Hydroxyapatite for environmental remediation of water/wastewater

Hydroxyapatite (HAP) (Ca10(PO4)6(OH)2) is a calcium phosphate mineral that is considered as one of the widely used inorganic biocompatible materials for contaminant removal. This is a particular composition that specific methods can easily produce as dry methods, wet methods, high-temperature processes, from biogenic sources and a combination of few aforementioned procedures. Depending on the synthesis route of HAP, its porosity is varied, leading to having different adsorption properties. Further, it is considered an appealing option for pollutant remediation due to its abundance, mineral makeup, and ability to reuse without loss of functionality, thermal stability, acid-based ion exchange ability, and economic viability. Notably, these properties are useful in capturing many contaminants, namely dye, heavy metal, and fluoride, in water bodies. Dissolution–precipitation, adsorption, sorption-ion exchange, and Ca2+ ion substitution in mineral content can be utilized as the main mechanisms of contaminant immobilization by HAP. It was proven that pH and contact time are two essential factors that can influence adsorption efficiency. The recent trend on environmental remediation by HAP focuses on tailoring it with another material to improve its adsorption potential. Hence, the use of HAP nanocomposites, HAP nanohybrids, and HAP with organic modifiers can be stated as novel technological improvements.