Application of Hydroxyapatite (HAp) to Remove Copper (II) from Water

Abstract

The contamination of water sources by heavy metals such as copper (Cu²?) poses a serious threat to human health and environment diversity. In this study, hydroxyapatite (HAp), a calcium phosphate-based material, was investigated for its adsorption capacity in the removal of Cu²? ions from aqueous solutions. So, in this study HAp was synthesized via chemical precipitation and characterized using SEM techniques, that acts as an absorbent. This study covers, the effects of initial copper concentration, contact time, adsorbent dosage, and solution pH when exposed to HAp. The results demonstrated that HAp exhibited high affinity for Cu²? ions, with maximum removal efficiency observed at pH 5.5 and contact time of 350 minutes. Based on the results of the adsorption experiments, a treatment unit was designed and developed for the removal of copper from water. Prototype units were constructed to test copper ion concentrations of 4 mg/L and 6 mg/L. These prototypes demonstrated effective performance, successfully treating over 1000 liters of copper-contaminated water.

Introduction

Heavy metal pollution, especially copper contamination in water, poses significant environmental and health risks due to copper’s toxicity, persistence, and bioaccumulation. Although copper is essential in trace amounts, excessive exposure can cause serious health problems like liver and kidney damage. Traditional removal methods such as chemical precipitation and membrane filtration are costly and produce secondary waste. Adsorption has emerged as a cost-effective and efficient alternative, with thermodynamic parameters (?G, ?H, ?S) playing a key role in adsorbent selection and performance.

Hydroxyapatite (HAp), a calcium phosphate compound similar to human bone mineral, has gained attention for copper removal due to its ion-exchange properties. Initially used for biomedical applications, HAp’s potential in wastewater treatment was identified in the 1980s and further studied through various synthesis techniques to optimize adsorption efficiency. Factors like pH, contact time, and adsorbent dosage affect copper ion removal, with HAp showing high removal efficiency (>90%) under slightly acidic to neutral conditions.

A sustainable approach involves synthesizing HAp from biowaste (fish bones, eggshells, animal bones), aligning with “waste-to-wealth” principles by simultaneously addressing pollution and waste management.

In this study, HAp was chemically prepared via precipitation, calcined, milled, and combined with activated charcoal in a custom gravity-driven filter setup. SEM analysis revealed a porous structure favorable for adsorption. Experiments with copper-contaminated water at various concentrations showed high removal efficiencies (~93.5% to 95.4%), with increased copper concentrations enhancing overall adsorption capacity despite slightly reduced percentage removal. The filter system demonstrated effective copper ion removal, making HAp a promising low-cost, sustainable adsorbent for water purification.

Conclusion

This study confirms that hydroxyapatite (HAp) serves as an effective and environmentally friendly adsorbent for the removal of copper (II) ions from aqueous solutions. The adsorption efficiency was notably influenced by factors such as pH, contact time, and the dosage of the adsorbent. The research successfully demonstrated the synthesis of HAp powder using a chemical precipitation method. Additionally, a functional filter unit with a specially designed cartridge was developed for capturing copper (II) ions from polluted or industrial wastewater. Experimental results clearly showed that the presence of HAp significantly enhanced the removal of copper (II) ions from water. The quantity of HAp used played a crucial role in determining the removal efficiency. Therefore, it can be concluded that HAp is a highly effective adsorbent for the treatment of water contaminated with heavy metals.

References

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Copyright

Copyright © 2025 Amitesh Sen, Shiv Kumar Tripathi, Ashish Kumar Srivastava. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.