Eco-Friendly Synthesis of SphericalLanthanum-Doped Hydroxyapatite from Phosphogypsum Waste: A High-EfficiencyStrategy for Fluoride Removal in Aqueous Solutions

Abstract

To address theenvironmental challenges posed by massive phosphogypsum (PG) stockpiles and groundwaterfluoride contamination, this study developed an eco-friendly strategy forsynthesizing lanthanum-doped hydroxyapatite (La-PGHAP) from PG waste via anacid precipitation-hydrothermal method. The synthesized La-PGHAP exhibited aspherical morphology, high crystallinity, and a significantly enhanced specificsurface area of 53.11 m²/g. Batch adsorption experiments revealedthat pH critically influenced fluoride (F^-)removal, with maximum adsorption capacities of 8.20 mg/g (PGHAP) and 31.98 mg/g(La-PGHAP) at pH 4. The adsorption process followed pseudo-second-orderkinetics and the Langmuir isotherm model, indicating chemisorption-dominatedmonolayer adsorption. La doping introduced Lewis acid-base interactions throughLa³⁺-F^- coordination, improving both adsorption capacityand stability across a wide pH range (2-10). Reusability tests demonstratedthat La-PGHAP retained 85.4% of its initial capacity after 4 cycles. This "waste-to-waste"approach not only repurposes PG into a high-efficiency adsorbent but alsoprovides a sustainable solution for mitigating fluoride pollution, showcasingsignificant potential for industrial-scale water treatment applications.

Keywords

Phosphogypsum / Hydroxyapatite / Lanthanum-doped / Fluorine ion / Adsorption

Statement of the Use of Generative AI and AI-Assisted Technologies in the Writing Process

During the preparation of this manuscript, the author(s) used Deepseek in order to optimize the logical flow of the manuscript structure, refine English expression accuracy, and check for grammatical and typographical errors. After using these tools, the author(s) thoroughly reviewed and edited the content, verified all scientific data, experimental details, and conclusion validity, and take(s) full responsibility for the content of the published article.

Acknowledgements

The authors gratefully acknowledge financial support from the Natural Science Foundation of Hubei Province (Grant No. 2025AFD245), and the Natural Science Foundation of Yichang Municipality (Grant No. A24-3-043). The authors extend their gratitude to Scientific Compass (www.shiyanjia.com, accessed on 8 July 2025) for providing invaluable assistance with characterization analysis.

Author Contributions

Conceptualization, Z.W.; Methodology, S.J.; Investigation, S.J. and Y.Q.; Resources, Z.W., B.C. and R.C.; Data Curation, S.J. and Y.Q.; Writing—Original Draft Preparation, S.J.; Writing—Review & Editing, Z.W.; Visualization, B.C.; Supervision, Z.W. and R.C.; Project Administration, Z.W.; Funding Acquisition, Z.W.

Ethics Statement

“Not applicable” for studies not involving humans or animals.

Informed Consent Statement

“Not applicable” for studies not involving humans.

Data Availability Statement

The data used in this study are not publicly accessible and cannot be made available due to internal research policies.

Funding

This research was funded by the Natural Science Foundation of Hubei Province grant number 2025AFD245 and the Natural Science Foundation of Yichang Municipality grant number A24-3-043.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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