15th December 2020 | Steel is the world’s most popular construction and engineering material. Just over 50% of all steel produced is used in the construction and infrastructure industries. From houses to multi-storey buildings, street furniture to bridges, whether it be in the components used or the fabric of the structure itself, steel will almost certainly play an integral part.
Steel’s value to the world is immense. It represents around 95% of all metals manufactured and makes an enormous contribution to society and economies, and not just in terms of economic wealth; steel’s versatility, ease of conversion, strength and practicality make it an essential raw material for innumerable products and applications.
What is steel?
Before considering the environmental impact of steel, it is worth reminding ourselves what steel is. Put simply, steel is an alloy of iron, carbon and manganese with a few other trace elements, such as silicon, sulphur and oxygen. Carbon and manganese respectively account for 2% and 1% of this alloy, although commercial quality steels typically have much lower proportions of these elements, with low, medium and high carbon steels being produced.
Carbon is what gives steel its hardness and strength, but it also increases its brittleness and reduces workability. Controlling carbon content is, therefore, key in assuring that steel is of the right quality for its intended use. Most steel contains 0.35% carbon and few go beyond 1.85%.
Other elements can be added to this mix to provide the steel with desired performance properties. For example, stainless steel is produced by the addition of chromium.
Is steel a natural resource?
Clearly, steel is not, in itself, a natural resource. However, it does emanate from iron, one of the most abundant naturally-occurring elements in the earth’s crust.
As with most natural resources creating a usable material from the substance’s natural state requires processing.
How is steel made?
The iron from which steel is manufactured is extracted from iron ore, a combination of iron, other minerals and oxygen that is found near the earth’s surface, making it easy and economical to extract using opencast mining. Australia, Brazil and China account for around 60% of global iron ore extraction.
Coke-fired blast furnaces are used to melt the iron ore and sinter (pellets manufactured from iron ore dust, metallurgical waste and other compounds). Limestone is added to the process to remove acidic impurities from the iron.
The iron forms a pool of molten metal at the bottom of the furnace. Impurities and molten rock from the process, being lighter than the metal, form a liquid ‘slag’ which floats on top and is easily removed.
The molten metal is called pig iron, which is collected and used primarily in the production of steel but can also be used to make cast iron.
Steel is manufactured using one of two processes, Basic Oxygen Furnaces (BOF) or Electric Arc Furnaces (EAF). BOF mix recycled steel scrap (around 25%) with the pig iron to manufacture the steel, with oxygen and chemical cleaning agents being introduced to the process to lower carbon content as well as levels of silicon, manganese, sulphur and phosphorous. Alternatively, steel manufactured through the EAF method is composed of 90-100% recycled steel scrap which is melted using electric arcs and converted to high quality steel.
How does steel impact the environment?
From the extraction of iron ore through opencast mining to the ultimate manufacture and use of a steel product, steel impacts the environment on numerous levels.
In addition to the effects of opencast mining, the various stages of processing, conversion, treatment, manufacture and transport consume energy, generate emissions to air and water, and create waste.
The steel industry is acutely aware of these impacts and continues to take great strides to reduce its effect on the environment.
Energy consumption creates emissions of carbon dioxide, or CO2, one of the greenhouse gases. Worldwide, steel production accounts for around 6% of total CO2 emissions. In the past 50 years, the steel industry has reduced the energy required to create a tonne of steel by more than 60% by adopting more efficient processes and systems.
Production of the coke used to fuel furnaces consumes energy and results in emissions to air and water (used to cool the coke after baking), with several compounds being released.
Energy consumption, and the consequent emission of CO2, during coke production is minimised by efficient processes and energy in steam that would normally be wasted can be recovered to generate electricity.
The by-products of coke production, which might be released into the air and water, are controlled through filtration and modern production methods, such as full combustion technology.
The major source of waste from steel production is the slag created when iron is extracted from iron ore. Gaseous compounds are extracted using specialist emissions control systems, whilst the solid residues are used in the construction industry, such as for road bases and concrete mixes.
Is steel an environmentally-friendly building product?
Whilst the environmental impact of steel might appear considerable, many of the potentially undesirable consequences, such as CO2 emissions and air/water contamination, can be moderated through recapture, filtration and reuse.
Compared to other building materials, steel is still one of the most sustainable products available when it comes to delivering the strength, performance and versatility demanded by the modern construction industry.
Steel’s innate strength and workability mean that products can be designed and engineered to deliver higher performance levels, reducing the amount of material required.
Steel components are manufactured to precise tolerances under quality-controlled factory conditions. Engineered specifically for the application for which they are being used, these components are quickly and easily installed with minimum waste.
Steel is endlessly recyclable; it is estimated that more than 85% of steel is recycled and manufacturing new steel from old costs around one third of that from iron ore. Not only is steel readily recyclable, but it is also easy to recover thanks to its magnetic properties making it easy to extract from waste.
What is Metsec’s impact on the environment?
Our manufacturing processes do not directly use coal, oil or gas; electricity is used for production and gas only for heating the work area. The conversion of steel to the rolled steel section used in our products adds just 0.04 tonnes of CO2 to the world average of 1.85 tonnes of CO2 per tonne of steel.
For more than 10 years now, we have been implementing measures to reduce the impact of our activities on the environment, with a Carbon Trust survey highlighting areas for improvement which include heating, lighting and energy monitoring systems.
New, more efficient boilers have been installed together with advanced energy monitoring systems, which have resulted in a 10% reduction in the amount of gas used for heating.
Energy-efficient lighting and lighting control systems have delivered savings in the amount of electricity that we use. Since 2009, the electricity we use per tonne of material produced has fallen by 30%, reducing energy consumption by the equivalent of that used by 400 households per year.
You can find out more about our commitment to the environment by following these links:-