A recent study published in *Sustainable Chemistry and Engineering* by the American Chemical Society outlines the process, which can be integrated into current cement manufacturing practices, potentially offering a more cost-effective route for industry-wide decarbonization.
Cement's significant carbon footprint
Ordinary Portland cement is a primary material used in almost all modern concrete, the world's second most-utilized material after water. Its production, however, has a large carbon footprint due to the use of limestone, a readily available and low-cost source of lime. The traditional production process, which involves heating limestone in fossil fuel-powered kilns to break its chemical bonds, emits nearly 1 kilogram of carbon dioxide for each kilogram of cement produced.
The process generates carbon emissions from two main sources: the decomposition of limestone into lime, which accounts for about 60% of emissions, and the burning of fossil fuels to heat the kiln, responsible for the remaining 40%. Additionally, producing a metric ton of lime requires approximately 1.4 megawatt-hours of energy - sufficient to power an average American household for about 45 days.
The 'ZeroCAL' approach: Aiming for zero CO2 emissions
Aiming to address this, a team led by Gaurav Sant, director of the Institute for Carbon Management and professor of civil and environmental engineering at UCLA Samueli School of Engineering, developed "ZeroCAL," a new method for producing calcium hydroxide, a zero-carbon precursor for cement.
The process begins with dissolving limestone in a water-based solution containing ethylenediaminetetraacetic acid, an industrial acid. Through membrane nanofiltration, calcium is separated from the limestone, followed by an electrochemical step to produce calcium hydroxide. Unlike traditional methods, heating calcium hydroxide in a kiln only releases water, significantly reducing CO2 emissions.
The researchers estimate that ZeroCAL could eliminate 98% of the emissions from conventional lime production. Byproducts of the process include hydrochloric acid, baking soda, and hydrogen gas, which could potentially be used as a clean-burning fuel for cement kilns.
"The ZeroCAL approach offers an elegant solution to eliminate carbon dioxide emissions associated with the process of cement production," said Sant, the study's corresponding author. "It addresses emissions from limestone's decomposition and provides clean hydrogen and oxygen for heating the kiln while allowing decarbonization without the need for separate carbon-capture facilities."
Potential for scaling and further improvements
Though the ZeroCAL process currently requires more energy than traditional methods, the researchers are exploring ways to achieve energy efficiency by streamlining operations and better utilizing co-produced chemicals. They also propose locating cement plants near water sources, such as rivers or coastal areas, to meet the process's water needs.
The team is collaborating with Ultratech Cement Limited, India's largest cement manufacturer, to establish a demonstration plant capable of producing several metric tons of lime daily using ZeroCAL.
Fabian Rosner, a study co-author and assistant professor of civil and environmental engineering at UCLA Samueli, emphasized the importance of rapid, scalable decarbonization. "It has become crystal clear that mitigating climate change demands urgent, paradigm-shifting actions," Rosner said. "The ZeroCAL process offers a unique pathway to enable accessible and rapidly scalable decarbonization of cement production."
The ZeroCAL approach also has potential applications in decarbonizing steel production by providing low-carbon lime for the process.
Research and collaboration
The project received funding from organizations including the Chan-Zuckerberg Initiative, the Grantham Foundation, the Schmidt Family Foundation, Shell, the U.S. Department of Energy's ARPA-E, and UCLA's Institute for Carbon Management.
The study was co-authored by Adriano Leao, David Jassby, Dante Simonetti, and other researchers from institutions such as the Technical University of Munich, UC Davis, and the UCLA startup Equatic Inc. Sant and Jassby are also affiliated with the California NanoSystems Institute at UCLA, with Sant holding a joint appointment in materials science and engineering.
Research Report:ZeroCAL: Eliminating Carbon Dioxide Emissions from Limestone's Decomposition to Decarbonize Cement Production
Related Links
UCLA's Institute for Carbon Management
Space Technology News - Applications and Research
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