Two types of magnetic nanoparticles prepared with chemical agents (cMNP) and iron-containing sludge (iMNP), respectively, were synthesized by co-precipitation process and used to remove arsenate [As(V)] from water. The synthesized magnetic adsorbents were characterized by XRD, XPS, TEM, BET, VSM and FTIR. The adsorbents iMNP and cMNP were both mainly γ-Fe2O3 in nanoscale particles with the saturation magnetization of 35.5 and 69.0 emu/g respectively and could be easily separated from water with a simple hand-held magnet in 2 minutes. At pH 6.6, over 90% of As(V), about 400 μg/L, could be removed by both adsorbents (0.2 g/L) within 60 min. The adsorption isotherm of both fabricated materials could be better described by the Langmuir adsorption isotherm model than the Freundlich’s, In addition, the adsorption kinetics of both adsorbents described well by the pseudo-second order model revealed that the intraparticle diffusion was not just the only rate controlling step in adsorption process. With the larger maximum As(V) adsorption capacity of iMNP (12.74 mg/g), compared with that of cMNP (11.76 mg/g), the iMNP could be regarded as an environmentally friendly substitute for the traditional magnetic nanoparticles prepared with chemical agents.

BACKGROUND Iron (Fe)‐containing groundwater treatment residual is a kind of waste from groundwater treatment plants, showing good potential to be reused. Attention has been paid to Fe‐based magnetic water treatment materials for their easy magnetic separation, and in the meantime, kinds of adsorbents were developed to address the severe global dyes pollution. RESULTS Black magnetic material was obtained with using the iron‐containing wastes as iron source without adding other iron chemical reagents by hydrothermal reaction. The X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS) and Fourier‐transform infrared (FTIR) results show that the product is comprised of crystalline iron(II,III) oxide (Fe3O4) core and amorphous carbon shell (Fe3O4@C), and the core‐shell structure can also been seen clearly in transmission electron microscopy (TEM) images. Vibrating sample magnetometer (VSM) result shows its saturation magnetization is 33.56 emu/g. This sample's sorption experiments for methylene blue (MB) removal were conducted, and the experiment results indicated that this sample could be used in a wide range of pH (5–12) and the adsorption might be a complex chemical diffusion process consisting of boundary layer effect due to kinetic modeling fitting analysis. The maximum sorption amount of MB was 16.33 and 19.13 mg/g, respectively at 298 K and 308 K. This sample after five regeneration cycles still had 72.1% MB removal rate. CONCLUSION The Fe3O4@C particles with good magnetism were synthesized successfully with Fe‐containing water treatment residuals, water treatment waste sludge, via a one‐step hydrothermal reaction, which could be of reasonable analogy for treating other Fe‐containing industrial waste. Furthermore, this sample could be used as adsorbent for MB molecules removal from dyed water with good reusability and easy magnetic separation. © 2019 Society of Chemical Industry

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The development of low-cost adsorbent is an urgent need in the field of wastewater treatment. In this study, sludge-based magnetic biochar (SMB) was prepared by pyrolysis of sewage sludge and backwashing iron mud without any chemical agents. The samples were characterized by TGA, XRD, ICP, Organic element analysis, SEM, TEM, VSM and BET. Characterization analysis indicated that the magnetic substance in SMB was Fe3O4, and the saturation magnetization was 25.60 emu·g−1, after the adsorption experiment, SMB could be separated from the solution by a magnet. The batch adsorption experiment of methylene blue (MB) adsorption showed that the adsorption capacities of SMB at 298 K, 308 K and 318 K were 47.44 mg·L−1, 39.35 mg·L−1, and 25.85 mg·L−1, respectively. After one regeneration with hydrochloric acid, the maximum adsorption capacity of the product reached 296.52 mg·g−1. Besides, the adsorption kinetic described well by the pseudo-second order model revealed that the intraparticle diffusion was not just the only rate controlling step in adsorption process. This study gives a reasonable reference for the treatment of sewage sludge and backwashing iron mud. The product could be used as a low-cost adsorbent for MB removal.

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