The Big CO2 Emitters: A Few Steps Forward


I’ve long been interested in cement production, ever since, as a young project engineer in the 70’s, I was tasked with building a cement terminal. My interest was piqued again recently when I learnt that the cement and steel industries are by far the biggest CO2 emitters in heavy industry, contributing almost half of industrial carbon emissions into the atmosphere!

This realization has led to some major advances in the reduction of greenhouse gases in certain process industries in the past few years. A bit of research has prompted me to outline a few advances in the reduction of industrial carbon dioxide emissions from the cement, steel and aluminium industries.


The production of cement, a key component of concrete, involves combustion processes that release CO2 into the atmosphere, contributing to global climate change. Each year, approximately 3 billion tons of CO2 can be traced back to cement production, representing 8% of global carbon emissions, so there is an urgent need to develop more sustainable alternatives. Currently, for every ton of cement produced, a ton of CO2 is pumped into the atmosphere.

Current low impact initiatives

There are three aspects which are currently being addressed: the reduction of raw clinker cement in the mix, cutting back the quantity of cement in the concrete mix and the addition of CO2 from another source into the concrete mix.  Bear in mind that these initiatives only reduce the amount of cement used and don’t address the amount of CO2 emitted in the clinker production.

‘Green’ cement in Malaysia

YTL Cement started production of so-called ‘green’ cement by mixing slag, a waste from steel mills, and fly ash from coal fired power stations. Slagcem is also being produced in other countries where cement plants are located near steel mills and coal fired power stations. Slagcem can contain up to 65% slag and could even be stronger than pure clinker cement. So with 35% clinker cement per bag, there is up to 65% reduction in the CO2 produced per bag of final product.

Concrete recycling in Switzerland

The Swiss construction company Eberhard has introduced Zirkulit, a low-carbon, circular concrete that is largely composed of recycled materials. The aggregate material in Zirkulit  is made up of about 85% recycled, secondary material, massively reducing the need to mine primary material from gravel quarries. The use of recycled building material reduces the waste stream, and recycling cuts down the transport distance of heavy materials. Zirkulit concrete is also optimized to use about 7% less cement than conventional concrete while providing the same mechanical and chemical qualities as conventional concrete.

Concrete CO2 injection in USA

CarbonCure manufactures a technology for the concrete industry that introduces recycled CO₂ from any source into fresh concrete to reduce its carbon footprint without compromising performance. Once injected, the CO₂ undergoes a mineralization process and becomes permanently embedded. They claim to save 15 kg of CO2 per cubic meter of ready-mix. This results in economic and climate benefits for concrete producers.

High impact initiatives

The aforementioned initiatives are all very well, yet they don’t go far enough to be anywhere near net zero. So how are cement companies actually going to achieve net zero? Nevertheless, there have been some assurances that cement production will be carbon neutral by 2050. That remains to be seen. A few areas of interest follow.

Fossil fuel replacement

Many alternatives to fossil fuels are being researched, but this only deals with the replacement of  fossil heating fuel and not actual emissions of CO2 from the calcining process (the conversion of limestone into cement).

Carbon Capture and Utilization (CCU)

This is an area which may show some surprising results. I found two examples:

To make air transport and cement production more sustainable, three players from completely different backgrounds have joined forces in the “Concrete Chemicals” project consortium. Global cement producer CEMEX, Sasol ecoFT (part of the integrated chemicals and energy company Sasol), and renewable energy company ENERTRAG are planning to produce a sustainable aviation fuel by using CO2 from cement factories, which will contribute to the overall decarbonization of the cement industry.

Sumitomo Osaka Cement is working on a CO2 mineralisation research project with Yamaguchi University, Kyushu University and the New Energy and Industrial Technology Development Organisation. The partners are developing a process that captures CO2 exhaust from cement and power plants and then mineralises it with calcium-containing waste materials, with the aim of making it available for commercial use by 2030.

Carbon Capture and Storage (CCS)

Heidelberg Cement started to investigate emission mitigation 15 years ago. They combined technologies and industries to deposit CO2 into spent offshore oil and gas wells and plan to have the first industrial-scale carbon capture and storage (CCS) project at a cement production facility in the world at Brevik in Norway. They aim to capture 400,000 tonnes of CO2 annually and transport it to permanent storage.

There are strong hopes that many more such agreements between cement producers and those with suitable storage, such as depleted oil and gas wells, will follow.

Support for other industries trying to dispose of waste

Hazardous waste

Cement companies also provide hazardous waste management services by ‘co-processing’ waste materials in their cement manufacturing processes. Cement kilns are able to tolerate very high temperatures for extended periods and can be used to safely capture and dispose of hazardous waste materials. Qatar Cement, for example, processes refinery sludge from their local refinery.

Scrap tyres for cement production in South Africa

A South African cement company has a novel way of reducing emissions and saving costs. Pretoria Portland Cement’s de Hoek plant burns waste tyres as an alternative to coal to make cement. The project, which enables de Hoek’s kiln number 6 to burn up to six tyres per minute, reduces the plant’s coal use by an estimated 10%, while significantly reducing nitrous oxide emissions. It simultaneously decreases landfill requirements for waste tyres, achieving a positive and sustainable environmental impact. The company also blends waste slag from a nearby steelworks to produce ‘Slagcem’, or so-called ‘green’ cement.


