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Product Abstract

Guidance for Comanagement of Mill Rejects at Coal-Fired Power Plants

Product ID:TR-108994
Date Published:22-Jun-1999
Sector Name:Environment
Document Type:Technical Results
Price:No Charge

This Product is publicly available

   7.44 MB - Adobe PDF (.pdf)

Traditionally, utilities have comanaged some or all of their low-volume wastes with their high-volume combustion by-products in disposal facilities. This report presents guidance on comanagement of coal combustion by-products and mill rejects containing pyrites at coal-fired power plants. The report specifically addresses the issue of environmental protection from leachates due to oxidation of pyrites under certain conditions. Included is a discussion of acid-base accounting and neutralization capacity of alkaline coal ash to assist in appropriate comanagement of mill rejects in landfills and impoundments.


The electric utility industry annually generates more than 100 million tons of high-volume coal combustion by-products (CCBs) consisting of fly ash, bottom ash, boiler slag, and flue gas desulfurization (FGD) sludge. Historically, about 25 percent of high-volume by-products have been used for construction materials and other applications; most of the remaining 75 percent have been disposed of in landfills or impoundments. Utilities also generate a number of low-volume wastes as a result of coal fuel preparation, equipment maintenance, water purification, and materials storage and handling practices associated with fossil fuel combustion. This study was part of an EPRI multiyear effort, performed in cooperation with the Utility Solid Waste Activities Group (USWAG) and individual utility companies. The study was designed to characterize utility comanagement practices as well as collect and analyze a comprehensive set of data pertinent to environmental effects and best management practices.


To characterize mill rejects generated as a by-product of coal processing; to assess environmental effects from comanagement of high-volume CCBs and coal mill rejects; to develop guidance for environmentally effective comanagement practices for mill rejects containing pyrites.


Investigators conducted a survey of 40 power plants in 1996 to obtain information on power plant equipment, coal types burned, coal mill rejects generation rates, and handling/disposal methods. They next performed limited sampling and laboratory analyses to establish chemical composition and mineralogy of mill rejects. In addition, they researched literature and completed laboratory tests to develop an understanding of acid-base accounting and neutralization potential for CCBs as well as comanagement systems for mill rejects. Finally, they developed alternatives for coal mill rejects management/comanagement and modified the EPA's draft Industrial D guidance material on performing closure and postclosure operations (included here).


This report summarizes six case studies developed as a result of the 1996 EPRI survey. These studies revealed the following:

o From 55-75 percent of the coal-fired power plants comanage mill rejects and CCBs in landfills or impoundments. Because many plants do not record mill rejects production, limited data were available on the amount of mill rejects generated. Based on available data, mill rejects generation ranged from 0.15 lbs/hr to 2800 lbs/hr.

o Analysis of mill reject samples revealed that quartz, pyrite, calcite, dolomite, kaolinite, siderite, marcasite and two types of feldspars were the minerals most often present. Pyritic sulfur ranged from less than 0.01 percent to 20.85 percent.

o Three of the six case studies showed the presence of leachates formed by pyrite oxidation. These acidic leachates were characterized by elevated concentrations of sulfate and metals such as iron, nickel, and arsenic.

o Tests on regrinding and coburning of coal mill rejects showed that coburning in utility boilers is a technically feasible management option. The study provides guidelines for comanagement of rejects with coal ash in an impoundment or landfill.

EPRI Perspective

Previous EPRI research provided technical inputs to the EPA, leading to its 1993 determination that regulation of high-volume fossil fuel combustion by-products as hazardous waste was unwarranted. At that time, the EPA deferred its determination on low-volume wastes as well as the comanagement of high-volume by-products with low-volume wastes, pending further study. In its March 1999 Report to Congress, the EPA noted its limited concern for the comanagement of pyritic materials and indicated the Agency had engaged the utility industry in a program to appropriately manage these wastes. EPRI developed this technical guidance manual in close consultation with the EPA Office of Solid Waste, in particular with the staff of the Industrial and Extractive Waste Branch. The manual fulfills the need for industrywide technical guidance on appropriate management/comanagement of mill rejects containing pyrites.

Program 49   Coal Combustion Products - Environmental Issues
  • Groundwater
  • Water Quality
  • By-Products
  • Groundwater Management
  • Pyrite

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