New insights into synergistic effects and active species toward Hg 0 emission control by Fe(VI) absorbent Yinghui Han a,b,c , Maohong Fan a,b,⇑ , Armistead G. Russell b a School of Energy Resources and Department of Chemical & Petroleum Engineering, University of Wyoming, Laramie, WY 82071, USA b School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA c School of Mathematics & Physics, North China Electric Power University, Baoding 071003, People’s Republic of China highlights  Fe(VI) is a promising agent for Hg 0 control.  Removal of Hg 0 was optimized with the response surface methodology.  Synergic effect of pH and temperature is considerable.  Species analysis and thermodynamics revealed Hg 0 removal mechanism. graphical abstract article info Article history: Received 25 June 2014 Received in revised form 4 September 2014 Accepted 19 September 2014 Available online 11 October 2014 Keywords: Ferrate(VI) Removal of mercury Synergistic effects Response surface methodology Active species abstract With the timelines for implementation of the U.S. Environmental Protection Agency’s mercury emission control rules approaching soon, finding an innovative and cost-effective mercury removal technology has become increasingly important. The most challenging species in all the mercury forms is gaseous elemen- tal mercury (Hg 0 ). The objective of this work is to inspect the absorption behavior and removal of Hg 0 by Fe(VI). The synergistic effects of various factors were investigated and the optimization for Hg 0 removal by Fe(VI) was achieved based on the response surface methodology. The speciation of Fe(VI) and Hg reac- tion species was emphatically analyzed in the entire pH range in order to clarify the possible Fe(VI)-based Hg 0 removal mechanism in depth. According to the thermodynamics calculation, the Gibbs free energies for the reaction between Fe(VI) and Hg 0 in the weak alkaline/acid medium are determined as 120.03 kJ/ mol and 235.42 kJ/mol, respectively, implying the oxidation of Hg 0 by Fe(VI) is spontaneous and thorough. Finally, industrial feasibility analysis indicates that Fe(VI) has the practical potential to be a promising removal agent for Hg 0 emission control from coal-fired flue gas, which might be integrated into the existing mainstream flue gas desulfurization scrubber to achieve the removal of multi-pollutants simultaneously, in prospect. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction People have become increasingly concerned about the toxic effect of Hg 0 since it was first recognized in the early 1950s [1]. http://dx.doi.org/10.1016/j.fuel.2014.09.072 0016-2361/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: School of Energy Resources and Department of Chemical & Petroleum Engineering, University of Wyoming, Laramie, WY 82071, USA. E-mail address: mfan@uwyo.edu (M. Fan). Fuel 140 (2015) 309–316 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel