Adsorption and interaction mechanism of uranium (VI) from aqueous solutions on phosphate-impregnation biochar cross-linked Mg-Al layered double-hydroxide composite

The phosphate pre-impregnation pyrolysis followed by a hydrothermal method was used to synthesize a novel phosphate-impregnation biochar (PBC) cross-linked Mg-Al layered double-hydroxide composite (PBC@LDH) for U(VI) removal from aqueous solution. Physicochemical analysis revealed that the PBC@LDH possessed the high surface area and abundant surface functional groups. XPS and FTIR analysis confirmed that the highly efficient adsorption of U(VI) by PBC@LDH was attributed to the strong complexation and reduction reaction of P-O, Mg-O-H, and -OH groups to U(VI) as well as the co-precipitation of polyhydroxy aluminum cations captured U(VI). Adsorption equilibrium of U(VI) on PBC@LDH was reached within 2 h of contact time, and the process of the material for U(VI) adsorption was optimally described with the pseudo-second-order kinetic model (R2nd 2 >0.99). Moreover, the adsorption isotherm of U(VI) on PBC@LDH was better simulated by the Langmuir model (RLan 2 >0.97). The maximum adsorption capacity of U(VI) by the PBC@LDH was calculated to be -274.15 mg/g at pHinitial 4 and 298 K, which was an improvement of -17 times than that of unmodified biochar and, furthermore, PBC@LDH texted had the most strongly adsorb U(VI) between approximately pHinitial 4 and 8. It was verified an endothermic, favorable, and spontaneous adsorption process. After five successive sorbent reuses, the elimination rate was still 77.9%. These results suggest that PBC@LDH is a promising candidate for desirable separation of uranium from uranium-waste water.

Automated summary

The novel phosphate-impregnation biochar cross-linked Mg-Al layered double-hydroxide composite (PBC@LDH) exhibited high U(VI) removal efficiency from aqueous solution. The adsorption equilibrium was reached quickly, and the process followed pseudo-second-order kinetics and Langmuir isotherm. The adsorption process was endothermic, favorable, and spontaneous, with a high reusability rate.