Batch Production of Lead Sulfate from Spent Lead–Acid Batteries via an Oxygen-Free Roasting Route: A Negative-Carbon Strategy

Multicomponent lead compounds, including lead (Pb), lead oxide (PbO), lead dioxide (PbO2), and lead sulfate (PbSO4), in spent lead–acid batteries (LABs), if not properly disposed of and recycled, will cause serious pollution and damage to the ecological environment. Pyrometallurgical smelting performed above 1000 °C often incurs high energy consumption and lead pollution. In this study, a low-temperature (300 °C), oxygen-free roasting process was proposed. With potassium bisulfate (KHSO4) as the roasting reagent, the uniform conversion of multicomponent lead compounds from spent lead paste (SLP) to PbSO4 was successfully realized in one step. We observed that PbO2 species were relatively chemically stable, during the oxygen-free roasting. However, the decomposition of PbO2 into PbO can be achieved by heating to 300 °C, resulting in an effective conversion to PbSO4. The optimal conditions for PbSO4 production were a heating temperature of 300 °C, an SLP/KHSO4 mass ratio of 1:1, and a holding time of 10.0 min. Life cycle assessment results show that the recycling of 1.0 t spent LABs can reduce carbon emissions of 2.45 t CO2 and smog of 0.13 t. Our research provides an emission-free, low-temperature, and negative-carbon strategy for facile and cost-effective recycling of spent LABs, as an alternative to traditional pyrometallurgical smelting.