Copper slag assisted coke reduction of phosphogypsum for sulphur dioxide preparation

doi:10.1016/j.cjche.2023.07.008

摘要/Abstract

摘要： The reduction of phosphogypsum (PG) to lime slag and SO₂ using coke can effectively alleviate the environmental problems caused by PG. However, the PG decomposition temperature remains high and the product yield remains poor. By adding additives, the decomposition temperature can be further reduced and PG decomposition rate and product yield can be improved. However, the use of current additives such as Fe₂O₃ and SiO₂ brings the problem of increasing economic cost. Therefore, it is proposed to use solid waste copper slag (CS) as a new additive to reduce PG to prepare SO₂, which can reduce the cost and meet the environmental benefits at the same time. The effects of proportion, temperature and thermostatic time on PG decomposition are investigated by experimental and kinetic analysis combined with FactSage thermodynamic calculations to optimize the roasting conditions. Finally, the reaction mechanism is proposed. It is found that adding CS to the coke and PG system can increase the rate of PG decomposition and SO₂ yield while lowering the PG decomposition temperature. For example, when the CS/PG mass ratio increases from 0 to 1, PG decomposition rate increases from 83.38% to 99.35%, SO₂ yield increases from 78.62% to 96.81%, and PG decomposition temperature decreases from 992.4 ℃ to 949.6 ℃. The optimal reaction parameters are CS/PG mass ratio of 1, Coke/PG mass ratio of 0.06 at 1100 ℃ for 20 min with 99.35% PG decomposition rate and 96.81% SO₂ yield. The process proceeds according to the following reactions:2CaSO₄+0.7C+0.8Fe₂SiO₄→0.8Ca₂SiO₄+0.2Ca₂Fe₂O₅+0.4Fe₃O₄+2SO₂+0.7CO₂ Finally, a process for decomposing PG with coke and CS is proposed.

关键词: Phosphogypsum, Sulfur dioxide, Copper slag, Fluidized-bed, Reduction, Waste treatment

Abstract: The reduction of phosphogypsum (PG) to lime slag and SO₂ using coke can effectively alleviate the environmental problems caused by PG. However, the PG decomposition temperature remains high and the product yield remains poor. By adding additives, the decomposition temperature can be further reduced and PG decomposition rate and product yield can be improved. However, the use of current additives such as Fe₂O₃ and SiO₂ brings the problem of increasing economic cost. Therefore, it is proposed to use solid waste copper slag (CS) as a new additive to reduce PG to prepare SO₂, which can reduce the cost and meet the environmental benefits at the same time. The effects of proportion, temperature and thermostatic time on PG decomposition are investigated by experimental and kinetic analysis combined with FactSage thermodynamic calculations to optimize the roasting conditions. Finally, the reaction mechanism is proposed. It is found that adding CS to the coke and PG system can increase the rate of PG decomposition and SO₂ yield while lowering the PG decomposition temperature. For example, when the CS/PG mass ratio increases from 0 to 1, PG decomposition rate increases from 83.38% to 99.35%, SO₂ yield increases from 78.62% to 96.81%, and PG decomposition temperature decreases from 992.4 ℃ to 949.6 ℃. The optimal reaction parameters are CS/PG mass ratio of 1, Coke/PG mass ratio of 0.06 at 1100 ℃ for 20 min with 99.35% PG decomposition rate and 96.81% SO₂ yield. The process proceeds according to the following reactions:2CaSO₄+0.7C+0.8Fe₂SiO₄→0.8Ca₂SiO₄+0.2Ca₂Fe₂O₅+0.4Fe₃O₄+2SO₂+0.7CO₂ Finally, a process for decomposing PG with coke and CS is proposed.

Key words: Phosphogypsum, Sulfur dioxide, Copper slag, Fluidized-bed, Reduction, Waste treatment

Dong Ma, Qinhui Wang. Copper slag assisted coke reduction of phosphogypsum for sulphur dioxide preparation[J]. 中国化学工程学报, 2024, 65(1): 43-53.

Dong Ma, Qinhui Wang. Copper slag assisted coke reduction of phosphogypsum for sulphur dioxide preparation[J]. Chinese Journal of Chemical Engineering, 2024, 65(1): 43-53.

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