Synthesis and characterization of ecological-nanohydroxyapatite for adsorption of Cd2+.

[Display omitted] • Synthesis of ecological-nanohydroxylapatite (ECO-NHAp) made from Fine–grained calcareous sludge waste. • The obtained materials were found to be effective adsorbents for Cd2+ metal ions from water. • The adsorption revealed Langmuir isotherms reaction. • More than 99% heavy metal pollutants removal using ECO-NHAp. This paper reports on the hydrothermal synthesis of ecological-nanohydroxyapatite (ECO-NHAp) using Ca extracted from fine-grained calcareous sludge via acid dissolution for use as an adsorbent in the removal of Cd2+ from wastewater. The ECO-NHAp was characterized using Fourier transform infrared spectroscopy, transmission electron microscopy, Brunauer-Emmett-Teller surface analysis, and nuclear magnetic resonance spectrometry. Batch adsorption experiments were performed to investigate the effects of contact time and initial Cd2+ concentration on adsorption efficiency. Kinetics and adsorption behavior were examined using Langmuir, Freundlich, Dubinin–Radushkevich, Temkin, and Sips isotherms. Overall, the Cd2+ adsorption capacity of ECO-NHAp was good (35.09 mg/g) and Langmuir isotherms indicated monolayer adsorption. After controlling for entropy, we found the changes in enthalpy and entropy were positive, while the Gibbs energy was negative. The proposed ECO-NHAp synthesized using raw materials from fine-grained calcareous sludge could be used as a rapid adsorbent for metal ion extraction. [ABSTRACT FROM AUTHOR]