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.
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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