Long-term carbon dioxide emissions from cement production can be
drastically reduced

Date:
November 9, 2021
Source:
Johannes Gutenberg Universitaet Mainz
Summary:
Concrete is very versatile, inexpensive, literally hard, and can
be cast into almost any shape. It consists, in principle, only of
sand, gravel, water, and the binder cement. The latter is made
by the calcination of lime, clay, and some other components,
and forms stable calcium silicate hydrates during hardening,
which are responsible for the properties of concrete. However,
the problem lies precisely in the calcination of lime, because for
every molecule of calcium oxide produced, the so-called 'burnt
lime' or 'quicklime', one molecule of the greenhouse gas carbon
dioxide is released. For an annual world production of around 4.5
billion tons of cement, this is translated into 2.7 billion tons
of carbon dioxide.



FULL STORY ========================================================================== Global warming and affordable housing are two dominant topics of public
debate.

Climate protection is achieved by reducing emissions of the greenhouse
gas carbon dioxide (CO2). Housing is generated through more housing
being built.

This requires concrete, the most important building material in our modern world. At first glance, concrete appears to be unproblematic. It does not contain any fossil fuels, it is non-toxic, and it does not float in the
oceans in the form of plastic waste. But this impression is misleading,
because cement production is currently the largest industrial emitter of
CO2 emissions worldwide, accounting for about 8 percent or 2.7 billion
tons of CO2 per year.

This is due to the combustion of fossil fuels -- mostly coal -- at
temperatures of around 1,000 degrees Celsius and sintering at around
1,450 degrees Celsius.


========================================================================== Concrete is very versatile, inexpensive, literally hard, and can be cast
into almost any shape. It consists, in principle, only of sand, gravel,
water, and the binder cement. The latter is made by the calcination of
lime, clay, and some other components, and forms stable calcium silicate hydrates during hardening, which are responsible for the properties
of concrete.

However, the problem lies precisely in the calcination of lime (CaCO3),
because for every molecule of calcium oxide (CaO) produced, the so-called "burnt lime" or "quicklime," one molecule of the greenhouse gas CO2 is released. For an annual world production of around 4.5 billion tons
of cement, this is translated into 2.7 billion tons of CO2. This is
equivalent to about half the annual CO2 emissions of all transport. China
is responsible for about 50 percent, Germany for about 1.5 percent of
the emissions from cement production.

Environmentally harmful calcination of lime is circumvented by grinding
raw lime with sodium silicate Chemists at Johannes Gutenberg University
Mainz (JGU) in Germany have now developed a method that could drastically reduce CO2 emissions from cement production in the long run. In this
process, the raw lime (CaCO3) is no longer converted into burnt lime
in coal-fired kilns but is simply milled with solid sodium silicate
(Na2SiO3). This milling step produces an "activated" intermediate that
contains the constituents of the cement in uniform distribution. When
reacted with sodium hydroxide solution, a product is formed that is structurally similar to the calcium silicate hydrates. The formation
of the cement paste and the setting with water proceed via a complex
reaction cascade, the elementary steps of which have been analytically elucidated using high-tech methods.

While the calcination of the lime requires temperatures of 1,000 to 1,500 degrees Celsius, the milling step is carried out at room temperature. At
120 kilowatt hours per ton, the mechanical energy input for grinding conventional cement is only about 10 percent of the energy used for the calcination process.

However, this is only equivalent to the energy saved -- and the associated
CO2 emissions -- by burning fossil fuels in cement production. More importantly, bypassing lime calcination could ideally avoid CO2 emissions
in the gigaton range. Since grinding is a standard process in the cement industry, it would be conceivable to implement the process from laboratory
to industrial scale.

Process potentially suitable for large-scale production The Mainz-based chemists emphasize that the cost and energy estimates are only rough approximations and that laboratory tests cannot be compared to an
industrial process, where development, design, feasibility, maintenance,
and various other parameters must be considered. A lot of development
work is needed for this. "This may be a first step for a non-conventional
way of cement production, but it is not yet a fully developed solution," emphasized co-author Marcel Maslyk.

Professor Wolfgang Tremel and Dr. Ute Kolb of Mainz University share
this view: "The process is potentially suitable for producing cement for large-scale processes," said the two group leaders at the JGU Department
of Chemistry.

"However, carrying it out on a technical scale would take many years and
thus would not provide a short- or medium-term remedy for CO2 emissions." ========================================================================== Story Source: Materials provided by
Johannes_Gutenberg_Universitaet_Mainz. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. Marcel Maslyk, Tobias Ga"b, Galina Matveeva, Phil Opitz, Mihail
Mondeshki, Yasar Krysiak, Ute Kolb, Wolfgang Tremel. Multistep
Crystallization Pathways in the Ambient‐Temperature Synthesis
of a New Alkali‐Activated Binder. Advanced Functional
Materials, 2021; 2108126 DOI: 10.1002/adfm.202108126 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/11/211109120321.htm

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