Fe-Mn based minerals with remarkable redox characteristics for chemical looping combustion

Searching for naturally occurring minerals/ores which can only be crushed down and sieved before they are used as oxygen carrier materials (OCM) is one of the main quests of the chemical looping combustion (CLC) community. Three cheap iron and manganese based minerals directly taken from the mining industry are investigated in this study. These minerals are Sinai manganese mineral (Egypt), Guizhou iron mineral (China) and Kryvbas iron mineral (Ukraine). Samples are studied with respect to oxygen capacity and redox kinetics by isothermal hydrogen and methane redox cycling experiments (800-1000 °C) and are compared to ilmenite as a widely used state-of-the-art reference. As one of the goals of this benchmarking is to spot minerals which are needless of pre-treatment and activation, no thermal treatment on the samples was performed prior to testing. Degradation issues have also been studied and investigated by SEM. Both Sinai manganese mineral and Kryvbas iron mineral perform well in respect to oxygen capacity and redox kinetics. However the post characterisation demonstrates that cation diffusion is much higher for Fe-based systems compared to the Fe-Mn system which shows much less swelling after 200 cycles.