Ca-modified
Fe3O4 nanoparticles encapsulated
in humic acid (HA-Ca/Fe3O4) were produced using
a co-precipitation method. Furthermore, the adsorption performance
of HA-Ca/Fe3O4 as well as the effect of coexisting
ions and mechanisms were evaluated. A good description of the adsorption
process was given using pseudo-second-order kinetic and Langmuir models.
The adsorption capacities of HA-Ca/Fe3O4 for
Pb2+, Cu2+, and Cd2+ were 208.33,
98.33, and 99.01 mg g–1, respectively. The 0.02–0.1
times concentrations in alkali and alkaline-earth metals promoted
Pb2+ and Cd2+ adsorption; however, any concentration
of alkali and alkaline-earth metals inhibited Cu2+-ion
adsorption, probably owing to the differences in ionic radii between
the interfering and heavy-metal ions. Pb2+, Cu2+, and Cd2+ removal using HA-Ca/Fe3O4 occurred via ion exchange, complexation of O-containing functional
groups, mineral precipitation, and π-electron coordination.
A method was proposed to calculate the contribution of these mechanisms
to the adsorption process. In practice, HA-Ca/Fe3O4 can remove 99% Pb2+ and 91% Cu2+ and
Cd2+ from real wastewater samples. Following five adsorption–desorption
cycles, HA-Ca/Fe3O4 adsorption capacity did
not change significantly. The aforementioned results indicated that
HA-Ca/Fe3O4 presented a good potential in removing
heavy metals in wastewater.
The coexistence of organic and inorganic pollutants in
industrial
wastewater has emerged as a concerning environmental issue worldwide
due to the critical levels of biological toxicity of these pollutants.
In this context, the present study proposes a sandwich structure of
fulvic acid and PMIDA-modified LDHs (FA/PMIDA-LDHs) for the simultaneous
removal of Cu2+ and aniline from wastewater. The specific
structure was synthesized using a combination of coprecipitation and
impregnation methods. Abundant benzene rings and oxygen-containing
functional groups greatly increased the number of sites for the adsorption
of both Cu2+ and aniline. The maximum adsorption capacity
of Cu2+ and aniline in solution with initial pH 5.0 at
25 °C could reach 221.24 and 132.28 mg/g, respectively. Cu2+ could be chelated by the functional groups in the FA/PMIDA-LDHs
structure, and a coupled reduction–complexation mechanism was
proposed for this process. The uptake of aniline on FA/PMIDA-LDHs
was demonstrated to be a result of the combination of coordination
forces, hydrophobic effects, π–π interactions,
and hydrogen bonds. In a multicomponent solution, FA/PMIDA-LDHs exhibited
excellent salt tolerance of up to 1000 mg/L of Na+ or Ca2+. The effects of Fe3+, Ni2+, Cl–, Cr2O7
2–,
SO4
2–, and H2PO4
– on the uptakes of Cu2+ and aniline
were also investigated.
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