Synthesis of rod-like hydroxyapatite with high surface area and pore volume from eggshells for effective adsorption of aqueous Pb(II)

•RHNPs with large surface area and pore volume were produced from burnt eggshells.•The RHNP samples produced with 100–400 ml/h were much stable after calcination.•The RHNP samples showed fast adsorption with high adsorption capacity of Pb2+.•The adsorption revealed Langmuir isotherms and a pseudo-second-order reaction.

We report the synthesis of rod-like hydroxyapatite nanopowder from waste eggshells (decomposed to CaO) and phosphoric acid at room temperature without pH control. The procedure involves the use of a syringe pump to control the addition rate of the phosphoric acid in order to maintain a stable pH. Results revealed that pure, rod-like, and nano-size hydroxyapatite particles were produced at various addition rates. Moreover, the sample obtained from 200 ml/h addition rate exhibited large surface area (160.1 m2/g) and pore volume (1.0 cm3/g). Consequently, the prepared hydroxyapatite and that previously produced as adsorbents showed fast adsorption rates (10 min) as well as very high maximum adsorption (qm = 994.5 mg/g and 1000.5 mg/g, respectively) for Pb2+ in aqueous solution. Furthermore, the adsorption process revealed a pseudo-second-order reaction model and the equilibrium adsorption could be described by Langmuir model.

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