Materials

New electrolysis technique makes cement, minus the carbon emissions

New electrolysis technique mak...
An experiment illustrates the electrolysis process using dye: pink represents the acid created at one electrode and purple the base at the other end
An experiment illustrates the electrolysis process using dye: pink represents the acid created at one electrode and purple the base at the other end.
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An experiment illustrates the electrolysis process using dye: pink represents the acid created at one electrode and purple the base at the other end
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An experiment illustrates the electrolysis process using dye: pink represents the acid created at one electrode and purple the base at the other end.
One electrode produces acid (pink) while the other produces a base (purple), in a demonstration of an electrolysis technique similar to that used in a new cement-making process
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One electrode produces acid (pink) while the other produces a base (purple), in a demonstration of an electrolysis technique similar to that used in a new cement-making process

As the most widely-used building material in the world, it’s no surprise that making cement is one of the single biggest contributors to our carbon emissions problem. MIT researchers now claim to have developed a new method that can clean up the cement production process, removing most of the carbon emissions without affecting the resulting product.

Portland cement, which is the most common type, is made by grinding up limestone, mixing it with sand and clay then cooking it at extremely high heat – up to 1,450° C (2,642° F). Not only does the energy used to heat the mixture produce huge amounts of carbon dioxide, but the greenhouse gas is also released by the limestone itself during this process. In all, that means about 1 kg of CO2 is released for every kilogram of cement produced, which adds up to a staggering 8 percent of global CO2 emissions.

While it’s been argued that concrete eventually sponges up much of the CO2 emitted during its production, it still wouldn’t be a bad idea to try to clean up the manufacturing process. Researchers have experimented with changing ratios of ingredients, developing new “geopolymer” recipes, or replacing cement with environmentally-friendly composite binders.

The problem with all of those ideas is that the end result is a different type of concrete. And the building industry may be reluctant, at least at first, to start using a different material. So the researchers on the new study focused on improving one step of the regular process, making plain old cement greener without having to change the material itself.

One electrode produces acid (pink) while the other produces a base (purple), in a demonstration of an electrolysis technique similar to that used in a new cement-making process
One electrode produces acid (pink) while the other produces a base (purple), in a demonstration of an electrolysis technique similar to that used in a new cement-making process

Rather than heating the ground-up limestone, the new process uses an electrolyzer, where electrodes split water molecules into oxygen and hydrogen. Doing so creates an acid at one electrode and a base at the other. The limestone is dissolved in the acid, and calcium hydroxide is created at the other end, in solid flakes. These flakes of lime can then be harvested to produce cement.

Of course, carbon dioxide is still produced during the process, as the limestone dissolves. But it isn’t released into the air – instead, it can be captured and because it’s pure, used for other purposes, such as making liquid fuels or carbonating drinks. The team even says that it can be combined with oxygen produced by the same system, and burned to fuel the rest of the new cement-making process.

The researchers demonstrated the technique in the lab, and showed that it worked on a small scale. The team says it could be scaled up quite easily, but it is still just one part of the larger process of making cement. More work needs to be done before it can be implemented in the real world, but it’s an promising step.

The research was published in the journal PNAS.

Source: MIT

3 comments
Jose Gros
Fine! So you say you put limestone in acid to solve it, under and electrolyis current to have the Calcium hydroxide floculating in the basic side of solution. But how much CO2 is emitted to produce the electricity used in the process? Would you show a comparative balance? Thanks. Salut +
SuziJet
The cement making process as described in the article is out of sequence. The first step is to heat limestone to 2700 degrees F to break the bond of the water that holds the limestone together. After it is cooked the 'clinker' is ground extremely fine and that is Portland cement - the main ingredient in concrete. Concrete happens when the water physically recombines with the cement to effectively make limestone - sand and aggregate take up volume and give concrete extra strength and handling qualities. BTW - any CO2 released in the entire process just feeds plants so it doesn't hurt the environment.
Daniel Williams
There is already a retrofitting technique that can capture a pure CO2 stream called 'direct separation'. Heidelberg cement have pledged to go completely carbon-neutral by 2050, as well as a number of other manufacturers involved with the initiative. [project-leilac .eu/faq]