A method and an apparatus for producing direct reduced iron (DRI) move a material comprising iron ore and biomass through a preheat zone (20) and then a reduction zone (30) of a hearth furnace (3) and heat and progressively reduce iron ore and discharge DRI. Reduction gases flow in an opposite direction to material, and combustible gases in the reduction gases are combusted in the preheat zone and generate heat. Microwave energy heats material and reduces iron ore in the reduction zone. The microwave energy is supplied via a plurality of microwave applicators (66) arranged in a plurality of rows of applicators extending across a width of and along a section of a length of the reduction zone. The reduction zone (56) includes a lower sub zone (58) and an upper sub zone separated by an interface (80). The interface is configured to so that (a) microwave energy is at least substantially prevented from passing through the interface to the upper sub zone and (b) reduction gases produced in the lower sub zone from reduction of iron ore can flow through the interface into the upper sub zone.