Using waste materials from other industries to form new products is not a new concept. Lafarge Corp.'s new cement plant in Alpena, Mich., however, has gone one step further. Not only will the facility use waste from other industries, it also will produce a higher-quality product and will actually use more waste material than it generates.
Usually, limestone and shale are combined and processed to form portland cement, but this process creates large amounts of waste materials, known as cement kiln dust (CKD). By substituting taconite tailings and fly ash, both residues from other industries, for shale, Lafarge will create a new, efficient raw materials mix. The new cement will meet the company's highest quality standards and will meet both Type I and Type II specifications, rather than just Type I, as Lafarge's old mixture did. The new product also exhibits a higher ultimate strength gain.
By the time the new raw materials enter production, the company will have spent more than $25 million implementing the change. In order to prevent contamination of the materials by the weather and to prevent dust escaping into the environment, Lafarge has built a vinyl covered dome to store the fly ash and an A-frame storage barn for the taconite tailings. They have also installed completely enclosed conveyor belts and transfer points, equipped with a vacuum system that automatically removes dust as the materials move through the plant.