Low-temperature desulfurization of phosphogypsum via co-thermal reduction of carbon-based fuels

High-temperature reduction offers the opportunity for value-added recovery of calcium and sulfur from phosphogypsum (PG), but the process energy consumption and cost of using a single fuel as a reducing agent are relatively high (1100°C). The reducing atmosphere suitable for industrial applications was determined through thermogravimetric analysis. The results show that samples corresponding to high-volatile pine wood and lignite have an earlier weight loss and a lower weight loss temperature, which has the potential to reduce the desulfurization temperature of PG. The feasibility of reduction PG by single/dual fuel was verified relying on a fluidized bed. The results find that, thanks to the synergistic effect and catalytic properties of lignite and pine wood, the low-temperature calcination mode (1050°C) using dual fuel achieves a PG conversion rate (95%) similar to that of single/dual fuel high-temperature reduction processes. The low-temperature desulfurization mechanism of carbon-based fuel co-thermal reduction of PG was revealed by means of thermodynamic methods. The results indicate that the introduction of biomass enhances the reaction spontaneity and proceeding degree of the reducing volatiles and PG, accelerate the formation and accumulation of the intermediate product CaS, and ensure the sufficient decomposition and desulfurization of reducing atmosphere and CaSO₄/oxidizing atmosphere and CaS. The successful verification of the co-thermal reduction PG by lignite and pine wood has pioneered the low-temperature calcination of PG using solid-phase carbon-based fuels to recover CaO and SO₂.