Water is an essential need for human life, which is polluted due to various reasons. The water pollution is a universal subject and the world community is facing problems caused by it. One of the main causes of environmental water pollution is anthropogenic actions and industrial activities in the world. Water pollutants include thousands of organic (pesticides, fertilizers, hydrocarbons, phenols, plasticizers, biphenyls, detergents, oils, greases, pharmaceuticals, etc.), inorganic (heavy metals, nitrate, sulfate, phosphate, fluoride, etc.), and biological pollutants (virus, bacteria, fungi, algae, amoebas, and planktons, etc.). Many studies were performed to remove emerging pollutants by the adsorption process. These processes do not add unfavorable by-products to the environment and have been proven to be superior to other wastewater treatment techniques in terms of the simplicity of design, operation, and insensitivity to toxic compounds. Due to the presence of both cationic and anionic groups in the structure of hydroxyapatite, this compound is a good candidate for absorbing cationic and anionic pollutants from water. Hydroxyapatite is widely used for adsorbing pollutants from water due to its properties such as low cost, ion exchange properties, high biocompatibility, and high adsorption capacity. Although, the use of pure HAP nanoparticles is very useful for removing toxic substances, but its preparation process is expensive. Also, the amount of HAP nanoparticles during filtration shows a significant drop due to their small size. A literature review shows how to overcome these problems as well as the applications and advantages of HAP nanoparticles. It is essential to prepare adsorbents based on HAP in a usable form by combining them with other inorganic materials such as synthetic and natural zeolite, Fe3O4, MnO2 and Al2O3.
