40 | New Scientist | 16 November 2019
like copper can build up and make recycled
steel poorer quality, reducing its potential uses.
“At the moment, we can make construction
grade steel from recycling, but not automotive
grade,” says Allwood. Yet he adds that such
impurities can be minimised by better sorting
of materials before recycling them and by
removing impurities from the molten steel.
The other option is to make fresh steel using
a greener process – and to that end there is a
push in some quarters to convert iron ore
not with coking coal but hydrogen. The idea
is that the oxygen in the iron ore will combine
with the hydrogen to produce water instead
of CO 2. SSAB, a steel-making company
headquartered in Stockholm, Sweden,
is among those exploring this strategy,
which it has called HYBRIT. It has begun
construction of a pilot plant in Sweden that
could, the firm claims, produce steel with
“virtually no carbon footprint”.
There is a caveat. For the moment, hydrogen
is overwhelmingly made from fossil fuels,
such as natural gas, and that means
greenhouse gas emissions: the carbon
footprint of global hydrogen production is
on a par with the emissions of the UK and
Indonesia combined. But it is possible to make
hydrogen from water using an electrolyser
powered by electricity from renewable sources.If we one day have enough excess wind power,
we could potentially produce all the hydrogen
we need for large-scale clean steel production
via electrolysis – that is, if the economics
somehow worked out.
Promising. But part of the problem when it
comes to decarbonising steel is the state of the
industry. Unlike oil and gas, which continue to
yield extravagant profits for producers, steel
makers outside China are struggling to stay
afloat. As a result, they don’t have much leeway
to cover the costs of new low-carbon
technology. Nor have they enjoyed the support
of governments in the same way as the
renewable electricity sector, which has
benefited from subsidies for over a decade.
SSAB says its hydrogen-produced steel could
be 30 per cent more expensive than normalALUMINIUM
Aluminium production accounts for
about 1 per cent of global carbon
emissions. The problem comes when
aluminium ore is converted to pure
metal. This involves inserting an
electrode made of carbon, which
combines with oxygen in the ore to
produce CO₂. Last year Apple, a major
aluminium user, announced a
partnership with miner Rio Tinto and
aluminium maker Alcoa to develop
an alternative electrode that would
produce oxygen instead of CO₂ as a
by-product. But the technology won't
be commercialised until 2024.PLASTIC
Making plastics is energy intensive,
and the raw materials for producing
them are often obtained from the
refining of crude oil. That means they
come with a sizeable carbon footprint.
The good news is that increasing use
of renewable energy, the rise of plastic
recycling and reduction in demand
could bring emissions to 2015 levels
by 2050, according to a study
published in April. Oil giant BP says
bans around the world on single-use
plastics – like those planned by the EU
and Canada – will also curb growth in
the demand for crude oil.AMMONIA
Ammonia, a key ingredient in
fertilisers, is made from nitrogen and
hydrogen. The latter is almost always
made from fossil fuels, primarily
natural gas – and the most common
production process for turning it into
ammonia, known as Haber-Bosch, is
energy intensive. Emissions could be
cut by making the hydrogen from
natural gas but also using carbon
capture and storage, or making it via
electrolysis of water powered by
renewable energy, but one analysis
says such approaches add 60 per cent
to the cost of ammonia production.The heavy mob
Concrete and steel aren’t the only industries that need
cleaning up if we want to reach net-zero carbon emissionssteel, meaning it would require governments
to introduce some form of carbon levy on
steel production to make it economically
competitive. “Until you think there is going
to be a significant and sustained carbon price,
the commercial driver is just to produce iron
and steel in the way you already produce it,”
says Fennell.
Concrete suffers with many of the same
problems, starting with the basic chemistry
involved in its production: CO 2 emissions
are inherent in making its component parts.
Take cement, the “glue” that holds concrete
together. To make it, you first grind and heat
limestone in rotating kilns. The ensuing
process of calcination decomposes the
limestone’s calcium carbonate into calcium
oxide, releasing CO 2. The next stage requires
yet more energy to heat calcium oxide with
other materials to make a substance called
clinker. Add this to the soft mineral gypsum
and you get cement.
Many observers think the sector is almost
impossible to clean up. Allwood puts it bluntly:
“There are no options to decarbonise cement.”
But that hasn’t stopped people from trying.
One option is to use a different kind of
cement. Almost all concrete is made using
Portland cement, a 19th century formula that
works well. But there are plausible alternatives.“ Many observers think
concrete production is
almost impossible to
decarbonise”