At the sharp end

What’s the deal with steel? (8 minute read)

The wild beaches of the North Island’s west coast hold a special place in the hearts of many New Zealanders. Whether it’s the pounding waves, the whip of the wind or the stretches of black sand, there’s something about these beaches which sings of the power of nature. They make humans seem insignificant. The west coast beaches are the kind of place where climate change is hard to comprehend – how can humans have such a large impact on such an imposing environment?

Of course, just because climate change is hard to comprehend, that doesn’t mean it’s not a crisis. But I think it’s important to step back occasionally and acknowledge that sometimes our emotions tell us something different from our minds. When we are faced with the vastness of nature, it’s sometimes hard to see ourselves knocking everything out of balance.

And yet we are, in ways that most of us barely think about.

I started with the stunning west coast beaches for a very specific reason – the black sand has a connection with climate change. Most sand is predominantly a chemical called silicon dioxide, derived from quartz rock. On tropical islands, the pure white sand is often a different chemical, calcium carbonate derived from ground up coral fragments. But the black sand beaches of the North Island west coast are something different. The colour comes from a mineral known as titanomagnetite, which was washed down rivers from volcanic rocks in Taupō and Taranaki.

The wild west coast at Awakino (image credit: Peter Newfield)

As its name suggests, titanomagnetite is a magnetic compound. It’s magnetic because it is rich in iron, the most common magnetic element. In fact, New Zealand’s black sand is sometimes known as ironsand. This ironsand is mined from near the Waikato Heads and shipped north to Glenbrook, where New Zealand’s only steel mill turns it into steel. Glenbrook is unique in the world in using ironsand as its source of iron.

Steel, like concrete, is so commonplace that we barely give it a thought. In 2021, the world produced nearly two billion tonnes of it. Among other things, steel is used in buildings, motor vehicles, bridges, power plants and domestic appliances. But, as with concrete, there’s a cost to steel production. It is responsible for around 7-11% of global greenhouse gas emissions. Those figures put it at about the same level as concrete production, perhaps even higher. And, as far as I can tell, the climate impacts of steel production have received even less attention than the climate impacts of concrete.

Steel production emits so much carbon dioxide because of the process that ironsand and other types of iron-bearing minerals must undergo to become steel. The process uses a massive amount of energy, because it requires very high temperatures. But it is more complex than that. As with concrete, emissions also result from the chemical reaction which turns sand or stone into iron.

Steel production begins with iron-bearing minerals where the iron has combined with oxygen to form an oxide. To get iron from iron oxides, the chemical reaction which formed the oxides in the first place needs to be reversed. Although the reactions which form oxides happen easily – the process happens every time something rusts – undoing that process is not so easy.

In typical steel production, the iron oxides are combined with coke (formed by heating coal so hot that it melts), and limestone. The three compounds are mixed with hot air in a blast furnace, and at the intense temperatures inside the furnace, around 1800oC, several different chemical reactions take place. The coke burns, the iron oxide converts to molten iron, and the rocky parts of the iron-bearing minerals react with the limestone to form slag. What all of the chemical reactions have in common is that each one produces carbon dioxide. In addition, the hot air which enters the blast furnace must be pre-heated to around 1000oC, and that takes a lot of energy, often supplied by fossil fuels.

Still more energy is required to turn the iron from the blast furnace into steel. The iron which drips out of the bottom of the blast furnace, usually known as pig iron, has around 2-4% carbon in it. Pig iron also contains impurities such as sulphur, phosphorus and silicon. The high carbon content makes the iron brittle, although it can be used as cast iron – shaped by pouring into moulds.

Turning the pig iron into steel requires processes which remove the impurities and reduce, but do not eliminate, the carbon. Without any carbon at all, iron is soft and of limited use. It is the presence of some carbon, from 0.25-2%, which turns iron into steel. The small percentage of carbon gives the iron enough strength so that a sharpened blade doesn’t easily become blunt, and bridges can survive both the weight of traffic passing over them and the constant vibration.

