Metal fuels have been proposed as advanced storage and transport systems for clean energy, because of their inherently low safety risk and high energy densities. To ensure a clean metal fuel energy cycle, metal fuel utilization products, i.e., metal oxide powders, need to be captured and cyclically reduced back into metal fuel powder via advanced technology that is powered by renewable energy. In this work we focus on hydrogen reduction of iron oxides under fluidization conditions for recycling of iron powder as energy carrier. Iron is selected because of its favorable properties of heterogenic combustion, abundance and low price. Dynamic and thermodynamic behavior of this fluidization reduction process are studied via a combination of numerical modelling and experimental measurements. In this talk, we will discuss the main technical issues linked to the use of fine iron powders as a dense renewable energy carrier.