Lanthanide-alkali double sulfate precipitation from strong sulfuric acid NiMH battery waste leachate. (January 2018)

• Record Type: Journal Article
• Authors: Porvali, Antti; Wilson, Benjamin P.; Lundström, Mari
• Is Part Of: Waste management. Volume 71(2018)
• Page Start: 381
• Page End: 389
• Publication Date: 2018-01
• Subjects: Nickel metal hydride battery -- Hydrometallurgy -- Double sulfate -- Rare earths -- Recycling; Hazardous wastes -- Periodicals; Refuse and refuse disposal -- Periodicals; 363.728
• DOI: 10.1016/j.wasman.2017.10.031
• Languages: English
• ISSNs: 0956-053X

Abstract

Graphical abstract: Highlights: NaOH and KOH from crushed batteries caused REE precipitation during leaching. 2-stage leaching with H2 SO4 and subsequent H2 O leaching provided high REE yields. Both H2 SO4 and Na2 SO4 concentrations had an effect on the REE precipitation. Mixed K and Na REE double sulfate crystals were formed. Precipitate yields from H2 SO4 leachate should not be reported as a function of pH. Abstract: In NiMH battery leaching, rare earth element (REE) precipitation from sulfate media is often reported as being a result of increasing pH of the pregnant leach solution (PLS). Here we demonstrate that this precipitation is a phenomenon that depends on both Na + and SO4 2− concentrations and not solely on pH. A two-stage leaching for industrially crushed NiMH waste is performed: The first stage consists of H2 SO4 leaching (2 M H2 SO4, L/S = 10.4, V = 104 ml, T = 30 °C) and the second stage of H2 O leaching ( V = 100 ml, T = 25 °C). Moreover, precipitation experiments are separately performed as a function of added Na2 SO4 and H2 SO4 . During the precipitation, higher than stoichiometric quantities of Na to REE are utilized and this increase in both precipitation reagent concentrations results in an improved double sulfate precipitation efficiency. The best REE precipitation efficiencies (98–99%) – achieved by increasing concentrations of H2 SO4 and Na2 SO4 by 1.59 M and 0.35 M, respectively – results in a 21.8 times Na (as Na2 SO4 ) and 58.3 times SO4 change in stoichiometric ratio to REE. Results strongly indicate a straightforward approach for REE recovery from NiMH battery waste without the need to increase the pH of PLS.