Recycling lead paste from lead-acid batteries through ammonium bicarbonate derived from carbon dioxide in flue gases: A pilot test in an actual factory

Recycling of scrapped lead-acid batteries have been a primary source of secondary lead. With the increasing depletion of lead mines and the rise in lead consumption, recycling the scrapped lead-acid batteries has become an inevitable trend. Among the components of scrapped lead-acid batteries, lead paste including lead sludge and lead sand is the most complex. Ammonium bicarbonate (NH₄HCO₃) was employed as a desulfurizer to convert lead sulfate (PbSO₄) to lead carbonate (PbCO₃). The advantages of this innovative technology include high purity of lead ingots, low energy consumption, and minimal odorous pollution and corrosion risks. Notably, NH₄HCO₃ can be regenerated by absorbing CO₂ from the flue gases using NH₄OH, which could also reduce greenhouse gas emissions from the secondary lead manufacturing processes. The optimal parameters for the desulfurization of lead paste were obtained from this study as follows: a mass ratio of NH₄HCO₃ and lead paste of 1:2, 15 % simulated CO₂ with a sampling flowrate of 3 L/min, an absorption time of 60 min, and a stirring speed of 150 rpm. Under the operating conditions, the desulfurization efficiency (DSE) for lead sludge reached 94.7 %, while the DSE for lead sand was 87.8 %. Based on the optimal operational parameters, a pilot plan was implemented at a scrapped lead-acid battery recycling plant. The cost-benefit analysis of the actual operation revealed that the desulfurization processes using NH₄HCO₃ increased lead ingot yield and enabled the desulfurization trial at the factory to break even.