Beneficial uses of cement kiln dust

Cement manufacturing is a critically important industry in the United States and throughout the world. In 2006, U.S. cement plants produced 99.8 million metric tons of cement. Worldwide production accounted for about 2.5 billion metric tons. As with most large manufacturing industries, by-product materials are generated. These industrial by-product and waste materials must be managed responsibly to insure a clean and safe environment. Cement kiln dust (CKD) is a significant by-product material of the cement manufacturing process. Over the past several years dramatic advances have been achieved in the management and use of cement kiln dust, thus reducing its dependency on landfill disposal. Sustainability is the cornerstone of the cement industry, not only in the products that use cement, but also in its manufacturing process. From 1990 to 2006, the U.S. cement industry has reduced the amount of landfilled CKD 47 percent. This reduction in landfilled CKD comes despite the fact that domestic clinker production, as reported by the participants in the PCA CKD study, increased 95 percent during this same period. Overall clinker capacity in the U.S. has increased 28 percent since 1990. Many of the older, inefficient plants are being replaced by more model plants or being renovated with new technologies to be more efficient as well as more environmentally friendly. The majority of CKD is recycled back into the cement kiln as raw feed. In addition, new technology has allowed the use of previously landfilled CKD to be used as raw feed stock. Recycling this by-product back into the kiln not only reduces the amount of CKD to be managed outside the kiln, it also reduces the need for limestone and other raw materials, which saves natural resources and helps conserve energy. Another principal use of CKD is for various types of commercial applications. These applications depend primarily on the chemical and physical characteristics of the CKD. The major parameters that determine CKD characteristics are the raw feed material, type of kiln operation, dust collection systems, and fuel type. Since the properties of CKD can be significantly affected by the design, operation and materials used in a cement kiln, the chemical and physical characteristics of CKD must be evaluated on an individual plant basis. This paper will discuss the basic characteristics of CKD including current production status and regulatory requirements. Beneficial commercial uses are then presented covering a wide variety of applications including agricultural soil enhancement, base stabilizing for pavements, wastewater treatment, waste remediation, low-strength backfill and municipal landfill cover.