Preparation of sulfur dioxide by divalent iron synergistic coke reduction of phosphogypsum in a fluidized bed

Phosphogypsum (PG) can be reduced by thermal treatment and produces SO 2 and lime slag. Unfortunately, the SO 2 yield is low and the PG decomposition temperature is high. This problem can be resolved by adding reducing agents and additives. However, the current studies mainly investigate the effect of Fe 3+ on the PG reduction in a fixed bed, while there are few studies on the preparation of SO 2 from Fe 2+ -assisted coke reduction of PG in a fluidized bed and lack of analysis of the sulfur form in the gas products. Consequently, using coke as the reducing agent and Fe 2+ as the additive, together with thermodynamic simulation and kinetic calculation, the impacts of Fe/Ca molar ratio, C/Ca molar ratio and reaction temperature on SO 2 yield by PG decomposition in a fluidized bed are explored. It is found that the addition of Fe 2+ could reduce reaction temperature and activation energy of the PG-C system. The inclusion of Fe 2+ boosts the SO 2 yield and PG decomposition rate in comparison to PG-C system. The SO 2 yield and PG decomposition rate under these circumstances are 95.41% and 99.07%, respectively, with C/Ca of 0.5 and Fe/Ca of 1 at 1100 °C. The S in the gas products is in the form of SO 2 , COS and S 2 . Kinetic calculations reveal that the PG-C system and the PG-C-Fe 2+ system are consistent with the nucleation and growth models with g(α) = -ln(1-α). The preparation of SO 2 from PG reduction by Fe 2+ synergistic coke is mainly achieved through the valence transition of Fe 2+ . Graphical abstract