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.