Cradle To Cradle : The Life Cycle Of Steel

By Graham Hepburn

Steel can be recycled forever without degradation. Recovery is estimated at 85%. 459.3 million tonnes are recycled world wide every year

Every kilogram of recycled steel  saves 12.5 MJ of energy, 86% less air emissions air, 40% less water and 97% less mining waste

Recycled steel uses 25% less energy.300,000 tonnes are recycled each year in NZ

2% of NZ Steel’s  “new steel” production uses recycled steel

Slag generated in NZ Steel ‘s production is used in products such as road  surfacing, drainage  and filtering

Sand tailings at NZ Steel’s Waikato North Head mine site are returned to the mined area and marram grass and pine trees are planted.

Waste gases at NZ Steel’s Glenbrook plant are recycled to produce up to 70 per cent of the electricity used.

Water at NZ Steel’s Glenbrook plant is cleaned, cooled and recirculated, only 1% is discharged.”

Building sustainably is a hot topic both locally and internationally but when it comes to choosing materials, it’s tough to work out what is truly the “greenest” option.

It’s like trying to compare apples with oranges. Take roofing for example: steel roofing is considered a good environmental choice although some people are put off by its high embodied energy – that is, the energy required to make it. But when you do a life-cycle analysis – a cradle to cradle study of a product – steel’s average embodied energy is greatly reduced because of its ability to be recycled endlessly, but this is only part of the picture.  Embodied Energy is generally quoted for a mass of material, however for roofs square metres are more relevant.  A steel roof is approximately 1/10th the weight of a concrete tile roof and requires less weight in the roof structure.  Not only is a steel roof durable- but when a roof needs replacing, the old one can be melted down and re-used in other steel products.

And that is one of the huge environmental advantages of using steel. It can be recycled forever without any worries about product degradation, what is known as “downcycling”, when a material is recycled into an inferior product.  Products that lose their original properties when recycled include some types of wood, which can be chipped, and glass, which can be turned into insulation. Plastics for example can be recycled but when they are, they produce an inferior and less valuable product.  The fact that steel can be recycled endlessly and flawlessly makes it a valuable commodity backed by a well-established infrastructure for the recovery and reprocessing of scrap metal - and markets for it worldwide. And that means it is not ending up in landfill like other waste or demolition building materials, where products such as wood emit CO2 as they degrade. The recovery rate of steel from buildings is estimated at 85% and a recent report on commercial construction waste found that more than 90% of steel was recycled.

Steel is the most recycled product in the world and was one of the first to be recycled because it is easy to recycle – all you need is a magnet to help separate it from other waste. Worldwide more than 459.3 million tonnes of steel scrap are recycled each year, more than paper, aluminium, glass and plastic combined.

Steel might be the most recycled but all metals used in roofing such as aluminium, copper, zinc and lead can be fully recycled and are valuable.

Scrap metal is a vital part of the process for New Zealand’s two steel-makers. Pacific Steel, a division of Fletcher Building, makes all its steel from scrap. New Zealand produces about 500,000 tonnes of scrap metal a year. Pacific Steel uses about 300,000 tonnes of that to make products such as reinforcing steel and wire, with the rest of the scrap metal being exported.
New Zealand Steel, which makes around 600,000 tonnes of steel a year, has an average recycled content of about 12% in its products.  New Zealand Steel manufactures coil and sheet for use in building cladding and other industries. The coil may be metal coated with zinc – commonly known as galvanized steel – or a combination of aluminium and zinc (ZINCALUME®) and may be painted on its own coil coating line to produce COLORSTEEL® or trucked a small distance to an independent coil coating line (Pacific Coil Coaters) to produce ColorCote®.

As well as providing a source of feed in this process, scrap metal is used to control the temperature generated by the chemical reactions in the furnace. 

Recycled steel can be made by using as little as 25 per cent of the energy it takes to make virgin steel and that doesn’t take into account the savings in terms of mining, transportation, landfill and greenhouse gas emissions.

The American Institute of Architects’ Environmental Resource Guide says that each tonne of recycled steel saves 1100 kg of iron ore, 600 kg of coal, and 50 kg of limestone. The AIA also states that every kilogram of steel produced from recycled sources rather than raw materials saves 12.5 MJ of energy, 86% less emissions to air are produced; 40% less water is used; and 97% less mining waste is created.

And it’s not just the steel that’s recycled. At New Zealand Steel’s Glenbrook plant the large quantities of slag generated by the steel-making process are sold for use in products such as road surfacing or for drainage and filtering. Huge amounts of water – around 1 million tonnes a day are needed to make steel but that is also recycled – cleaned, cooled and recirculated so that so that only 1% of it is discharged and what is discharged is clean enough to drink.

Even the waste gases from the kilns used in the steel making process at Glenbrook are recycled in a cogeneration plant that produces up to 70 per cent of the electricity used on site.

Unlike other steel makers, who use iron ore, New Zealand Steel uses iron sand from Waikato North Head not far from Glenbrook. And even these sands are recycled. When the iron sand is removed, which makes up about 25 per cent of the excavated sand, the rest of the sand – or tailings - is returned to where it was extracted. Marram grass is planted to stabilise it and when that takes root, pine trees go in.

Whether steel products are manufactured from virgin or recycled steel, it’s important for environmentally conscious specification to remember that the two processes are mutually dependent. Given that all recycled steel products once came through the primary manufacturing route, it’s not simply a case of specifying recycled steel products to benefit the environment.  Green building tools need developing to enable specifiers to easily select steel products – whether they are manufactured from virgin or recycled steel – from best practice manufacturers. 

The properties of steel combined with market driven demand for scrap steel give rise to an enviable end of life product stewardship programme,