Valorisation of Fire-Assay waste cupels for lead (II) oxide regeneration via acetic acid leaching

Waste cupels generated during fire assaying contain high amounts of lead (II) oxide (PbO), making them hazardous and difficult to dispose of. In this study, spent fire-assay cupels were recovered as a secondary resource for the regeneration of PbO. The cupels were mechanically processed to < 75 μm and characterized to establish their chemical and phase composition prior to leaching. Lead was selectively extracted using acetic acid solutions of varying concentrations (1–4 M) under different solid-to-liquid ratios. A maximum lead recovery of 88% was achieved using 4 M acetic acid at a solid/liquid ratio of 1:4. The recovered lead was subsequently converted into PbCO₃ via ammonium carbonate precipitation and thermally decomposed at 350–365 °C to regenerate PbO. Phase analysis confirmed the formation of well-crystallized litharge constituting (87.8%) with minor massicot (12.2%), demonstrating controlled PbO regeneration. The process demonstrates a practical way for recycling spent cupels into functional PbO, reducing environmental risks and conserving primary lead resources.