Energy-efficient recycling in metals manufacturing

The US Energy Information Administration has revealed that the use of recycling in the manufacture of iron, steel and aluminium - an otherwise energy-intensive process - is driving improvements in energy efficiency within the industry.

Primary production, in which steel is made from iron ore and aluminium from bauxite ore, is energy intensive. Secondary production involves the use of recycling scrap - such as discarded automobiles, appliances, machinery and demolished steel structures - and is much more energy efficient. The Environmental Protection Agency estimates that secondary steel production uses about 74% less energy than the production of steel from iron ore, while the US Department of Energy reports that secondary aluminium production requires 90% less energy than primary production.

Source: US Energy Information Administration, Manufacturing Energy Consumption Survey.

Secondary production accounts for nearly 60% of US aluminium production. Similarly, recycling is used in most steel production. According to the US Geological Survey (USGS), 40% of US steel production in 2011 came from basic oxygen furnaces (BOF), whose inputs are almost 80% pig iron (molten iron), whereas 60% of production came from electric arc furnaces (EAF), which use more than 90% scrap.

Primary production of steel usually involves using a blast furnace to produce molten iron from iron ore, coal and coke, using fluxing agents such as limestone to remove impurities. The molten iron (pig iron) is then converted into steel by a BOF. Secondary production facilities typically use an EAF, with scrap providing the main input. In an EAF, scrap is melted using electric arcs, which can be supplemented with natural gas-fuelled combustion. Another alternative to using a blast furnace to produce pig iron is using direct-reduced iron (DRI), a process typically fuelled by natural gas.

Source: US Geological Survey, Iron and Steel Minerals Yearbook.

In addition to domestic use in steel production, iron and steel scrap trade is significant. In 2011, USGS reported that the United States exported 24.3 million tonnes of scrap and imported 4 million tonnes.

Source: US Energy Information Administration