Recovery of Lead from Spent Lead Paste by Pre-desulfurization and Low-Temperature Reduction Smelting

The treatment of spent lead paste is essential for the recycling of spent lead-acid batteries. In this study, we propose a facile route for the recovery of lead from spent lead paste by pre-desulfurization followed by low-temperature reduction smelting. The effects of two desulfurization methods, i.e., high-pressure and normal-pressure processes, on the desulfurization efficiency of spent lead paste were compared. The high-pressure process was found to be more effective than the normal-pressure process; 99.1% of sulfur was removed under the high pressure conditions with NaOH excess of 1.1 at 150°C for 30 min. Moreover, a part of PbO 2 reacted with PbO to form Pb 3 O 4 . Afterwards, the desulfurized residue, mainly consisting of Pb 3 O 4 and PbO 2 , was directly used in low-temperature reduction smelting, and the optimum smelting conditions were determined to be: starch/Pb-residue mass ratio = 1/6.3; Na 2 O/Pb-residue mass ratio = 1/15; B 2 O 3 /Pb-residue mass ratio = 1/7.5; smelting temperature 700°C; and smelting duration 90 min. The lead recovery under the optimum conditions was as high as 93%. Scanning electron microscope images of the smelting slag showed that the smelting slag mainly consisted of PbO x and Na 2 O.