Traditional metal production is inherently polluting, with data from energy research and consultancy company Wood Mackenzie’s Emissions Benchmarking Tool concluding that it is currently responsible for 9% of global greenhouse-gas emissions.

Many of the metals produced in smelting operations around the world will play a vital role in the energy transition. For example, nickel and cobalt are used in electric vehicle batteries, while copper and aluminium are increasingly used in power generation decarbonisation.

As major economies march towards a net-zero future, there is understandably a growing endeavour to produce metals with little-to-no carbon footprint.

“Smelting is highly energy intensive. Traditionally, the power for smelting has come from either grids using both renewable and non-renewable sources, or [through] onsite generation from hydrocarbons or coal. Sustainable smelting will therefore require greening the energy supply to smelting plants through a 100% renewable grid, clean onsite generation or buying into offsite renewables,” says Wood Mackenzie research manager Dominic Wells.

“Smelters are already making commitments to power their operations either partly or wholly through dedicated solar and wind power from partners and third-party companies in the next few years.”

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lthough using renewable energy can remove carbon emissions from the power used in smelting, it cannot decarbonise the process completely. When metal ore is decomposed using a source of carbon, such as coke or coal, as a reductant, carbon dioxide (CO₂) is inevitably created as a by-product.

One solution is carbon capture. Captured CO2 _{can be stored in depleted oil and gas fields, or deep saline aquifers. It can also potentially be injected in liquefied form into suitable rock formations or sequestered into concrete.}

Another technique is to reinject the CO2 from furnaces as part of a synthetic gas for use as part of the process chemistry. These approaches are still in their infancy, but significant progress can be expected in the future.

One technology which has enormous potential in metallurgical operations is green hydrogen, that is, hydrogen produced from water by renewables-powered electrolysis in an essentially clean process.

Hydrogen can essentially replace the use of carbon in smelting, preventing CO2 _{being emitted at all. However, there are a lot of obstacles to overcome before this becomes a viable large-scale option.}

Perhaps the world could take its cue from China. Chinese producers are already starting to relocate their smelters away from city centres. As well as providing better access to clean energy sources and raw materials, relocation can also enable the combined treatment of residues from the smelting of different metals on one site.

At the same time, new technology can be introduced to reduce residues and abate emissions, while older, more polluting processes can be abandoned.