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Raw and calcination-modified coal waste as adsorbents to remove cadmium from simulated mining wastewater
Zhang, M. & Wang, H.
Abstract
The adsorption of cadmium from simulated
mining wastewater by coal waste (CW) and calcinationmodified
coal waste (MCW) was investigated. Effects of
pH, initial concentration, particle size of adsorbent,
adsorbent dosage and temperature were studied in batch
experiments. The adsorption efficiency for cadmium
increased with increasing pH, and the optimum pH for
cadmium adsorption onto MCW and CW was 6.0 and 6.5,
respectively. Kinetic experiments showed that the adsorption
equilibrium was reached within 120 min and followed
pseudo-second-order model well. The adsorption isotherm
data fit Langmuir and Freundlich models, and the adsorption
capacity of cadmium on the two adsorbents increased
with increasing temperature from 298 to 318 K. MCW had
a higher adsorption capacity of cadmium than CW, because
calcination treatment can make CW to have more loose
structure and higher specific surface area. Thermodynamic
parameters, the Gibbs free energy change (ΔG°), enthalpy
change (ΔH°) and entropy change (ΔS°), were calculated
and the results showed that the adsorption of cadmium on
CW and MCW was spontaneous and endothermic. Fourier
transform infrared studies indicated silanol and aluminol
groups were responsible for cadmium binding. The
desorption results indicated that the two adsorbents could
be used repeatedly at least three times without significant
decrease in the adsorption capacity for cadmium. The
results suggested that modified CW could have high
potential as low-cost adsorbent for cadmium removal.
Keywords
Adsorption; Desorption; Heavy metal; Thermodynamic parameters
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