Liquid–liquid extraction of yttrium from the sulfate leach liquor of waste fluorescent lamp powder: Process parameters and analysis

Global demand for rare earth metals (REMs), including yttrium, has motivated the scientific community to focus on the recovery of such metals from electronic waste materials. Herein, a solvent extraction method was used to isolate and recover yttrium from the original leaching solution from the fluorescent lamp waste powder dissolved by sulfate. The operating parameters were systematically investigated, including pH, equilibrium time, concentration of extractants, and organic/aqueous ratio using Versatic Acid 10, TOPO, D2EHPA, and Alamine 336. The extracting capacities were in the order of D2EHPA > Versatic Acid 10 > TOPO > Alamine 336. The reaction mechanism of yttrium with each extractant demonstrated the formation of complex compounds with concentration ratios of 1:3, 1:1, and 1:2 with Versatic Acid 10, D2EHPA, and TOPO, respectively. On investigating the extraction mode for yttrium and impurities in the range of equilibrium pH (pH_eq) values from 0.95 to 2.25 using D2EHPA, pH_e 2.02 (initial pH 2.53) was found to be the most suitable for extraction. Fe in the original leaching solution could be utterly eradicated through the acidity control method. Upon calculating the theoretical number of mixer–settler plates, more than 99% of yttrium was extracted in solution with only two plates as the organic phase. Finally, the stripping test showed favorable stripping rates and followed the order HCl (78.12%) > H₂SO₄ (76.36%) > HNO₃ (74.86%) within 10 min. This study is a first step toward developing large-scale operations for extracting REMs from fluorescent lamp waste powder.