Efficient Adsorption and Desorption of Uranium(VI) Using a Polymeric Adsorbent: A Combined Theoretical and Experimental Approach with Real-Life Alkaline Leach Liquor

Alkaline leaching is used for the extraction of uranium from rarely available carbonate ore. A hyperbranched cross-linked polymeric adsorbent (HCPA) was developed for selective recovery of uranium(VI) (U) from real-life alkaline leach liquor. HCPA was synthesized using the free radical copolymerization of acrylamide and N, N-methylene bis(acrylamide). In addition, potassium persulfate (as the initiator) and dodecanethiol (as the brancher) were used to transfer the radicals for faster chain formation and smooth branching of the long-chain polymer. Several methods were used extensively to characterize the adsorbent. The Langmuir maximum U adsorption capacity of HCPA was 1012 mg/g at 303 K, and 98% of U was removed from alkaline leach liquor. U was adsorbed at pH 8.5 in the presence of various interfering co-ions and desorbed at pH 11.5 in the form of sodium diuranate (Na2U2O7) precipitate. The adsorption was monolayer, exothermic, and spontaneous in nature. The C–N, CO–NH2, and C–OH groups of HCPA interacted with uranyl ions initiating the coordinative and electrostatic interactions leading to U adsorption. Continuous fixed-bed column runs were performed using the actual leach liquor, and a fundamental kinetic model was used to quantify the performance of columns. The transport parameters were estimated from the model, and scaling-up calculations were performed using these parameters. Five adsorption–desorption cycles were conducted to determine the reusability and structural stability of the synthesized polymeric adsorbent.