Magnetite double-network composite using hydroxyapatite-manganese dioxide for Sr2+ removal from aqueous solutions

Abstract

Composites consisting of magnetic hydroxyapatite coated with manganese dioxide (mHAP@MnO2) were synthesized, and their Sr2+ adsorption capacities in aqueous solution were investigated. The results of various experiments, including adsorption isotherm, kinetics, pH effect, and competing ion adsorption experiments showed that the mHAP@MnO2 composites exhibited excellent Sr2+ removal, which could be attributed to their large specific surface area and appropriate pore size. Scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), Brunauer-Emmett-Teller (BET), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and vibrating-sample magnetometer (VSM) analyzes were performed to determine the morphology, pore size, elemental content, and magnetization (11.713 emu/g) characteristics of the developed composites. The adsorption isotherm experiments revealed that the composites had a maximum adsorption capacity of 37.37 mg/g, and the Sr2+ adsorption process fitted well with the Langmuir isotherm (R2= 0.9380) and the pseudo-second order kinetic model (R2= 0.9487 at 100 ppm of Sr2+). Additionally, under a wide range(pH 3–11) of pH values, the composites remained stable and showed high Sr2+ selectivity. These results illustrate the possibility of their application in Sr2+ removal from actual Sr2+-containing liquid wastes.