Preparation of Biobased Porous Hydrogels by Citric Acid Grafted Polyacrylic Acid for Rare Earth Elements Separation

Rare earth elements (REEs) are essential for advanced technologies such as energy, electronics, and aerospace.Efficient separation of REEs is critical for the full utilization of natural limited resources.To obtain biobased absorbents with large adsorption capacity, high selectivity, and good reusability, a larger surface area and functionalized surface of absorbents are required.In this work, the porous PAA-CA (citric acidgrafted polyacrylic acid) hydrogels were prepared using a high internal phase emulsion templating method.The physical and chemical properties of PAA-CA were characterized by FTIR, XPS, and SEM.The influence of pH, temperature, initial concentration, and contact time on the adsorption capacity of Pr 3+ (light REE) and Er 3+ (heavy REE) was investigated and analyzed.The results show that PAA-CA hydrogels exhibited good adsorption performance with a better adsorption capacity for Er 3+ of around 400 mg/g.The adsorption process was pH-dependent, with optimal adsorption at pH = 3-7.Kinetic studies revealed that the adsorption followed a pseudo-second-order model, while thermodynamic analyses confirmed the process was spontaneous and endothermic.PAA-CA exhibited good selectivity for Er 3+ in a binary ion system, especially containing K + or Fe 3+ .Furthermore, the hydrogels retained high adsorption capacities across 10 adsorption-desorption cycles,