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"What happens to the chemicals used in bleaching paper pulp?"

Once paper pulp is cooked, the cooking chemicals are washed out of the pulp then recovered through an extensive recovery system.

We use a "white liquor," a mixture of water and chemicals, to remove compounds found in wood that are undesirable for making paper. We add the liquor to the cooking pulp, and as these compounds leave the wood, the liquor becomes dirty. Dirty liquor is called "black liquor" because of the dark color after cooking, and it contains both chemicals and wood residues.

We then wash the black liquor out of the pulp, then evaporate the water, leaving a condensed black liquor that contains 65 percent solids. The condensed liquor is then burned inside of large, hot furnaces. The burning process produces a solid called "smelt," which is then treated with a chemical called calcium hydroxide to create more white liquor!

At the Boise Cascade mill, almost 95 percent of the original chemicals are recovered through this process. Moreover, nearly 40 percent of the steam used to run the mill is created in the recovery furnaces.

Other chemicals are used in the bleaching process, which is used to turn the cooked, dark pulp into white pulp. Like the Boise Cascade mill, many mills in Oregon have changed the chemicals used in bleaching in order to minimize the amount of elemental chlorine used in the process. Boise Cascade invested nearly 40 million dollars back in 1993 to do just that— now the chemicals used to bleach paper have less "dioxins," which are chemicals that have been linked to cancer in humans.

All of the water used in the paper making process, 30 million gallons per day in the Boise Cascade plant, goes through a primary clarifier separator and a secondary water treatment pond before the water is returned the river.

"What about paper recycling?"

Learn more about how we can reuse forest products!