A "Solid" Solution for Global Warming?

DOE Researchers Turning Greenhouse Gas Into Geologically-Stable Mineral

Albany, OR - Inside a Department of Energy research center tucked away in Albany, Oregon, researchers are making rocks - and in the process, perhaps, finding an answer to the problem of global warming.

	TURNING CO2 TO MINERALS - Gaseous carbon dioxide can be captured and converted into these environmentally-safe, magnesite minerals. The brown mineral is produced when olivine is used in the reaction; the white powder is produced when serpintine is used.

The researchers are studying "mineral carbonation," a method that mimics the way nature forms some of the most widely distributed minerals in the Earth's crust. But the Albany Research Center scientists are accomplishing in less than hour what it takes nature thousands of years to achieve.

Key technical hurdles remain, but the scientists' amazing progress in transforming carbon dioxide - a gas known to contribute to the greenhouse effect - into a solid, environmentally benign mineral has raised the prospects of a new approach for countering the threat of global climate change.

Mineral carbonation is one of a family of technologies called "carbon sequestration."

In recent years, the Energy Department has increased research into carbon sequestration as a way to capture and store the gases that can cause the Earth's surface to warm abnormally. Researchers in industry, national laboratories and universities across the country are studying a variety of sequestration concepts, from injecting carbon dioxide into geologic formations or deep into the ocean, to chemically transforming it into various products.

Mineral carbonation is one of the chemical transformation approaches. Here is how the process works:

Carbon dioxide gas, or CO2, is pumped into a vigorously stirred slurry of water, a salt, and finely ground magnesium silicate. Like a high-speed blender, the vessel creates a frothy mixture which is heated to temperatures of 311 degrees F (or 155 degrees C) and compressed under pressures of more than 2700 pounds per square inch. The CO2 reacts with the water, then with the magnesium to form a solid carbonate mineral called magnesite. Later, the mineral broth is filtered and dried, leaving a solid rock, now with the CO2 chemically transformed into a mineral that will remain stable over geologic time periods.

The real breakthrough may not be the process - the chemistry is relatively straightforward - but the time it takes to perform the chemical transformation. When Albany researchers began studying the reactions two years ago, it took six days for the slurry to absorb most of the CO2 which made the process unrealistically slow for commercial applications. Now the scientists can complete over 80 percent of the reaction in less than an hour.

The next major technical challenge will be to reduce the energy consumed by the process. Currently, the heat needed to activate the magnesium silicate would make an aboveground processing plant too energy-intensive to be economically viable. Researchers are looking into alternative heating methods, including conducting the reaction underground, or "in-situ," to reduce or eliminate the pre-heating required.

If researchers can further improve the process by eliminating the high-temperature mineral pre-treatments, they have real hopes of engineering a process that will be viable at commercially-relevant scales.

Currently, bench-scale research is about 50% complete, and researchers are focusing on ways to improve results in batch tests. The goal is to accelerate the reaction under reduced pressures, develop a complete characterization of the products and byproducts, including their potential beneficial uses, and develop a geochemical model that applies to aboveground industrial processes and potentially to in-situ mineral sequestration.

During the engineering development phase, researchers hope to move from five pounds per hour of minerals being processed to 500 pounds per hour and ultimately to 10 tons per hour. The 10-ton-per-hour unit would be capable of processing the carbon dioxide expelled from a 10-megawatt power plant. Under an aggressive research plan, it could be operating in six years.

Already, however, mineral carbonation is attracting the attention of power plant designers. The concept has been integrated into the design of a pollution-free, coal-fueled power plant being developed by the Zero Emission Coal Alliance, an international consortium of utilities, mining companies, engineering firms and government laboratories. The Energy Department is also evaluating the process as part of its Vision 21 program, an effort to develop a zero-polluting, multi-product energy plant, and researchers are working on ways to apply the technology to existing, conventional power plants.

The fact that a mineral carbonation breakthrough may take place at the Albany Research Center should not be a surprise. The Center has a nearly 50-year history of research into the chemical and physical properties of materials and their products. Known especially for its expertise in metallurgical processes - it pioneered the production methods for zirconium and produced all the zirconium used in the USS Nautilus - the Center became part of the Energy Department in 1996 after being transferred from the now-abolished Bureau of Mines.

The ongoing efforts are part of the Mineral Carbonation Working Group established within the Energy Department's Office of Fossil Energy and managed by the National Energy Technology Laboratory. Other participants include the Los Alamos National Laboratory, Arizona State University and Science Applications International Corporation.

-End of Techline -

For more information, contact:
Robert C. Porter, DOE Office of Fossil Energy, (202) 586-6503, e-mail: robert.porter@hq.doe.gov

Technical Program Contacts:
William Riley, DOE Albany Research Center, (541) 967-5851, e-mail: riley@alrc.doe.gov
or
Richard Walters, DOE Albany Research Center, (541) 967-5873, e-mail: walters@alrc.doe.gov