The construction of magnetic hydroxyapatite-functionalized pig manure-derived biochar for the efficient uranium separation

In this work, three magnetic biochar-supported nano-hydroxyapatite materials were prepared by endowing different magnetic sources, which showed excellent reusability and adsorption ability. It was worth mentioning that the maximum adsorption capacity of the magnetic biochar-hydroxyapatite composite with nickel chloride as the magnetic source reached 1723.5 mg/g and the residual concentration of uranium in the solution could reach the limit standard of China for the discharge of uranium-containing wastewater at low uranium concentration. The removal efficiencies of the composite for uranium in different water systems were all higher than 90.2 %, which reflected the applicability of the composite. Besides, the material was easy to be recycled and reused due to the magnetization. After eight times of reuse, the uranium removal efficiency was still higher than 96.3 % and the magnetism was not significantly weakened. The multiple strong chemical reactions of active sites with uranium, including ion exchange, surface complexation and ionization-precipitation, were the major reason for the excellent adsorption ability. In conclusion, the magnetization of biochar-based materials might be a promising uranium adsorbent, which would open a new direction for the design of biochar-based adsorbents for uranium removal.