Dialkyl-(2-amino-2-(hydroxyimino) ethyl) phosphonate as a new uranium extractant: Extraction mechanism and cost analysis

• DAAHEP containing both phosphoryl and amidoxime groups was designed and synthesized. • DAAHEP exhibited an excellent extraction efficiency for uranyl ions. • DHAHEP showed excellent selectivity for extraction uranyl and could be recycled at least 4 times. • DHAHEP reacted with uranyl via amidoxime and phosphoryl groups. • Amidoxime plays an important role in improving the chemical activity of neutral phosphonates. To efficiently enrich uranyl ions, a novel extractant, dialkyl-(2-amino-2-(hydroxyimino) ethyl) phosphonate (DAAHEP), was firstly synthesized by modifying dibutyl butylphosphonate (DBBPP) with amidoxime groups. Under optimized experimental conditions, the extraction efficiency of uranyl ions by dihexyl-(2-amino-2-(hydroxyimino) ethyl) phosphonate (DHAHEP) and dibutyl-(2-amino-2-(hydroxyimino) ethyl) phosphonate (DBAHEP) reached 98.1 % and 87.0 %, respectively, which were much higher than the extraction efficiency of 70.6 % by DBBPP. Extraction saturation capacity results indicated that the saturation capacity of DHAHEP continuous extraction can reach 584.3 % after 8 times of extraction. Reusability and selectivity experiment demonstrated that DHAHEP exhibited excellent selectivity for uranyl extraction and achieved about 85% extraction efficiency after 4 consecutive extraction-strip cycles. Extraction mechanism studies further revealed that DHAHEP complexed with uranyl ions in a 1:1 ratio via C(=N-OH)-NH 2 and P=O groups. Furthermore, the production cost of DHAHEP is about one-tenth of that of DBBPP, indicating its potential for industrial application.