Evaluation of N,N-dibutyloctanamide as a ligand for supercritical CO₂-mediated plutonium recovery: Solubility, model correlations and extraction studies

Abstract

N,N-dialkylamides are increasingly recognized as superior to well-established organophosphorus compounds for extraction/recovery of actinides. This study investigates the development of a green supercritical fluid extraction technique for efficient recovery of plutonium from aqueous waste solutions using N,N-dibutyloctanamide (DBOA). In this context, solubility of DBOA in supercritical carbon dioxide (SCCO₂) is measured to demonstrate its potential in CO₂-assisted green approach for extraction of plutonium. A dynamic flow method was employed to measure the solubilities, over a pressure range of 10 MPa to 20 MPa and temperature ranging from 313 K to 343 K. Solubility was found to be in the order of 10⁻² mol∙mol⁻¹, increasing with pressure while exhibiting retrograde solubility with temperature. Experimental data were correlated using five different models for predictive analysis. Of the models applied, Mendez-Teja equation demonstrated superior prediction with the lowest average deviation and optimal fitting parameters. These results demonstrated that DBOA has adequate solubility in SCCO₂, making it a viable ligand for the recovery of actinides. DBOA was subsequently employed as a ligand for the recovery of plutonium from aqueous waste using an in-house designed glove box. The influence of temperature, pressure and acidity on extraction efficiency was investigated and conditions were optimized. Under optimized conditions, an extraction efficiency of 96 % was achieved. This approach offers a promising route for plutonium recovery from waste matrices with minimum secondary liquid waste generation.