Hydroxyapatite as an advanced adsorbent for removal of heavy metal ions from water: Focus on its applications and limitations

Abstract

Adsorbent materials are known to have favorable surface physico-chemical features that enable them to bind to different pollutants in aqueous medium. Complexity in wastewater generation due to presence of diversified nature of pollutants demand enhanced performance from adsorbent materials. An advanced adsorbent requires greater selectivity, enhanced performance in adsorption capacity over a wide range of pH and pollutant concentration as well as faster kinetics. The economics of the treatment process depend not only on the cost efficiency of the synthesis of the adsorbent material but also on the regeneration capacity of the used adsorbent. Hydroxyapatite derived either from synthetic or biogenic waste resources have demonstrated suitable physical and chemical properties that have enabled it for faster and greater efficiency for binding to different pollutants. Its major constituent being calcium and phosphorus, hydroxyapatite is a biomaterial, is biocompatible and is non-toxic in nature. The present review has discussed on the properties of hydroxyapatite as an advanced adsorbent material in the context of its performance for removal of metal ion pollutants from not only a single metal ion suspension but also from multi-metal ion solution. The high specificity of hydroxyapatite is also highlighted during its application as an adsorbent. The major highlights of this review are on the limitations for use of hydroxyapatite as an advanced adsorbent. Current research work undertaken to curtail some of its limitations is also discussed.