Global cement production accounts for about 2 billion tonnes of CO2 every year – that’s 5% of all CO2 emissions and more than the entire aviation industry.
Now a company has come up with a way of producing cement actually reduces carbon dioxide emissions.
Cement is traditionally made by heating calcium carbonate, found in limestone, with clay. The limestone thermally decomposes into calcium oxide and carbon dioxide. It is not just the release of carbon dioxide during the reaction that is the problem, coke or coal has to be burnt in order to supply the extremely high temperatures (1 500°C) that are needed to break down the limestone. This burning of coal also releases carbon dioxide.
The new green technique is being developed by a company based in California. It uses two abundant materials – hard water and flue gases from power stations. The CO2 from the flue gas reacts with the calcium and magnesium salts in the water to form solid carbonates and bicarbonates, which are then removed from the water and processed for use as cement.
Talking about this new technology could be an interesting way of revising the limestone cycle and production of cement which is found in most GCSE chemistry specifications.
Students can be asked why cement production is so environmentally unfriendly but why it is so important to industry. Their answers could include the points mentioned above, as well as references to the impact of quarrying the limestone.
The new technique can then be discussed. How is this better for the environment?
There are other green makeovers for cement production in development. This article outlines some more.