furnace

Trapping carbon with rocks

March 25, 2025 By EarthWise Leave a Comment

Many experts say that combating global warming will require both drastically reducing the use of fossil fuels and permanently removing billions of tons of CO2 already in the atmosphere. Developing practical, large-scale technologies for carbon removal is a significant challenge.

There is a nearly inexhaustible supply of minerals that are capable of removing carbon dioxide from the atmosphere, but they don’t do it quickly enough to make a significant dent in the ever-growing supply in the atmosphere. In nature, silicate minerals react with water and atmospheric CO2 to form minerals in the process called weathering. But this chemical reaction can take hundreds or even thousands of years.

Researchers at Stanford University have developed a new process for converting slow-weathering silicates into much more reactive minerals that capture and store carbon quickly. The new approach resembles a centuries-old technique for making cement. They combine calcium oxide and another common mineral containing magnesium and silicate ions in a furnace. The result are new materials that, when exposed to water, quickly trap carbon from the atmosphere.

In their experiments, the carbonation process took weeks to months to occur, thousands of times faster than natural weathering.

The idea would be to spread these materials over large land areas to remove CO2 from the air. Meaningful use for trapping carbon would require annual production of millions of tons. But the same kiln designs used to make cement could produce the needed materials using abundant minerals found in many places. In fact, the required minerals are often common leftover materials – or tailings – from mining.

**********

Web Links

Scientists discover low-cost way to trap carbon using common rocks

Photo courtesy of Renhour48 via Wikimedia.

Earth Wise is a production of WAMC Northeast Public Radio

Recycling cement

June 21, 2024 By EarthWise Leave a Comment

Concrete is the second-most-used material on the planet. Only water is used more. Producing concrete is responsible for 7.5% of human-produced carbon dioxide emissions. So, finding a cost-effective way to reduce these emissions is a major challenge in the face of ever-growing global demand for concrete.

Researchers at Cambridge University have found that used cement is an effective substitute for lime flux, which is an essential material used in steel recycling that results in a waste product called slag. When lime is replaced with used cement, the end product instead is recycled cement that can be used to make new concrete.

The process does not add any significant costs to concrete or steel production and significantly reduces the emissions associated with both.

Concrete is made from sand, gravel, water, and cement. Cement is made by a process called clinkering, in which limestone and other materials are heated to 2,600 degrees Fahrenheit. The process converts the materials into cement but releases large amounts of CO2 as limestone decarbonates into lime.

Cambridge researchers found that using cement clinker and iron oxide instead of lime works well in steel recycling. Crushing old concrete and taking out the sand and stone results in a cement that is reactivated by the recycling furnace to produce a material with excellent properties.

Recent tests by the Materials Processing Institute showed that recycled cement can be produced at scale in an electric arc furnace. Ultimately, this method could produce zero emission cement if the electricity for the furnace comes from renewable sources.

**********

Web Links

Cement recycling method could help solve one of the world’s biggest climate challenges

Photo, posted July 18, 2011, courtesy of Kenta Mabuchi via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Red mud and steel

February 21, 2024 By EarthWise Leave a Comment

Most of us have never heard of red mud. Otherwise known as bauxite residue, it is an industrial waste product generated by the most common process by which aluminum is made and the world produces 200 million tons of red mud each year. The stuff is a significant environmental hazard being extremely alkaline and corrosive. Most of it ends up in large landfills and the costs associated with disposing of red mud are substantial.

Red mud is red because it contains large amounts of iron oxide, often as much as 60% of it. Scientists at the Max-Planck Institute in Germany have developed a method for producing steel from red mud that is much less carbon intensive than traditional steel production and that is economically viable.

The scientists melt the red mud in an electric furnace powered in part by green hydrogen. Running the furnace this way, even when using electricity from only partially renewable sources, results in far fewer greenhouse gas emissions as well as economic benefits. In the furnace, liquid iron separates from the other liquid oxides and can be extracted easily. The resultant iron is so pure that it can processed directly into steel. The remaining metal oxides are no longer corrosive, and they solidify into a glass-like material that can have practical uses in construction.

There are 4 billion tons of red mud that have accumulated worldwide to date. According to the researchers, their process could produce over 700 million tons of green steel from it, potentially saving 1.6 billion tons of carbon dioxide emissions.

**********

Web Links

Green steel from toxic red mud

Photo, posted September 7, 2021, courtesy of Healthy Gulf via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Electric Steel Furnaces | Earth Wise

August 29, 2023 By EarthWise 1 Comment

Steel was first made thousands of years ago. The discovery that heating up iron ore in a hot enough charcoal fire could purify the iron into a strong and valuable material was the start of the Iron Age. In many ways, things have changed very little since then.

Global iron and steel production accounts for 7% of society’s carbon emissions. Making steel generally involves burning coal in a blast furnace to produce the very high temperatures required to turn iron into steel. The coal is used both as a feedstock and as a fuel. Steel is made from iron and a substance called coke, which is basically coal that has been carbonized at high temperatures. Coal itself is burned to provide the high temperatures needed.

A new analysis from the Global Energy Monitor think tank shows that the global steel industry is slowly embracing electric-arc furnaces to produce the necessary heat, which is a cleaner alternative. The analysis found that 43% of forthcoming steelmaking capacity will rely on electric-arc furnaces, up from 33% last year.

According to the study, the shift to cleaner steel is not happening fast enough. To meet the emissions reductions goals of the Paris Climate Agreement, electric-arc furnaces must account for 53% of global steelmaking capacity by 2050. Based on the current plans, those furnaces would only account for 32% of total capacity by that year.

In order to meet these goals, the steel industry will need to retire or cancel about 381 million tons of coal-based manufacturing capacity and add 670 million tons of electric-arc furnace capacity.

**********

Web Links

Steel Industry Pivoting to Electric Furnaces, Analysis Shows

Photo, posted March 3, 2012, courtesy of Jeronimo Nisa via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio