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Scientific reports2025; 15(1); 33990; doi: 10.1038/s41598-025-11961-4

Influence of calcination temperature on equine bone hydroxyapatite structure and lead adsorption efficiency.

Abstract: Lead (Pb²⁺) contamination in aquatic environments represents a serious global threat due to its toxicity, persistence, and non-biodegradable nature. In this study, hydroxyapatite (HA) was synthesized from equine scapula bone and investigated as a low-cost, sustainable adsorbent for Pb²⁺ removal from aqueous media. HA was thermally treated at 100 °C, 500 °C, and 900 °C to assess the effect of calcination on physicochemical and adsorption properties. Characterization techniques including XRD, FTIR, SEM/EDX, TGA and XRF confirmed structural and compositional evolution with temperature. Among the samples, HA-500 exhibited the highest adsorption performance, achieving 99% Pb²⁺ removal and a maximum capacity of 50 mg/g under optimal conditions (0.25 g dose, 20 mg/L initial Pb²⁺ concentration). Kinetic studies followed a pseudo-second-order model (R² > 0.999), and equilibrium data were best described by the Freundlich isotherm (R² = 0.9839), indicating multilayer adsorption on heterogeneous surfaces. Thermodynamic analysis revealed that Pb²⁺ adsorption is spontaneous and exothermic, with negative Gibbs free energy values and positive entropy changes, confirming increased randomness at the solid-liquid interface. Furthermore, regeneration studies showed that HA-500 retained 73% of its efficiency after three cycles. These findings demonstrate the potential of equine bone as a novel bio-based source of hydroxyapatite for efficient and sustainable heavy metal remediation.
© 2025. The Author(s).
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Publication Date: 2025-09-30 PubMed ID: 41028228PubMed Central: PMC12485134DOI: 10.1038/s41598-025-11961-4Google Scholar: Lookup
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Summary

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Overview

  • This research explores the preparation of hydroxyapatite (HA) from equine scapula bone calcined at different temperatures and evaluates its effectiveness in adsorbing toxic lead (Pb²⁺) ions from water.
  • The study identifies the optimal calcination temperature to maximize lead adsorption, characterizes the material’s physicochemical properties, and investigates adsorption kinetics, thermodynamics, and reusability.

Background

  • Lead contamination in water is a significant environmental and health problem due to lead’s toxicity, persistence, and difficulty to break down.
  • Hydroxyapatite, a calcium phosphate compound commonly derived from bone, has good adsorption properties for removing heavy metals.
  • Utilizing waste equine bone as a bio-based source for HA provides a sustainable, low-cost material for water purification.

Materials and Methodology

  • Equine scapula bones were cleaned and then subjected to thermal treatment (calcination) at three different temperatures: 100 °C, 500 °C, and 900 °C.
  • This calcination process aimed to alter the structural and chemical properties of HA to evaluate how temperature affects adsorption capacity.
  • Characterization techniques employed included:
    • X-ray diffraction (XRD) to analyze crystal structure changes.
    • Fourier-transform infrared spectroscopy (FTIR) to identify functional groups.
    • Scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX) to examine surface morphology and elemental composition.
    • Thermogravimetric analysis (TGA) to assess thermal stability and composition changes.
    • X-ray fluorescence (XRF) for elemental composition confirmation.

Results: Structural and Compositional Changes

  • Increasing calcination temperature influenced HA’s structural properties, improving crystallinity and removing organic components at higher temperatures.
  • At 500 °C, HA showed an optimal balance of structural integrity and surface features favorable for Pb²⁺ adsorption.
  • At 900 °C, though crystallinity increased, excessive sintering likely reduced adsorption sites.

Lead Adsorption Efficiency

  • HA calcined at 500 °C (HA-500) demonstrated the best performance, removing 99% of Pb²⁺ from aqueous solutions.
  • Maximum adsorption capacity for HA-500 was determined as 50 mg of Pb²⁺ per gram of adsorbent under optimal conditions (using 0.25 g of adsorbent and 20 mg/L initial Pb²⁺ concentration).
  • Lower temperature HA (100 °C) and higher temperature HA (900 °C) showed reduced adsorption efficiencies relative to HA-500.

Kinetic and Isotherm Modeling

  • Kinetic data fitted a pseudo-second-order adsorption model with a high correlation coefficient (R² > 0.999), suggesting chemisorption dominates the process.
  • Equilibrium adsorption data best corresponded to the Freundlich isotherm model (R² = 0.9839), indicating:
    • Multilayer adsorption on heterogeneous surface sites.
    • Non-uniform distribution of adsorption energies across the HA surface.

