Solvated Electron (Na/NH_3) Dechlorination of Model Compounds and Remediation of PCB- and CAH-Contaminated Wet Soils

摘要

Soils, sludges and aggregates contaminated with polychlorobiphenyls (PCBs) and chlorinated aliphatic hydrocarbons (CAHs) have been remediated by simply slurrying in liquid NH_3, at ambient or low temperature, followed by addition of Na. Na dissolves generating solvated electrons which dechlorinate PCBs and CAHs at diffusion controlled rates. Na/NH_3 remediation treatments work well on wet soils and sludges because the lifetime of a solvated electron in 20% H_2O/80% NH_3 is ～100 sec. and longer when less water is present. This lifetime sufficient so that the reactions of NH_3 , H_2O 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, CCl_4, dichlorotoluenes, dichlorobenzenes and CH_3CCl_3, 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_3 treatment technology can simultaneously react and destroy PCBs, CAHs, polynuclear aromatic hydrocarbons, pentachlorophenol, dioxins/furans and possibly organic nitroitrates (munitions wastes) in soils or sludges while also lowering the concentrations of several metals in these samples.