Highly Selective Recovery of Lanthanum and Cerium from Wastewater by Amidoxime-Modified Biochar

Abstract

Graphic Abstract,Efficient recovery of rare earth elements is crucial for promoting resource utilisation and environmental protection. In this study, a new type of biochar adsorbent (AOBC300, AOBC500, AOBC700) was synthesised by grafting amidoxime groups onto corn stover biochar (BC300, BC500, BC700) prepared at temperatures ranging from 300 to 700 ℃. The adsorption and selective removal ability of these adsorbents for La(III) and Ce(III) were evaluated. The results showed that AOBC700 achieved an adsorption capacity of 60.24 for La(III) and 45.20 mg/g for Ce(III). Additionally, AOBC700 demonstrated excellent selective removal capacity in fly ash and red mud leaching solutions, maintaining an adsorption capacity of over 75% after five adsorption-desorption cycles. Density functional theory calculations further elucidated the adsorption mechanism of different REEs on AOBC700. Machine learning prediction using various models was employed to assess the adsorbent performance, with the eXtreme Gradient Boosting (XGB) model showing superior prediction accuracy. The characteristic Shapley addition interpretation indicated that the order of the influence of each factor on the REEs adsorption amount was: time > initial concentration > dosage > pH > electronegativity. These findings confirm the significant potential of AOBC700 for the selective extraction of rare earth elements from waste streams.

Keywords: Biochar；Rare earth metals；Amidoxime group；DFT calculation；Machine learning