A B S T R A C TNewly obtained results on mercury retention in fly ashes and activated carbons during coal combustion are compared with previous findings. The influence of different variables on mercury capture, including the composition and nature of the sorbents, the composition of the flue gas and the mercury species in gas phase is investigated.Coal-fired utility boilers are currently the largest single-known source of mercury emissions. According to the USEPA's Information Collection Request (ICR), on average, only 40% of the mercury entering a coal-fired power plant is captured, while 60% is emitted into the atmosphere. Several solid materials, including activated carbons, are considered to be effective sorbents for Hg control in flue gases from coal combustion. However, more economical alternatives to retain mercury such as the optimization of conditions for improving mercury capture in fly ashes in the installation also need to be studied.In this work, the mercury retention capacity of different fly ashes was compared with retention by commercial activated carbons in different experimental conditions. As might be expected, the results obtained indicate that the quantity of mercury captured depends on the characteristics of the fly ashes and on the mode of occurrence of mercury in gas phase. The retention of elemental mercury in the fly ashes, unlike activate carbons, was greatly influenced by the gas composition. Although the efficiency of the mercury retention was higher in activated carbons than in fly ashes, some activated carbon showed a lower retention capacity for elemental mercury than some fly ashes in the simulated flue gas.