Abstract:
Toxic cadmium (Cd) was removed from water using eggshell-based hydroxyapatite (HAp) grafted
bentonite (HAp/bentonite) composite through a straightforward chemical synthesis route. The
as-prepared adsorbents were characterized using X-ray difraction (XRD), scanning electron
microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Brunauer–Emmett–Teller
analysis (BET). Optimization of the initial adsorbate concentration, adsorbent dosage, pH, and
contact time—all of which afect the adsorption process—was performed using the central composite
design (CCD) of the response surface methodology (RSM). 99.3 percent adsorptive removal efciency
was observed at an initial concentration of 61.58 mg/L of Cd (II), with an adsorbent dosage of 1.58 g, a
solution pH of 5.88, and a contact time of 49.63 min. The analysis of variance (ANOVA) was performed,
and the multiple correlation coefcient (R2
) was found to be 0.9915 which confrms the signifcance
of the predicted model. The Langmuir isotherm model best represented the adsorption isotherm
data, which also predicted a maximum sorption capacity of 125.47 mg/g. The kinetic data were best
described by the pseudo-second order model.
