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

Li Yun,Taskinen Pekka,Wang Yuejun,Yang Shenghai,Tang Chaobo,Chen Yongming,Jokilaakso Ari

A promising lead-containing waste recycling method, with sulfur conservation and reductive sulfur-fixing co-smelting process (RSFCS), is proposed. This work investigated the PbSO 4 reduction equilibrium composition, phase conversions, and microscopic transformation mechanisms during the RSFCS process at different temperatures, times, and CO-CO 2 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) PbSO 4 \( \to ^{{ {\text{CO/CO}}_{{2}} }} \) PbO·PbSO 4 +SO 2 \(\to ^{{ {\text{CO/CO}}_{{2}} }}\) 2PbO·PbSO 4 +SO 2 \(\to ^{{ {\text{CO/CO}}_{{2}} }} \) 4PbO·PbSO 4 +SO 2 \(\to ^{{ {\text{CO/CO}}_{{2}} }} \) PbO+SO 2 \( \to ^{{ {\text{CO/CO}}_{{2}} }}\) Pb; (2) PbSO 4 \( \to ^{{ {\text{CO/CO}}_{{2}} }} \) PbS; (3) PbSO 4 → PbO·PbSO 4 +SO 3 → 2PbO·PbSO 4 +SO 3 → 4PbO·PbSO 4 +SO 3 → PbO+SO 3 . Reduction temperature and CO concentration were determined as major factors in the PbSO 4 reduction. In a relatively weak reductive atmosphere and at low temperature, x PbO·PbSO 4 ( x  = 1, 2, 4), PbO, Pb, and SO 2 were the major products. When temperature and the CO concentration increased, PbSO 4 was selectively reduced to PbS, with sulfur in the PbSO 4 fixed in PbS, instead of emitting SO 2 /SO 3 .