Preparation of Emulsion Hydrogels Encapsulating P204 by the Pickering Emulsion Templates for the Adsorption of Ce(III) in Aqueous Solutions

This study reports a novel adsorbent prepared via a Pickering emulsion-template method for the efficient adsorption of Ce(III) from aqueous solutions. Water-in-oil Pickering emulsions were first stabilized by commercial nano-SiO2, using an aqueous sodium alginate solution as the dispersed phase and kerosene-diluted di-(2-ethylhexyl) phosphate (P204) as the continuous phase. The emulsion droplets were then gelled in a Ca 2 + solution to form stable Pickering emulsion hydrogel beads (PEHG), thereby encapsulating the P204-containing organic phase within a calcium alginate matrix. Fourier transform infrared spectroscopy and scanning electron microscopy confirmed the successful encapsulation and the structural integrity of the PEHG. Batch adsorption experiments demonstrated that the adsorption kinetics followed a pseudo-second-order model, indicative of chemisorption, while the equilibrium data were best described by the Redlich-Peterson isotherm, suggesting a complex adsorption mechanism involving both monolayer and multilayer interactions. Remarkably, the PEHG retained a Ce(III) removal efficiency above 99% over five consecutive adsorption-desorption cycles, with no observable structural degradation or leakage of the encapsulated phase. This strategy of encapsulating the functional organic phase (P204) within a hydrogel matrix not only enhances its utilization efficiency but also effectively prevents its leakage into the aqueous environment, offering a promising and sustainable approach for rare earth element recovery.