Thermodynamic Analysis

  • Adsorption of Pb²⁺ onto HA-500 was spontaneous, as evident from negative Gibbs free energy (ΔG) values.
  • The process was exothermic, demonstrated by negative enthalpy change (ΔH).
  • Positive entropy change (ΔS) suggested increased disorder at the solid-liquid interface during adsorption.

Regeneration and Reusability

  • HA-500 retained approximately 73% of its Pb²⁺ removal efficiency after three adsorption-desorption cycles, showing reasonable reusability.
  • This regeneration potential enhances HA’s viability as a sustainable adsorbent for heavy metal remediation.

Conclusions and Implications

  • This study demonstrates that calcination temperature strongly influences the physicochemical properties and adsorption performance of hydroxyapatite derived from equine bone.
  • HA-500 provides an efficient, low-cost, and bio-based adsorbent for removing toxic Pb²⁺ from contaminated water.
  • The findings support the use of waste animal bone as a sustainable resource for producing advanced materials in environmental remediation applications.
  • Future work may explore scaling up the process and testing against other heavy metals and real wastewater matrices.

Cite This Article

APA
Touareb D, Latifi S, Saoiabi S, Habraji L, Hammani O, Azzaoui K, Jodeh S, Yaghi S, Sabbahi R, Hammouti B, Saoiabi S. (2025). Influence of calcination temperature on equine bone hydroxyapatite structure and lead adsorption efficiency. Sci Rep, 15(1), 33990. https://doi.org/10.1038/s41598-025-11961-4

Publication

Scientific reports
ISSN: 2045-2322
NlmUniqueID: 101563288
Country: England
Language: English
Volume: 15
Issue: 1
Pages: 33990
PII: 33990

Researcher Affiliations

Touareb, Douae
  • Laboratory of Applied Chemistry of Materials, Department of Chemistry, Faculty of Sciences, Mohammed V University in Rabat, Rabat, 10090, Morocco.
Latifi, Souhayla
  • Laboratory of Applied Chemistry of Materials, Department of Chemistry, Faculty of Sciences, Mohammed V University in Rabat, Rabat, 10090, Morocco.
Saoiabi, Sarah
  • Avian Pathology Unit, Department of Veterinary Pathology and Public Health and Food, Hassan II Agronomic and Veterinary Institute, Rabat, 10101, Morocco. s.saoiabi@yahoo.com.
Habraji, Lamiaa
  • Laboratory of Applied Chemistry of Materials, Department of Chemistry, Faculty of Sciences, Mohammed V University in Rabat, Rabat, 10090, Morocco.
Hammani, Othmane
  • National Center for Scientific and Technical Research (CNRST), Rabat, 10102, Morocco.
Azzaoui, Khalil
  • Engineering Laboratory of Organometallic, Molecular Materials and Environment, Faculty of Sciences, Sidi Mohamed Ben Abdellah University, Fez, 30000, Morocco.
  • Laboratory of Industrial Engineering, Energy and the Environment (LI3E) SUPMTI, Rabat, Morocco.
Jodeh, Shehdeh
  • Department of Chemistry, An-Najah National University, P. O. Box 7, Nablus, Palestine. sjodeh@najah.edu.
Yaghi, Sobhi
  • Department of Chemistry, An-Najah National University, P. O. Box 7, Nablus, Palestine.
Sabbahi, Rachid
  • Higher School of Technology, Ibn Zohr University, Quartier 25 Mars, P.O. Box 3007, Laayoune, Morocco.
Hammouti, Belkheir
  • Euromed University of Fes, UEMF, Fes, Morocco.
Saoiabi, Sanaa
  • Laboratory of Applied Chemistry of Materials, Department of Chemistry, Faculty of Sciences, Mohammed V University in Rabat, Rabat, 10090, Morocco.

MeSH Terms

  • Durapatite / chemistry
  • Animals
  • Lead / chemistry
  • Lead / isolation & purification
  • Adsorption
  • Horses
  • Temperature
  • Bone and Bones / chemistry
  • Thermodynamics
  • Water Pollutants, Chemical / chemistry
  • Water Pollutants, Chemical / isolation & purification
  • Kinetics
  • Water Purification / methods
  • X-Ray Diffraction

Conflict of Interest Statement

Declarations. Competing interests: The authors declare no competing interests.

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Citations

This article has been cited 1 times.
  1. Berrahou S, Latifi S, Saoiabi S, Abidi N, Saoiabi S, Azzaoui K, Hanbali G, Jodeh S, Hammouti B, Sabbahi R. Hydroxyapatite-cellulose composites: properties, fabrication methods, and applications. J Mater Sci Mater Med 2026 Jan 23;37(1):27.
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