New Delhi, May 15 (PTI) Producing cement from carbon-free, calcium-rich silicate rocks such as basalt, instead of the currently used raw material limestone, which is also calcium-rich but releases carbon,
could reduce carbon dioxide emissions from the cement production industry by more than 80 per cent, a study has found.
Researchers, including those from the University of California, Santa Barbara in the US, said that the switch in raw materials can be made using existing technologies and that theoretically, 60 per cent lesser energy could be required to produce cement from basalt rocks, compared to limestone.
Limestone, or calcium carbonate (CaCO3), is heated to over 1,500 degrees Celsius to produce calcium oxide (CaO), a key ingredient key for cement's strength and setting.
However, a large quantity of carbon dioxide (CO2) of about 500 kilograms is released for every tonne of cement, or 'Portland cement', produced.
The cement production industry is estimated to account for 8 per cent of total global CO2 emissions and 4.4 per cent of global greenhouse gas emissions, and thus, reductions in the sector could contribute substantially towards meeting net-zero targets.
The authors wrote in the study published in the journal Communications Sustainability, "We examine the viability of making ordinary Portland cement using carbon-free silicate rocks (like common basalt) instead of limestone."
The team first assessed the availability of basalt rock types at the surface for mining using existing geological maps, and found sufficient quantities to supply cement production for several hundred thousand years at current production levels.
The authors then estimated the energy requirements and carbon dioxide emissions of cement production using silicate rocks, finding that the theoretical minimum energy requirement is more than 40 per cent lower than that for limestone.
Using natural gas as a power source, the minimum carbon dioxide emissions per tonne of cement produced decreased from 609 kilograms using limestone to 43-59 kilograms, depending on the specific type of silicate rock used.
The analysis "shows that producing Portland cement from basalt could require less energy than traditional limestone production, highlighting the potential to simultaneously reduce cost and emissions."
The authors also identified a viable process to produce cement with existing technology and found that, even when using current fossil fuel-dominated energy mixes, carbon dioxide emissions could be reduced by more than 25 per cent, compared to the current standard process using limestone.
Silicate rocks typically contain a variety of economically valuable metals that could be recovered as by-products during industrial cement production, the team said.
They added that compared to existing green cement alternatives, the proposed solution should bypass the significant development, validation, and demonstration time required before the construction industry will adopt a new material, as the final product in the study is standard Portland cement. PTI KRS KRS MAH
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