This paper studied the bivalent mercury reduction behaviors after Mg 2+ addition in the simulated Ca-based and Dual-Alkali flue gas desulfurization (FGD) absorbents. Experimental results showed that the reduction of bivalent mercury was increased in the Ca-based FGD absorbent and inhibited in the Dual-Alkali FGD absorbent. It was proposed that the former was mainly attributed to the enhanced dissolution and recrystallization of CaSO 3 particles by Mg 2+ addition, which provided more active surface for mercury adsorption and reduction, whilst the latter was mainly due to the formation of neutral MgSO 3 0 ion pair, which tended to lower the active sulfite concentration in the simulated solution.