Synthesising lead oxide and oxychloride minerals from spent lead acid battery waste using a choline-chloride based deep eutectic solvent

Abstract

In this study, spent lead–acid battery (LAB) paste was chemically converted into PbC₂O₄ using a choline chloride–oxalic acid deep eutectic solvent (DES). The conversion occurred at room temperature (23 ± 2 °C) within 24 h, yielding a pure PbC₂O₄ intermediate as confirmed by PXRD and XPS. Subsequent calcination produced a range of oxychloride phases depending on the temperature (300–500 °C, 1 hour) which were identified by PXRD and XPS. At 300 °C, PbC₂O₄ did not substantially decompose although yielded some traces of lead metal at the surface likely from the evolution of some CO. At 400 °C Pb₂C₂O₄Cl₂ and Pb₃O₂Cl₂ were observed in the bulk, elucidating the calcination mechanism in the presence of chlorine. Finally at 500 °C Pb₃O₂Cl₂ and PbO phases were obtained in the bulk with traces of oxalate remaining at the surface. Due to the room temperature nature of the conversion and the low calcination temperature, this process reduces the energy demand relative to conventional pyrometallurgy (>1000 °C) for recovering lead minerals from lead acid batteries. However, the formation of non-conductive oxychlorides presents a challenge for direct reuse in LAB manufacture. These findings highlight both the potential and limitations of if chlorine containing DES are used for battery recycling.