Chapter 18
Sulfur Polymer Cement as a Final Waste Form for Radioactive Hazardous Wastes
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G. Ross Darnell Idaho National Engineering Laboratory, Transuranic Waste Programs, EG&G Idaho, Inc., Idaho Falls, ID 83415
With ever-increasing emphasis on high-temperature treatment of radioactive and hazardous wastes, the unusual ability of sulfur polymer cement (SPC) to stabilize high loadings of the most troublesome volatilized toxic metals is exciting. SPC is a sulfur polymer composite material that begins melting between 110 and 120°C. Upon cooling it achieves an average compressive strength of 27.6 MPa (4,000 psi), and can triple that strength in 2 years. SPC resists attack by most acids and salts, and its structure suggests long life. We are only on the threshold of developing different formulations of SPC that can accommodate even higher loadings of difficult-to-stabilize wastes. Ongoing SPC tests include stabilizing toxic metals, establishing expected longevity, and evaluating (in nonradioactive full-scale tests) SPC ladened with incinerator ash. Since there are no known perfect solidification and stabilization agents for radioactive or hazardous wastes, the search continues for individual agents for specific wastes. The U.S. Department of Energy (DOE) began in the early 1980s to test SPC as a radioactive and hazardous waste solidification and stabilization agent because of its unusual properties. Perhaps SPCs strongest selling point is that it will always melt when elevated to the correct temperature. This feature allows hazardous or radioactivefinalwaste forms that do not pass required tests to be remelted in a low-temperature process and reformulated until the waste forms do pass the tests. (NOTE: Portland cement has been used for 5 decades as the principal radioactive waste solidification agent, and thus it is accepted as the standard of
0097-6156/94/0554-0299$08.00/0 © 1994 American Chemical Society
In Emerging Technologies in Hazardous Waste Management IV; Tedder, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.
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EMERGING TECHNOLOGIES FOR HAZARDOUS WASTE MANAGEMENT
comparison for other waste solidification and stabilization agents [final waste forms]. Correct titles for the substance addressed in this paper are "modified sulfur cement" and "sulfur polymer cement." For simplicity, the titles are given the single acronym "SPC." The acronym for sulfur polymer cement concrete is "SPCC." The words cement and concrete refer to the generic family of hydraulic cements and concretes, while PCC refers to the specific concrete known as Portland cement concrete. Hazardous waste that is also radioactively contaminated is called mixed waste.) With waste stabilization and minimization being the primary goals in waste treatment and disposal, DOE's Defense Low-Level Waste Management Program funded tests of SPC ladened with low-level radioactive waste. The research was performed at Brookhaven National Laboratory. DOE's Hazardous Waste Remedial Action Program added funding later. This paper summarizes these and other tests. Developing and Testing Commercial SPC and SPCC for Harsh Chemical Environs Pertinent data provided by commercial tests of SPC and SPCC are vital to understanding SPC's potential for stabilizing low-level radioactive, mixed, and hazardous wastes. Developmental Background. In 1972, the U.S. Bureau of Mines discovered that the addition of dicyclopentadiene and oligomers of cyclopentadiene in equal quantities totaling 5 wt% of the sulfur phase resulted in a construction concrete having advantageous properties not found in other concretes (7,2,5). The Bureau of Mines and the Sulphur Institute thereafter joined forces. In 1973, the Sulphur Development Institute of Canada also joined the effort (4). Properties of SPC and SPCC. SPC is a sulfur polymer composite material that begins melting between 110 and 120°C (230 and 248°F), with an optimum pour temperature between 127-138°C (260-280°F). While it takes the average PCC approximately 28 days to achieve a compressive strength of 27.6 MPa (4,000 psi), SPCC reaches that approximate strength upon cooling. In 2 years, its strength can increase by a factor of three (J). In remelting SPC, when heat is removed, SPCC will regain its original strength very rapidly as it cools. The various mechanical strengths of SPCC are approximately double those of routine PCC and are not specifically cited herein; however, they are detailed in Reference (
