This series of papers describes the development of technology to convert Hg(0) to Hg(II) in coal-derived flue gas based on the wellknown Fenton reactions so that a Hg control strategy can be implemented in a wet scrubber. This effort consists of both bench-scale and pilot-scale work. This first paper reports on the bench-scale tests. The bench-scale results showed that Hg(0) oxidation can be achieved by the Fenton reactions and the oxidation rate is quantitatively dependent on the residence time of the Hg stream in the solution. An average of 750%, oxidation of Hg(0) was achieved. Iron-based Fenton-type additives gave much more promising results compared to Cu-based Fenton-like additives for Hg(0) oxidation. The pH value of the sorbent solution also had a significant effect on the oxidation of Hg(0) and a suitable pH window was found to lie between 1.0 and 3.0 for this application. This may be attributed to the chain reaction mechanisms of Fe3+/H2O2 for Fenton reactions, i.e., the decomposition of H2O2 for the production of center dot OOH radicals in the Fe3+/H2O2 system which is kinetically favoured under a wide range of conditions at pH values of 3 or less. At higher pH values, H2O2 is converted to H2O instead of center dot OOH radicals in the presence of Fe3+ Crown Copyright (c) 2007 Published by Elsevier Ltd. All rights reserved.