Magnetite and anthracite assisted microwave heating flue gas desulfurization gypsum

• The microwave heating rates of magnetite and anthracite are partially overlapped.
• Gypsum-8 wt% anthracite-10 wt% magnetite is the optimal mixture to convert microwaves.
• Water, magnetite and burning of anthracite promote the microwave heating of gypsum.
• Within 82 min microwave heating, final temperature of the mixture rose to 1040 °C.

The heating characteristics of flue gas desulfurization (FGD) gypsum and their mixtures have been investigated with a microwave reactor. The influences of three factors(water in FGD gypsum and the additives, anthracite and magnetite), on the microwave heating are the focuses of this work. The heating curves revealed that the temperature of FGD gypsum only reached to 299 °C after microwave heating for 90 min. With increasing proportions of magnetite and/or anthracite, the final temperature of sample rose significantly. The peaks of the heating rates between magnetite and anthracite are partially overlapped. Adding both of them to FGD gypsum, continuous increase of temperature was achieved. When adding 10 wt% magnetite and 8 wt% anthracite to FGD gypsum, a relatively high heating rate was obtained. The heating rate is intensified, in sequence, by water, magnetite, burning of anthracite and hot spots caused by agglomerates of anthracite and magnetite. Within 82 min of microwave radiation, temperature of the mixture rose to 1040 °C which met the decomposition temperature of FGD gypsum.