Synthesis of core–shell magnetic nanocomposite bearing phosphonic acid ligand for uranium extraction from strong HNO3 solution

Recovery of uranium from strong acid media using magnetic nanomaterials as sorbents is vital for sustainable nuclear energy, due to their superparamagnetism and large specific surface energy. However, it remains a huge challenge to develop magnetic nanomaterials for extracting uranium from strong acid media, since magnetic nanomaterials often suffer from poor structural stability and low uranium adsorption performance in strong acid media. Herein, a novel core–shell magnetic nanocomposite Fe3O4@SiO2/P (MBA-VPA) bearing phosphonic acid was fabricated by distillation-precipitation polymerization of N, N'-methylene diacrylamide (MBA) with vinylphosphonic acid (VPA) around the surface of Fe3O4 decorated by SiO2 (Fe3O4@SiO2). By optimizing the polymerization system, high concentration of phosphonic acid with high free movement degree was led into the surface of the sorbent. Under applied conditions (c(H+) = 4 mol L−1, T = 298 K and t = 3 h), the sorbent showed a record-breaking maximum adsorption capacity (qmax) of 262.5 mg g−1 with an excellent selectivity for uranium in the presence of multi-ions. The adsorption capacity of the sorbent in strong HNO3 increased remarkably with increase of the concentration and free movement degree of phosphonic acid. By coating Fe3O4 with an inert SiO2, the sorbent exhibited excellent acidic resistance in strong HNO3. The sorbent could also be magnetically recovered within 15 s, and repeated at least six times without obvious reduction in adsorption capacity. The excellent adsorption performance in strong HNO3 media was primarily assigned to the abundant accessible PO groups, evidenced by X-ray photoelectron spectroscopy (XPS), control experiments and density functional theory (DFT). Most importantly, this work provides a new perspective for developing highly active, excellent acidic resistance, and recyclable magnetic nanomaterials for extracting uranium from strong acid media.