Efficient removal of phenol from aqueous solutions using hydroxyapatite and substituted hydroxyapatites

Abstract

Adsorbent materials based on apatites (non-substituted and substituted with Sr and Ba) were used for the adsorption of phenol from aqueous solution at 10, 20 and 30 °C and three pH values (3, 6 and 10.5). Structural studies show the formation of the apatite materials and the replacement of Ca by Sr and Ba. The adsorption isotherms of phenol were determined and modelled with two parameter equations (Langmuir, Freundlich and Temkin) or with three parameter equations (Sips and Dubinin–Radushkevich). Taking into account the Sips isotherm, the maximum amount of phenol uptake was 220 mg g−1 for Ba based adsorbent. Thermodynamic parameters were calculated and indicated that the adsorption of phenol onto prepared apatites was spontaneous and exothermic. The DRIFTS studies detected both phenol and phenolate species adsorbed on the surface. It was also shown that phenol molecules were adsorbed by hydrogen bonding between apatite metal ion or oxygen atom from P–O group and the hydrogen of the phenol functional group. The kinetic data indicate that physical and chemical adsorption, may be involved in the adsorption process.