Oxy-coal combustion is a novel technology that seeks to reduce carbon dioxide emissions from electricity generating units, but the unique combustion environment could potentially affect the manner in which the flue gas and fly ash interact. Of particular interest is the ability of fly ash to reduce SOx emissions, a source of concern in implementing oxy-coal technology. This study seeks to examine the way SOx interacts with calcium oxide, an important fly ash metal oxide, under a variety of flue gas conditions and temperatures. Using DRIFTS and XRD, the major products under the various reaction conditions were analyzed. The dominant sulfur containing product was found to be calcium sulfate. However, a secondary calcium carbonate product was formed under certain oxy-fuel conditions. Additionally, EDX was employed to examine the temperature dependence for sulfur retention. (C) 2016 Elsevier B.V. All rights reserved.