Highly efficient separation of uranium from wastewater by in situ synthesized hydroxyapatite modified coal fly ash composite aerogel

In this work, hydroxyapatite (HAP) was in situ synthesized on coal fly ash (CFA) to prepare hydroxyapatite modified coal fly ash composite aerogel (HCFAA). The maximum removal efficiency and capability of uranium(VI) on HCFAA were 97.6 % and 205.7 mg g−1, respectively, which was much higher than those of CFA (83.6 % and 59.1 mg g−1) (pH = 3.0, m/V = 1.0 g/L and T = 298 K). The desorption efficiency of uranium(VI) by HCFAA was even more than 80 % after five cycles, demonstrating that the introduction of HAP had improved uranium(VI) removal performances. Pseudo-second-order and Langmuir models were fitted better with the experimental data, indicating the uranium(VI) removal process was a homogeneous monolayer chemisorption. Meanwhile, the uranium(VI) removal efficiency for HCFAA in actual wastewater was higher to 80.6 % and uranium(VI) could even be completely separated from actual wastewater by HCFAA during dynamic adsorption (m = 50 mg, V = 400 mL, C0 = 10 mg/L), further illustrating that the introduction of HAP was an available method to modify CFA. Characterizations results demonstrated that uranium(VI) was successfully immobilized on HCFAA through ion exchange, dissolution-precipitation and surface complexation. In conclusion, HCFAA was a prospective adsorbent for uranium(VI) separation in practical application.