Recovery of sulphur dioxide by converter dust synergistic coke decomposition of phosphogypsum

Abstract

To further improve the decomposition ratio and sulfur dioxide mass yield of coke-reduced solid waste phosphogypsum (PG), converter dust (CD) is proposed as a novel additive. The effects of raw material ratio, time and temperature for roasting on the decomposition process of PG were inspected by simulation calculations and fluidized bed experiments. It turns out that the optimized reaction conditions are Fe3O4/Ca of 0.6, C/Ca of 0.4 at 1100 °C for 24 min, under which the PG decomposition ratio and SO2 mass yield are 99.56 % and 97.64 %, respectively. The addition of CD is able to reduce the initial reaction temperature from 975 °C to 914 °C, and promote the release of SO2. Kinetic analysis shows the mechanistic equation for this process is obtained as G(α) = [−ln(1 − α)]3/2, indicating that the decomposition reaction mechanism is a crystal nucleation and growth-controlled process. The chemical mechanism of the process is that coke and Fe3O4 in the CD convert CaSO4 to the intermediate CaS, and Fe3O4 is oxidized to Fe2O3. Then CaS and CaSO4 continue to react with Fe2O3 to form Ca2Fe2O5 and SO2. The presence of Fe2O3 accelerations the rate of CaS and CaSO4 roasting reaction and lowers the reaction temperature. Meanwhile, the self-decomposition of PG also produces CaO and SO2. Finally, a process for SO2 recovery from CD synergized with coke decomposition of PG is proposed.