Enhanced cadmium removal from water by hydroxyapatite subjected to different thermal treatments


Hydroxyapatite powders were synthesized according to a wet precipitation route and then subjected to heat treatments within the temperature range of 200-800 degrees C. The prepared samples were tested as sorbents for cadmium in an aqueous medium. The best performances were obtained with the material treated at 200 degrees C (HAp(200)), as the relevant sorbent textural features (S-BET - specific surface area and V-p - total volume of pores) were least affected at this low calcination temperature. The maximum adsorption capacity at standard ambient temperature and pressure was 216.6 mg g(-1), which increased to 240.7 mg g(-1) by increasing the temperature from 25 to 40 degrees C, suggesting an endothermic nature of the adsorption process. Moreover, these data indicated that a thermal treatment at 200 degrees C enhanced the ability of the material in Cd2+ uptake by more than 100% compared to other similar studies. The adsorption kinetic process was better described by the pseudo-second-order kinetic model. Langmuir, Freundlich, and Dubinin-Kaganer-Radushkevich isotherms were applied to describe the sorption behaviour of Cd2+ ions onto the best adsorbent. Furthermore, a thermodynamic study was also performed to determine Delta H degrees, Delta S degrees, and Delta G degrees of the sorption process of this adsorbent. The adsorption mechanisms were investigated by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy-transmission electron microscopy (SEM-TEM) observations.



subject category

Engineering; Water Resources


Aouay, R; Jebri, S; Rebelo, A; Ferreira, JMF; Khattech, I



This study was supported by the Ministry of Higher Education and Scientific Research of Tunisia, in collaboration with the CICECO-Aveiro Institute of Materials, FCT Ref. UID/CTM/50011/2019, financed by national funds through the FCT/MCTES. Avito H. S. Rebelo acknowledges the Portuguese Foundation for Science and Technology (FCT) for the PhD fellowship grant (SFRH/BD/36101/2007).

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