Evaluation of oxygen carriers based on manganese‑iron mixed oxides prepared from natural ores or industrial waste products for chemical looping processes

Abstract

Manganese‑iron mixed oxides have been identified as promising oxygen carrier materials in chemical looping processes. In this work, low-cost raw materials are considered for the production of this type of oxygen carrier. Four manganese based minerals from deposits of different locations – South Africa, Gabon(x2) and Brazil – and two iron based materials (Fe-ore from Spain and Redmud waste) were used to prepare suitable oxygen carriers through a new two-step production method: a mixing-grinding (about 5 μm) pre-treatment followed by pelletizing, crushing and sieving to produce particles of the desired size (100–300 μm). This method was required in order to form the MnFe mixed oxide and to provide permanent magnetic properties, which were not found when the oxygen carriers were prepared by the classical one-step method, i.e. crushing and sieving of raw materials to the desired particle size (100–300 μm). The oxygen uncoupling capability of the developed materials was extremely low and even completely lost after repeated redox cycles. However, they were reactive under chemical looping conditions with H2, CO and CH4. Reactivity varied with the raw materials used and with the redox cycles, being of crucial importance for its evolution the intensity of the chemical stress during hundreds of redox cycles.