Performance and mechanism of phosphorus-containing agricultural fertilizer modified biochar for uranium removal from water

Fitting analyses were performed by combining adsorption kinetics, adsorption isotherms, and thermodynamic processes. Finally, an in-depth study of the uranium adsorption behavior and removal mechanism of P/CSB was conducted, elucidating how surface complexation, electrostatic interactions, and phosphate mineralization synergistically promote uranium immobilization.[Results]The optimal mass ratio of phosphorus-containing fertilizer to biochar is m(P):m(CSB) = 8:1.

Under conditions of pH 5.0, an adsorbent dose of 0.01 g, a U(VI) concentration of 10 mg·L⁻¹, a solution volume of 50 mL, and a reaction time of 12 h, the U(VI) removal efficiency reached 98.2%. The Langmuir maximum adsorption capacity was 547.37 mg·g⁻¹, and the adsorption kinetics followed a pseudo-second-order kinetic model. XPS and XRD results indicated that P–O, P=O, C=O, and –OH groups facilitated the binding of U(VI), leading to the formation of uranium phosphate minerals such as H₂(UO₂)₂(PO₄)₂·8H₂O. [Conclusion] The removal of U(VI) by P/CSB is primarily controlled by inner-sphere coordination and phosphate precipitation, with surface adsorption playing a secondary role.

P/CSB is a promising and low-cost adsorbent that can be used to treat uranium-containing wastewater and also serves as a viable means of utilizing coconut shell waste.