Effect of coal ash on the reduction and roasting processes of phosphogypsum

Phosphogypsum (PG) is a solid waste generated in the phosphate fertilizer industry and decomposing PG to recover calcium and sulfur is an appropriate way to reuse PG. The present work aims to enrich the basic theory of coal decomposition PG process, focusing on the effect of coal ash on the reduction roasting of PG and CaS oxidation process. Firstly, typical substances in coal ash such as SiO 2 , Fe 2 O 3 and Al 2 O 3 are investigated using fixed-bed experiments, TG-DSC combined with FactSage simulations. Finally, coal ash is used for experimental verification. It is found that SiO 2 , Fe 2 O 3 and Al 2 O 3 reduce the CaS yield in the reduction process and CaO yield in the roasting process. The results obtained from the addition of coal ash are consistent with those obtained from typical substances. The addition of coal ash reduce the temperature of the PG reduction and roasting processes, while it has little effect on the CaS oxidation process. For example, the addition of 20% coal ash reduce the CaS yield from 68.32 to 57.32% and reduce the CaO yield from 87.23 to 51.87%. In addition, the addition of 20% coal ash reduce the melting temperature of PG-CaS system from 1556.15 to 1490.15 K. The experimental results are consistent with FactSage simulations. Graphical abstract