INTERIM FINAL TECHNICAL REPORT

September 1, 1996, through August 31, 1997

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 products with characteristics suitable for mine reclamation. The proposed approach has significant merit over the current practice and can result in considerable savings for coal and electric utility companies. This two-year (Phase I) cooperative project, 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.

In the first year of the project (September 1, 1995 - August 31, 1996), raw materials were procured from two coal companies, four utility companies and one limestone processing plant (lime waste). Physical and environmental properties of the raw materials were studied in laboratory prior to the development of mixes for the surface demonstration.

Mixing and pumping systems for the field demonstration were investigated and six test cells were filled at two mine sites during November/December, 1996. Environmental properties of the grouts in the test cells were studied and compared with the laboratory-prepared grouts. It was found that a good correlation exists between the laboratory prepared grouts and the grouts placed in the test cells at the two mine sites. Though not a scope of this project, limited study indicates that potential exists for growing crops in these engineered soils without using any natural top soils. A thorough hydrogeology study of the two demonstration sites was conducted and groundwater monitoring at two sites was initiated before the placement of by-products-based mixes in the demonstration pits. To date, samples collected from the monitoring wells reveal no impact of the test pits on ground water quality at either sites.

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EXECUTIVE SUMMARY

Fine coal slurry waste (-28 mesh) from processing plants constitutes about ten to twenty percent (10-20%) of the run-of-mine coal. It is estimated that coal operators currently spend between five and eight dollars per ton of slurry waste. The current disposal technology of pumping 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.

The Principal Investigator (PI) recently 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 disposal cost of slurry alone ($5-8/t) or CCB alone ($8-10/t).

This cooperative research and demonstration project between coal companies, electric utilities, and CCRM program at SIUC was initiated to further develop and demonstrate the concept. During September 1, 1995 to August 30, 1996, extensive laboratory studies were conducted to identify seven mixes suitable for surface demonstration. The raw materials for the mixes were coal slurries, fresh F type fly ash (PCC and cyclone boilers), ponded F-type fly ash, fly ash stabilized and forced oxidation scrubber sludge, FBC fly ash, and lime waste. Forty three (43) combinations of different by-products were investigated for their strength, flow and environmental properties and seven final mixes were selected for field demonstration. However, only five different mixes could be demonstrated in the field due to the unavailability of ponded fly ash and fly ash stabilized scrubber sludge.

Two sites were selected for the field demonstration--Marissa mine of Peabody Coal Company and Crown III mine of Freeman United Coal Company. A thorough hydrogeology study of the two demonstration sites was conducted and groundwater monitoring wells were installed and wells were prepared for monitoring impacts of surface placements of byproducts-based mixes on the groundwater.

Three test cells (20 ft x 20 ft x 8 ft) at Marissa were filled during November, 1996. A field demonstration of materials mixing and pumping was held for representatives of funding agencies and cooperative organizations on November 21, 1996. The project team successfully demonstrated mixing materials in a concrete truck and in a large pit and pumping of 5.75 inch slump grouts over a distance of 250 ft using a concrete pump.

At Crown III mine, two shuttle cars (at right angle to each other) were used to blend coal slurry, FBC fly ash, F-type fly ash, and scrubber sludge. The blended materials were taken to the test cells using a two-cubic yard front-end loader. Water was added in the pit and the blended material was mixed in the pit using a one cubic-yard back hoe. On December 19, 1996, a second field demonstration was conducted for representatives of funding agencies and cooperative organizations at Crown III site. Four (4) cubic yards of blended material was put in an open-top concrete truck and mixed with water for approximately 15 minutes. The grout was then pumped to the test cell over a distance of 280 ft using a concrete pump. A very lean grout of approximately 8-inch slump and a very thick grout of approximately 4-inch slump were pumped using the same pump.

Grout samples from the field were brought to the laboratory and the laboratory-cured samples were tested for their compressive strength. It was found that the strength of the field prepared samples closely matched that of the laboratory-prepared samples. Grouts collected from the test cells were tested for their environmental properties. The basic environmental thesis of this work that individual coal combustion and slurry wastes can be mixed to produce a material more environmentally safe than any of the components is now firmly supported by results on both a field and laboratory scale

Groundwater flow at the Freeman site is primarily within a shallow confined glacial aquifer. The aquifer is bounded below by Pennsylvanian rocks, primarily shale, and above by Quaternary silty deposits. Nine field tests yield a geometric mean hydraulic conductivity of 2.9E-5 ft/s (8.8E-6 m/s) for the aquifer. Groundwater flows through strip mine spoils at the Peabody site. This unconfined hydrostratigraphic unit is bounded below by Pennsylvanian rocks, primarily shale. Ten field tests yield a geometric mean hydraulic conductivity of 1.3E-5 ft/s (3.9E-6 m/s) for the spoil. At each demonstration site, two upgradient wells provide background water quality samples, whereas four wells provide downgradient water quality samples.

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.

Though not a scope of this project, the PI believes that to reclaim the lands after disposal of coal slurry and CCBs-based mixes, it is essential to study the potential of crop growth on these engineered soils without using any natural top soil. Preliminary study indicates that the potential exists for growing crops in these soils using foliar feeding technique. Oats were grown successfully by supplying only iron through foliar feeding. A sufficient quantity of oat leaves was available for nutrient analysis. Some of the oat plants were harvested for nutrient analysis while the remainder of the plants were harvested for grain.

"The remainder of this report contains propriety information and is not available for distribution except to the sponsors"

OBJECTIVE

The goal of this study is to scientifically develop and perform small scale (100-200 tons) demonstration of the concept of intimately mixing coal slurries and natural resources by-products for reclamation and acid mine drainage control. Specific objectives are to:

1. develop physical and chemical characterization data for fine coal waste slurry, selected coal combustion by-products and natural resource utilization by-products that may have potential for co-disposal,

2. develop kinetic reaction rate constants for coal pyrite and alkaline by-products from coal burning power plants and utilize them to develop mixtures which will be environmentally benign in both the short-term and the long-term,

3. identify and characterize six (6) environmentally-sound mixes of waste slurry and by-products which would be suited for mine reclamation at selected mines,

4. assemble and test equipment for a small-scale demonstration system for the proposed concept,

5. perform small-scale demonstration studies for three (3) 100-200 ton cells at each of two mines utilizing identified environmentally-sound mixes,

6. assess the performance and environmental impacts of developed mixes disposed in cells, and

7. assess the performance of small-scale demonstration equipment.

Objectives 1 to 4 were intended to be accomplished in the first year of the project. Objectives 5 through 7 are intended for the second year of the project. In the first year of the project, objectives 1 through 4 were accomplished successfully. Different tasks that are scheduled to meet the current year's objectives are:

8. conduct field demonstration of mixing and pumping of grouts at two mine sites and fill at least three test cells at each mine site,

9. evaluate different mixer-pump combinations and/or mixing methods for small scale field demonstrations,

10. monitor groundwater after filling the test cells with the grouts,

11. monitor curing characteristics of the grouts placed in the test cells,

12. propose a viable commercial system based on the field experience.