This work investigates the scope of a mercury temperature programmed desorption (HgTPD) technique for identifying mercury species in solids. The specific objective of this study was to clarify the mechanism of mercury retention by chars used as sorbents in coal combustion in air and oxy-combustion atmospheres based on the identification of the mercury species retained. Different mercury species were identified by HgTPD depending on the flue gas composition and the type of char. The results led to the conclusion that depending on these conditions the main mechanism of mercury retention will be the interaction of mercury with organic matter, or the interaction of mercury with sulfur to form HgS. In a few particular cases Hg-2(NO3)(2)2H(2)O was produced on the char surface. It was found that HgTPD is a highly useful technique for investigating the different mechanisms of mertury/char/gas interactions. (C) 2014 Elsevier B.V. All rights reserved.