Packed beds of coal and iron ore (mostly in the size range 425–850 mm) were heated by thermal
radiation to the bed surface, to test possible rate determining steps, the effect of coal volatiles, and whether the previously predicted near constant and approximately linear relationship between heat transfer and reduction holds. Bed depths were mostly 40 mm and 16 mm in some cases. The results confirm that coal volatiles contribute significantly to reduction, reducing the bed temperature slightly, decreasing the energy requirement for reduction, and increasing the extent of reduction. A one-dimensional heat transfer and reaction rate model suggests that the thermal conductivity through reacted layers is higher than predicted, likely by the formation of continuous metal paths and of openings which support radiative heat transfer.