Cement Kiln Dust
Description
Cement Kiln Dust (CKD) is a by-product of the cement manufacturing process. The dust is a particulate mixture of partially calcined and unreacted raw feed, clinker dust and ash, enriched with alkali sulfates, halides and other volatiles. This dust is captured from the cement kiln’s exhaust gas by the air pollution control system.
CDK is a solid, grey or tan, odorless powder. It is not combustible or explosive. It is largely composed of raw feed materials, fuel ash, and minerals/salts created from the volatile alkali compounds released from the heating of raw feed materials in the kiln. CKD is a corrosive, toxic substance, but is not combustible or explosive.
Environmental Issues
CKD can lead to serious air, groundwater and surface water pollution. The CDK that is not returned to the kiln or otherwise beneficially used is often dumped into unlined landfills, and old quarries, causing toxic leachate to foul ground and surface water. As well, the portion of CKD particles that is not captured by pollution control device is released directly into the air. The smaller particles are the most likely to escape capture by pollution control devices or to be resuspended or washed from CKD stored in piles or pits. CKD has been excluded from otherwise applicable hazardous waste regulations; no federal standards for CKD disposal exist today.
The cement industries contribute approximately 7.3% of all greenhouse gas emissions from manufacturing and mining industries in Canada. Along with greenhouse gas emissions, the cement industry is also responsible for releasing several pollutants. For example, the cement industry is a leading emitter of nitrous oxides in Canada. As well, while Canada-wide standards for mercury, dioxin and furan emissions from hazardous waste incineration activities have been adopted, they do not apply to ‘energy recovery’ activities, providing a type of exemption to the cement industry.
Human Health
A single, short-term exposure to the dry powder presents little or no hazard. Exposure of sufficient duration to wet kiln dust on moist areas of the body can cause serious, potentially irreversible tissue (skin, eye, respiratory tract) damage due to chemical burns, including third degree burns.
Eye contact with large amounts of dry powder or with wet kiln dust can cause moderate eye irritation, chemical burns and blindness. Kiln dust may cause dry skin, discomfort, irritation, severe burns, and dermatitis. Between 15 and 90% of CDK has a diameter below 10 microns, which is within the respirable range for humans. Breathing dust may cause nose, throat or lung irritation, including choking. Inhalation of high levels of dust can cause chemical burns to the nose, throat and lungs. Prolonged or repeated inhalation of respirable crystalline silica, an ingredient of CKD, can cause silicosis, a seriously disabling and fatal lung disease.
Kiln dust is not listed as a carcinogen by IARC or NTP; however, kiln dust contains trace amounts of crystalline silica and hexavalent chromium which are classified by IARC and NTP as known human carcinogens. Some studies show that exposure to respirable crystalline silica or that the disease silicosis may be associated with the increased incidence of several autoimmune disorders such as scleroderma (thickening of the skin), systemic lupus erythematosus, rheumatoid arthritis and diseases affecting the kidneys. Silicosis increases the risk of tuberculosis. Some studies show an increased incidence of chronic kidney disease and end-stage renal diseases in workers exposed to respirable crystalline silica.
References
Greenpeace. Burning Hazardous Wastes in Cement Kilns.
IEEE-IAS Cement Industry Committee, 2008. Beneficial Uses of Cement Kiln Dust. 50th Cement Industry Technical Conference, Miami, FL.
Jacott, M., C. Reed, A. Taylor, M. Winfield, 2003. Energy Use in the Cement Industry in North America: Emissions, Waste Generation and Pollution Control, 1990-2001. 2nd North American Symposium on Assessing the Environmental Effects of Trade.
Lake Ontario Waterkeeper and Gord Downie, 2006. Submission to Ontario Ministry of the Environment.