Removal of manganese from aqueous solution by a permeable reactive barrier loaded with hydroxyapatite-coated quartz sand

Hydroxyapatite-coated quartz sands were synthesized by the sol–gel method and employed as a permeable reactive barrier (PRB) medium for the manganese contaminated aqueous solution treatment. The effects of composite particle size, initial concentration of manganese, and hydraulic load on the manganese removal in aqueous solution were investigated by column test. The Thomas and Yoon-Nelson dynamic models were used to reproduce the Mn(II) adsorption behavior observed in these column experiments. The scanning electron microscope (SEM) coupled with energy dispersive spectrometer (EDS), X-ray diffractometer (XRD), and X-ray photoelectron spectroscopy (XPS) were employed to investigate the Mn(II) removal mechanism. Results showed that the initial concentration of manganese had the greatest influence on Mn(II) removal when the initial concentration of manganese is 3 mg/L, the particle size is 0.15 ~ 0.3 mm, the hydraulic load is 5.5 m/m·d, and the adsorption capacity of the composites reached the maximum of 1.10 mg/g. The Thomas model fitted the breakthrough curves better. The maximum adsorption capacity of Mn(II) is 0.7546 mg/g. The adsorption mechanisms are mainly ion exchange and dissolution–precipitation. The results indicate that the hydroxyapatite-coated quartz sands could be an effective PRB media for the manganese-contaminated water treatment.