Simply synthesized apatites precipitated onto porous rice husk charcoal for the extraction of cadmium (II) and copper (II) ions

A simple low-temperature method for the deposition of apatite on porous charcoal from rice husk is proposed. The deposition was carried out by impregnation and subsequent treatment of porous charcoal with inorganic compounds of phosphorus and calcium, followed by hydrothermal treatment at 120 degrees C. The composites obtained in this way were investigated by XRD, electron microscopy, nitrogen porosimetry and ion-exchange adsorption of copper and cadmium ions. XRD of the synthesized composites showed the formation of hydroxyapatites with different degrees of crystallization. Electron microscopy showed the presence in the composites of pore-channels with a diameter of up to 10 microns in which apatite grains up to 300 nanometers in length are deposited. The study of the kinetics of ion exchange shows that the diffusion of ions into the grains of hydroxyapatite occurs slowly and does not end during 60 days. Adsorption of cadmium and copper ions during 24 hours occurs mainly on the surface of grains and is characterized by a high degree of ion adsorption and solution purification.