It's the Bloom Energy for March.

Calera, the often-controversial company that says it can capture carbon dioxide and turn it into cement, will get a $15 million injection of capital from Peabody Energy, according to the New York Times. Hype, hope and a lot of talk about cement will follow.

The company, funded and guided in part by Vinod Khosla, claims it can mix carbon dioxide into seawater to produce calcium carbonate, which in turn gets mixed into cement. Founder Brent Constanz allegedly approached Khosla and said he wanted to make cement the way the ancient Egyptians did, but presumably without the slave labor.

"The heart of the Calera process is the technology associated with carbon capture and conversion to stable solid minerals. We refer to this new process as Mineralization via Aqueous Precipitation, or MAP for short. In its simplest form, MAP involves contacting gas from the power plant with water. The water chemistry is controlled such that the carbon dioxide in the power plant gas is absorbed into the water and reacts with the water hardness to form solid mineral carbonates and bicarbonates, which are very similar to finely disseminated 'whitings' seen in tropical oceans at mid-day," the company's website says.

But beyond that, Calera takes a "Just believe us. We're out to save the world. Don't slow us down by asking for petty details" approach when asked about the technical details of its process. The company is notoriously reticent. Alex Kinnier once joked that the secret ingredient was pixie dust.

The coy silence has helped fuel criticism from figures such as Ken Caldeira, a well-regarded and notable climate scientist with the Department of Global Ecology at the Carnegie Institution of Washington, who say the process won't work. Carbon sequestered in the process will be generated during processing. Naturally, a war of words between detractors and supporters has emerged. J.R. O'Neil, a professor emeritus of geological sciences at Michigan, says Caldeira goofed "big time." Others, however, have supported Caldeira's assertions. It's as close to mud wrestling as you can get in Silicon Valley.

Meanwhile, other companies -- Novacem, Zeobond, Calstar -- are working on similar products. You can look up a bit on Calera's patents here.

Even if it does work, Calera faces even a bigger problem: the economy. Building materials are in the dumps because of the prolonged slump in construction. Serious Materials, which earlier hoped to build a volume factory in 2008, still does not have a factory for mass commercial manufacturing of its eco-friendly drywall and doesn't even have plans to erect one at the moment. Why? Slack demand.

Some of these green building companies had also hoped that cap and trade systems would make their products attractive. Because they generally use less energy to produce, these products would have an advantage in a carbon-adjusted economy. Cap and trade may not occur for quite a while in the U.S., which puts a lot of these products at a disadvantage against traditional -- albeit energy-intensive -- mainstays like plain cement.