Conversion of Waste-Derived Potato Starch into a β-CD Nanosponge Sorbent for Rare Earth Recovery from Mining Wastewater

Recovering rare earth (RE) ions from mining wastewater offers several advantages, including reducing resource scarcity, minimizing environmental pollution, and lowering biological toxicity hazards. In this study, we synthesized a green adsorbent material, potato starch-derived β-cyclodextrin nanosponges (β-CD@PCPP NSs), via ionic cross-linking of β-cyclodextrin (β-CD), functionalized polyethylenimine (PEI), potato starch (PS), and chitosan (CS). The β-CD@PCPP NSs demonstrated favorable selectivity for cerium (Ce3+) and holmium (Ho3+), achieving maximum adsorption capacities of 147.79 mg/g and 151.21 mg/g, respectively, as described by the Langmuir isotherm model. Batch adsorption experiments revealed that the adsorption process followed pseudo-second-order kinetics, suggesting that chemisorption is the dominant mechanism. Characterization techniques, including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA), together with density functional theory (DFT) calculations, indicated that the porous three-dimensional structure and the presence of abundant O-, N-, and P-containing functional groups facilitate adsorption through inner-sphere complexation. The adsorbent maintained over 71% removal efficiency after five adsorption-desorption cycles and exhibited strong selectivity in mining wastewater, achieving RE ion removal rates greater than 93% compared with less than 8% for competing ions. A cost evaluation revealed a low synthesis cost of $0.3471 per gram, suggesting good scalability. This paper presents a sustainable strategy for recovering RE ions and remediating wastewater, aligning with the principles of cleaner production and a circular economy.