Brent Constantz, CEO of green cement company Calera, forwarded us a document from one of his scientific advisers today that partly explains what they are doing and to further respond to criticism from Ken Caldeira. It's still vague, it's one they showed to BusinessWeek where the story broke, but good to have on the record. The document was prepared by J.R. O'Neil, Professor Emeritus, Department of Geological Science at the University of Michigan. There is clearly no love lost here. "In essence, Caldeira goofed up big time and should have known better," O'Neil wrote. The story has no legs." Caldeira, however, is not some random Internet crank. He's a climate scientist at the Carnegie Institute of Washington, which is at Stanford. He says it doesn't add up and the selective secrecy of the company (we sequester carbon dioxide but won't completely explain how) is misleading the public. O'Neil essentially says that Caldera is pumping carbon dioxide from smokestacks into treated seawater to produce solid carbonates out of the magnesium and calcium found inside seawater. These carbonates, such as calcium carbonate (CO3) can be used in cement production. In the process, the solids in the seawater react with the carbon dioxide, typically a very low energy molecule: "because the pH of the seawater (normally around 8) has been raised to the point where CO3 is the dominant and stable species of dissolved carbonate. Alkaline solutions like this are very effective sinks for gaseous CO2. Calera's methods for making seawater appropriately alkaline are proprietary, but it can be done simply by the addition of a base like sodium hydroxide." In a patent application bearing Constantz's name that emerged earlier this year, the application discussed running the process with pH 10 or 11 seawater. "Above pH 10.33, greater than 90% of the carbonate is in the form of carbonate ion, and no CO.sub.2 is released during the precipitation of calcium carbonate," the application states. Caldeira's reply? Sodium hydroxide is somewhat rare, so that won't work. The company could also be using magnesium hydroxide, but that actually might just involve taking magnesium carbonate, transforming it into hydroxide, and then back to magnesium carbonate. In other words, no gain. Then there is the theory touted earlier by some sources that there could be a biological mechanism turning carbon dioxide into carbonates. Coral do this. But that would involve tightly controlling pH balances and massive ponds. As a side note, some of the argument might also be wrapped up in business model nuances. What if Calera is really just doing a version of carbon sequestration? The carbonate plan is very similar to the business plan of Carbon Sciences. But Carbon Sciences' business plan relies on carbon taxes. Calera's public interviews have made it seem a bit "cake and eat it too." Calera and its investors have also strongly indicated that they won't be forwarding any more information. Constantz, who came to prominence years ago with bone treatments, is also said to be quite secretive.