Preparation of lead carbonate from spent lead paste via chemical conversion

Lead paste generated from spent and discarded lead acid battery has been converted to lead carbonate and lead oxides with a view to investigate a method for minimizing environmental pollution associated with spent lead paste recycling. The process includes four steps: namely desulfurization, leaching, carbonation and calcination, presented in the details as the follows. (1) In a spent lead paste, lead sulfate is the major component and is accompanied by lead oxides and metallic lead. On reacting the paste with (NH4)2CO3, the PbSO4 is converted to lead carbonate with (NH4)2SO4, generated as a by-product. (2) The desulfurized paste consisting of lead carbonate and the unreacted lead oxides are then leached with an aqueous solution of nitric acid and H2O2. At a molar ratio of H to Pb > 2.5 and at a slurry density of 100 g · L− 1, the extraction yield of lead from the paste into the aqueous solution is achieved up to 98.0%. (3) In the next step, the Pb (II) in the leaching solution is converted with the addition of Na2CO3 (aq) into a lead carbonate precipitate. It was found that under optimal conditions more than 99.9% of Pb can be extracted from the leaching solution into the solid lead carbonate phase. (4) In the final step, the lead carbonate is readily converted by thermal decomposition at a relatively low temperature of 350–450 °C into lead monoxide (PbO) or lead tetroxide powders (Pb3O4) that can serve as precursor for making new lead paste and other lead products.

► The extraction yield from desulfurized paste was around 98.0% with nitric acid.
► Over 99.9% of lead nitrate was converted into lead carbonate in the size of 0.1–1 μm.
► Ultra-fine PbO and Pb3O4 were produced by thermal decomposition of lead carbonate.
► A chemical conversion process for recovering lead from lead paste was proposed.