Abstract: In order to convert as much as possible S in pyrite and phosphogypsum (PG) into SO₂, effects of pyrite addition and reaction temperature on PG decomposition were systematically investigated using fluidized bed combined with thermogravimetric and thermodynamic calculations.The results show that the addition of pyrite decreases PG decomposition temperature and increases PG decomposition ratio.The most probabilistic mechanism function of the process is G(α)=1-(1-α)^1/3, which indicates that the reaction is controlled by phase boundary.The optimized reaction condition is 30%pyrite addition at 1 100 ℃ for 20 min, under which the PG decomposition ratio and SO₂ yield are 99.95%and 95.95%, respectively.The by-product CaS was produced when the pyrite addition was 30%~70%.When the addition was more than 70%, solid melt Ca₃Fe₄S₃O₆ was produced.There are mainly two different mechanistic paths in this process according to different pyrite additions.This study enriches the process theory of SO₂ preparation from reduced PG of pyrite.