PbSO₄ Reduction Mechanism and Gas Composition at 600–1000°C

A promising lead-containing waste recycling method, with sulfur conservation and reductive sulfur-fixing co-smelting process (RSFCS), is proposed. This work investigated the PbSO₄ reduction equilibrium composition, phase conversions, and microscopic transformation mechanisms during the RSFCS process at different temperatures, times, and CO-CO₂ mixtures using thermodynamic modeling, thermogravimetric analysis, x-ray diffraction, and SEM-EDS analysis techniques. At the same time, the gaseous products were collected and analyzed. The results showed that three reduction paths existed: (1) PbSO₄→CO/CO2 PbO·PbSO₄+SO₂→CO/CO2 2PbO·PbSO₄+SO₂→CO/CO2 4PbO·PbSO₄+SO₂→CO/CO2 PbO+SO₂→CO/CO2 Pb; (2) PbSO₄→CO/CO2 PbS; (3) PbSO₄ → PbO·PbSO₄+SO₃ → 2PbO·PbSO₄+SO₃ → 4PbO·PbSO₄+SO₃ → PbO+SO₃. Reduction temperature and CO concentration were determined as major factors in the PbSO₄ reduction. In a relatively weak reductive atmosphere and at low temperature, xPbO·PbSO₄ (x = 1, 2, 4), PbO, Pb, and SO₂ were the major products. When temperature and the CO concentration increased, PbSO₄ was selectively reduced to PbS, with sulfur in the PbSO₄ fixed in PbS, instead of emitting SO₂/SO₃.