Selective recovery of rare earth elements (REEs) from spent NiMH batteries by two-stage acid leaching. Issue 5 (October 2021)

• Record Type: Journal Article
• Authors: Lie, Jenni; Liu, Jhy-Chern
• Is Part Of: Journal of environmental chemical engineering. Volume 9:Issue 5(2021)
• Publication Date: 2021-10
• Subjects: Leaching -- Rare earth elements -- Recovery -- Selective precipitation -- Spent NiMH batteries -- Subcritical water extraction; Chemical engineering -- Environmental aspects -- Periodicals; Environmental engineering -- Periodicals; Chemical engineering -- Environmental aspects; Environmental engineering; Periodicals; 660.0286
• DOI: 10.1016/j.jece.2021.106084
• Languages: English
• ISSNs: 2213-2929

Abstract

Abstract: The current study investigated selective recovery of rare earth elements (REEs) from spent nickel metal hydride (NiMH) batteries using two-stage acid leaching followed by precipitation at acidic pH. The first-stage conventional leaching using 2.5 M of waste phosphoric acid (H3 PO4 ) at 25 °C for 60 min removed 60–100% heavy metals, such as Ni, Co, Zn and Cd, and converted more than 90% REEs into insoluble phosphate precipitates, REE(PO4 ). Subcritical water extraction (SWE) using mild concentration of sulfuric acid (H2 SO4 ) in the second stage leached out all REEs. The leaching efficiency of REEs increased by increasing acid concentration, and 100% leaching efficiency of REEs, Ni, Co and Mn were achieved using 1 M of H2 SO4, solid concentration of 20 g/L, at 125 °C for 30 min. As predicted by species distribution of metals at equilibrium, REEs in the leaching solution were selectively precipitated as NaREE(SO4 )2 ·H2 O at low pH (0.5–2) by the addition of NaOH solution, and separated from other metals (Ni, Co, Mn). Precipitation at pH 1 resulted in 82.59% of La, 90.75% of Ce, and 85.97% of Nd recovered as hexagonal rod crystals. This study provides an alternative process to selectively recover REEs from electronic waste (e-waste). Graphical Abstract: ga1 Highlights: Two-stage leaching of spent NiMH batteries for selective recovery of REEs. First-stage using waste H3 PO4 for heavy metals, while converting REEs to REE(PO4 ). Subcritical water extraction using H2 SO4 in second-stage to leach out all metals. Selective precipitation of REEs in at low pH as NaREE(SO4 )2 ·H2 O precipitates.