Hydroxyapatite-based materials for adsorption, and adsorptive membrane process for heavy metal removal from wastewater: Recent progress, bottleneck and opportunities

Background Heavy metals in water pose grave risks to human health and the environment, necessitating the development of cost-effective and sustainable materials to combat heavy metal pollution in water. Natural and waste-based materials have received exceptional attention among researchers in removing heavy metals. Methods The efficient hydroxyapatite (HAp) and its composites have been utilized as adsorbents and membrane materials for the efficient elimination of heavy metals from wastewater, capitalizing on their low cost, eco-friendliness, thermal stability, and efficiency. Significant findings The review commences with a brief highlight and comparison of methods of heavy metal removal. Then, it delves into HAp properties, synthesis methods, and the influence of preparation conditions on HAp characteristics. The paper evaluates heavy metal adsorption in terms of equilibrium conditions, isotherms, and kinetics. While adsorption is effective for heavy metal removal, it can be labor-intensive for regenerating adsorbents and costly for large-scale applications. Therefore, the paper discusses the potential of HAp-based membranes fabricated via electrospinning and phase inversion techniques. It explores the characteristics and heavy metal removal performance of HAp membranes. In conclusion, the review discusses limitations and future directions for HAp-based membranes. This article serves as a valuable resource for understanding the capabilities of HAp-based adsorbents and membranes for sustainable heavy metal removal.