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Tempest in a Cement Mixer

The world of carbonate chemistry is rocking over claims that a new kind of cement can sequester carbon.
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Calera Corporation sparked a lot of media attention (including at with its claims for carbon neutral, or even carbon-negative, cement produced primarily by bubbling industrial carbon dioxide (CO2) emissions through seawater.

The Los Gatos, Calif.-based company says its process, unlike conventional cement manufacture, is a win/win for the environment: It doesn't create CO2 and instead permanently traps huge volumes of the global-warming gas in the finished concrete.

That all sounded just too good to be true to a number of commentators who lit up online chat forums earlier this year; in a spirited debate that soon grew personal, with flaming messages "sent from my iPhone with radical intent."

Chief skeptic is Ken Caldeira, senior scientist in the Department of Global Ecology at Stanford's Carnegie Institution for Science, who doesn't buy what he likens to alchemist claims of being able to turn lead into gold.

Wally Broecker, Newberry Professor of Geology in the Department of Earth and Environmental Sciences at Columbia University — where he's been on the faculty for half a century — also has serious doubts about Calera's claims.

Just show me the chemistry, Caldeira says. "Every other proposed process to sequester carbon has been clear about the fundamental inputs to and outputs from the process, in ways that allow the fundamental chemistry, and energy and mass balances, to be assessed.

"They (Calera) can be secretive about what goes on in their black box, but they cannot be secretive about what goes in and what comes out, and they cannot be secretive about where they intend to source those inputs or dispose of those outputs."

But Calera CEO Brent Constantz, a consulting professor at Stanford University's Department of Geological and Environmental Sciences, questions Caldeira's motives and says his unfounded assertions illustrate a lack of understanding about even "basic carbonate chemistry."

Constantz says a wealth of information about Calera's processes is publicly available. For example, he says 10 times more detail than Caldeira has been requesting can be found by reading his company's patents filed in Australia. (If you want to look, click on "Specification/e-Register" link on the specific patents to see a PDF.)

He says the company's studies and research have been thoroughly and objectively evaluated by leading scientists and academics; the strength of the technology has also been endorsed by the company's scientific advisory board and is the reason top executives from other companies have joined Calera.

Constantz says he cannot understand why Caldeira is "trying to trash" Calera and wonders if he is being paid by the energy industry, which sees profit in injecting CO2 into empty fossil fuel reservoirs.

He says companies like Calera could put a dent in that carbon capture and storage (CCS) revenue, making it worthwhile for oil and gas companies to use lobbyists and others to discredit alternative technologies.

An outraged Caldeira says he's never taken a penny from oil and gas interests and is willing to show tax returns and bank statements to prove it. He also brushes aside hints of a conflict of interest arising from his co-ownership of a patent for extracting and sequestering CO2, saying if the patent ever yields any money, he'll give his share to charity.

Caldeira also bridles at comments questioning his grasp of the science behind Calera. Besides his body of published work dating back almost two decades, he points to a 2005 special report on climate change and reducing CO2 emissions, published by the Intergovernmental Panel on Climate Change.

The 400-plus page report includes a chapter on carbon storage in the ocean for which Caldeira was coordinating lead author. "Would the IPCC choose me to lead this chapter if the community felt that I was ignorant of basic chemistry?" he asks.

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