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

Magnetic particle adsorbent (MPA) was prepared using iron-containing sludge by solvothermal process for As­(V) removal from the water solution. The magnetic property, structure features, and surface morphology of MPA were characterized by a vibrating-sample magnetometer, X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, and Brunauner–Emmett–Teller analysis. Laboratory experiments were also conducted to investigate the adsorption capability and adaptability of MPA for As­(V) removal in the water. MPA mainly consisted of γ-Fe2O3, and its saturation magnetization is 16.95 emu/g. It can be simply separated from water just using a simple magnet. It was mesoporous material with rough surface morphology and large specific surface area (238.7 m2/g). The Langmuir adsorption isotherm model could better described the As­(V) adsorption behavior than the Freundlich model, which indicated that As­(V) adsorbed on the surface of MPA appeared a monolayer distribution. Maximum As­(V) adsorption capacities at 25, 35, and 45 °C were 8.694, 10.050, and 13.400 mg/g, respectively. As­(V) adsorption onto MPA was jointly controlled by intraparticle and film diffusion which was revealed by kinetic studies. There was no conspicuous influence on As­(V) adsorption in a broad range of pH from 3 to 10. Among the coexisting anions with As­(V) in water, PO4 3–, and SiO3 2– had obvious suppression on As­(V) adsorption, while HCO3 –, SO4 2–, and Cl– had negligible influence.

Water treatment residuals (WTRs), obtained from a groundwater treatment plant for biological iron and manganese removal, were investigated and used as adsorbents for arsenic removal. The surface morphology and structural features of the WTRs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Brunauner–Emmett–Teller analysis (BET). Laboratory experiments were also carried out to test the adsorption capability and adaptability of WTRs on both As (III) and As (V) removal from the water. The results showed that the WTRs were mainly amorphous and had a large specific surface area of 253.152 m2/g. The maximum adsorption capacities, evaluated using the Langmuir isotherm equation, were 36.53 mg/g and 40.37 mg/g for As (III) and As (V), respectively. The pseudo-second-order model fitted the kinetic data better, with R2 more than 0.99 for both As (III) and As (V). The removal of As (V) decreased with the increase in pH, especially when the pH was above 9, whereas for As (III), the removal effectiveness almost remained constant at both acidic and neutral pHs. H2PO4− and SiO32− could strongly inhibit arsenic adsorption onto the WTRs, and the effect of other ions was little.

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