Chapter 25 Solvated Electron (Na/NH ) Dechlorination of Model Compounds and Remediation of PCBand CAH-Contaminated Wet Soils
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Charles U. Pittman, Jr.*, Jinbao He, and Guang-Ri Sun Department of Chemistry, Mississippi State University, Mississippi State, M S 39762 Soils, sludges and aggregates contaminated with polychlorobiphenyls (PCBs) and chlorinated aliphatic hydrocarbons (CAHs) have been remediated by simply slurrying in liquid N H , at ambient or low temperature, followed by addition of Na. N a dissolves generating solvated electrons which dechlorinate PCBs and C A H s at diffusion controlled rates. Na/NH remediation treatments work well on wet soils and sludges because the lifetime of a solvated electron in 20% H O/80% NH is ~100 sec. and longer when less water is present. This lifetime sufficient so that the reactions of N H , H O and impurities with the solvated electron do not compete efficiently with dechlorination until the concentrations of the chloroorganic compounds are very low. Reductions of the model compounds, CCl4, dichlorotoluenes, dichlorobenzenes and CH3CCl3, produced only completely dechlorinated products and unreacted starting materials when a deficiency of sodium was used. The consumption of Na (per chlorine removed) was studied as a function of water concentration and the chlorocarbon contaminant's concentration in model compound reductions and in soil remediations. Sample remediations of soils and sludges from superfund sites are presented. It seems likely that Na/NH treatment technology can simultaneously react and destroy PCBs, CAHs, polynuclear aromatic hydrocarbons, pentachlorophenol, dioxins/furans and possibly organic nitro/nitrates (munitions wastes) in soils or sludges while also lowering the concentrations of several metals in these samples. 3
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© 2002 American Chemical Society Lipnick et al.; Chemicals in the Environment ACS Symposium Series; American Chemical Society: Washington, DC, 2002.
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420 Polychlorinated biphenyls (PCBs) and other chlorinated compounds are distributed in soils, sludges, estuaries, etc. at over 400 sites i n the United States. Chlorinated aliphatic hydrocarbons (CAHs) occur as serious contaminants at 358 major hazardous waste sites. CAHs migrate vertically through soils to form dense nonaqueous phase liquids (DNAPLs) on aquifer bottoms. Both ex-situ methods to remediate PCBs, CAHs are critically needed. Therefore, our goal has been to develop a generalized technology to decontaminate soils (ex-situ and in-situ) contaminated with these compounds. Ideally, such methodology should operate very rapidly at ambient temperatures. Chlorinated organics are also found frequently i n mixed wastes (those containing radioactive contaminants). Usually such hazardous organic wastes must be removed before dealing, finally, with the radionucleotides. Thus, several treatment options are needed for all the reasons listed above. These considerations highlight the need to provide many economical methods, both ex-situ and in-situ, to decontaminate soils, sludges and aggregates containing chlororganics. " Such remediations have been a high priority research area at the US Environmental Protection Agency and also at the Department of Energy and Department of Defence. In addition to chlorinated organic pollutants, many soils are contaminated with polynuclear aromatic hydrocarbons (PAHs) from coal tar operations, wood treatment processes (e. g. creasote treatments of telephone poles, railroad ties etc.). Other locations are contaminated with nitrated organic compounds associated with munitions and explosives manufacture. Metal ion contamination constitutes another troublesome problem. For example, lead, chromium, vanadium, cadmium, mercury as well as the radionucleotides are serious problems at many contaminated sites. Our recent studies " and those at Commodore Solution Technologies " have now demonstrated a generalized solvated electron technology which can decontaminate both neat samples and soils or sludges which are contaminated with PCBs, CAHs, CFCs, explosive's wastes, cyanides, chemical warfare agents and even reduce the contamination levels of some metals. 1
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Results PCBs, PCB-contaminated soils, CAHs and CAH-contaminated soils (as received clay loam and sandy soils) were readily decontaminated in our laboratory with N a / N H at ambient temperature. Example decontaminations of PCBs from soils are illustrated in Table 1. Typically, the soil is slurred in liquid N H and then metallic Na is added. No special effort is made to dry the soil. Soil slurry reactions are completed within about 30 sec. and the N H is flashed off and recovered for recycle. PCB-destruction efficiencies of >99.9 have been demonstrated both in our laboratory and at Commodore Solutions Technologies. In these reactions all chlorine is converted to NaCl. Similar results have been achieved with CAH-contaminated soils. This is illustrated in Table 2 for soils contaminated with carbon tetrachloride, CCI4. These soils were not dried and in 3
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Lipnick et al.; Chemicals in the Environment ACS Symposium Series; American Chemical Society: Washington, DC, 2002.
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Table 1. Destruction of PCBs in various soils with N a / N H
Soil Type
Sand, clay
Pre-Treatment P C B Level (ppm)
3
Sand, silt, clay Sand, silt
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Sand, silt, clay
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Post-Treatment P C B Level (ppm)
0
