Limitations of Acid-Induced EDTA Recovery from Citrate-Based Metal Leaching Solutions

Abstract

This study investigates acid-induced precipitation of ethylenediaminetetraacetic acid (EDTA) from citrate-based solutions relevant to spent lithium-ion battery leaching. Three systems were evaluated to assess the impact of matrix composition: an aqueous Na₂EDTA solution (E), Na₂EDTA in a citrate buffer (CBE), and a simulated pregnant leach solution containing Na2EDTA, citrate, and Li, Co, Ni, and Mn ions (CBEM). Increasing matrix complexity hindered EDTA precipitation. While the simple E system achieved 95–98% EDTA removal from the liquid phase at pH 2.7–1.5, the citrate-containing CBE system required a lower pH (2.0–1.0) to reach 90–96% removal. In the metal-containing CBEM system, maximum removal was approximately 65% at pH 0.5. Analytical methods confirmed H₄EDTA formation in the E and CBE systems, whereas the CBEM precipitate exhibited an unidentified phase composition with trace amounts of transition metals. These findings show that precipitation behavior observed in simple solutions cannot be directly extrapolated to complex, metal-containing leachates and indicate the need to evaluate preliminary metal removal or solution purification before EDTA regeneration.