BATON ROUGE, La. (AP) - A Colorado pollution control company has asked for a permit to build what it says would be the world's largest activated carbon plant, producing up to 350 million pounds a year.

Red River Environmental Products LLC, a subsidiary of ADA-ES Inc. in Littleton, Colo., also says it has plans for two similar plants in North Dakota.

The company said in a statement that it has the rights to acquire land next to a lignite mine in Red River Parish. The Louisiana mine has agreed to provide 20 years worth of coal if the factory is built, the company said.

ADA-ES announced in April that it has an option to buy land near the Falkirk coal mine in Underwood, N.D., for a $400 million plant to make activated carbon. ADA-ES would use Falkirk's lignite to make a porous carbon that sponges mercury from coal-fired power plant gases. The federal government is working toward requiring mercury removal from coal-fired plants.

Red River Environmental says it has filed an air permit application with the Louisiana Department of Environmental Quality.

Project manager Sheila Glesmann said ADA-ES has not filed a North Dakota air quality permit application. North Dakota regulators said it could take six months to review the application.

Glesmann said the company has plans for a second plant in North Dakota, though its location has not been released.

The company said it doesn't know whether the North Dakota or Louisiana plant will be built first.

Construction could start in 2008 if the company gets the operating permits and financing in place. The first plant could be open by 2010, officials said.

"The market will dictate at what rate we build these things out," Glesmann said.

Glesmann said each of the three plants would employ about 70 people.

Activated carbon is made by burning lignite into a powdery carbon that gets blown through a plant's flue gas. The porous nature of the activated carbon sponges up the vapor mercury, which eventually would get buried in disposal pits. It is similar to the activated carbon that is used in water and air purifiers.

ADA-ES did not say how much activated carbon is currently produced, but said it expects an additional 400 million pounds a year will be needed by 2010, and up to a billion pounds per year by 2012 to 2015.