Hydrogen Plasma Processing of Iron Ore
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and ANTHONY B. MURPHY
Iron is currently produced by carbothermic reduction of oxide ores. This is a multiple-stage process that requires large-scale equipment and high capital investment, and produces large amounts of CO2. An alternative to carbothermic reduction is reduction using a hydrogen plasma, which comprises vibrationally excited molecular, atomic, and ionic states of hydrogen, all of which can reduce iron oxides, even at low temperatures. Besides the thermodynamic and kinetic advantages of a hydrogen plasma, the byproduct of the reaction is water, which does not pose any environmental problems. A review of the theory and practice of iron ore reduction using a hydrogen plasma is presented. The thermodynamic and kinetic aspects are considered, with molecular, atomic and ionic hydrogen considered separately. The importance of vibrationally excited hydrogen molecules in overcoming the activation energy barriers, and in transferring energy to the iron oxide, is emphasized. Both thermal and nonthermal plasmas are considered. The thermophysical properties of hydrogen and argon–hydrogen plasmas are discussed, and their influence on the constriction and flow in the of arc plasmas is considered. The published R&D on hydrogen plasma reduction of iron oxide is reviewed, with both the reduction of molten iron ore and in-flight reduction of iron ore particles being considered. Finally, the technical and economic feasibility of the process are discussed. It is shown that hydrogen plasma processing requires less energy than carbothermic reduction, mainly because pelletization, sintering, and cokemaking are not required. Moreover, the formation of the greenhouse gas CO2 as a byproduct is avoided. In-flight reduction has the potential for a throughput at least equivalent to the blast furnace process. It is concluded that hydrogen plasma reduction of iron ore is a potentially attractive alternative to standard methods. DOI: 10.1007/s11663-017-0957-1 The Minerals, Metals & Materials Society and ASM International 2017
I.
INTRODUCTION
Almost all economically important metals are extracted from naturally occurring ores. Of these metals, the d-block transition metals play a particularly significant role in our day-to-day life. These transition metals have assumed utmost importance due to our ever-growing population and economy. The most widely used transition metal in modern times is iron, in the form of steel. Globally, iron and steel production has surpassed 1660 million tonnes per annum, and is increasing day-by-day.[1] Steel production is not only energy intensive, but also environmentally sensitive, at a time when climate change is a great concern throughout the world. The steel industry has been successful in reducing the energy consumption per tonne of steel by 60 pct in the last 50 years. This drastic change leaves little room for improvement of conventional technologies. Of these technologies, blast furnace–basic oxygen furnace— accounts for 70 pct of the total world steel production.[2]
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