Page 75 - Highway Engineering Handbook Building and Rehabilitating the Infrastructure

58 CHAPTER ONE

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Foundry Wastes. It is estimated that 3 million tons (2.7 10 kg) of foundry wastes
are produced annually in the United States, including furnace dust, arc furnace dust, and
sand residue. Foundries are concentrated primarily in the Great Lakes states. Foundry
dust is often disposed of as hazardous material because of its high concentration of
metals. Foundry sand, however, is not generally hazardous and has been used as fill
material, pipe bedding, and fine aggregate in paving mixtures. Tests must be conducted
on the material prior to reuse to determine the properties of the leachate and to ensure
that it is environmentally safe. Research into the use of foundry sand is being conducted
by departments of transportation in five states, and its use has met with limited success.
The permanence of foundry sand as pipe bedding in Illinois, however, was not consid-
ered acceptable.
Flue Gas Desulfurization Sludge. Flue gas desulfurization sludge (FGD) is the product
of wet scrubbing of flue gases at coal-burning plants and consists of calcium sulfate or
sulfite slurry. These slurries are generally landfilled. By dewatering FGD (especially the
sulfate slurries) and blending it with a reactant such as portland cement, or cement fly ash,
the mixture can be used as stabilized base material or as fill material. FGD has also been
used as a dust control palliative, and additional uses are being investigated.
Paper Mill Wastes. Inorganic paper mill sludge has been used occasionally for dust con-
trol on highway projects. Although research has indicated that spent sulfide liquor from the
paper milling process may have application in soil stabilization, it is believed that a higher
level of use exists for the material within the paper industry. The ash residue from burning
bark at paper mills, when pulverized with coal and burned, has been shown to be as effec-
tive a portland cement substitute as class F fly ash and is being considered for use in high-
way projects.

1.6.5 Mining Waste
Coal Refuse. Coarse coal refuse from mining operations is produced at a rate of
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120 million tons (109 10 kg) per year. Coarse material is banked, while fine coal
refuse is put into a silt-sized slurry mix and placed in impoundments. It is estimated that
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up to 4 billion tons (3.6 10 kg) of coal mining refuse has accumulated in the United
States. Concern about spontaneous combustion and leachate of the material (composed
of slate and shale with sandstone and clay mixed in) has impeded in-depth studies of the
use of coal waste. It is currently being evaluated for use in embankments and as subbase
material, two applications that reportedly have been used in the past.
Quarry Wastes. Fairly consistent wastes consisting of fines from stone washing,
crushing, and screening and wet, silty clay from washing of sand and gravel are pro-
duced from quarrying operations. Most quarry waste is not reusable or sized within stan-
dard specifications, are stockpiled in ponds. Reclamation through dewatering and
segregating coarse and fine materials would be necessary to use the 175 million tons
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(159 10 kg) of quarry waste produced each year, or any of the approximately 4 billion
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tons (3.6 10 kg) that have accumulated in the United States. The mineral properties
and characteristics of the waste differ from quarry to quarry, limiting the beneficial end
use, but quarry wastes have been used as fill and borrow material, flowable fill, and
cement-treated subbase.
Mill Tailings. Mill tailings are the remains left after processing ore to concentrate it.
Large amounts of mill tailing are generated from copper, iron, lead, zinc, and uranium ores.