Iron and steel recycling: Review, conceptual model, irreducible mining requirements, and energy implications

Production of new steel by recycling steel requires up to 10 times less energy than the production of steel from virgin iron ore (primary steel). In a hypothetical future world with an unchanging, saturated stock of steel, new steel would be needed only to replace steel in products at the end of their lives. However, some primary steel would be needed to make up for less than 100% collection of end-of-life (EOL) steel and for mass losses during the processing of EOL steel, and also to dilute contaminants in melted EOL steel or to bring concentrations of alloy additives to acceptable ranges after mixing of different alloys. This paper reviews the ways in which primary and secondary steel are produced and used today, and reviews the constraints on the recycling of EOL steel today and the prospects for reducing these constraints in the future. A simple conceptual model is presented and applied to the computation of iron ore mining requirements in a hypothetical world where steel stocks are four times larger than today but have reached a steady state. Even with drastic improvement in all the parameters that determine the amount of recycling possible and no further growth in steel stocks, iron ore mining requirements would still be over 10% of present-day mining, thereby undermining long term (1000-yr) sustainability. Energy requirements would be comparable to present-day iron and steel energy use with no improvement in recycling parameters, decreasing by a factor of four for the most extreme case considered.