Calcium carbonate and climate change

Aug 30, 2010

(PhysOrg.com) -- What links sea urchins, limestone and climate change? The common thread is calcium carbonate, one of the most widespread minerals on Earth. UC Davis researchers have now measured the energy changes among different forms of calcium carbonate, from its messy noncrystalline forms to beautiful calcite crystals that could lock away carbon underground for thousands to millions of years.

" is the major long-term sink for ," said Alexandra Navrotsky, the Edward Roessler Chair in Mathematical and Physical Sciences and Distinguished Professor of Ceramic, Earth and Environmental Materials at UC Davis.

Steps to mitigate global will likely include extracting carbon dioxide from power plant flues and the atmosphere and storing it underground, initially as a dense gas in old mines and depleted oil reservoirs that would eventually turn into solid, stable calcium carbonate through chemical reactions.

"By measuring the heat liberated during these transformations, we can study the process by which carbon dioxide is trapped and transformed to stable carbonate minerals," Navrotsky said.

Navrotsky is senior author on a paper describing the results, published this week in the journal .

Calcium carbonate exists in several forms with different levels of stability. The first stage is noncrystalline, amorphous calcium carbonate. It forms when carbon dioxide mixes with calcium dissolved in water, either in the soil or in the oceans. Animals such as and shellfish also make amorphous calcium carbonate and use it as a first step to build their spines and shells.

More stable forms have a repeating geometric crystal structure, culminating in calcite (Iceland spar), one of the most abundant minerals in the Earth's crust.

Navrotsky and her colleagues at UC Davis' Peter A. Rock Thermochemistry Laboratory have now measured with high accuracy the heat lost or gained as calcium carbonate changes from one form to another. They found that amorphous calcium carbonate made by chemical reactions is energetically similar to amorphous calcium carbonate extracted from a sea urchin, and that there is a series of downhill transformations ending in calcite as the most energetically stable version.

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eachus
not rated yet Aug 30, 2010
It's a pretty picture, but where does the calcium (or calcium oxide or hydroxide) come from? The easiest source is cooking calcium carbonate. Oops! Useless in sequestering CO2. Calcium sulfate as a source is not so bad, but you still have all that sulfur dioxide or trioxide to deal with. Some can be used instead of mined sulfur to make sulfuric acid a major chemical in any industrialized economy.
Grallen
not rated yet Aug 30, 2010
It's been bugging me...

If we start capturing CO2 are we not also lowering atmospheric oxygen? Isn't that bad? I can't find good material on this, any links would be appreciated.
eachus
5 / 5 (2) Aug 30, 2010
If we start capturing CO2 are we not also lowering atmospheric oxygen? Isn't that bad? I can't find good material on this, any links would be appreciated.


The current level of CO2 in the atmosphere is 0.039% or 0.00039. It is a trace gas. You will see lots of different numbers for Oxygen but it is around 20% of the atmosphere. Depending on where you are, water vapor can make up 10% or more of the atmosphere. So we deal every day with variations in the partial O2 pressure greater than would occur if all the known gas and oil was burned. (The CO2 level would (relatively) shoot out of sight--but we wouldn't notice the change in O2 levels.)