1998 Progress Report: Destruction of PCBs, CAHs, CFCs and Organic Nitro/Nitrate Wastes in Soils and Bulk with Ca/NH3 at Ambient Temperature

EPA Grant Number: R826180
Title: Destruction of PCBs, CAHs, CFCs and Organic Nitro/Nitrate Wastes in Soils and Bulk with Ca/NH3 at Ambient Temperature
Investigators: Pittman, Charles U.
Institution: Mississippi State University - Main Campus
EPA Project Officer: Lasat, Mitch
Project Period: February 1, 1998 through January 31, 2001 (Extended to January 31, 2002)
Project Period Covered by this Report: February 1, 1998 through January 31, 1999
Project Amount: $317,027
RFA: Exploratory Research - Environmental Chemistry (1997) RFA Text |  Recipients Lists
Research Category: Water , Land and Waste Management , Air , Engineering and Environmental Chemistry

Objective:

The major objective is to develop basic knowledge on the use of solvated electron chemistry for possible use as a single, multifunctional, portable technology applicable to both on site in-situ and on site ex-situ destruction of PCBs, CAHs, CFCs, munition/explosive residues, discarded propellants and chemical warfare agents. The immediate objectives include the complete dechlorination of CAHs in Na/NH3 and Ca/NH3 in the presence of increasing quantities of water and learning if the reaction of solvated electron with water competes with dechlorination. Another objective is the destruction (complete dechlorination) of PCBs and CAHs in a variety of wet soils. The key goal is to remediate PCB-contaminated and CAH-contaminated soils in the presence of water without excessive consumption of Na or Ca via on-site slurrying of contaminated soil in Na/NH3 or Ca/NH3. Similar reductions of CFCs, nitro compounds both neat and in soils are being studied.

Progress Summary:

We have demonstrated that the reductions of CCl4, CH3Cl3, 2,4,6-trichlorophenol and chloroform in Na/NH3 are diffusion controlled. For example, when CCl4 is reduced by adding two equivalents of Na to NH3/CCl4 solutions only CH4 and CCl4 are observed. No intermediate dechlorination products (CHCl3, CH2Cl2 or CH3Cl) are found. Thus, CCl4 is completely reduced before more CCl4 diffuses to the solution region containing electrons. Likewise, CH3CCl3 produced only ethane and recovered CH3CCl3. Trichlorophenol gave phenol plus recovered trichlorophenol when reacted with a deficiency of Na in NH3. Thus, dissociative electron transfer is occurring extremely rapidly.

The amount of Na required for the complete dehalogenation of aromatic model compounds was greater for fluoromated aromatics then for chloro- or bromoaromatics. To achieve complete dechlorination of chlorinated aromatics, less Na is consumed than either K or Ca (correcting for the fact Ca can donate two electrons).

CAHs, PCBs and other chlorinated aromatics were completely dechlorinated in liquid NH3 in the presence of a 50 mole excess of water over the chlorinated substrate. The amount of Na required to obtain complete reduction increased, but only modestly, as the amount of water was raised. CCl4 required 4.6 equivalents of Na to be completely converted to CH4 in NH3 with no water added. In the presence of 20 and 50 equivalents of H2O the Na requirements increased to 5.5 and 6.4 equivalents to complete dechlorination. Several other model compounds have given similar results. This suggested that soils contaminated with PCBs or CAHs could be remediated by slurrying in NH3 followed by the addition of reasonable amounts of Na. As the concentration of the chlorinated compounds decrease, the competition from the reaction of water to remove solvated electrons should get more critical because the [H2O]/[RCl] ratio will become extremely large. Therefore soil studies were undertaken.

Montmorillinite clay-rich soil (75g samples) from Starkville, MS was purposely contaminated with the PCB mixture Arochlor 1016 to PCB levels of 2140 and 486 ppm. After being slurried in NH3(l) at room temperature Ca was added and after stirring 5 min. the NH3 was removed. Reanalysis of these samples found 2 to 3 ppm and <1.5 ppm, respectively, in these samples. This corresponds to destruction efficiencies of >99.8 and >99.7. Similar results were obtained using organic soils contaminated with 1980 and 620 ppm of Aroclor 1254 (destruction efficiencies >99.8 and >99.7, respectively, were achieved with Ca/NH3). Preliminary laboratory CCl4-contaminated soil remediation studies with Na/NH3 also appear to be highly successful. One gram samples of clayey-mixed thermic typic hapludults were contaminated with 3000 ppm of CCl4. The samples were slurried in NH3(l) at room temperature and Na was added for 30 seconds. Then the reactor contents were cooled quickly to -80EC. Water was added to dilute the NH3 and the soil/NH3/H2O mixture was extracted with toluene to remove CCl4. No CCl4 or other chlorinated organic compounds could be detected by gc. The analytical sensitivity in this case was only enough to assure that the upper limit of CCl4 present could not more than 5 ppm (it could be lower).

Future Activities:

Model competitive dehalogenations will continue to be studied in the presence of incremental amounts of water. As water concentration increases in NH3 the lifetime of the solvated electron decreases. Soil decontamination studies will be carried out to determine the minimum amounts of Na and Ca that can be used at defined dechlorination efficiencies. The amount of Na versus Ca consumption needed during the remediation of different PCB- and CAH-contaminated soils (as a function of added water) will be central to comparing the relative economics of Na vs. Ca. This will be studied as the amount of water is raised. Work on aromatic nitro compounds, chemical warfare simulants. Studies of trichloroethylene and tetrachloroethylene will also begin (neat, with added water and in soils).

Journal Articles:

No journal articles submitted with this report: View all 22 publications for this project

Supplemental Keywords:

Toxics, toxic substances, restoration., Scientific Discipline, Waste, Remediation, Environmental Chemistry, dechlorination, organic nitro/nitrate, chemical contaminants, contaminated soil, DNAPLs, CFCs, slurry, PCB dechlorination

Progress and Final Reports:

Original Abstract
  • 1999 Progress Report
  • 2000 Progress Report
  • Final Report