A clean process for liquid-phase synthesis of α-PbO based on the selective leaching of lead sulfate from spent lead paste

In the recycling process of waste lead-acid battery paste, the traditional hydrometallurgical process of recovering α-PbO as a product presents the issues of the high concentration of alkali and the waste alkaline solution cannot be recycled. This study seeks a clean process for the liquid-phase synthesis of α-PbO based on the selective leaching of lead sulfate from spent lead paste. The pre-treated spent lead paste was initially leached with a sodium acetate solution to obtain a lead acetate solution. The leaching rate of PbSO4 in the leaching process was 99.87%. Metal impurities such as Fe and Ba could be removed. Then the lead acetate solution was mixed with NaOH particles to synthesize α-PbO. The purity of α-PbO obtained could be reached above 99.99% when the molar ratio of M(nOH-/Pb2+) was 3:1, the reaction temperature was 85 ℃, and the reaction time was 40 min. Meanwhile, a reaction pathway was also proposed in which β-PbO could be converted to α-PbO rapidly at low alkali concentrations. Furthermore, the recirculation process of the waste alkaline solution did not result in the accumulation of metal impurities and did not affect the purity of the α-PbO. The non-recyclable waste alkaline solution could be used to prepare sodium acetate solutions and sodium sulfate by-products. This study provides a feasible method for green recycling of spent lead paste.