BACKGROUND: Phosphogypsum (PG) is a solid waste. For a fluidized bed, current research has focused on the preparation of CaO and SO 2 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.RESULTS: PG decomposition is a combination of solid-solid reaction (carbon reacting with CaSO 4 ) and gas-solid reaction (reducing gas reacting with CaSO 4 ), 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.CONCLUSIONS: CaS 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.
A diverse library of pyrimidine–N-heterocycle hybrids was developed through a step-economical diversity-oriented synthesis strategy. In vivo biological screening showed some derivatives exhibited significant potential herbicidal activity.
Reduction of phosphogypsum (PG) to calcium sulfide (CaS) using thermochemical methods solve the environmental problems caused by PG. However, the commonly used reducing agents are coal and CO. The use of the above‐mentioned reducing agents is not economically efficient. In this paper, rice husk (RH) is used as a reducing agent and sludge (SL) as an additive to reduce PG. The effect of the two on PG decomposition and the mechanism of the synergistic effect are also investigated in combination with kinetic calculations. It is found that decomposition rate of CaSO4 in PG is 99.99% and yield of CaS is 98.38% when 40% RH + 20% SL is used as the reducing agent at 900°C for 30 min. The combined use of RH + SL is superior to RH alone in reducing the initial decomposition temperature and Ea. The mechanism functions of both reduced PG are G(α) = −ln(1 − α). There is a synergistic mechanism between RH and SL. The Fe2O3 in SL increases the cleavage of nitrogen oxide‐containing compounds and PAHs in tar to monocyclic aromatic and aliphatic hydrocarbons while producing more CO, H2, and CH4. Meanwhile, SL ash can promote the reaction process of carbon with CaSO4, thus increasing the decomposition rate of PG.
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