As raw feed travels through the portland cement kiln system,particulates of the raw materials,partially processed feed,and components of the final product are entrained in the combustion gases flowing countercurrent to the feed.These particulates and combustion gas precipitates are collected in the particulate matter control device(PMCD)and are collectively referred to as cement kiln dust(CKD).In general,CKD is a very heterogeneous mix both by chemistry and particulate size,and these characteristics are dependent on the raw materials,fuels,kiln pyroprocessing type,overall equipment layout,and type of cement being manufactured.It is incorrect to label all dusts collected in the PMCD as a waste.Many facilities return all or a major portion of the CKD to the kiln as a feedstock while other facilities sell the dust for numerous beneficial uses,such as an agricultural liming agent,roadbed stabilization,and other uses.For CKD not returned to the kiln system,the most common reasons are equipment limitations for handling the dust and chemical constituents in it that would be detrimental to the final cement product.The fraction of CKD that is not returned to the kiln or otherwise beneficially used is placed in landfills.CKD stored or disposed in landfills has been the subject of an ongoing policy assessment by the United States Environmental Protection Agency(USEPA),pursuant to provisions in the Resource Conservation and Recovery Act(RCRA)addressing high volume,low toxicity materials like CKD.USEPA issued a Report to Congress addressing CKD and its potential risks to human health and the environment in 1993.In 1995,the agency published a regulatory determination in which USEPA committed to developing a federal program for CKD that is disposed.Since that time,the cement industry has worked extensively with state environmental agencies to devise and implement appropriate management standards for CKD that is disposed.States have undertaken a myriad of efforts to address,though tailored state programs,any potential concern posed by CKD that is disposed.USEPA has every intention of relying on these state initiatives and may assist them with guidance on appropriate management standards similar to those contained in a rule proposed by the agency in 1999.
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