Equilibrium, kinetic, and selectivity studies for high-capacity and -selectivity uranium adsorption on polyacrylic acid copolymer hydrogel

• RSM optimized uranium adsorption of hydrogel at pH 4.3, 0.06 g/100 mL dose, 126 min contact time. • Record U(VI) adsorption capacity of 1111.11 mg/g in acidic media, exceeding most reported absorbents. • Adsorption followed pseudo-second-order kinetics and fit the Langmuir isotherm equilibrium model. • Hydrogel rapidly uptake over 90 % of uranyl in under 15 min. • Thermal stability up to 120 °C with <5 % mass loss, ideal for acidic industrial effluents. Efficient uranium recovery from acidic solutions is challenging due to competing metal ions and low pH, which reduce conventional absorbents’ effectiveness. This research aims to fill a gap by enhancing the adsorption capabilities of a polyacrylic acid-co-polyacrylamide copolymer (p(AA-co-Am)) hydrogel, which has been optimized through response surface methodology (RSM) to attain exceptional uranium adsorption capacity while ensuring selective removal in acidic multi-ionic environments. The hydrogel's physicochemical, structural, and thermal characteristics were analyzed using various methods, including gel content measurement, swelling degree assessment, equilibrium water content evaluation, scanning electron microscopy, thermogravimetric analysis, and infrared spectroscopy. We employed RSM utilizing a five-level, three-variable central composite design (CCD) to optimize the uranium adsorption conditions of p(AA-co-Am) hydrogel. The independent variables analyzed were absorbent mass, pH, and adsorption time. This led to optimum conditions of 0.06 g absorbent mass per 100 mL of solution, pH of 4.3-, and 126-min adsorption time, validated through repeated experiments. A pseudo-second-order mechanism was observed for uranium adsorption, and the equilibrium data fit the Langmuir isotherm model, which indicates it has an impressive capacity of 1111.11 mg/g, higher than most absorbents reported to date. In complex ion systems and acidic solutions, the hydrogel showed high selectivity for UO 2 2+ , positioning it as an absorbent of next-generation for uranium remediation.