Preparation of High-Purity PbO Powder from Waste Lead Paste via Leaching Reagents Recovery

The hydrometallurgical recycling of spent lead-acid battery has received extensive attention benefitting from its features of cleanability and process controllability, but the process still suffers from significant challenges of huge chemical consumption and low economic efficiency. Here, a sustainable green approach that enables closed-loop recovery of leaching reagent NH₄Ac to obtain high-purity PbO powder from discarded lead paste is proposed. The process includes dissolution, chemical transformation, carbonization, and calcination stages. Under the optimal leaching condition of NH₄Ac concentration 4.5 mol L^–1, H₂O₂/PbO₂ molar ratio 1.5, reaction temperature 40 °C, and time 60 min, the leaching ratio of lead reaches as high as 99.35%. The exceptionally high concentration of NH₄Ac to dissolve PbSO₄ phases than theoretical ratio could be attributed to the distribution state of Pb substances. With (NH₄)₂CO₃ as carbonizing agent, above 99.9% of lead could be precipitated as PbCO₃ products when the molar ratio CO₃^2–/Pb is 1.2. High-purity β-PbO powder is subsequently achieved from the thermal decomposition of PbCO₃ precursor, where the effect of calcination temperature and atmosphere on the chemical compositions are examined. Economic analysis reveals the economic feasibility and profits of the recycling approach. The process produces high-purity PbCO₃ and PbO products enabling leaching reagents NH₄Ac reuse, providing a practicable solution for sustainable recovery of lead from waste lead paste.