Synthesis of core-shell structured microspheres and their application in separation of cadmium from aqueous solutions

Abstract EN

A simple process to fabricate magnetic porous microspheres of calcium hydroxyapatite was demonstrated.

The magnetic microspheres were synthesized by utilizing calcium hydroxyapatite as a core and iron oxide nanoparticles as a shell.

The properties of the prepared magnetic microspheres were characterized by BET surface area measurements, Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD) analysis, scanning electron microscopy (SEM) and energy dispersive analysis system of X-ray (EDS).

Furthermore, the microspheres were applied to remove cadmium from aqueous solutions using batch technique.

The influence of different sorption parameters, such as equilibration time, initial concentration of metal ion, pH value of solution, temperature and ionic strength on the separation of cadmium were studied and discussed.

It was found that the amount of Cd(II) ion sorbed at equilibrium was 61.22 mg g-1 with 75 % removal occurring at the first 5 hrs.

The removal was pH and ionic strength dependent and was hypothesized to be achieved through an ion exchange process and surface complex mechanism in neutral medium.

Meanwhile, precipitation was the relevant mechanism in removal of cadmium at pH > 9.

The isotherm models of Temkin, Dubinin–Radushkevich (D–R) and Redlich–Peterson (R-P) were used to describe the sorption at the solid-liquid interface.

Data suggest that there may be variation in the physicochemical phenomena involving metal adsorption.

The mean adsorption energies evaluated using the D–R model indicated that the separation of Cd(II) was taken place by chemisorption.

The thermodynamic parameters (ΔGo, ΔHo and ΔSo) showed that the removal of cadmium ions was feasible, spontaneous and endothermic process at 30–60 °C.