Molecular sieving meets ion exchange: KCoFC@UiO-66 as a multi-functional adsorbent for high-efficiency rubidium recovery from lithium tailing leachate

Rubidium (Rb), a critical strategic metal with extensive applications in energy storage, electronics, and nuclear medicine, faces extraction challenges due to its low natural abundance and dispersed occurrence. To address the inefficiency and selectivity limitations of conventional extraction methods, this study synthesized a core-shell composite metal-organic framework (MOF) material, KCoFC@UiO-66, via a solvothermal coordination strategy. The material synergistically integrates the ion-exchange capability of potassium cobalt hexacyanoferrate (KCoFC) with the hierarchical porosity and structural stability of zirconium 1,4-dicarboxybenzene MOF (UiO-66). Structural characterization confirmed the core-shell architecture, where the KCoFC core facilitates selective Rb capture via ion exchange and cyano coordination, while the UiO-66 shell enhances Rb enrichment through electrostatic interactions and size-selective sieving. Adsorption kinetics followed a pseudo-second-order model, indicating chemisorption dominance, while isotherm studies aligned with Freundlich and Dubinin-Radushkevich models, revealing heterogeneous multilayer adsorption. The composite demonstrated remarkable selectivity for rubidium, achieving a recovery rate of 98.7 % from lithium tailing leachates, along with notable regeneration stability, retaining 86.2 % of its capacity after five cycles. This performance can be ascribed to the ability of UiO-66 to inhibit the aggregation of KCoFC and to the effects of pore confinement. This work establishes a multi-mechanistic adsorption paradigm combining ion exchange, electrostatic attraction, and pore confinement, offering a scalable solution for Rb recovery from complex matrices.