Recovery of Scandium from Nitric Acid Leachate of Scandium-bearing Aluminum Residue by D2EHPA-TBP Synergistic Extraction System

Abstract

Scandium is an important strategic metal. This work focuses on its recovery from nitric acid leachate of Sc-bearing aluminum residue, a typical by-product of aluminum production. The leachate contains high levels of impurity metals (Fe, Al, Mg) that hinder direct scandium recovery, necessitating a selective separation method. Here, a synergistic solvent extraction process using D2EHPA and TBP was developed, which involved synergistic extraction with a D2EHPA-TBP system, followed by acid scrubbing and alkaline stripping. The results show that scandium extraction efficiency was 99.95%, while those of Fe, Al, and Mg were 90.1%, 91.3%, and 94.3%, respectively, through three-stage counter-current extraction under the following optimum conditions: 15% D2EHPA + 5% TBP + 80% sulfonated kerosene, at an aqueous-to-organic (A/O) phase ratio of 12, pH 0.1, and oscillation time 10 min. The loaded organic phase was then scrubbed with 315 g/L HNO₃ at an A/O ratio of 4, achieving removal efficiencies of 95.5% for Mg, 91.64% for Al, and 90.16% for Fe, with a scandium loss of less than 1%. A stripping efficiency of scandium was 90.24% using 120 g/L NaOH solution at A/O ratio of 3. The solvent extraction of scandium was confirmed by Fourier-transform infrared spectrometer (FTIR). This work is of significant importance for the extraction of scandium from the nitric acid leachate of laterite nickel ore.