Dechlorination of PCBs, CAHs, herbicides and pesticides neat and in soils at 25 degrees C using Na/NH3.
Na/NH3 reductions have been used to dehalogenate polychlorinated biphenyls (PCBs), chlorinated aliphatic hydrocarbons (CAHs) and pesticides at diffusion controlled rates at room temperature in model compound studies in both dry NH3 and when water was added. The rate ratio of dechlorination (aliphatic and aromatic compounds) versus reaction of the solvated electron with water is very large, allowing wet soils or sludges to be remediated without an unreasonable consumption of sodium. Several soils, purposely contaminated with 1,1,1-trichloroethane, 1-chlorooctane and tetrachloroethylene, were remediated by slurring the soils in NH3 followed by addition of sodium. The consumption of sodium per mole of chlorine removed was examined as a function of both the hazardous substrate's concentration in the soil and the amount of water present. The Na consumption per Cl removed increases as the amount of water increases and as the substrate concentration in soil decreases. However, remediation was still readily accomplished from 5000 to 3000ppm to sub ppm levels of RCl in the presence of substantial amounts of water. PCB- and dioxin-contaminated oils were remediated with Na/NH3 as were PCB-contaminated soils and sludges from contaminated sites. Ca/NH3 treatments also successfully remediated PCB-contaminated clay, sandy and organic soils but laboratory studies demonstrated that Ca was less efficient than Na when substantial amounts of water were present. The advantages of solvated electron reductions using Na/NH3 include: (1) very rapid dehalogenation rates at ambient temperature, (2) soils (even clay soils) break down into particles and slurry nicely in NH3, (3) liquid ammonia handling technology is well known and (4) removal from soils, recovery and recycle of ammonia is easy due to its low boiling point. Finally, dechlorination is extremely fast even for the 'corner' chlorines in the substrate Mirex (structure in Eq. (5)).
Pittman
Charles U
CU
Department of Chemistry, University Chemical Research Center, Mississippi State University, 39762, USA. cpittman@ra.msstate.edu
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Jinbao
J
D004785:Environmental Pollutants / Q000032:analysis*; D006540:Herbicides / Q000737:chemistry*; D006843:Hydrocarbons, Chlorinated / Q000737:chemistry*; D010575:Pesticides / Q000737:chemistry*; D011078:Polychlorinated Biphenyls / Q000737:chemistry*; D012964:Sodium / Q000737:chemistry; D012989:Soil Pollutants / Q000032:analysis*; D013696:Temperature
D004785:Environmental Pollutants; D006540:Herbicides; D006843:Hydrocarbons, Chlorinated; D010575:Pesticides; D012989:Soil Pollutants; D012964:Sodium; D011078:Polychlorinated Biphenyls