Study of defluorination by thermal treatment of phosphogypsum under steam atmosphere

This study investigates the removal of fluorine (F) impurities from phosphogypsum (PG) using steam as the reaction medium. The effects of the reaction atmosphere, temperature, time, and steam velocity on F impurities removal were systematically examined. The results showed that with a steam velocity of 0.0184 m⋅s⁻¹, a reaction temperature of 700 °C, and a reaction time of 60 min, the F removal rate reached 95.87%. Further investigations into the defluorination mechanism revealed that steam and SiO₂ synergistically enhance fluoride removal, playing a crucial role in improving the defluorination efficiency. Kinetic analysis of the defluorination process, based on the shrinking core model (SCM), indicated that internal diffusion is the rate-controlling step, with the activation energy of 30.12 kJ·mol⁻¹. This study identifies optimal conditions for PG defluorination and proposes a defluorination mechanism, contributing to the theoretical understanding of impurity removal through the thermal treatment of PG.