15 Sept 99
B-5. Types and Pavement Applications of Mineral Waste. Mineral wastes are
produced from various mining processes. The amount of mineral waste generated in the
U.S. is about 1.8 billion tons annually. The largest percentage of this amount, over 1
billion tons, is waste rock (Shelburne and DeGroot 1998).
a. Coal refuse. Coal refuse can be any material that is removed during the cleaning
and processing of the mined coal. The amount generated depends upon the purity or
absence of unwanted seams of material within the coal (Collins and Miller 1976). In
1994, approximately 120 million tons of coal refuse were being produced each year, with
the total existing amount of coal refuse probably in the range of 4 billion tons; although
all of it may not be available for use, due to ownership questions (Collins and Miller
1976 and Collins and Ciesielski 1994).
The majority of the refuse is slate or shale, with some sandstone or clay. Coal refuse is
sized from coarse to fine, with the 4.75 mm (No. 4) sieve as the dividing point. The
coarse portion is normally well graded and makes up roughly 80 percent of the amount
Several large coal producing states in the north central and north east U.S. have
constructed embankments with coal refuse, and at least one state used it as a stabilized
subbase (Collins and Ciesielski 1994). Applications of this type of construction have not
been widespread. If placed in thick layers there is a possibility of spontaneous combus-
tion and the possibility of acidic leachate moving into the groundwater.
b. Mill tailings. Mill tailings are the wastes produced during the processing of
various types of mineral ores. These ores include: copper, iron ore and taconite, lead-
zinc, uranium and to lesser degrees gold, molybdenum, phosphate, and alumina (Collins
and Miller 1976 and Collins and Ciesielski 1994). The total amount of tailings produced
each year is approximately 500 million tons.
The size of the tailings produced can vary widely, depending upon the type of mineral ore
and the method of processing. The leaching characteristics of the tailings should be
investigated prior to use. Because of increased surface area, pre-use testing becomes
more important for fine-grained tailings.
Mill tailings have been used extensively for some time in areas where the mining or
processing occurs. They have been used as fill in embankments, in subbase and base
courses and as aggregate in concrete and hot-mix asphalt mixtures (Collins and Miller
1976 and Collins and Ciesielski 1994). For example, in 1970, more than 3 million tons
of copper tailings were used to construct embankments along an interstate highway in
Utah (Collins and Ciesielski 1994).
c. Phosphogypsum. Phosphogypsum is a solid by-product of the production of
phosphoric acid a major component of agricultural fertilizers (Taha and Seals 1992a). In
1992, it was estimated that about 800 million tons were stockpiled, with another 35 to
60 million tons being produced yearly (Taha and Seals 1992 and Collins and Ciesielski