This paper studied the bivalent mercury reduction behaviors after Mg2+ 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 CaSO3 particles by Mg2+ addition, which provided more active surface for mercury adsorption and reduction, whilst the latter was mainly due to the formation of neutral MgSO30 ion pair, which tended to lower the active sulfite concentration in the simulated solution. (C) 2012 Elsevier B.V. All rights reserved.