was 20 mg/L). The reaction confirmed to follow the pseudo-second-order reaction kinetics, and the order of the reaction rate constant k was as follows: [email protected] > [email protected] > SC-nZVI > nZVI. In addition, the mechanism of Cr(Ⅵ) removal by [email protected] mainly involved adsorption, reduction and co-precipitation, and the reduction of Cr(Ⅵ) to Cr(Ⅲ) by nano Fe⁰ played a vital role. Findings from the present study demonstrated that the [email protected] exhibited excellent removal efficiency toward Cr(Ⅵ) with an improved synergistic characteristic by SC and BC.     

Environmental impact of China''''s village and township industry(1988-1992): a comparison with urban industry

１ＩｎｔｒｏｄｕｃｔｉｏｎＶｉｌａｇｅａｎｄｔｏｗｎｓｈｉｐｉｎｄｕｓｔｒｙ（ＶＴＩ）ｉｓｂｅｃｏｍｉｎｇａｖｅｒｙｉｍｐｏｒｔａｎｔｃｏｍｐｏｎｅｎｔｏｆＣｈｉｎａｓｅｃｏｎｏｍｙａｎｄｅｎｖｉｒｏｎｍｅｎｔ．Ｉｎ１９９２，ＶＴＩｐｒｏｄｕｃｅｄ...