Efficient and rapid recovery of scandium from acidic wastewater using a β-cyclodextrin-based...

Motivated by the growing demand for rare earth elements (REEs), it is crucial to design effective adsorbents capable of separating and reclaiming REEs from acidic wastewater. Herein, a phosphorus-functionalized covalent organic polymer (β-HCCD) was successfully synthesized via a straightforward nucleophilic substitution reaction, utilizing two cost-effective monomers, β-cyclodextrin (β-CD) and hexachlorocyclotriphosphazene (HCCP). Owing to the presence of abundant P-O bonds in β-HCCD and the unique cavity structure of β-CD, β-HCCD exhibits adsorption efficiency exceeding 98% for scandium ions (Sc³⁺) in an acidic solution with the hydrogen ion concentration ranging from 5 mol L^-1 to 10^-5 mol L^-1. Meanwhile, the complete capture of Sc³⁺ by β-HCCD can be accomplished within 2 minutes, and the adsorption isotherms demonstrated an outstanding alignment with the Freundlich model, exhibiting a maximum adsorption capacity of 101.0 mg g^-1. What's more, β-HCCD can be directly applied to industrial acidic wastewater without prior pretreatment, achieving an efficient recovery rate of 87% for Sc³⁺. These notable advantages including minimal expense, a straightforward preparation process, fast adsorption dynamics and substantial adsorption ability demonstrate that β-HCCD holds significant promise in the recovery of REEs.