FINAL TECHNICAL REPORT
September 1, 1996, through March 31, 1998
Project Title: DEVELOPMENT AND DEMONSTRATION OF A NEW APPROACH FOR
WASTE COAL SLURRY MANAGEMENT USING NATURAL RESOURCE UTILIZATION
BY-PRODUCTS
Principal Investigator: Dr. Y. P. Chugh
Southern Illinois University at Carbondale
Other Investigators: Dr. D. Dutta, Dr. S. Esling, and Dr. B. Paul
Southern Illinois University at Carbondale
Project Manager: Mr. Richard Shockley, ICCI
ABSTRACT
Dr. Chugh recently proposed an alternative approach for management of fine
coal waste slurry (-28 mesh) involving natural resources utilization (coal
burning power plants, limestone processing plants, cement plants, etc.)
by-products. The approach involves formulating environmentally-benign beneficial
use mixes with characteristics suitable for mine reclamation, acid mine drainage
control, or surface subsidence control. The proposed approach has significant
merit over the current practice and can result in considerable savings for
coal and electric utility companies. This three-year cooperative project
(1995-1998), between coal companies, electric utilities, and the Coal Combustion
Residues Management Program (CCRM) at SIUC, has developed the approach
scientifically and performed small scale (100-200 ton) demonstrations for
five (5) mixtures at two mine sites in Illinois. Environmentally benign and
structurally appropriate mixes were developed in the laboratory using coal
slurries from two coal companies, coal combustion by-products from four utility
companies and lime waste.
Mixing and pumping systems for the field demonstration were investigated
and six test cells were filled at two mine sites. Environmental properties
of grouts in the test cells were similar to the grouts prepared in the
laboratory. Core samples obtained from the test pits after one year of mix
placement indicated bearing capacity of the top two feet of the materials
in the range of 20-40 psi--capable of allowing large equipment to operate
on them. Two FBC-based mixes showed strength in excess of 100 psi at depths
six feet or more. Leaching characteristics of the cores did not indicate
any harmful effect on the environment. A hydrogeology study of the two sites
and groundwater monitoring at two sites were performed. To date, samples
collected from the monitoring wells reveal no impact of the test pits on
ground water quality at either sites. Based on the studies to date, it is
suggested that the developed concept be demonstrated on a large scale (10,000
to 100,000 tons) with monitoring of groundwater.
"Pages 1 to 34 contain proprietary information"
EXECUTIVE SUMMARY
Ten to Twenty percent of coal processing rejects are less than -28
mesh sizes and the disposal cost of these fine coal prcessing wastes (FCPW)
is between five to eight dollars per ton. The current practice of disposing
a relatively-low-solids-content (5-15%) slurry into leveed ponds presents
long-term environmental problems related to ground water contamination, acid
drainage and the stability of impounding structures. The coal burning power
plants and other natural resource utilization industries, such as limestone
processing plants and cement plants, similarly produce low or zero value
byproducts which are alkaline and pose long-term environmental problems similar
to slurry waste disposal. The disposal cost for these by-products currently
varies between five and ten dollars per ton and is expected to increase further
over the next decade.
In 1995, the Principal Investigator (PI) proposed an approach to
develop environmentally benign mixtures involving coal slurry waste and natural
resource utilization by-products. The developed mixes may be used in conjunction
with disposal of coarse coal refuse or deposited in coal refuse embankment
ponds. A preliminary economic evaluation of this alternative estimated the
cost to be $2.27/ton, excluding transportation costs of CCBs, which is
significantly lower than the disposal cost of slurry ($5-8/t) or CCBs alone
($8-10/t).
A cooperative research and demonstration project between coal companies,
electric utilities, and CCRM program at SIUC was initiated to develop and
demonstrate the concept. Laboratory developed mixes of coal slurry, CCBs
and lime wastes were used to fill two test pits (8 ft deep, 20 ft long, and
20 ft wide) at Marissa site of Peabody Coal company and three test pits at
Crown III site of Freeman United Coal company during November/December, 1996.
Core samples were obtained in March 1998 from the test pits to study
characteristics of the deposited material. Results and conclusions of various
tests conducted in the laboratory and in the field and are highlighted below.
1. Besides water content, the flow characteristics of mixes of coal slurry
and coal combustion by-products are also governed by the type and amounts
of coal slurry and fly ash. However, it is possible to develop high solids
pumpable mixes (>60% solids content). The 28-day cured strength of the
mixes vary in the range of 150 to 300 psi. The initial high lime based phases
(ph 10-12) of mixes do not persist in a wet low temperature environment and
soon return to carbonate and sulfate phases with a long-term (more than two
years) pH in the range of 7.5 to 8.5. Leaching studies of cured mixes indicate
no detectable iron and massive reduction in boron compared to the individual
mix components.
2. Field demonstration indicates that handling of ponded coal slurry and
lime waste for feeding into a small-size mixer is difficult. For proper mixing,
a pug mill type mixer is preferred. Pumping of these high-solids mixes over
a long distance (250-300 ft) can be done using a concrete pump.
3. Core samples from the pits reveal the bearing capacity of the top two
feet of the deposited materials in the range of 20 to 40 psi. FBC-based mixes
showed higher strength at greater depths (more than 100 psi at six ft or
more depth). The surface load bearing characteristics indicate that large
equipment can easily operate on the cured materials. The top two feet of
the cured materials had 30% to 40% moisture, indicating moisture holding
characteristics of these material suitable for crop growth. Environmental
characterizations of cored samples of deposited materials indicate the calcium
carbonate equivalent (CCE) in the range of 15 to 40% after one year of placement.
The CCE values are adequate for neutralizing the acid producing potential
of slurry. ASTM leachate analysis indicates boron level in the deposited
materials well below the boron level of F-type fly ash--a component of some
of the mixes.
4. The ambient water quality at the Peabody site is typical of areas impacted
by surface mining. The ambient water quality of the Freeman site shows little
impact from current mining operations. To date, samples collected from the
monitoring wells reveal no impact of the test pits at either the Freeman
or Peabody sites on groundwater quality.
5. Though not a scope of this project, preliminary study indicates that potential
exists for growing crops in these soils using a foliar feeding technique.
Oats were grown successfully by supplying only iron through foliar feeding.
We believe that the project has enhanced our current knowledge of management
of by-products of coal usage (coal processing and coal combustion). The concept
of co-disposal of coal usage by-products differs from the earlier concepts
where the two by-products were disposed of separately, creating their own
environmental problems. Though earlier attempts have been made to treat fine
and coarse coal processing wastes by FBC fly ash, the treatment was limited
to the top surface of waste ponds. This type of treatment may not provide
a permanent solutions to the acid drainage problems because vast majority
of potential acid producing materials remain untreated. Moreover, current
treatment practices are expensive and may require continual maintenance.
By thoroughly mixing coal producing wastes and coal combustion by-products,
coating of coal pyrites by alkaline materials is assured throughout the disposed
materials. We have shown that the leaching characteristics of the individual
mix components is altered due to the curing of mixes. The basic environmental
thesis of this project that individual coal combustion and slurry wastes
can be mixed to produce a material more environmentally safe than any of
the components is well established. Structural properties of the mix materials
assure that the reclamation practice can be initiated after one year of mix
placement in the waste containment areas. Based on the result to date, it
is recommended that this concept be demonstrated on a much larger scale (10,000
to 100,000 tons).
"The remainder of this report contains propriety information and is not available for distribution except to the sponsors"