Preparation of calcium sulfide by sludge‐assisted rice husk reduction of phosphogypsum.

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. [ABSTRACT FROM AUTHOR]