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 pore structure and oxygen-containing
functional groups of lignite play an important role in drying behavior,
spontaneous combustion characteristics, and other applications of
lignite. In this paper, Zhaotong lignite was modified by steam explosion
(SE) technology. The changes in pore structure and fractal characteristics
were analyzed by mercury intrusion porosimetry (MIP). The effect of
SE modification on surface oxygen-containing functional groups was
studied by Fourier transform infrared spectroscopy. Finally, the relationships
between the water adsorption capacity of modified lignite and pore
structure or oxygen-containing functional groups were investigated.
The results indicated that the macroporous and mesoporous pore volumes
of modified lignite can be increased to the greatest extent by SE
modification at 130 °C. For transition pores and micropores,
the maximum pore volume can be obtained by SE modification at 230
°C. The irregularity of the pore structure surface of modified
lignite can be increased by SE modification. In particular, the surface
of all porous structures can be destroyed to the greatest extent by
SE modification at 230 °C. Oxygen-containing functional groups
in Zhaotong lignite can be effectively removed by SE modification,
and the removal amount is positively correlated with the temperature
of SE modification. Moreover, the decrease in monolayer water adsorbed
on the modified lignite surface is due to the reduction in the number
of oxygen-containing functional groups on the surface after SE modification.
The pore volume of modified lignite is increased by SE modification,
which clearly increases the amount of capillary water adsorbed by
the modified lignite.
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