Enhanced fluoride removal behaviour and mechanism by dicalcium phosphate from aqueous solution

ABSTRACT

Dicalcium phosphate was prepared by ethylenediaminetetraacetic acid as a calcium chelating agent, and further explored to remove the fluoride ions from aqueous solution. The as-prepared samples main existed in the monetite phase from the result of XRD. The dried sample consisted of small nanoparticles and displayed irregular particles with a size of ca. 3 μm due to the agglomeration. The fluoride removal ability was evaluated by batch adsorption experiments. The as-prepared adsorbent exhibited the enhanced fluoride removal behaviour with the maximum adsorption capacity of 66.72 mg/g from the Langmuir isotherm model, which was higher than that of other previously reported calcium phosphate. The adsorbent could be utilized in the wide pH range of 3–10. The adsorption kinetics could be better described by the pseudo-second-order model than first-second-order model. The co-existing anions had a negligible influence on the fluoride adsorption. The investigation of adsorption mechanism suggested that the chemical reaction and/or dissolution – precipitation mechanism should be dominant in the fluoride adsorption process, accompanying with electronic interaction and ions exchange, which enhanced the fluoride removal performance.

GRAPHICAL ABSTRACT

KEYWORDS:

• Dicalcium phosphate
• monetite
• fluoride
• kinetics
• adsorption mechanism

Acknowledgements

This project was supported by the National Natural Science Foundation of China (21407152, 21590811, 31200439, 21777166); and Science and Technology Planning Project of Guangdong Province, China (2016A010103046).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This project was supported by the National Natural Science Foundation of China [grant number 21407152], [grant number 21590811], [grant number 31200439], and [grant number 21777166]; and Science and Technology Planning Project of Guangdong Province, China [grant number 2016A010103046].