But not all steel is the same when it comes to climate change.

New Zealand’s ironsands proved a difficult prospect for the people working to produce steel from them. The fine texture of the sand and the high proportion of titanium in the titanomagnetite clogged the blast furnaces, and numerous attempts to produce steel from ironsand failed. Eventually, using technology developed in Norway, New Zealand scientists developed a process which used rotary kilns and electric arc furnaces.

Steel from electricity? Is there really such a simple solution?

Yes and no. The process of converting the ironsand to a product called sponge iron in the rotary kilns substitutes coke with coal. Although some sources suggest that using coal instead of coke can reduce carbon emissions from steel production, how much reduction is debatable. It also depends where the electricity comes from, and whether other energy sources are used.

I’ve spent some time trying to get an idea of how efficient, in terms of carbon emissions, New Zealand steel production is, and information has proved difficult to find. I’ve found two different numbers for how much carbon dioxide is emitted per tonne of steel produced – 1.8 tonnes and 2.5 tonnes. These figures suggest that New Zealand steel production could be among the worst for carbon emissions globally, but without knowing how the figures for the world were calculated, in comparison with the New Zealand figures, comparisons are unfair. In general, those countries which use electric arc furnaces instead of blast furnaces emit less carbon dioxide per tonne of steel, which suggests that New Zealand might be better than indicated by the figures I have found.

It is clear that there are massive differences between countries. A recent analysis found that Italy, the USA and Türkiye emit less than a tonne of carbon dioxide per tonne of steel. On the other hand, the worst countries, India and Ukraine, emit more than two tonnes of carbon dioxide per tonne of steel, and China is very close behind them.

On the one hand, that is terrible news, because China is, by far, the world's largest producer of steel. India is number two (Ukraine was 14th in 2021, but that figure has probably changed now). On the other hand, it is great news, because it proves that the steel industry could make huge improvements with current technology, if there were sufficient incentives and support.

But current technology can do only so much. As long as steel production depends on carbon to remove the oxygen from iron oxides, it is going to emit large amounts of carbon dioxide. This leaves two potential solutions for the steel industry – use something other than carbon to remove the oxygen, or somehow capture the carbon dioxide so it doesn’t end up in the atmosphere.

Both options are currently under investigation. One option is to use hydrogen in place of coal. This has been investigated by Victoria University researchers, who have demonstrated that the process works on a small scale. They still face two crucial challenges: scaling up the technology for commercial use and producing hydrogen in a manner which doesn’t create its own carbon emissions. But it’s a start. The other option is carbon capture, which means taking the carbon dioxide which is emitted and ensuring it isn’t released into the atmosphere. The technology exists, but it’s energy intensive and expensive, so it doesn’t yet provide the answer.

There’s another part to the solution, and it’s the most obvious, when you think about it. Steel can be recycled. It’s not like plastic and paper either, which can only be recycled into products of lower quality, and only a certain number of times. Steel is like glass – it can be recycled again and again, without losing quality. That’s good news, but the problem is that demand for steel continues to outstrip the supply of scrap for recycling.

There’s one other solution, too. It is the one that gets, in my opinion, far too little attention and it’s certainly something that the steel industry isn’t talking about. That solution is to use less steel. This shouldn’t worry the steel industry though. There’s no danger of demand for steel disappearing. For a start, a new wind turbine of the size used at the White Hill wind farm in Southland takes 260 tonnes of steel to build. We need steel, but we don’t need to waste it. University of Cambridge researchers in Britain have identified six steps that industries and countries can take in order to waste less steel and other industrial materials.

Individually, there isn’t a lot we can do about steel – it’s not like meat or food waste where we can, and need to, make personal choices which collectively add up. But we can have conversations about it, and ask questions of our politicians and industry leaders. We need to keep up the pressure on crucial industries like concrete and steel to ensure that they are part of the solution to the climate crisis we now face.