Synthesis and highly selective adsorption of hydroxyapatite in situ self-Co-doped by magnesium-fluorine in phosphate tailings.

The main components of waste phosphate tailings (WPT) were used in this study for high-value purposes. In particular, these tailings were utilized as raw materials to create magnesium-fluoride self-co-doped hydroxyapatite (abbreviated Mg-F-HAP), a material with a high adsorption capacity and selectivity. Notably, fluorine doping raises the materials' adsorption capacity, whereas magnesium doping improves selectivity. Using the original WPT components in a one-pot process, self-co-doping of Mg-F-HAP at room temperature and pressure was accomplished. It is a mesoporous material with a specific surface area of 117.05 m2/g. This material exhibited very high adsorption capacity for anionic organic pollutants (methyl orange) with the maximum adsorption capacity calculated from Langmuir fitting was 2172 mg/g at pH 7. Which is 51.42, 17.46 and 1.54 times higher than that of commercially available HAP, HAP containing fluoride, and HAP containing magnesium, respectively. The adsorption experiments conducted with a mixture of methyl orange (MO) and cationic organic pollutants (methylene blue) confirmed that the novel material exhibits exceptionally high selectivity towards MO. Furthermore, we have explored its application in adsorbing organic substances from real water bodies, resulting in a 34.1 % reduction in the COD value (from 4100 mg/L to 2700 mg/L).