After successful operation of a 200 kW gas circulating combustion system for over 100 h with NiO/Al2O3 oxygen carrier (OC) particles, we are ready to scale-up the process up to a 1-10 MW system. To supply large quantity of OC particles for the scaled-up system at a lower cost, iron oxides are considered as a cheaper source material of OC. Mixed NiO/Fe2O3/Al2O3 OC particles were fabricated with commercial iron oxide reagents by a spray-dryer and tested for oxygen transfer capacity (OTC) and physical/chemical properties to investigate the feasibility of mass production. While looking for cheap iron oxides from wastes or industrial products, considerable amounts of scale and sludge were found from power plants. The main component of the sludge and scale collected from power plants was more than 95% of iron oxides and the residue was also oxides, such as MnO, SiO2, Cr2O3 and CaO, which can be an active material or a binder for OC. The particle size of the sludge and scale is also suitable for the OC fabrication, eliminating the need of pre-treatment. Four different OC particles were fabricated by a spray-dryer, calcined at 1100, 1200 and 1300 degrees C, and their physical/chemical properties were measured. It was found that mixed NiO/Fe2O3/Al2O3 oxide carriers are good candidates for a 1-10MW class circulation combustion of fluidized bed. The contribution of this research is that the sludge and scale collected from power plants can be used to capture CO2 emitted from power plants. (C) 2013 Elsevier Ltd. All rights reserved.