Experimental study of CaS preparation from lignite‐reduced phosphogypsum in a fluidized bed

Abstract

AbstractBACKGROUNDPhosphogypsum (PG) is a solid waste. For a fluidized bed, current research has focused on the preparation of CaO and SO2 by PG decomposition, while less research has been conducted with calcium sulfide (CaS) as the target product. Therefore, the effect of different conditions on the preparation of CaS by coal reduction of PG was investigated in a fluidized bed. The mechanism of the reaction between coal and PG was revealed through experiments and kinetic calculations.RESULTSPG decomposition is a combination of solid–solid reaction (carbon reacting with CaSO4) and gas–solid reaction (reducing gas reacting with CaSO4), among which the solid–solid reaction plays a major role. A PG decomposition rate of 99.42% and CaS yield of 91.55% are obtained at 850 °C for 60 min when the Ca/C molar ratio is less than 0.25 and coal particle size is less than 0.075 mm. Lignite, bituminous coal and anthracite can promote the decomposition of PG. However, the higher viscosity of bituminous coal can lead to molten coking of the product, while anthracite is less economical, so lignite is the most suitable. Minerals in coal can improve the decomposition rate of PG. A fluidized bed improves the PG decomposition rate compared to a fixed bed.CONCLUSIONSCaS is obtained by combined solid–solid and gas–solid reactions. Decreasing the Ca/C ratio and coal particle size as well as controlling the reaction temperature below 850 °C are beneficial for CaS generation. The minerals in coal can reduce the PG decomposition temperature and increase the PG decomposition rate. © 2022 Society of Chemical Industry (SCI).