Steel Making

If the steel industry were a country, its carbon dioxide emissions would rank third in the world, just below the US and above India. Aside from churning out 1.86 billion metric tons of steel last year, steelmakers generated over 3 billion tons of CO2, corresponding to an astonishing 7 to 9% of all human-made greenhouse gas emissions, which is equal to the emissions from cement production.

Proprietary technology is being used to reduce emissions from existing steel plants and to change the way steel is being made. This is what’s being done:

Lanzatech bio remediation

LanzaTech’s carbon recycling technology uses bacteria to convert pollution to fuels and chemicals.

LanzaTech, and its joint venture partner, Shougang Group, a leading Chinese iron and steel producer, recently announced the successful start-up of the world’s first commercial facility converting industrial emissions to sustainable ethanol.

Use of Hydrogen

Some approaches rely on hydrogen from electrolyzers which are powered by renewable electricity, while others use that energy directly in electrochemical reactions. 

The Hydrogen Breakthrough Iron-making Technology (HYBRIT) process aims to replace the coke and other fossil fuels used in traditional, blast furnace-based steel-making and instead relies on hydrogen created with renewable electricity. The process should lower carbon dioxide emissions in all stages of steel-making, including pelletizing iron ore, reducing iron oxides to iron, and producing crude steel.

German steelmaker Thyssenkrupp plans to phase out CO2-intensive coke-based steel production and replace it with a hydrogen-based process by 2050.

In Spain, Iberdrola and H2 Green Steel have signed an agreement to build a green hydrogen plant. It will power a direct steel reduction furnace with clean fuel, and produce around 2 million tons per year of pure green steel, with a 95% reduction in CO2 emissions.

Rio Tinto’s alternative approaches

The world’s second-largest metals and mining corporation, Rio Tinto, said it was focused on studying three potential pathways towards net neutral steelmaking: using sustainable biomass with Pilbara iron ore to replace coking coal in the iron and steelmaking process; using hydrogen-based hot-briquetted iron (HBI) with high-grade ores in Canada; and using hydrogen direct reduced iron (DRI) with a smelter for Pilbara ores. (Pilbara is in West Australia.)

Carbon Capture and Storage (CCS)

In June 2021, US Steel signed an agreement with Norwegian energy company Equinor to explore the possibility of undertaking CCS and hydrogen development in Ohio, Pennsylvania and West Virginia. Hopefully more such agreements will evolve between steel companies and those with the technology and storage for disposal of carbon emissions from steel plants.

Combined effort

A Chinese chemical plant is set to become the world’s largest facility for recycling carbon dioxide into fuel. It will combine CO2 from a lime kiln with excess hydrogen, and CO2 from a steel coking furnace to produce methanol. Carbon Recycling International (CRI), the Reykjavik-based firm behind the operation, says that the Tongyezhen plant will recycle about 160,000 tonnes of CO2 per year.

Steel Recycling

The scrap steel market is enormous. Alang Ship Breaking Yard in Gujarat, India, is the largest ship-breaking graveyard in the world, and oversees ship dismantling for almost 50% of the world’s vessels. The use of blended scrap is common in the manufacture of certain steel products and can produce steel of equal quality to that from virgin stock.



Aluminium production accounts for about 0.8% of global greenhouse gas emissions and demand is rising. Smelting aluminium conventionally requires anodes made of carbon-rich material as carbon is a good conductor of electricity as well as being cheap and plentiful. During the process the carbon anodes are destroyed, releasing carbon dioxide gas.

Power requirement

Unlike cement and steel, which use coal or gas as their primary source of energy, aluminium manufacturing requires a lot of electricity. Initially, aluminium smelters used hydro electric power and, as a consequence, many large aluminium companies in Canada, US, Norway and Russia have extensive hydro power supplies. (During the Second World War, the Grand Coulee dam on the Columbia river supplied electricity for aluminium smelters which provided the metal for Boeing aircraft company in Washington State. Boeing contributed to the production of almost 99 000 aircraft, including the famous B-17 Flying Fortress). 

Today, electricity for aluminium smelters is also produced from low grade waste gas which is derived directly from gas fields such as those in Qatar, Emirates and Bahrain. The largest aluminium smelter in the world is in Bahrain, a country barely bigger than Singapore.


In May 2018, the Canadian government and two of the world’s biggest aluminium producers, Alcoa and Rio Tinto, hailed a “breakthrough” technology that would remove carbon dioxide from the smelting process. Alcoa and Rio Tinto’s new process involves the use of a proprietary material they invented and developed over a decade that can be used in place of carbon. When used in smelting, it releases oxygen instead. They are aiming to complete demonstration by 2024, with commercialisation to follow.

RUSAL’s Krasnoyarsk plant in Russia has produced primary aluminium using inert anode technology at industrial scale (1 tonne of aluminium per day per cell). Test deliveries of a pilot batch of aluminium commenced in the spring of 2021, and the company aims for mass-scale production by 2023.


Aluminium is easily recycled and can be blended with virgin stock to produce a product comparable to that made from 100% virgin stock. This scrap metal also has a high value which encourages recycling. There have been advances in packaging as well, which includes easy separation. For instance, beer cans are now made exclusively from aluminium (where previously cans had tabs made of steel).


There are clearly some strides being made in the cement, steel and aluminium industries to manage the amount of CO2 being released. It’s very heartening to see the co-operation between different industries, but government support is also much needed to make the final transition to net zero. I’ll be watching with interest to see how new innovations develop.

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